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Sample records for adsorbed water molecules

  1. Relaxation dynamics of surface-adsorbed water molecules in nanoporous silica probed by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Huang, Yu-Ru; Liu, Kao-Hsiang; Mou, Chung-Yuan; Sun, Chi-Kuang

    2015-08-01

    Relaxation dynamics of an exclusively adsorbed water molecule in mesoporous silica MCM-41-S was studied by using terahertz spectroscopy. With the temperature controlled from 0 to 50 °C, we observed strongly frequency- and temperature-dependent dielectric relaxation responses, implying that, unlike ice, surface-adsorbed water molecules retained flourishing picosecond dynamics. Based on the Debye relaxation model, a relaxation time constant was found to increase from 1.77 to 4.83 ps when the water molecule was cooled from 50 to 0 °C. An activation energy of ˜15 kJ/mol, which was in close agreement with a hydrogen-bonding energy, was further extracted from the Arrhenius analysis. Combined with previous molecular dynamics simulations, our results indicate that the reorientation relaxation originated from the "flip-flop" rotation of a three hydrogen-bonded surface-adsorbed water molecule.

  2. Adsorbed Water Illustration

    NASA Technical Reports Server (NTRS)

    2008-01-01

    The Thermal and Electrical Conductivity Probe on NASA's Phoenix Mars Lander detected small and variable amounts of water in the Martian soil.

    In this schematic illustration, water molecules are represented in red and white; soil minerals are represented in green and blue. The water, neither liquid, vapor, nor solid, adheres in very thin films of molecules to the surfaces of soil minerals. The left half illustrates an interpretation of less water being adsorbed onto the soil-particle surface during a period when the tilt, or obliquity, of Mars' rotation axis is small, as it is in the present. The right half illustrates a thicker film of water during a time when the obliquity is greater, as it is during cycles on time scales of hundreds of thousands of years. As the humidity of the atmosphere increases, more water accumulates on mineral surfaces. Thicker films behave increasingly like liquid water.

    The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  3. Infrared spectroscopy of water clusters co-adsorbed with hydrogen molecules on a sodium chloride film

    NASA Astrophysics Data System (ADS)

    Yamakawa, Koichiro; Fukutani, Katsuyuki

    2016-06-01

    Hydrogen gas containing a trace of water vapor was dosed on a vacuum-evaporated sodium chloride film at 13 K, and water clusters formed on the substrate were investigated by infrared absorption spectroscopy. Absorption bands due to (H2O)n clusters with n = 3-6 and an induced absorption band due to hydrogen were clearly observed. With increasing gas dosage, the intensities of the cluster bands increased linearly while the intensity of the hydrogen band was constant. This suggests that the water clusters were formed in two-dimensional matrices of hydrogen. We found that the water clusters did exist on the surface upon heating even after the hydrogen molecules had desorbed. A further rise of the substrate temperature up to 27 K yielded the formation of larger clusters, (H2O)n with n > 6 . We also discuss the origins of the two bands of the trimer in terms of pseudorotation and a metastable isomer.

  4. Hydrophobic Porous Material Adsorbs Small Organic Molecules

    NASA Technical Reports Server (NTRS)

    Sharma, Pramod K.; Hickey, Gregory S.

    1994-01-01

    Composite molecular-sieve material has pore structure designed specifically for preferential adsorption of organic molecules for sizes ranging from 3 to 6 angstrom. Design based on principle that contaminant molecules become strongly bound to surface of adsorbent when size of contaminant molecules is nearly same as that of pores in adsorbent. Material used to remove small organic contaminant molecules from vacuum systems or from enclosed gaseous environments like closed-loop life-support systems.

  5. Size selective hydrophobic adsorbent for organic molecules

    NASA Technical Reports Server (NTRS)

    Sharma, Pramod K. (Inventor); Hickey, Gregory S. (Inventor)

    1997-01-01

    The present invention relates to an adsorbent formed by the pyrolysis of a hydrophobic silica with a pore size greater than 5 .ANG., such as SILICALITE.TM., with a molecular sieving polymer precursor such as polyfurfuryl alcohol, polyacrylonitrile, polyvinylidene chloride, phenol-formaldehyde resin, polyvinylidene difluoride and mixtures thereof. Polyfurfuryl alcohol is the most preferred. The adsorbent produced by the pyrolysis has a silicon to carbon mole ratio of between about 10:1 and 1:3, and preferably about 2:1 to 1:2, most preferably 1:1. The pyrolysis is performed as a ramped temperature program between about 100.degree. and 800.degree. C., and preferably between about 100.degree. and 600.degree. C. The present invention also relates to a method for selectively adsorbing organic molecules having a molecular size (mean molecular diameter) of between about 3 and 6 .ANG. comprising contacting a vapor containing the small organic molecules to be adsorbed with the adsorbent composition of the present invention.

  6. Imaging the wave functions of adsorbed molecules.

    PubMed

    Lüftner, Daniel; Ules, Thomas; Reinisch, Eva Maria; Koller, Georg; Soubatch, Serguei; Tautz, F Stefan; Ramsey, Michael G; Puschnig, Peter

    2014-01-14

    The basis for a quantum-mechanical description of matter is electron wave functions. For atoms and molecules, their spatial distributions and phases are known as orbitals. Although orbitals are very powerful concepts, experimentally only the electron densities and -energy levels are directly observable. Regardless whether orbitals are observed in real space with scanning probe experiments, or in reciprocal space by photoemission, the phase information of the orbital is lost. Here, we show that the experimental momentum maps of angle-resolved photoemission from molecular orbitals can be transformed to real-space orbitals via an iterative procedure which also retrieves the lost phase information. This is demonstrated with images obtained of a number of orbitals of the molecules pentacene (C22H14) and perylene-3,4,9,10-tetracarboxylic dianhydride (C24H8O6), adsorbed on silver, which are in excellent agreement with ab initio calculations. The procedure requires no a priori knowledge of the orbitals and is shown to be simple and robust.

  7. The condensation of water on adsorbed viruses.

    PubMed

    Alonso, José María; Tatti, Francesco; Chuvilin, Andrey; Mam, Keriya; Ondarçuhu, Thierry; Bittner, Alexander M

    2013-11-26

    The wetting and dewetting behavior of biological nanostructures and to a greater degree single molecules is not well-known even though their contact with water is the basis for all biology. Here, we show that environmental electron microscopy (EM) can be applied as a means of imaging the condensation of water onto viruses. We captured the formation of submicrometer water droplets and filaments on single viral particles by environmental EM and by environmental transmission EM. The condensate structures are compatible with capillary condensation between adsorbed virus particles and with known droplet shapes on patterned surfaces. Our results confirm that such droplets exist down to <50 nm. The viruses preserved their shape after a condensation/evaporation cycle as expected from their stability in air and water. Moreover we developed procedures that overcome problems of beam damage and of resolving structures with a low atomic number.

  8. Molecule-specific interactions of diatomic adsorbates at metal-liquid interfaces

    PubMed Central

    Kraack, Jan Philip; Kaech, Andres; Hamm, Peter

    2017-01-01

    Ultrafast vibrational dynamics of small molecules on platinum (Pt) layers in water are investigated using 2D attenuated total reflectance IR spectroscopy. Isotope combinations of carbon monoxide and cyanide are used to elucidate inter-adsorbate and substrate-adsorbate interactions. Despite observed cross-peaks in the CO spectra, we conclude that the molecules are not vibrationally coupled. Rather, strong substrate-adsorbate interactions evoke rapid (∼2 ps) vibrational relaxation from the adsorbate into the Pt layer, leading to thermal cross-peaks. In the case of CN, vibrational relaxation is significantly slower (∼10 ps) and dominated by adsorbate-solvent interactions, while the coupling to the substrate is negligible.

  9. Chiral switching by spontaneous conformational change in adsorbed organic molecules.

    PubMed

    Weigelt, Sigrid; Busse, Carsten; Petersen, Lars; Rauls, Eva; Hammer, Bjørk; Gothelf, Kurt V; Besenbacher, Flemming; Linderoth, Trolle R

    2006-02-01

    Self-assembly of adsorbed organic molecules is a promising route towards functional surface nano-architectures, and our understanding of associated dynamic processes has been significantly advanced by several scanning tunnelling microscopy (STM) investigations. Intramolecular degrees of freedom are widely accepted to influence ordering of complex adsorbates, but although molecular conformation has been identified and even manipulated by STM, the detailed dynamics of spontaneous conformational change in adsorbed molecules has hitherto not been addressed. Molecular surface structures often show important stereochemical effects as, aside from truly chiral molecules, a large class of so-called prochiral molecules become chiral once confined on a surface with an associated loss of symmetry. Here, we investigate a model system in which adsorbed molecules surprisingly switch between enantiomeric forms as they undergo thermally induced conformational changes. The associated kinetic parameters are quantified from time-resolved STM data whereas mechanistic insight is obtained from theoretical modelling. The chiral switching is demonstrated to enable an efficient channel towards formation of extended homochiral surface domains. Our results imply that appropriate prochiral molecules may be induced (for example, by seeding) to assume only one enantiomeric form in surface assemblies, which is of relevance for chiral amplification and asymmetric heterogenous catalysis.

  10. Adsorbed molecules in external fields: Effect of confining potential

    NASA Astrophysics Data System (ADS)

    Tyagi, Ashish; Silotia, Poonam; Maan, Anjali; Prasad, Vinod

    2016-12-01

    We study the rotational excitation of a molecule adsorbed on a surface. As is well known the interaction potential between the surface and the molecule can be modeled in number of ways, depending on the molecular structure and the geometry under which the molecule is being adsorbed by the surface. We explore the effect of change of confining potential on the excitation, which is largely controlled by the static electric fields and continuous wave laser fields. We focus on dipolar molecules and hence we restrict ourselves to the first order interaction in field-molecule interaction potential either through permanent dipole moment or/and the molecular polarizability parameter. It is shown that confining potential shapes, strength of the confinement, strongly affect the excitation. We compare our results for different confining potentials.

  11. Adsorbed molecules in external fields: Effect of confining potential.

    PubMed

    Tyagi, Ashish; Silotia, Poonam; Maan, Anjali; Prasad, Vinod

    2016-12-05

    We study the rotational excitation of a molecule adsorbed on a surface. As is well known the interaction potential between the surface and the molecule can be modeled in number of ways, depending on the molecular structure and the geometry under which the molecule is being adsorbed by the surface. We explore the effect of change of confining potential on the excitation, which is largely controlled by the static electric fields and continuous wave laser fields. We focus on dipolar molecules and hence we restrict ourselves to the first order interaction in field-molecule interaction potential either through permanent dipole moment or/and the molecular polarizability parameter. It is shown that confining potential shapes, strength of the confinement, strongly affect the excitation. We compare our results for different confining potentials.

  12. Forces from periodic charging of adsorbed molecules

    NASA Astrophysics Data System (ADS)

    Kocić, N.; Decurtins, S.; Liu, S.-X.; Repp, J.

    2017-03-01

    In a recent publication [Kocić et al., Nano Lett. 15, 4406 (2015)], it was shown that gating of molecular levels in the field of an oscillating tip of an atomic force microscope can enable a periodic charging of individual molecules synchronized to the tip's oscillatory motion. Here we discuss further implications of such measurements, namely, how the force difference associated with the single-electron charging manifests itself in atomic force microscopy images and how it can be detected as a function of tip-sample distance. Moreover, we discuss how the critical voltage for the charge-state transition depends on distance and how that relates to the local contact potential difference. These measurements allow also for an estimate of the absolute tip-sample distance.

  13. Controlling the magnetism of adsorbed metal-organic molecules.

    PubMed

    Kuch, Wolfgang; Bernien, Matthias

    2017-01-18

    Gaining control on the size or the direction of the magnetic moment of adsorbed metal-organic molecules constitutes an important step towards the realization of a surface-mounted molecular spin electronics. Such control can be gained by taking advantage of interactions of the molecule's magnetic moment with the environment. The paramagnetic moments of adsorbed metal-organic molecules, for example, can be controlled by the interaction with magnetically ordered substrates. Metalloporphyrins and -phthalocyanines display a quasi-planar geometry, allowing the central metal ion to interact with substrate electronic states. This can lead to magnetic coupling with a ferromagnetic or even antiferromagnetic substrate. The molecule-substrate coupling can be mediated and controlled by insertion layers such as oxygen atoms, graphene, or nonmagnetic metal layers. Control on the magnetic properties of adsorbed metalloporphyrins or -phthalocyanines can also be gained by on-surface chemical modification of the molecules. The magnetic moment or the magnetic coupling to ferromagnetic substrates can be changed by adsorption and thermal desorption of small molecules that interact with the fourfold-coordinated metal center via the remaining axial coordination site. Spin-crossover molecules, which possess a metastable spin state that can be switched by external stimuli such as temperature or light, are another promising class of candidates for control of magnetic properties. However, the immobilization of such molecules on a solid surface often results in a quench of the spin transition due to the interaction with the substrate. We present examples of Fe(II) spin-crossover complexes in direct contact with a solid surface that undergo a reversible spin-crossover transition as a function of temperature, by illumination with visible light, or can be switched by the tip of a scanning tunneling microscope.

  14. Controlling the magnetism of adsorbed metal-organic molecules

    NASA Astrophysics Data System (ADS)

    Kuch, Wolfgang; Bernien, Matthias

    2017-01-01

    Gaining control on the size or the direction of the magnetic moment of adsorbed metal-organic molecules constitutes an important step towards the realization of a surface-mounted molecular spin electronics. Such control can be gained by taking advantage of interactions of the molecule’s magnetic moment with the environment. The paramagnetic moments of adsorbed metal-organic molecules, for example, can be controlled by the interaction with magnetically ordered substrates. Metalloporphyrins and -phthalocyanines display a quasi-planar geometry, allowing the central metal ion to interact with substrate electronic states. This can lead to magnetic coupling with a ferromagnetic or even antiferromagnetic substrate. The molecule-substrate coupling can be mediated and controlled by insertion layers such as oxygen atoms, graphene, or nonmagnetic metal layers. Control on the magnetic properties of adsorbed metalloporphyrins or -phthalocyanines can also be gained by on-surface chemical modification of the molecules. The magnetic moment or the magnetic coupling to ferromagnetic substrates can be changed by adsorption and thermal desorption of small molecules that interact with the fourfold-coordinated metal center via the remaining axial coordination site. Spin-crossover molecules, which possess a metastable spin state that can be switched by external stimuli such as temperature or light, are another promising class of candidates for control of magnetic properties. However, the immobilization of such molecules on a solid surface often results in a quench of the spin transition due to the interaction with the substrate. We present examples of Fe(II) spin-crossover complexes in direct contact with a solid surface that undergo a reversible spin-crossover transition as a function of temperature, by illumination with visible light, or can be switched by the tip of a scanning tunneling microscope.

  15. Candidate Source of Flux Noise in SQUIDs: Adsorbed Oxygen Molecules

    NASA Astrophysics Data System (ADS)

    Wang, Hui; Shi, Chuntai; Hu, Jun; Han, Sungho; Yu, Clare C.; Wu, R. Q.

    2015-08-01

    A major obstacle to using superconducting quantum interference devices (SQUIDs) as qubits is flux noise. We propose that the heretofore mysterious spins producing flux noise could be O2 molecules adsorbed on the surface. Using density functional theory calculations, we find that an O2 molecule adsorbed on an α-alumina surface has a magnetic moment of ˜1.8 μB . The spin is oriented perpendicular to the axis of the O-O bond, the barrier to spin rotations is about 10 mK. Monte Carlo simulations of ferromagnetically coupled, anisotropic X Y spins on a square lattice find 1 /f magnetization noise, consistent with flux noise in Al SQUIDs.

  16. Resonant vibrational excitation of adsorbed molecules by electron impact

    NASA Astrophysics Data System (ADS)

    Djamo, V.; Teillet-Billy, D.; Gauyacq, J. P.

    1993-11-01

    The vibrational excitation of N2 molecules adsorbed on a silver surface by low energy electron impact is studied within the newly developed coupled angular mode method. The process involves the formation of a transient negative molecular ion. The results account well for the observations of Demuth and co-workers. They also reveal that most of the vibrational excitation corresponds to electrons scattered into the metal and thus unobservable in a scattering experiment.

  17. SPR-MS: from identifying adsorbed molecules to image tissues

    NASA Astrophysics Data System (ADS)

    Masson, Jean-François; Breault-Turcot, Julien; Forest, Simon; Chaurand, Pierre

    2015-03-01

    Surface plasmon resonance (SPR) sensors have become valuable analytical sensors for biomolecule detection. While SPR is heralded with high sensitivity, label-free and real-time detection, nonspecific adsorption and detection of ultralow concentrations remain issues. Nonspecific adsorption can be minimized using adequate surface chemistry. For example, we have employed peptide monolayers to reduce nonspecific adsorption of crude serum or cell lysate. It is important to uncover the nature of molecules nonspecifically adsorbing to surfaces in these biofluids, to further improve understanding of the nonspecific adsorption processes. Mass spectrometry (MS) provides a complementary tool to SPR to identify biomolecule adsorbed to surface. Trypsic digestion of the proteins adsorbed to surfaces led to identification of characteristic peptides from the proteins involved in nonspecific adsorption. Nonspecific adsorption in crude cell lysate results mainly from lipids, as confirmed with SPR and MS but proteins were observed on some surfaces. In another application of SPR and MS, imaging SPR can be used in combination to imaging MS to image tissue sections. Thin sections of mouse liver were inserted in the fluidic chamber of a SPRi instrument and proteins were transferred to the SPRi chip. The SPR chip was then imaged using MALDI imaging MS to identify the biomolecules that were transferred to the SPRi chip.

  18. Multiple species of noninteracting molecules adsorbed on a Bethe lattice.

    PubMed

    Cohen, Michael; Harris, A B

    2008-10-01

    A simple method, previously used to calculate the equilibrium concentration of dimers adsorbed on a Bethe lattice as a function of the dimer activity, is generalized to solve the problem of a Bethe lattice in contact with a reservoir containing a mixture of molecules. The molecules may have arbitrary sizes and shapes consistent with the geometry of the lattice and the molecules do not interact with one another except for the hard-core restriction that two molecules cannot touch the same site. We obtain a set of simultaneous nonlinear equations, one equation for each species of molecule, which determines the equilibrium concentration of each type of molecule as a function of the (arbitrary) activities of the various species. Surprisingly, regardless of the number of species, the equilibrium concentrations are given explicitly in terms of the solution of a single equation in one unknown which can be solved numerically, if need be. Some numerical examples show that increasing the activity of one species need not necessarily decrease the equilibrium concentration of all other species. We also calculate the adsorption isotherm of an "annealed" Bethe lattice consisting of two types of sites which differently influence the activity of an adsorbed molecule. We prove that if the reservoir contains a finite number of molecular species, regions of two different polymer densities cannot simultaneously exist on the lattice. The widely used Guggenheim theory of mixtures, which can also be construed as a theory of adsorption, assumes for simplicity that the molecules in the mixture are composed of elementary units, which occupy sites of a lattice of coordination number q . Guggenheim's analysis relies on approximate combinatorial formulas which become exact on a Bethe lattice of the same coordination number, as we show in an appendix. Our analysis involves no combinatorics and relies only on recognizing the statistical independence of certain quantities. Despite the nominal

  19. Detection of individual gas molecules adsorbed on graphene.

    PubMed

    Schedin, F; Geim, A K; Morozov, S V; Hill, E W; Blake, P; Katsnelson, M I; Novoselov, K S

    2007-09-01

    The ultimate aim of any detection method is to achieve such a level of sensitivity that individual quanta of a measured entity can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity. The fundamental reason limiting the resolution of such sensors is fluctuations due to thermal motion of charges and defects, which lead to intrinsic noise exceeding the sought-after signal from individual molecules, usually by many orders of magnitude. Here, we show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphene's surface. The adsorbed molecules change the local carrier concentration in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chemical detectors but also for other applications where local probes sensitive to external charge, magnetic field or mechanical strain are required.

  20. Hydration level dependence of the microscopic dynamics of water adsorbed in ultramicroporous carbon

    SciTech Connect

    Mamontov, Eugene; Yue, Yanfeng; Bahadur, Jitendra; Guo, Junjie; Contescu, Cristian I.; Gallego, Nidia C.; Melnichenko, Yuri B.

    2016-10-20

    Even when not functionalized intentionally, most carbon materials are not hydrophobic and readily adsorb water molecules from atmospheric water vapor. We have equilibrated an ultramicroporous carbon at several levels of relative humidity, thereby attaining various hydration levels. The water molecules were adsorbed on the pore walls (but did not fill completely the pore volume) and thus could be better described as hydration, or surface, rather than confined, water. We used quasielastic neutron scattering to perform a detailed investigation of the dependence of microscopic dynamics of these adsorbed water species on the hydration level and temperature. The behavior of hydration water in ultramicroporous carbon clearly demonstrates the same universal traits that characterize surface (hydration) water in other materials that are surface-hydrated. In addition, unless special treatment is intentionally applied to ultramicroporous carbon, the species filling its pores in various applications, ranging from hydrogen molecules to electrolytes, likely find themselves in contact with non-freezing water molecules characterized by rich microscopic dynamics.

  1. Controlling spins in adsorbed molecules by a chemical switch

    PubMed Central

    Wäckerlin, Christian; Chylarecka, Dorota; Kleibert, Armin; Müller, Kathrin; Iacovita, Cristian; Nolting, Frithjof; Jung, Thomas A.; Ballav, Nirmalya

    2010-01-01

    The development of chemical systems with switchable molecular spins could lead to the architecture of materials with controllable magnetic or spintronic properties. Here, we present conclusive evidence that the spin of an organometallic molecule coupled to a ferromagnetic substrate can be switched between magnetic off and on states by a chemical stimulus. This is achieved by nitric oxide (NO) functioning as an axial ligand of cobalt(II)tetraphenylporphyrin (CoTPP) ferromagnetically coupled to nickel thin-film (Ni(001)). On NO addition, the coordination sphere of Co2+ is modified and a NO–CoTPP nitrosyl complex is formed, which corresponds to an off state of the Co spin. Thermal dissociation of NO from the nitrosyl complex restores the on state of the Co spin. The NO-induced reversible off–on switching of surface-adsorbed molecular spins observed here is attributed to a spin trans effect. PMID:20975713

  2. Thermodynamic formalism of water uptakes on solid porous adsorbents for adsorption cooling applications

    NASA Astrophysics Data System (ADS)

    Sun, Baichuan; Chakraborty, Anutosh

    2014-05-01

    This Letter presents a thermodynamic formulation to calculate the amount of water vapor uptakes on various adsorbents such as zeolites, metal organic frameworks, and silica gel for the development of an advanced adsorption chiller. This formalism is developed from the rigor of the partition distribution function of each water vapor adsorptive site on adsorbents and the condensation approximation of adsorptive water molecules and is validated with experimental data. An interesting and useful finding has been established that the proposed model is thermodynamically connected with the pore structures of adsorbent materials, and the water vapor uptake highly depends on the isosteric heat of adsorption at zero surface coverage and the adsorptive sites of the adsorbent materials. Employing the proposed model, the thermodynamic trends of water vapor uptakes on various adsorbents can be estimated.

  3. Adsorption mechanism of water molecule on goethite (010) surface

    NASA Astrophysics Data System (ADS)

    Xiu, Fangyuan; Zhou, Long; Xia, Shuwei; Yu, Liangmin

    2016-12-01

    Goethite widely exists among ocean sediments; it plays an important role in fixing heavy metals and adsorbing organic contaminants. So the understanding of the adsorbing process of water molecule on its surface will be very helpful to further reveal such environmental friendly processes. The configuration, electronic properties and interaction energy of water molecules adsorbed on pnma goethite (010) surface were investigated in detail by using density functional theory on 6-31G (d,p) basis set and projector- augment wave (PAW) method. The mechanism of the interaction between goethite surface and H2O was proposed. Despite the differences in total energy, there are four possible types of water molecule adsorption configurations on goethite (010) surface (Aa, Ab, Ba, Bb), forming coordination bond with surface Fe atom. Results of theoretical modeling indicate that the dissociation process of adsorbed water is an endothermic reaction with high activation energy. The dissociation of adsorbed water molecule is a proton transportation process between water's O atoms and surface. PDOS results indicate that the bonding between H2O and (010) surface is due to the overlapping of water's 2p orbitals and Fe's 3d orbitals. These results clarify the mechanism on how adsorbed water is dissociated on the surface of goethite and potentially provide useful information of the surface chemistry of goethite.

  4. Procedure for freeze-drying molecules adsorbed to mica flakes.

    PubMed

    Heuser, J E

    1983-09-05

    The quick-freeze, deep-etch, rotary-replication technique is useful for visualizing cells and cell fractions but does not work with suspensions of macromolecules. These inevitably clump or collapse during deep-etching, presumably due to surface tension forces that develop during their transfer from ice to vacuum. Previous protocols have attempted to overcome such forces by attaching macromolecules to freshly cleaved mica before drying and replication. I describe here an adaptation of this procedure to the deep-etch technique as otherwise practiced. My innovation is to mix the molecules with an aqueous suspension of tiny flakes of mica and then to quick-freeze and freeze-fracture the suspension exactly as if one were dealing with cells. The fracture inevitably strikes the surfaces of many mica flakes and thereby cleaves the adsorbed macromolecules cleanly enough to reveal interesting substructure within them. The subsequent step of deep-etching exposes large expanses of unfractured mica and thus reveals intact macromolecules. These macromolecules are not obscured by salt deposits, even if they were frozen in hypertonic solutions, apparently because the fracturing step removes nearly all of the overlying electrolyte. Moreover, these macromolecules are minimally freeze-dried (since exposure is sufficient after only 3 min of etching at -102 degrees C) so they retain their three-dimensional topology. I show that molluscan hemocyanin is a good internal standard for this new technique. It is available commercially in stable solutions, mixes well with all sizes of macromolecules, and consists of particles that display distinct five-start surface helices, which have been measured carefully in the past and which possess a known handedness, useful for determining the orientation of micrographs when examining the various helical patterns possessed by most types of extended macromolecules. The fractured hemocyanin particles also display characteristic internal structures, which

  5. Application of 1H NMR spectroscopy method for determination of characteristics of thin layers of water adsorbed on the surface of dispersed and porous adsorbents.

    PubMed

    Turov, V V; Leboda, R

    1999-02-01

    The paper presents 1H NMR spectroscopy as a perspective method of the studies of the characteristics of water boundary layers in the hydrated powders and aqueous dispergated suspensions of the adsorbents. The method involves measurements of temperature dependence proton signals intensity in the adsorbed water at temperatures lower than 273 K. Free energy of water molecules at the adsorbent/water interface is diminished due to the adsorption interactions causing the water dosed to the adsorbent surface freezes at T < 273 K. Thickness of a non-freezing layer of water can be determined from the intensity of the water signal of 1H NMR during the freezing-thawing process. Due to a disturbing action of the adsorbent surface, water occurs in the quasi-liquid state. As a result, it is observed in the 1H NMR spectra as a relatively narrow signal. The signal of ice is not registered due to great differences in the transverse relaxation times of the adsorbed water and ice. The method of measuring the free surface energy of the adsorbents from the temperature dependence of the signal intensity of non-freezing water is based on the fact that the temperature of water freezing decreases by the quantity which depends on the surface energy and the distance of the adsorbed molecules from the solid surface. The water at the interface freezes when the free energies of the adsorbed water and ice are equal. To illustrate the applicability of the method under consideration the series of adsorption systems in which the absorbents used differed in the surface chemistry and porous structure. In particular, the behaviour of water on the surface of the following adsorbents is discussed: non-porous and porous silica (aerosils, silica gels); chemically and physically modified non-porous and porous silica (silanization, carbonization, biopolymer deposition); and pyrogeneous Al2O3 and aluminasilicas. The effect of preliminary treatment of the adsorbent (thermal, high pressure, wetting with polar

  6. First-principles study of the dielectric functions of carbon nanotubes with adsorbed water

    NASA Astrophysics Data System (ADS)

    Iwasaki, Daisuke; Suzuki, Yasumitsu; Watanabe, Kazuyuki

    2017-04-01

    A recent study demonstrated adsorption of water molecules on the surfaces of carbon nanotubes (CNTs). Importantly, it was reported that the peak positions in the absorption and photoluminescence spectra of the CNTs were shifted to lower energy as the number of adsorbed water molecules increased. Here, we investigated the mechanism by which this redshift occurs by calculating the dielectric functions of CNTs following water adsorption using density functional theory. Our calculations reproduced the redshifts and demonstrated that they can be attributed to decreases in the band gaps, which result from electronic coupling between the CNTs and the water molecules.

  7. Substrate-mediated interactions and intermolecular forces between molecules adsorbed on surfaces.

    PubMed

    Sykes, E Charles H; Han, Patrick; Kandel, S Alex; Kelly, Kevin F; McCarty, Gregory S; Weiss, Paul S

    2003-12-01

    Adsorbate interactions and reactions on metal surfaces have been investigated using scanning tunneling microscopy. The manners in which adsorbates perturb the surface electronic structure in their vicinity are discussed. The effects these perturbations have on other molecules are shown to be important in overlayer growth. Interactions of molecules with surface steps are addressed, and each molecule's electron affinity is shown to dictate its adsorption sites at step edges. Standing waves emanating from steps are demonstrated to effect transient molecular adsorption up to 40 A away from the step edge. Halobenzene derivatives are used to demonstrate how the surface is important in aligning reactive intermediates.

  8. Laser electrospray mass spectrometry of adsorbed molecules at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Brady, John J.; Judge, Elizabeth J.; Simon, Kuriakose; Levis, Robert J.

    2010-02-01

    Atmospheric pressure mass analysis of solid phase biomolecules is performed using laser electrospray mass spectrometry (LEMS). A non-resonant femtosecond duration laser pulse vaporizes native samples at atmospheric pressure for subsequent electrospray ionization and transfer into a mass spectrometer. LEMS was used to detect a complex molecule (irinotecan HCl), a complex mixture (cold medicine formulation with active ingredients: acetaminophen, dextromethorphan HBr and doxylamine succinate), and a biological building block (deoxyguanosine) deposited on steel surfaces without a matrix molecule.

  9. Unconventional superconductivity induced in Nb films by adsorbed chiral molecules

    NASA Astrophysics Data System (ADS)

    Alpern, H.; Katzir, E.; Yochelis, S.; Katz, N.; Paltiel, Y.; Millo, O.

    2016-11-01

    Motivated by recent observations of chiral-induced magnetization and spin-selective transport we studied the effect of chiral molecules on conventional BCS superconductors. By applying scanning tunneling spectroscopy, we demonstrate that the singlet-pairing s-wave order parameter of Nb is significantly altered upon adsorption of chiral polyalanine alpha-helix molecules on its surface. The tunneling spectra exhibit zero-bias conductance peaks embedded inside gaps or gap-like features, suggesting the emergence of unconventional triplet-pairing components with either d-wave or p-wave symmetry at the Nb organic-molecules interface, as corroborated by simulations. These results may open a way for realizing simple superconducting spintronics devices.

  10. Hydration level dependence of the microscopic dynamics of water adsorbed in ultramicroporous carbon

    DOE PAGES

    Mamontov, Eugene; Yue, Yanfeng; Bahadur, Jitendra; ...

    2016-10-20

    Even when not functionalized intentionally, most carbon materials are not hydrophobic and readily adsorb water molecules from atmospheric water vapor. We have equilibrated an ultramicroporous carbon at several levels of relative humidity, thereby attaining various hydration levels. The water molecules were adsorbed on the pore walls (but did not fill completely the pore volume) and thus could be better described as hydration, or surface, rather than confined, water. We used quasielastic neutron scattering to perform a detailed investigation of the dependence of microscopic dynamics of these adsorbed water species on the hydration level and temperature. The behavior of hydration watermore » in ultramicroporous carbon clearly demonstrates the same universal traits that characterize surface (hydration) water in other materials that are surface-hydrated. In addition, unless special treatment is intentionally applied to ultramicroporous carbon, the species filling its pores in various applications, ranging from hydrogen molecules to electrolytes, likely find themselves in contact with non-freezing water molecules characterized by rich microscopic dynamics.« less

  11. Transient magnetization of core excited organic molecules adsorbed on graphene

    NASA Astrophysics Data System (ADS)

    Ravikumar, Abhilash; Baby, Anu; Lin, He; Brivio, Gian Paolo; Fratesi, Guido

    This work presents a density functional theory based computational investigation of electronic and magnetic properties of physisorbed and chemisorbed organic molecules on graphene in the ground state and core excited one at low molecular coverage. For physisorbed molecules, where the interaction with graphene is dominated by van der Waals forces and the system is non-magnetic in the ground state, it is found that the valence electrons relax towards a spin polarized configuration upon excitation of a core-level electron. The magnetism depends on efficient electron transfer from graphene on the femtosecond time scale. On the contrary, when graphene is covalently functionalized, the system is magnetic in the ground state presenting two spin dependent mid gap states localized around the adsorption site. At variance with the physisorbed case upon core-level excitation, the LUMO of the molecule and the mid gap states of graphene hybridize and the relaxed valence shell is not magnetic anymore. This project has received funding from the European Union Seventh Framework Programme under grant agreement n∘ 607232 [THINFACE].

  12. Resonant electron scattering by molecules adsorbed on a surface: N2-Ag system

    NASA Astrophysics Data System (ADS)

    Teillet-Billy, D.; Djamo, V.; Gauyacq, J. P.

    1992-05-01

    A model study of resonant electron scattering by static molecules adsorbed on a metal surface is presented, using the recently developed coupled angular mode (CAM) method. It is applied to the case of N2 molecules adsorbed on an Ag surface. The N2-2πg resonance characteristics (energy position and width) are determined and shown to be modified by the presence of the surface in qualitative agreement with the experimental results of Demuth et al. [Phys. Rev. Lett. 47 (1981) 1166].

  13. Rotational Spectromicroscopy: Imaging the Orbital Interaction between Molecular Hydrogen and an Adsorbed Molecule

    NASA Astrophysics Data System (ADS)

    Li, Shaowei; Yuan, Dingwang; Yu, Arthur; Czap, Gregory; Wu, Ruqian; Ho, W.

    2015-05-01

    A hydrogen molecule can diffuse freely on the surface and be trapped above an adsorbed molecule within the junction of a scanning tunneling microscope. The trapped dihydrogen exhibits the properties of a free rotor. Here we show that the intermolecular interaction between dihydrogen and Mg-porphyrin (MgP) can be visualized by imaging j =0 to 2 rotational excitation of dihydrogen. The interaction leads to a weakened H-H bond and modest electron donation from the dihydrogen to the lowest unoccupied molecular orbital of MgP, a process similarly observed for the interaction between dihydrogen and an adsorbed Au atom.

  14. Structure of water adsorbed on a single graphene sheet

    NASA Astrophysics Data System (ADS)

    Gordillo, M. C.; Martí, J.

    2008-08-01

    We present the result of molecular-dynamics simulations of water adsorbed on top of a single graphene layer at temperatures between 25 and 50°C . The analysis of the energy per particle and the density profiles indicate that the behavior of the adsorbed liquid is similar to the case of multiple graphene layers (graphite) with the only difference being the values of configurational energy. Other structural properties, such as stability ranges, hydrogen bond distributions, and molecular orientations are also presented.

  15. Dynamics of Molecules Adsorbed in Zeolitic Systems: Neutron Scattering and MD Simulation Studies

    NASA Astrophysics Data System (ADS)

    Mitra, S.; Sharma, V. K.; Mukhopadhyay, R.

    2011-07-01

    Zeolites represent a class of technologically important materials because of their characteristic properties of molecular sieving and catalysis, which makes them indispensable in the petroleum industries. While the catalytic properties depend upon many factors, a major role is played by the dynamics of hydrocarbon gases. In order to be able to tailor make these materials for use in industry for catalytic and sieving purposes, it is important to understand the dynamical properties of the guest molecules adsorbed in the zeolitic materials. It is of interest to study the effects of size and shape of guest molecules and also the host zeolitic structure, governing the diffusion mechanism of the adsorbed species. Here we report the results of Quasielastic Neutron Scattering (QENS) and classical molecular dynamics (MD) simulation studies of two hydrocarbons namely acetylene and propylene adsorbed in two structurally different zeolites Na-Y and ZSM-5.

  16. Spectroscopic observations of the displacement dynamics of physically adsorbed molecules-CO on C60

    NASA Astrophysics Data System (ADS)

    Yuan, Chunqing; Yates, John T.

    2016-10-01

    In this paper, we observed physically adsorbed CO molecules on C60 surface being displaced by impinging noble gas atoms (He, Ne, Ar, Kr), either through a dynamic displacement process or an exothermic replacement process, depending on their adsorption energies. This displacement mechanism could shift from one to the other depending on the surface coverage and temperature. Furthermore, rotational energy of the impinging molecules may also contribute to the dynamic displacement process by supplying additional energy.

  17. Vibrational excitation of adsorbed molecules by low-energy photon-emitted electrons: A dynamical model

    NASA Astrophysics Data System (ADS)

    González Ureña, A.; Telle, H. H.; Tornero, J.

    2013-01-01

    A simple, inelastic electron-scattering dynamical model is presented to account for vibrational excitation in molecular adsorbates. The basic two ingredients of the theoretical model are: (i) the conservation of the total angular momentum, and (ii) the requirement of a critical time to allow for the intra-molecular energy re-arrangement of the transient negative-ion complex. The model is applied to the vibrational excitation dynamics of molecules chemisorbed at sub-monolayer conditions on ordered metal surfaces. This was exemplified for Acrylonitrile adsorbed on Cu(1 0 0), whose vibrational excitation was studied via energy loss spectra of low-energy two-photon photoemission (2PPE) electrons, and for ammonia (NH3 and ND3) adsorbed on Cu(1 0 0), being probed in a STM experiment. Fits of the model to the data allowed for deducing the energy threshold of the vibrational excitation of the Cdbnd C and Ctbnd N bonds of the ACN adsorbate molecules, and the threshold for the symmetric ν1-stretch mode excitation of adsorbed NH3/ND3. Also, information about the temporal dynamics underlying the inelastic electron scattering was gained.

  18. Structure, Dynamics, and Thermodynamics of Small Molecules Adsorbed in Zeolite Micropores: Simulation and Statistical Mechanics.

    NASA Astrophysics Data System (ADS)

    van Tassel, Paul Robert

    1993-01-01

    This thesis describes a fully detailed molecular simulation and modeling effort aimed at understanding the fundamentals of adsorption and diffusion of small molecules in zeolite micropores. The primary emphasis is on determining the relationship between the structure and chemistry of the zeolite adsorbent and the structure, dynamics, and thermodynamics of the adsorbed phase. Further emphasis is on developing simple, predictive models of zeolite adsorption and diffusion. We begin by presenting a Monte Carlo simulation of single component adsorption of xenon, methane, and argon in zeolite NaA. The form of the adsorbate density distribution indicates the presence of discrete adsorption sites which arrange in polyhedra whose geometry depends on the number and position of zeolite framework ions. Isotherm plateaus are attributed to either (i) a low energy adsorbate configuration or (ii) the saturation of polyhedral sites. Viewing the adsorbed phase as an ordered arrangement differs from the conventional delocalized model, yet it helps explain certain experimental observations. Next, a study of binary mixtures of small molecules in zeolite NaA using the Monte Carlo method is presented. The mixing in the pore is determined to be highly nonideal by comparison to a simple pore volume filling model. Strong selectivity for a more polarizable molecule (xenon) is observed only at low pore loading. At higher pore loading, a smaller, less polarizable molecule (argon) adsorbs selectively at a significantly lower pressure than predicted by the model. This enhanced selectivity is due to the ability of the smaller molecule to pack more efficiently inside of the pore. Finally, we present two simple lattice models whose forms are arrived at following careful consideration of simulation results. The first describes the adsorption of small molecules in a zeolite. A polyhedral lattice is postulated whose neighboring sites interact energetically and entropically. The second model describes

  19. Hydraulic properties of adsorbed water films in unsaturated porous media

    SciTech Connect

    Tokunaga, Tetsu K.

    2009-03-01

    Adsorbed water films strongly influence residual water saturations and hydraulic conductivities in porous media at low saturations. Hydraulic properties of adsorbed water films in unsaturated porous media were investigated through combining Langmuir's film model with scaling analysis, without use of any adjustable parameters. Diffuse double layer influences are predicted to be important through the strong dependence of adsorbed water film thickness (f) on matric potential ({Psi}) and ion charge (z). Film thickness, film velocity, and unsaturated hydraulic conductivity are predicted to vary with z{sup -1}, z{sup -2}, and z{sup -3}, respectively. In monodisperse granular media, the characteristic grain size ({lambda}) controls film hydraulics through {lambda}{sup -1} scaling of (1) the perimeter length per unit cross sectional area over which films occur, (2) the critical matric potential ({Psi}{sub c}) below which films control flow, and (3) the magnitude of the unsaturated hydraulic conductivity when {Psi} < {Psi}{sub c}. While it is recognized that finer textured sediments have higher unsaturated hydraulic conductivities than coarser sands at intermediate {Psi}, the {lambda}{sup -1} scaling of hydraulic conductivity predicted here extends this understanding to very low saturations where all pores are drained. Extremely low unsaturated hydraulic conductivities are predicted under adsorbed film-controlled conditions (generally < 0.1 mm y{sup -1}). On flat surfaces, the film hydraulic diffusivity is shown to be constant (invariant with respect to {Psi}).

  20. Rod-like cyanophenyl probe molecules nanoconfined to oxide particles: Density of adsorbed surface species

    NASA Astrophysics Data System (ADS)

    Frunza, Stefan; Frunza, Ligia; Ganea, Constantin Paul; Zgura, Irina; Brás, Ana Rita; Schönhals, Andreas

    2016-02-01

    Surface layers have already been observed by broadband dielectric spectroscopy for composite systems formed by adsorption of rod-like cyanophenyl derivates as probe molecules on the surface of oxide particles. In this work, features of the surface layer are reported; samples with different amounts of the probe molecules adsorbed onto oxide (nano) particles were prepared in order to study their interactions with the surface. Thermogravimetric analysis (TGA) was applied to analyze the amount of loaded probe molecules. The density of the surface species ns was introduced and its values were estimated from quantitative Fourier transform infrared spectroscopy (FTIR) coupled with TGA. This parameter allows discriminating the composites into several groups assuming a similar interaction of the probe molecules with the hosts of a given group. An influence factor H is further proposed as the ratio of the number of molecules in the surface layer showing a glassy dynamics and the number of molecules adsorbed tightly on the surface of the support: It was found for aerosil composites and used for calculating the maximum filling degree of partially filled silica MCM-41 composites showing only one dielectric process characteristic for glass-forming liquids and a bulk behavior for higher filling degrees.

  1. Stability, structural and electronic properties of benzene molecule adsorbed on free standing Au layer

    NASA Astrophysics Data System (ADS)

    Katoch, Neha; Kapoor, Pooja; Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.

    2016-05-01

    We report stability and electronic properties of benzene molecule adsorbed on the Au atomic layer within the framework of density function theory (DFT). Horizontal configuration of benzene on the top site of Au monolayer prefers energetically over other studied configurations. On the adsorption of benzene, the ballistic conductance of Au monolayer is found to decrease from 4G0 to 2G0 suggesting its applications for the fabrications of organic sensor devices based on the Au atomic layers.

  2. Detection of adsorbed water and hydroxyl on the Moon.

    PubMed

    Clark, Roger N

    2009-10-23

    Data from the Visual and Infrared Mapping Spectrometer (VIMS) on Cassini during its flyby of the Moon in 1999 show a broad absorption at 3 micrometers due to adsorbed water and near 2.8 micrometers attributed to hydroxyl in the sunlit surface on the Moon. The amounts of water indicated in the spectra depend on the type of mixing and the grain sizes in the rocks and soils but could be 10 to 1000 parts per million and locally higher. Water in the polar regions may be water that has migrated to the colder environments there. Trace hydroxyl is observed in the anorthositic highlands at lower latitudes.

  3. Detection of adsorbed water and hydroxyl on the moon

    USGS Publications Warehouse

    Clark, R.N.

    2009-01-01

    Data from the Visual and Infrared Mapping Spectrometer (VIAAS) on Cassini during its flyby of the AAoon in 1999 show a broad absorption at 3 micrometers due to adsorbed water and near 2.8 micrometers attributed to hydroxyl in the sunlit surface on the AAoon. The amounts of water indicated in the spectra depend on the type of mixing and the grain sizes in the rocks and soils but could be 10 to 1000 parts per million and locally higher. Water in the polar regions may be water that has migrated to the colder environments there. Trace hydroxyl is observed in the anorthositic highlands at lower latitudes.

  4. Role(s) of adsorbed water in the surface chemistry of environmental interfaces.

    PubMed

    Rubasinghege, Gayan; Grassian, Vicki H

    2013-04-18

    The chemistry of environmental interfaces such as oxide and carbonate surfaces under ambient conditions of temperature and relative humidity is of great interest from many perspectives including heterogeneous atmospheric chemistry, heterogeneous catalysis, photocatalysis, sensor technology, corrosion science, and cultural heritage science. As discussed here, adsorbed water plays important roles in the reaction chemistry of oxide and carbonate surfaces with indoor and outdoor pollutant molecules including nitrogen oxides, sulfur dioxide, carbon dioxide, ozone and organic acids. Mechanisms of these reactions are just beginning to be unraveled and found to depend on the details of the reaction mechanism as well as the coverage of water on the surface. As discussed here, adsorbed water can: (i) alter reaction pathways and surface speciation relative to the dry surface; (ii) hydrolyze reactants, intermediates and products; (iii) enhance surface reactivity by providing a medium for ionic dissociation; (iv) inhibit surface reactivity by blocking sites; (v) solvate ions; (vi) enhance ion mobility on surfaces and (vii) alter the stability of surface adsorbed species. In this feature article, drawing on research that has been going on for over a decade on the reaction chemistry of oxide and carbonate surfaces under ambient conditions of temperature and relative humidity, a number of specific examples showing the multi-faceted roles of adsorbed water are presented.

  5. Adsorbent selection for endosulfan removal from water environment.

    PubMed

    Sudhakar, Y; Dikshit, A K

    1999-01-01

    In the present study, an attempt was made to select a low cost adsorbing material for the removal of endosulfan [C,C'-(1,4,5,6,7,7-hexachloro-8,9,10- trinorborn-5-en-2,3-ylene)(dimethylsulphite)] from water. Various low cost adsorbents like wood charcoal, kimberlite tailings, silica, macro fungi sojar caju were tried with activated charcoal as reference material. The above materials were selected from various sources encompassing organic, inorganic, clayey, and biological sources. For the selection of suitable adsorbent for endosulfan uptake, maximum adsorption capacity (Qmax) was chosen as the parameter. Kinetic profiles of removal were generated for all the materials to assess the equilibrium time. Equilibrium studies were carried out for all materials to assess the adsorption equilibrium model that they followed. The model that gave the best correlation coefficient by linear regression analysis, was adopted for the calculation of Qmax of the corresponding adsorbent material. Using linearised forms of equilibrium models like Langmuir, BET, and Freundlich, maximum adsorptive capacities were determined. Activated charcoal showed the best adsorptive capacity with Qmax of 2.145 mg/g followed by wood charcoal 1.773 mg/g, sojar caju 1.575 mg/g, kimberlite tailings 0.8821 mg/g, and silica 0.3231 mg/g. Albeit activated charcoal gave better performance, it was not considered as a candidate material because of its high cost. Wood charcoal was the next best adsorbent with Qmax 1.773 mg/g. Therefore, wood charcoal was chosen as the best material for endosulfan removal. The study of physical and chemical characteristics of wood charcoal revealed that it is a potential adsorbent and can even be improved further.

  6. Turning things downside up: Adsorbate induced water flipping on Pt(111)

    SciTech Connect

    Kimmel, Greg A. E-mail: bruce.kay@pnnl.gov; Zubkov, Tykhon; Smith, R. Scott; Petrik, Nikolay G.; Kay, Bruce D. E-mail: bruce.kay@pnnl.gov

    2014-11-14

    We have examined the adsorption of the weakly bound species N{sub 2}, O{sub 2}, CO, and Kr on the (√(37)×√(37))R25.3{sup ∘} water monolayer on Pt(111) using a combination of molecular beam dosing, infrared reflection absorption spectroscopy, and temperature programmed desorption. In contrast to multilayer crystalline ice, the adsorbate-free water monolayer is characterized by a lack of dangling OH bonds protruding into the vacuum (H-up). Instead, the non-hydrogen-bonded OH groups are oriented downward (H-down) to maximize their interaction with the underlying Pt(111) substrate. Adsorption of Kr and O{sub 2} have little effect on the structure and vibrational spectrum of the “√(37)” water monolayer while adsorption of both N{sub 2}, and CO are effective in “flipping” H-down water molecules into an H-up configuration. This “flipping” occurs readily upon adsorption at temperatures as low as 20 K and the water monolayer transforms back to the H-down, “√(37)” structure upon adsorbate desorption above 35 K, indicating small energy differences and barriers between the H-down and H-up configurations. The results suggest that converting water in the first layer from H-down to H-up is mediated by the electrostatic interactions between the water and the adsorbates.

  7. Turning things downside up: Adsorbate induced water flipping on Pt(111)

    SciTech Connect

    Kimmel, Gregory A.; Zubkov, Tykhon; Smith, R. Scott; Petrik, Nikolay G.; Kay, Bruce D.

    2014-11-14

    We have examined the adsorption of the weakly bound species N2, O2, CO and Kr on the water monolayer on Pt(111) using a combination of molecular beam dosing, infrared reflection absorption spectroscopy (IRAS), and temperature programmed desorption (TPD). In contrast to multilayer crystalline ice, the adsorbate-free water monolayer is characterized by a lack of dangling OH bonds protruding into the vacuum (H-up). Instead, the non-hydrogen-bonded OH groups are oriented downward (H-down) to maximize their interaction with the underlying Pt(111) substrate. Adsorption of Kr and O2 have little effect on the structure and vibrational spectrum of the “ ” water monolayer while adsorption of both N2, and CO are effective in “flipping” H-down water molecules into an H-up configuration. This “flipping” occurs readily upon adsorption at temperatures as low as 20 K and the water monolayer transforms back to the H-down, “ ” structure upon adsorbate desorption above 35 K, indicating small energy differences and barriers between the H-down and H-up configurations. The results suggest that converting water in the first layer from H-down to H-up is mediated by the electrostatic interactions between the water and the adsorbates.

  8. Chemical effects on vibrational properties of adsorbed molecules on metal surfaces: Coverage dependence

    NASA Astrophysics Data System (ADS)

    Ueba, H.

    1987-10-01

    Vibrational properties of chemisorbed molecules on metal surfaces are studied with a focus on the coverage dependent chemical shift of the frequencies. Available experimental data of a CO adsorption on transition metal and noble metal surfaces are analyzed in the light of the coverage dependent back-donation into the 2 π* orbitals of chemisorbed CO molecules. The vibrational frequency ωCO of the intramolecular stretching mode exhibits a downward shift of varying magnitude, depending on the amount of back-donation into the 2 π* orbitals of the chemisorbed CO. On increasing the coverage θ, ωCO usually increases due to the dipole-dipole interaction. On Cu surfaces, however, the shifts are relatively small, or in some cases, negative. So far, this anomalous frequency shift with θ is understood as a result of competitive effect between the upward dipole Ωdip and the downward chemical shift Ωchem associated with back-donation. The purpose of this paper is to establish the possible origin of the downward frequency shift through the electronic properties of an incomplete monolayer of adsorbates. The adsorbate density of states ρa is calculated by means of the coherent potential approximation, in which the electron hopping between the adsorbates (band formation effect) and the depolarization effect due to the proximity of ionized adsorbed molecules are taken into account. The change of the occupied portion of ρa and ρa ( ɛF) at the Fermi level ɛF with increasing θ then manifests itself in the coverage dependent Ωchem not only due to the static back-donation, but also due to the dynamical charge fluctuation during vibrational excitation. It is found that in a weakly chemisorbed system, such as CO/Cu, the negative Ωchem amounts to Ωdip at low θ. Consequently the apparent total frequency shift remains almost constant. As the coverage increases, Ωchem becomes larger than Ωdip due to the band effect. It is also shown that the variation of the back

  9. Removal of antibiotics from water using sewage sludge- and waste oil sludge-derived adsorbents.

    PubMed

    Ding, Rui; Zhang, Pengfei; Seredych, Mykola; Bandosz, Teresa J

    2012-09-01

    Sewage sludge- and waste oil sludge-derived materials were tested as adsorbents of pharmaceuticals from diluted water solutions. Simultaneous retention of eleven antibiotics plus two anticonvulsants was examined via batch adsorption experiments. Virgin and exhausted adsorbents were examined via thermal and FTIR analyses to elucidate adsorption mechanisms. Maximum adsorption capacities for the 6 materials tested ranged from 80 to 300 mg/g, comparable to the adsorption capacities of antibiotics on various activated carbons (200-400 mg/g) reported in the literature. The performance was linked to surface reactivity, polarity and porosity. A large volume of pores similar in size to the adsorbate molecules with hydrophobic carbon-based origin of pore walls was indicated as an important factor promoting the separation process. Moreover, the polar surface of an inorganic phase in the adsorbents attracted the functional groups of target molecules. The presence of reactive alkali metals promoted reaction with acidic groups, formation of salts and their precipitation in the pore system.

  10. Formation of Adsorbed Oxygen Radicals on Minerals at the Martian Surface and the Decomposition of Organic Molecules

    NASA Technical Reports Server (NTRS)

    Yen, A. S.; Kim, S. S.; Freeman, B. A.; Hecht, M. H.

    2000-01-01

    We present experimental evidence that superoxide ions form on mineral grains at the martian surface and show that these adsorbates can explain the unusual reactivity of the soil as well as the apparent absence of organic molecules.

  11. Homeotropic orientation of a nematic liquid crystal by bent-core molecules adsorbed on its surface

    NASA Astrophysics Data System (ADS)

    Hwang, Jiyong; Yang, Seungbin; Lee, Hyojin; Kim, Jongyoon; Lee, Ji-Hoon; Kang, Shin-Woong; Choi, E.-Joon

    2015-06-01

    We reported the promotion of a homeotropic alignment of a nematic liquid crystal (NLC) by bent-core liquid-crystal (BLC) Molecules adsorbed its surface. The BLC was mixed at various concentrations with the NLC, and the mixtures were injected into an empty cell with a cell gap of 13 μm. Although the pure NLC showed a heterogeneous orientation, the BLC-NLC mixture was gradually transformed to a homeotropic alignment with increasing concentration of the BLC. We investigated the surface topography of the samples by using an atomic force microscopy (AFM) and found that the BLC molecules were segregated into a polyimide (PI) surface and formed protrusion domains with diameters of 50-100 nm. The BLC protrusions might promote the homeotropic orientation of the NLC molecules.

  12. Structure of water adsorbed on a mica surface

    SciTech Connect

    Park, Sung-Ho; Sposito, Garrison

    2002-01-29

    Monte Carlo simulations of hydration water on the mica (001) surface under ambient conditions revealed water molecules bound closely to the ditrigonal cavities in the surface, with a lateral distribution of approximately one per cavity, and water molecules interposed between K{sup +} counter ions in a layer situated about 2.5 {angstrom} from a surface O along a direction normal to the (001) plane. The calculated water O density profile was in quantitative agreement with recent X-ray reflectivity measurements indicating strong lateral ordering of the hydration water but liquid-like disorder otherwise.

  13. Structure formation in adsorbed overlayers comprising functional cross-shaped molecules: A Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Kasperski, Adam; Nieckarz, Damian; Szabelski, Paweł

    2015-11-01

    Surface confined self-assembly of functional star-shaped organic molecules is a promising method to create nanoporous networks with tailorable structure and functions. In this work we use the Monte Carlo simulation method to demonstrate how the morphology of these supramolecular assemblies can be tuned by manipulating intrinsic parameters of the building blocks and modified by the presence of co-adsorbed metal atoms. To that purpose we study the 2D self-assembly of planar cruciform molecules modeled as collections of interconnected segments, some of which were activated to represent discrete interaction centers. We consider a few exemplary adsorbed systems in which the molecules with different size, aspect ratio and intramolecular distribution of active centers form superstructures stabilized by short-range segment-segment interactions or by metal-segment interactions. These two situations correspond to supramolecular assemblies sustained by, for example, hydrogen bonding and metal-organic ligand coordination, respectively. The simulated results show that proper encoding of intramolecular interactions into the cruciform building bricks allows for directing the self-assembly towards largely diversified structures ranging from nanoclusters to porous grids. The obtained findings can facilitate designing and optimization of molecular networks comprising cross-shaped units including functionalized porphyrins and phthalocyanines and they can be helpful in preliminary selection of these building blocks.

  14. Adsorption of prototypical amino acids on silica: Influence of the pre-adsorbed water multilayer

    NASA Astrophysics Data System (ADS)

    Remesal, Elena R.; Amaya, Javier; Graciani, Jesús; Márquez, Antonio M.; Sanz, Javier Fdez.

    2016-04-01

    We explore the interaction between acetic acid, some typical α-amino acids (α-AAs), and a fully hydroxylated (0001) surface of α-quartz by means of theoretical calculations based on the density functional theory (DFT) under periodic boundary conditions. The influence of microsolvation, represented by a water multilayer, and dispersion forces is analyzed. All the considered molecules strongly adsorb on the hydroxylated surface and prefer to adsorb molecularly. The inclusion of dispersion forces increases the interaction energies by 15-30 kJ/mol, without significant changes in structure and mode of adsorption except for histidine where the interaction is improved through protonation of the α-amine group. When the water multilayer is included a decrease in the surface-adsorbate interaction energies is observed. Also, some α-AAs, glycine and alanine, change their adsorption mode and, now, the more stable structure is the zwitterion. Adsorption as zwitterions is always favored with respect to molecular interaction when dispersion forces are taken into account. Comparing the energies of adsorbed and solvated α-AA zwitterions, it turns out that inclusion of dispersion forces predicts that solvated zwitterions are the lower energy configurations.

  15. Aging of the nanosized photochromic WO3 films and the role of adsorbed water in the photochromism

    NASA Astrophysics Data System (ADS)

    Gavrilyuk, A. I.

    2016-02-01

    Here it has been reported on aging of the nanosized WO3 film, which is revealed is continuous reduction of the photochromic sensitivity over time. Water molecules physically adsorbed on the film surface from ambient air form donor-acceptor and hydrogen bonds, changing gradually the adsorption state to chemisorption which prevents an access of organic molecules that serve as hydrogen donors by the photochromism. The mechanism of the process has been investigated and discussed. The role of water in the photochromism has been highlighted. The difference in the efficiency for being of a hydrogen donor in the photochromic process between water and organic molecules is discussed.

  16. Water: a responsive small molecule.

    PubMed

    Shultz, Mary Jane; Vu, Tuan Hoang; Meyer, Bryce; Bisson, Patrick

    2012-01-17

    Unique among small molecules, water forms a nearly tetrahedral yet flexible hydrogen-bond network. In addition to its flexibility, this network is dynamic: bonds are formed or broken on a picosecond time scale. These unique features make probing the local structure of water challenging. Despite the challenges, there is intense interest in developing a picture of the local water structure due to water's fundamental importance in many fields of chemistry. Understanding changes in the local network structure of water near solutes likely holds the key to unlock problems from analyzing parameters that determine the three dimensional structure of proteins to modeling the fate of volatile materials released into the atmosphere. Pictures of the local structure of water are heavily influenced by what is known about the structure of ice. In hexagonal I(h) ice, the most stable form of solid water under ordinary conditions, water has an equal number of donor and acceptor bonds; a kind of symmetry. This symmetric tetrahedral coordination is only approximately preserved in the liquid. The most obvious manifestation of this altered tetrahedral bonding is the greater density in the liquid compared with the solid. Formation of an interface or addition of solutes further modifies the local bonding in water. Because the O-H stretching frequency is sensitive to the environment, vibrational spectroscopy provides an excellent probe for the hydrogen-bond structure in water. In this Account, we examine both local interactions between water and small solutes and longer range interactions at the aqueous surface. Locally, the results suggest that water is not a symmetric donor or acceptor, but rather has a propensity to act as an acceptor. In interactions with hydrocarbons, action is centered at the water oxygen. For soluble inorganic salts, interaction is greater with the cation than the anion. The vibrational spectrum of the surface of salt solutions is altered compared with that of neat

  17. Water molecules orientation in surface layer

    NASA Astrophysics Data System (ADS)

    Klingo, V. V.

    2000-08-01

    The water molecules orientation has been investigated theoretically in the water surface layer. The surface molecule orientation is determined by the direction of a molecule dipole moment in relation to outward normal to the water surface. Entropy expressions of the superficial molecules in statistical meaning and from thermodynamical approach to a liquid surface tension have been found. The molecules share directed opposite to the outward normal that is hydrogen protons inside is equal 51.6%. 48.4% water molecules are directed along to surface outward normal that is by oxygen inside. A potential jump at the water surface layer amounts about 0.2 volts.

  18. Molecular resonant dissociation of surface-adsorbed molecules by plasmonic nanoscissors

    NASA Astrophysics Data System (ADS)

    Zhang, Zhenglong; Sheng, Shaoxiang; Zheng, Hairong; Xu, Hongxing; Sun, Mengtao

    2014-04-01

    The ability to break individual bonds or specific modes in chemical reactions is an ardently sought goal by chemists and physicists. While photochemistry based methodologies are very successful in controlling e.g. photocatalysis, photosynthesis and the degradation of plastic, it is hard to break individual molecular bonds for those molecules adsorbed on the surface because of the weak light-absorption in molecules and the redistribution of the resulting vibrational energy both inside the molecule and to its surrounding environment. Here we show how to overcome these obstacles with a plasmonic hot-electron mediated process and demonstrate a new method that allows the sensitive control of resonant dissociation of surface-adsorbed molecules by `plasmonic' scissors. To that end, we used a high-vacuum tip-enhanced Raman spectroscopy (HV-TERS) setup to dissociate resonantly excited NC2H6 fragments from Malachite green. The surface plasmons (SPs) excited at the sharp metal tip not only enhance the local electric field to harvest the light incident from the laser, but crucially supply `hot electrons' whose energy can be transferred to individual bonds. These processes are resonant Raman, which result in some active chemical bonds and then weaken these bonds, followed by dumping in lots of indiscriminant energy and breaking the weakest bond. The method allows for sensitive control of both the rate and probability of dissociation through their dependence on the density of hot electrons, which can be manipulated by tuning the laser intensity or tunneling current/bias voltage in the HV-TERS setup, respectively. The concepts of plasmonic scissors open up new versatile avenues for the deep understanding of in situ surface-catalyzed chemistry.The ability to break individual bonds or specific modes in chemical reactions is an ardently sought goal by chemists and physicists. While photochemistry based methodologies are very successful in controlling e.g. photocatalysis

  19. Water molecules in clay minerals: Thermodynamic functions and hydration

    NASA Astrophysics Data System (ADS)

    Gailhanou, Helène; Amouric, Marc; Olives, Juan; Rogez, Jacques; van Miltenburg, J. C.; van der Berg, G. J. K.; de Weireld, G.; Gaucher, E.; Blanc, P.

    2010-05-01

    Thermodynamic functions and adsorption of water molecules are very important properties for clay minerals. Smectite MX-80 and mixed-layer illite-smectite ISCz-1 were selected. They were first carefully characterized (HRTEM with EDX analysis), revealing original results. Then, the thermodynamic properties of water in clay were obtained by (i) comparison of the thermodynamic properties of anhydrous and hydrated minerals, between 0 and 350 K (adiabatic calorimetry, solution isothermal calorimetry), and (ii) water vapor adsorption isotherms, between 300 and 380 K (magnetic suspension thermobalance). Solution isothermal calorimetry is used to determine the enthalpies of formation of the minerals (1 bar and 298 K). Comparison of the results, for the anhydrous and the hydrated minerals, leads to the enthalpies of hydration at 298 K. Adiabatic calorimetry measurements give the heat capacities of the minerals from 5 to 350 K. Entropies, enthalpies of formation and Gibbs free energies of formation, for the anhydrous and the hydrated minerals, and then, entropies of hydration, enthalpies of hydration and Gibbs free energies of hydration, between 0 and 350 K, are finally obtained. Comparison of two close hydration states leads to the entropy, the enthalpy and the Gibbs free energy of the adsorption reaction: H2O free - H2O adsorbed. The Cp(T) curve, for the heat capacity of water in clay - i.e., the difference between the heat capacities of the hydrated and the anhydrous minerals -, shows that water in clay is a glass at low temperature, undergoes one or two continuous glass transitions between 150 and 270 K, and behaves as free liquid water above 273 K. The two glass transitions might correspond to two types of water molecules: (i) first adsorbed water molecules, bound to the interlayer cations of the clay mineral; (ii) last adsorbed water molecules, not bound to the interlayer cations. In addition, water vapor adsorption isotherms are obtained from 298 to 378 K (magnetic

  20. Utility of adsorbents in the purification of drinking water: a review of characterization, efficiency and safety evaluation of various adsorbents.

    PubMed

    Dubey, Shashi Prabha; Gopal, Krishna; Bersillon, J L

    2009-05-01

    Clean drinking water is one of the implicit requisites fora healthy human population. However the growing industrialization and extensive use of chemicals for various concerns, has increased the burden of unwanted pollutants in the drinking water of developing countries like India. The entry of potentially hazardous substances into the biota has been magnifying day by day. In the absence of a possible stoppage of these, otherwise, useful chemicals, the only way to maintain safer water bodies is to develop efficient purifying technologies. One such immensely beneficial procedure that has been in use is that of purification of water using 'adsorbents'. Indigenous minerals and natural plants products have potential for removing many pollutants viz. fluoride, arsenic, nitrate, heavy metals, pesticides as well as trihalomethanes. Adsorbents which are derived from carbon, alumina, zeolite, clay minerals, iron ores, industrial by products, and natural products viz. parts of the plants, herbs and algal biomass offer promising potential of removal. In the recent years attention has been paid to develop process involving screening/pretreatment/activation/impregnation using alkalies, acids, alum, lime, manganese dioxide, ferric chloride and other chemicals which are found to enhance their adsorbing efficiency. Chemical characterization of these adsorbents recapitulates the mechanism of the process. It is imperative to observe that capacities of the adsorbents may vary depending on the characteristics, chemical modifications and concentration of the individual adsorbent. Removal kinetics is found to be based on the experimental conditions viz. pH, concentration of the adsorbate, quantity of the adsorbent and temperature. It is suggested that isotherm model is suitable tool to assess the adsorption capacities in batch and column modes. Safety evaluation and risk assessment of the process/products may be useful to provide guidelines for its sustainable disposal.

  1. Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field

    PubMed Central

    Ben Dor, Oren; Yochelis, Shira; Radko, Anna; Vankayala, Kiran; Capua, Eyal; Capua, Amir; Yang, See-Hun; Baczewski, Lech Tomasz; Parkin, Stuart Stephen Papworth; Naaman, Ron; Paltiel, Yossi

    2017-01-01

    Ferromagnets are commonly magnetized by either external magnetic fields or spin polarized currents. The manipulation of magnetization by spin-current occurs through the spin-transfer-torque effect, which is applied, for example, in modern magnetoresistive random access memory. However, the current density required for the spin-transfer torque is of the order of 1 × 106 A·cm−2, or about 1 × 1025 electrons s−1 cm−2. This relatively high current density significantly affects the devices' structure and performance. Here we demonstrate magnetization switching of ferromagnetic thin layers that is induced solely by adsorption of chiral molecules. In this case, about 1013 electrons per cm2 are sufficient to induce magnetization reversal. The direction of the magnetization depends on the handedness of the adsorbed chiral molecules. Local magnetization switching is achieved by adsorbing a chiral self-assembled molecular monolayer on a gold-coated ferromagnetic layer with perpendicular magnetic anisotropy. These results present a simple low-power magnetization mechanism when operating at ambient conditions. PMID:28230054

  2. Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field.

    PubMed

    Ben Dor, Oren; Yochelis, Shira; Radko, Anna; Vankayala, Kiran; Capua, Eyal; Capua, Amir; Yang, See-Hun; Baczewski, Lech Tomasz; Parkin, Stuart Stephen Papworth; Naaman, Ron; Paltiel, Yossi

    2017-02-23

    Ferromagnets are commonly magnetized by either external magnetic fields or spin polarized currents. The manipulation of magnetization by spin-current occurs through the spin-transfer-torque effect, which is applied, for example, in modern magnetoresistive random access memory. However, the current density required for the spin-transfer torque is of the order of 1 × 10(6) A·cm(-2), or about 1 × 10(25) electrons s(-1) cm(-2). This relatively high current density significantly affects the devices' structure and performance. Here we demonstrate magnetization switching of ferromagnetic thin layers that is induced solely by adsorption of chiral molecules. In this case, about 10(13) electrons per cm(2) are sufficient to induce magnetization reversal. The direction of the magnetization depends on the handedness of the adsorbed chiral molecules. Local magnetization switching is achieved by adsorbing a chiral self-assembled molecular monolayer on a gold-coated ferromagnetic layer with perpendicular magnetic anisotropy. These results present a simple low-power magnetization mechanism when operating at ambient conditions.

  3. Titanate-based adsorbents for radioactive ions entrapment from water.

    PubMed

    Yang, Dongjiang; Liu, Hongwei; Zheng, Zhanfeng; Sarina, Sarina; Zhu, Huaiyong

    2013-03-21

    This feature article reviews some titanate-based adsorbents for the removal of radioactive wastes (cations and anions) from water. At the beginning, we discuss the development of the conventional ion-exchangeable titanate powders for the entrapment of radioactive cations, such as crystalline silicotitanate (CST), monosodium titanate (MST), peroxotitanate (PT). Then, we specially emphasize the recent progress in the uptake of radioactive ions by one-dimensional (1D) sodium titanate nanofibers and nanotubes, which includes the synthesis and phase transformation of the 1D nanomaterials, adsorption ability (capacity, selectivity, kinetics, etc.) of radioactive cations and anions, and the structural evolution during the adsorption process.

  4. Induced IR overtone and fundamental bands of isotopic H 2 molecules adsorbed in NaCaA zeolites

    NASA Astrophysics Data System (ADS)

    Förster, H.; Frede, W.

    1984-05-01

    NIR spectroscopy has been successfully applied to surface chemical problems, using the FT transmission technique. Vibrational spectra of H 2 and D 2, adsorbed in NaA and NaCaA zeolites, have been recorded in the fundamental regions of both adsorbates and, for the first time, in the overtone region of D 2. Useful information on the properties of the adsorbed molecules can be derived from the overtone spectra of D 2 and the fine structure of the H 2 fundamental. It turns out that the properties of the D 2 molecules, e.g. dissociation energy and anharmonicity, are hardly affected by adsorption. The fine structure of the H 2 fundamental, however, indicates the rotation to be strongly hindered. The ortho-para splitting is decreased with respect to the free molecule value and approaches that for planarly rotating molecules. Due to this hindrance, the corresponding D 2 splitting is not resolved.

  5. Spins of adsorbed molecules investigated by the detection of Kondo resonance

    NASA Astrophysics Data System (ADS)

    Komeda, Tadahiro

    2014-12-01

    Surface magnetism has been one of the platforms to explore the magnetism in low dimensions. It is also a key component for the development of quantum information processes, which utilizes the spin degree of freedom. The Kondo resonance is a phenomenon that is caused by an interaction between an isolated spin and conduction electrons. First observed in the 1930s as an anomalous increase in the low-temperature resistance of metals embedded with magnetic atoms, the Kondo physics mainly studied the effects of bulk magnetic impurities in the resistivity. In the last 15 years it has undergone a revival by a scanning tunneling microscope (STM) which enables the measurement of the Kondo resonance at surfaces using an atomic scale point contact. The detection of the Kondo resonance can be a powerful tool to explore surface magnetism. In this article, I review recent studies of the surface spin of adsorbed molecules by the detection of the Kondo resonance. Researches on metal phthalocyanine (MPc) and porphyrin molecules will be examined. In addition, the Kondo resonance for double-decker lanthanoide Pc molecules will be discussed. Some of the double-decker Pc molecules show single-molecule magnet (SMM) behavior, which attracts attention as a material for electronic devices. For both classes, the ligand plays a crucial role in determining the parameters of the Kondo resonance, such as the Kondo temperature and the change of the shape from peak to Fano-dip. In addition, the spin in delocalized molecular orbital forms the Kondo resonance, which shows significant differences from the Kondo resonance formed by the metal spins. Since molecular orbital can be tuned in a flexible manner by the design of the molecule, the Kondo resonance formed by delocalized molecular orbital might expand the knowledge of this field.

  6. From single molecules to water networks: Dynamics of water adsorption on Pt(111)

    NASA Astrophysics Data System (ADS)

    Naderian, Maryam; Groß, Axel

    2016-09-01

    The adsorption dynamics of water on Pt(111) was studied using ab initio molecular dynamics simulations based on density functional theory calculations including dispersion corrections. Sticking probabilities were derived as a function of initial kinetic energy and water coverage. In addition, the energy distribution upon adsorption was monitored in order to analyze the energy dissipation process. We find that on the water pre-covered surface the sticking probability is enhanced because of the attractive water-water interaction and the additional effective energy dissipation channels to the adsorbed water molecules. The water structures forming directly after the adsorption on the pre-covered surfaces do not necessarily correspond to energy minimum structures.

  7. Impacts of surface adsorbed catechol on tropospheric aerosol surrogates: heterogeneous ozonolysis and its effects on water uptake.

    PubMed

    Woodill, Laurie A; O'Neill, Erinn M; Hinrichs, Ryan Z

    2013-07-11

    Surface adsorbed organics are ubiquitous components of inorganic tropospheric aerosols and have the potential to alter aerosol chemical and physical properties. To assess the impact of adsorbed organics on water uptake by inorganic substrates, we used diffuse reflectance infrared spectroscopy to compared water adsorption isotherms for uncoated NaCl and α-Al2O3 samples, samples containing a monolayer of adsorbed catechol, and adsorbed catechol samples following ozonolysis. Adsorption of gaseous catechol on to the inorganic substrates produced vibrational features indicating physisorption on NaCl and displacement of surface hydroxyl groups forming binuclear bidentate catecholate on α-Al2O3, with surface concentrations of 2-3 × 10(18) molecules m(-2). Subsequent heterogeneous ozonolysis produced muconic acid at a rate 4-5 times faster on NaCl compared to α-Al2O3, with predicted atmospheric lifetimes of 4.3 and 18 h, respectively, assuming a tropospheric ozone concentration of 40 ppb. Water adsorption isotherms for all NaCl samples were indistinguishable within experimental uncertainty, indicating that these organic monolayers had negligible impact on coadsorbed water surface concentrations for these systems. α-Al2O3-catechol samples exhibited dramatically less water uptake compared to uncoated α-Al2O3, while oxidation of surface adsorbed catechol had no effect on the extent of water uptake. For both substrates, adsorbed organics increased the relative abundance of "ice-like" versus "liquid-like" water, with the effect larger for catechol than oxidized ozonolysis products. These results highlight the importance of aerosol substrate in understanding the heterogeneous ozonolysis of adsorbed polyphenols and suggest such coatings may impair ice nucleation by aluminosilicate mineral aerosol.

  8. Removal of acutely hazardous pharmaceuticals from water using multi-template imprinted polymer adsorbent.

    PubMed

    Venkatesh, Avinash; Chopra, Nikita; Krupadam, Reddithota J

    2014-05-01

    Molecularly imprinted polymer adsorbent has been prepared to remove a group of recalcitrant and acutely hazardous (p-type) chemicals from water and wastewaters. The polymer adsorbent exhibited twofold higher adsorption capacity than the commercially used polystyrene divinylbenzene resin (XAD) and powdered activated carbon adsorbents. Higher adsorption capacity of the polymer adsorbent was explained on the basis of high specific surface area formed during molecular imprinting process. Freundlich isotherms drawn showed that the adsorption of p-type chemicals onto polymer adsorbent was kinetically faster than the other reference adsorbents. Matrix effect on adsorption of p-type chemicals was minimal, and also polymer adsorbent was amenable to regeneration by washing with water/methanol (3:1, v/v) solution. The polymer adsorbent was unaltered in its adsorption capacity up to 10 cycles of adsorption and desorption, which will be more desirable in cost reduction of treatment compared with single-time-use activated carbon.

  9. Density functional analysis of gaseous molecules adsorbed on metal ion/defective nano-sheet graphene

    NASA Astrophysics Data System (ADS)

    Deng, Jin-Pei; Chuang, Wen-Hua; Tai, Chin-Kuen; Kao, Hsien-Chang; Pan, Jiunn-Hung; Wang, Bo-Cheng

    2016-11-01

    Density functional theory was applied to calculate the adsorption property of metal/hexa-vacancy defective graphene (denoted as HDG-M, M: Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) with O- and N-dopants. We investigate the adsorption properties of these complexes between gaseous molecules and HDG-M. Our results show that HDG-Cu has a high selectivity for O2, but HDG-Fe has a good ability to capture many gases such as CO, NO and O2. Our calculations could provide useful information for designing new graphene-based adsorbents to remove undesired gases, which may poison the metal catalysts in reaction processes.

  10. Comparative FTIR spectroscopy of HX adsorbed on solid water: Ragout-jet water clusters vs ice nanocrystal arrays.

    PubMed

    Devlin, J P; Farník, M; Suhm, M A; Buch, V

    2005-02-17

    In addition to revealing the stretch-mode bands of the smallest mixed clusters of HCl and HBr (HX) with water, the ragout-jet FTIR spectra of dense mixed water-acid supersonic jets include bands that result from the interaction of HX with larger water clusters. It is argued here that low jet temperatures prevent the water-cluster-bound HX molecules from becoming sufficiently solvated to induce ionic dissociation. The molecular nature of the HX can be deduced directly from the observed influence of changing from HCl to HBr and from replacing H2O with D2O. Furthermore, the band positions of HX are roughly coincidental with bands assigned to molecular HCl and HBr adsorbed on ice nanocrystal surfaces at temperatures below 100 K. It is also interesting that the HX band positions and widths approximate those of HX bound to the surface of amorphous ice films at <60 K. Though computational results suggest the adsorbed HX molecules observed in the jet expansions are weakly distorted by single coordination with surface dangling-oxygen atoms, on-the-fly trajectories indicate that the cluster skeletons undergo large-amplitude low-frequency vibrations. Local HX solvation, the extent of proton sharing, and the HX vibrational spectra undergo serious modulation on a picosecond time scale.

  11. Electronic structure and binding geometry of tetraphenylporphyrin-derived molecules adsorbed on metal and metal oxide surfaces

    NASA Astrophysics Data System (ADS)

    Coh, Senia

    Tetraphenylporphyrin (TPP)-derived molecules have been studied extensively as efficient photosensitizers when chemisorbed on the metal oxide substrates in dye-sensitized solar cells. Still, many fundamental electronic properties of the dye/oxide interface are not understood and need careful consideration. In this thesis we present a comprehensive study of the electronic structure, energy level alignment and the adsorption geometry of the TPP-derived dye molecules adsorbed on TiO2(110), ZnO(1120) and Ag(100) single crystal surfaces using ultra-high vacuum (UHV) based surface sensitive techniques. The alignment of the molecular energy levels with respect to the TiO 2 and ZnO band edges for all TPP-derived molecules we studied was found to be insensitive to either the nature of the functional groups located on the phenyl rings, presence of zinc as a central metal ion and different binding geometry of the molecules. Binding geometry, molecule-molecule interaction and the aggregation effects in the adsorbed layer, that were observed in the UV-visible spectra of the molecules adsorbed on ZnO substrate were not observed in the ultraviolet photoemission (UPS) and inverse photoemission (IPS) spectra of the occupied and unoccupied molecular states. Using near edge X-ray absorption fine structure (NEXAFS) and scanning tunneling microscopy (STM), binding geometry of the two representative TPP-derivatives was directly determined to be upright, with the porphyrin ring under large angle with respect to the surface for the p-ZnTCPP molecules and with the porphyrin ring parallel to the surface for the m-ZnTCPP molecules. We observe that the energies and the energy level alignment of the ZnTPP molecular levels measured in UPS and IPS depend on the substrate on which the molecules are adsorbed (Ag(100) or TiO2(110) single crystal surfaces). The differences are attributed to different charge screening properties of these two materials. Image charges created in the substrates during

  12. Conserved water molecules in bacterial serine hydroxymethyltransferases.

    PubMed

    Milano, Teresa; Di Salvo, Martino Luigi; Angelaccio, Sebastiana; Pascarella, Stefano

    2015-10-01

    Water molecules occurring in the interior of protein structures often are endowed with key structural and functional roles. We report the results of a systematic analysis of conserved water molecules in bacterial serine hydroxymethyltransferases (SHMTs). SHMTs are an important group of pyridoxal-5'-phosphate-dependent enzymes that catalyze the reversible conversion of l-serine and tetrahydropteroylglutamate to glycine and 5,10-methylenetetrahydropteroylglutamate. The approach utilized in this study relies on two programs, ProACT2 and WatCH. The first software is able to categorize water molecules in a protein crystallographic structure as buried, positioned in clefts or at the surface. The other program finds, in a set of superposed homologous proteins, water molecules that occur approximately in equivalent position in each of the considered structures. These groups of molecules are referred to as 'clusters' and represent structurally conserved water molecules. Several conserved clusters of buried or cleft water molecules were found in the set of 11 bacterial SHMTs we took into account for this work. The majority of these clusters were not described previously. Possible structural and functional roles for the conserved water molecules are envisaged. This work provides a map of the conserved water molecules helpful for deciphering SHMT mechanism and for rational design of molecular engineering experiments.

  13. Ro-vibrational Stark effect on H2 and D2 molecules adsorbed in NaA zeolite

    NASA Astrophysics Data System (ADS)

    Bras, N.

    1999-03-01

    In order to explain the induced infrared bands of H2 and D2 adsorbed in NaA zeolites the Stark effect on the ro-vibrational levels of these molecules is considered for electric fields created by various charge distributions. The shift and intensity of the induced ro-vibration transitions are calculated.

  14. The National Shipbuilding Research Program, Heavy Metal Adsorbents for Storm Water Pollution Prevention

    DTIC Science & Technology

    1997-12-01

    Heavy Metal Adsorbents for Storm Water Pollution Prevention U.S. DEPARTMENT OF THE NAVY CARDEROCK DIVISION, NAVAL SURFACE WARFARE CENTER in...National Shipbuilding Research Program, Heavy Metal Adsorbents for Storm Water Pollution Prevention 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM...States Navy. ANY POSSIBLE IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR PURPOSE ARE SPECIFICALLY DISCLAIMED. FINAL REPORT HEAVY METAL ADSORBENTS

  15. Micro-differential thermal analysis detection of adsorbed explosive molecules using microfabricated bridges.

    PubMed

    Senesac, Larry R; Yi, Dechang; Greve, Anders; Hales, Jan H; Davis, Zachary J; Nicholson, Don M; Boisen, Anja; Thundat, Thomas

    2009-03-01

    Although micromechanical sensors enable chemical vapor sensing with unprecedented sensitivity using variations in mass and stress, obtaining chemical selectivity using the micromechanical response still remains as a crucial challenge. Chemoselectivity in vapor detection using immobilized selective layers that rely on weak chemical interactions provides only partial selectivity. Here we show that the very low thermal mass of micromechanical sensors can be used to produce unique responses that can be used for achieving chemical selectivity without losing sensitivity or reversibility. We demonstrate that this method is capable of differentiating explosive vapors from nonexplosives and is additionally capable of differentiating individual explosive vapors such as trinitrotoluene, pentaerythritol tetranitrate, and cyclotrimethylenetrinitromine. This method, based on a microfabricated bridge with a programmable heating rate, produces unique and reproducible thermal response patterns within 50 ms that are characteristic to classes of adsorbed explosive molecules. We demonstrate that this micro-differential thermal analysis technique can selectively detect explosives, providing a method for fast direct detection with a limit of detection of 600x10(-12) g.

  16. Micro differential thermal analysis detection of adsorbed explosive molecules using microfabricated bridges

    SciTech Connect

    Senesac, Larry R; Yi, Dechang; Greve, Anders; Hales, Jan; Davis, Zachary; Nicholson, Don M; Boisen, Anja; Thundat, Thomas George

    2009-01-01

    Although micromechanical sensors enable chemical vapor sensing with unprecedented sensitivity using variations in mass and stress, obtaining chemical selectivity using the micromechanical response still remains as a crucial challenge. Chemoselectivity in vapor detection using immobilized selective layers that rely on weak chemical interactions provides only partial selectivity. Here we show that the very low thermal mass of micromechanical sensors can be used to produce unique responses that can be used for achieving chemical selectivity without losing sensitivity or reversibility. We demonstrate that this method is capable of differentiating explosive vapors from nonexplosives and is additionally capable of differentiating individual explosive vapors such as trinitrotoluene, pentaerythritol tetranitrate, and cyclotrimethylenetrinitromine. This method, based on a microfabricated bridge with a programmable heating rate, produces unique and reproducible thermal response patterns within 50 ms that are characteristic to classes of adsorbed explosive molecules. We demonstrate that this micro-differential thermal analysis technique can selectively detect explosives, providing a method for fast direct detection with a limit of detection of 600 x 10{sup -12} g.

  17. Classical and quantum studies of the photodissociation of a HX (X=Cl,F) molecule adsorbed on ice.

    PubMed

    Woittequand, S; Duflot, D; Monnerville, M; Pouilly, B; Toubin, C; Briquez, S; Meyer, H-D

    2007-10-28

    The photodissociation dynamics of a HX (X = Cl,F) molecule adsorbed on a hexagonal ice surface at T = 0 K is studied using time-dependent quantum wave packets and quasiclassical trajectories. The relevant potential energy surfaces are calculated using high-level ab initio methods. We present here two dimensional calculations for the dynamics of the hydrogen photofragment for both HCl and HF molecules. The purpose of this paper is to compare the photodissociation dynamics of the two molecules which are adsorbed on the ice surface with different equilibrium geometries. The total photodissociation cross section and the angular distribution are calculated. The comparison with classical trajectory calculations provides evidence for typical quantum effects and reveals rainbow structures.

  18. Electric field effect observed on the infrared spectra of the N2O molecule adsorbed in NaA zeolite

    NASA Astrophysics Data System (ADS)

    Bras, N.; Cohen de Lara, E.

    1995-05-01

    The spectrum of the N2O molecule adsorbed in the cavity of NaA zeolite presents two main components for each of the stretching vibrational modes. It is assumed that they correspond to molecules parallel and antiparallel to the electric field of the inner surface of the zeolite cavity. In order to verify this assumption, the frequency shifts and the intensities of these components have been calculated for the two orientations of the molecule with respect to the field, by applying the model of Bishop for the vibrational Stark effect. These calculations require the knowledge of molecular quantities such as derivatives of permanent electric moments and polarizability.

  19. Direct comparison of the electronic coupling efficiency of sulfur and selenium anchoring groups for molecules adsorbed onto gold electrodes

    NASA Astrophysics Data System (ADS)

    Patrone, L.; Palacin, S.; Bourgoin, J. P.; Lagoute, J.; Zambelli, T.; Gauthier, S.

    2002-08-01

    We performed air and ultra-high vacuum scanning tunneling microscopy experiments in order to compare the electronic coupling provided by S and by Se used as alligator clips for bisthiol- and biselenol-terthiophene molecules adsorbed onto gold. The molecules were inserted in a dodecanethiol self-assembled monolayer. Their apparent height above the dodecanethiol matrix was used as a measure of the electronic coupling strength corresponding to S and Se, respectively. We show that the insertion behaviors of the two molecules are qualitatively the same, and that Se provides systematically a better coupling link than S whatever the tunneling conditions.

  20. Direct comparison of the electronic coupling efficiency of sulfur and selenium alligator clips for molecules adsorbed onto gold electrodes

    NASA Astrophysics Data System (ADS)

    Patrone, L.; Palacin, S.; Bourgoin, J. P.

    2003-05-01

    Scanning tunneling microscopy experiments have been performed to compare the electronic coupling provided by S and by Se used as alligator clips for bisthiol- and biselenol-terthiophene molecules adsorbed onto gold. The molecules were inserted in a dodecanethiol (DT) self-assembled monolayer. Their apparent height above the dodecanethiol matrix was used as a measure of the electronic coupling strength corresponding to S and Se, respectively. We show that the insertion behaviors of the two molecules are qualitatively the same, and that Se provides systematically a better coupling link than S, whatever the tunneling conditions.

  1. Oil palm biomass-based adsorbents for the removal of water pollutants--a review.

    PubMed

    Ahmad, Tanweer; Rafatullah, Mohd; Ghazali, Arniza; Sulaiman, Othman; Hashim, Rokiah

    2011-07-01

    This article presents a review on the role of oil palm biomass (trunks, fronds, leaves, empty fruit bunches, shells, etc.) as adsorbents in the removal of water pollutants such as acid and basic dyes, heavy metals, phenolic compounds, various gaseous pollutants, and so on. Numerous studies on adsorption properties of various low-cost adsorbents, such as agricultural wastes and its based activated carbons, have been reported in recent years. Studies have shown that oil palm-based adsorbent, among the low-cost adsorbents mentioned, is the most promising adsorbent for removing water pollutants. Further, these bioadsorbents can be chemically modified for better efficiency and can undergo multiple reuses to enhance their applicability at an industrial scale. It is evident from a literature survey of more than 100 recent papers that low-cost adsorbents have demonstrated outstanding removal capabilities for various pollutants. The conclusion is been drawn from the reviewed literature, and suggestions for future research are proposed.

  2. Selection and evaluation of adsorbents for the removal of anionic surfactants from laundry rinsing water.

    PubMed

    Schouten, Natasja; van der Ham, Louis G J; Euverink, Gert-Jan W; de Haan, André B

    2007-10-01

    Low-cost adsorbents were tested to remove anionic surfactants from laundry rinsing water to allow re-use of water. Adsorbents were selected corresponding to the different surfactant adsorption mechanisms. Equilibrium adsorption studies of linear alkyl benzene sulfonate (LAS) show that ionic interaction results in a high maximum adsorption capacity on positively charged adsorbents of 0.6-1.7 gLAS/g. Non-ionic interactions, such as hydrophobic interactions of LAS with non-ionic resins or activated carbons, result in a lower adsorption capacity of 0.02-0.6 gLAS/g. Negatively charged materials, such as cation exchange resins or bentonite clay, have negligible adsorption capacities for LAS. Similar results are obtained for alpha olefin sulfonate (AOS). Cost comparison of different adsorbents shows that an inorganic anion exchange material (layered double hydroxide) and activated carbons are the most cost-effective materials in terms of the amount of surfactant adsorbed per dollar worth of adsorbent.

  3. Tunneling Spectroscopy Studies of Urea, Thiourea, and Selected Phosphonate Molecules Adsorbed on Aluminum Oxide

    NASA Astrophysics Data System (ADS)

    Crowder, Charles D.

    Experimental and calculated inelastic electron tunneling intensities were compared for several of the vibrational modes of thiourea adsorbed on aluminum oxide. The partial charge model of Kirtley, Scalapino, and Hansma was used to compute the theoretical intensities of each mode. The required partial charges were determined using a method developed by Momany. Essentially, the Coulomb potential resulting from point charges located at atom sites was fitted to the quantum mechanical electrostatic potential of a molecule calculated from Hartree-Fock theory. The effect of a vibrational mode pattern on the electrostatic potential of a molecule was investigated. This effect could not be acceptably modeled with a single point charge located on each atom, so one charge was used to represent the positive nucleus of each atom and a second charge was used to represent the valence cloud. The valence charge was allowed to move independently of the nuclear charge during a molecular vibration, and the motions of the two charges were found to be very different for hydrogen atoms. This model gave very reasonable agreement between the theoretical and observed relative intensities for the in plane vibrational modes of thiourea. An acceptable set of out of plane force constants could not be found. This caused problems in the interpretation of the out of plane relative intensities. Based on the in plane modes, it was concluded that thiourea bonded to aluminum oxide with the sulfur atom near the oxide and the sulfur-carbon bond perpendicular to the aluminum oxide surface. Quantum mechanical electrostatic potentials were also calculated for urea, phosphoric acid (PA), methylphosphonic acid (MPA), hydroxymethylphosphonic acid (HMP), and nitrotrismethylphosphonic acid (NTMP). Electron tunneling spectra were taken for PA, HMP and NTMP, and the observed frequencies were compared to values obtained from Fourier transform infrared, infrared and Raman spectroscopy. Upward shifts in the P=O and P

  4. Affinity transformation from hydrophilicity to hydrophobicity of water molecules on the basis of adsorption of water in graphitic nanopores.

    PubMed

    Ohba, Tomonori; Kanoh, Hirofumi; Kaneko, Katsumi

    2004-02-11

    The interaction of water with hydrophobic surfaces is quite important in a variety of chemical and biochemical phenomena. The coexistence of water and oil can be realized by introduction of surfactants. In the case of water vapor adsorption on graphitic nanopores, plenty of water can be adsorbed in graphitic nanopores without surfactants, although the graphitic surface is not hydrophilic. Why are water molecules adsorbed in hydrophobic nanopores remarkably? This work can give an explicit insight to water adsorption in hydrophobic graphite nanopores using experimental and theoretical approaches. Water molecules are associated with each other to form the cluster of 1 nm in size, leading to a significant stabilization of the cluster in the graphitic nanopores. This mechanism can be widely applied to interfacial phenomena relating to coexistence of water and nanostructural materials of hydrophobicity.

  5. Selective binding of single-stranded DNA-binding proteins onto DNA molecules adsorbed on single-walled carbon nanotubes.

    PubMed

    Nii, Daisuke; Hayashida, Takuya; Yamaguchi, Yuuki; Ikawa, Shukuko; Shibata, Takehiko; Umemura, Kazuo

    2014-09-01

    Single-stranded DNA-binding (SSB) proteins were treated with hybrids of DNA and single-walled carbon nanotubes (SWNTs) to examine the biological function of the DNA molecules adsorbed on the SWNT surface. When single-stranded DNA (ssDNA) was used for the hybridization, significant binding of the SSB molecules to the ssDNA-SWNT hybrids was observed by using atomic force microscopy (AFM) and agarose gel electrophoresis. When double-stranded DNA (dsDNA) was used, the SSB molecules did not bind to the dsDNA-SWNT hybrids in most of the conditions that we evaluated. A specifically modified electrophoresis procedure was used to monitor the locations of the DNA, SSB, and SWNT molecules. Our results clearly showed that ssDNA/dsDNA molecules on the SWNT surfaces retained their single-stranded/double-stranded structures.

  6. Modelling water molecules inside cyclic peptide nanotubes

    NASA Astrophysics Data System (ADS)

    Tiangtrong, Prangsai; Thamwattana, Ngamta; Baowan, Duangkamon

    2016-03-01

    Cyclic peptide nanotubes occur during the self-assembly process of cyclic peptides. Due to the ease of synthesis and ability to control the properties of outer surface and inner diameter by manipulating the functional side chains and the number of amino acids, cyclic peptide nanotubes have attracted much interest from many research areas. A potential application of peptide nanotubes is their use as artificial transmembrane channels for transporting ions, biomolecules and waters into cells. Here, we use the Lennard-Jones potential and a continuum approach to study the interaction of a water molecule in a cyclo[(- D-Ala- L-Ala)_4-] peptide nanotube. Assuming that each unit of a nanotube comprises an inner and an outer tube and that a water molecule is made up of a sphere of two hydrogen atoms uniformly distributed over its surface and a single oxygen atom at the centre, we determine analytically the interaction energy of the water molecule and the peptide nanotube. Using this energy, we find that, independent of the number of peptide units, the water molecule will be accepted inside the nanotube. Once inside the nanotube, we show that a water molecule prefers to be off-axis, closer to the surface of the inner nanotube. Furthermore, our study of two water molecules inside the peptide nanotube supports the finding that water molecules form an array of a 1-2-1-2 file inside peptide nanotubes. The theoretical study presented here can facilitate thorough understanding of the behaviour of water molecules inside peptide nanotubes for applications, such as artificial transmembrane channels.

  7. Study for Reduction of Outgassing Property of Adsorbed Water Gas for Improved Surface Finished Titanium Material

    NASA Astrophysics Data System (ADS)

    Takeda, Masatoshi; Kurisu, Hiroki; Uchida, Takashi; Yamamoto, Setsuo; Ishizawa, Katsunobu; Nomura, Takeru; Eda, Takahiro; Murashige, Nobuyuki

    This paper addresses the development of the surface finishing for a titanium material and the study for the reduction of outgassing property of adsorbed water (H2O) molecules. Developed surface finishing is composed of the buffing for the reduction of the surface roughness and improved chemical polishing for the thick surface oxide layer compared with the chemical polishing so far. The surface roughness of the surface finished titanium material is reduced 35% and the thickness of the surface oxide layer increases by 30%. The total amount of thermal desorbed H2O gas for the new surface finished titanium is reduced 30%. It is considered that the origin for the decrease of the amount of desorption H2O gas is the reduction of the adsorption sites due to the decrease of the surface roughness and the reduction of adsorption energy of H2O gas due to the strong surface oxidation for a titanium material.

  8. Infrared-Laser Excitation of the Internal Vibrational Mode of a Diatomic Molecule Adsorbed on a Metal Surface.

    DTIC Science & Technology

    1986-11-01

    Excitation of the Internal Vibrational Mode of a Diatomic Molecule Adsorbed on a Metal Surface m by ’ Andre Peremans, Jacques Darville , Jean-Marie...Andre Peremans, Jacques Darville , Jean-Marie Gilles and Thomas F. George 13. TYPE OF REPORT 13b. TIME COVERED 14. DATE OF REPORT (Yr. Mo.. Dayl As...ON A METAL SURFACE h Andr& Peremans , Jacques Darville and Jean-Marie Gilles _ _ _ _ Laboratoire de Spectroscopie Mol6culaire de Surface Accesnion

  9. Classical interaction model for the water molecule.

    PubMed

    Baranyai, András; Bartók, Albert

    2007-05-14

    The authors propose a new classical model for the water molecule. The geometry of the molecule is built on the rigid TIP5P model and has the experimental gas phase dipole moment of water created by four equal point charges. The model preserves its rigidity but the size of the charges increases or decreases following the electric field created by the rest of the molecules. The polarization is expressed by an electric field dependent nonlinear polarization function. The increasing dipole of the molecule slightly increases the size of the water molecule expressed by the oxygen-centered sigma parameter of the Lennard-Jones interaction. After refining the adjustable parameters, the authors performed Monte Carlo simulations to check the ability of the new model in the ice, liquid, and gas phases. They determined the density and internal energy of several ice polymorphs, liquid water, and gaseous water and calculated the heat capacity, the isothermal compressibility, the isobar heat expansion coefficients, and the dielectric constant of ambient water. They also determined the pair-correlation functions of ambient water and calculated the energy of the water dimer. The accuracy of theirs results was satisfactory.

  10. Gold nanoparticle-aluminum oxide adsorbent for efficient removal of mercury species from natural waters.

    PubMed

    Lo, Sut-I; Chen, Po-Cheng; Huang, Chih-Ching; Chang, Huan-Tsung

    2012-03-06

    We report a new adsorbent for removal of mercury species. By mixing Au nanoparticles (NPs) 13 nm in diameter with aluminum oxide (Al(2)O(3)) particles 50-200 μm in diameter, Au NP-Al(2)O(3) adsorbents are easily prepared. Three adsorbents, Al(2)O(3), Au NPs, and Au NP-Al(2)O(3), were tested for removal of mercury species [Hg(2+), methylmercury (MeHg(+)), ethylmercury (EtHg(+)), and phenylmercury (PhHg(+))]. The Au NP adsorbent has a higher binding affinity (dissociation constant; K(d) = 0.3 nM) for Hg(2+) ions than the Al(2)O(3) adsorbent (K(d) = 52.9 nM). The Au NP-Al(2)O(3) adsorbent has a higher affinity for mercury species and other tested metal ions than the Al(2)O(3) and Au NP adsorbents. The Au NP-Al(2)O(3) adsorbent provides a synergic effect and, thus, is effective for removal of most tested metal ions and organic mercury species. After preconcentration of mercury ions by an Au NP-Al(2)O(3) adsorbent, analysis of mercury ions down to the subppq level in aqueous solution was performed by inductively coupled plasma mass spectrometry (ICP-MS). The Au NP-Al(2)O(3) adsorbent allows effective removal of mercury species spiked in lake water, groundwater, and seawater with efficiencies greater than 97%. We also used Al(2)O(3) and Au NP-Al(2)O(3) adsorbents sequentially for selectively removing Hg(2+) and MeHg(+) ions from water. The low-cost, effective, and stable Au NP-Al(2)O(3) adsorbent shows great potential for economical removal of various mercury species.

  11. The effect of mineral bond strength and adsorbed water on fault gouge frictional strength

    USGS Publications Warehouse

    Morrow, C.A.; Moore, Diane E.; Lockner, D.A.

    2000-01-01

    Recent studies suggest that the tendency of many fault gouge minerals to take on adsorbed or interlayer water may strongly influence their frictional strength. To test this hypothesis, triaxial sliding experiments were conducted on 15 different single-mineral gouges with various water-adsorbing affinities. Vacuum dried samples were sheared at 100 MPa, then saturated with water and sheared farther to compare dry and wet strengths. The coefficients of friction, μ, for the dry sheet-structure minerals (0.2-0.8), were related to mineral bond strength, and dropped 20-60% with the addition of water. For non-adsorbing minerals (μ = 0.6-0.8), the strength remained unchanged after saturation. These results confirm that the ability of minerals to adsorb various amounts of water is related to their relative frictional strengths, and may explain the anomalously low strength of certain natural fault gouges.

  12. Retention of radium from thermal waters on sand filters and adsorbents.

    PubMed

    Elejalde, C; Herranz, M; Idoeta, R; Legarda, F; Romero, F; Baeza, A

    2007-06-18

    This study was focussed on laboratory experiences of retention of radium from one thermal water on sand filters and adsorbents, trying to find an easy method for the elimination in drinkable waters polluted with this natural radio-nuclide. A thermal water from Cantabria (Spain) was selected for this work. Retention experiences were made with columns of 35 mm of diameter containing 15 cm layers of washed river sand or 4 cm layers of zeolite A3, passing known volumes of thermal water at flows between 4 and 40 ml/min with control of the retained radium by determining the amount in the water after the treatment. The statistical analysis of data suggests that retention depends on the flow and the volume passed through the columns. As additional adsorbents were used kaolin and a clay rich in illite. Jar-test experiences were made agitating known weights of adsorbents with the selected thermal water, with addition of flocculants and determination of radium in filtrated water after the treatment. Data suggest that retention is related to the weight of adsorbent used, but important quantities of radium seem remain in solution for higher amounts of adsorbents, according to the statistical treatment of data. The elution of retained radium from columns or adsorbents, previously used in experiences, should be the aim of a future research.

  13. Removal of arsenic from water using nano adsorbents and challenges: A review.

    PubMed

    Lata, Sneh; Samadder, S R

    2016-01-15

    Many researchers have used nanoparticles as adsorbents to remove water pollutants including arsenic after modifying the properties of nanoparticles by improving reactivity, biocompatibility, stability, charge density, multi-functionalities, and dispersibility. For arsenic removal, nano adsorbents emerged as the potential alternatives to existing conventional technologies. The present study critically reviewed the past and current available information on the potential of nano adsorbents for arsenic removal from contaminated water and the challenges involved in that. The study discussed the separation and regeneration techniques of nano adsorbents and the performance thereof. The study evaluated the adsorption efficiency of the various nanoparticles based on size of nanoparticles, types of nano adsorbents, method of synthesis, separation and regeneration of the nano adsorbents. The study found that more studies are required on suitable holding materials for the nano adsorbents to improve the permeability and to make the technology applicable at the field condition. The study will help the readers to choose suitable nanomaterials and to take up further research required for arsenic removal using nano adsorbents.

  14. Thermodynamic properties of adsorbed water on silica gel - Exergy losses in adiabatic sorption processes

    NASA Astrophysics Data System (ADS)

    Worek, W. M.; Zengh, W.; San, J.-Y.

    1991-09-01

    In order to perform exergy analyses to optimize the transient heat and mass transfer processes involving sorption by solid adsorbents, the thermodynamic properties of adsorbed water must be determined. In this paper, the integral enthalpy and entropy are determined directly from isotherm data of water adsorbed on silica gel particles and silica gel manufactured in the form of a felt with 25 percent cotton as a support and Teflon as a binder. These results are then used to evaluate the exergy losses, due to the sorption and the convective heat and mass transfer processes, that occur in each portion of an adiabatic desiccant dehumidificaton cycle.

  15. Evidence of water molecules--a statistical evaluation of water molecules based on electron density.

    PubMed

    Nittinger, Eva; Schneider, Nadine; Lange, Gudrun; Rarey, Matthias

    2015-04-27

    Water molecules play important roles in many biological processes, especially when mediating protein-ligand interactions. Dehydration and the hydrophobic effect are of central importance for estimating binding affinities. Due to the specific geometric characteristics of hydrogen bond functions of water molecules, meaning two acceptor and two donor functions in a tetrahedral arrangement, they have to be modeled accurately. Despite many attempts in the past years, accurate prediction of water molecules-structurally as well as energetically-remains a grand challenge. One reason is certainly the lack of experimental data, since energetic contributions of water molecules can only be measured indirectly. However, on the structural side, the electron density clearly shows the positions of stable water molecules. This information has the potential to improve models on water structure and energy in proteins and protein interfaces. On the basis of a high-resolution subset of the Protein Data Bank, we have conducted an extensive statistical analysis of 2.3 million water molecules, discriminating those water molecules that are well resolved and those without much evidence of electron density. In order to perform this classification, we introduce a new measurement of electron density around an individual atom enabling the automatic quantification of experimental support. On the basis of this measurement, we present an analysis of water molecules with a detailed profile of geometric and structural features. This data, which is freely available, can be applied to not only modeling and validation of new water models in structural biology but also in molecular design.

  16. A discrete interaction model/quantum mechanical method for describing response properties of molecules adsorbed on metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Morton, Seth Michael; Jensen, Lasse

    2010-08-01

    A new polarizable quantum mechanics/molecular mechanics method for the calculation of response properties of molecules adsorbed on metal nanoparticles is presented. This method, which we denote the discrete interaction model/quantum mechanics (DIM/QM) method, represents the nanoparticle atomistically which enables the modeling of the influence of the local environment of a nanoparticle surface on the optical properties of a molecule. Using DIM/QM, we investigate the excitation energies of rhodamine-6G (R6G) and crystal violet (CV) adsorbed on silver and gold nanoparticles of different quasispherical shapes and sizes. The metal nanoparticle is characterized by its static total polarizability, a reasonable approximation for frequencies far from the plasmon resonance. We observe that for both R6G and CV, the presence of the nanoparticle shifts the strongest excitation to the red ˜40 nm and also increases the oscillator strength of that excitation. The shifts in excitation energies due to the nanoparticle surface are found to be comparable to those due to solvation. We find that these shifts decay quickly as the molecule is moved away from the surface. We also find that the wavelength shift is largest when the transition dipole moment is aligned with the edges of the nanoparticle surface where the electric field is expected to be the largest. These results show that the molecular excitations are sensitive to the local environment on the nanoparticle as well as the specific orientation of the molecule relative to the surface.

  17. The origin of the low efficiency of carbon removal from the Nickel/Yttrium-Stabilized Zirconia triple-phase boundary by adsorbed water

    NASA Astrophysics Data System (ADS)

    Zhang, Yanxing; Yang, Zongxian

    2015-04-01

    Carbon removal from the anode triple-phase boundary (TPB) of solid oxide fuel cells (SOFCs) by adsorbed water molecule was studied using the density functional calculations, and a detailed dynamic picture was presented. It is found that the adsorbed H2O molecule can dissociate easily at the Ni/YSZ interface and on the YSZ part compared with the Ni part and react with the interface carbon to form the CHO species. The dissociation process of CHO to CH and O is more favorable as compared with that of CHO to CO and H. The CH fragment can easily diffuse to the O vacancy formed in the dynamic reaction processes and dissociate into C and H, which regenerates carbon at the interface. This might be the main reasons for the low efficiency of carbon removal from the TPB of Ni/YSZ by adsorbed water.

  18. Chemical reactions of water molecules on Ru(0001) induced by selective excitation of vibrational modes

    SciTech Connect

    Mugarza, Aitor; Shimizu, Tomoko K.; Ogletree, D. Frank; Salmeron, Miquel

    2009-05-07

    Tunneling electrons in a scanning tunneling microscope were used to excite specific vibrational quantum states of adsorbed water and hydroxyl molecules on a Ru(0 0 0 1) surface. The excited molecules relaxed by transfer of energy to lower energy modes, resulting in diffusion, dissociation, desorption, and surface-tip transfer processes. Diffusion of H{sub 2}O molecules could be induced by excitation of the O-H stretch vibration mode at 445 meV. Isolated molecules required excitation of one single quantum while molecules bonded to a C atom required at least two quanta. Dissociation of single H{sub 2}O molecules into H and OH required electron energies of 1 eV or higher while dissociation of OH required at least 2 eV electrons. In contrast, water molecules forming part of a cluster could be dissociated with electron energies of 0.5 eV.

  19. Clustering of water molecules in ultramicroporous carbon: In-situ small-angle neutron scattering

    SciTech Connect

    Bahadur, Jitendra; Contescu, Cristian I.; Rai, Durgesh K.; Gallego, Nidia C.; Melnichenko, Yuri B.

    2016-10-19

    The adsorption of water is central to most of the applications of microporous carbon as adsorbent material. We report early kinetics of water adsorption in the microporous carbon using in-situ small-angle neutron scattering. It is observed that adsorption of water occurs via cluster formation of molecules. Interestingly, the cluster size remains constant throughout the adsorption process whereas number density of clusters increases with time. The role of surface chemistry of microporous carbon on the early kinetics of adsorption process was also investigated. Lastly, the present study provides direct experimental evidence for cluster assisted adsorption of water molecules in microporous carbon (Do-Do model).

  20. Submerged membrane adsorption hybrid system using four adsorbents to remove nitrate from water.

    PubMed

    Kalaruban, Mahatheva; Loganathan, Paripurnanda; Kandasamy, Jaya; Vigneswaran, Saravanamuthu

    2017-04-05

    Nitrate contamination of ground and surface waters causes environmental pollution and human health problems in many parts of the world. This study tests the nitrate removal efficiencies of two ion exchange resins (Dowex 21K XLT and iron-modified Dowex 21K XLT (Dowex-Fe)) and two chemically modified bio-adsorbents (amine-grafted corn cob (AG corn cob) and amine-grafted coconut copra (AG coconut copra)) using a dynamic adsorption treatment system. A submerged membrane (microfiltration) adsorption hybrid system (SMAHS) was used for the continuous removal of nitrate with a minimal amount of adsorbents. The efficiency of membrane filtration flux and replacement rate of adsorbent were studied to determine suitable operating conditions to maintain the effluent nitrate concentration below the WHO drinking standard limit of 11.3 mg N/L. The volume of water treated and the amount of nitrate adsorbed per gramme of adsorbent for all four flux tested were in the order Dowex-Fe > Dowex > AG coconut copra > AG corn cob. The volumes of water treated (L/g adsorbent) were 0.91 and 1.85, and the amount of nitrate removed (mg N/g adsorbent) were 9.8 and 22.2 for AG corn cob and Dowex-Fe, respectively, at a flux of 15 L/(m(2)/h).

  1. Evaluating of arsenic(V) removal from water by weak-base anion exchange adsorbents.

    PubMed

    Awual, M Rabiul; Hossain, M Amran; Shenashen, M A; Yaita, Tsuyoshi; Suzuki, Shinichi; Jyo, Akinori

    2013-01-01

    Arsenic contamination of groundwater has been called the largest mass poisoning calamity in human history and creates severe health problems. The effective adsorbents are imperative in response to the widespread removal of toxic arsenic exposure through drinking water. Evaluation of arsenic(V) removal from water by weak-base anion exchange adsorbents was studied in this paper, aiming at the determination of the effects of pH, competing anions, and feed flow rates to improvement on remediation. Two types of weak-base adsorbents were used to evaluate arsenic(V) removal efficiency both in batch and column approaches. Anion selectivity was determined by both adsorbents in batch method as equilibrium As(V) adsorption capacities. Column studies were performed in fixed-bed experiments using both adsorbent packed columns, and kinetic performance was dependent on the feed flow rate and competing anions. The weak-base adsorbents clarified that these are selective to arsenic(V) over competition of chloride, nitrate, and sulfate anions. The solution pH played an important role in arsenic(V) removal, and a higher pH can cause lower adsorption capacities. A low concentration level of arsenic(V) was also removed by these adsorbents even at a high flow rate of 250-350 h(-1). Adsorbed arsenic(V) was quantitatively eluted with 1 M HCl acid and regenerated into hydrochloride form simultaneously for the next adsorption operation after rinsing with water. The weak-base anion exchange adsorbents are to be an effective means to remove arsenic(V) from drinking water. The fast adsorption rate and the excellent adsorption capacity in the neutral pH range will render this removal technique attractive in practical use in chemical industry.

  2. Heat capacity measurements of atoms and molecules adsorbed on evaporated metal films

    SciTech Connect

    Kenny, T.W.

    1989-05-01

    Investigations of the properties of absorbed monolayers have received great experimental and theoretical attention recently, both because of the importance of surface processes in practical applications such as catalysis, and the importance of such systems to the understanding of the fundamentals of thermodynamics in two dimensions. We have adapted the composite bolometer technology to the construction of microcalorimeters. For these calorimeters, the adsorption substrate is an evaporated film deposited on one surface of an optically polished sapphire wafer. This approach has allowed us to make the first measurements of the heat capacity of submonolayer films of /sup 4/He adsorbed on metallic films. In contrast to measurements of /sup 4/He adsorbed on all other insulating substrates, we have shown that /sup 4/He on silver films occupies a two-dimensional gas phase over a broad range of coverages and temperatures. Our apparatus has been used to study the heat capacity of Indium flakes. CO multilayers, /sup 4/He adsorbed on sapphire and on Ag films and H/sub 2/ adsorbed on Ag films. The results are compared with appropriate theories. 68 refs., 19 figs.

  3. Sticking of Molecules on Nonporous Amorphous Water Ice

    NASA Astrophysics Data System (ADS)

    He, Jiao; Acharyya, Kinsuk; Vidali, Gianfranco

    2016-05-01

    Accurate modeling of physical and chemical processes in the interstellar medium (ISM) requires detailed knowledge of how atoms and molecules adsorb on dust grains. However, the sticking coefficient, a number between 0 and 1 that measures the first step in the interaction of a particle with a surface, is usually assumed in simulations of ISM environments to be either 0.5 or 1. Here we report on the determination of the sticking coefficient of H2, D2, N2, O2, CO, CH4, and CO2 on nonporous amorphous solid water. The sticking coefficient was measured over a wide range of surface temperatures using a highly collimated molecular beam. We showed that the standard way of measuring the sticking coefficient—the King-Wells method—leads to the underestimation of trapping events in which there is incomplete energy accommodation of the molecule on the surface. Surface scattering experiments with the use of a pulsed molecular beam are used instead to measure the sticking coefficient. Based on the values of the measured sticking coefficient, we suggest a useful general formula of the sticking coefficient as a function of grain temperature and molecule-surface binding energy. We use this formula in a simulation of ISM gas-grain chemistry to find the effect of sticking on the abundance of key molecules both on grains and in the gas phase.

  4. Anisotropic orientational motion of molecular adsorbates at the air-water interface

    SciTech Connect

    Zimdars, D.; Dadap, J.I.; Eisenthal, K.B.; Heinz, T.F.

    1999-04-29

    The ultrafast orientational motions of coumarin 314 (C314) adsorbed at the air/water interface were investigated by time-resolved surface second harmonic generation (TRSHG). The theory and method of using TRSHG to detect both out-of-plane and in-plane orientational motions are discussed. The interfacial solute motions were found to be anisotropic, with differing out-of-plane and in-plane reorientation time constants. This report presents the first direct observation of in-plane orientational motion of a molecule (C314) at the air/water interface using TRSHG. The in-plane reorientation time constant is 600 {+-} 40 ps. The out-of-plane reorientation time constant is 350 {+-} 20 ps. The out-of-plane orientational motion of C314 is similar to the previous results on rhodamine 6G at the air/water interface which indicated increased interfacial friction compared with bulk aqueous solution. The surface reorientation times are 2--3 times slower than the bulk isotropic orientational diffusion time.

  5. Toward 3D graphene oxide gels based adsorbents for high-efficient water treatment via the promotion of biopolymers.

    PubMed

    Cheng, Chong Sage; Deng, Jie; Lei, Bei; He, Ai; Zhang, Xiang; Ma, Lang; Li, Shuang; Zhao, Changsheng

    2013-12-15

    Recent studies showed that graphene oxide (GO) presented high adsorption capacities to various water contaminants. However, the needed centrifugation after adsorption and the potential biological toxicity of GO restricted its applications in wastewater treatment. In this study, a facile method is provided by using biopolymers to mediate and synthesize 3D GO based gels. The obtained hybrid gels present well-defined and interconnected 3D porous network, which allows the adsorbate molecules to diffuse easily into the adsorbent. The adsorption experiments indicate that the obtained porous GO-biopolymer gels can efficiently remove cationic dyes and heavy metal ions from wastewater. Methylene blue (MB) and methyl violet (MV), two cationic dyes, are chosen as model adsorbates to investigate the adsorption capability and desorption ratio; meanwhile, the influence of contacting time, initial concentration, and pH value on the adsorption capacity of the prepared GO-biopolymer gels are also studied. The GO-biopolymer gels displayed an adsorption capacity as high as 1100 mg/g for MB dye and 1350 mg/g for MV dye, respectively. Furthermore, the adsorption kinetics and isotherms of the MB were studied in details. The experimental data of MB adsorption fitted well with the pseudo-second-order kinetic model and the Langmuir isotherm, and the results indicated that the adsorption process was controlled by the intraparticle diffusion. Moreover, the adsorption data revealed that the porous GO-biopolymer gels showed good selective adsorbability to cationic dyes and metal ions.

  6. Sensitivity of photoelectron diffraction to conformational changes of adsorbed molecules: Tetra-tert-butyl-azobenzene/Au(111)

    PubMed Central

    Schuler, A.; Greif, M.; Seitsonen, A. P.; Mette, G.; Castiglioni, L.; Osterwalder, J.; Hengsberger, M.

    2017-01-01

    Electron diffraction is a standard tool to investigate the atomic structure of surfaces, interfaces, and adsorbate systems. In particular, photoelectron diffraction is a promising candidate for real-time studies of structural dynamics combining the ultimate time resolution of optical pulses and the high scattering cross-sections for electrons. In view of future time-resolved experiments from molecular layers, we studied the sensitivity of photoelectron diffraction to conformational changes of only a small fraction of molecules in a monolayer adsorbed on a metallic substrate. 3,3′,5,5′-tetra-tert-butyl-azobenzene served as test case. This molecule can be switched between two isomers, trans and cis, by absorption of ultraviolet light. X-ray photoelectron diffraction patterns were recorded from tetra-tert-butyl-azobenzene/Au(111) in thermal equilibrium at room temperature and compared to patterns taken in the photostationary state obtained by exposing the surface to radiation from a high-intensity helium discharge lamp. Difference patterns were simulated by means of multiple-scattering calculations, which allowed us to determine the fraction of molecules that underwent isomerization. PMID:28217715

  7. Sensitivity of photoelectron diffraction to conformational changes of adsorbed molecules: Tetra-tert-butyl-azobenzene/Au(111).

    PubMed

    Schuler, A; Greif, M; Seitsonen, A P; Mette, G; Castiglioni, L; Osterwalder, J; Hengsberger, M

    2017-01-01

    Electron diffraction is a standard tool to investigate the atomic structure of surfaces, interfaces, and adsorbate systems. In particular, photoelectron diffraction is a promising candidate for real-time studies of structural dynamics combining the ultimate time resolution of optical pulses and the high scattering cross-sections for electrons. In view of future time-resolved experiments from molecular layers, we studied the sensitivity of photoelectron diffraction to conformational changes of only a small fraction of molecules in a monolayer adsorbed on a metallic substrate. 3,3',5,5'-tetra-tert-butyl-azobenzene served as test case. This molecule can be switched between two isomers, trans and cis, by absorption of ultraviolet light. X-ray photoelectron diffraction patterns were recorded from tetra-tert-butyl-azobenzene/Au(111) in thermal equilibrium at room temperature and compared to patterns taken in the photostationary state obtained by exposing the surface to radiation from a high-intensity helium discharge lamp. Difference patterns were simulated by means of multiple-scattering calculations, which allowed us to determine the fraction of molecules that underwent isomerization.

  8. Low-cost magnetic adsorbent for As(III) removal from water: adsorption kinetics and isotherms.

    PubMed

    Kango, Sarita; Kumar, Rajesh

    2016-01-01

    Magnetite nanoparticles as adsorbent for arsenic (As) were coated on sand particles. The coated sand was used for the removal of highly toxic element 'As(III)' from drinking water. Here, batch experiments were performed with the variation of solution pH, adsorbent dose, contact time and initial arsenic concentration. The adsorbent showed significant removal efficiency around 99.6 % for As(III). Analysis of adsorption kinetics revealed that the adsorbent follows pseudo-second-order kinetics model showing R (2) = 0.999, whereas for pseudo-first-order kinetics model, the value of R (2) was 0.978. In the case of adsorption equilibrium, the data is well fitted with Langmuir adsorption isotherm model (R (2) > 0.99), indicating monolayer adsorption of As(III) on the surface of adsorbent. The existence of commonly present ions in water influences the removal efficiency of As(III) minutely in the following order PO4 (3-) > HCO3 (-) > Cl(-) > SO4 (2-). The obtained adsorbent can be used to overcome the problem of water filtration in rural areas. Moreover, as the nano-magnetite is coated on the sand, it avoids the problem of extraction of nanoparticles from treated water and can easily be removed by a simple filtration process.

  9. Adsorption and Desorption of Carbon Dioxide and Water Mixtures on Synthetic Hydrophobic Carbonaceous Adsorbents

    NASA Technical Reports Server (NTRS)

    Finn, John E.; Harper, Lynn D. (Technical Monitor)

    1994-01-01

    Several synthetic carbonaceous adsorbents produced through pyrolysis of polymeric materials are available commercially. Some appear to have advantages over activated carbon for certain adsorption applications. In particular, they can have tailored hydrophobicities that are significantly greater than that of activated carbon, while moderately high surfaces areas are retained. These sorbents are being investigated for possible use in removing trace contaminants and excess carbon dioxide from air in closed habitats, plant growth chambers, and other applications involving purification of humid gas streams. We have analyzed the characteristics of a few of these adsorbents through adsorption and desorption experiments and standard characterization techniques. This paper presents pure and multicomponent adsorption data collected for carbon dioxide and water on two synthetic carbonaceous adsorbents having different hydrophobicities and capillary condensation characteristics. The observations are interpreted through consideration of the pore structure and surface chemistry of the solids and interactions between adsorbed carbon dioxide, water, and the solvent gas.

  10. Water clusters adsorbed on polycyclic aromatic hydrocarbons: Energetics and conformational dynamics

    NASA Astrophysics Data System (ADS)

    Simon, Aude; Spiegelman, Fernand

    2013-05-01

    In this work, we present some classical molecular dynamics (MD) simulations and finite temperature infrared (IR) spectra of water clusters adsorbed on coronene (C24H12), a compact polycyclic aromatic hydrocarbon (PAH). The potential energy surface is obtained within the self-consistent-charge density-functional based tight-binding approach with modifications insuring the correct description of water-water and water-PAH interactions. This scheme is benchmarked for the minimal energy structures of (C24H12)(H2O)n (n = 3-10) against density-functional theory (DFT) calculations and for the low-energy isomers of (H2O)6 and (C6H6)(H2O)3 against correlated wavefunction and DFT calculations. A detailed study of the low energy isomers of (C24H12)(H2O)3, 6 complexes is then provided. On-the-fly Born-Oppenheimer MD simulations are performed in the temperature T range 10-350 K for (C24H12)(H2O)n (n = 3-7) complexes. The description of the evolution of the systems with T is provided with emphasis on (C24H12)(H2O)n (n = 3,6). For T in the range 50-150 K, isomerisation processes are observed and when T increases, a solid-to-liquid phase-change like behavior is shown. The desorption of one water molecule is frequently observed at 300 K. The isomerisation processes are evidenced on the finite temperature IR spectra and the results are presented for (C24H12)(H2O)n (n = 3,6). A signature for the edge-coordination of the water cluster on the PAH is also proposed.

  11. Sorption of organic molecules on surfaces of a microporous polymer adsorbent modified with different quantities of uracil

    NASA Astrophysics Data System (ADS)

    Gus'kov, V. Yu.; Ganieva, A. G.; Kudasheva, F. Kh.

    2016-11-01

    The sorption of organic molecules on the surfaces of a number of adsorbents based on a microporous copolymer of styrene and divinylbenzene modified with different quantities of uracil is studied by means of inverse gas chromatography at infinite dilution. Samples containing 10-6, 10-5, 10-4, 10-3, 10-2, and 0.5 × 10‒1 weight parts of uracil (the pC of uracil ranges from 1.3 to 6) are studied. The contributions from different intermolecular interactions to the Helmholtz energy of sorption are calculated via the linear free energy relationship. It is found that as the concentration of uracil on the surface of the polymer adsorbent grows, the contributions from different intermolecular interactions and the conventional polarity of the surface have a bend at pC = 3, due probably to the formation of a supramolecular structure of uracil. Based on the obtained results, it is concluded that the formation of the supramolecular structure of uracil on the surface of the polymer adsorbent starts when pC < 3.

  12. Why can water cages adsorb aqueous methane? A potential of mean force calculation on hydrate nucleation mechanisms.

    PubMed

    Guo, Guang-Jun; Li, Meng; Zhang, Yi-Gang; Wu, Chang-Hua

    2009-11-28

    By performing constrained molecular dynamics simulations in the methane-water system, we successfully calculated the potential of mean force (PMF) between a dodecahedral water cage (DWC) and dissolved methane for the first time. As a function of the distance between DWC and methane, this is characterized by a deep well at approximately 6.2 A and a shallow well at approximately 10.2 A, separated by a potential barrier at approximately 8.8 A. We investigated how the guest molecule, cage rigidity and the cage orientation affected the PMF. The most important finding is that the DWC itself strongly adsorbs methane and the adsorption interaction is independent of the guests. Moreover, the activation energy of the DWC adsorbing methane is comparable to that of hydrogen bonds, despite differing by a factor of approximately 10% when considering different water-methane interaction potentials. We explain that the cage-methane adsorption interaction is a special case of the hydrophobic interaction between methane molecules. The strong net attraction in the DWC shell with radii between 6.2 and 8.8 A may act as the inherent driving force that controls hydrate formation. A cage adsorption hypothesis for hydrate nucleation is thus proposed and discussed.

  13. Microscopic resolution of the interplay of Kondo screening and superconducting pairing: Mn-phthalocyanine molecules adsorbed on superconducting Pb(111)

    NASA Astrophysics Data System (ADS)

    Bauer, Johannes; Pascual, Jose I.; Franke, Katharina J.

    2013-02-01

    Magnetic molecules adsorbed on a superconductor give rise to a local competition of Cooper pair and Kondo singlet formation inducing subgap bound states. For manganese-phthalocyanine molecules on a Pb(111) substrate, scanning tunneling spectroscopy resolves pairs of subgap bound states and two Kondo screening channels. We show in a combined approach of scaling and numerical renormalization group calculations that the intriguing relation between Kondo screening and superconducting pairing is solely determined by the hybridization strength with the substrate. We demonstrate that an effective one-channel Anderson impurity model with a sizable particle-hole asymmetry captures universal and nonuniversal observations in the system quantitatively. The model parameters and disentanglement of the two screening channels are elucidated by scaling arguments.

  14. Control of the dipole layer of polar organic molecules adsorbed on metal surfaces via different charge-transfer channels

    NASA Astrophysics Data System (ADS)

    Lin, Meng-Kai; Nakayama, Yasuo; Zhuang, Ying-Jie; Su, Kai-Jun; Wang, Chin-Yung; Pi, Tun-Wen; Metz, Sebastian; Papadopoulos, Theodoros A.; Chiang, T.-C.; Ishii, Hisao; Tang, S.-J.

    2017-02-01

    Organic molecules with a permanent electric dipole moment have been widely used as a template for further growth of molecular layers in device structures. Key properties of the resulting organic films such as energy level alignment (ELA), work function, and injection/collection barrier are linked to the magnitude and direction of the dipole moment at the interface. Using angle-resolved photoemission spectroscopy (ARPES), we have systematically investigated the coverage-dependent work function and spectral line shapes of occupied molecular energy states (MESs) of chloroaluminium-phthalocyanine (ClAlPc) grown on Ag(111). We demonstrate that the dipole orientation of the first ClAlPc layer can be controlled by adjusting the deposition rate and postannealing conditions, and we find that the ELA at the interface differs by ˜0.4 eV between the Cl up and down configurations of the adsorbed ClAlPc molecules. These observations are rationalized by density functional theory (DFT) calculations based on a realistic model of the ClAlPc/Ag(111) interface, which reveal that the different orientations of the ClAlPc dipole layer lead to different charge-transfer channels between the adsorbed ClAlPc and Ag(111) substrate. Our findings provide a useful framework toward method development for ELA tuning.

  15. Charge-transfer photodissociation of adsorbed molecules via electron image states

    SciTech Connect

    Jensen, E. T.

    2008-01-28

    The 248 and 193 nm photodissociations of submonolayer quantities of CH{sub 3}Br and CH{sub 3}I adsorbed on thin layers of n-hexane indicate that the dissociation is caused by dissociative electron attachment from subvacuum level photoelectrons created in the copper substrate. The characteristics of this photodissociation-translation energy distributions and coverage dependences show that the dissociation is mediated by an image potential state which temporarily traps the photoelectrons near the n-hexane-vacuum interface, and then the charge transfers from this image state to the affinity level of a coadsorbed halomethane which then dissociates.

  16. Adsorption and removal kinetics of phosphonate from water using natural adsorbents.

    PubMed

    Kumar, R Anil; Velayudhan, K T; Ramachandran, V; Bhai, R Susheela; Unnikrishnan, G; Vasu, K

    2010-01-01

    The removal of phosphonate from water was studied using some natural adsorbents. Potassium phosphonate is a fungicide used for the control of Phytophthora capsici, which is prevalent in black pepper (Piper nigrum L.). Batch adsorption kinetic experiments were conducted on the adsorption of phosphonate onto the adsorbents. The concentration of phosphonate was measured on a high-performance liquid chromatograph fitted with a conductivity detector. The percentage removal of phosphonate by powdered laterite stone (PLS) from water was 40.4%, within a residence time of 15 minutes. The mechanisms of the rate of adsorption were analyzed and compared using the pseudo-second-order, Elovich, and intraparticle diffusion models. The experimental data was found to correlate well with the pseudo-second-order kinetic model, indicating adsorption as a chemisorption process. A possible reaction in the phosphonate-PLS system also has been proposed. The PLS can be used as a low-cost natural adsorbent for phosphonate removal from water.

  17. Preliminary results on the immobilisation of radionuclides from waters with specific adsorbers based on phosphate salts.

    PubMed

    Valentini Ganzerli, Maria Teresa; Maggi, Luigino; Crespi Caramella, Vera; Berzero, Antonella

    2004-11-01

    The present paper is focused on the ability of aluminium phosphate (ALPC), magnesium ammonium phosphate (MGPC), magnesium hydrogen phosphate (MGHPC), and calcium hydrogenphosphate (CAHPC), adsorbed onto charcoal, to immobilise actinides by adsorption from natural waters. The objective of this process is to evaluate the environmental pollution due to the actinides. Europium, thorium, protactinium, neptunyl, and uranyl ions were chosen to simulate actinides in the +3, +4, +5 and +6 oxidation state. The adsorbers were tested using natural waters samples. The adsorption trends and capacities were analysed. ALPC and MGPC exhibited a similar behaviour and adsorbed demonstrating that the +5, +4 and +3 actinide ions can be easily immobilised from natural waters and may be successfully used at pH 7-8. MGHPC may be used at a higher pH, whereas CAHPC is effective in the whole pH range. In all cases, thorium, protactinium and europium were strongly

  18. Driving force behind adsorption-induced protein unfolding: a time-resolved X-ray reflectivity study on lysozyme adsorbed at an air/water interface.

    PubMed

    Yano, Yohko F; Uruga, Tomoya; Tanida, Hajime; Toyokawa, Hidenori; Terada, Yasuko; Takagaki, Masafumi; Yamada, Hironari

    2009-01-06

    Time-resolved X-ray reflectivity measurements for lysozyme (LSZ) adsorbed at an air/water interface were performed to study the mechanism of adsorption-induced protein unfolding. The time dependence of the density profile at the air/water interface revealed that the molecular conformation changed significantly during adsorption. Taking into account previous work using Fourier transform infrared (FTIR) spectroscopy, we propose that the LSZ molecules initially adsorbed on the air/water interface have a flat unfolded structure, forming antiparallel beta-sheets as a result of hydrophobic interactions with the gas phase. In contrast, as adsorption continues, a second layer forms in which the molecules have a very loose structure having random coils as a result of hydrophilic interactions with the hydrophilic groups that protrude from the first layer.

  19. A Comprehensive Study of Hydrogen Adsorbing to Amorphous Water ice: Defining Adsorption in Classical Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Dupuy, John L.; Lewis, Steven P.; Stancil, P. C.

    2016-11-01

    Gas-grain and gas-phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas-grain reactions require a substrate (e.g., a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H2) in the ISM is the prototypical example of a gas-grain reaction. In these reactions, an atom of hydrogen will strike a surface, stick to it, and diffuse across it. When it encounters another adsorbed hydrogen atom, the two can react to form molecular hydrogen and then be ejected from the surface by the energy released in the reaction. We perform in-depth classical molecular dynamics simulations of hydrogen atoms interacting with an amorphous water-ice surface. This study focuses on the first step in the formation process; the sticking of the hydrogen atom to the substrate. We find that careful attention must be paid in dealing with the ambiguities in defining a sticking event. The technical definition of a sticking event will affect the computed sticking probabilities and coefficients. Here, using our new definition of a sticking event, we report sticking probabilities and sticking coefficients for nine different incident kinetic energies of hydrogen atoms [5-400 K] across seven different temperatures of dust grains [10-70 K]. We find that probabilities and coefficients vary both as a function of grain temperature and incident kinetic energy over the range of 0.99-0.22.

  20. From illite/smectite clay to mesoporous silicate adsorbent for efficient removal of chlortetracycline from water.

    PubMed

    Wang, Wenbo; Tian, Guangyan; Zong, Li; Zhou, Yanmin; Kang, Yuru; Wang, Qin; Wang, Aiqin

    2017-01-01

    A series of mesoporous silicate adsorbents with superior adsorption performance for hazardous chlortetracycline (CTC) were sucessfully prepared via a facile one-pot hydrothermal reaction using low-cost illite/smectite (IS) clay, sodium silicate and magnesium sulfate as the starting materials. In this process, IS clay was "teared up" and then "rebuilt" as new porous silicate adsorbent with high specific surface area of 363.52m(2)/g (about 8.7 folds higher than that of IS clay) and very negative Zeta potential (-34.5mV). The inert SiOSi (Mg, Al) bonds in crystal framework of IS were broken to form Si(Al) O(-) groups with good adsorption activity, which greatly increased the adsorption sites served for holding much CTC molecules. Systematic evaluation on adsorption properties reveals the optimal silicate adsorbent can adsorb 408.81mg/g of CTC (only 159.7mg/g for raw IS clay) and remove 99.3% (only 46.5% for raw IS clay) of CTC from 100mg/L initial solution (pH3.51; adsorption temperature 30°C; adsorbent dosage, 3g/L). The adsorption behaviors of CTC onto the adsorbent follows the Langmuir isotherm model, Temkin equation and pseudo second-order kinetic model. The mesopore adsorption, electrostatic attraction and chemical association mainly contribute to the enhanced adsorption properties. As a whole, the high-efficient silicate adsorbent could be candidates to remove CTC from the wastewater with high amounts of CTC.

  1. Enhanced removal of nitrate from water using surface modification of adsorbents--a review.

    PubMed

    Loganathan, Paripurnanda; Vigneswaran, Saravanamuthu; Kandasamy, Jaya

    2013-12-15

    Elevated concentration of nitrate results in eutrophication of natural water bodies affecting the aquatic environment and reduces the quality of drinking water. This in turn causes harm to people's health, especially that of infants and livestock. Adsorbents with the high capacity to selectively adsorb nitrate are required to effectively remove nitrate from water. Surface modifications of adsorbents have been reported to enhance their adsorption of nitrate. The major techniques of surface modification are: protonation, impregnation of metals and metal oxides, grafting of amine groups, organic compounds including surfactant coating of aluminosilicate minerals, and heat treatment. This paper reviews current information on these techniques, compares the enhanced nitrate adsorption capacities achieved by the modifications, and the mechanisms of adsorption, and presents advantages and drawbacks of the techniques. Most studies on this subject have been conducted in batch experiments. These studies need to include continuous mode column trials which have more relevance to real operating systems and pilot-plant trials. Reusability of adsorbents is important for economic reasons and practical treatment applications. However, only limited information is available on the regeneration of surface modified adsorbents.

  2. Adsorption of methylene blue using modified adsorbents from drinking water treatment sludge.

    PubMed

    Nageeb Rashed, M; El-Daim El Taher, M A; Fadlalla, Somaya M M

    2016-10-01

    This study aims to explore the preparation and application of alum sludge (AS) and mud sludge (MS) from a drinking water treatment plant to remove methylene blue (MB) dye from aqueous solution. The sludge (MS and AS) was treated by chemical and physical activation to obtain new adsorbents. The adsorption experiments were carried out under different conditions of initial dye concentration (50-100 mg/L) adsorbent dosage (0.05-0.25 g), solution pH (3-9), temperature (20-60 °C) and contact time (20-90 min). Scanning electron microscopy (SEM) and X-ray diffraction instruments were used for characterization of the developed adsorbents. The results show that sludge activated by nitric acid (0.25 M HNO3) and pyrolysis at 700 °C were the best chemically and physically activated adsorbents. The optimum adsorption conditions for the adsorption of MB are 100 ppm initial dye concentration, 1 hour contact time, 250 °C solution temperature, pH 7 and 0.25 g adsorbent dosage. Application of the Langmuir and Freundlich Isotherm models showed that adsorbents fitted the Langmuir model well. SEM studies indicated the porous structural aspects of sludge suitable for removing MB dye.

  3. Immobilized smart RNA on graphene oxide nanosheets to specifically recognize and adsorb trace peptide toxins in drinking water.

    PubMed

    Hu, Xiangang; Mu, Li; Wen, Jianping; Zhou, Qixing

    2012-04-30

    The contaminations of peptide toxins in drinking water lead directly to sickness and even death in both humans and animals. A smart RNA as aptamer is covalently immobilized on graphene oxide to form a polydispersed and stable RNA-graphene oxide nanosheet. RNA-graphene oxide nanosheets can resist nuclease and natural organic matter, and specifically adsorb trace peptide toxin (microcystin-LR) in drinking water. The adsorption data fit the pseudo-second-order kinetics and the Langmuir isotherm model. The adsorption capacity of RNA-graphene oxide nanosheets decreases at extreme pH, temperature, ionic strength and natural organic matter, but it is suitable to adsorb trance pollutants in contaminated drinking water. Compared with other chemical and biological sorbents, RNA-graphene oxide nanosheets present specific and competitive adsorption, and are easily synthesized and regenerated. Aptamer (RNA) covalently immobilized on graphene oxide nanosheets is a potentially useful tool in recognizing, enriching and separating small molecules and biomacromolecules in the purification of contaminated water and the preparation of samples.

  4. Some features of raman scattering by molecules adsorbed on metal crystal faces and a fine light structure

    NASA Astrophysics Data System (ADS)

    Polubotko, A. M.

    2013-07-01

    The paper analyzes some experiments on Raman scattering by molecules adsorbed on the face (111) of silver monocrystals performed by A. Campion et al. From the existence of the forbidden line A 2 u of benzene, the conclusion about existence of the surface field, caused by atomic structure of the surface is made. The relatively large intensity of this line allows to make a conclusion about large influence of the electromagnetic field spatial inhomogeneity in crystals on their optical properties. The difference between this field and a regular plane wave, which usually describes propagation of electromagnetic field in solids is named as a fine light structure. The influence of this structure on optical properties of solids is pointed out.

  5. Effects of non-local exchange on core level shifts for gas-phase and adsorbed molecules

    NASA Astrophysics Data System (ADS)

    Van den Bossche, M.; Martin, N. M.; Gustafson, J.; Hakanoglu, C.; Weaver, J. F.; Lundgren, E.; Grönbeck, H.

    2014-07-01

    Density functional theory calculations are often used to interpret experimental shifts in core level binding energies. Calculations based on gradient-corrected (GC) exchange-correlation functionals are known to reproduce measured core level shifts (CLS) of isolated molecules and metal surfaces with reasonable accuracy. In the present study, we discuss a series of examples where the shifts calculated within a GC-functional significantly deviate from the experimental values, namely the CLS of C 1s in ethyl trifluoroacetate, Pd 3d in PdO and the O 1s shift for CO adsorbed on PdO(101). The deviations are traced to effects of the electronic self-interaction error with GC-functionals and substantially better agreements between calculated and measured CLS are obtained when a fraction of exact exchange is used in the exchange-correlation functional.

  6. Enhanced Raman scattering by molecules adsorbed at the surface of colloidal spheroids

    NASA Astrophysics Data System (ADS)

    Wang, D.-S.; Kerker, M.

    1981-08-01

    Equations are derived and calculations are presented for the electrodynamic mechanism of enhanced Raman scattering by molecules at the surface of prolate and oblate spheroids in the small-particle limit. The molecules may be arbitrarily distributed; the particles may be arbitrarily oriented. Calculations are presented for a monolayer distributed over randomly oriented spheroids. The effects of particle shape are considered for Ag, Au, and Cu hydrosols. The peak enhancement moves to longer wavelengths, and in the case of Au and Cu the magnitude of the enhancement increases strikingly as the eccentricity increases. The relation between the dependence of the Raman enhancement upon excitation wavelength and the extinction spectra is discussed, including the precariousness of extrapolating such relations beyond the small-particle limit.

  7. Hindered and modulated rotational states and spectra of adsorbed diatomic molecules

    SciTech Connect

    Shih, Y.T.; Chuu, D.S.; Mei, W.N.

    1996-10-01

    Both vertical and horizontal adsorption configurations of a diatomic molecule were modeled as the rigid rotor with which the spatial motion was confined by a finite conical well. In addition to the polar hindering potential, a sinusoidal azimuthal modulation, which bears the local symmetry of the adsorption site, was incorporated. Eigenfunctions for different models were expressed analytically in terms of the hypergeometric functions, and eigenvalues were solved numerically. We found that the rotational energy levels exhibit oscillatory behavior when plotted as functions of the hindrance angle. This particular phenomenon was interpreted as the occurrence of resonance transmission of the rotor wave function at certain hindrance condition. We also found that the rotational levels were grouped into bands when the azimuthal modulation strength was increased. The solutions were used to calculate the rotational-state distribution of desorbed molecules, and agreement with the previous experiment was obtained. {copyright} {ital 1996 The American Physical Society.}

  8. The origin of 1560 cm-1 band in experimental IR spectra of water adsorbed on TiO2 surface: Ab initio assessment

    NASA Astrophysics Data System (ADS)

    Kevorkyants, Ruslan; Rudakova, Aida V.; Chizhov, Yuri V.; Bulanin, Kirill M.

    2016-10-01

    We present DFT study on vibrational spectrum of water layer on a surface of TiO2 which is modeled via Ti8O16 nanocluster. In contrast to ν2 mode's frequency of liquid water (1645 cm-1) for the water layer theory predicts considerably lower ν2 frequency (1570 cm-1) which matches experimentally observed shoulder in IR spectrum (1560 cm-1). We demonstrate that the calculated ν2 frequencies depend linearly on a distance between adsorbed water molecules and a surface of Ti8O16 nanocluster! We also show that hydrogen bonding strongly affects ν1 vibrational frequencies but leaves ν2 and ν3 ones almost intact.

  9. Formation of 1D adsorbed water structures on CaO(001)

    NASA Astrophysics Data System (ADS)

    Zhao, Xunhua; Bhattacharya, Saswata; Ghiringhelli, Luca M.; Levchenko, Sergey V.; Scheffler, Matthias

    2015-03-01

    Understanding the interaction of water with oxide surfaces is of fundamental importance for basic and engineering sciences. Recently, a spontaneous formation of one-dimensional (1D) adsorbed water structures have been observed on CaO(001). Interestingly, at other alkaline earth metal oxides, in particular MgO(001) and SrO(001), such structures have not been found experimentally. We calculate the relative stability of adsorbed water structures on the three oxides using density-functional theory combined with the ab initio atomistic thermodynamics. Low-energy structures at different coverages are obtained with a first-principles genetic algorithm. Finite-temperature vibrational spectra are calculated using ab initio molecular dynamics. We find a range of (T, p) conditions where 1D structures are thermodynamically stable on CaO(001). The orientation and vibrational spectra of the 1D structures are in agreement with the experiments. The formation of the 1D structures is found to be actuated by a symmetry breaking in the adsorbed water tetramer, as well as by a balance between water-water and water-substrate interactions, determined by the lattice constant of the oxide.

  10. Removal of lead and zinc ions from water by low cost adsorbents.

    PubMed

    Mishra, P C; Patel, R K

    2009-08-30

    In this study, activated carbon, kaolin, bentonite, blast furnace slag and fly ash were used as adsorbent with a particle size between 100 mesh and 200 mesh to remove the lead and zinc ions from water. The concentration of the solutions prepared was in the range of 50-100 mg/L for lead and zinc for single and binary systems which are diluted as required for batch experiments. The effect of contact time, pH and adsorbent dosage on removal of lead and zinc by adsorption was investigated. The equilibrium time was found to be 30 min for activated carbon and 3h for kaolin, bentonite, blast furnace slag and fly ash. The most effective pH value for lead and zinc removal was 6 for activated carbon. pH value did not effect lead and zinc removal significantly for other adsorbents. Adsorbent doses were varied from 5 g/L to 20 g/L for both lead and zinc solutions. An increase in adsorbent doses increases the percent removal of lead and zinc. A series of isotherm studies was undertaken and the data evaluated for compliance was found to match with the Langmuir and Freundlich isotherm models. To investigate the adsorption mechanism, the kinetic models were tested, and it follows second order kinetics. Kinetic studies reveals that blast furnace slag was not effective for lead and zinc removal. The bentonite and fly ash were effective for lead and zinc removal.

  11. Copper ions removal from water using functionalized carbon nanotubes–mullite composite as adsorbent

    SciTech Connect

    Tofighy, Maryam Ahmadzadeh; Mohammadi, Toraj

    2015-08-15

    Highlights: • CNTs–mullite composite was prepared via chemical vapor deposition (CVD) method. • The prepared composite was modified with concentrated nitric acid and chitosan. • The modified CNTs–mullite composites were used as novel adsorbents. • Copper ion removal from water by the prepared adsorbents was performed. • Langmuir and Freundlich isotherms and two kinetic models were applied to fit the experimental data. - Abstract: Carbon nanotubes–mullite composite was synthesized by direct growth of carbon nanotubes on mullite particles via chemical vapor deposition method using cyclohexanol and ferrocene as carbon precursor and catalyst, respectively. The carbon nanotubes–mullite composite was oxidized with concentrated nitric acid and functionalized with chitosan and then used as a novel adsorbent for copper ions removal from water. The results demonstrated that modification with concentrated nitric acid and chitosan improves copper ions adsorption capacity of the prepared composite, significantly. Langmuir and Freundlich isotherms and two kinetic models were applied to fit the experimental data. The carbon nanotubes growth on mullite particles to form the carbon nanotubes–mullite composite with further modification is an inherently safe approach for many promising environmental applications to avoid some concerns regarding environment, health and safety. It was found that the modified carbon nanotubes–mullite composite can be considered as an excellent adsorbent for copper ions removal from water.

  12. Switching orientation of adsorbed molecules: Reverse domino on a metal surface

    NASA Astrophysics Data System (ADS)

    Braatz, C. R.; Esat, T.; Wagner, C.; Temirov, R.; Tautz, F. S.; Jakob, P.

    2016-01-01

    A thus far unknown phase of 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) on Ag(111), characterized by an all perpendicular orientation of the planar molecules and bound to the Ag substrate through the carboxyl oxygen atoms has been identified using infrared absorption spectroscopy and scanning tunneling microscopy. Its formation process requires second layer NTCDA to squeeze into empty spaces between relaxed monolayer NTCDA molecules. Remarkably, this process causes initially parallel oriented NTCDA to likewise adopt the new, highly inclined adsorption geometry. According to our SPA-LEED and STM findings, the new phase displays a distinct long range order and shows a pronounced tendency to form 1D rows or narrow islands. We suggest that extra NTCDA preferentially transforms into the upright configuration close to existing islands and attaches to them, i.e. the transformation process proceeds in a directed and recurrent manner (reverse domino scenario). Identical processing starting with a compressed NTCDA/Ag(111) monolayer leads to a purely parallel oriented bilayer, that is, the NTCDA monolayer phase is retained and merely acts as a passive template for bilayer NTCDA. The new vertical NTCDA phase represents an unusual molecular system with π-orbitals oriented parallel to a metal surface. A substantially reduced coupling of these orbitals to Ag(111) electronic levels is conjectured, which will have a major impact on intermolecular couplings and electronically excited state lifetimes.

  13. Rotational motion of a single water molecule in a buckyball.

    PubMed

    Farimani, A Barati; Wu, Yanbin; Aluru, N R

    2013-11-07

    Encapsulation of a single water molecule in a buckyball (C60) can provide fundamental insights into the properties of water. Investigation of a single water molecule is feasible through its solitary confinement in C60. In this paper, we performed a detailed study of the properties and dynamics of a single water molecule in a buckyball using DFT and MD simulations. We report on the enhancement of rotational diffusion and entropy of a water molecule in C60, compared to a bulk water molecule. H2O@C60 has zero translational diffusion and terahertz revolution frequency. The harmonic, high amplitude rotation of a single water molecule in C60 is compared to stochastic behavior of bulk water molecules. The combination of large rotational and negligible translational motion of water in C60 creates new opportunities in nanotechnology applications.

  14. Tribochemical synthesis of nano-lubricant films from adsorbed molecules at sliding solid interface: Tribo-polymers from α-pinene, pinane, and n-decane

    NASA Astrophysics Data System (ADS)

    He, Xin; Barthel, Anthony J.; Kim, Seong H.

    2016-06-01

    The mechanochemical reactions of adsorbed molecules at sliding interfaces were studied for α-pinene (C10H16), pinane (C10H18), and n-decane (C10H22) on a stainless steel substrate surface. During vapor phase lubrication, molecules adsorbed at the sliding interface could be activated by mechanical shear. Under the equilibrium adsorption condition of these molecules, the friction coefficient of sliding steel surfaces was about 0.2 and a polymeric film was tribochemically produced. The synthesis yield of α-pinene tribo-polymers was about twice as much as pinane tribo-polymers. In contrast to these strained bicyclic hydrocarbons, n-decane showed much weaker activity for tribo-polymerization at the same mechanical shear condition. These results suggested that the mechanical shear at tribological interfaces could induce the opening of the strained ring structure of α-pinene and pinane, which leads to polymerization of adsorbed molecules at the sliding track. On a stainless steel surface, such polymerization reactions of adsorbed molecules do not occur under typical surface reaction conditions. The mechanical properties and boundary lubrication efficiency of the produced tribo-polymer films are discussed.

  15. The Impact of Adsorbed Triethylene Glycol on Water Wettability of the {1014} Calcium Carbonate Surface

    NASA Astrophysics Data System (ADS)

    Olsen, R.

    2015-12-01

    Water flooding is increasingly being used as a method of enhanced oil recovery and frequently involves calcium carbonate reservoirs. Very often, thermodynamic conditions in the upper few hundred meters allow for hydrate formation. One possible method of preventing hydrates is to inject hydrate inhibitors such as triethylene glycol (TEG) into the reservoir. Thus, it is of importance to know how such glycols affect water wettability, which is an important factor defining the oil behavior in such reservoirs. Wettability of a surface is defined by the contact angle of a liquid drop on the surface. The stronger the liquid is attracted to the surface, the smaller the wetting angle becomes, implying an increased degree of wetting. Therefore, it is possible to gain qualitative knowledge of the change in wetting properties with respect to external influences by studying corresponding changes in free energy of adsorption of the liquid. In our work [1], we used molecular dynamics (MD) and Born-Oppenheimer molecular dynamics (BOMD) to study how adsorbed TEG on the {1014} calcium carbonate surface affected adsorbed water. We used the changes in density profiles of water to estimate changes in adsorption free energy of water. The adaptive biasing force (ABF) method was applied to TEG to calculate the adsorption free energy of TEG on the calcium carbonate surface. We found that water wetting of the calcium carbonate surface decreased in the presence of adsorbed TEG. [1] - Olsen, R.; Leirvik, K.; Kvamme, B.; Kuznetsova, T. Adsorption Properties of Triethylene Glycol on a Hydrated {1014} Calcite Surface and Its Effect on Adsorbed Water, Langmuir 2015, DOI: 10.1021/acs.langmuir.5b02228

  16. Far-Infrared Dielectric Properties Of Adsorbed Water In A Cellulose-Air Matrix

    NASA Astrophysics Data System (ADS)

    Bernard, Pierre; Belanger, Pierre-Andre; Boulay, Russel; Drouin, Bernard; Gagnon, Richard

    1986-09-01

    A standard three components mixture model for the dielectric constant is compared to the measured transmittance and reflectance of FIR radiation through a wet cellulose matrix. This model reproduces, at least qualitatively, the peculiar behaviour of the reflectance versus water content curve. However, the absorption coefficient for water content above 5% can only be reproduced if we postulate that the water adsorbed between 5% and 10% in volume possesses an anomalously high absorption coefficient. This is interpreted in terms of the flickering clusters model for water and the structure breaking role of the cellulose surface.

  17. Arsenic removal from water using a novel amorphous adsorbent developed from coal fly ash.

    PubMed

    Zhang, Kaihua; Zhang, Dongxue; Zhang, Kai

    2016-01-01

    A novel effective adsorbent of alumina/silica oxide hydrate (ASOH) for arsenic removal was developed through simple chemical reactions using coal fly ash. The iron-modified ASOH with enhancing adsorption activity was further developed from raw fly ash based on the in situ technique. The adsorbents were characterized by X-ray diffraction, Fourier transform infrared spectrometry, scanning electron micrograph, laser particle size and Brunauer-Emmet-Teller surface area. The results show that the adsorbents are in amorphous and porous structure, the surface areas of which are 8-12 times that of the raw ash. The acidic hydrothermal treatment acts an important role in the formation of the amorphous structure of ASOH rather than zeolite crystal. A series of adsorption experiments for arsenic on them were studied. ASOH can achieve a high removal efficiency for arsenic of 96.4% from water, which is more than 2.5 times that of the raw ash. Iron-modified ASOH can enhance the removal efficiency to reach 99.8% due to the in situ loading of iron (Fe). The condition of synthesis pH = 2-4 is better for iron-modified ASOH to adsorb arsenic from water.

  18. Pore distribution effect of activated carbon in adsorbing organic micropollutants from natural water.

    PubMed

    Ebie, K; Li, F; Azuma, Y; Yuasa, A; Hagishita, T

    2001-01-01

    Adsorption isotherms of organic micropollutants in coexistence with natural organic matter (NOM) were analyzed to evaluate the impacts of pore size distribution of activated carbon (AC) on the competition effects of the NOM. Single solute adsorption experiments and simultaneous adsorption experiments with NOM contained in a coagulation-pretreated surface water were performed for four agricultural chemicals and three coal-based activated carbons (ACs) having different pore distributions. The results showed that, for all the carbons used, the adsorption capacity of the chemicals was reduced distinctly in the presence of NOM. Such a reduction was more apparent for AC with a larger portion of small pores suitable for the adsorption of small organic molecules and for the agricultural chemicals with a more hydrophilic nature. Ideal adsorbed solution theory (IAST) incorporated with the Freundlich isotherm expression (IAST-Freundlich model) could not interpret the impact of NOM on the adsorption capacity of the chemicals unless a pore blockage effect caused by the adsorption of NOM was also considered. By taking into account this effect, the adsorption isotherm of the chemicals in the presence of NOM was well described, and the capacity reduction caused by the NOM was quantitatively assessed from the viewpoints of the site competition and the pore blockage. Analytical results clearly indicated that pore blockage was an important competition mechanism that contributed to 10-99% of the total capacity reductions of the chemicals, the level depended greatly on the ACs, the chemicals and the equilibrium concentrations, and could possibly be alleviated by broadening the pore size distributions of the ACs to provide a large volume percentage for pores with sizes above 30 A.

  19. Study of IR laser photoacoustic spectra of organic molecules adsorbed on metal surface

    NASA Astrophysics Data System (ADS)

    Lu, Huizong; Chen, Kaitai; Wang, Zhaoyong

    1987-06-01

    Using a branch-tuning CW CO2 laser in the range of 0.2 to 10.8 microns, the IR photoacoustic spectra of organic molecules absorbed on a silver surface were studied. The absorbed molecular spectra of four layers of arachidic acid and cellulose diacetate with different surface densities was studied. No peak shift was found in a comparison between IR photoacoustic spectra of solid arachidic acid near 944/cm and the corresponding IR Fourier spectra of solid archidic acid. The IR photoacoustic spectra of cellulose diacetate with sigma sub 1 = 14,000/sq cm and sigma sub 1 = 5.5 x 10 to the 15th/sq cm respectively was compared with the corresponding transmission spectra of solid cellulose diacetate. It was found that the peak of the former near 1054/cm had a red shift of about 5/cm while the peak of the latter had no obvious shift within the range of accuracy of the experiment.

  20. Effect of substrate thickness on ejection of phenylalanine molecules adsorbed on free-standing graphene bombarded by 10 keV C60

    NASA Astrophysics Data System (ADS)

    Golunski, M.; Verkhoturov, S. V.; Verkhoturov, D. S.; Schweikert, E. A.; Postawa, Z.

    2017-02-01

    Molecular dynamics computer simulations have been employed to investigate the effect of substrate thickness on the ejection mechanism of phenylalanine molecules deposited on free-standing graphene. The system is bombarded from the graphene side by 10 keV C60 projectiles at normal incidence and the ejected particles are collected both in transmission and reflection directions. It has been found that the ejection mechanism depends on the substrate thickness. At thin substrates mostly organic fragments are ejected by direct collisions between projectile atoms and adsorbed molecules. At thicker substrates interaction between deforming topmost graphene sheet and adsorbed molecules becomes more important. As this process is gentle and directionally correlated, it leads predominantly to ejection of intact molecules. The implications of the results to a novel analytical approach in Secondary Ion Mass Spectrometry based on ultrathin free-standing graphene substrates and a transmission geometry are discussed.

  1. Dissociative Electron Attachment of Water Molecules

    NASA Astrophysics Data System (ADS)

    Belkacem, Ali; Adaniya, Hidehito; Osipov, Timur; Weber, Thorsten; Lee, Sun Y.; Hertlein, Marcus; Rudek, Benedikt

    2008-05-01

    A Coltrims method is developed to measure the kinetic energy and angular distribution of fragment negative ions arising from dissociative electron attachment of molecules. A low energy pulsed electron gun is used in combination with pulsing the extraction plates of the Coltrims spectrometer. This technique is applied to study the negative oxygen anion channel for the three resonances, ^2B1, ^2A1, and ^2B2 resonances of water. The measured kinetic energy of the O- fragment gives a good measure of the two-body channel versus three-body channel for each resonance. The angular distribution of the O- fragments with respect tom the electron beam direction is found reflect well the symmetry of the resonance state. The experimental results are compared to the theoretical predictions.

  2. Role of Adsorbed Water on Charge Carrier Dynamics in Photoexcited TiO2

    PubMed Central

    2017-01-01

    Overall photocatalytic water splitting is one of the most sought after processes for sustainable solar-to-chemical energy conversion. The efficiency of this process strongly depends on charge carrier recombination and interaction with surface adsorbates at different time scales. Here, we investigated how hydration of TiO2 P25 affects dynamics of photogenerated electrons at the millisecond to minute time scale characteristic for chemical reactions. We used rapid scan diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS). The decay of photogenerated electron absorption was substantially slower in the presence of associated water. For hydrated samples, the charge carrier recombination rates followed an Arrhenius-type behavior in the temperature range of 273–423 K; these became temperature-independent when the material was dehydrated at temperatures above 423 K or cooled below 273 K. A DFT+U analysis revealed that hydrogen bonding with adsorbed water stabilizes surface-trapped holes at anatase TiO2(101) facet and lowers the barriers for hole migration. Hence, hole mobility should be higher in the hydrated material than in the dehydrated system. This demonstrates that adsorbed associated water can efficiently stabilize photogenerated charge carriers in nanocrystalline TiO2 and suppress their recombination at the time scale up to minutes.

  3. Removal of arsenate from water by adsorbents: a comparative case study.

    PubMed

    Bang, Sunbaek; Pena, Maria E; Patel, Manish; Lippincott, Lee; Meng, Xiaoguang; Kim, Kyoung-Woong

    2011-01-01

    Laboratory and field filtration experiments were conducted to study the effectiveness of As(V) removal for five types of adsorbent media. The media included activated alumina (AA), modified activated alumina (MAA), granular ferric hydroxide (GFH), granular ferric oxide (GFO), and granular titanium dioxide (TiO₂). In laboratory batch and column experiments, the synthetic challenge water was used to evaluate the effectiveness for five adsorbents. The results of the batch experiments showed that the As(V) adsorption decreased as follows at pH 6.5: TiO₂ > GFO > GFH > MAA > AA. At pH 8.5, however, As(V) removal decreased in the following order: GFO = TiO₂ > GFH > MAA > AA. In column experiments, at pH 6.5, the adsorbed As(V) for adsorbents followed the order: TiO₂ > GFO > GFH, whereas at pH 8.5 the order became: GFO = TiO₂ > GFH when the challenge water containing 50 μg/L of As(V) was used. Field filtration experiments were carried out in parallel at a wellhead in New Jersey. Before the effluent arsenic concentration increased to 10 μg/L, approximately 58,000 and 41,500 bed volumes of groundwater containing an average of 47 μg/L of As(V) were treated by the filter system packed with GFO and TiO₂, respectively. The As(V) adsorption decreased in the following sequence: GFO > TiO₂ > GFH > MAA > AA. Filtration results demonstrated that GFO and TiO₂ adsorbents could be used as media in small community filtration systems for As(V) removal.

  4. A multifunctional azobenzene-based polymeric adsorbent for effective water remediation

    NASA Astrophysics Data System (ADS)

    Wan, Decheng; Chen, Feng; Geng, Qingrui; Lu, Hang; Willcock, Helen; Liu, Qiuming; Wang, Fangyingkai; Zou, Kaidian; Jin, Ming; Pu, Hongting; Du, Jianzhong

    2014-12-01

    The efficient removal of trace carcinogenic organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs) and ionic dyes, from water is an important technical challenge. We report a highly effective recyclable multifunctional azobenzene (AZ)-based silica-supported polymeric adsorbent which can simultaneously remove both PAHs and anionic dyes from water to below parts per billion (ppb) level based on multiple interactions such as the hydrophobic effect, π-π stacking and electrostatic interactions, thus providing a new strategy for designer water remediation materials.

  5. A multifunctional azobenzene-based polymeric adsorbent for effective water remediation.

    PubMed

    Wan, Decheng; Chen, Feng; Geng, Qingrui; Lu, Hang; Willcock, Helen; Liu, Qiuming; Wang, Fangyingkai; Zou, Kaidian; Jin, Ming; Pu, Hongting; Du, Jianzhong

    2014-12-03

    The efficient removal of trace carcinogenic organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs) and ionic dyes, from water is an important technical challenge. We report a highly effective recyclable multifunctional azobenzene (AZ)-based silica-supported polymeric adsorbent which can simultaneously remove both PAHs and anionic dyes from water to below parts per billion (ppb) level based on multiple interactions such as the hydrophobic effect, π-π stacking and electrostatic interactions, thus providing a new strategy for designer water remediation materials.

  6. Photon-exposure-dependent photon-stimulated desorption for obtaining photolysis cross section of molecules adsorbed on surface by monochromatic soft x-ray photons.

    PubMed

    Chou, L-C; Jang, C-Y; Wu, Y-H; Tsai, W-C; Wang, S-K; Chen, J; Chang, S-C; Liu, C-C; Shai, Y; Wen, C-R

    2008-12-07

    Photon-exposure-dependent positive- and negative-ion photon-stimulated desorption (PSD) was proposed to study the photoreactions and obtain the photolysis cross sections of molecules adsorbed on a single-crystal surface by monochromatic soft x-ray photons with energy near the core level of adsorbate. The changes in the F(+) and F(-) PSD ion yields were measured from CF(3)Cl molecules adsorbed on Si(111)-7x7 at 30 K (CF(3)Cl dose=0.3x10(15) molecules/cm(2), approximately 0.75 monolayer) during irradiation of monochromatic soft x-ray photons near the F(1s) edge. The PSD ion yield data show the following characteristics: (a) The dissociation of adsorbed CF(3)Cl molecules is due to a combination of direct photodissociation via excitation of F(1s) core level and substrate-mediated dissociation [dissociative attachment and dipolar dissociation induced by the photoelectrons emitting from the silicon substrate]. (b) the F(+) ion desorption is associated with the bond breaking of the surface CF(3)Cl, CF(2)Cl, CFCl, and SiF species. (c) the F(-) yield is mainly due to DA and DD of the adsorbed CF(3)Cl molecules. (d) The surface SiF is formed by reaction of the surface Si atom with the neutral fluorine atom, F(+), or F(-) ion produced by scission of C-F bond of CF(3)Cl, CF(2)Cl, or CFCl species. A kinetic model was proposed for the explanation of the photolysis of this submonolayer CF(3)Cl-covered surface. Based on this model and the variation rates of the F(+)F(-) signals during fixed-energy monochromatic photon bombardment at 690.2 and 692.6 eV [near the F(1s) edge], the photolysis cross section was deduced as a function of energy.

  7. Water: one molecule, two surfaces, one mistake

    NASA Astrophysics Data System (ADS)

    Vega, Carlos

    2015-05-01

    In order to rigorously evaluate the energy and dipole moment of a certain configuration of molecules, one needs to solve the Schrödinger equation. Repeating this for many different configurations allows one to determine the potential energy surface (PES) and the dipole moment surface (DMS). Since the early days of computer simulation, it has been implicitly accepted that for empirical potentials the charges used to fit the PES should also be used to describe the DMS. This is a mistake. Partial charges are not observable magnitudes. They should be regarded as adjustable fitting parameters. Optimal values used to describe the PES are not necessarily the best to describe the DMS. One could use two fits: one for the PES and the other for the DMS. This is a common practice in the quantum chemistry community, but not used so often by the community performing computer simulations. This idea affects all types of modelling of water (with the exception of ab initio calculations) from coarse-grained to non-polarisable and polarisable models. We anticipate that an area that will benefit dramatically from having both, a good PES and a good DMS, is the modelling of water in the presence of electric fields.

  8. Clustering of water molecules in ultramicroporous carbon: In-situ small-angle neutron scattering

    DOE PAGES

    Bahadur, Jitendra; Contescu, Cristian I.; Rai, Durgesh K.; ...

    2016-10-19

    The adsorption of water is central to most of the applications of microporous carbon as adsorbent material. We report early kinetics of water adsorption in the microporous carbon using in-situ small-angle neutron scattering. It is observed that adsorption of water occurs via cluster formation of molecules. Interestingly, the cluster size remains constant throughout the adsorption process whereas number density of clusters increases with time. The role of surface chemistry of microporous carbon on the early kinetics of adsorption process was also investigated. Lastly, the present study provides direct experimental evidence for cluster assisted adsorption of water molecules in microporous carbonmore » (Do-Do model).« less

  9. Effect of side by side interactions on the thermodynamic properties of adsorbed CO molecules on the Ni(111) surface: a cluster model study

    NASA Astrophysics Data System (ADS)

    Shamkhali, Amir N.; Parsafar, Gholamabbas

    2010-05-01

    The effect of electrostatic interactions on vibrational frequencies and thermodynamic properties of CO adsorbate on the Ni(111) surface is calculated by taking the first and second nearest-neighbour interactions into account. In order to obtain reasonable results, the cluster model of various surface adsorption sites with CO adsorbate is partially optimized, using Density Functional Theory and also the MP2 method for the hcp site. Comparison between DFT and MP2 results shows that DFT results are more reliable for this system. The stretching and bending frequencies of CO adsorbate are calculated using both Partial Hessian Analysis and Cluster-Adsorbate Coupling methods. Stretching and bending frequencies are both shifted by the side by side interactions. The coupling of surface phonons and adsorbate vibrations reduces the side effects. The largest side effects on the vibrational internal energy, isochoric heat capacity, entropy and total Helmholtz free energy of adsorbed CO molecule calculated using the CAC method are found for 0.5 ML coverage. The results of the CAC method are better, but the PHA method can be used as a simple upper bound estimation. The adsorptive phase acts as an intelligent material in such a way that it changes its configuration in order to reduce the side effects.

  10. Chemical characterization of organic carbon dissolved in natural waters using inorganic adsorbents.

    PubMed

    Sugiyama, Y; Kumagai, T

    2001-01-01

    Dissolved organic carbon (DOC) in water samples from Lake Biwa was chemically characterized by two inorganic adsorbents with completely different surface characteristics. The two adsorbents were HIO (hydrous iron oxide) and SG (silica gel). Solutions of reference standard materials were analyzed concerning their adsorption behavior to HIO and SG for bovine serum albumin (BSA), fulvic acid extracted from the bottom sediments of Lake Biwa, phthalic acid, and starch. The adsorption of DOC to HIO was mainly controlled by ligand exchange and electrostatic interaction; that of SG was by electrostatic interaction. It was found that in a weak acid solution of around pH 5, BSA adsorbs to both HIO and SG, but that fulvic acid, phthalic acid and starch only show adsorption to HIO. Using these characteristics, DOC samples in natural water samples were characterized into pro-DOC, which adsorbs to both HIO and SG at pH 5, and car-DOC, which only adsorbs to HIO at pH 5. The DOC samples in Lake Biwa on October 7, 1997, at sampling sites Nb-2 and Nb-5 (south basin of Lake Biwa, the depths were about 2 and 4 m), and Ie-1 (north basin of Lake Biwa, the depth was about 75 m) were characterized. The pro-DOC has different values, depending on their sampling sites and depths, and had the maximum value of 0.42 mg C l(-1) at the surface water of Ie-1, and had the lowest values at middle to deeper water depths (0.18-0.27 mg C l(-1)). The car-DOC showed a relatively stable value at Ie-1 regardless of the depth (0.63-0.83 mg C l(-1)), and the maximum value was observed in Nb-2 and Nb-5 (1.2 and 1.3 mg C l(-1)). The ratios between car-DOC and pro-DOC concentrations were 0.2-0.5, and had different values for different sampling sites and depths. The ratios were significantly different for surface water samples where the biological activities are high and for bottom water samples where decomposition predominates.

  11. Method for the calculation of the vibrational frequency shift of physisorbed molecules. Application to H2 adsorbed in NaA zeolite

    NASA Astrophysics Data System (ADS)

    Larin, A. V.; Cohen De Lara, E.

    1994-11-01

    The vibrational frequency shift of physisorbed diatomic molecules is related to the interaction with the adsorbent expressed in terms of the internuclear distance ρ. It is calculated by the Schrödinger equation, the perturbation theory, and a simplified method. We show that it is sufficient to calculate the interaction potential for the values of ρ in the ground and first vibrational states in order to get a precision of 10% on the frequency shift. The comparison between the theoretical and experimental frequency shift of H2 adsorbed in NaA zeolite is used to adjust the interaction potential, especially in terms of the ionicity of the crystal.

  12. Molecular Dynamics Study of Small PNA Molecules in Lipid-Water System

    PubMed Central

    Weroński, Paweł; Jiang, Yi; Rasmussen, Steen

    2007-01-01

    We present the results of molecular dynamics simulations of small peptide nucleic acid (PNA) molecules, synthetic analogs of DNA, at a lipid bilayer in water. At neutral pH, without any salt, and in the NPnγT ensemble, two similar PNA molecules (6-mers) with the same nucleic base sequence and different terminal groups are investigated at the interface between water and a 1-palmitoyl-2-oleoylphosphatidylcholine lipid bilayer. The results of our simulations suggest that at low ionic strength of the solution, both PNA molecules adsorb at the lipid-water interface. In the case where the PNA molecule has charged terminal groups, the main driving force of adsorption is the electrostatic attraction between the charged groups of PNA and the lipid heads. The main driving force of adsorption of the PNA molecule with neutral terminal groups is the hydrophobic interaction of the nonpolar groups. Our simulations suggest that the system free energy change associated with PNA adsorption at the lipid-water interface is on the order of several tens of kT per PNA molecule in both cases. PMID:17307825

  13. Conformation of adsorbed bovine serum albumin governing its desorption behavior at alumina-water interfaces.

    PubMed

    Urano, H; Fukuzaki, S

    2000-01-01

    The mode of initial adsorption of bovine serum albumin (BSA) onto positively charged Al2O3 particles was studied as a function of surface coverage (theta). The adsorption isotherm of BSA exhibited saturation (theta = 1) and the existence of an inflection point at theta of 0.82. The relative numbers of ionic groups on a BSA molecule interacting with the Al2O3 surface at various theta were monitored by measuring the relative adsorption density of H+ and OH-, ([gamma(H+) - gamma(OH-)]), for BSA-adsorbed Al2O3 using potentiometric titration. The [gamma(H+) - gamma(OH-)] curves for Al2O3, BSA, and BSA-adsorbed Al2O3 at various KNO3 concentrations showed a common intersection point (cip) which was the pH giving the acid-base equivalence point, respectively. Compared with the cip's of Al2O3 (5.6) and BSA (5.2), the cip's of BSA-adsorbed Al2O3 were situated at points corresponding to more alkaline pH values over the theta range of 0.13 to 1.0. These results suggested that negatively charged groups, mainly carboxyl groups, on the BSA molecule electrostatically interacted with the Al2O3 surface. The degree of shift in the cip increased gradually with increasing theta from 0.13 to 0.70, while it decreased markedly over the theta range of 0.82 to 1.0. The variation in the cip reflected the change in the total number of ion pairs formed between BSA molecules and Al2O3. The initial rates of BSA desorption during alkali cleaning were low and almost constant over the theta range of 0.13 to 0.70, but increased markedly at theta higher than 0.82. It is suggested that the conformational changes of BSA adsorbed on Al2O3, involving changes in the relative magnitude of electrostatic interaction forces, occur discretely at theta of approximately 0.8.

  14. The Large Quadrupole of Water Molecules

    SciTech Connect

    Niu, Shuqiang; Tan, Ming-Liang; Ichiye, Toshhiko

    2011-04-07

    Many quantum mechanical calculations indicate water molecules in the gas and liquid phase have much larger quadrupole moments than any of the common site models of water for computer simulations. Here, comparisons of multipoles from quantum mechanical/molecular mechanical (QM/MM) calculations at the MP2/aug-cc-pVQZ level on a B3LYP/aug-cc-pVQZ level geometry of a waterlike cluster and from various site models show that the increased square planar quadrupole can be attributed to the p-orbital character perpendicular to the molecular plane of the highest occupied molecular orbital as well as a slight shift of negative charge toward the hydrogens. The common site models do not account for the p-orbital type electron density and fitting partial charges of TIP4P- or TIP5P-type models to the QM/MM dipole and quadrupole give unreasonable higher moments. Furthermore, six partial charge sites are necessary to account reasonably for the large quadrupole, and polarizable site models will not remedy the problem unless they account for the p-orbital in the gas phase since the QM calculations show it is present there too. On the other hand, multipole models by definition can use the correct multipoles and the electrostatic potential from the QM/MM multipoles is much closer than that from the site models to the potential from the QM/MM electron density. Finally, Monte Carlo simulations show that increasing the quadrupole in the soft-sticky dipole-quadrupole-octupole multipole model gives radial distribution functions that are in good agreement with experiment

  15. Arsenic removal from water/wastewater using adsorbents--A critical review.

    PubMed

    Mohan, Dinesh; Pittman, Charles U

    2007-04-02

    Arsenic's history in science, medicine and technology has been overshadowed by its notoriety as a poison in homicides. Arsenic is viewed as being synonymous with toxicity. Dangerous arsenic concentrations in natural waters is now a worldwide problem and often referred to as a 20th-21st century calamity. High arsenic concentrations have been reported recently from the USA, China, Chile, Bangladesh, Taiwan, Mexico, Argentina, Poland, Canada, Hungary, Japan and India. Among 21 countries in different parts of the world affected by groundwater arsenic contamination, the largest population at risk is in Bangladesh followed by West Bengal in India. Existing overviews of arsenic removal include technologies that have traditionally been used (oxidation, precipitation/coagulation/membrane separation) with far less attention paid to adsorption. No previous review is available where readers can get an overview of the sorption capacities of both available and developed sorbents used for arsenic remediation together with the traditional remediation methods. We have incorporated most of the valuable available literature on arsenic remediation by adsorption ( approximately 600 references). Existing purification methods for drinking water; wastewater; industrial effluents, and technological solutions for arsenic have been listed. Arsenic sorption by commercially available carbons and other low-cost adsorbents are surveyed and critically reviewed and their sorption efficiencies are compared. Arsenic adsorption behavior in presence of other impurities has been discussed. Some commercially available adsorbents are also surveyed. An extensive table summarizes the sorption capacities of various adsorbents. Some low-cost adsorbents are superior including treated slags, carbons developed from agricultural waste (char carbons and coconut husk carbons), biosorbents (immobilized biomass, orange juice residue), goethite and some commercial adsorbents, which include resins, gels, silica

  16. On the reactive uptake of gaseous PAH molecules by micron-sized atmospheric water droplets

    NASA Astrophysics Data System (ADS)

    Raja, S.; Valsaraj, K. T.

    2006-10-01

    A falling droplet reactor was used to study the heterogeneous oxidation of gaseous PAH molecules adsorbed on a 92 μm diameter water droplet by ozone. The dynamic partition constant for the PAH between the droplet and air and the first-order surface rate constant was measured. The increase in uptake with ozone concentration was due to increased mass transfer via surface reaction of co-adsorbed ozone and PAH. The surface rate constant was rationalized through the Langmuir-Hinshelwood mechanism. The rate constant was smaller for phenanthrene than naphthalene. The main reaction products identified in the aqueous phase indicated the peroxidic route for surface reaction of ozone with PAH. The heterogeneous reaction rate of ozone with adsorbed phenanthrene at the air-water interface of a 92-μm droplet was estimated to be 9300 times larger than the homogeneous reaction of ozone with phenanthrene in the gas phase and it was 76 times larger than the homogeneous oxidation by hydroxyl radical in the gas phase. For naphthalene that is more volatile, however, the homogeneous reaction with hydroxyl was more important. Increased organic carbon added to the droplet increased both the partition constant for phenanthrene and surface reaction with ozone. The partition constant for a droplet formed from actual fog water was much larger than for pure distilled water.

  17. Origin of subdiffusion of water molecules on cell membrane surfaces

    PubMed Central

    Yamamoto, Eiji; Akimoto, Takuma; Yasui, Masato; Yasuoka, Kenji

    2014-01-01

    Water molecules play an important role in providing unique environments for biological reactions on cell membranes. It is widely believed that water molecules form bridges that connect lipid molecules and stabilize cell membranes. Using all-atom molecular dynamics simulations, we show that translational and rotational diffusion of water molecules on lipid membrane surfaces exhibit subdiffusion and aging. Moreover, we provide evidence that both divergent mean trapping time (continuous-time random walk) and long-correlated noise (fractional Brownian motion) contribute to this subdiffusion. These results suggest that subdiffusion on cell membranes causes the water retardation, an enhancement of cell membrane stability, and a higher reaction efficiency. PMID:24739933

  18. Zinc peroxide nanomaterial as an adsorbent for removal of Congo red dye from waste water.

    PubMed

    Chawla, Sneha; Uppal, Himani; Yadav, Mohit; Bahadur, Nupur; Singh, Nahar

    2017-01-01

    In the past decade, various natural byproducts, advanced metal oxide composites and photocatalysts have been reported for removal of dyes from water. Although these materials are useful for select applications, they have some limitations such as use at fixed temperature, ultra violet (UV) light and the need for sophisticated experimental set up. These materials can remove dyes up to a certain extent but require long time. To overcome these limitations, a promising adsorbent zinc peroxide (ZnO2) nanomaterial has been developed for the removal of Congo red (CR) dye from contaminated water. ZnO2 is highly efficient even in the absence of sunlight to remove CR from contaminated water upto the permissible limits set by the World Health Organization (WHO) and the United States- Environmental Protection Agency (US-EPA). The adsorbent has a specific property to adjust the pH of the test solution within 6.5-7.5 range irrespective of acidic or basic nature of water. The adsorption capacity of the material for CR dye was 208mgg(-1) within 10min at 2-10pH range. The proposed material could be useful for the industries involved in water purification. The removal of CR has been confirmed by spectroscopic and microscopic techniques. The adsorption data followed a second order kinetics and Freundlich isotherm.

  19. In situ STM imaging of bis-3-sodiumsulfopropyl-disulfide molecules adsorbed on copper film electrodeposited on Pt(111) single crystal electrode.

    PubMed

    Tu, HsinLing; Yen, PoYu; Chen, Sihzih; Yau, ShuehLin; Dow, Wei-Ping; Lee, Yuh-Lang

    2011-06-07

    The adsorption of bis-3-sodiumsulfopropyldi-sulfide (SPS) on metal electrodes in chloride-containing media has been intensively studied to unveil its accelerating effect on Cu electrodeposition. Molecular resolution scanning tunneling microscopy (STM) imaging technique was used in this study to explore the adsorption and decomposition of SPS molecules concurring with the electrodeposition of copper on an ordered Pt(111) electrode in 0.1 M HClO(4) + 1 mM Cu(ClO(4))(2) + 1 mM KCl. Depending on the potential of Pt(111), SPS molecules could react, adsorb, and decompose at chloride-capped Cu films. A submonolayer of Cu adatoms classified as the underpotential deposition (UPD) layer at 0.4 V (vs Ag/AgCl) was completely displaced by SPS molecules, possibly occurring via RSSR (SPS) + Cl-Cu-Pt → RS(-)-Pt(+) + RS(-) (MPS) + Cu(2+) + Cl(-), where MPS is 3-mercaptopropanesulfonate. By contrast, at 0.2 V, where a full monolayer of Cu was presumed to be deposited, SPS molecules were adsorbed in local (4 × 4) structures at the lower ends of step ledges. Bulk Cu deposition driven by a small overpotential (η < 50 mV) proceeded slowly to yield an atomically smooth Cu deposit at the very beginning (<5 layers). On a bilayer Cu deposit, the chloride adlayer was still adsorbed to afford SPS admolecules arranged in a unique 1D striped phase. SPS molecules could decompose into MPS upon further Cu deposition, as a (2 × 2)-MPS structure was observed with prolonged in situ STM imaging. It was possible to visualize either SPS admolecules in the upper plane or chloride adlayer sitting underneath upon switching the imaging conditions. Overall, this study established a MPS molecular film adsorbed to the chloride adlayer sitting atop the Cu deposit.

  20. Oscillating electric-field effects on adsorbed-water at rutile- and anatase-TiO2 surfaces

    NASA Astrophysics Data System (ADS)

    Futera, Zdenek; English, Niall J.

    2016-11-01

    We have performed non-equilibrium molecular dynamics simulations of various TiO2/water interfaces at ambient temperature in presence of oscillating electric fields in frequency range 20-100 GHz and RMS intensities 0.05-0.25 V/Å. Although the externally applied fields are by one order of magnitude lower than the intrinsic electric field present on the interfaces (˜1.5-4.5 V/Å), significant non-thermal coupling of rotational and translational motion of water molecules was clearly observed. Enhancement of the motion, manifested by increase of diffusivity, was detected in the first hydration layer, which is known to be heavily confined by adsorption to the TiO2 surface. Interestingly, the diffusivity increases more rapidly on anatase than on rutile facets where the adsorbed water was found to be more organized and restrained. We observed that the applied oscillating field reduces number of hydrogen bonds on the interface. The remaining H-bonds are weaker than those detected under zero-field conditions; however, their lifetime increases on most of the surfaces when the low-frequency fields are applied. Reduction of adsorption interaction was observed also in IR spectra of interfacial water where the directional patterns are smeared as the intensities of applied fields increase.

  1. SiO(2)-LiBr Nanocomposite Sol-Gel Adsorbents of Water Vapor: Preparation and Properties.

    PubMed

    Mrowiec-Bialoń; Lachowski; Jarz&ecedil;bski; Gordeeva; Aristov

    1999-10-15

    Water vapor adsorption on SiO(2)-LiBr sol-gel materials strongly depends on bromide content. Adsorption capacities exhibited by these materials at higher relative pressures can be as high as 0.8 kg of water/kg of adsorbent. These adsorbents can be regenerated by heating at 473 K and reused. However, a gradual decay of adsorption properties occurs during repeated adsorption-desorption cycles. Thus, this family of adsorbents seems to be less attractive than the corresponding SiO(2)-CaCl(2) composites. Copyright 1999 Academic Press.

  2. Structure and dynamics of water molecules confined in triglyceride oils.

    PubMed

    Groot, Carien C M; Velikov, Krassimir P; Bakker, Huib J

    2016-10-26

    Though it is commonly known that a small amount of water can be present in triglyceride oil, a molecular picture of how water molecules organize in the oil phase is lacking. We investigate the hydrogen-bond configuration and dynamics of water in triacetin, tributyrin and trioctanoin using linear infrared and time-resolved two-dimensional infrared (2DIR) spectroscopy of the water hydroxyl stretch vibration. We identify water molecules with a single strong hydrogen bond to the triglyceride, water molecules with two weaker hydrogen bonds to the triglycerides, and water clusters. These species do not interconvert on the 20 ps timescale of the experiment, as evidenced by the absence of cross-peaks in the 2DIR spectrum. The vibrational response of water molecules with a single strong hydrogen bond to the triglyceride depends strongly on the excitation frequency, revealing the presence of different subspecies of singly-bound water molecules that correspond to different hydrogen-bond locations. In contrast, the water molecules with two weaker hydrogen bonds to the triglyceride correspond to a single, specific hydrogen-bond configuration; these molecules likely bridge the carbonyl groups of adjacent triglyceride molecules, which can have considerable influence on liquid triglyceride properties.

  3. The role of adsorbed water on the friction of a layer of submicron particles

    USGS Publications Warehouse

    Sammis, Charles G.; Lockner, David A.; Reches, Ze’ev

    2011-01-01

    Anomalously low values of friction observed in layers of submicron particles deformed in simple shear at high slip velocities are explained as the consequence of a one nanometer thick layer of water adsorbed on the particles. The observed transition from normal friction with an apparent coefficient near μ = 0.6 at low slip speeds to a coefficient near μ = 0.3 at higher slip speeds is attributed to competition between the time required to extrude the water layer from between neighboring particles in a force chain and the average lifetime of the chain. At low slip speeds the time required for extrusion is less than the average lifetime of a chain so the particles make contact and lock. As slip speed increases, the average lifetime of a chain decreases until it is less than the extrusion time and the particles in a force chain never come into direct contact. If the adsorbed water layer enables the otherwise rough particles to rotate, the coefficient of friction will drop to μ = 0.3, appropriate for rotating spheres. At the highest slip speeds particle temperatures rise above 100°C, the water layer vaporizes, the particles contact and lock, and the coefficient of friction rises to μ = 0.6. The observed onset of weakening at slip speeds near 0.001 m/s is consistent with the measured viscosity of a 1 nm thick layer of adsorbed water, with a minimum particle radius of approximately 20 nm, and with reasonable assumptions about the distribution of force chains guided by experimental observation. The reduction of friction and the range of velocities over which it occurs decrease with increasing normal stress, as predicted by the model. Moreover, the analysis predicts that this high-speed weakening mechanism should operate only for particles with radii smaller than approximately 1 μm. For larger particles the slip speed required for weakening is so large that frictional heating will evaporate the adsorbed water and weakening will not occur.

  4. Fluorescence dynamics of microsphere-adsorbed sunscreens

    NASA Astrophysics Data System (ADS)

    Krishnan, R.

    2005-03-01

    Sunscreens are generally oily substances which are prepared in organic solvents, emulsions or dispersions with micro- or nanoparticles. These molecules adsorb to and integrate into skin cells. In order to understand the photophysical properties of the sunscreen, we compare steady-state and time-resolved fluorescence in organic solvent of varying dielectric constant ɛ and adsorbed to polystyrene microspheres and dispersed in water. Steady-state fluorescence is highest and average fluorescence lifetime longest in toluene, the solvent of lowest ɛ. However, there is no uniform dependence on ɛ. Sunscreens PABA and padimate-O show complex emission spectra. Microsphere-adsorbed sunscreens exhibit highly non-exponential decay, illustrative of multiple environments of the adsorbed molecule. The heterogeneous fluorescence dynamics likely characterizes sunscreen adsorbed to cells.

  5. Theoretical Study on Surface-Enhanced Raman Spectra of Water Adsorbed on Noble Metal Cathodes of Nanostructures

    NASA Astrophysics Data System (ADS)

    Wu, De-Yin; Pang, Ran; Tian, Zhong-Qun

    2016-06-01

    The observed surface-enhanced Raman scattering (SERS) spectra of water adsorbed on metal film electrodes of silver, gold, and platinum nanoparticles were used to infer interfacial water structures. The basis is the change of the electrochemical vibrational Stark tuning rates and the relative Raman intensity of the stretching and bending modes. How it is not completely understood the reason why the relative Raman intensity ratio of the bending and stretching vibrations of interfacial water increases at the very negative potential region. Density functional theory calculations provide the conceptual model. The specific enhancement effect for the bending mode was closely associated with the water adsorption structure in a hydrogen bonded configuration through its H-end binding to surface sites with large polarizability due to strong cathodic polarization. The present theoretical results allow us to propose that interfacial water molecules exist on these metal cathodes with different hydrogen bonding interactions, the HO-H…Ag(Au) for silver and gold. In acidic solution, a surface electron-hydronium ion-pair was proposed as an adsorption configuration of interfacial water structures on silver and gold cathodes based on density functional theory (DFT) calculations. The EHIP is in the configuration of H3O+(H2O)ne-, where the hydronium H3O+ and the surface electron is separated by water layers. The electron bound in the EHIP can first be excited under light irradiation, subsequently inducing a structural relaxation into a hydrated hydrogen atom. Thus, Raman intensities of the interfacial water in the EHIP species are signifcantly enhanced due to the cathodic polarization on silver and gold electrodes.

  6. Selective capture of water using microporous adsorbents to increase the lifetime of lubricants.

    PubMed

    Ng, Eng-Poh; Delmotte, Luc; Mintova, Svetlana

    2009-01-01

    Long live lubricants: The selective capture of water from lubricants using nanosized microporous aluminophosphate (AEI) and aluminosilicate materials was studied. Nearly 98 % of the moisture was removed from the lubricating oil under ambient conditions, resulting in a significant improvement in the lubricating service lifetime. Moreover, both the lubricant and the microporous sorbents can be recovered and reused.The selective capture of water from lubricants using nanosized microporous aluminophosphate and aluminosilicate materials was studied with an aim to increase the lifetime of the lubricating mineral oil. The amount of water present in oxidized lubricating oil before and after treatment with microporous materials was studied by FTIR spectroscopy and determined quantitatively using the Karl Fischer titration method. Nanosized aluminophosphate revealed a high selectivity for water without adsorbing other additives, in contrast to nanosized aluminosilicates which also adsorb polar oxidation products and ionic additives. About 98 % of the initial moisture could be removed from the lubricating oil under ambient conditions, resulting in a significant improvement in the lubricating service lifetime. Moreover, no by-products are formed during the process and both the lubricant and the sorbents can be recovered and reused, thus the method is environmentally friendly.

  7. Feasibility of using drinking water treatment residuals as a novel chlorpyrifos adsorbent.

    PubMed

    Zhao, Yuanyuan; Wang, Changhui; Wendling, Laura A; Pei, Yuansheng

    2013-08-07

    Recent efforts have increasingly focused on the development of low-cost adsorbents for pesticide retention. In this work, the novel reuse of drinking water treatment residuals (WTRs), a nonhazardous ubiquitous byproduct, as an adsorbent for chlorpyrifos was investigated. Results showed that the kinetics and isothermal processes of chlorpyrifos sorption to WTRs were better described by a pseudo-second-order model and by the Freundlich equation, respectively. Moreover, compared with paddy soil and other documented absorbents, the WTRs exhibited a greater affinity for chlorpyrifos (log Koc = 4.76-4.90) and a higher chlorpyrifos sorption capacity (KF = 5967 mg(1-n)·L·kg(-1)) owing to the character and high content of organic matter. Further investigation demonstrated that the pH had a slight but statistically insignificant effect on chlorpyrifos sorption to WTRs; solution ionic strength and the presence of low molecular weight organic acids both resulted in concentration-dependent inhibition effects. Overall, these results confirmed the feasibility of using WTRs as a novel chlorpyrifos adsorbent.

  8. A review of the use of red mud as adsorbent for the removal of toxic pollutants from water and wastewater.

    PubMed

    Bhatnagar, Amit; Vilar, Vítor J P; Botelho, Cidália M S; Boaventura, Rui A R

    2011-01-01

    Red mud (an aluminium industry waste) has received wide attention as an effective adsorbent for water pollution control, showing significant adsorption potential for the removal of various aquatic pollutants. In this review, an extensive list of red-mud-based adsorbents has been compiled and their adsorption capacities (maximum uptake value of the adsorbent for the pollutant or adsorbate being removed) for various aquatic pollutants (metal ions, dyes, phenolic compounds, inorganic anions) are presented. The review provides a summary of recent information obtained using batch studies and deals with the adsorption mechanisms involved. It is evident from the literature survey that red mud has been found to be efficient for the removal of various aquatic pollutants, especially arsenic and phosphate. However, there is still a need to investigate the practical utility of these adsorbents on a commercial scale.

  9. Application of near infrared spectroscopy for the determination of adsorbed p-nitrophenol on HDTMA organoclay--implications for the removal of organic pollutants from water.

    PubMed

    Zhou, Qin; Xi, Yunfei; He, Hongping; Frost, Ray L

    2008-03-01

    NIR spectroscopy has been used to measure the adsorption of p-nitrophenol on untreated montmorillonite and surfactant exchanged montmorillonite. p-Nitrophenol is characterised by an intense NIR band at 8890 cm(-1) which shifts to 8840 cm(-1) upon adsorption on organoclay. The band was not observed for p-nitrophenol adsorbed on untreated montmorillonite. Both the montmorillonite and the surfactant modified montmorillonite are characterised by NIR bands at 7061 and 6791 cm(-1). The organoclay is characterised by two prominent bands at 5871 and 5667 cm(-1) assigned to the fundamental overtones of the mid-IR bands at 2916 and 2850 cm(-1). A band at 6017 cm(-1) is attributed to the p-nitrophenol adsorbed on the organoclay. The band is not observed for the montmorillonite with adsorbed p-nitrophenol. It is concluded that p-nitrophenol is adsorbed to significantly greater amounts on the organoclay compared with the untreated montmorillonite. The implication is that organoclays are most useful for removing organic molecules from water through adsorption.

  10. Adsorption characteristics of water vapor on gear-pellet and honeycomb-pellet types of adsorbents containing A-type zeolite

    SciTech Connect

    Nakamura, A.; Munakata, K.; Hara, K.; Narita, S.; Sugiyama, T.; Kotoh, K.; Tanaka, M.; Uda, T.

    2015-03-15

    It is necessary to recover or process tritiated species that are extensively coexistent in nuclear fusion installations. A conventional way to recover tritium release to atmosphere is catalytic oxidation of tritiated species and adsorption of tritiated water vapor on adsorbents with high surface areas. Therefore, new adsorbents with low pressure loss and high surface areas need to be developed and utilized for such large-scale adsorption systems. In this study, attention was focused on new adsorbents, which are gear-type pellet MS5A adsorbent, gear-type pellet MS4A adsorbent and honeycomb-type pellet MS5A adsorbent. The adsorption characteristics of the new adsorbent were comparatively studied with conventional type of adsorbents (pellet-type MS5A adsorbent and pebble-type MS5A adsorbent), in terms of adsorption capacity, pressure loss and adsorption rate. It was found that the adsorption capacity of water vapor on the gear-type adsorbents is higher than that on a honeycomb-type adsorbent. The experimental breakthrough curves indicate that the adsorption rates of water vapor on gear-type and honeycomb-type adsorbents are smaller than that on conventional type adsorbents. Various adsorption models were also tested to correlate the experimental isotherms. It was found that the Langmuir-Freundlich model could properly correlate the experimental adsorption isotherms.

  11. Forsterite Carbonation in Wet-scCO2: Dependence on Adsorbed Water Concentration

    NASA Astrophysics Data System (ADS)

    Loring, J.; Benezeth, P.; Qafoku, O.; Thompson, C.; Schaef, T.; Bonneville, A.; McGrail, P.; Felmy, A.; Rosso, K.

    2013-12-01

    Capturing and storing CO2 in basaltic formations is one of the most promising options for mitigating atmospheric CO2 emissions resulting from the burning of fossil fuels. These geologic reservoirs have high reactive potential for CO2-mineral trapping due to an abundance of divalent-cation containing silicates, such as forsterite (Mg2SiO4). Recent studies have shown that carbonation of these silicates under wet scCO2 conditions, e. g. encountered near a CO2 injection well, proceeds along a different pathway and is more effective than in CO2-saturated aqueous fluids. The presence of an adsorbed water film on the forsterite surface seems to be key to reactivity towards carbonation. In this study, we employed in situ high pressure IR spectroscopy to investigate the dependence of adsorbed water film thickness on forsterite carbonation chemistry. Post reaction ex situ SEM, TEM, TGA, XRD, and NMR measurements will also be discussed. Several IR titrations were performed of forsterite with water at 50 °C and 90 bar scCO2. Aliquots of water were titrated at 4-hour reaction-time increments. Once a desired total water concentration was reached, data were collected for about another 30 hours. One titration involved 10 additions, which corresponds to 6.8 monolayers of adsorbed water. Clearly, a carbonate was precipitating, and its spectral signature matched magnesite. Another titration involved 8 aliquots, or up to 4.4 monolayers of water. The integrated absorbance under the CO stretching bands of carbonate as a function of time after reaching 4.4 monolayers showed an increase and then a plateau. We are currently unsure of the identity of the carbonate that precipitated, but it could be an amorphous anhydrous phase or magnesite crystals with dimensions of only several nanometers. A third titration only involved 3 additions, or up to 1.6 monolayers of water. The integrated absorbance under the CO stretching bands of carbonate as a function of time after reaching 1.6 monolayers

  12. Fluoride removal in water by a hybrid adsorbent lanthanum-carbon.

    PubMed

    Vences-Alvarez, Esmeralda; Velazquez-Jimenez, Litza Halla; Chazaro-Ruiz, Luis Felipe; Diaz-Flores, Paola E; Rangel-Mendez, Jose Rene

    2015-10-01

    Various health problems associated with drinking water containing high fluoride levels, have motivated researchers to develop more efficient adsorbents to remove fluoride from water for beneficial concentrations to human health. The objective of this research was to anchor lanthanum oxyhydroxides on a commercial granular activated carbon (GAC) to remove fluoride from water considering the effect of the solution pH, and the presence of co-existing anions and organic matter. The activated carbon was modified with lanthanum oxyhydroxides by impregnation. SEM and XRD were performed in order to determine the crystal structure and morphology of the La(III) particles anchored on the GAC surface. FT-IR and pK(a)'s distribution were determined in order to elucidate both the possible mechanism of the lanthanum anchorage on the activated carbon surface and the fluoride adsorption mechanism on the modified material. The results showed that lanthanum ions prefer binding to carboxyl and phenolic groups on the activated carbon surface. Potentiometric titrations revealed that the modified carbon (GAC-La) possesses positive charge at a pH lower than 9. The adsorption capacity of the modified GAC increased five times in contrast to an unmodified GAC adsorption capacity at an initial F(-) concentration of 20 mg L(-1). Moreover, the presence of co-existing anions had no effect on the fluoride adsorption capacity at concentrations below 30 mg L(-1), that indicated high F(-) affinity by the modified adsorbent material (GAG-La).

  13. Water hyacinth (Eichhornia crassipes) waste as an adsorbent for phosphorus removal from swine wastewater.

    PubMed

    Chen, Xi; Chen, Xiuxia; Wan, Xianwei; Weng, Boqi; Huang, Qin

    2010-12-01

    Both live plants and dried straw of water hyacinth were applied to a sequential treatment of swine wastewater for nitrogen and phosphorus reduction. In the facultative tank, the straw behaved as a kind of adsorbent toward phosphorus. Its phosphorus removal rate varied considerably with contact time between the straw and the influent. In the laboratory, the straw displayed a rapid total phosphorus reduction on a KH(2)PO(4) solution. The adsorption efficiency was about 36% upon saturation. At the same time, the water hyacinth straw in the facultative tank enhanced NH(3)-N removal efficiency as well. However, no adsorption was evident. This study demonstrated an economically feasible means to apply water hyacinth phosphorus straw for the swine wastewater treatment. The sequential system employed significantly reduced the land use, as compared to the wastewater stabilization pond treatment, for pollution amelioration of swine waste.

  14. Adsorbent materials from paper industry waste materials and their use in Cu(II) removal from water.

    PubMed

    Méndez, A; Barriga, S; Fidalgo, J M; Gascó, G

    2009-06-15

    This paper deals with the removal of Cu(2+) from water using adsorbent materials prepared from paper industry waste materials (one de-inking paper sludge and other sludge from virgin pulp mill). Experimental results showed that de-inking paper sludge leads to mesoporous materials (V(mic)/V(T)=0.13 and 0.14), whereas the sludge from virgin pulp mill produces high microporous adsorbents (V(mic)/V(T)=0.39 and 0.41). Adsorbent materials were then used for Cu(2+) removal from water at acid pH. During water treatment, heavy metals lixiviation from adsorbent materials was not produced. However, important Ca and Mg leaching was observed. Final pH significantly increases after treatment of water with adsorbent materials probably due to their elevated CaCO(3) content. In general, highest Cu(2+) removal was obtained using adsorbent materials from de-inking paper sludge. This result could be due to their higher content in oxygenated surface groups, high average pore diameter, elevated superficial charge density, high CaCO(3) amount and high Ca and Mg exchange content.

  15. A study of the alumina-silica gel adsorbent for the removal of silicic acid from geothermal water: increase in adsorption capacity of the adsorbent due to formation of amorphous aluminosilicate by adsorption of silicic acid.

    PubMed

    Yokoyama, Takushi; Ueda, Akira; Kato, Koichi; Mogi, Katsumi; Matsuo, Shorin

    2002-08-01

    Two kinds of adsorbents (Si adsorbent and Al adsorbent) for the removal of silicic acid from geothermal water to retard the formation of silica scales were prepared using silicic acid contained in geothermal water. The Si adsorbent was prepared by evaporating geothermal water, and the Al adsorbent was prepared by evaporating geothermal water after the addition of aluminum chloride. The specific surface area of the Si adsorbent was small and it's adsorption capacity of silicic acid was low. Although the specific surface area of the Al adsorbent was also small, it was significantly increased by the adsorption of silicic acid and it's adsorption capacity was high. Based on the change in the local structure of aluminum ion by the adsorption of silicic acid, the Al adsorbent was considered to be silica particles covered with crystalline aluminum hydroxide. Moreover, it was concluded that the increase in the specific surface area of the Al adsorbent and the decrease in the zeta potential were due to the formation of an amorphous aluminosilicate with a large surface area and a negative charge (one 4-coordinated Al) by the reaction between aluminum ions and silicic acids.

  16. Mechanical properties of hexadecane-water interfaces with adsorbed hydrophobic bacteria

    NASA Astrophysics Data System (ADS)

    Kang, Zhewen

    Certain strains of hydrophobic bacteria are known to play critical roles in petroleum-related applications. The aim of this study was to investigate how hydrophobic bacteria in their stationary phase could adsorb onto the hexadecane-water interface and alter its mechanical properties. The two strains of bacteria used in forming the interfacial films were Acinetobacter venetianus RAG-1 (a Gram-negative bacterium) and Rhodococcus erythropolis 20S-E1-c (Gram-positive). Experiments at two different length scales (millimetre and micrometre) were conducted and the results were compared. In addition, a simple flow experiment was designed in a constricted channel and the results were related to the intrinsic mechanical properties of bacteria-adsorbed films. On the millimetre scale, using the pendant drop technique, the film interfacial tension was monitored as the surface area was made to undergo changes. Under static conditions, both types of bacteria showed no significant effect on the interfacial tension. When subjected to transient excitations, the two bacterial films exhibited qualitatively similar, yet quantitative distinct rheological properties (including film elasticities and relaxation times). Under continuous reduction of surface area, the RAG-1 system showed a "paper-like" interface, while the interface of the 20S-E1-c system was "soap film-like." These macroscopic observations could be explained by the surface ultrastructures of the two cell strains. On the micrometre scale, using the micropipette technique, colloidal stability of the bacteria-coated oil droplets was examined through direct-contact experiments. Both types of bacteria were seen to function as effective stabilizers. In addition, the adsorbed bacteria also interacted with one another at the interface, giving rise to higher order 2-D rheological properties. A technique of directly probing the mechanical properties of the emulsion drop surfaces revealed that (a) the films behaved as purely elastic

  17. Ceria modified activated carbon: an efficient arsenic removal adsorbent for drinking water purification

    NASA Astrophysics Data System (ADS)

    Sawana, Radha; Somasundar, Yogesh; Iyer, Venkatesh Shankar; Baruwati, Babita

    2016-03-01

    Ceria (CeO2) coated powdered activated carbon was synthesized by a single step chemical process and demonstrated to be a highly efficient adsorbent for the removal of both As(III) and As(V) from water without any pre-oxidation process. The formation of CeO2 on the surface of powdered activated carbon was confirmed by X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. The percentage of Ce in the adsorbent was confirmed to be 3.5 % by ICP-OES. The maximum removal capacity for As(III) and As(V) was found to be 10.3 and 12.2 mg/g, respectively. These values are comparable to most of the commercially available adsorbents. 80 % of the removal process was completed within 15 min of contact time in a batch process. More than 95 % removal of both As(III) and As(V) was achieved within an hour. The efficiency of removal was not affected by change in pH (5-9), salinity, hardness, organic (1-4 ppm of humic acid) and inorganic anions (sulphate, nitrate, chloride, bicarbonate and fluoride) excluding phosphate. Presence of 100 ppm phosphate reduced the removal significantly from 90 to 18 %. The equilibrium adsorption pattern of both As(III) and As(V) fitted well with the Freundlich model with R 2 values 0.99 and 0.97, respectively. The material shows reusability greater than three times in a batch process (arsenic concentration reduced below 10 ppb from 330 ppb) and a life of at least 100 L in a column study with 80 g material when tested under natural hard water (TDS 1000 ppm, pH 7.8, hardness 600 ppm as CaCO3) spiked with 330 ppb of arsenic.

  18. Removal of cadmium and lead ions from water by sulfonated magnetic nanoparticle adsorbents.

    PubMed

    Chen, Kai; He, Junyong; Li, Yulian; Cai, Xingguo; Zhang, Kaisheng; Liu, Tao; Hu, Yi; Lin, Dongyue; Kong, Lingtao; Liu, Jinhuai

    2017-05-15

    A new adsorbent, Fe3O4 sulfonated magnetic nanoparticle (Fe3O4-SO3H MNP), was developed for heavy metal ions removal from water, which could be effectively separated from the solution owing to the superparamagnetic property. The nanoparticles can be used to remove heavy metal ions due to the additional active site, "sulfo-group", introduced by the AMPS branches grafted onto the iron oxide. The as-synthesized materials were characterized by SEM, TEM, FT-IR and BET. The FTIR, XPS and Zeta potential were used to describe the adsorption mechanism. The Fe3O4-SO3H MNPs showed rapid removal for Pb(2+) and Cd(2+) with maximum of adsorption capacity of 108. 93 and 80.9mg/g at 25°C, respectively. The adsorption isotherms for Pb(2+) and Cd(2+) fitted better with Langmuir than Freundlich models, indicated that the processes of the removal of Pb(2+) and Cd(2+) could follow a kind of similar adsorption manner. The adsorption kinetic was consistent with pseudo-second-order model. Furthermore, the reuse experiments results showed the adsorbent might have potential in treating heavy metal ions pollution in water.

  19. Water and ion transport in ultra-adsorbing porous magnesium carbonate studied by dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Pochard, Isabelle; Frykstrand, Sara; Ahlström, Olle; Forsgren, Johan; Strømme, Maria

    2014-01-01

    Porous materials are used in application areas ranging from drug and vaccine delivery, medical implants, molecular sieves and cosmetics to catalysis and humidity control. In the present work, we employed an alternative approach to gain in-depth understanding about water interaction properties in such materials by the use of dielectric spectroscopy and thereby show that it is possible to obtain information that is not accessible from the more commonly employed water interaction analysis techniques. Specifically, the complex dielectric response of Upsalite, a novel, super-hydroscopic, high-surface area, porous magnesium carbonate material was measured in isothermal frequency scans between 10-3 and 106 Hz at controlled relative humidity (RH). We found the dielectric constant of the dry material to be 1.82. The ratio of bound to free water present in Upsalite after adsorption at room temperature was found to be high irrespective of the surrounding humidity with values ranging from ˜67% to ˜90%. We further found that OH- ions are the charge carriers responsible for the electrode polarization observed in the dielectric response and that the amount of these ions that are free to move in the material corresponds to a concentration of the order of 1-10 μmol l-1 independent of RH. Finally, the OH- diffusion coefficient displayed a drastic decrease with decreasing RH, typical of transport in unsaturated conditions. The presented results provide detailed insight about water interactions in the novel water adsorbing material under study and it is foreseen that the employed analysis methods can be used to evaluate other types of moisture adsorbing materials as well as the movement of functional species in the pores of inorganic drug delivery materials and materials tailored for adsorption of harmful charged species.

  20. Adsorption Characteristics of Different Adsorbents and Iron(III) Salt for Removing As(V) from Water

    PubMed Central

    Ćurko, Josip; Matošić, Marin; Crnek, Vlado; Stulić, Višnja

    2016-01-01

    Summary The aim of this study is to determine the adsorption performance of three types of adsorbents for removal of As(V) from water: Bayoxide® E33 (granular iron(III) oxide), Titansorb® (granular titanium oxide) and a suspension of precipitated iron(III) hydroxide. Results of As(V) adsorption stoichiometry of two commercial adsorbents and precipitated iron(III) hydroxide in tap and demineralized water were fitted to Freundlich and Langmuir adsorption isotherm equations, from which adsorption constants and adsorption capacity were calculated. The separation factor RL for the three adsorbents ranged from 0.04 to 0.61, indicating effective adsorption. Precipitated iron(III) hydroxide had the greatest, while Titansorb had the lowest capacity to adsorb As(V). Comparison of adsorption from tap or demineralized water showed that Bayoxide and precipitated iron(III) hydroxide had higher adsorption capacity in demineralized water, whereas Titansorb showed a slightly higher capacity in tap water. These results provide mechanistic insights into how commonly used adsorbents remove As(V) from water. PMID:27904416

  1. Novel Anionic Clay Adsorbents for Boiler-Blow-Down Waters Reclaim and Reuse

    SciTech Connect

    Muhammad Sahimi; Theodore Tsotsis

    2010-01-08

    Arsenic (As) and Selenium (Se) are found in water in the form of oxyanions. Relatively high concentrations of As and Se have been reported both in power plant discharges, as well as, in fresh water supplies. The International Agency for Research on Cancer currently classifies As as a group 1 chemical, that is considered to be carcinogenic to humans. In Phase I of this project we studied the adsorption of As and Se by uncalcined and calcined layered double hydroxide (LDH). The focus of the present work is a systematic study of the adsorption of As and Se by conditioned LDH adsorbents. Conditioning the adsorbent significantly reduced the Mg and Al dissolution observed with uncalcined and calcined LDH. The adsorption rates and isotherms have been investigated in batch experiments using particles of four different particle size ranges. As(V) adsorption is shown to follow a Sips-type adsorption isotherm. The As(V) adsorption rate on conditioned LDH increases with decreasing adsorbent particle size; the adsorption capacity, on the other hand, is independent of the particle size. A homogeneous surface diffusion model (HSDM) and a bi-disperse pore model (BPM) - the latter viewing the LDH particles as assemblages of microparticles and taking into account bulk diffusion in the intraparticle pore space, and surface diffusion within the microparticles themselves - were used to fit the experimental kinetic data. The HSDM estimated diffusivity values dependent on the particle size, whereas the BPM predicted an intracrystalline diffusivity, which is fairly invariant with particle size. The removal of As(V) on conditioned LDH adsorbents was also investigated in flow columns, where the impact of important solution and operational parameters such as influent As concentration, pH, sorbent particle size and flow rate were studied. An early breakthrough and saturation was observed at higher flow rates and at higher influent concentrations, whereas a decrease in the sorbent particle

  2. Removal of atrazine from water by low cost adsorbents derived from agricultural and industrial wastes.

    PubMed

    Sharma, Rajendra Kumar; Kumar, Anoop; Joseph, P E

    2008-05-01

    In the present study six adsorbents viz. wood charcoal, fly ash, coconut charcoal, saw dust, coconut fiber and baggasse charcoal were studied for their capacity to remove atrazine from water. The removal efficiency of different adsorbents varied from 76.5% to 97.7% at 0.05 ppm concentration and 78.5% to 95.5% at 0.1 ppm concentration of atrazine solution, which was less than removal efficiency of activated charcoal reported as 98% for atrazine (Adams and Watson, J Environ Eng ASCE 39:327-330, 1996). Wood charcoal was a cheap (Rs 15 kg(-1)) and easily available material in house holds. Since wood charcoal was granular in nature, it could be used for the removal of atrazine from water to the extent of 95.5%-97.7%. Fly ash is a waste product of thermal plant containing 40%-50% silica, 20%-35% alumina, 12%-30% carbon and unburnt minerals having a high pH of 9-10. It is very cheap and abundant material and has comparatively good adsorption capacity. It was found that fly ash effectively removed about 84.1%-88.5% atrazine from water at 0.05 and 0.1 ppm levels. Coconut shell is also waste product. Therefore, both are inexpensive. The removal efficiency of atrazine from water was 92.4%-95.2% by coconut shell charcoal and 85.9%-86.3% by coconut fiber. Sawdust is generally used as domestic fuel and found everywhere. It is also very cheap (Re. 1 kg(-1)). Baggasse charcoal is a waste product of sugar mill and abundant material. Its cost is due to transport expense, which depends upon distance from the sugar mill. The removal efficiency of sawdust and baggasse charcoal was found 78.5-80.5 and 76.5-84.6, respectively. The efficacy of chemically treated adsorbents for the removal of atrazine from water is in the order: wood charcoal > coconut shell charcoal > fly ash > coconut fiber charcoal > baggasse charcoal > sawdust.

  3. Free enthalpies of replacing water molecules in protein binding pockets

    NASA Astrophysics Data System (ADS)

    Riniker, Sereina; Barandun, Luzi J.; Diederich, François; Krämer, Oliver; Steffen, Andreas; van Gunsteren, Wilfred F.

    2012-12-01

    Water molecules in the binding pocket of a protein and their role in ligand binding have increasingly raised interest in recent years. Displacement of such water molecules by ligand atoms can be either favourable or unfavourable for ligand binding depending on the change in free enthalpy. In this study, we investigate the displacement of water molecules by an apolar probe in the binding pocket of two proteins, cyclin-dependent kinase 2 and tRNA-guanine transglycosylase, using the method of enveloping distribution sampling (EDS) to obtain free enthalpy differences. In both cases, a ligand core is placed inside the respective pocket and the remaining water molecules are converted to apolar probes, both individually and in pairs. The free enthalpy difference between a water molecule and a CH3 group at the same location in the pocket in comparison to their presence in bulk solution calculated from EDS molecular dynamics simulations corresponds to the binding free enthalpy of CH3 at this location. From the free enthalpy difference and the enthalpy difference, the entropic contribution of the displacement can be obtained too. The overlay of the resulting occupancy volumes of the water molecules with crystal structures of analogous ligands shows qualitative correlation between experimentally measured inhibition constants and the calculated free enthalpy differences. Thus, such an EDS analysis of the water molecules in the binding pocket may give valuable insight for potency optimization in drug design.

  4. Free enthalpies of replacing water molecules in protein binding pockets.

    PubMed

    Riniker, Sereina; Barandun, Luzi J; Diederich, François; Krämer, Oliver; Steffen, Andreas; van Gunsteren, Wilfred F

    2012-12-01

    Water molecules in the binding pocket of a protein and their role in ligand binding have increasingly raised interest in recent years. Displacement of such water molecules by ligand atoms can be either favourable or unfavourable for ligand binding depending on the change in free enthalpy. In this study, we investigate the displacement of water molecules by an apolar probe in the binding pocket of two proteins, cyclin-dependent kinase 2 and tRNA-guanine transglycosylase, using the method of enveloping distribution sampling (EDS) to obtain free enthalpy differences. In both cases, a ligand core is placed inside the respective pocket and the remaining water molecules are converted to apolar probes, both individually and in pairs. The free enthalpy difference between a water molecule and a CH(3) group at the same location in the pocket in comparison to their presence in bulk solution calculated from EDS molecular dynamics simulations corresponds to the binding free enthalpy of CH(3) at this location. From the free enthalpy difference and the enthalpy difference, the entropic contribution of the displacement can be obtained too. The overlay of the resulting occupancy volumes of the water molecules with crystal structures of analogous ligands shows qualitative correlation between experimentally measured inhibition constants and the calculated free enthalpy differences. Thus, such an EDS analysis of the water molecules in the binding pocket may give valuable insight for potency optimization in drug design.

  5. Silanization of polyelectrolyte-coated particles: an effective route to stabilize Raman tagging molecules adsorbed on micrometer-sized silver particles.

    PubMed

    Kim, Kwan; Lee, Hyang Bong; Shin, Kuan Soo

    2008-06-03

    Micrometer-sized Ag (microAg) powders are very efficient surface-enhanced Raman scattering (SERS) substrates. To use microAg powders as a core material for molecular sensors operating via SERS, it is necessary to stabilize the tagging (i.e., SERS-marker) molecules adsorbed onto them. We demonstrate in this work that once the tagging molecules are coated with aliphatic polyelectrolytes such as poly(allylamine hydrochloride), the base-catalyzed silanization can be readily carried out to form stable silica shells around the polyelectrolyte layers by a biomimetic process; any particle can therefore be coated with silica since polyelectrolytes can be deposited beforehand via a layer-by-layer deposition method. Even after silanization, the SERS peaks of marker molecules on microAg particles are the only observable peaks since aliphatic polyelectrolytes, as well as silica shells, are intrinsically weak Raman scatterers, and more importantly, the SERS signals must be derived mostly from the first layer of the adsorbates (i.e., the marker molecules) in direct contact with the microAg particles. Silica shells, once fabricated, can further be derivatized to possess biofunctional groups; therefore, the modified microAg particles can be used as platforms of highly stable SERS-based biological sensors, as well as barcoding materials.

  6. Ratio of the surface-enhanced anti-Stokes scattering to the surface-enhanced Stokes-Raman scattering for molecules adsorbed on a silver electrode

    NASA Astrophysics Data System (ADS)

    Brolo, A. G.; Sanderson, A. C.; Smith, A. P.

    2004-01-01

    Surface-enhanced Raman scattering (SERS) from oxazine 720 (oxa), rhodamine 6G (R6G), and pyridine (py) adsorbed on a rough silver surface was observed. The silver electrode was immersed in aqueous solutions permitting control of the potential bias applied to the surface. SERS spectra in the Stokes and anti-Stokes regions were obtained for several applied potentials and two laser excitation energies. Normalized ratios between the anti-Stokes and the Stokes intensities K were calculated from the SERS spectra. The K ratios differed from unity for all the systems investigated. A preferential enhancement of the (surface-enhanced) Stokes scattering was observed for oxa and py. In contrast, the K ratios were higher than unity for R6G, indicating an increase in the anti-Stokes signal. The K ratios measured in this work decreased with the excitation energy and showed a dependence on the energy of the vibrational modes. These results were satisfactorily explained using resonance models, based on the charge-transfer and electromagnetic theories for SERS. No evidence for a SERS-induced nonthermal population distribution among the vibrational states of the adsorbed molecules (vibrational optical pumping) was found. Therefore, we conclude that the main features of the preferential enhancement of the anti-Stokes scattering for an adsorbed molecule on rough silver can be fully understood in the context of current SERS theories.

  7. A method for preparing ferric activated carbon composites adsorbents to remove arsenic from drinking water.

    PubMed

    Zhang, Qiao Li; Lin, Y C; Chen, X; Gao, Nai Yun

    2007-09-30

    Iron oxide/activated carbon (FeO/AC) composite adsorbent material, which was used to modify the coal-based activated carbon (AC) 12 x 40, was prepared by the special ferric oxide microcrystal in this study. This composite can be used as the adsorbent to remove arsenic from drinking water, and Langmuir isotherm adsorption equation well describes the experimental adsorption isotherms. Then, the arsenic desorption can subsequently be separated from the medium by using a 1% aqueous NaOH solution. The apparent characters and physical chemistry performances of FeO/AC composite were investigated by X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Batch and column adsorption experiments were carried out to investigate and compare the arsenic removal capability of the prepared FeO/AC composite material and virgin activated carbon. It can be concluded that: (1) the main phase present in this composite are magnetite (Fe(3)O(4)), maghemite (gamma-Fe(2)O(3)), hematite (alpha-Fe(2)O(3)) and goethite (alpha-FeO(OH)); (2) the presence of iron oxides did not significantly affect the surface area or the pore structure of the activated carbon; (3) the comparisons between the adsorption isotherms of arsenic from aqueous solution onto the composite and virgin activated carbon showed that the FeO/AC composite behave an excellent capacity of adsorption arsenic than the virgin activated carbon; (4) column adsorption experiments with FeO/AC composite adsorbent showed that the arsenic could be removed to below 0.01 mg/L within 1250 mL empty bed volume when influent concentration was 0.5mg/L.

  8. Relaxational dynamics of water molecules at protein surface

    NASA Astrophysics Data System (ADS)

    Dellerue, S.; Bellissent-Funel, M.-C.

    2000-08-01

    Relaxational dynamics of water molecules at the surface of a C-phycocyanin protein is studied by high resolution quasi-elastic neutron scattering. The neutron quasi-elastic spectra are well described by the α-relaxation process of mode coupling theory of supercooled liquids. The relaxation times of interfacial water exhibit a power law dependence on the wave vector Q. The average diffusion coefficient is 10 times lower than that of bulk water. This confirms that there is a retardation of water molecules at the protein surface which is in good agreement with the results of water at the surface of hydrophilic model systems.

  9. Development of long-life-cycle tablet ceramic adsorbent for geosmin removal from water solution

    NASA Astrophysics Data System (ADS)

    Chen, Rongzhi; Xue, Qiang; Zhang, Zhenya; Sugiura, Norio; Yang, Yingnan; Li, Miao; Chen, Nan; Ying, Zhao; Lei, Zhongfang

    2011-01-01

    In this study, the tablet ceramic adsorbent (TCA), a silica/iron(III) oxide composite material, has been developed for geosmin (GSM) removal from the water solution. The physicochemical characteristics of TCA were examined with XRD, SEM, EDX and BET analyses. The sorption characteristics of GSM on TCA were investigated in a batch system. Attempts have been made to understand the adsorption kinetics, the effect of initial GSM concentration, solution pH, and reaction time. The batch experiments equilibrium data were well fitted to the Lagergren kinetic equation, which indicate the first-order nature adsorption. Over 82% of the GSM was removed by the TCA within 600 min at an initial concentration of 200 ng/L with 20 g/L of TCA dose. The batch and regeneration study indicated that the TCA is a cost-effective GSM adsorbent with sufficient mechanical strength to retain its physical integrity after long-time adsorption, and high regeneration performance for long-life-cycle application. Almost no second contamination (toxic sludge or leached iron) was observed after adsorption, and the gas resultant of thermal regeneration is harmless to atmospheric environment.

  10. Activated carbons and low cost adsorbents for remediation of tri- and hexavalent chromium from water.

    PubMed

    Mohan, Dinesh; Pittman, Charles U

    2006-09-21

    Hexavalent chromium is a well-known highly toxic metal, considered a priority pollutant. Industrial sources of Cr(VI) include leather tanning, cooling tower blowdown, plating, electroplating, anodizing baths, rinse waters, etc. The most common method applied for chromate control is reduction of Cr(VI) to its trivalent form in acid (pH approximately 2.0) and subsequent hydroxide precipitation of Cr(III) by increasing the pH to approximately 9.0-10.0 using lime. Existing overviews of chromium removal only cover selected technologies that have traditionally been used in chromium removal. Far less attention has been paid to adsorption. Herein, we provide the first review article that provides readers an overview of the sorption capacities of commercial developed carbons and other low cost sorbents for chromium remediation. After an overview of chromium contamination is provided, more than 300 papers on chromium remediation using adsorption are discussed to provide recent information about the most widely used adsorbents applied for chromium remediation. Efforts to establish the adsorption mechanisms of Cr(III) and Cr(VI) on various adsorbents are reviewed. Chromium's impact environmental quality, sources of chromium pollution and toxicological/health effects is also briefly introduced. Interpretations of the surface interactions are offered. Particular attention is paid to comparing the sorption efficiency and capacities of commercially available activated carbons to other low cost alternatives, including an extensive table.

  11. Interactions of water, methanol and diethyl ether molecules with the surface of oxidized activated carbon

    NASA Astrophysics Data System (ADS)

    Salame, Issa I.; Bandosz, Teresa J.

    Two samples of oxidized activated carbon of wood origin were used as adsorbents of water, methanol, and diethyl ether. Structural and chemical characteristics of the samples' surfaces were obtained using adsorption of nitrogen and Boehm titration. The adsorption isotherms of water and methanol were measured using a volumetric apparatus whereas the adsorption of diethyl ether was studied by means of inverse gas chromatography at finite concentration. Then the isotherms at three different temperatures were used to calculate the isosteric heats of adsorption. The results showed that the strength of interaction depends on the porosity of the sample and its surface chemistry. The effect of surface chemistry and the presence of oxygenated groups are predominant in the case of water and the least important in the case of diethyl ether. This is the result of the chemical nature of the molecules, their sizes, and the relative strengths of the dispersive interactions in small pores in comparison with hydrogen bonding to surface functional groups.

  12. Shape-selective adsorption of aromatic molecules from water by tetramethylammonium-smectite

    USGS Publications Warehouse

    Lee, J.; Mortland, M.M.; Boyd, S.A.; Chiou, C.T.

    1989-01-01

    The adsorption of aromatic compounds by smectite exchanged with tetramethylammonium (TMA) has been studied. Aromatic compounds adsorbed by TMA-smectite are assumed to adopt a tilted orientation in a face-to-face arrangment with the TMA tetrahedra. The sorptive characteristics of TMA-smectite were influenced strongly by the presence of water. The dry TMA-smectite showed little selectivity in the uptake of benzen, toluene and xylene. In the presence of water, TMA-smectite showed a high degree of selectivity based on molecular size/shape, resulting in high uptake of benzene and progressively lower uptake of larger aromatic molecules. This selectivity appeared to result from the shrinkage of interlamellar cavities by water.

  13. Rapid removal of aniline from contaminated water by a novel polymeric adsorbent.

    PubMed

    Huang, Yunhong; Xu, Yang; He, Qinghua; Cao, Yusheng; Du, Bibai

    2014-01-01

    Dummy molecularly imprinted polymers (DMIPs) for aniline were synthesized by a thermal polymerization method using acrylamide as a functional monomer, ethylene dimethacrylate as a crosslinker, 2,2-azobisisobutyronitrile as a free radical initiator, acetonitrile as a porogenic solvent, and analogues of aniline, namely sulfadiazine, as the template. The DMIPs that were obtained showed a high affinity to aniline compared to non-imprinted polymers. It was proven that the DMIPs obtained using sulfadiazine as the template were much better than the molecularly imprinted polymers using aniline as the template. The results indicated that the Freundlich model was fit for the adsorption model of DMIP for aniline and the adsorption model of the DMIP for aniline was multilayer adsorption. Furthermore, the results showed that the DMIP synthesized by bulk polymerization could be used as a novel adsorbent for removal of aniline from contaminated water.

  14. Arsenic adsorption and speciation in drinking water by GAC-based iron-containing adsorbents

    NASA Astrophysics Data System (ADS)

    Gim, Yewon; Terry, Jeff; Gu, Zhimang; Hua, B.; Deng, Baolin

    2008-04-01

    Granular Activated Carbon (GAC) with Iron adsorbents were developed for effective removal of arsenic from drinking water. The structure and proposed mechanism for As removal was studied using X-ray absorption spectroscopy. The oxidation state of As(III)GAC sample was calculated using XANES spectra and verified to be predominantly As(V). The structure was determined using EXAFS spectra of As(V) and Fe. The Fe spectra suggested thin layer of Fe oxide formation on GAC surface. As data showed As oxide formed bond on the Fe oxide surface. The spectra were calculated using multiple geometrically optimized models calculated using density functional theory. Further calculations were done to verify the structure, and further examine the structure.

  15. On the several molecules and nanostructures of water.

    PubMed

    Whitney, Cynthia Kolb

    2012-01-01

    This paper investigates the water molecule from a variety of viewpoints. Water can involve different isotopes of Hydrogen and Oxygen, it can form differently shaped isomer molecules, and, when frozen, it occupies space differently than most other substances do. The tool for conducting the investigation of all this is called 'Algebraic Chemistry'. This tool is a quantitative model for predicting the energy budget for all sorts of changes between different ionization states of atoms that are involved in chemical reactions and in changes of physical state. The model is based on consistent patterns seen in empirical data about ionization potentials, together with rational scaling laws that can interpolate and extrapolate for situations where no data are available. The results of the investigation of the water molecule include comments, both positive and negative, about technologies involving heavy water, poly water, Brown's gas, and cold fusion.

  16. On the Several Molecules and Nanostructures of Water

    PubMed Central

    Whitney, Cynthia Kolb

    2012-01-01

    This paper investigates the water molecule from a variety of viewpoints. Water can involve different isotopes of Hydrogen and Oxygen, it can form differently shaped isomer molecules, and, when frozen, it occupies space differently than most other substances do. The tool for conducting the investigation of all this is called ‘Algebraic Chemistry’. This tool is a quantitative model for predicting the energy budget for all sorts of changes between different ionization states of atoms that are involved in chemical reactions and in changes of physical state. The model is based on consistent patterns seen in empirical data about ionization potentials, together with rational scaling laws that can interpolate and extrapolate for situations where no data are available. The results of the investigation of the water molecule include comments, both positive and negative, about technologies involving heavy water, poly water, Brown’s gas, and cold fusion. PMID:22312305

  17. Comparison of calculated cross sections for secondary electron emission from a water molecule and clusters of water molecules by protons

    SciTech Connect

    Long, K.A.; Paretzke, H.G. )

    1991-07-15

    Double-differential cross sections for the emission of secondary electrons, as a function of emission angle and energy, from a water molecule, a cluster of water molecules, and liquid water due to proton impact have been calculated using the dielectric response function of the target material and a method which uses an integral formulation of the density-functional theory. From these double-differential cross sections, single-differential and total cross sections, and the energy loss per unit path length, have been calculated by successive integration. The results have been compared to available experimental results and, in the case of single-differential cross sections, also to empirical models. A comparison has been made between the results for the molecule and the central molecule of the cluster in order to obtain insight into how the cross sections might change in the condensed phase, namely in liquid water.

  18. Quantum Behavior of Water Molecules Confined to Nanocavities in Gemstones.

    PubMed

    Gorshunov, Boris P; Zhukova, Elena S; Torgashev, Victor I; Lebedev, Vladimir V; Shakurov, Gil'man S; Kremer, Reinhard K; Pestrjakov, Efim V; Thomas, Victor G; Fursenko, Dimitry A; Dressel, Martin

    2013-06-20

    When water is confined to nanocavities, its quantum mechanical behavior can be revealed by terahertz spectroscopy. We place H2O molecules in the nanopores of a beryl crystal lattice and observe a rich and highly anisotropic set of absorption lines in the terahertz spectral range. Two bands can be identified, which originate from translational and librational motions of the water molecule isolated within the cage; they correspond to the analogous broad bands in liquid water and ice. In the present case of well-defined and highly symmetric nanocavities, the observed fine structure can be explained by macroscopic tunneling of the H2O molecules within a six-fold potential caused by the interaction of the molecule with the cavity walls.

  19. On equilibrium structures of the water molecule

    NASA Astrophysics Data System (ADS)

    Császár, Attila G.; Czakó, Gábor; Furtenbacher, Tibor; Tennyson, Jonathan; Szalay, Viktor; Shirin, Sergei V.; Zobov, Nikolai F.; Polyansky, Oleg L.

    2005-06-01

    Equilibrium structures are fundamental entities in molecular sciences. They can be inferred from experimental data by complicated inverse procedures which often rely on several assumptions, including the Born-Oppenheimer approximation. Theory provides a direct route to equilibrium geometries. A recent high-quality ab initio semiglobal adiabatic potential-energy surface (PES) of the electronic ground state of water, reported by Polyansky et al. [Polyansky et al.Science 299, 539 (2003)] and called CVRQD here, is analyzed in this respect. The equilibrium geometries resulting from this direct route are deemed to be of higher accuracy than those that can be determined by analyzing experimental data. Detailed investigation of the effect of the breakdown of the Born-Oppenheimer approximation suggests that the concept of an isotope-independent equilibrium structure holds to about 3×10-5Å and 0.02° for water. The mass-independent [Born-Oppenheimer (BO)] equilibrium bond length and bond angle on the ground electronic state PES of water is reBO=0.95782Å and θeBO=104.485°, respectively. The related mass-dependent (adiabatic) equilibrium bond length and bond angle of H2O16 is read=0.95785Å and θead=104.500°, respectively, while those of D2O16 are read=0.95783Å and θead=104.490°. Pure ab initio prediction of J =1 and 2 rotational levels on the vibrational ground state by the CVRQD PESs is accurate to better than 0.002cm-1 for all isotopologs of water considered. Elaborate adjustment of the CVRQD PESs to reproduce all observed rovibrational transitions to better than 0.05cm-1 (or the lower ones to better than 0.0035cm-1) does not result in noticeable changes in the adiabatic equilibrium structure parameters. The expectation values of the ground vibrational state rotational constants of the water isotopologs, computed in the Eckart frame using the CVRQD PESs and atomic masses, deviate from the experimentally measured ones only marginally, especially for A0 and B0. The

  20. Removal efficiency of water purifier and adsorbent for iodine, cesium, strontium, barium and zirconium in drinking water.

    PubMed

    Sato, Itaru; Kudo, Hiroaki; Tsuda, Shuji

    2011-01-01

    The severe incident of Fukushima Daiichi Nuclear Power Station has caused radioactive contamination of environment including drinking water. Radioactive iodine, cesium, strontium, barium and zirconium are hazardous fission products because of the high yield and/or relatively long half-life. In the present study, 4 pot-type water purifiers and several adsorbents were examined for the removal effects on these elements from drinking water. Iodide, iodate, cesium and barium were removed by all water purifiers with efficiencies about 85%, 40%, 75-90% and higher than 85%, respectively. These efficiencies lasted for 200 l, which is near the recommended limits for use of filter cartridges, without decay. Strontium was removed with initial efficiencies from 70% to 100%, but the efficiencies were slightly decreased by use. Zirconium was removed by two models, but hardly removed by the other models. Synthetic zeolite A4 efficiently removed cesium, strontium and barium, but had no effect on iodine and zirconium. Natural zeolite, mordenite, removed cesium with an efficiency as high as zeolite A4, but the removal efficiencies for strontium and barium were far less than those of zeolite A4. Activated carbon had little removal effects on these elements. In case of radioactive contamination of tap water, water purifiers may be available for convenient decontamination of drinking water in the home.

  1. Sulfonated graphene nanosheets as a superb adsorbent for various environmental pollutants in water.

    PubMed

    Shen, Yi; Chen, Baoliang

    2015-06-16

    Graphene nanosheets, as a novel nanoadsorbent, can be further modified to optimize the adsorption capability for various pollutants. To overcome the structural limits of graphene (aggregation) and graphene oxide (hydrophilic surface) in water, sulfonated graphene (GS) was prepared by diazotization reaction using sulfanilic acid. It was demonstrated that GS not only recovered a relatively complete sp(2)-hybridized plane with high affinity for aromatic pollutants but also had sulfonic acid groups and partial original oxygen-containing groups that powerfully attracted positively charged pollutants. The saturated adsorption capacities of GS were 400 mg/g for phenanthrene, 906 mg/g for methylene blue and 58 mg/g for Cd(2+), which were much higher than the corresponding values for reduced graphene oxide and graphene oxide. GS as a graphene-based adsorbent exhibits fast adsorption kinetic rate and superior adsorption capacity toward various pollutants, which mainly thanks to the multiple adsorption sites in GS including the conjugate π region sites and the functional group sites. Moreover, the sulfonic acid groups endow GS with the good dispersibility and single or few nanosheets which guarantee the adsorption processes. It is great potential to expose the adsorption sites of graphene nanosheets for pollutants in water by regulating their microstructures, surface properties and water dispersion.

  2. Study on nicotinamide adenine dinucleotide adsorbed at nano-boehmite/water and nano-corundum/water interfaces.

    PubMed

    Li, Li; Xie, Yanfang; Wang, Yanping; Yang, Xiaodi; Chen, Rong Fu; Shen, Ren Fang

    2013-02-01

    In this study, the adsorption behaviors of nicotinamide adenine dinucleotide (NAD(+)) on nano-boehmite (γ-AlOOH) and nano-corundum (γ-Al(2)O(3)) surfaces were investigated. The results showed that NAD(+) was predominantly adsorbed at the boehmite/water and corundum/water interfaces in outer-sphere fashions by electrostatic interaction between NAD(+) phosphate and surface hydroxyl groups. However, the features of ATR-FTIR spectra suggested that some minor inner-sphere complex should be considered at low pH conditions on corundum surface, which was consistent with the effect of NAD(+) on dissolution rate of corundum. In addition, the adsorption data well fitted with Langmuir and Freundlich isotherms on the boehmite and corundum surfaces, respectively. Also, the Gibbs adsorption energy was negative on the boehmite surface, which indicated that the adsorption behavior was spontaneous.

  3. Local order and mobility of water molecules around ambivalent helices.

    PubMed

    Bhattacharjee, Nicholus; Biswas, Parbati

    2011-10-27

    Water on a protein surface plays a key role in determining the structure and dynamics of proteins. Compared to the properties of bulk water, many aspects of the structure and dynamics of the water surrounding the proteins are less understood. It is interesting therefore to explore how the properties of the water within the solvation shell around the peptide molecule depend on its specific secondary structure. In this work we investigate the orientational order and residence times of the water molecules to characterize the structure, energetics, and dynamics of the hydration shell water around ambivalent peptides. Ambivalent sequences are identical sequences which display multiple secondary structures in different proteins. Molecular dynamics simulations of representative proteins containing variable helix, variable nonhelix, and conserved helix are also used to explore the local structure and mobility of water molecules in their vicinity. The results, for the first time, depict a different water distribution pattern around the conserved and variable helices. The water molecules surrounding the helical segments in variable helices are found to possess a less locally ordered structure compared to those around their corresponding nonhelical counterparts and conserved helices. The long conserved helices exhibit extremely high local residence times compared to the helical conformations of the variable helices, whereas the residence times of the nonhelical conformations of the variable helices are comparable to those of the short conserved helices. This differential pattern of the structure and dynamics of water molecules in the vicinity of conserved/variable helices may lend valuable insights for understanding the role of solvent effects in determining sequence ambivalency and help in improving the accuracy of water models used in the simulations of proteins.

  4. How mobile are dye adsorbates and acetonitrile molecules on the surface of TiO2 nanoparticles? A quasi-elastic neutron scattering study

    NASA Astrophysics Data System (ADS)

    Vaissier, Valerie; Sakai, Victoria Garcia; Li, Xiaoe; Cabral, João T.; Nelson, Jenny; Barnes, Piers R. F.

    2016-12-01

    Motions of molecules adsorbed to surfaces may control the rate of charge transport within monolayers in systems such as dye sensitized solar cells. We used quasi-elastic neutron scattering (QENS) to evaluate the possible dynamics of two small dye moieties, isonicotinic acid (INA) and bis-isonicotinic acid (BINA), attached to TiO2 nanoparticles via carboxylate groups. The scattering data indicate that moieties are immobile and do not rotate around the anchoring groups on timescales between around 10 ps and a few ns (corresponding to the instrumental range). This gives an upper limit for the rate at which conformational fluctuations can assist charge transport between anchored molecules. Our observations suggest that if the conformation of larger dye molecules varies with time, it does so on longer timescales and/or in parts of the molecule which are not directly connected to the anchoring group. The QENS measurements also indicate that several layers of acetonitrile solvent molecules are immobilized at the interface with the TiO2 on the measurement time scale, in reasonable agreement with recent classical molecular dynamics results.

  5. How mobile are dye adsorbates and acetonitrile molecules on the surface of TiO2 nanoparticles? A quasi-elastic neutron scattering study

    PubMed Central

    Vaissier, Valerie; Sakai, Victoria Garcia; Li, Xiaoe; Cabral, João T.; Nelson, Jenny; Barnes, Piers R. F.

    2016-01-01

    Motions of molecules adsorbed to surfaces may control the rate of charge transport within monolayers in systems such as dye sensitized solar cells. We used quasi-elastic neutron scattering (QENS) to evaluate the possible dynamics of two small dye moieties, isonicotinic acid (INA) and bis-isonicotinic acid (BINA), attached to TiO2 nanoparticles via carboxylate groups. The scattering data indicate that moieties are immobile and do not rotate around the anchoring groups on timescales between around 10 ps and a few ns (corresponding to the instrumental range). This gives an upper limit for the rate at which conformational fluctuations can assist charge transport between anchored molecules. Our observations suggest that if the conformation of larger dye molecules varies with time, it does so on longer timescales and/or in parts of the molecule which are not directly connected to the anchoring group. The QENS measurements also indicate that several layers of acetonitrile solvent molecules are immobilized at the interface with the TiO2 on the measurement time scale, in reasonable agreement with recent classical molecular dynamics results. PMID:27991538

  6. Autodissociation of doubly charged water molecules

    NASA Astrophysics Data System (ADS)

    Scully, S. W. J.; Wyer, J. A.; Senthil, V.; Shah, M. B.; Montenegro, E. C.

    2006-04-01

    The electron impact dissociative double-ionization cross sections for H2O between 45 and 1500eV have been measured using time of flight mass spectrometry. The energy dependence of the H++OH+ and H++O+ ion pair production cross sections indicate that Auger-like autoionization following a vacancy in the 2a1 molecular orbital is the main double ionization channel at high velocities. In contrast to expectation, these findings show that dissociation through the H2O2+ precursor state is a significant process at high collision energies. Knowledge of this process is vital as it has a direct affect on the production of important molecular species, such as H2 , during water radiolysis. Branching ratios of the various fragments produced following both autoionization and double ionization have also been obtained.

  7. Dynamics of Confined Water Molecules in Aqueous Salt Hydrates

    SciTech Connect

    Werhahn, Jasper C.; Pandelov, S.; Yoo, Soohaeng; Xantheas, Sotiris S.; Iglev, H.

    2011-04-01

    The unusual properties of water are largely dictated by the dynamics of the H bond network. A single water molecule has more H bonding sites than atoms, hence new experimental and theoretical investigations about this peculiar liquid have not ceased to appear. Confinement of water to nanodroplets or small molecular clusters drastically changes many of the liquid’s properties. Such confined water plays a major role in the solvation of macro molecules such as proteins and can even be essential to their properties. Despite the vast results available on bulk and confined water, discussions about the correlation between spectral and structural properties continue to this day. The fast relaxation of the OH stretching vibration in bulk water, and the variance of sample geometries in the experiments on confined water obfuscate definite interpretation of the spectroscopic results in terms of structural parameters. We present first time-resolved investigations on a new model system that is ideally suited to overcome many of the problems faced in spectroscopical investigation of the H bond network of water. Aqueous hydrates of inorganic salts provide water molecules in a crystal grid, that enables unambiguous correlations of spectroscopic and structural features. Furthermore, the confined water clusters are well isolated from each other in the crystal matrix, so different degrees of confinement can be achieved by selection of the appropriate salt.

  8. Roles of water molecules in trapping carbon dioxide molecules inside the interlayer space of graphene oxides.

    PubMed

    Yumura, Takashi; Yamasaki, Ayumi

    2014-05-28

    Density functional theory (DFT) calculations were employed to investigate the energetics of carbon dioxide migration within hydrated or anhydrous graphene oxides (GOs). When anhydrous GO structures contain a carbon dioxide molecule, the carbon dioxide interacts repulsively with the GO layers to increase the interlayer spacing. The repulsive electrostatic interactions are reduced by the insertion of water molecules into CO2-containing GO structures due to the occurrence of attractive water-layer interactions through hydrogen bonding. Consequently, the interlayer spacings in CO2-containing hydrated structures are shortened compared with those in the anhydrous structures. The results indicate that the intercalated water molecules have the ability to connect the GO layers in the presence of carbon dioxide. Furthermore, the DFT calculations indicated that the GO interlayer spacings, which are influenced by the intercalation of water molecules, control carbon dioxide migration within the GO layers. The importance of the interlayer spacings on the migration of carbon dioxide arises from the occurrence of repulsive interactions between CO2 and oxygen-containing groups attached on the graphene sheets. When the GO interlayer spacings are short due to the presence of intercalated water molecules, the repulsive interactions between carbon dioxide and the GO layers are strong enough to prevent CO2 from migrating from its original position. Such repulsive interactions do not occur during the migration of CO2 within anhydrous GO structures because of the relatively longer interlayer spacing. Accordingly, CO2 migrates within anhydrous GO with a less significant barrier, indicating that carbon dioxide molecules are easily released from the GO.

  9. Polymer composite adsorbents using particles of molecularly imprinted polymers or aluminium oxide nanoparticles for treatment of arsenic contaminated waters.

    PubMed

    Önnby, L; Pakade, V; Mattiasson, B; Kirsebom, H

    2012-09-01

    Removal of As(V) by adsorption from water solutions was studied using three different synthetic adsorbents. The adsorbents, (a) aluminium nanoparticles (Alu-NPs, <50 nm) incorporated in amine rich cryogels (Alu-cryo), (b) molecular imprinted polymers (<38 μm) in polyacrylamide cryogels (MIP-cryo) and (c) thiol functionalised cryogels (SH-cryo) were evaluated regarding material characteristics and arsenic removal in batch test and continuous mode. Results revealed that a composite design with particles incorporated in cryogels was a successful means for applying small particles (nano- and micro- scale) in water solutions with maintained adsorption capacity and kinetics. Low capacity was obtained from SH-cryo and this adsorbent was hence excluded from the study. The adsorption capacities for the composites were 20.3 ± 0.8 mg/g adsorbent (Alu-cryo) and 7.9 ± 0.7 mg/g adsorbent (MIP-cryo) respectively. From SEM images it was seen that particles were homogeneously distributed in Alu-cryo and heterogeneously distributed in MIP-cryo. The particle incorporation increased the mechanical stability and the polymer backbones of pure polyacrylamide (MIP-cryo) were of better stability than the amine containing polymer backbone (Alu-cryo). Both composites worked well in the studied pH range of pH 2-8. Adsorption tested in real wastewater spiked with arsenic showed that co-ions (nitrate, sulphate and phosphate) affected arsenic removal for Alu-cryo more than for MIP-cryo. Both composites still adsorbed well in the presence of counter-ions (copper and zinc) present at low concentrations (μg/l). The unchanged and selective adsorption in realistic water observed for MIP-cryo was concluded to be due to a successful imprinting, here controlled using a non-imprinted polymer (NIP). A development of MIP-cryo is needed, considering its low adsorption capacity.

  10. Natural attenuation of pesticide water contamination by using ecological adsorbents: Application for chlorinated pesticides included in European Water Framework Directive

    NASA Astrophysics Data System (ADS)

    El Bakouri, Hicham; Morillo, José; Usero, José; Ouassini, Abdelhamid

    2009-01-01

    SummaryIn this work, a series of experiments were performed to demonstrate the potential use of natural organic substances (NOS) as an ecological technique to prevent pesticide contamination of ground water resources. A preliminary test has been carried out for determining the potentialities of ten NOS in the elimination of alachlor, aldrin, atrazine, chlorpyrifos, chlorfenvinphos, dieldrin, alpha-endosulfan, endrin, hexachlorobenzene, beta-HCH, gamma-HCH (lindane), simazine and trifluralin. The best adsorbents that present higher removal efficiency were date and olives stones, and in minor measurement Raphanus raphanistrum and Cistus ladaniferus. Experimental results showed that the pH and temperature of pesticide solutions negatively affect the adsorption process. According to adsorption kinetic data, 8 h were considered as the equilibrium time for realizing adsorption isotherms. Adsorption data were fit with Freundlich isotherm model which describes better the adsorption process. The K f values depended mainly on the nature of each adsorbent and ranged from 4.53 for Eucalyptus gomphocephala to 13.54 for date stones.

  11. Investigation of interparticle forces in natural waters: effects of adsorbed humic acids on iron oxide and alumina surface properties.

    PubMed

    Sander, Sylvia; Mosley, Luke M; Hunter, Keith A

    2004-09-15

    The nature of interparticle forces acting on colloid particle surfaces with adsorbed surface films of the internationally used humic acid standard material, Suwannee River Humic Acid (SHA), has been investigated using an atomic force microscope (AFM). Two particle surfaces were used, alumina and a hydrous iron oxide film coated onto silica particles. Adsorbed SHA dominated the interactive forces for both surface types when present. At low ionic strength and pH > 4, the force curves were dominated by electrostatic repulsion of the electrical double layers, with the extent of repulsion decreasing as electrolyte (NaCl) concentration increased, scaling with the Debye length (kappa(-1)) of the electrolyte according to classical theory. At pH approximately 4, electrostatic forces were largely absent, indicating almost complete protonation of carboxylic acid (-COOH) functional groups on the adsorbed SHA. Under these conditions and also at high electrolyte concentration ([NaCl] > 0.1 M), the absence of electrostatic forces allowed observation of repulsion forces arising from steric interaction of adsorbed SHA as the oxide surfaces approached closely to each other (separation < 10 nm). This steric barrier shrank as electrolyte concentration increased, implying tighter coiling of the adsorbed SHA molecules. In addition, adhesive bridging between surfaces was observed only in the presence of SHA films, implying a strong energy barrier to spontaneous detachment of the surfaces from each other once joined. This adhesion was especially strong in the presence of Ca2+ which appears to bridge SHA layers on each surface. Overall, our results show that SHA is a good model for the NOM adsorbed on colloids.

  12. Anisotropic diffusion of water molecules in hydroxyapatite nanopores

    NASA Astrophysics Data System (ADS)

    Prakash, Muthuramalingam; Lemaire, Thibault; Caruel, Matthieu; Lewerenz, Marius; de Leeuw, Nora H.; Di Tommaso, Devis; Naili, Salah

    2017-03-01

    New insights into the dynamical properties of water in hydroxyapatite (HAP) nanopores, a model system for the fluid flow within nanosize spaces inside the collagen-apatite structure of bone, were obtained from molecular dynamics simulations of liquid water confined between two parallel HAP surfaces of different sizes (20 Å ≤ H ≤ 240 Å). Calculations were conducted using a core-shell interatomic potential for HAP together with the extended simple point charge model for water. This force field gives an activation energy for water diffusion within HAP nanopores that is in excellent agreement with available experimental data. The dynamical properties of water within the HAP nanopores were quantified in terms of the second-order water diffusion tensor. Results indicate that water diffuses anisotropically within the HAP nanopores, with the solvent molecules moving parallel to the surface twice as fast as the perpendicular direction. This unusual dynamic behaviour is linked to the strong polarizing effect of calcium ions, and the synergic interactions between the water molecules in the first hydration layer of HAP with the calcium, hydroxyl, and phosphate ions, which facilitates the flow of water molecules in the directions parallel to the HAP surface.

  13. Can the state of platinum species be unambiguously determined by the stretching frequency of an adsorbed CO probe molecule?

    PubMed

    Aleksandrov, Hristiyan A; Neyman, Konstantin M; Hadjiivanov, Konstantin I; Vayssilov, Georgi N

    2016-08-10

    The paper addresses possible ambiguities in the determination of the state of platinum species by the stretching frequency of a CO probe, which is a common technique for characterization of platinum-containing catalytic systems. We present a comprehensive comparison of the available experimental data with our theoretical modeling (density functional) results of pertinent systems - platinum surfaces, nanoparticles and clusters as well as reduced or oxidized platinum moieties on a ceria support. Our results for CO adsorbed on-top on metallic Pt(0), with C-O vibrational frequencies in the region 2018-2077 cm(-1), suggest that a decrease of the coordination number of the platinum atom, to which CO is bound, by one lowers the CO frequency by about 7 cm(-1). This trend corroborates the Kappers-van der Maas correlation derived from the analysis of the experimental stretching frequency of CO adsorbed on platinum-containing samples on different supports. We also analyzed the effect of the charge of platinum species on the CO frequency. Based on the calculated vibrational frequencies of CO in various model systems, we concluded that the actual state of the platinum species may be mistaken based only on the measured value of the C-O vibrational frequency due to overlapping regions of frequencies corresponding to different types of species. In order to identify the actual state of platinum species one has to combine this powerful technique with other approaches.

  14. Determination of surface properties of iron hydroxide-coated alumina adsorbent prepared for removal of arsenic from drinking water.

    PubMed

    Hlavay, József; Polyák, Klára

    2005-04-01

    A novel type adsorbent was prepared by in situ precipitation of Fe(OH)3 on the surface of activated Al2O3 as a support material. The iron content of the adsorbent was 0.31+/-0.003% m/m (56.1 mmol/g); its mechanical and chemical stability proved to be appropriate in solutions. The total capacity of the adsorbent was 0.12 mmol/g, and the pH of zero point of charge, pH(zpc) = 6.9+/-0.3. Depending on the pH of solutions, the adsorbent can be used for binding of both anions and cations, if pH(eq) < pH(zpc) anions are sorbed on the surface of adsorbent (S) through [SOH2+] and [SOH] groups. A graphical method was used for the determination of pH(iep) (isoelectric points) of the adsorbent and values of pH(iep) = 6.1+/-0.3 for As(III) and pH(iep) = 8.0+/-0.3 for As(V) ions were found. The amount of surface charged groups (Q) was about zero within the a pH range of 6.5-8.6, due to the practically neutral surface formed on the adsorption of As(V) ions. At acidic pH (pH 4.7), Q = 0.19 mol/kg was obtained. The adsorption of arsenate and arsenite ions from solutions of 0.1-0.4 mmol/L was represented by Langmuir-type isotherms. A great advantage of the adsorbent is that it can be used in adsorption columns, and low waste technology for removal of arsenic from drinking water can be developed.

  15. Transport behavior of water molecules through two-dimensional nanopores

    SciTech Connect

    Zhu, Chongqin; Li, Hui; Meng, Sheng

    2014-11-14

    Water transport through a two-dimensional nanoporous membrane has attracted increasing attention in recent years thanks to great demands in water purification and desalination applications. However, few studies have been reported on the microscopic mechanisms of water transport through structured nanopores, especially at the atomistic scale. Here we investigate the microstructure of water flow through two-dimensional model graphene membrane containing a variety of nanopores of different size by using molecular dynamics simulations. Our results clearly indicate that the continuum flow transits to discrete molecular flow patterns with decreasing pore sizes. While for pores with a diameter ≥15 Å water flux exhibits a linear dependence on the pore area, a nonlinear relationship between water flux and pore area has been identified for smaller pores. We attribute this deviation from linear behavior to the presence of discrete water flow, which is strongly influenced by the water-membrane interaction and hydrogen bonding between water molecules.

  16. Soluble hydrocarbons uptake by porous carbonaceous adsorbents at different water ionic strength and temperature: something to consider in oil spills.

    PubMed

    Flores-Chaparro, Carlos E; Ruiz, Luis Felipe Chazaro; Alfaro-De la Torre, Ma Catalina; Rangel-Mendez, Jose Rene

    2016-06-01

    Nowadays, petrochemical operations involve risks to the environment and one of the biggest is oil spills. Low molecular aromatics like benzene, toluene, and naphthalene dissolve in water, and because of their toxicological characteristics, these produce severe consequences to the environment. The oil spill cleanup strategies are mainly designed to deal with the heavy fractions accumulated on the water surface. Unfortunately, very limited information is available regarding the treatment of dissolved fractions.A commercial (Filtrasorb 400) and modified activated carbons were evaluated to remove benzene, toluene, and naphthalene from water, which are the most soluble aromatic hydrocarbons, at different ionic strengths (I) and temperatures (0-0.76 M and 4-25 °C, respectively). This allowed simulating the conditions of fresh and saline waters when assessing the performance of these adsorbents. It was found that the hydrocarbons adsorption affinity increased 12 % at a I of 0.5 M, due to the less negative charge of the adsorbent, while at a high I (≃0.76 M) in a synthetic seawater, the adsorption capacity decreased 21 % that was attributed to the adsorbent's pores occlusion by water clusters. Approximately, 40 h were needed to reach equilibrium; however, the maximum adsorption rate occurred within the first hour in all the cases. Moreover, the hydrocarbons adsorption and desorption capacities increased when the temperature augmented from 4 to 25 °C. On the other hand, thermally and chemically modified materials showed that the interactions between adsorbent-contaminant increased with the basification degree of the adsorbent surface.

  17. Adsorption of apolar molecules at the water liquid-vapor interface: A Monte Carlo simulations study of the water-n-octane system

    NASA Astrophysics Data System (ADS)

    Jedlovszky, Pál; Varga, Imre; Gilányi, Tibor

    2003-07-01

    The adsorption of n-octane at the water liquid-vapor interface has been investigated by Monte Carlo computer simulation. For this purpose, simulation of five different water-apolar interfacial systems have been performed, in which the number of n-octane molecules has been varied. The results clearly show that the apolar n-octane molecules are adsorbed from the vapor phase at the interface. The adsorption is driven by the weak attraction due to the dispersion forces acting between the water molecules and the methyl and methylene groups of the octanes. This weak attraction is, however, amplified by the fact that it is added up for the CH2 and CH3 groups belonging to the same molecule. Consistently, the n-octane molecules located closest to the aqueous phase are found to prefer all-trans conformation and parallel alignment with the plane of the interface. On the other hand, entropic effects become more important among the molecules of the outer part of the adsorption layer. Hence, the preferred orientation of these molecules is perpendicular to the interface, as they can be extended toward the less dense region of the apolar phase; and gauche dihedrals appear more frequently here than among the molecules located next to the aqueous phase.

  18. Rotovibrational states of the water molecule on the sun.

    PubMed

    Leite, Bruno S; Bastos, Cristiano C; Pavão, Antonio C

    2016-12-01

    The infrared spectrum of water observed in sunspots is complex and dense, with bands separated by approximately 0.01 cm(-1). For top asymmetrical molecules, there is no theoretical approach that allows for the calculation of rotovibrational energy with such precision. Experimentally derived rotovibracional energy levels of water at high temperatures combined with variational calculations have been used for the band assignments. These energy levels are employed to refine the analysis of a small portion of the infrared absorption spectrum. Such procedure has allowed for the identification of additional 55 bands to the 70 already identified as rotovibrational transitions of the water molecule. Our new assignments, which include pure and cross transitions, offer additional evidence of the existence of water on the sun, but above all they illustrate the complexity of the solar spectrum that involves states with higher levels of rotational excitation. Given the conditions on the sun, more molecules of water would occur in excited electronic states, which include apolar and paramagnetic states, generating intense bands in the spectrum. Since there is an analytical solution for the rotovibrational transitions of linear molecules, we were able to identify 16 bands relative to the excited electronic states (1)B2 and (3)A1 in the sunspot spectrum. Density functional B3LYP/AUG-cc-pVTZ calculations of the electric and magnetic dipole are employed to discuss some consequences of the presence of excited states of water in the dynamics of sunspots and solar magnetic field.

  19. Unprecedentedly rapid transport of single-file rolling water molecules

    NASA Astrophysics Data System (ADS)

    Qiu, Tong; Huang, Ji-Ping

    2015-10-01

    The realization of rapid and unidirectional single-file water-molecule flow in nanochannels has posed a challenge to date. Here, we report unprecedentedly rapid unidirectional single-file water-molecule flow under a translational terahertz electric field, which is obtained by developing a Debye doublerelaxation theory. In addition, we demonstrate that all the single-file molecules undergo both stable translation and rotation, behaving like high-speed train wheels moving along a railway track. Independent molecular dynamics simulations help to confirm these theoretical results. The mechanism involves the resonant relaxation dynamics of H and O atoms. Further, an experimental demonstration is suggested and discussed. This work has implications for the design of high-efficiency nanochannels or smaller nanomachines in the field of nanotechnology, and the findings also aid in the understanding and control of water flow across biological nanochannels in biology-related research.

  20. Control of the electrostatic effect on DAM-adsorbent for the water-soluble compounds by HPLC.

    PubMed

    Kamichatani, Waka; Inoue, Yoshinori; Yamamoto, Atsushi

    2012-01-01

    The effect of the mobile phase pH on the control of the electrostatic interaction was evaluated on a column packed with water-holding adsorbent on which diallylamine-maleic acid copolymers were immobilizing. The adsorbent showed extraordinary retention behaviors of water-soluble solutes under acidic conditions, however, their behavior became stable along with increasing pH. Hydrating water contents tended to level off at pH above 8. Thus, the electrostatic interaction with the stationary phase can be controlled by adjusting the mobile phase pH above 8. In this region, the retention of water-soluble solutes appears to be mainly governed by the hydrophilic partition interaction.

  1. SPAM: A Simple Approach for Profiling Bound Water Molecules.

    PubMed

    Cui, Guanglei; Swails, Jason M; Manas, Eric S

    2013-12-10

    A method that identifies the hydration shell structure of proteins and estimates the relative free energies of water molecules within that hydration shell is described. The method, which we call "SPAM" (maps spelled in reverse), utilizes explicit solvent molecular dynamics (MD) simulations to capture discrete hydration sites at the water-protein interface and computes a local free energy measure from the distribution of interaction energies between water and the environment at a specific site. SPAM is able to provide a qualitative estimate of the thermodynamic profile of bound water molecules that correlates nicely with well-studied structure-activity relationships and observed binding "hot spots". This is demonstrated in retrospective analyses of HIV1 protease and hen egg white lysozyme, where the effects of water displacement and solvent binding have been studied extensively. The simplicity and effectiveness of SPAM allow for prospective application during the drug discovery process.

  2. Valorization of solid waste products from olive oil industry as potential adsorbents for water pollution control--a review.

    PubMed

    Bhatnagar, Amit; Kaczala, Fabio; Hogland, William; Marques, Marcia; Paraskeva, Christakis A; Papadakis, Vagelis G; Sillanpää, Mika

    2014-01-01

    The global olive oil production for 2010 is estimated to be 2,881,500 metric tons. The European Union countries produce 78.5% of the total olive oil, which stands for an average production of 2,136,000 tons. The worldwide consumption of olive oil increased of 78% between 1990 and 2010. The increase in olive oil production implies a proportional increase in olive mill wastes. As a consequence of such increasing trend, olive mills are facing severe environmental problems due to lack of feasible and/or cost-effective solutions to olive-mill waste management. Therefore, immediate attention is required to find a proper way of management to deal with olive mill waste materials in order to minimize environmental pollution and associated health risks. One of the interesting uses of solid wastes generated from olive mills is to convert them as inexpensive adsorbents for water pollution control. In this review paper, an extensive list of adsorbents (prepared by utilizing different types of olive mill solid waste materials) from vast literature has been compiled, and their adsorption capacities for various aquatic pollutants removal are presented. Different physicochemical methods that have been used to convert olive mill solid wastes into efficient adsorbents have also been discussed. Characterization of olive-based adsorbents and adsorption mechanisms of various aquatic pollutants on these developed olive-based adsorbents have also been discussed in detail. Conclusions have been drawn from the literature reviewed, and suggestions for future research are proposed.

  3. Structures of water molecules in carbon nanotubes under electric fields.

    PubMed

    Winarto; Takaiwa, Daisuke; Yamamoto, Eiji; Yasuoka, Kenji

    2015-03-28

    Carbon nanotubes (CNTs) are promising for water transport through membranes and for use as nano-pumps. The development of CNT-based nanofluidic devices, however, requires a better understanding of the properties of water molecules in CNTs because they can be very different from those in the bulk. Using all-atom molecular dynamics simulations, we investigate the effect of axial electric fields on the structure of water molecules in CNTs having diameters ranging from (7,7) to (10,10). The water dipole moments were aligned parallel to the electric field, which increases the density of water inside the CNTs and forms ordered ice-like structures. The electric field induces the transition from liquid to ice nanotubes in a wide range of CNT diameters. Moreover, we found an increase in the lifetime of hydrogen bonds for water structures in the CNTs. Fast librational motion breaks some hydrogen bonds, but the molecular pairs do not separate and the hydrogen bonds reform. Thus, hydrogen bonds maintain the water structure in the CNTs, and the water molecules move collectively, decreasing the axial diffusion coefficient and permeation rate.

  4. Structures of water molecules in carbon nanotubes under electric fields

    NASA Astrophysics Data System (ADS)

    Winarto, Takaiwa, Daisuke; Yamamoto, Eiji; Yasuoka, Kenji

    2015-03-01

    Carbon nanotubes (CNTs) are promising for water transport through membranes and for use as nano-pumps. The development of CNT-based nanofluidic devices, however, requires a better understanding of the properties of water molecules in CNTs because they can be very different from those in the bulk. Using all-atom molecular dynamics simulations, we investigate the effect of axial electric fields on the structure of water molecules in CNTs having diameters ranging from (7,7) to (10,10). The water dipole moments were aligned parallel to the electric field, which increases the density of water inside the CNTs and forms ordered ice-like structures. The electric field induces the transition from liquid to ice nanotubes in a wide range of CNT diameters. Moreover, we found an increase in the lifetime of hydrogen bonds for water structures in the CNTs. Fast librational motion breaks some hydrogen bonds, but the molecular pairs do not separate and the hydrogen bonds reform. Thus, hydrogen bonds maintain the water structure in the CNTs, and the water molecules move collectively, decreasing the axial diffusion coefficient and permeation rate.

  5. Structures of water molecules in carbon nanotubes under electric fields

    SciTech Connect

    Winarto,; Takaiwa, Daisuke; Yamamoto, Eiji; Yasuoka, Kenji

    2015-03-28

    Carbon nanotubes (CNTs) are promising for water transport through membranes and for use as nano-pumps. The development of CNT-based nanofluidic devices, however, requires a better understanding of the properties of water molecules in CNTs because they can be very different from those in the bulk. Using all-atom molecular dynamics simulations, we investigate the effect of axial electric fields on the structure of water molecules in CNTs having diameters ranging from (7,7) to (10,10). The water dipole moments were aligned parallel to the electric field, which increases the density of water inside the CNTs and forms ordered ice-like structures. The electric field induces the transition from liquid to ice nanotubes in a wide range of CNT diameters. Moreover, we found an increase in the lifetime of hydrogen bonds for water structures in the CNTs. Fast librational motion breaks some hydrogen bonds, but the molecular pairs do not separate and the hydrogen bonds reform. Thus, hydrogen bonds maintain the water structure in the CNTs, and the water molecules move collectively, decreasing the axial diffusion coefficient and permeation rate.

  6. Density functional theory study the effects of oxygen-containing functional groups on oxygen molecules and oxygen atoms adsorbed on carbonaceous materials.

    PubMed

    Qi, Xuejun; Song, Wenwu; Shi, Jianwei

    2017-01-01

    Density functional theory was used to study the effects of different types of oxygen-containing functional groups on the adsorption of oxygen molecules and single active oxygen atoms on carbonaceous materials. During gasification or combustion reactions of carbonaceous materials, oxygen-containing functional groups such as hydroxyl(-OH), carbonyl(-CO), quinone(-O), and carboxyl(-COOH) are often present on the edge of graphite and can affect graphite's chemical properties. When oxygen-containing functional groups appear on a graphite surface, the oxygen molecules are strongly adsorbed onto the surface to form a four-member ring structure. At the same time, the O-O bond is greatly weakened and easily broken. The adsorption energy value indicates that the adsorption of oxygen molecules changes from physisorption to chemisorption for oxygen-containing functional groups on the edge of a graphite surface. In addition, our results indicate that the adsorption energy depends on the type of oxygen-containing functional group. When a single active oxygen atom is adsorbed on the bridge site of graphite, it gives rise to a stable epoxy structure. Epoxy can cause deformation of the graphite lattice due to the transition of graphite from sp2 to sp3 after the addition of an oxygen atom. For quinone group on the edge of graphite, oxygen atoms react with carbon atoms to form the precursor of CO2. Similarly, the single active oxygen atoms of carbonyl groups can interact with edge carbon atoms to form the precursor of CO2. The results show that oxygen-containing functional groups on graphite surfaces enhance the activity of graphite, which promotes adsorption on the graphite surface.

  7. Density functional theory study the effects of oxygen-containing functional groups on oxygen molecules and oxygen atoms adsorbed on carbonaceous materials

    PubMed Central

    Song, Wenwu; Shi, Jianwei

    2017-01-01

    Density functional theory was used to study the effects of different types of oxygen-containing functional groups on the adsorption of oxygen molecules and single active oxygen atoms on carbonaceous materials. During gasification or combustion reactions of carbonaceous materials, oxygen-containing functional groups such as hydroxyl(-OH), carbonyl(-CO), quinone(-O), and carboxyl(-COOH) are often present on the edge of graphite and can affect graphite’s chemical properties. When oxygen-containing functional groups appear on a graphite surface, the oxygen molecules are strongly adsorbed onto the surface to form a four-member ring structure. At the same time, the O-O bond is greatly weakened and easily broken. The adsorption energy value indicates that the adsorption of oxygen molecules changes from physisorption to chemisorption for oxygen-containing functional groups on the edge of a graphite surface. In addition, our results indicate that the adsorption energy depends on the type of oxygen-containing functional group. When a single active oxygen atom is adsorbed on the bridge site of graphite, it gives rise to a stable epoxy structure. Epoxy can cause deformation of the graphite lattice due to the transition of graphite from sp2 to sp3 after the addition of an oxygen atom. For quinone group on the edge of graphite, oxygen atoms react with carbon atoms to form the precursor of CO2. Similarly, the single active oxygen atoms of carbonyl groups can interact with edge carbon atoms to form the precursor of CO2. The results show that oxygen-containing functional groups on graphite surfaces enhance the activity of graphite, which promotes adsorption on the graphite surface. PMID:28301544

  8. Adsorbent synthesis of polypyrrole/TiO2 for effective fluoride removal from aqueous solution for drinking water purification: Adsorbent characterization and adsorption mechanism.

    PubMed

    Chen, Jie; Shu, Chiajung; Wang, Ning; Feng, Jiangtao; Ma, Hongyu; Yan, Wei

    2017-06-01

    More than 20 countries are still suffering problems of excessive fluoride containing water, and greater than 8mg/L fluoride groundwater has been reported in some villages in China. In order to meet the challenge in the drinking water defluoridation engineering, a high efficiency and affinity defluoridation adsorbent PPy/TiO2 composite was designed and synthetized by in-situ chemical oxidative polymerization. Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction Investigator (XRD), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TG), N2 isotherm analysis, Scanning Electron Microscopy (SEM) and Zeta potential analysis were conducted to characterize surface and textural properties of the as-prepared PPy/TiO2, and the possibility of fluoride adsorption was carefully estimated by adsorption isotherm and kinetic studies. Characterization investigations demonstrate the uniqueness of surface and textural properties, such as suitable specific surface area and abundant positively charged nitrogen atoms (N(+)), which indicate the composite is a suitable material for the fluoride adsorption. Adsorption isotherms and kinetics follow better with Langmuir and pseudo-second-order model, respectively. The maximum adsorption capacity reaches 33.178mg/g at 25°C according to Langmuir model, and particular interest was the ability to reduce the concentration of fluoride from 11.678mg/L to 1.5mg/L for drinking water at pH of 7 within 30min. Moreover, the adsorbent can be easily recycled without the loss of adsorption capacity after six cycles, greatly highlighting its outstanding affinity to fluoride, low-cost and novel to be used in the purification of fluoride containing water for drinking. Furthermore, the adsorption mechanism was extensively investigated and discussed by FTIR investigation and batch adsorption studies including effect of pH, surface potential and thermodynamics. The adsorption is confirmed to be a spontaneous and exothermic process

  9. Preparation of Al-Ce hybrid adsorbent and its application for defluoridation of drinking water.

    PubMed

    Liu, Han; Deng, Shubo; Li, Zhijian; Yu, Gang; Huang, Jun

    2010-07-15

    A novel Al-Ce hybrid adsorbent with high sorption capacity for fluoride was prepared through the coprecipitation method in this study, and its preparation conditions were optimized. X-ray diffraction (XRD) and scanning electron microscope (SEM) results showed that the hybrid adsorbent was of amorphous structure and constituted by some aggregated nanoparticles. As the adsorbent had the zero point of zeta potential at pH 9.6, it was very effective in fluoride removal from aqueous solution via electrostatic interaction. The results of sorption experiments including sorption kinetics, isotherms, and the effect of solution pH showed that the sorption of fluoride on the Al-Ce adsorbent was fast and pH-dependent. Especially, the adsorbent had high sorption capacity up to 27.5 mg g(-1) for fluoride at the equilibrium fluoride concentration of 1 mg L(-1), much higher than that of the conventional adsorbents. Fourier transform infrared (FTIR) analysis and zeta potential measurement showed that the hydroxyl groups and the protonated hydroxyl groups on the adsorbent surface were involved in the fluoride adsorption.

  10. Cellulose based cationic adsorbent fabricated via radiation grafting process for treatment of dyes waste water.

    PubMed

    Goel, Narender Kumar; Kumar, Virendra; Misra, Nilanjal; Varshney, Lalit

    2015-11-05

    A cationized adsorbent was prepared from cellulosic cotton fabric waste via a single step-green-radiation grafting process using gamma radiation source, wherein poly[2-(methacryloyloxy) ethyl]trimethylammonium chloride (PMAETC) was covalently attached to cotton cellulose substrate. Radiation grafted (PMAETC-g-cellulose) adsorbent was investigated for removal of acid dyes from aqueous solutions using two model dyes: Acid Blue 25 (AB25) and Acid Blue 74 (AB74). The equilibrium adsorption data was analyzed by Langmuir and Freundlich isotherms, whereas kinetic data was analyzed by pseudo first order, pseudo second order, intra particle diffusion and Boyd's models. The PMAETC-g-cellulose adsorbent with 25% grafting yield exhibited equilibrium adsorption capacities of ∼ 540.0mg/g and ∼ 340.0mg/g for AB25 and AB74, respectively. Linear and nonlinear fitting of adsorption data suggested that the equilibrium adsorption process followed Langmuir adsorption isotherm model, whereas, the kinetic adsorption process followed pseudo-second order model. The multi-linearities observed in the intra-particle kinetic plots suggested that the intraparticle diffusion was not the only rate-controlling process in the adsorption of acid dyes on the adsorbent, which was further supported by Boyd's model. The adsorbent could be regenerated by eluting the adsorbed dye from the adsorbent and could be repeatedly used.

  11. Coordination structure of adsorbed Zn(II) at Water-TiO2 interfaces

    SciTech Connect

    He, G.; Pan, G.; Zhang, M.; Waychunas, G.A.

    2011-01-15

    The local structure of aqueous metal ions on solid surfaces is central to understanding many chemical and biological processes in soil and aquatic environments. Here, the local coordination structure of hydrated Zn(II) at water-TiO{sub 2} interfaces was identified by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopy combined with density functional theory (DFT) calculations. A nonintegral coordination number of average {approx}4.5 O atoms around a central Zn atom was obtained by EXAFS analysis. DFT calculations indicated that this coordination structure was consistent with the mixture of 4-coordinated bidentate binuclear (BB) and 5-coordinated bidentate mononuclear (BM) metastable equilibrium adsorption (MEA) states. The BB complex has 4-coordinated Zn, while the monodentate mononuclear (MM) complex has 6-coordinated Zn, and a 5-coordinated adsorbed Zn was found in the BM adsorption mode. DFT calculated energies showed that the lower-coordinated BB and BM modes were thermodynamically more favorable than the higher-coordinated MM MEA state. The experimentally observed XANES fingerprinting provided additional direct spectral evidence of 4- and 5-coordinated Zn-O modes. The overall spectral and computational evidence indicated that Zn(II) can occur in 4-, 5-, and 6-oxygen coordinated sites in different MEA states due to steric hindrance effects, and the coexistence of different MEA states formed the multiple coordination environments.

  12. Selective concentration of aromatic bases from water with a resin adsorbent

    USGS Publications Warehouse

    Stuber, H.A.; Leenheer, J.A.

    1983-01-01

    Aromatic bases are concentrated from water on columns of a resin adsorbent and recovered by aqueous-acid elution. The degree of concentration attainable depends on the ratio of the capacity factor (k) of the neutral form of the amine to that of the ionized form. Capacity factors of ionic forms of amines on XAD-8 resin (a methylacrylic ester polymer) are greater than zero, ranging from 20 to 250 times lower than those of their neutral forms; they increase with increasing hydrophobicity of the amine. Thus, desorption by acid is an edition (k during desorption >0) rather than a displacement (k during desorption = 0) process. The degree of concentration attainable on XAD-8 resin varies with the hydrophobicity of the amine, being limited for hydrophilic solutes (for example, pyridine) by small neutral-form k's, reaching a maximum for amines of intermediate hydrophobicity (for example, quinoline), and decreasing for more hydrophobc solutes (for example, acridine) because of their large ionic-form k's.

  13. Visualizing Water Molecules in Transmembrane Proteins Using Radiolytic Labeling Methods

    SciTech Connect

    Orban, T.; Gupta, S; Palczewski, K; Chance, M

    2010-01-01

    Essential to cells and their organelles, water is both shuttled to where it is needed and trapped within cellular compartments and structures. Moreover, ordered waters within protein structures often colocalize with strategically placed polar or charged groups critical for protein function, yet it is unclear if these ordered water molecules provide structural stabilization, mediate conformational changes in signaling, neutralize charged residues, or carry out a combination of all these functions. Structures of many integral membrane proteins, including G protein-coupled receptors (GPCRs), reveal the presence of ordered water molecules that may act like prosthetic groups in a manner quite unlike bulk water. Identification of 'ordered' waters within a crystalline protein structure requires sufficient occupancy of water to enable its detection in the protein's X-ray diffraction pattern, and thus, the observed waters likely represent a subset of tightly bound functional waters. In this review, we highlight recent studies that suggest the structures of ordered waters within GPCRs are as conserved (and thus as important) as conserved side chains. In addition, methods of radiolysis, coupled to structural mass spectrometry (protein footprinting), reveal dynamic changes in water structure that mediate transmembrane signaling. The idea of water as a prosthetic group mediating chemical reaction dynamics is not new in fields such as catalysis. However, the concept of water as a mediator of conformational dynamics in signaling is just emerging, because of advances in both crystallographic structure determination and new methods of protein footprinting. Although oil and water do not mix, understanding the roles of water is essential to understanding the function of membrane proteins.

  14. Removal of microcystin-LR from drinking water using a bamboo-based charcoal adsorbent modified with chitosan.

    PubMed

    Zhang, Hangjun; Zhu, Guoying; Jia, Xiuying; Ding, Ying; Zhang, Mi; Gao, Qing; Hu, Ciming; Xu, Shuying

    2011-01-01

    A new kind of low-cost syntactic adsorbent from bamboo charcoal and chitosan was developed for the removal of microcystin-LR from drinking water. Removal efficiency was higher for the syntactic adsorbent when the amount of bamboo charcoal was increased. The optimum dose ratio of bamboo charcoal to chitosan was 6:4, and the optimum amount was 15 mg/L; equilibrium time was 6 hr. The adsorption isotherm was non-linear and could be simulated by the Freundlich model (R2 = 0.9337). Adsorption efficiency was strongly affected by pH and natural organic matter (NOM). Removal efficiency was 16% higher at pH 3 than at pH 9. Efficiency rate was reduced by 15% with 25 mg/L NOM (UV254 = 0.089 cm(-1)) in drinking water. This study demonstrated that the bamboo charcoal modified with chitosan can effectively remove microcystin-LR from drinking water.

  15. Adsorption removal of cesium from drinking waters: a mini review on use of biosorbents and other adsorbents.

    PubMed

    Liu, Xiang; Chen, Guan-Ru; Lee, Duu-Jong; Kawamoto, Tohru; Tanaka, Hisashi; Chen, Man-Li; Luo, Yu-Kuo

    2014-05-01

    Radiocesium (Cs) removal from waters becomes an emerging issue after the Fukushima Daiichi Nuclear Power Plant Disaster, during which a total of approximately 3.3×10(16) Bq Cs was released to contaminate the environment. This mini-review provided a summary on literature works to develop efficient adsorbent for removing Cs from waters. Adsorbent made of raw and modified minerals, composites particles, and biosorbents that are highly specific to Cs in the presence of other alkali and alkali earth metals were summarized. Development of Prussian blue (PB) nanoparticles on Cs removal and its potential use in drinking waterworks was discussed. This review is a unique report for adsorption removal of Cs from contaminated waters.

  16. The adsorption and dissociation of water molecule on goethite (010) surface: A DFT approach

    NASA Astrophysics Data System (ADS)

    Zhou, Long; Xiu, Fangyuan; Qiu, Meng; Xia, Shuwei; Yu, Liangmin

    2017-01-01

    Using density functional theory (DFT) calculation, we investigate the configuration, stability and electronic properties of fresh cleaved (010) goethite surface (Pnma) and this surface exposed to water monolayer at low, medium and high coverage. Water is predicted to be chemisorbed to the surface, together with the surface reconstruction. The interaction energy of the most stable configuration of both low and medium coverage per water molecule is almost the same (-1.17 eV), while that of high coverage is much lower (less than 1.03 eV). It indicates that highly hydrated surface is less stable. PDOS analysis reveals the adsorption of H2O is due to the formation of Fesbnd O bond, caused by overlapping of Fe's 3d and O's 2p orbitals. Dissociation processes at low and medium water coverage are non-spontaneous; while at high coverage, it can undertake spontaneously both thermodynamically and dynamically. The dissociation paths of all three water coverage are the similar. The proton from one adsorbed water is likely to dissociate to bind to the vicinal surface μ3sbnd O as an intermediate product; the proton belonged to μ3sbnd O transferred to the neighbor surface μ2sbnd O as the dissociative configuration.

  17. Application of ultradisperse magnetic adsorbents for removal of small concentrations of pollutants from large volumes of water

    NASA Astrophysics Data System (ADS)

    Nechitailo, Galina S.; Kuznetsov, Anatoli; Kuznetsov, Oleg

    2016-07-01

    Pollution of natural bodies of water (rivers, lakes, ground water, etc) is unfortunately very common, both from natural sources like volcanic activity; and, even more importantly, from human activity, including disposal of industrial and municipal waste, mining, etc. Many toxic substances are harmful for humans and other organisms even in very low concentrations (e.g., less than 1 µg/L of cadmium is harmful, for Hg it is 0.5 µg/L, for phenol - 1 µg/L), and can remain in water for decades or longer. Cleaning large volumes of water even from low concentrations of pollutants is a challenging technological task and is very expensive. We propose to use suspension of ultradisperse magnetic adsorbents, for example, nanostructured ferro-carbon particles, produced by plasmachemical technique, for removing small concentrations of pollutants from large volumes of water. The suspension is introduced into the water. Due to their small sizes and densities similar to water (we measured the density of FC-4 ferro-carbon to be about 1 g/cm3; presumably due to porosity) the particles do not sediment for a long time (hours, days or longer), move due to Brownian motion and adsorb a variety of substances from the water. The particle surface can be modified to provide selectivity of the adsorption. Sorption capacities of ferro-carbon adsorbents is in dozens of percent. Therefore, to collect 1 kg of a pollutant, 2 to 20 kg of the adsorbents is required. Then the particles with the adsorbed contaminant can be collected (e.g., downstream of the river) using a variety of magnetic traps. The traps can consist of ferromagnetic wires and permanent magnets, a variety of simple and inexpensive designs are available. As a model system, the kinetics of adsorption of a highly diluted (0.002 mg/ml) aqueous solution of a low molecular weight compound (toluidine blue) by a small concentration of a ferro-carbon powder (FC-4) was studied by spectrophotometry. Before each measurement, the particles

  18. Metal-free phthalocyanine (H2Pc) molecule adsorbed on the Au(111) surface: formation of a wide domain along a single lattice direction

    PubMed Central

    Komeda, Tadahiro; Isshiki, Hironari; Liu, Jie

    2010-01-01

    Using low-temperature scanning tunneling microscopy (STM), we observed the bonding configuration of the metal-free phthalocyanine (H2Pc) molecule adsorbed on the Au(111) surface. A local lattice formation started from a quasi-square lattice aligned to the close-packed directions of the Au(111) surface. Although we expected the lattice alignment to be equally distributed along the three crystallographically equivalent directions, the domain aligned normal to the ridge of the herringbone structure was missing in the STM images. We attribute this effect to the uniaxial contraction of the reconstructed Au(111) surface that can account for the formation of a large lattice domain along a single crystallographical direction. PMID:27877365

  19. David Adler Lectureship Award Talk: Friction and energy dissipation mechanisms in adsorbed molecules and molecularly thin films

    NASA Astrophysics Data System (ADS)

    Krim, Jacqueline

    2015-03-01

    Studies of the fundamental origins of friction have undergone rapid progress in recent years, with the development of new experimental and computational techniques for measuring and simulating friction at atomic length and time scales. The increased interest has sparked a variety of discussions and debates concerning the nature of the atomic-scale and quantum mechanisms that dominate the dissipative process by which mechanical energy is transformed into heat. Measurements of the sliding friction of physisorbed monolayers and bilayers can provide information on the relative contributions of these various dissipative mechanisms. Adsorbed films, whether intentionally applied or present as trace levels of physisorbed contaminants, moreover are ubiquitous at virtually all surfaces. As such, they impact a wide range of applications whose progress depends on precise control and/or knowledge of surface diffusion processes. Examples include nanoscale assembly, directed transport of Brownian particles, material flow through restricted geometries such as graphene membranes and molecular sieves, passivation and edge effects in carbon-based lubricants, and the stability of granular materials associated with frictional and frictionless contacts. Work supported by NSFDMR1310456.

  20. On the widths of Stokes lines in Raman scattering from molecules adsorbed at metal surfaces and in molecular conduction junctions

    NASA Astrophysics Data System (ADS)

    Gao, Yi; Galperin, Michael; Nitzan, Abraham

    2016-06-01

    Within a generic model we analyze the Stokes linewidth in surface enhanced Raman scattering (SERS) from molecules embedded as bridges in molecular junctions. We identify four main contributions to the off-resonant Stokes signal and show that under zero voltage bias (a situation pertaining also to standard SERS experiments) and at low bias junctions only one of these contributions is pronounced. The linewidth of this component is determined by the molecular vibrational relaxation rate, which is dominated by interactions with the essentially bosonic thermal environment when the relevant molecular electronic energy is far from the metal(s) Fermi energy(ies). It increases when the molecular electronic level is close to the metal Fermi level so that an additional vibrational relaxation channel due to electron-hole (eh) exciton in the molecule opens. Other contributions to the Raman signal, of considerably broader linewidths, can become important at larger junction bias.

  1. Novel insights in Al-MCM-41 precursor as adsorbent for regulated haloacetic acids and nitrate from water.

    PubMed

    Bruzzoniti, Maria Concetta; De Carlo, Rosa Maria; Sarzanini, Corrado; Caldarola, Dario; Onida, Barbara

    2012-11-01

    High concentration of NO (3) (-) in groundwater has raised concern over possible contamination of drinking water supplies. In addition, the formation of haloacetic acids (HAAs) as by-products during disinfection with chlorine-based agents is still a relevant issue, since HAAs pose serious health hazard. In this work, we investigated the affinity of a precursor of Al-MCM-41 (a mesostructured hexagonal aluminosilicate containing the template surfactant) towards nitrate and HAAs, for its possible application in the removal of these pollutants from natural and drinking waters. Additionally, adsorption kinetics and isotherms were studied. The adsorbent was synthesized using cetyltrimethylammonium bromide as surfactant and characterized by physico-chemical techniques. Simulated drinking water was spiked with the EPA-regulated HAAs (monochloroacetic (MCAA), monobromoacetic (MBAA), dichloroacetic (DCAA), dibromoacetic (DBAA), and trichloroacetic (TCAA) acids) and placed in contact with the adsorbent. The effect of matrix composition was studied. Adsorption kinetic studies were performed testing three kinetics models. For the adsorption studies, three adsorption isotherm approaches have been tested to experimental data. The pollutant recoveries were evaluated by suppressed ion chromatography. The affinity of the adsorbent was TCAA = DBAA = DCAA > MBAA > MCAA with DCAA, DBAA, and TCAA completely removed. A removal as high as 77 % was achieved for 13 mg/L nitrate. The adsorption isotherms of NO (3) (-) and monochloroacetic acid can be modeled by the Freundlich equation, while their adsorption kinetics follow a pseudo-second-order rate mechanism. The adsorbent exhibited high affinity towards HAAs in simulated drinking water even at relevant matrix concentrations, suggesting its potential application for water remediation technologies.

  2. A transferable classical potential for the water molecule.

    PubMed

    Baranyai, András; Kiss, Péter T

    2010-10-14

    We developed a new model for the water molecule which contains only three Gaussian charges. Using the gas-phase geometry the dipole moment of the molecule matches, the quadrupole moment closely approximates the experimental values. The negative charge is connected by a harmonic spring to its gas-phase position. The polarized state is identified by the equality of the intermolecular electrostatic force and the spring force acting on the negative charge. In each timestep the instantaneous position of the massless negative charge is determined by iteration. Using the technique of Ewald summation, we derived expressions for the potential energy, the forces, and the pressure for Gaussian charges. The only properties to be fitted are the half-width values of the Gaussian charge distributions and the parameters of the nonelectrostatic repulsion-attraction potential. We determined the properties of gas-phase clusters up to six molecules, the internal energy and density of ambient water and hexagonal ice. We calculated the equilibrium density of ice VII as a function of pressure. As an additional test, we calculated the pair-correlation function, the isotherm compressibility, the heat capacity, and the self-diffusion coefficients for ambient water. As far as we know, this is the first classical model of water which is able to estimate both ends of the phase diagram, the high pressure ice VII, and the gas clusters of water with excellent accuracy.

  3. Reorientional dynamics of water molecules in anionic hydration shells

    PubMed Central

    Laage, Damien; Hynes, James T.

    2007-01-01

    Water molecule rotational dynamics within a chloride anion's first hydration shell are investigated through simulations. In contrast to recent suggestions that the ion's hydration shell is rigid during a water's reorientation, we find a labile hydration sphere, consistent with previous assessments of chloride as a weak structure breaker. The nondiffusive reorientation mechanism found involves a hydrogen-bond partner switch with a large amplitude angular jump and the water's departure from the anion's shell. An analytic extended jump model accounts for the simulation results, as well as available NMR and ultrafast spectroscopic data, and resolves the discrepancy between them. PMID:17581877

  4. A new polymeric ionic liquid-based magnetic adsorbent for the extraction of inorganic anions in water samples.

    PubMed

    Chen, Lei; Huang, Xiaojia; Zhang, Yong; Yuan, Dongxing

    2015-07-17

    In this work, a novel type of polymeric ionic liquid (PIL)-based magnetic adsorbent was successfully synthesized and applied for the extraction and determination of seven inorganic anions in water samples by coupling with ion chromatography. The new adsorbent was synthesized by simple free radical copolymerization of 1-ally-3-vinylimidazolium chloride, ethylene glycol dimethacrylate and silica-coated magnetite. The adsorbent exhibited well-defined core-shell structure and good magnetic response ability. Furthermore, due to the presence of abundant anion-exchange groups in the PIL, the adsorbent displayed expected extraction performance for anions including F(-), Cl(-), Br(-), NO2(-), NO3(-), PO4(3-) and SO4(2-). Various experimental parameters that could affect the extraction performance, such as the amount of adsorbent, desorption solvent, extraction and desorption time, the pH value of sample solution were investigated in detail. Under the optimized conditions, low limits of detection (S/N=3) and quantification limits (S/N=10) of the proposed method for the target anions were achieved within the range of 0.061-0.73μg/L and 0.19-2.41μg/L, respectively. The repeatability was investigated by evaluating the intra-day, inter-day precisions and batch-to-batch reproducibility with relative standard deviations (RSDs) lower than 11%. At the same time, the method also showed high extraction speed, simplicity, practicality and low cost for the extraction inorganic anions. Finally, the proposed method was used to detect anions in different water samples successfully. The recoveries were in the range of 71.0-111%, and the RSDs were below 12% in the all cases.

  5. Development of high efficiency silica coated β-cyclodextrin polymeric adsorbent for the removal of emerging contaminants of concern from water.

    PubMed

    Bhattarai, Bikash; Muruganandham, M; Suri, Rominder P S

    2014-05-30

    This article reports the removal of several emerging contaminants (ECs) from water using novel adsorbent comprising of β-cyclodextrin (β-CD) coated on silica. Fourteen different adsorbents were synthesized under different experimental conditions using two different crosslinking agents (hexamethylene diisocyanate (HMDI) and epichlorohydrin (EPI)) and co-polymers (glycidoxypropyl trimethoxysilane (GPTS) and aminopropyl triethoxysilane (APTES). The adsorption capacities of the synthesized adsorbents were initially evaluated using 17β-estradiol, perfluorooctanoic acid (PFOA), and bisphenol-A (BPA) as adsorbates. The adsorbent prepared by using HMDI as crosslinking agent with DMSO as solvent was observed to perform the best, and removed more than 90% of 17β-estradiol, PFOA, and BPA. Furthermore, the β-CD loading on the ECs removal was studied which showed that the adsorbate removal increases with increase in loading of β-CD on the substrate. The best adsorbent was resynthesized in seven batches and its performance was reproducible for the removal of ten steroid hormones. The adsorbent showed very good regeneration potential for four successive adsorption-regeneration cycles to remove steroid hormones and PFOA. A plausible mechanism of adsorption is proposed. The synthesized best adsorbent is characterized using FTIR, HR-TEM, TGA and nitrogen adsorption analysis. The TGA results showed that the adsorbent has thermal stability of upto 300°C.

  6. Expanded graphite loaded with lanthanum oxide used as a novel adsorbent for phosphate removal from water: performance and mechanism study.

    PubMed

    Zhang, Ling; Gao, Yan; Li, Mengxue; Liu, Jianyong

    2015-01-01

    A novel adsorbent of expanded graphite (EG) loaded with lanthanum oxide (EG-LaO) was prepared for phosphate removal from water and characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. The effects of impregnation time, La3+ concentration, activation time, and activation temperature on the phosphate removal performance of the adsorbent were studied for optimization of preparation conditions. Isothermal adsorption studies suggested that the Langmuir model fits the experimental data well. Adsorption kinetics investigation showed that the pseudo-second-order model fits the experimental data quite well, indicating that the adsorption process is mainly a process of chemical adsorption, and chloride ions compete to react with the active sites of the adsorbent but do not prevent phosphate from adsorbing onto EG-LaO. The adsorption mechanism studies were performed by a pH dependence study of the adsorption amount. The results demonstrated that the probable mechanisms of phosphate adsorption on EG-LaO were electrostatic and Lewis acid-base interactions in addition to ion exchange.

  7. Abiotic properties of landfill leachate controlling arsenic release from drinking water adsorbents.

    PubMed

    Stuckman, Mengling Y; Lenhart, John J; Walker, Harold W

    2011-10-15

    In this study, As leaching from five arsenic bearing solid residuals (ABSRs) comprised of the iron hydroxide adsorbent Bayoxide E33 used in long-term operations was evaluated in leaching trials using California Waste Extraction Test (CalWET) and Toxicity Characteristic Leaching Protocol (TCLP) leachate solutions, a landfill leachate (LL), and synthetic leachate (SL). The initial As loading of the media, which reflects the influence of source water chemistry and varying treatment conditions at the point of removal, strongly influenced the magnitude of As release. The chemical composition of the leachate also influenced As release and demonstrated the relative importance of different release mechanisms, namely media dissolution, pH-dependent sorption/desorption, and ion exchange. The CalWET solution, which partially dissolved the iron-based media, resulted in 100 times more As release than did the TCLP solution, which did not dissolve the media. The LL had a higher pH than the TCLP solution, and even though its organic carbon content was lower it tended to release more As. Tests with the SL were conducted to determine the influence of variations in leachate pH, phosphate, bicarbonate, sulfate, silicate, and natural organic matter (NOM). Release increased at high pH, in the presence of high concentrations of phosphate and bicarbonate, and in the presence of high NOM concentrations. For pH, this reflects the pH-dependence of sorption reactions, whereas for the anions and NOM, direct competition appeared important. Similar to the CalWET solution, excess NOM dissolved portions of the media thereby facilitating As release. In general, our results suggest that estimating As release into landfills will remain a challenge as it depends upon As loading, which reflects site-specific properties, and the composition of the leachate, which varies from landfill to landfill.

  8. Novel Anionic Clay Adsorbents for Boiler-Blow Down Waters Reclaim and Reuse

    SciTech Connect

    Muhammad Sahimi; Theodore T. Tsotsis

    2005-12-01

    Our goal in this study is to utilize novel anionic clay sorbents for treating and reclaiming/reusing power-plant effluents, in particular, boiler blow-down waters containing heavy metals, such as As and Se. Developing and using novel materials for such application is dictated by the challenge posed by reclaiming and recycling these too-clean-to-clean effluent streams, generated during electricity production, whose contaminant levels are in the ppm/ppb (or even less) trace levels. During the study model blow-down streams have been treated in batch experiments. Adsorption isotherms as a function of pH/temperature have been established for both As and Se. Adsorption rates have also measured as a function of concentration, temperature, pH, and space time. For both the equilibrium and rate measurements, we have studied the As/Se interaction, and competition from background anions. A homogeneous surface diffusion model is used to describe the experimental kinetic data. The estimated diffusivity values are shown to depend on the particle size. On the other hand, a model taking into account the polycrystalline nature of these adsorbent particles, and the presence of an intercrystallite porous region predicts correctly that the surface diffusivity is particle size independent. A mathematical model to describe flow experiments in packed-beds has also been developed during phase I of this project. The goal is to validate this model with flow experiments in packed-beds during the phase II of this project, to determine the adsorption capacity under flow conditions, and to compare it with the capacity estimated from the adsorption isotherms determined from the batch studies.

  9. Orbital tomography: Molecular band maps, momentum maps and the imaging of real space orbitals of adsorbed molecules.

    PubMed

    Offenbacher, Hannes; Lüftner, Daniel; Ules, Thomas; Reinisch, Eva Maria; Koller, Georg; Puschnig, Peter; Ramsey, Michael G

    2015-10-01

    The frontier orbitals of molecules are the prime determinants of their chemical, optical and electronic properties. Arguably, the most direct method of addressing the (filled) frontier orbitals is ultra-violet photoemission spectroscopy (UPS). Although UPS is a mature technique from the early 1970s on, the angular distribution of the photoemitted electrons was thought to be too complex to be analysed quantitatively. Recently angle resolved UPS (ARUPS) work on conjugated molecules both, in ordered thick films and chemisorbed monolayers, has shown that the angular (momentum) distribution of the photocurrent from orbital emissions can be simply understood. The approach, based on the assumption of a plane wave final state is becoming known as orbital tomography. Here we will demonstrate, with selected examples of pentacene (5A) and sexiphenyl (6P), the potential of orbital tomography. First it will be shown how the full angular distribution of the photocurrent (momentum map) from a specific orbital is related to the real space orbital by a Fourier transform. Examples of the reconstruction of 5A orbitals will be given and the procedure for recovering the lost phase information will be outlined. We then move to examples of sexiphenyl where we interrogate the original band maps of thick sexiphenyl in the light of our understanding of orbital tomography that has developed since then. With comparison to theoretical simulations of the molecular band maps, the molecular conformation and orientation will be concluded. New results for the sexiphenyl monolayer on Al(1 1 0) will then be presented. From the band maps it will be concluded that the molecule is planarised and adopts a tilted geometry. Finally the momentum maps down to HOMO-11 will be analysed and real space orbitals reconstructed.

  10. State of water molecules and silanol groups in opal minerals: a near infrared spectroscopic study of opals from Slovakia

    NASA Astrophysics Data System (ADS)

    Boboň, Miroslav; Christy, Alfred A.; Kluvanec, Daniel; Illášová, L'udmila

    2011-12-01

    Recently, near infrared spectroscopy in combination with double derivative technique has been effectively used by Christy (Vib Spectrosc 54:42-49, 2010) to study and differentiate between free and hydrogen bonded silanol groups on silica gel surface. The method has given some insight into the type of functionalities, their location in silica gel samples, and the way the water molecules bind onto the silanol groups. The important information in this respect comes from the overtones of the OH groups of water molecules hydrogen-bonded to free silanol groups, and hydrogen-bonded silanol groups absorbing in the region 5,500-5,100 cm-1. Chemically, opal minerals are hydrated silica and the same approach was adapted to study the state of water molecules, silanol functionalities, and their locations in opal samples from Slovakia. Twenty opal samples classified into CT and A classes and one quartz sample were used in this work. The samples were crushed using a hydraulic press and powderized. Each sample was then subjected to evacuation process to remove surface-adsorbed water at 200°C, and the near infrared spectrum of each sample was measured using a Perkin Elmer NTS FT-NIR spectrometer equipped with a transflectance accessory and a DTGS detector. The samples were also heated to 750°C to remove the hydrogen-bonded silanol groups on the surface to reveal their locality. Second derivative profiles of the near infrared reflectance spectra were obtained using the instrument's software and used in the detailed analysis of the samples. The analysis of the near infrared spectra and their second derivative profiles had the aim in finding relationships between the surface chemical structure and the classification of opal samples. The dry opal samples were also tested for their surface adsorption effectivity toward water molecules. The results indicate that the opal samples contain (1) surface-adsorbed water, (2) free and hydrogen-bonded silanol groups on the surface, (3) trapped

  11. Ionic strength affects tertiary structure and aggregation propensity of a monoclonal antibody adsorbed to silicone oil-water interfaces.

    PubMed

    Gerhardt, Alana; Bonam, Kurt; Bee, Jared S; Carpenter, John F; Randolph, Theodore W

    2013-02-01

    Therapeutic proteins formulated in prefilled syringes lubricated with silicone oil come in contact with silicone oil-water interfaces for their entire shelf lives. Thus, the interactions between protein and silicone oil were studied to determine the effect of silicone oil on a monoclonal antibody's stability, both at the interface and in the bulk solution. The influence of ionic strength on these interactions was also investigated through the addition of various monovalent and divalent salts to sample formulations. The tertiary structure of the antibody was perturbed when it adsorbed to the silicone oil-water interface in solutions at low ionic strength. However, the tertiary structure of the antibody at the interface was not perturbed when the ionic strength of the formulation was increased. Even at low ionic strength, the secondary structure of the antibody adsorbed to the silicone oil-water interface was retained, suggesting that at low ionic strength, the adsorbed antibody assumes a molten globule-like conformation. This partially unfolded species was aggregation-prone, especially during agitation. Silicone oil-induced aggregation of the antibody was inhibited at higher ionic strength.

  12. Novel deep eutectic solvent-functionalized carbon nanotubes adsorbent for mercury removal from water.

    PubMed

    AlOmar, Mohamed Khalid; Alsaadi, Mohammed Abdulhakim; Jassam, Taha M; Akib, Shatirah; Ali Hashim, Mohd

    2017-07-01

    Due to the interestingly tolerated physicochemical properties of deep eutectic solvents (DESs), they are currently in the process of becoming widely used in many fields of science. Herein, we present a novel Hg(2+) adsorbent that is based on carbon nanotubes (CNTs) functionalized by DESs. A DES formed from tetra-n-butyl ammonium bromide (TBAB) and glycerol (Gly) was used as a functionalization agent for CNTs. This novel adsorbent was characterized using Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, XRD, FESEM, EDX, BET surface area, and Zeta potential. Later, Hg(2+) adsorption conditions were optimized using response surface methodology (RSM). A pseudo-second order model accurately described the adsorption of Hg(2+). The Langmuir and Freundlich isotherm models described the absorption of Hg(2+) on the novel adsorbent with acceptable accuracy. The maximum adsorption capacity was found to be 177.76mg/g.

  13. Removal of 1,2-dichlorobenzene from water emulsion using adsorbent catalysts and its regeneration.

    PubMed

    Netskina, O V; Tayban, E S; Moiseenko, A P; Komova, O V; Mukha, S A; Simagina, V I

    2015-03-21

    Purification of emulsions of 1,2-dichlorobenzene (1,2-DCB) by carbon-based adsorbent catalysts has been studied. The cycle of purification includes: (1) adsorption of 1,2-DCB from the aqueous phase and (II) reductive regeneration by hydrodechlorination of the adsorbed 1,2-DCB by molecular hydrogen in the liquid phase. 1,2-DCB adsorption from aqueous solutions has been found to proceed by the mechanism of volume filling of pores. The rate of hydrodechlorination was shown to correlate with the particle size of the active component: the finer the particles, the higher the activity of the adsorbent catalyst. Pd/FAS with an average Pd particle size of 2.8 nm was found to be the most efficient catalyst.

  14. Variational path integral molecular dynamics study of a water molecule

    NASA Astrophysics Data System (ADS)

    Miura, Shinichi

    2013-08-01

    In the present study, a variational path integral molecular dynamics method developed by the author [Chem. Phys. Lett. 482, 165 (2009)] is applied to a water molecule on the adiabatic potential energy surface. The method numerically generates an exact wavefunction using a trial wavefunction of the target system. It has been shown that even if a poor trial wavefunction is employed, the exact quantum distribution is numerically extracted, demonstrating the robustness of the variational path integral method.

  15. Excited-state potential-energy surfaces of metal-adsorbed organic molecules from linear expansion Δ-self-consistent field density-functional theory (ΔSCF-DFT)

    NASA Astrophysics Data System (ADS)

    Maurer, Reinhard J.; Reuter, Karsten

    2013-07-01

    Accurate and efficient simulation of excited state properties is an important and much aspired cornerstone in the study of adsorbate dynamics on metal surfaces. To this end, the recently proposed linear expansion Δ-self-consistent field method by Gavnholt et al. [Phys. Rev. B 78, 075441 (2008)], 10.1103/PhysRevB.78.075441 presents an efficient alternative to time consuming quasi-particle calculations. In this method, the standard Kohn-Sham equations of density-functional theory are solved with the constraint of a non-equilibrium occupation in a region of Hilbert-space resembling gas-phase orbitals of the adsorbate. In this work, we discuss the applicability of this method for the excited-state dynamics of metal-surface mounted organic adsorbates, specifically in the context of molecular switching. We present necessary advancements to allow for a consistent quality description of excited-state potential-energy surfaces (PESs), and illustrate the concept with the application to Azobenzene adsorbed on Ag(111) and Au(111) surfaces. We find that the explicit inclusion of substrate electronic states modifies the topologies of intra-molecular excited-state PESs of the molecule due to image charge and hybridization effects. While the molecule in gas phase shows a clear energetic separation of resonances that induce isomerization and backreaction, the surface-adsorbed molecule does not. The concomitant possibly simultaneous induction of both processes would lead to a significantly reduced switching efficiency of such a mechanism.

  16. Optimal Electromagnetic (EM) Geophysical Techniques to Map the Concentration of Subsurface Ice and Adsorbed Water on Mars and the Moon

    NASA Astrophysics Data System (ADS)

    Stillman, D. E.; Grimm, R. E.

    2013-12-01

    Water ice is ubiquitous in our Solar System and is a probable target for planetary exploration. Mapping the lateral and vertical concentration of subsurface ice from or near the surface could determine the origin of lunar and martian ice and quantify a much-needed resource for human exploration. Determining subsurface ice concentration on Earth is not trivial and has been attempted previously with electrical resistivity tomography (ERT), ground penetrating radar (GPR), airborne EM (AEM), and nuclear magnetic resonance (NMR). These EM geophysical techniques do not actually detect ice, but rather the absence of unfrozen water. This causes a non-unique interpretation of frozen and dry subsurface sediments. This works well in the arctic because most locations are not dry. However, for planetary exploration, liquid water is exceedingly rare and subsurface mapping must discriminate between an ice-rich and a dry subsurface. Luckily, nature has provided a unique electrical signature of ice: its dielectric relaxation. The dielectric relaxation of ice creates a temperature and frequency dependence of the electrical properties and varies the relative dielectric permittivity from ~3.1 at radar frequencies to >100 at low frequencies. On Mars, sediments smaller than silt size can hold enough adsorbed unfrozen water to complicate the measurement. This is because the presence of absorbed water also creates frequency-dependent electrical properties. The dielectric relaxation of adsorbed water and ice can be separated as they have different shapes and frequency ranges as long as a spectrum spanning the two relaxations is measured. The volume concentration of ice and adsorbed water is a function of the strength of their relaxations. Therefore, we suggest that capacitively-coupled dielectric spectroscopy (a.k.a. spectral induced polarization or complex resistivity) can detect the concentration of both ice and adsorbed water in the subsurface. To prove this concept we have collected

  17. Interaction Of Water Molecules With SiC(001) Surfaces

    SciTech Connect

    Cicero, G; Catellani, A; Galli, G

    2004-08-10

    We have investigated the interaction of water molecules with the polar Si- and C- terminated surfaces of cubic Silicon Carbide by means of ab initio molecular dynamics simulations at finite temperature. Different water coverages were considered, from {1/4} to a complete monolayer. Irrespective of coverage, we find that water dissociates on the silicon terminated surfaces, leading to important changes in both its structural and electronic properties. On the contrary, the carbon terminated surface remains inert when exposed to water. We propose experiments to reveal the ionic and electronic structure of wet Si-terminated surfaces predicted by our calculations, which at full coverage are notably different from those of hydrated Si(001) substrates. Finally, we discuss the implications of our results for SiC surface functionalization.

  18. Amorphous boron-doped sodium titanates hydrates: Efficient and reusable adsorbents for the removal of Pb(2+) from water.

    PubMed

    di Bitonto, Luigi; Volpe, Angela; Pagano, Michele; Bagnuolo, Giuseppe; Mascolo, Giuseppe; La Parola, Valeria; Di Leo, Paola; Pastore, Carlo

    2017-02-15

    Amorphous titanium hydroxide and boron-doped (B-doped) sodium titanates hydrates were synthetized and used as adsorbents for the removal of Pb(2+) from water. The use of sodium borohydride (NaBH4) and titanium(IV) isopropoxide (TTIP) as precursors permits a very easy synthesis of B-doped adsorbents at 298K. The new adsorbent materials were first chemically characterized (XRD, XPS, SEM, DRIFT and elemental analysis) and then tested in Pb(2+) adsorption batch experiments, in order to define kinetics and equilibrium studies. The nature of interaction between such sorbent materials and Pb(2+) was also well defined: besides a pure adsorption due to hydroxyl interaction functionalities, there is also an ionic exchange between Pb(2+) and sodium ions even working at pH 4.4. Langmuir model presented the best fitting with a maximum adsorption capacity up to 385mg/g. The effect of solution pH and common ions (i.e. Na(+), Ca(2+) and Mg(2+)) onto Pb(2+) sorption were also investigated. Finally, recovery was positively conducted using EDTA. Very efficient adsorption (>99.9%) was verified even using tap water spiked with traces of Pb(2+) (50ppb).

  19. Halloysite Nanotubes as a New Adsorbent for Solid Phase Extraction and Spectrophotometric Determination of Iron in Water and Food Samples

    NASA Astrophysics Data System (ADS)

    Samadi, A.; Amjadi, M.

    2016-07-01

    Halloysite nanotubes (HNTs) have been introduced as a new solid phase extraction adsorbent for preconcentration of iron(II) as a complex with 2,2-bipyridine. The cationic complex is effectively adsorbed on the sorbent in the pH range of 3.5-6.0 and efficiently desorbed by trichloroacetic acid. The eluted complex has a strong absorption around 520 nm, which was used for determination of Fe(II). After optimizing extraction conditions, the linear range of the calibration graph was 5.0-500 μg/L with a detection limit of 1.3 μg/L. The proposed method was successfully applied for the determination of trace iron in various water and food samples, and the accuracy was assessed through the recovery experiments and analysis of a certified reference material (NIST 1643e).

  20. A theoretical study of the XP and NEXAFS spectra of alanine: gas phase molecule, crystal, and adsorbate at the ZnO(10 ̅10) surface.

    PubMed

    Gao, You Kun; Traeger, Franziska; Kotsis, Konstantinos; Staemmler, Volker

    2011-06-14

    The adsorption of alanine on the mixed-terminated ZnO(10 ̅10) surface is studied by means of quantum-chemical ab initio calculations. Using a finite cluster model and the adsorption geometry as obtained both by periodic CPMD and embedded cluster calculations, the C1s, N1s and O1s X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra are calculated for single alanine molecules on ZnO(10 ̅10). These spectra are compared with the spectra calculated for alanine in the gas phase and in its crystalline form and with experimental XPS and NEXAFS data for the isolated alanine molecule and for alanine adsorbed on ZnO(10 ̅10) at multilayer and monolayer coverage. The excellent agreement between the experimental and calculated XP and NEXAFS spectra confirms the calculated adsorption geometry: A single alanine molecule is bound to ZnO(10 ̅10) in a dissociated bidentate form with the two O atoms of the acid group bound to two Zn atoms of the surface and the proton transferred to one O atom of the surface. Other possible structures, such as adsorption of alanine in one of its neutral or zwitterionic forms in which the proton of the -COOH group remains at this group or is transferred to the amino group, can be excluded since they would give rise to quite different XP spectra. In the multilayer coverage regime, on the other hand, alanine is in its crystalline form as is also shown by the analysis of the XP spectra.

  1. Enhanced adsorption of phenol from water by a novel polar post-crosslinked polymeric adsorbent.

    PubMed

    Zeng, Xiaowei; Fan, Yunge; Wu, Guolin; Wang, Chunhong; Shi, Rongfu

    2009-09-30

    A novel post-crosslinked polymeric adsorbent PDM-2 was prepared by Friedel-Crafts reaction of pendant vinyl groups without external crosslinking agent. Both the specific surface area and the pore volume of starting copolymer PDM-1 increased significantly after post-crosslinking. Batch adsorption runs of phenol from aqueous solution onto PDM-1 and PDM-2 were investigated. Commercial macroporous resins XAD-4 and AB-8 were chosen as the comparison. Experimental results showed that isotherms of phenol adsorption onto these four polymeric adsorbents could be represented by Freundlich model reasonably. PDM-2 exhibited higher adsorption capacity of phenol than other three adsorbents, which resulted from synergistic effect of larger specific surface area and polar groups on the network. The adsorption process for phenol was proved to be exothermic and spontaneous in nature. Thermodynamic parameters such as Gibb's free energy (DeltaG), change in enthalpy (DeltaH) and change in entropy (DeltaS) were calculated. Kinetics studies indicated that phenol uptake onto PDM-1 and PDM-2 followed the pseudo-second order model and the intraparticle diffusion process was a rate-controlling step. Column adsorption runs demonstrated that nearly 100% regeneration efficiency for PDM-2 by 3BV industrial alcohol and the adsorbate phenol can be easily recovered by further distilling. Continuous column adsorption-regeneration cycles indicated negligible capacity loss of PDM-2 during operation.

  2. Dynamic mechanical properties of a polyelectrolyte adsorbed insoluble lipid monolayer at the air-water interface.

    PubMed

    Park, Chang Young; Kim, Mahn Won

    2015-04-23

    Polymers have been used to stabilize interfaces or to tune the mechanical properties of interfaces in various contexts, such as in oil emulsions or biological membranes. Although the structural properties of these systems are relatively well-studied, instrumental limitations continue to make it difficult to understand how the addition of polymer affects the dynamic mechanical properties of thin and soft films. We have solved this challenge by developing a new instrument, an optical-tweezer-based interface shear microrheometer (ISMR). With this technique, we observed that the interface shear modulus, G*, of a dioctadecyldimethylammonium chloride (DODAC) monolayer at the air-water interface significantly increased with adsorption of polystyrenesulfonate (PSS). In addition, the viscous film (DODAC monolayer) became a viscoelastic film with PSS adsorption. At a low salt concentration, 10 mM of NaCl in the subphase, the viscoelasticity of the DODAC/PSS composite was predominantly determined by a particular property of PSS, that is, it behaves as a Gaussian chain in a θ-solvent. At a high salt concentration, 316 mM of NaCl, the thin film behaved as a polymer melt excluding water molecules.

  3. Modeling adsorption: Investigating adsorbate and adsorbent properties

    NASA Astrophysics Data System (ADS)

    Webster, Charles Edwin

    1999-12-01

    Surface catalyzed reactions play a major role in current chemical production technology. Currently, 90% of all chemicals are produced by heterogeneously catalyzed reactions. Most of these catalyzed reactions involve adsorption, concentrating the substrate(s) (the adsorbate) on the surface of the solid (the adsorbent). Pore volumes, accessible surface areas, and the thermodynamics of adsorption are essential in the understanding of solid surface characteristics fundamental to catalyst and adsorbent screening and selection. Molecular properties such as molecular volumes and projected molecular areas are needed in order to convert moles adsorbed to surface volumes and areas. Generally, these molecular properties have been estimated from bulk properties, but many assumptions are required. As a result, different literature values are employed for these essential molecular properties. Calculated molar volumes and excluded molecular areas are determined and tabulated for a variety of molecules. Molecular dimensions of molecules are important in the understanding of molecular exclusion as well as size and shape selectivity, diffusion, and adsorbent selection. Molecular dimensions can also be used in the determination of the effective catalytic pore size of a catalyst. Adsorption isotherms, on zeolites, (crystalline mineral oxides) and amorphous solids, can be analyzed with the Multiple Equilibrium Analysis (MEA) description of adsorption. The MEA produces equilibrium constants (Ki), capacities (ni), and thermodynamic parameters (enthalpies, ΔHi, and entropies, ΔSi) of adsorption for each process. Pore volumes and accessible surface areas are calculated from the process capacities. Adsorption isotherms can also be predicted for existing and new adsorbate-adsorbent systems with the MEA. The results show that MEA has the potential of becoming a standard characterization method for microporous solids that will lead to an increased understanding of their behavior in gas

  4. The spontaneous synchronized dance of pairs of water molecules

    SciTech Connect

    Roncaratti, Luiz F.; Cappelletti, David Pirani, Fernando

    2014-03-28

    Molecular beam scattering experiments have been performed to study the effect of long-range anisotropic forces on the collision dynamics of two small polar molecules. The main focus of this paper is on water, but also ammonia and hydrogen sulphide molecules have been investigated, and some results will be anticipated. The intermolecular distances mainly probed are of the order of 1 nm and therefore much larger than the molecular dimensions. In particular, we have found that the natural electric field gradient, generated by different spatial orientations of the permanent electric dipoles, is able to promote the transformation of free rotations into coupled pendular states, letting the molecular partners involved in the collision complex swinging to and fro around the field direction. This long-ranged concerted motion manifested itself as large increases of the magnitude of the total integral cross section. The experimental findings and the theoretical treatment developed to shed light on the details of the process suggest that the transformation from free rotations to pendular states depends on the rotational level of both molecules, on the impact parameter, on the relative collision velocity, on the dipole moment product and occurs in the time scale of picoseconds. The consequences of this intriguing phenomenon may be important for the interpretation and, in perspective, for the control of elementary chemical and biological processes, given by polar molecules, ions, and free radicals, occurring in several environments under various conditions.

  5. Geometry-dependent distributed polarizability models for the water molecule

    SciTech Connect

    Loboda, Oleksandr; Ingrosso, Francesca; Ruiz-López, Manuel F.; Millot, Claude; Szalewicz, Krzysztof

    2016-01-21

    Geometry-dependent distributed polarizability models have been constructed by fits to ab initio calculations at the coupled cluster level of theory with up to noniterative triple excitations in an augmented triple-zeta quality basis set for the water molecule in the field of a point charge. The investigated models include (i) charge-flow polarizabilities between chemically bonded atoms, (ii) isotropic or anisotropic dipolar polarizabilities on oxygen atom or on all atoms, and (iii) combinations of models (i) and (ii). For each model, the polarizability parameters have been optimized to reproduce the induction energy of a water molecule polarized by a point charge successively occupying a grid of points surrounding the molecule. The quality of the models is ascertained by examining their ability to reproduce these induction energies as well as the molecular dipolar and quadrupolar polarizabilities. The geometry dependence of the distributed polarizability models has been explored by changing bond lengths and HOH angle to generate 125 molecular structures (reduced to 75 symmetry-unique ones). For each considered model, the distributed polarizability components have been fitted as a function of the geometry by a Taylor expansion in monomer coordinate displacements up to the sum of powers equal to 4.

  6. Synthesis and properties of water-soluble asterisk molecules.

    PubMed

    Menger, Fredric M; Azov, Vladimir A

    2002-09-18

    An asterisk is comprised of six semirigid arms projecting from a benzene nucleus. In the case at hand, asterisks were synthesized with one, two, or three aromatic rings (connected by sulfur atoms) in each of the six arms. A phosphomonoester at the termini of each arm solubilized the asterisks in water. The colloidal properties of these amphiphilic molecules were investigated by UV-vis and fluorescence spectroscopy, calorimetry, light scattering, surface tensiometry, and pulse-gradient spin-echo NMR. Solubility, solubilization, metal binding, and micelle "seeding" experiments were also carried out. Chain-conformation and supramolecular assembly into remarkable molecular "scrolls" were investigated by X-ray analysis and electron microscopy, respectively. One of the more interesting properties of the asterisks is that they remain monomeric in water despite having as many as 19 hydrophobic aromatic rings exposed to the water. The reasons for this behavior, and the possibility of exploiting it for constructing enzyme models free from aggregation equilibria, are discussed.

  7. Host and adsorbate dynamics in silicates with flexible frameworks: Empirical force field simulation of water in silicalite

    NASA Astrophysics Data System (ADS)

    Bordat, Patrice; Cazade, Pierre-André; Baraille, Isabelle; Brown, Ross

    2010-03-01

    Molecular dynamics simulations are performed on the pure silica zeolite silicalite (MFI framework code), maintaining via a new force field both framework flexibility and realistic account of electrostatic interactions with adsorbed water. The force field is similar to the well-known "BKS" model [B. W. H. van Beest et al., Phys. Rev. Lett. 64, 1955 (1990)], but with reduced partial atomic charges and reoptimized covalent bond potential wells. The present force field reproduces the monoclinic to orthorhombic transition of silicalite. The force field correctly represents the hydrophobicity of pure silica silicalite, both the adsorption energy, and the molecular diffusion constants of water. Two types of adsorption, specific and weak unspecific, are predicted on the channel walls and at the channel intersection. We discuss molecular diffusion of water in silicalite, deducing a barrier to crossing between the straight and the zigzag channels. Analysis of the thermal motion shows that at room temperature, framework oxygen atoms incurring into the zeolite channels significantly influence the dynamics of adsorbed water.

  8. Water-insoluble sericin/β-cyclodextrin/PVA composite electrospun nanofibers as effective adsorbents towards methylene blue.

    PubMed

    Zhao, Rui; Wang, Yong; Li, Xiang; Sun, Bolun; Jiang, Ziqiao; Wang, Ce

    2015-12-01

    A novel water-insoluble sericin/β-cyclodextrin/poly (vinyl alcohol) composite nanofiber adsorbent was prepared by electrospinning and followed by thermal crosslinking for removal of cationic dye methylene blue from aqueous solution. Fourier transform infrared spectroscopy and solubility experiments confirmed that sericin and β-cyclodextrin were incorporated into the nanofibers and the crosslinking reaction occurred successfully. Kinetics, isotherms and thermodynamics analysis were studied for adsorption of methylene blue. The adsorption process is better fitted with the pseudo-second-order model and Langmuir isotherm model. The maximum adsorption capacities are 187.97, 229.89, and 261.10mg/g at the temperatures 293, 313 and 333 K, respectively. Thermodynamic parameters showed that methylene blue adsorption was endothermic and spontaneous. In addition, the fiber membrane adsorbent could be easily separated from dye solution and showed high recyclable removal efficiency. All these results suggest that crosslinked sericin/β-cyclodextrin/poly(vinyl alcohol) composite nanofibers could be potential recyclable adsorbents in dye wastewater treatment.

  9. Potassium Niobate Nanolamina: A Promising Adsorbent for Entrapment of Radioactive Cations from Water

    PubMed Central

    Sun, Jin; Yang, Dongjiang; Sun, Cuihua; Liu, Long; Yang, Shuanglei; (Alec) Jia, Yi; Cai, Rongsheng; Yao, Xiangdong

    2014-01-01

    Processing and managing radioactive waste is a great challenge worldwide as it is extremely difficult and costly; the radioactive species, cations or anions, leaked into the environment are a serious threat to the health of present and future generations. We report layered potassium niobate (K4Nb6O17) nanolamina as adsorbent to remove toxic Sr2+, Ba2+ and Cs+ cations from wastewater. The results show that K4Nb6O17 nanolamina can permanently confine the toxic cations within the interlayer spacing via a considerable deformation of the metastable layered structure during the ion exchange process. At the same time, the nanolaminar adsorbent exhibits prompt adsorption kinetics, high adsorption capacity and selectivity, and superior acid resistance. These merits make it be a promising material as ion exchanger for the removal of radioactive cations from wastewater. PMID:25472721

  10. Single ionization of water molecules in collisions with bare ions

    NASA Astrophysics Data System (ADS)

    Mondal, A.; Mandal, C. R.; Purkait, M.

    2016-04-01

    We present the double differential cross sections (DDCSs) for the direct ionization of water molecules by impact of fully stripped helium, carbon and oxygen atoms, respectively. In the present formalism, we have represented the wavefunction in the entrance channel as the product of a plane wave for the projectile and an accurate one-center-molecular wavefunction of the water molecule by Moccia (1964 J. Chem. Phys. 40 2186). In the exit channel, we have expressed the total wavefunction as the product of pair-wise Coulomb wavefunctions among the ejected electron, projectile ion and the residual target ion, respectively. The contributions of DDCSs for five different molecular orbitals of water to the spectrum of angular distributions have been analyzed for several electron emission energies. The present results for DDCSs are compared with existing experimental and theoretical findings. We find an overall good agreement between our calculated results and the experimental findings for electron emission cross sections. In addition, DDCS results for ionization from different orbitals at a few electron emission energies are given in tabular form.

  11. Expansion Hamiltonian model for a diatomic molecule adsorbed on a surface: Vibrational states of the CO/Cu(100) system including surface vibrations

    NASA Astrophysics Data System (ADS)

    Meng, Qingyong; Meyer, Hans-Dieter

    2015-10-01

    Molecular-surface studies are often done by assuming a corrugated, static (i.e., rigid) surface. To be able to investigate the effects that vibrations of surface atoms may have on spectra and cross sections, an expansion Hamiltonian model is proposed on the basis of the recently reported [R. Marquardt et al., J. Chem. Phys. 132, 074108 (2010)] SAP potential energy surface (PES), which was built for the CO/Cu(100) system with a rigid surface. In contrast to other molecule-surface coupling models, such as the modified surface oscillator model, the coupling between the adsorbed molecule and the surface atoms is already included in the present expansion SAP-PES model, in which a Taylor expansion around the equilibrium positions of the surface atoms is performed. To test the quality of the Taylor expansion, a direct model, that is avoiding the expansion, is also studied. The latter, however, requests that there is only one movable surface atom included. On the basis of the present expansion and direct models, the effects of a moving top copper atom (the one to which CO is bound) on the energy levels of a bound CO/Cu(100) system are studied. For this purpose, the multiconfiguration time-dependent Hartree calculations are carried out to obtain the vibrational fundamentals and overtones of the CO/Cu(100) system including a movable top copper atom. In order to interpret the results, a simple model consisting of two coupled harmonic oscillators is introduced. From these calculations, the vibrational levels of the CO/Cu(100) system as function of the frequency of the top copper atom are discussed.

  12. Expansion Hamiltonian model for a diatomic molecule adsorbed on a surface: Vibrational states of the CO/Cu(100) system including surface vibrations

    SciTech Connect

    Meng, Qingyong; Meyer, Hans-Dieter

    2015-10-28

    Molecular-surface studies are often done by assuming a corrugated, static (i.e., rigid) surface. To be able to investigate the effects that vibrations of surface atoms may have on spectra and cross sections, an expansion Hamiltonian model is proposed on the basis of the recently reported [R. Marquardt et al., J. Chem. Phys. 132, 074108 (2010)] SAP potential energy surface (PES), which was built for the CO/Cu(100) system with a rigid surface. In contrast to other molecule-surface coupling models, such as the modified surface oscillator model, the coupling between the adsorbed molecule and the surface atoms is already included in the present expansion SAP-PES model, in which a Taylor expansion around the equilibrium positions of the surface atoms is performed. To test the quality of the Taylor expansion, a direct model, that is avoiding the expansion, is also studied. The latter, however, requests that there is only one movable surface atom included. On the basis of the present expansion and direct models, the effects of a moving top copper atom (the one to which CO is bound) on the energy levels of a bound CO/Cu(100) system are studied. For this purpose, the multiconfiguration time-dependent Hartree calculations are carried out to obtain the vibrational fundamentals and overtones of the CO/Cu(100) system including a movable top copper atom. In order to interpret the results, a simple model consisting of two coupled harmonic oscillators is introduced. From these calculations, the vibrational levels of the CO/Cu(100) system as function of the frequency of the top copper atom are discussed.

  13. Measurement of laser activated electron tunneling from semiconductor zinc oxide to adsorbed organic molecules by a matrix assisted laser desorption ionization mass spectrometer.

    PubMed

    Zhong, Hongying; Fu, Jieying; Wang, Xiaoli; Zheng, Shi

    2012-06-04

    Measurement of light induced heterogeneous electron transfer is important for understanding of fundamental processes involved in chemistry, physics and biology, which is still challenging by current techniques. Laser activated electron tunneling (LAET) from semiconductor metal oxides was observed and characterized by a MALDI (matrix assisted laser desorption ionization) mass spectrometer in this work. Nanoparticles of ZnO were placed on a MALDI sample plate. Free fatty acids and derivatives were used as models of organic compounds and directly deposited on the surface of ZnO nanoparticles. Irradiation of UV laser (λ=355 nm) with energy more than the band gap of ZnO produces ions that can be detected in negative mode. When TiO(2) nanoparticles with similar band gap but much lower electron mobility were used, these ions were not observed unless the voltage on the sample plate was increased. The experimental results indicate that laser induced electron tunneling is dependent on the electron mobility and the strength of the electric field. Capture of low energy electrons by charge-deficient atoms of adsorbed organic molecules causes unpaired electron-directed cleavages of chemical bonds in a nonergodic pathway. In positive detection mode, electron tunneling cannot be observed due to the reverse moving direction of electrons. It should be able to expect that laser desorption ionization mass spectrometry is a new technique capable of probing the dynamics of electron tunneling. LAET offers advantages as a new ionization dissociation method for mass spectrometry.

  14. Continuum simulations of water flow past fullerene molecules

    NASA Astrophysics Data System (ADS)

    Popadić, A.; Praprotnik, M.; Koumoutsakos, P.; Walther, J. H.

    2015-09-01

    We present continuum simulations of water flow past fullerene molecules. The governing Navier-Stokes equations are complemented with the Navier slip boundary condition with a slip length that is extracted from related molecular dynamics simulations. We find that several quantities of interest as computed by the present model are in good agreement with results from atomistic and atomistic-continuum simulations at a fraction of the cost. We simulate the flow past a single fullerene and an array of fullerenes and demonstrate that such nanoscale flows can be computed efficiently by continuum flow solvers, allowing for investigations into spatiotemporal scales inaccessible to atomistic simulations.

  15. Ionization of water molecules by fast charged projectiles

    SciTech Connect

    Dubois, A.; Carniato, S.; Fainstein, P. D.; Hansen, J. P.

    2011-07-15

    Single-ionization cross sections of water molecules colliding with fast protons are calculated from lowest-order perturbation theory by taking all electrons and molecular orientations consistently into account. Explicit analytical formulas based on the peaking approximation are obtained for differential ionization cross sections with the partial contribution from the various electron orbitals accounted for. The results, which are in very good agreement with total and partial cross sections at high electron and projectile energies, display a strong variation on molecular orientation and molecular orbitals.

  16. Functionalized paper--A readily accessible adsorbent for removal of dissolved heavy metal salts and nanoparticles from water.

    PubMed

    Setyono, Daisy; Valiyaveettil, Suresh

    2016-01-25

    Paper, a readily available renewable resource, comprises of interwoven cellulosic fibers, which can be functionalized to develop interesting low-cost adsorbent material for water purification. In this study, polyethyleneimine (PEI)-functionalized paper was used for the removal of hazardous pollutants such as Au and Ag nanoparticles, Cr(VI) anions, Ni(2+), Cd(2+), and Cu(2+) cations from spiked water samples. Compared to untreated paper, the PEI-coated paper showed significant improvement in adsorption capacities toward the pollutants investigated in this study. Kinetics, isotherm models, pH, and desorption studies were carried out to study the adsorption mechanism of pollutants on the adsorbent surface. Adsorption of pollutants was better described by pseudo-second order kinetics and Langmuir isotherm model. Maximum adsorption of anionic pollutants was achieved at pH 5 while that of cations was at pH>6. Overall, the PEI-functionalized paper showed interesting Langmuir adsorption capacities for heavy metal ions such as Cr(VI) (68 mg/g), Ni(2+) (208 mg/g), Cd(2+) (370 mg/g), and Cu(2+) (435 mg/g) ions at neutral pH. In addition, the modified paper was also used to remove Ag-citrate (79 mg/g), Ag-PVP (46 mg/g), Au-citrate (30 mg/g), Au-PVP (17 mg/g) nanoparticles from water. Desorption of NPs from the adsorbent was done by washing with 2 M HCl or thiourea solution, while heavy metal ions were desorbed using 1 M NaOH or HNO3 solution. The modified paper retained its extraction efficiencies upon desorption of pollutants.

  17. Characterizing Structural Stability of Amyloid Motif Fibrils Mediated by Water Molecules.

    PubMed

    Choi, Hyunsung; Chang, Hyun Joon; Lee, Myeongsang; Na, Sungsoo

    2017-02-04

    In biological systems, structural confinements of amyloid fibrils can be mediated by the role of water molecules. However, the underlying effect of the dynamic behavior of water molecules on structural stabilities of amyloid fibrils is still unclear. By performing molecular dynamics simulations, we investigate the dynamic features and the effect of interior water molecules on conformations and mechanical characteristics of various amyloid fibrils. We find that a specific mechanism induced by the dynamic properties of interior water molecules can affect diffusion of water molecules inside amyloid fibrils, inducing their different structural stabilities. The conformation of amyloid fibrils induced by interior water molecules show the fibrils' different mechanical features. We elucidate the role of confined and movable interior water molecules in structural stabilities of various amyloid fibrils. Our results offer insights not only in further understanding of mechanical features of amyloids as mediated by water molecules, but also in the fine-tuning of the functional abilities of amyloid fibrils for applications.

  18. Natural cotton fibers as adsorbent for solid-phase extraction of polycyclic aromatic hydrocarbons in water samples.

    PubMed

    Wang, Jianping; Liu, Shengquan; Chen, Chunyan; Zou, Ying; Hu, Huiping; Cai, Qingyun; Yao, Shouzhuo

    2014-07-21

    A natural material, cotton fiber, has been applied as a solid-phase extraction (SPE) adsorbent for sample preparation for the analysis of polycyclic aromatic hydrocarbons (PAH) in water samples using high-performance liquid chromatography. The cotton fiber was used directly without any chemical modifications, which avoided a complex synthesis process and consumption of a large volume of organic solvent. The conditions affecting the extraction efficiency were optimized to achieve high detection sensitivity, and included elution solvent, ultrasonic elution time, extraction time, sample volume, salt concentration and organic modifier addition. Under the optimal conditions, the detection limits for seven PAH compounds could reach up to 0.1-2.0 ng L(-1). The method accuracy was evaluated using recovery measurements in standard spiked samples and good recoveries of 70.69-110.04% with relative standard deviations of less than 10% have been achieved. Consequently, the method developed was successfully applied for determining PAH in environmental samples: snow water, metal-fabrication factory wastewater and Xiangjiang River water, with PAH contents ranging from 13.2 to 83.1 ng L(-1). Therefore, using cotton fiber as a new SPE adsorbent, was easy to prepare, had a low cost and great reusability, and this implies it is a promising method for sample preparation.

  19. Reliable determination of oxygen and hydrogen isotope ratios in atmospheric water vapour adsorbed on 3A molecular sieve.

    PubMed

    Han, Liang-Feng; Gröning, Manfred; Aggarwal, Pradeep; Helliker, Brent R

    2006-01-01

    The isotope ratio of atmospheric water vapour is determined by wide-ranging feedback effects from the isotope ratio of water in biological water pools, soil surface horizons, open water bodies and precipitation. Accurate determination of atmospheric water vapour isotope ratios is important for a broad range of research areas from leaf-scale to global-scale isotope studies. In spite of the importance of stable isotopic measurements of atmospheric water vapour, there is a paucity of published data available, largely because of the requirement for liquid nitrogen or dry ice for quantitative trapping of water vapour. We report results from a non-cryogenic method for quantitatively trapping atmospheric water vapour using 3A molecular sieve, although water is removed from the column using standard cryogenic methods. The molecular sieve column was conditioned with water of a known isotope ratio to 'set' the background signature of the molecular sieve. Two separate prototypes were developed, one for large collection volumes (3 mL) and one for small collection volumes (90 microL). Atmospheric water vapour was adsorbed to the column by pulling air through the column for several days to reach the desired final volume. Water was recovered from the column by baking at 250 degrees C in a dry helium or nitrogen air stream and cryogenically trapped. For the large-volume apparatus, the recovered water differed from water that was simultaneously trapped by liquid nitrogen (the experimental control) by 2.6 per thousand with a standard deviation (SD) of 1.5 per thousand for delta(2)H and by 0.3 per thousand with a SD of 0.2 per thousand for delta(18)O. Water-vapour recovery was not satisfactory for the small volume apparatus.

  20. A novel adsorbent obtained by inserting carbon nanotubes into cavities of diatomite and applications for organic dye elimination from contaminated water.

    PubMed

    Yu, Hongwen; Fugetsu, Bunshi

    2010-05-15

    A novel approach is described for establishing adsorbents for elimination of water-soluble organic dyes by using multi-walled carbon nanotubes (MWCNTs) as the adsorptive sites. Agglomerates of MWCNTs were dispersed into individual tubes (dispersed-MWCNTs) using sodium n-dodecyl itaconate mixed with 3-(N,N-dimethylmyristylammonio)-propanesulfonate as the dispersants. The resultant dispersed-MWCNTs were inserted into cavities of diatomite to form composites of diatomite/MWCNTs. These composites were finally immobilized onto the cell walls of flexible polyurethane foams (PUF) through an in situ PUF formation process to produce the foam-like CNT-based adsorbent. Ethidium bromide, acridine orange, methylene blue, eosin B, and eosin Y were chosen to represent typical water-soluble organic dyes for studying the adsorptive capabilities of the foam-like CNT-based adsorbent. For comparisons, adsorptive experiments were also carried out by using agglomerates of the sole MWCNTs as adsorbents. The foam-like CNT-based adsorbents were found to have higher adsorptive capacities than the CNT agglomerates for all five dyes; in addition, they are macro-sized, durable, flexible, hydrophilic and easy to use. Adsorption isotherms plotted based on the Langmuir equation gave linear results, suggesting that the foam-like CNT-based adsorbent functioned in the Langmuir adsorption manner. The foam-like CNT-based adsorbents are reusable after regeneration with aqueous ethanol solution.

  1. Adsorption and trace detection of pharmacologically significant 5-methylthio-1, 3, 4-thiadiazole-2-thiol molecule adsorbed on silver nanocolloids and understanding the role of Albrecht's “A” and Herzberg-Teller contributions in the SERS spectra

    NASA Astrophysics Data System (ADS)

    Chowdhury, Joydeep; Chandra, Subhendu; Ghosh, Manash

    2015-01-01

    The surface enhanced Raman scattering (SERS) spectra of biologically and industrially significant 5-methylthio-1, 3, 4-thiadiazole 2-thiol molecule have been investigated. The SERS spectra at various concentrations of the adsorbate are compared with the Fourier transform Infrared (FTIR) and normal Raman spectra (NRS) of the probe molecule recorded in different environmental conditions. The optimized molecular structures of the most probable thione and the thiol forms of the molecule have been estimated from the density functional theory (DFT) calculations. The vibrational signatures of the molecule have been assigned from the potential energy distributions (PEDs). The detail vibrational analyses reveal that ∼54% of the thione form of the molecule is prevalent in the solid state and its population increases to ∼65% in ACN solvent medium. Concentration dependent SERS, together with the 2-dimensional correlation spectra (2D-COS), corroborate the presence of both the thione and the thiol forms of the molecule even in the surface adsorbed state. The orientations of the thione and the thiol forms of the molecule on the nanocolloidal silver surface have been predicted from the surface selection rule. The selective enhancement of Raman bands in the SERS spectra have been explored from the view of the Albrecht's "A" and Herzberg-Teller (HT) charge transfer (CT) contribution.

  2. Optimization of tetravalent manganese feroxyhyte's negative charge density: A high-performing mercury adsorbent from drinking water.

    PubMed

    Kokkinos, E; Simeonidis, K; Pinakidou, F; Katsikini, M; Mitrakas, M

    2017-01-01

    This study demonstrates an optimization procedure for the development of an Hg-specified adsorbent able to comply with the regulation limit for drinking water of 1μg/L. On this purpose, the synthesis of Mn(IV)-feroxyhyte was modified to achieve high negative charge density by combining alkaline and extreme oxidizing conditions. In particular, precipitation of FeSO4 at pH9 and excess of KMnO4 follows a very fast nucleation step providing a product with very small nanocrystal size (1-2nm), high specific surface area (300m(2)/g) and maximum negative charge density (1.8mmol H(+)/g). The adsorbent was validated for Hg removal in batch experiments and column tests using natural-like water indicating an adsorption capacity as high as 2.5μg/mg at equilibrium concentration 1μg/L under reliable conditions of application. Importantly, the adsorption is an exothermic spontaneous process, resulting in the formation of inner sphere complexes by sharing both A-type and B-type oxygen atoms with the metal surface octahedral as revealed by the X-ray absorption fine structure results.

  3. Molecular multipole moments of water molecules in ice Ih

    NASA Astrophysics Data System (ADS)

    Batista, Enrique R.; Xantheas, Sotiris S.; Jónsson, Hannes

    1998-09-01

    We have used an induction model including dipole, dipole-quadrupole, quadrupole-quadrupole polarizability and first hyperpolarizability as well as fixed octopole and hexadecapole moments to study the electric field in ice. The self-consistent induction calculations gave an average total dipole moment of 3.09 D, a 67% increase over the dipole moment of an isolated water molecule. A previous, more approximate induction model study by Coulson and Eisenberg [Proc. R. Soc. Lond. A 291, 445 (1966)] suggested a significantly smaller average value of 2.6 D. This value has been used extensively in recent years as a reference point in the development of various polarizable interaction potentials for water as well as for assessment of the convergence of water cluster properties to those of bulk. The reason for this difference is not due to approximations made in the computational scheme of Coulson and Eisenberg but rather due to the use of less accurate values for the molecular multipoles in these earlier calculations.

  4. Searching for Water and Other Molecules with JWST

    NASA Astrophysics Data System (ADS)

    Valenti, Jeff

    2015-08-01

    The James Webb Space Telescope (JWST) will be a powerful tool for measuring water and other molecules in transiting exoplanets, warm circumstellar disks, brown dwarfs, and cool stars. In early 2019 the observatory is scheduled to begin science operations near the Sun-Earth L2 Lagrange point. The sunshield will allow the telescope and science instrument module to cool passively to approximately 40 K. The segmented primary mirror has 25 square meters of collecting area, giving the observatory unprecedented sensitivity in the infrared. JWST has four science instruments that cover wavelengths from 0.6 to 28 microns at spectral resolutions up to about R=3000. I will summarize relevant observatory constraints, instrument capabilities, and observing templates. I will illustrate practical issues with examples from the Science Operations Design Reference Mission. Finally, I will discuss the Cycle 1 proposal process, which begins in 2017.

  5. Effect of an electric field on a methane molecule. I. Infrared analysis of methane (CH4-CD4) adsorbed in NaA zeolite in the temperature range 150-20 K

    NASA Astrophysics Data System (ADS)

    De Lara, E. Cohen; Kahn, R.; Seloudoux, R.

    1985-09-01

    The spectra of methane adsorbed at low temperature in NaA zeolite show two strong effects of the field existing in the cavities: (i) the appearance of the ν1 forbidden band which increases when decreasing the temperature and (ii) the splitting of the ν3 degenerate band. The variation with T of its components lead to the conclusion that the molecule progressively is oriented in a C3V configuration with respect to the field.

  6. Artificial neural network modeling in competitive adsorption of phenol and resorcinol from water environment using some carbonaceous adsorbents.

    PubMed

    Aghav, R M; Kumar, Sunil; Mukherjee, S N

    2011-04-15

    This paper illustrates the application of artificial neural network (ANN) for prediction of performances in competitive adsorption of phenol and resorcinol from aqueous solution by conventional and low cost carbonaceous adsorbent materials, such as activated carbon (AC), wood charcoal (WC) and rice husk ash (RHA). The three layer's feed forward neural network with back propagation algorithm in MATLAB environment was used for estimation of removal efficiencies of phenol and resorcinol in bi-solute water environment based on 29 sets of laboratory batch study results. The input parameters used for training of the neural network include amount of adsorbent (g/L), initial concentrations of phenol (mg/L) and resorcinol (mg/L), contact time (h), and pH. The removal efficiencies of phenol and resorcinol were considered as an output of the neural network. The performances of the developed ANN models were also measured using statistical parameters, such as mean error, mean square error, root mean square error, and linear regression. The comparison of the removal efficiencies of pollutants using ANN model and experimental results showed that ANN modeling in competitive adsorption of phenolic compounds reasonably corroborated with the experimental results.

  7. Subharmonic excitation in amplitude modulation atomic force microscopy in the presence of adsorbed water layers

    SciTech Connect

    Santos, Sergio; Barcons, Victor; Verdaguer, Albert; Chiesa, Matteo

    2011-12-01

    In ambient conditions, nanometric water layers form on hydrophilic surfaces covering them and significantly changing their properties and characteristics. Here we report the excitation of subharmonics in amplitude modulation atomic force microscopy induced by intermittent water contacts. Our simulations show that there are several regimes of operation depending on whether there is perturbation of water layers. Single period orbitals, where subharmonics are never induced, follow only when the tip is either in permanent contact with the water layers or in pure noncontact where the water layers are never perturbed. When the water layers are perturbed subharmonic excitation increases with decreasing oscillation amplitude. We derive an analytical expression which establishes whether water perturbations compromise harmonic motion and show that the predictions are in agreement with numerical simulations. Empirical validation of our interpretation is provided by the observation of a range of values for apparent height of water layers when subharmonic excitation is predicted.

  8. Adsorption of drinking water fluoride on a micron-sized magnetic Fe3O4@Fe-Ti composite adsorbent

    NASA Astrophysics Data System (ADS)

    Zhang, Chang; Li, Yingzhen; Wang, Ting-Jie; Jiang, Yanping; Wang, Haifeng

    2016-02-01

    A micron-sized magnetic adsorbent (MMA) for fluoride removal from drinking water was prepared by spray drying and subsequent calcination of a magnetic Fe3O4@Fe-Ti core-shell nanoparticle slurry. The MMA granules had high mechanical strength and stability against water scouring, can be easily separated from the water by a magnet, and had a high selectivity for fluoride versus common co-existing ions and high fluoride removal efficiency in a wide range of initial pH of 3-11. Abundant hydroxyl groups on the MMA surface acted as the active sites for fluoride adsorption, which resulted in a high affinity of the MMA for fluoride. The pH in the adsorption process affected the adsorption significantly. At neutral initial pH, the adsorption isotherm was well fitted with the Langmuir model, and the maximum adsorption capacity reached a high value of 41.8 mg/g. At a constant pH of 3, multilayer adsorption of fluoride occurred due to the abundant positive surface charges on the MMA, and the adsorption isotherm was well fitted with the Freundlich model. The MMA had a fast adsorption rate, and adsorption equilibrium was achieved within 2 min. The adsorption kinetics followed a quasi-second order model. The regeneration of the MMA was easy and fast, and can be completed within 2 min. After 10 recycles, the fluoride removal efficiency of the MMA still remained high. These properties showed that the MMA is a promising adsorbent for fluoride removal.

  9. Incorporation and thermal evolution of rhodamine 6G dye molecules adsorbed in porous columnar optical SiO2 thin films.

    PubMed

    Sánchez-Valencia, Juan R; Blaszczyk-Lezak, Iwona; Espinós, Juan P; Hamad, Said; González-Elipe, Agustín R; Barranco, Angel

    2009-08-18

    Rhodamine 6G (Rh6G) dye molecules have been incorporated into transparent and porous SiO2 thin films prepared by evaporation at glancing angles. The porosity of these films has been assessed by analyzing their water adsorption isotherms measured for the films deposited on a quartz crystal monitor. Composite Rh6G/SiO2 thin films were prepared by immersion of a SiO2 thin film into a solution of the dye at a given pH. It is found that the amount of Rh6G molecules incorporated into the film is directly dependent on the pH of the solution and can be accounted for by a model based on the point of zero charge (PZC) concepts originally developed for colloidal oxides. At low pHs, the dye molecules incorporate in the form of monomers, while dimers or higher aggregates are formed if the pH increases. Depending on the actual preparation and treatment conditions, they also exhibit high relative fluorescence efficiency. The thermal stability of the composite films has been also investigated by characterizing their optical behavior after heating in an Ar atmosphere at increasing temperatures up to 275 degrees C. Heating induces a progressive loss of active dye molecules, a change in their agglomeration state, and an increment in their relative fluorescence efficiency. The obtained Rh6G/SiO2 composite thin films did not disperse the light and therefore can be used for integration into optical and photonic devices.

  10. Experimental Measurement of Water Bands in Anhydrous Minerals to Improve Modeling of Adsorbed and Bound Water on the Regoliths of Inner Solar System Airless Bodies

    NASA Astrophysics Data System (ADS)

    Young, B. C.

    2015-12-01

    Investigating the characteristics of H2O/OH-absorption bands is critical for understanding their abundance and adherence to remotely observed surfaces. Our goal is to experimentally measure the spectra of anhydrous minerals in thin section and as powders to distinguish between internal H2O, surface adsorbed H2O, adsorbed OH, and OH that was formed as a result of irradiation. From these spectra, we are developing a model that will allow us to better deconvolve the abundance of adsorbed H2O and internally bound OH-/H2O in these materials. With this model, we aim to be able to remove the effects of terrestrial adsorbed H2O, thus enabling us to use the dry spectra to model these materials in the regoliths of airless bodies found in the inner solar system. To complete this task, we created un-mounted thin sections of two ordinary chondrite meteorites (Kilabo - LL6 and Gao-Guenie - H5) and eight ultramafic and banded rocks collected at the Stillwater Intrusion to serve as analogs for the Earth's moon. These rocks host an abundance of three key mineral series of interest: olivine, pyroxene, and plagioclase. We conducted EDS scans of each rock to create an elemental map and assess the specific mineral composition of phases in each sample. Transmittance spectra of each thin section were also collected from the visible through mid-IR range using the FTIR microscope to characterize bound water in each sample. These thin sections will be heated up to ~1000°C in a vacuum to remove any internal water and will be measured in transmission for a second time to determine their true anhydrous spectral baseline. Subsets of the samples have been powdered and will be measured under ultra-high vacuum conditions at temperatures ranging from ~293K to 650K to examine the spectral parameters for adsorbed terrestrial water on each sample. Ultimately, these powdered samples will be used for space weathering experiments to examine the nature of the OH- bands induced by irradiation.

  11. Vibrational frequency shifts of diatomic molecules in interaction with a Na + cation by ab initio calculations. Comparison with experiment on H 2 and N 2 adsorbed in NaA zeolite

    NASA Astrophysics Data System (ADS)

    Koubi, Laure; Blain, Monique; de Lara, Evelyne Cohen; Leclerq, Jean-Marie

    1994-01-01

    Ab initio calculations on H 2 and N 2 and on the same molecules in the presence of a Na + cation are presented. The equilibrium configuration and the vibrational frequency shift due to the interaction are calculated. The potential energy surfaces are obtained by local osculatory interpolations and extrapolations. The vibrational frequencies are calculated by the Numerov—Cooley method. The direction of the frequency shift is found to be related to the orientation of the diatomic molecule with respect to the cation. The results are compared with experimental data on induced infrared bands of H 2 and N 2 adsorbed in NaA zeolite.

  12. Distribution of binding energies of a water molecule in the water liquid-vapor interface

    SciTech Connect

    Chempath, Shaji; Pratt, Lawrence R

    2008-01-01

    Distributions of binding energies of a water molecule in the water liquid-vapor interface are obtained on the basis of molecular simulation with the SPC/E model of water. These binding energies together with the observed interfacial density profile are used to test a minimally conditioned Gaussian quasi-chemical statistical thermodynamic theory. Binding energy distributions for water molecules in that interfacial region clearly exhibit a composite structure. A minimally conditioned Gaussian quasi-chemical model that is accurate for the free energy of bulk liquid water breaks down for water molecules in the liquid-vapor interfacial region. This breakdown is associated with the fact that this minimally conditioned Gaussian model would be inaccurate for the statistical thermodynamics of a dilute gas. Aggressive conditioning greatly improves the performance of that Gaussian quasi-chemical model. The analogy between the Gaussian quasi-chemical model and dielectric models of hydration free energies suggests that naive dielectric models without the conditioning features of quasi-chemical theory will be unreliable for these interfacial problems. Multi-Gaussian models that address the composite nature of the binding energy distributions observed in the interfacial region might provide a mechanism for correcting dielectric models for practical applications.

  13. Oxygen isotope fractionation effects in soil water via interaction with cations (Mg, Ca, K, Na) adsorbed to phyllosilicate clay minerals

    NASA Astrophysics Data System (ADS)

    Oerter, Erik; Finstad, Kari; Schaefer, Justin; Goldsmith, Gregory R.; Dawson, Todd; Amundson, Ronald

    2014-07-01

    In isotope-enabled hydrology, soil and vadose zone sediments have been generally considered to be isotopically inert with respect to the water they host. This is inconsistent with knowledge that clay particles possessing an electronegative surface charge and resulting cation exchange capacity (CEC) interact with a wide range of solutes which, in the absence of clays, have been shown to exhibit δ18O isotope effects that vary in relation to the ionic strength of the solutions. To investigate the isotope effects caused by high CEC clays in mineral-water systems, we created a series of monominerallic-water mixtures at gravimetric water contents ranging from 5% to 32%, consisting of pure deionized water of known isotopic composition with homoionic (Mg, Ca, Na, K) montmorillonite. Similar mixtures were also created with quartz to determine the isotope effect of non-, or very minimally-, charged mineral surfaces. The δ18O value of the water in these monominerallic soil analogs was then measured by isotope ratio mass spectrometry (IRMS) after direct headspace CO2 equilibration. Mg- and Ca-exchanged homoionic montmorillonite depleted measured δ18O values up to 1.55‰ relative to pure water at 5% water content, declining to 0.49‰ depletion at 30% water content. K-montmorillonite enriched measured δ18O values up to 0.86‰ at 5% water content, declining to 0.11‰ enrichment at 30% water. Na-montmorillonite produces no measureable isotope effect. The isotope effects observed in these experiments may be present in natural, high-clay soils and sediments. These findings have relevance to the interpretation of results of direct CO2-water equilibration approaches to the measurement of the δ18O value of soil water. The adsorbed cation isotope effect may bear consideration in studies of pedogenic carbonate, plant-soil water use and soil-atmosphere interaction. Finally, the observed isotope effects may prove useful as molecular scale probes of the nature of mineral-water

  14. Adsorbent phosphates

    NASA Technical Reports Server (NTRS)

    Watanabe, S.

    1983-01-01

    An adsorbent which uses as its primary ingredient phosphoric acid salts of zirconium or titanium is presented. Production methods are discussed and several examples are detailed. Measurements of separating characteristics of some gases using the salts are given.

  15. AFM observation of monatomic step movements on NaCl(001) with the help of adsorbed water

    NASA Astrophysics Data System (ADS)

    Shindo, H.; Ohashi, M.; Baba, K.; Seo, A.

    1996-06-01

    AFM observation of cleaved NaCl(001) surface in air at room temperature revealed spontaneous motion of monatomic steps, depending on relative humidity, to minimize one-dimensional surface free energy. While step motion was recognized only at the parts having large positive curvature at 52% humidity, even straight steps moved at 57%. The motion was accelerated toward higher humidity. It is suggested that adsorbed water having 2-dimensional nature transports ions at the surface. By holding the AFM tip at one place, salt solution was collected beneath the tip by capillary action. Upon removal of the tip, the solution droplet turned into a bell-shaped hillock of salt as high as 78 nm. Although the hillocks gradually flattened spontaneously, the method has potential application in pattern formation.

  16. Single-walled carbon nanohorn as new solid-phase extraction adsorbent for determination of 4-nitrophenol in water sample.

    PubMed

    Zhu, Shuyun; Niu, Wenxin; Li, Haijuan; Han, Shuang; Xu, Guobao

    2009-10-15

    Single-walled carbon nanohorn (SWCNH) was developed as new adsorbent for solid-phase extraction using 4-nitrophenol as representative. The unique exoteric structures and high surface area of SWCNH allow extracting a large amount of 4-nitrophenol over a short time. Highly sensitive determination of 4-nitrophenol was achieved by linear sweep voltammetry after only 120s extraction. The calibration plot for 4-nitrophenol determination is linear in the range of 5.0x10(-8) M-1.0x10(-5) M under optimum conditions. The detection limit is 1.1x10(-8) M. The proposed method was successfully employed to determine 4-nitrophenol in lake water samples, and the recoveries of the spiked 4-nitrophenol were excellent (92-106%).

  17. Magnetic nanoporous carbon as an adsorbent for the extraction of phthalate esters in environmental water and aloe juice samples.

    PubMed

    Liu, Li; Hao, Yunhui; Ren, Yiqian; Wang, Chun; Wu, Qiuhua; Wang, Zhi

    2015-05-01

    In this work, magnetic nanoporous carbon with high surface area and ordered structure was synthesized using cheap commercial silica gel as template and sucrose as the carbon source. The prepared magnetic nanoporous carbon was firstly used as an adsorbent for the extraction of phthalate esters, including diethyl phthalate, diallyl phthalate, and di-n-propyl-phthalate, from lake water and aloe juice samples. Several parameters that could affect the extraction efficiency were optimized. Under the optimum conditions, the limit of detection of the method (S/N = 3) was 0.10 ng/mL for water sample and 0.20 ng/mL for aloe juice sample. The linearity was observed over the concentration range of 0.50-150.0 and 1.0-200.0 ng/mL for water and aloe juice samples, respectively. The results showed that the magnetic nanoporous carbon has a high adsorptive capability toward the target phthalate esters in water and aloe juice samples.

  18. Use of industrial by-products and natural media to adsorb nutrients, metals and organic carbon from drinking water.

    PubMed

    Grace, Maebh A; Healy, Mark G; Clifford, Eoghan

    2015-06-15

    Filtration technology is well established in the water sector but is limited by inability to remove targeted contaminants, found in surface and groundwater, which can be damaging to human health. This study optimises the design of filters by examining the efficacy of seven media (fly ash, bottom ash, Bayer residue, granular blast furnace slag (GBS), pyritic fill, granular activated carbon (GAC) and zeolite), to adsorb nitrate, ammonium, total organic carbon (TOC), aluminium, copper (Cu) and phosphorus. Each medium and contaminant was modelled to a Langmuir, Freundlich or Temkin adsorption isotherm, and the impact of pH and temperature (ranging from 10 °C to 29 °C) on their performance was quantified. As retention time within water filters is important in contaminant removal, kinetic studies were carried out to observe the adsorption behaviour over a 24h period. Fly ash and Bayer residue had good TOC, nutrient and Cu adsorption capacity. Granular blast furnace slag and pyritic fill, previously un-investigated in water treatment, showed adsorption potential for all contaminants. In general, pH or temperature adjustment was not necessary to achieve effective adsorption. Kinetic studies showed that at least 60% of adsorption had occurred after 8h for all media. These media show potential for use in a multifunctional water treatment unit for the targeted treatment of specific contaminants.

  19. Light emission in water-containing cocrystals: the influence of water molecules on the fluorescence properties of a Schiff-base molecule.

    PubMed

    Zhou, Feng; Tan, Pengli; Ma, Yong; Li, Youyong; Li, Najun; Li, Hua; Wang, Lihua; Gu, Hongwei; Xu, Qingfeng; Lu, Jianmei

    2014-01-01

    In the presence or absence of water, a Schiff-base compound, 4-amino-3-(2-(2-hydroxybenzylidene)hydrazinyl)-1H-1,2,4-triazole-5(4H)-thione (HATT), forms different crystalline states (HATT, HATT·2H2O, and a lamellar structure, m-HATT·nH2O), which show different luminescence emission properties. Herein, we investigate the emission of HATT and the role of water molecules. A water molecule, which acts as both a hydrogen-bond acceptor and -donor, enlarges the distance between adjacent HATT molecules and hinders non-radiative decay pathways.

  20. Cleaning Water Contaminated with Heavy Metal Ions Using Pyrolyzed Biochar Adsorbents

    EPA Science Inventory

    The extraction of pollutants from water using activated biochar materials is a low cost, sustainable approach for providing safe water in developing countries. The adsorption of copper ions, Cu (II), onto banana peels that were dried, pyrolyzed and activated was studied and compa...

  1. Extending the range of low energy electron diffraction (LEED) surface structure determination: Co-adsorbed molecules, incommensurate overlayers and alloy surface order studied by new video and electron counting LEED techniques

    SciTech Connect

    Ogletree, D.F.

    1986-11-01

    LEED multiple scattering theory is briefly summarized, and aspects of electron scattering with particular significance to experimental measurements such as electron beam coherence, instrument response and phonon scattering are analyzed. Diffuse LEED experiments are discussed. New techniques that enhance the power of LEED are described, including a real-time video image digitizer applied to LEED intensity measurements, along with computer programs to generate I-V curves. The first electron counting LEED detector using a ''wedge and strip'' position sensitive anode and digital electronics is described. This instrument uses picoampere incident beam currents, and its sensitivity is limited only by statistics and counting times. Structural results on new classes of surface systems are presented. The structure of the c(4 x 2) phase of carbon monoxide adsorbed on Pt(111) has been determined, showing that carbon monoxide molecules adsorb in both top and bridge sites, 1.85 +- 0.10 A and 1.55 +- 0.10 A above the metal surface, respectively. The structure of an incommensurate graphite overlayer on Pt(111) is analyzed. The graphite layer is 3.70 +- 0.05 A above the metal surface, with intercalated carbon atoms located 1.25 +- 0.10 A above hollow sites supporting it. The (2..sqrt..3 x 4)-rectangular phase of benzene and carbon monoxide coadsorbed on Pt(111) is analyzed. Benzene molecules adsorb in bridge sites parallel to and 2.10 +- 0.10 A above the surface. The carbon ring is expanded, with an average C-C bond length of 1.72 +- 0.15 A. The carbon monoxide molecules also adsorb in bridge sites. The structure of the (..sqrt..3 x ..sqrt..3) reconstruction on the (111) face of the ..cap alpha..-CuAl alloy has been determined.

  2. Quantum Tunneling of Water in Beryl: A New State of the Water Molecule.

    PubMed

    Kolesnikov, Alexander I; Reiter, George F; Choudhury, Narayani; Prisk, Timothy R; Mamontov, Eugene; Podlesnyak, Andrey; Ehlers, George; Seel, Andrew G; Wesolowski, David J; Anovitz, Lawrence M

    2016-04-22

    Using neutron scattering and ab initio simulations, we document the discovery of a new "quantum tunneling state" of the water molecule confined in 5 Å channels in the mineral beryl, characterized by extended proton and electron delocalization. We observed a number of peaks in the inelastic neutron scattering spectra that were uniquely assigned to water quantum tunneling. In addition, the water proton momentum distribution was measured with deep inelastic neutron scattering, which directly revealed coherent delocalization of the protons in the ground state.

  3. Quantum Tunneling of Water in Beryl. A New State of the Water Molecule

    DOE PAGES

    Kolesnikov, Alexander I.; Reiter, George F.; Choudhury, Narayani; ...

    2016-04-22

    When using neutron scattering and ab initio simulations, we document the discovery of a new “quantum tunneling state” of the water molecule confined in 5 Å channels in the mineral beryl, characterized by extended proton and electron delocalization. We observed a number of peaks in the inelastic neutron scattering spectra that were uniquely assigned to water quantum tunneling. Additionally, the water proton momentum distribution was measured with deep inelastic neutron scattering, which directly revealed coherent delocalization of the protons in the ground state.

  4. Surfactant-modified alumina: an efficient adsorbent for malachite green removal from water environment.

    PubMed

    Das, Asit K; Saha, Sandip; Pal, Anjali; Maji, Sanjoy K

    2009-07-15

    Surface of alumina was modified with sodium dodecyl sulfate (SDS), an anionic surfactant. The surfactant-modified alumina (SMA) was characterized by FTIR and thermal analysis. The SMA was then used for the removal of malachite green (MG; Basic Green 4), a well-known toxic cationic dye from aqueous environment. The removal of MG takes place in the micellar structure formed on alumina surface, and the process is called adsolubilization. All the studies were carried out in batch mode. The kinetic studies showed that 1 h contact time was sufficient to attain equilibrium. SMA was very efficient to remove MG up to 99% under optimum conditions. The concentration range of MG was 20-100 mg/L. The isotherm studies showed that it follows Langmuir model better than the Freundlich model. The maximum adsorption capacity was 185 mg/g. The effects of various parameters such as pH, presence of interfering ions (Cl-, NO3-, H2PO4-, SO4(2-), Fe2+, Ca2+) and organics (pesticides such as 2,4-dichlorophenoxyacetic acid, atrazine, endosulfan, and humic acid) are evaluated. It was observed that H2PO4-, Fe2+, endosulfan, and humic acid have maximum interference. Desorption of MG from exhausted SMA using acetone, and its reuse was studied. The regenerated adsorbent shows approximately 80% efficiency on the removal of MG. The usability of SMA for the removal of MG from real wastewater was also examined. The kinetic equilibrium was attained within 1 h and the removal could be achieved up to approximately 95% at a dose of 20 g/L. The adsorption followed Freundlich isotherm model better than the Langmuir model.

  5. Electron capture by bare ions on water molecules

    NASA Astrophysics Data System (ADS)

    Rivarola, Roberto; Montenegro, Pablo; Monti, Juan; Fojón, Omar

    2016-05-01

    Single electron capture from water molecules by impact of bare ions is theoretically investigated at intermediate and high collision energies. This reaction is of fundamental importance to determine the deposition of energy in biological matter irradiated with ion beams (hadrontherapy), dominating other ionizing processes of the target at low-intermediate impact velocities and giving principal contributions to the energetic region where electronic stopping power maximizes. The dynamics of the interaction between the aggregates is described within the one active-electron continuum distorted wave-eikonal initial state theory. The orbitals of the target in the ground state are represented using the approximate self-consistent complete neglect of differential orbitals (SC-CNDO) model. The contribution of different molecular orbitals on the partial cross sections to selected n-principal quantum number projectile states is discriminated as well as the collaboration of these n-states on total cross sections. The latter ones are dominated by capture to n=1 states at high enough energies decreasing their contribution as n increases.

  6. O^- channels of Dissociative Electron Attachment to water and heavy water molecules

    NASA Astrophysics Data System (ADS)

    Adaniya, Hidehito; Rudek, Benedikt; Osipov, Timur; Lee, Sun; Weber, Thorsten; Hertlein, Marcus; Schoeffler, Markus; Prior, Mike; Belkacem, Ali

    2009-05-01

    A COLTRIM technique is modified to measure the kinetic energy and angular distribution of O^- ions arising from dissociative electron attachment to water and heavy water molecules. A low energy pulsed electron, an effusive water target, a pulsed extraction plate are used in combination with the COLTRIMS spectrometer. The spectrometer carries an electrostatic lens system to compensate the effusiveness of the target. This technique is applied to study the O^- channels in the three Feshbach resonances of water and heavy water anion. The measured kinetic energy release will give the energy partitioning among the fragments, and the means to identify the two-body and three-body breakup channels. The angular distribution of the O^- ions with respect to the electron beam is found to reflect well the breakup dynamics of the H2O^- at the dissociation. The experimental results are compared with the theoretical predictions.

  7. The Effect of monoglycerides on structural and topographical characteristics of adsorbed beta-casein films at the air-water interface.

    PubMed

    Fernández, Marta Cejudo; Sánchez, Cecilio Carrera; Rodríguez Niño, M Rosario; Rodríguez Patino, Juan M

    2006-02-01

    The effect of monoglycerides (monopalmitin and monoolein) on the structural and topographical characteristics of beta-casein adsorbed film at the air-water interface has been analyzed by means of surface pressure (pi)-area (A) isotherms and Brewster angle microscopy (BAM). At surface pressures lower than that for the beta-casein collapse (pi(c)(beta-casein)), attractive interactions between beta-casein and monoglycerides were observed. At higher surface pressures, the collapsed beta-casein is partially displaced from the interface by monoglycerides. However, beta-casein displacement by monoglycerides is not quantitative at the monoglyceride concentrations studied in this work. From the results derived from these experiments, we have concluded that interactions, miscibility, and displacement of proteins by monoglycerides in adsorbed mixed monolayers at the air-water interface depend on the particular protein-monoglyceride system, the interactions between film-forming components being higher for adsorbed than for spread films. The adsorbed films are more segregated than spread films, and both collapsed protein domains and monoglyceride domains in adsorbed films are smaller than for spread films.

  8. A theoretical study of the interaction of hydrogen and oxygen with palladium or gold adsorbed on pyridine-like nitrogen-doped graphene.

    PubMed

    Rangel, Eduardo; Magana, Luis Fernando; Sansores, Luis Enrique

    2014-12-15

    The interaction of H2 and O2 molecules in the presence of nitrogen-doped graphene decorated with either a palladium or gold atom was investigated by using density functional theory. It was found that two hydrogen molecules were adsorbed on the palladium atom. The interaction of these adsorbed hydrogen molecules with two oxygen molecules generates two hydrogen peroxide molecules first through a Eley-Rideal mechanism and then through a Langmuir-Hinshelwood mechanism. The barrier energies for this reaction were small; therefore, we expect that this process may occur spontaneously at room temperature. In the case of gold, a single hydrogen molecule is adsorbed and dissociated on the metal atom. The interaction of the dissociated hydrogen molecule on the surface with one oxygen molecule generates a water molecule. The competitive adsorption between oxygen and hydrogen molecules slightly favors oxygen adsorption.

  9. Phosphate Remediation and Recovery from Lake Water using Modified Iron Oxide-based Adsorbents

    EPA Science Inventory

    Adsorption behavior of Bayoxide ® E33 (E33) and three E33-modified sorbents for the removal of phosphate from lake water was investigated in this study. E33-modified sorbents were synthesized by coating with manganese and nanoparticles. Characterization was done by X-ray diffract...

  10. Proton magnetic relaxation study of the thermodynamic characteristics of water adsorbed by cellulose fibers

    NASA Astrophysics Data System (ADS)

    Grunin, Yu. B.; Grunin, L. Yu.; Masas, D. S.; Talantsev, V. I.; Sheveleva, N. N.

    2016-11-01

    The possibility of determining the thermodynamic parameters that characterize the sorption properties of cellulose and the state of water associated with its fibers is demonstrated using modern concepts of the structure of this vegetable polymer and methods based on theories of adsorption and NMR relaxation in heterogeneous systems.

  11. Magnetic spherical carbon as an efficient adsorbent for the magnetic extraction of phthalate esters from lake water and milk samples.

    PubMed

    Wu, Juanjuan; Wang, Chenhuan; Liang, Xinyu; Yang, Xiumin; Wang, Chun; Wu, Qiuhua; Wang, Zhi

    2017-03-29

    Magnetic spherical carbon was synthesized by a facile hydrothermal carbonization procedure with biomass glucose as the carbon precursor and nanoclusters iron colloid as magnetic precursor. The textures of the as-prepared magnetic spherical carbon were characterized by nitrogen adsorption-desorption isotherms, X-ray diffraction, transmission electron microscopy, scanning electron microscopy and vibration sample magnetometry. Results indicated that the magnetic spherical carbon possessed high surface area as well as strong magnetism, which endows the material with good adsorption capability and easy separation property. To assess its absorption performance, the magnetic spherical carbon was employed as adsorbent for the extraction and preconcentration of phthalate esters from lake water and milk samples before high-performance liquid chromatographic analysis. Some key parameters that could influence the enrichment efficiency were investigated. Under the optimum conditions, a good linearity was achieved with the linear correlation coefficients higher than 0.9973. The limits of detection (S/N = 3) were 0.05-0.08 ng mL(-1) for lake water and 0.1-0.2 ng mL(-1) for milk samples. The recoveries of the analytes for the method were in the range 80.1-112.6%. This article is protected by copyright. All rights reserved.

  12. Nano-silica fabricated with silver nanoparticles: antifouling adsorbent for efficient dye removal, effective water disinfection and biofouling control

    NASA Astrophysics Data System (ADS)

    Das, Sujoy K.; Khan, Md. Motiar R.; Parandhaman, T.; Laffir, Fathima; Guha, Arun K.; Sekaran, G.; Mandal, Asit Baran

    2013-05-01

    A nano-silica-AgNPs composite material is proposed as a novel antifouling adsorbent for cost-effective and ecofriendly water purification. Fabrication of well-dispersed AgNPs on the nano-silica surface, designated as NSAgNP, has been achieved through protein mediated reduction of silver ions at ambient temperature for development of sustainable nanotechnology. The coated proteins on AgNPs led to the formation of stable NSAgNP and protected the AgNPs from oxidation and other ions commonly present in water. The NSAgNP exhibited excellent dye adsorption capacity both in single and multicomponent systems, and demonstrated satisfactory tolerance against variations in pH and dye concentration. The adsorption mainly occurred through electrostatic interaction, though π-π interaction and pore diffusion also contributed to the process. Moreover, the NSAgNP showed long-term antibacterial activity against both planktonic cells and biofilms of Gram-negative Escherichia coli and Pseudomonas aeruginosa. The antibacterial activity of AgNPs retarded the initial attachment of bacteria on NSAgNP and thus significantly improved the antifouling properties of the nanomaterial, which further inhibited biofilm formation. Scanning electron and fluorescence microscopic studies revealed that cell death occurred due to irreversible damage of the cell membrane upon electrostatic interaction of positively charged NSAgNP with the negatively charged bacterial cell membrane. The high adsorption capacity, reusability, good tolerance, removal of multicomponent dyes and E. coli from the simulated contaminated water and antifouling properties of NSAgNP will provide new opportunities to develop cost-effective and ecofriendly water purification processes.A nano-silica-AgNPs composite material is proposed as a novel antifouling adsorbent for cost-effective and ecofriendly water purification. Fabrication of well-dispersed AgNPs on the nano-silica surface, designated as NSAgNP, has been achieved through

  13. Spectromicroscopy of C60 and azafullerene C59N: Identifying surface adsorbed water

    PubMed Central

    Erbahar, Dogan; Susi, Toma; Rocquefelte, Xavier; Bittencourt, Carla; Scardamaglia, Mattia; Blaha, Peter; Guttmann, Peter; Rotas, Georgios; Tagmatarchis, Nikos; Zhu, Xiaohui; Hitchcock, Adam P.; Ewels, Chris P.

    2016-01-01

    C60 fullerene crystals may serve as important catalysts for interstellar organic chemistry. To explore this possibility, the electronic structures of free-standing powders of C60 and (C59N)2 azafullerenes are characterized using X-ray microscopy with near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, closely coupled with density functional theory (DFT) calculations. This is supported with X-ray photoelectron spectroscopy (XPS) measurements and associated core-level shift DFT calculations. We compare the oxygen 1s spectra from oxygen impurities in C60 and C59N, and calculate a range of possible oxidized and hydroxylated structures and associated formation barriers. These results allow us to propose a model for the oxygen present in these samples, notably the importance of water surface adsorption and possible ice formation. Water adsorption on C60 crystal surfaces may prove important for astrobiological studies of interstellar amino acid formation. PMID:27748425

  14. Spectromicroscopy of C60 and azafullerene C59N: Identifying surface adsorbed water

    NASA Astrophysics Data System (ADS)

    Erbahar, Dogan; Susi, Toma; Rocquefelte, Xavier; Bittencourt, Carla; Scardamaglia, Mattia; Blaha, Peter; Guttmann, Peter; Rotas, Georgios; Tagmatarchis, Nikos; Zhu, Xiaohui; Hitchcock, Adam P.; Ewels, Chris P.

    2016-10-01

    C60 fullerene crystals may serve as important catalysts for interstellar organic chemistry. To explore this possibility, the electronic structures of free-standing powders of C60 and (C59N)2 azafullerenes are characterized using X-ray microscopy with near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, closely coupled with density functional theory (DFT) calculations. This is supported with X-ray photoelectron spectroscopy (XPS) measurements and associated core-level shift DFT calculations. We compare the oxygen 1s spectra from oxygen impurities in C60 and C59N, and calculate a range of possible oxidized and hydroxylated structures and associated formation barriers. These results allow us to propose a model for the oxygen present in these samples, notably the importance of water surface adsorption and possible ice formation. Water adsorption on C60 crystal surfaces may prove important for astrobiological studies of interstellar amino acid formation.

  15. Banana peel as an adsorbent for removing atrazine and ametryne from waters.

    PubMed

    Silva, Claudineia R; Gomes, Taciana F; Andrade, Graziela C R M; Monteiro, Sergio H; Dias, Ana C R; Zagatto, Elias A G; Tornisielo, Valdemar L

    2013-03-13

    The feasibility of using banana peel for removal of the pesticides atrazine and ametryne from river and treated waters has been demonstrated, allowing the design of an efficient, fast, and low-cost strategy for remediation of polluted waters. The conditions for removal of these pesticides in a laboratory scale were optimized as sample volume = 50 mL, banana mass = 3.0 g, stirring time = 40 min, and no pH adjustment necessary. KF(sor) values for atrazine and ametryne were evaluated as 35.8 and 54.1 μg g(-1) (μL mL(-1)) by using liquid scintillation spectrometry. Adsorption was also evaluated by LC-ESI-MS/MS. As quantification limits were 0.10 and 0.14 μg L(-1) for both pesticides, sample preconcentration was not needed. Linear analytical curves (up to 10 μg L(-1)), precise results (RSD < 4.5%), good recoveries (82.9-106.6%), and a > 90% removal efficiency were attained for both pesticides. Water samples collected near an intensively cultivated area were adequately remedied.

  16. Cu-Zn powders as potential Cr(VI) adsorbents for drinking water.

    PubMed

    Kaprara, E; Seridou, P; Tsiamili, V; Mitrakas, M; Vourlias, G; Tsiaoussis, I; Kaimakamis, G; Pavlidou, E; Andritsos, N; Simeonidis, K

    2013-11-15

    This work examines the possibility of applying CuZn alloys as a reducing medium for the efficient removal of hexavalent chromium from drinking water. In an effort to develop a route for producing powders of CuZn alloys under mild conditions and investigate the optimum composition for such application, a series of alloys in the form of powders were prepared, by a sequence of Cu and Zn ball-milling and low temperature annealing. Batch Cr(VI) removal tests, performed to evaluate and compare the efficiency of the products under typical natural water parameters (pH 7 and natural-like water), indicated that the best performing material have a composition around 50 wt% Cu. The dominant reduction mechanisms are both the corrosion of the alloy surface and the electron transfer to the solution. The behavior of granulated CuZn media was tested in rapid-scale column tests using the commercial KDF which verified the high potential of CuZn alloys in Cr(VI) removal. Nevertheless, Cu and Zn leaching problems should be also considered.

  17. Modelling and experimental investigation on the application of water super adsorbents in waste air biofilters.

    PubMed

    Danaee, Soroosh; Fazaelipoor, Mohammad Hassan; Gholami, Abdollah; Ataei, Seyed Ahmad; Afzali, Daryoush

    2015-01-01

    In this research work, a synthetic water super absorbent polymer was included in the bed of a perlite-based biofilter for the removal of ethanol from air. The performance of this biofilter was compared with the performance of a control perlite-based biofilter lacking the water super absorbent. With the empty bed residence time of 2 min, both biofilters were able to remove more than 90% of the entering pollutant with the concentration of 1 g /m3, when regular moistening was applied. After last irrigation on day 23, the performance of the control biofilter was unchanged until day 35. From day 36 onwards, the control biofilter lost its activity gradually and became totally inactive on day 45. The performance of the super absorbent containing biofilter, however, was unchanged until day 58 before starting to lose its activity. A mechanistic model was developed to describe the performance of a biofilter under drying effects. The model could predict the trends of experimental results reasonably well. The model was also applied to predict the trends of experimental data from a published paper on the removal of hexane in a perlite/super absorbent containing biofilter.

  18. A nano-sized container for specific encapsulation of isolated water molecules.

    PubMed

    Lavendomme, Roy; Marcélis, Lionel; Wouters, Johan; Luhmer, Michel; Jabin, Ivan

    2016-12-01

    A calix[4]arene-based molecular box was synthesized. Its properties were characterized through XRD and extensive NMR studies. This receptor is able to encapsulate specifically two isolated water molecules in both non-protic and protic solvents. This is a consequence of high size, geometric and electronic complementarity between the host and the water molecules.

  19. Key Role of Active-Site Water Molecules in Bacteriorhodopsin Proton-Transfer Reactions

    SciTech Connect

    Bondar, A.N.; Baudry, Jerome Y; Suhai, Sandor; Fischer, S.; Smith, Jeremy C

    2008-10-01

    The functional mechanism of the light-driven proton pump protein bacteriorhodopsin depends on the location of water molecules in the active site at various stages of the photocycle and on their roles in the proton-transfer steps. Here, free energy computations indicate that electrostatic interactions favor the presence of a cytoplasmic-side water molecule hydrogen bonding to the retinal Schiff base in the state preceding proton transfer from the retinal Schiff base to Asp85. However, the nonequilibrium nature of the pumping process means that the probability of occupancy of a water molecule in a given site depends both on the free energies of insertion of the water molecule in this and other sites during the preceding photocycle steps and on the kinetic accessibility of these sites on the time scale of the reaction steps. The presence of the cytoplasmic-side water molecule has a dramatic effect on the mechanism of proton transfer: the proton is channeled on the Thr89 side of the retinal, whereas the transfer on the Asp212 side is hindered. Reaction-path simulations and molecular dynamics simulations indicate that the presence of the cytoplasmic-side water molecule permits a low-energy bacteriorhodopsin conformer in which the water molecule bridges the twisted retinal Schiff base and the proton acceptor Asp85. From this low-energy conformer, proton transfer occurs via a concerted mechanism in which the water molecule participates as an intermediate proton carrier.

  20. Adsorption of Small Molecules at Water--Hexane and Water--Membrane Interfaces

    NASA Astrophysics Data System (ADS)

    Wilson, Michael A.

    1996-03-01

    The interaction of solutes with aqueous interfaces plays a significant role in a variety of physical processes, including general anesthesia and atmospheric chemistry. We present molecular dynamics results for the transfer of several small solutes across water liquid--vapor, water--hexane and water--GMO bilayer membrane interfaces. (A. Pohorille and M. A. Wilson, J. Chem. Phys. (in press, 1995).)^, (A. Pohorille, P. CIeplak, and M. A. Wilson, Chem. Phys. (in press, 1995).) The free energies of transferring small polar molecules across the interface exhibit fairly deep minima while those of nonpolar molecules do not. This is due to a balance between nonelectrostatic contributions --- primarily the work required to create a cavity large enough to accommodate the solute --- and the solute--solvent electrostatic interactions.^1 The surface excess of solute is calculated and compared with experimental results from the Gibbs adsorption isotherm. The interfacial solubilities correlate with measured anesthetic potencies of these compounds, implying that the binding sites for anesthetics are located near the water--membrane interface.

  1. Perfluorobutane sulfonic acid hydration and interactions with O2 adsorbed on Pt3.

    PubMed

    Yan, Liuming; Balbuena, Perla B; Seminario, Jorge M

    2006-04-06

    The side chain of NAFION, a proton conductive membrane used as electrolyte in low-temperature fuel cells, is modeled with perfluorobutane sulfonic acid. Density functional theory is used to characterize structures and energetics of hydration of the model system interacting with a proton solvated with up to 24 water molecules and analyze interactions of some of these hydrated complexes with O(2) adsorbed on Pt(3). It is found that at least three water molecules are needed to ionize the sulfonic acid, and higher degrees of hydration induce the formation of cages where the water molecules are held together via complex hydrogen-bond networks. The interaction between the complex formed by the ionized acid and the hydrated proton, in contact with a bridge-adsorbed O(2)-Pt(3), promotes the protonation of the adsorbed O(2). Upon protonation, the O(2)-Pt(3) system evolves from hydrophobic to hydrophilic behavior, which may facilitate further interfacial contact.

  2. Competitive Adsorption of Naphthenic Acids and Polyaromatic Molecules at a Toluene-Water Interface.

    PubMed

    Teklebrhan, Robel B; Jian, Cuiying; Choi, Phillip; Xu, Zhenghe; Sjöblom, Johan

    2016-12-22

    The early-stage competitive co-adsorption of interfacially active naphthenic acids (NAs) and polyaromatic (PA) molecules to a toluene-water interface from the bulk toluene phase was studied using molecular dynamics (MD) simulation. The NA molecules studied had the same polar functional group but different cycloaliphatic nonpolar tails, and a perylene bisimide (PBI)-based molecule was used as a representative PA compound. The results from our simulations suggest that the size and structural features of NA molecules greatly influence the interfacial activity of PA molecules and partitioning of NA molecules at the toluene-water interface. At low concentrations of PA (∼2.3 wt %) and NA (∼0.4 wt %) molecules, NA molecules containing large cycloaliphatic rings (e.g., four rings) or with a very long aliphatic tail (e.g., carbon chain length of 14) were observed to impede the migration of PA molecules to the interface, whereas small NA molecules containing two cycloaliphatic rings had little effect on the adsorption of PA molecules at the toluene-water interface. At high NA concentrations, the adsorption of PA molecules (∼5.75-17.25 wt %) was greatly hindered by the presence of small NA molecules (∼1.6-4.8 wt %) due to the solvation of PA nanoaggregates in the bulk. Adsorption mechanisms of PA and NA molecules at toluene-water interfaces were clarified through a detailed analysis on the interactions among different species in the system. The results obtained from this work provide insights into designing appropriate chemical demulsifiers or co-demulsifiers for breaking water-in-oil emulsions of great industrial applications.

  3. Subdivision of phase space for anisotropically interacting water molecules

    NASA Astrophysics Data System (ADS)

    Epifanov, S. Yu.; Vigasin, A. A.

    An efficient numerical algorithm is employed which enables one to perform multidimensional integrations of complicated integrands. Temperature dependence of the second virial coefficient for water is reproduced using the Matsuoka Clementi Yoshimine intermolecular water water potential. Metastable states are shown to occupy significant domain in the water dimer phase space.

  4. Mechanism of dialkyl phthalates removal from aqueous solution using γ-cyclodextrin and starch based polyurethane polymer adsorbents.

    PubMed

    Okoli, Chukwunonso Peter; Adewuyi, Gregory Olufemi; Zhang, Qian; Diagboya, Paul N; Guo, Qingjun

    2014-12-19

    Phthalate esters have been known as potent endocrine disruptors and carcinogens; and their removal from water have been of considerable concern recently. In the present study, γ-cyclodextrin polyurethane polymer (GPP), γ-cyclodextrin/starch polyurethane copolymer (GSP), and starch polyurethane polymer (SPP) have been synthesized and characterized. Their adsorption efficiencies for the removal of dimethyl phthalate (DMP) and diethyl phthalate (DEP) from aqueous solutions were investigated. The characterization results showed the success of the synthesis. The isotherms were L-type, and both the Langmuir and Freundlich adsorption isotherm gave good fittings to the adsorption data. Adsorption mechanisms suggested that these adsorbents spontaneously adsorb phthalate molecules driven mainly by enthalpy change, and the adsorption process was attributed to multiple adsorbent-adsorbate interactions such as hydrogen bonding, π-π stacking, and pore filling. The results showed that starch and γ-cyclodextrin polyurethane polymer adsorbents have excellent potential as adsorbent materials for the removal of phthalates from the contaminated water.

  5. Regenerable adsorbents for removal of arsenic from contaminated waters and synthesis and characterization of multifunctional magnetic nanoparticles for environmental and biomedical applications

    NASA Astrophysics Data System (ADS)

    Verdugo Gonzalez, Brenda

    The present work is divided into two sections. The first section deals with the synthesis of regenerable adsorbents for the removal of arsenic from contaminated waters. An adsorbent based on carboxymethylated polyethylenimine grafted agarose gels was synthesized and characterized as a regenerable synthetic ferric oxide adsorbent with high capacity for arsenate ions at pH 3.0. Similarly, four metal ion chelating adsorbents based on dipicolylamine were synthesized and characterized with respect to their Cu(II), Fe(III) and As(V) adsorption capacities. The most efficient adsorbents were Nov-PEI-DPA and Nov-TREN-DPA. Additionally, a commercial ion exchange resin was modified with permanganate to oxidize arsenite into arsenate. A complete oxidation-adsorption system was proposed in which a column packed with the oxidation resin was connected in series with an adsorbent column composed of the polyethylenimine grafted agarose gels. The second section involved work with magnetic nanoparticles. First, composite adsorbents consisting of magnetic particles encapsulated within agarose beads with and without grafted iminodiacetic acid (IDA) chelating groups were synthesized. The adsorption capacity of the adsorbents for Cu(II), Fe(III) and As(V) at different concentrations was investigated. Batch experiments were carried out to determine the Fe(III) and As(V) adsorption isotherms for the magnetic Novarose-IDA. Regenerability of the adsorbent was achieved with a pH change of the inlet solution, without affecting its magnetic or adsorption properties. Magnetic composite particles were synthesized for biomedical applications. First, magnetic nanoparticles were coated with silica and then used for gold nanoshell production. These nanoshells were functionalized with a Brij S10 derivative, containing carboxylic groups, using dodecanethiol as a bridging agent to incorporate a fluorescent biomolecule. Finally, magnetic and gold particles were encapsulated in PLGA nanoparticles

  6. Synthesis, characterization, and evaluation of simple aluminum-based adsorbents for fluoride removal from drinking water.

    PubMed

    Du, Junyi; Sabatini, David A; Butler, Elizabeth C

    2014-04-01

    Simple aluminum (hydr)oxides and layered double hydroxides were synthesized using common chemicals and equipment by varying synthesis temperature, concentrations of extra sulfate and citrate, and metal oxide amendments. Aluminum (hydr)oxide samples were aged at either 25 or 200°C during synthesis and, in some cases, calcined at 600 °C. Despite yielding increased crystallinity and mineral phase changes, higher temperatures had a generally negative effect on fluoride adsorption. Addition of extra sulfate during synthesis of aluminum (hydr)oxides led to significantly higher fluoride adsorption capacity compared to aluminum (hydr)oxides prepared with extra citrate or no extra ligands. X-ray diffraction results suggest that extra sulfate led to the formation of both pseudoboehmite (γ-AlOOH) and basaluminite (Al4SO4(OH)10⋅4H2O) at 200 °C; energy dispersive X-ray spectroscopy confirmed the presence of sulfur in this solid. Treatment of aluminum (hydr)oxides with magnesium, manganese, and iron oxides did not significantly impact fluoride adsorption. While layered double hydroxides exhibited high maximum fluoride adsorption capacities, their adsorption capacities at dissolved fluoride concentrations close to the World Health Organization drinking water guideline of 1.5 mg L(-1) were much lower than those for the aluminum (hydr)oxides.

  7. Multispectral actinometry of water and water-derivative molecules in moist, inert gas discharge plasmas

    NASA Astrophysics Data System (ADS)

    Bernatskiy, A. V.; Ochkin, V. N.; Kochetov, I. V.

    2016-10-01

    A new version of optical actinometry (OA) is used to determine the concentrations of water molecules and their fragments in hollow cathode discharge plasma in moist inert gases. Use is made of two actinometer particles, namely, the atoms Xe and Ar, for concurrent measurements of the concentrations of the H2O molecule and its fragments O, H, and OH. A self-consistent method is suggested for the determination of particle concentrations with due regard for the quenching of the emitting states. The temporal behavior of particles during discharge glow is studied. Noted are fast variations (lasting from a few to a few tens of s) in the concentrations of all the particles, followed by their stabilization (within a few to a few tens of mins). The scheme of the processes responsible for the observed dynamics of the plasma composition is discussed.

  8. Experimental Study of Water Cluster Molecules with Relevance to Mesospheric Clouds

    NASA Astrophysics Data System (ADS)

    Robertson, Scott; Sternovsky, Zoltan; Horanyi, Mihaly

    2000-10-01

    We have begun an experimental investigation of the properties of the water cluster molecules responsible for clouds occurring in the polar mesopause. These clusters disturb the charge balance in the ionosphere by attaching electrons which then creates localized reductions in the electron density. A supersonic nozzle sprays a mixture of water vapor and argon into vacuum and the expansion leads to condensation of clusters with 4 to 11 water molecules. Initial measurements are of the collision cross section of these molecules with neutral gas. The cross sections have a minimum at six waters consistent with the tighter molecular arrangement predicted for this cluster number. Additional measurements are underway for charging processes.

  9. Regenerative adsorbent heat pump

    NASA Technical Reports Server (NTRS)

    Jones, Jack A. (Inventor)

    1991-01-01

    A regenerative adsorbent heat pump process and system is provided which can regenerate a high percentage of the sensible heat of the system and at least a portion of the heat of adsorption. A series of at least four compressors containing an adsorbent is provided. A large amount of heat is transferred from compressor to compressor so that heat is regenerated. The process and system are useful for air conditioning rooms, providing room heat in the winter or for hot water heating throughout the year, and, in general, for pumping heat from a lower temperature to a higher temperature.

  10. Preparation and characterization of γ-AlOOH @CS magnetic nanoparticle as a novel adsorbent for removing fluoride from drinking water.

    PubMed

    Wan, Zhen; Chen, Wei; Liu, Cheng; Liu, Yu; Dong, Changlong

    2015-04-01

    For this study, a novel adsorbent of γ-AlOOH @CS (pseudoboehmite and chitosan shell) magnetic nanoparticles (ACMN) with magnetic separation capabilities was developed to remove fluoride from drinking water. The adsorbent was first characterized, and then its performance in removing fluoride was evaluated. Kinetic data demonstrated rapid fluoride adsorption with more than 80% fluoride adsorption within the initial 20 min and equilibrium reached in 60 min. Based on the results of kinetic and isotherm models, the fluoride adsorption process on the ACMN's surface was a monolayer adsorption on a homogeneous surface. Thermodynamic parameters presented that the adsorption process is spontaneous and endothermic in nature. The mechanism for the adsorption involved electrostatic interaction and hydrogen bonding. Moreover, the calculated adsorption capacity of the ACMN for fluoride using the Langmuir model was 67.5 mg/g (20°C, pH=7.0±0.1), higher than other fluoride removal adsorbents. This nanoadsorbent performed well over a pH range of 4-10. The study found that PO4(3-) was the co-existing anion most able to hinder the nanoparticle's fluoride adsorption, followed by NO3(-) then Cl(-). Experimental results suggest that ACMN is a promising adsorbent for treating fluoride-contaminated water.

  11. First-Principles Study of the Electric Field Effect on the Water-Adsorbed Rutile Titanium Dioxide Surface

    NASA Astrophysics Data System (ADS)

    Hmiel, Abraham L.

    TiO2 is a semiconducting material that has been used extensively in many industrial applications, and recently has become a candidate for photocatalytic water splitting, fuel cell anode support materials, sensors, and other novel nanodevices. The interface of TiO2 with water, historically well-studied but still poorly understood, presents a ubiquitous environmental challenge towards the ultimate practical usefulness of these technologies. Ground-state density functional theory (DFT) calculations studying the characteristics of molecular adsorption on model surfaces have been studied for decades, showing constant improvement in the description of the energetics and electronic structure at interfaces. These simulations are invaluable in the materials science innovation pipeline because they can interpret the results of experiments and investigate properties at the nanoscale that traditional methods cannot reach. In this work, spin-polarized DFT calculations within the generalized gradient approximation and with the recent self-consistent opt-B88 van der Waals functional have been applied to investigate the problem of molecularly adsorbed water on the rutile (110) TiO2 surface under the influence of an applied electric field. The effective screening medium theory is used to break the symmetry of the simulation in the slab normal direction and implement a metal-like boundary condition at the edges of the simulation cell to model the charged capacitor in a real electrochemical device. This study begins with an investigation of bulk and surface properties of TiO2 to obtain a sound theoretical baseline. Following that, an attempt to obtain simple and meaningful structure-property relationships of rectangular TiO 2 nanowires with (110) facets resulting from quantum confinement. Finally, a systematic study of energetics, geometrical configuration, charge partitioning, and electronic structure of water in monomer coverage up to monolayer coverage provides insight into the

  12. Hexagonal boron nitride nanosheets as adsorbents for solid-phase extraction of polychlorinated biphenyls from water samples.

    PubMed

    Jia, Shiliang; Wang, Zhenhua; Ding, Ning; Elaine Wong, Y-L; Chen, Xiangfeng; Qiu, Guangyu; Dominic Chan, T-W

    2016-09-14

    The adsorptive potential of hexagonal boron nitride nanosheets (h-BNNSs) for solid-phase extraction (SPE) of pollutants was investigated for the first time. Seven indicators of polychlorinated biphenyls (PCBs) were selected as target analytes. The adsorption of PCBs on the surface of the h-BNNSs in water was simulated by the density functional theory and molecular dynamics. The simulation results indicated that the PCBs are adsorbed on the surface by π-π, hydrophobic, and electrostatic interactions. The PCBs were extracted with an h-BNNS-packed SPE cartridge, and eluted by dichloromethane. Gas chromatography-tandem mass spectrometry working in the multiple reaction monitor mode was used for the sample quantification. The effect of extraction parameters, including the flow rate, pH value, breakthrough volume, and the ionic strength, were investigated. Under the optimal working conditions, the developed method showed low limits of detection (0.24-0.50 ng L(-1); signal-to-noise ratio = 3:1), low limits of quantification (0.79-1.56 ng L(-1); signal-to-noise ratio = 10:1), satisfactory linearity (r > 0.99) within the concentration range of 2-1000 ng L(-1), and good precision (relative standard deviation < 12%). The PCBs concentration in environmental water samples was determined by the developed method. This results demonstrate that h-BNNSs have high analytical potential in the enrichment of pollutants.

  13. A computer modelling study of the interaction of organic adsorbates with fluorapatite surfaces

    NASA Astrophysics Data System (ADS)

    Mkhonto, Donald; Ngoepe, Phuti E.; Cooper, Timothy G.; de Leeuw, Nora H.

    2006-08-01

    Computer modelling techniques were employed to investigate the adsorption of a selection of organic surfactant molecules to a range of fluorapatite surfaces, and new interatomic potential models for the apatite/adsorbate interactions are presented. The adsorbates coordinate mainly to the surfaces through interaction between their oxygen (or nitrogen) atoms to surface calcium ions, followed by hydrogen-bonded interactions to surface oxygen ions and, to a much lesser extent, surface fluorides. Bridging between two surface calcium ions is the preferred mode of adsorption, when the geometry of the adsorbates allows it, and multiple interactions between surfaces and adsorbate molecules lead to the largest adsorption energies. All adsorbates containing carbonyl and hydroxy groups interact strongly with the surfaces, releasing energies between approximately 100 and 215 kJ mol-1, but methylamine containing only the NH2 functional group adsorbs to the surfaces to a much lesser extent (25 95 kJ mol-1). Both hydroxy methanamide and hydroxy ethanal prefer to adsorb to some surfaces in an eclipsed conformation, which is a requisite for these functional groups. Sorption of the organic material by replacement of pre-adsorbed water at different surface features is calculated to be mainly exothermic for methanoic acid, hydroxy methanamide and hydroxy ethanal molecules, whereas methyl amine would not replace pre-adsorbed water at the fluorapatite surfaces. The efficacy of the surfactant molecules is calculated to be hydroxy aldehydes > alkyl hydroxamates > carboxylic acids ≫ alkyl amines. The results from this study suggest that computer simulations may provide a route to the identification or even design of particular organic surfactants for use in mineral separation by flotation.

  14. Methyl red removal from water by iron based metal-organic frameworks loaded onto iron oxide nanoparticle adsorbent

    NASA Astrophysics Data System (ADS)

    Dadfarnia, S.; Haji Shabani, A. M.; Moradi, S. E.; Emami, S.

    2015-03-01

    The objective followed by this research is the synthesis of iron based metal organic framework loaded on iron oxide nanoparticles (Fe3O4@MIL-100(Fe)) and the study of its capability for the removal of methyl red. Effective parameters in the selection of a new adsorbent, i.e. adsorption capacity, thermodynamics, and kinetics were investigated. All the studies were carried out in batch experiments. Removal of methyl red from aqueous solutions varied with the amount of adsorbent, methyl red contact time, initial concentration of dye, adsorbent dosage, and solution pH. The capability of the synthesized adsorbent in the removal of methyl red was compared with the metal organic framework (MIL-100(Fe)) and iron oxide nanoparticles. The results show that Fe3O4@MIL-100(Fe) nanocomposite exhibits an enhanced adsorption capacity.

  15. A comparison of different concentration methods for the detection of viruses present in bottled waters and those adsorbed to water bottle surfaces.

    PubMed

    Huguet, L; Carteret, C; Gantzer, C

    2012-04-01

    This study aimed to provide a tool for selecting the best approach to virological testing of bottled waters. Different methods were investigated. Method A examined the recovery of virus RNA following in situ lysis of virus particles in the aqueous phase and of those adhered to the bottle wall, method B examined the recovery of virus RNA following lysis of virus particles in the aqueous phase, and method C examined the recovery of intact virus particles. Method C generated the lowest genome recovery rate regardless of the water and virus type used, therefore comparison was mainly conducted between methods A and B.The effects of independent variables on the viral RNA recovery rate were determined by full factorial design. These independent variables included three waters (differing in mineral composition), four viruses (poliovirus 1, hepatitis A virus, Norovirus, and the MS2 phage), three incubation times (0, 10, and 20 days), and two methods (A and B). According to the results, each factor influenced the recovery rate of viral RNA with the exception of incubation time. Statistical analysis identified interactions between the factors. The strongest interactions involved the water and virus types, as well as the methods. The results suggested that method A should be used for the concentration and detection of hepatitis A virus, regardless of the divalent cation concentration of the bottled water. Method A was most suitable for water with the highest mineral content (divalent cation concentration of 250 mgL(-1)) and for the analysis of viruses capable of adsorbing onto the bottle walls (Poliovirus 1). Method B could be recommended for the analysis of water whose cation concentration is unknown.

  16. Solvated water molecules and hydrogen-bridged networks in liquid water

    NASA Astrophysics Data System (ADS)

    Corongiu, Giorgina; Clementi, Enrico

    1993-02-01

    We have analyzed the molecular-dynamics (MD) trajectories for the oxygen and hydrogen atoms of liquid water, at six temperatures (from hot, T=361 K, to supercooled water, T=242 K); in the MD simulations the Nieser-Corongiu-Clementi ab initio potential has been used, since it yields reliable x-ray and neutron-diffraction data as well as infrared, Raman, and neutron-scattering spectra. Our analysis leads to two complementary models where we can consider each water as a solvated molecule (placed at the center of a solvation shell) or as a component of a cyclic polymer, a substructure of the hydrogen-bonded network. In the first solvation shell all water molecules are solvated with coordination values in the range 2-8. The most probable solvation number is four, at low temperature, and five at high temperature considering oxygen-oxygen pairs; however, the coordination number is four at all the temperatures if we consider oxygen-hydrogen pairs. The lifetime of the tetra coordinated complexes is the largest one and increases as temperature decreases. The computed population of cyclic polymers is highest for the pentameters in the studied temperature range, the second most probable cyclic structure is for hexamers. The average O-O distances in the liquid are temperature dependent and shorter than those in the gas phase, approaching ice values at low temperature (except for cyclic trimers, for which the O-O distance is nearly temperature independent). As a preliminary result, the lifetime of the polygons is estimated to be around 0.01 ps.

  17. Observation of the interference between the intramolecular IR-visible and visible-IR processes in the doubly resonant sum frequency generation vibrational spectroscopy of Rhodamine 6G adsorbed at the air/water interface.

    PubMed

    Wu, Dan; Deng, Gang-Hua; Guo, Yuan; Wang, Hong-fei

    2009-05-28

    Using the picosecond visible light at 532.1 nm and infrared light at 2800-3100 cm(-1), we observed the interference between the intramolecular IR-visible and visible-IR processes in the doubly resonant sum frequency generation vibrational spectroscopy of Rhodamine 6G adsorbed at the air/water interface. The interference phenomenon exists for both the C-H stretching vibrations in the 2800-3100 cm(-1) region and the skeleton vibrations in the 1450-1700 cm(-1) region. The relative strength of the visible-IR process at different wavelengths is the result of the electronic structure of the molecule. This is the first direct observation of the visible-IR sum frequency generation process in the electronically excited state of a model molecular system.

  18. Quantifying the entropy of binding for water molecules in protein cavities by computing correlations.

    PubMed

    Huggins, David J

    2015-02-17

    Protein structural analysis demonstrates that water molecules are commonly found in the internal cavities of proteins. Analysis of experimental data on the entropies of inorganic crystals suggests that the entropic cost of transferring such a water molecule to a protein cavity will not typically be greater than 7.0 cal/mol/K per water molecule, corresponding to a contribution of approximately +2.0 kcal/mol to the free energy. In this study, we employ the statistical mechanical method of inhomogeneous fluid solvation theory to quantify the enthalpic and entropic contributions of individual water molecules in 19 protein cavities across five different proteins. We utilize information theory to develop a rigorous estimate of the total two-particle entropy, yielding a complete framework to calculate hydration free energies. We show that predictions from inhomogeneous fluid solvation theory are in excellent agreement with predictions from free energy perturbation (FEP) and that these predictions are consistent with experimental estimates. However, the results suggest that water molecules in protein cavities containing charged residues may be subject to entropy changes that contribute more than +2.0 kcal/mol to the free energy. In all cases, these unfavorable entropy changes are predicted to be dominated by highly favorable enthalpy changes. These findings are relevant to the study of bridging water molecules at protein-protein interfaces as well as in complexes with cognate ligands and small-molecule inhibitors.

  19. Quantifying the Entropy of Binding for Water Molecules in Protein Cavities by Computing Correlations

    PubMed Central

    Huggins, David J.

    2015-01-01

    Protein structural analysis demonstrates that water molecules are commonly found in the internal cavities of proteins. Analysis of experimental data on the entropies of inorganic crystals suggests that the entropic cost of transferring such a water molecule to a protein cavity will not typically be greater than 7.0 cal/mol/K per water molecule, corresponding to a contribution of approximately +2.0 kcal/mol to the free energy. In this study, we employ the statistical mechanical method of inhomogeneous fluid solvation theory to quantify the enthalpic and entropic contributions of individual water molecules in 19 protein cavities across five different proteins. We utilize information theory to develop a rigorous estimate of the total two-particle entropy, yielding a complete framework to calculate hydration free energies. We show that predictions from inhomogeneous fluid solvation theory are in excellent agreement with predictions from free energy perturbation (FEP) and that these predictions are consistent with experimental estimates. However, the results suggest that water molecules in protein cavities containing charged residues may be subject to entropy changes that contribute more than +2.0 kcal/mol to the free energy. In all cases, these unfavorable entropy changes are predicted to be dominated by highly favorable enthalpy changes. These findings are relevant to the study of bridging water molecules at protein-protein interfaces as well as in complexes with cognate ligands and small-molecule inhibitors. PMID:25692597

  20. Energetics of displacing water molecules from protein binding sites: consequences for ligand optimization.

    PubMed

    Michel, Julien; Tirado-Rives, Julian; Jorgensen, William L

    2009-10-28

    A strategy in drug design is to consider enhancing the affinity of lead molecules with structural modifications that displace water molecules from a protein binding site. Because success of the approach is uncertain, clarification of the associated energetics was sought in cases where similar structural modifications yield qualitatively different outcomes. Specifically, free-energy perturbation calculations were carried out in the context of Monte Carlo statistical mechanics simulations to investigate ligand series that feature displacement of ordered water molecules in the binding sites of scytalone dehydratase, p38-alphaMAP kinase, and EGFR kinase. The change in affinity for a ligand modification is found to correlate with the ease of displacement of the ordered water molecule. However, as in the EGFR example, the binding affinity may diminish if the free-energy increase due to the removal of the bound water molecule is not more than compensated by the additional interactions of the water-displacing moiety. For accurate computation of the effects of ligand modifications, a complete thermodynamic analysis is shown to be needed. It requires identification of the location of water molecules in the protein-ligand interface and evaluation of the free-energy changes associated with their removal and with the introduction of the ligand modification. Direct modification of the ligand in free-energy calculations is likely to trap the ordered molecule and provide misleading guidance for lead optimization.

  1. Adsorption of organic matter at mineral/water interfaces: I. ATR-FTIR spectroscopic and quantum chemical study of oxalate adsorbed at boehmite/water and corundum/water interfaces

    NASA Astrophysics Data System (ADS)

    Yoon, Tae Hyun; Johnson, Stephen B.; Musgrave, Charles B.; Brown, Gordon E.

    2004-11-01

    The types and structures of adsorption complexes formed by oxalate at boehmite (γ-AlOOH)/water and corundum (α-Al 2O 3)/water interfaces were determined using in situ attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy and quantum chemical simulation methods. At pH 5.1, at least four different oxalate species were found at or near the boehmite/water interface for oxalate surface coverages (Γ ox) ranging from 0.25 to 16.44 μmol/m 2. At relatively low coverages (Γ ox < 2.47), strongly adsorbed inner-sphere oxalate species (IR peaks at 1286, 1418, 1700, and 1720 cm -1) replace weakly adsorbed carbonate species, and a small proportion of oxalate anions are adsorbed in an outer-sphere mode (IR peaks at 1314 and 1591 cm -1). IR peaks indicative of inner-sphere adsorbed oxalate are also observed for oxalate at the corundum/water interface at Γ ox = 1.4 μmol/m 2. With increasing oxalate concentration (Γ ox > 2.47 μmol/m 2), the boehmite surface binding sites for inner-sphere adsorbed oxalate become saturated, and excess oxalate ions are present dominantly as aqueous species (IR peaks at 1309 and 1571 cm -1). In addition to these adsorption processes, oxalate-promoted dissolution of boehmite following inner-sphere oxalate adsorption becomes increasingly pronounced with increasing Γ ox and results in an aqueous Al(III)-oxalate species, as indicated by shifted IR peaks (1286 → 1297 cm -1 and 1418 → 1408 cm -1). At pH 2.5, no outer-sphere adsorbed oxalate or aqueous oxalate species were observed. The similarity of adsorbed oxalate spectral features at pH 2.5 and 5.1 implies that the adsorption mechanism of aqueous HOx - species involves loss of protons from this species during the ligand-exchange reaction. As a consequence, adsorbed inner-sphere oxalate and aqueous Al(III)-oxalate complexes formed at pH 2.5 have coordination geometries very similar to those formed at pH 5.1. The coordination geometry of inner-sphere adsorbed oxalate

  2. A study of the potential application of nano-Mg(OH)2 in adsorbing low concentrations of uranyl tricarbonate from water.

    PubMed

    Cao, Qing; Huang, Feng; Zhuang, Zanyong; Lin, Zhang

    2012-04-07

    This work aims at the investigation of nano-Mg(OH)(2) as a promising adsorbent for uranium recovery from water. Systematic analysis including the uranium adsorption isotherm, the kinetics and the thermodynamics of adsorption of low concentrations of uranyl tricarbonate (0.1-20 mg L(-1)) by nano-Mg(OH)(2) was carried out. The results showed a spontaneous and exothermic uranium adsorption process by Mg(OH)(2), which could be well described with pseudo second order kinetics. Surface site calculation and zeta potential measurement further demonstrated that UO(2)(CO(3))(3)(4-) was a monolayer adsorbed onto nano-Mg(OH)(2) by electrostatic forces. Accordingly, the adsorption behavior met the conditions of the Langmuir isotherm. Moreover, in most of the reported literature, nano-Mg(OH)(2) had a higher UO(2)(CO(3))(3)(4-) adsorption affinity b, which implied a higher adsorption amount at equilibrium in a dilute adsorbate system. The significance of the adsorption affinity b for choosing and designing adsorbents with respect to low concentration of resources/pollutants treatment has also been assessed.

  3. Development of magnetic graphene oxide adsorbent for the removal and preconcentration of As(III) and As(V) species from environmental water samples.

    PubMed

    Rashidi Nodeh, Hamid; Wan Ibrahim, Wan Aini; Ali, Imran; Sanagi, Mohd Marsin

    2016-05-01

    New-generation adsorbent, Fe3O4@SiO2/GO, was developed by modification of graphene oxide (GO) with silica-coated (SiO2) magnetic nanoparticles (Fe3O4). The synthesized adsorbent was characterized using Fourier transform infrared spectroscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, and field emission scanning electron microscopy. The developed adsorbent was used for the removal and simultaneous preconcentration of As(III) and As(V) from environmental waters prior to ICP-MS analysis. Fe3O4@SiO2/GO provided high adsorption capacities, i.e., 7.51 and 11.46 mg g(-1) for As(III) and As(V), respectively, at pH 4.0. Adsorption isotherm, kinetic, and thermodynamic were investigated for As(III) and As(V) adsorption. Preconcentration of As(III) and As(V) were studied using magnetic solid-phase extraction (MSPE) method at pH 9.0 as the adsorbent showed selective adsorption for As(III) only in pH range 7-10. MSPE using Fe3O4@SiO2/GO was developed with good linearities (0.05-2.0 ng mL(-1)) and high coefficient of determination (R (2) = 0.9992 and 0.9985) for As(III) and As(V), respectively. The limits of detection (LODs) (3× SD/m, n = 3) obtained were 7.9 pg mL(-1) for As(III) and 28.0 pg mL(-1) for As(V). The LOD obtained is 357-1265× lower than the WHO maximum permissible limit of 10.0 ng mL(-1). The developed MSPE method showed good relative recoveries (72.55-109.71 %) and good RSDs (0.1-4.3 %, n = 3) for spring water, lake, river, and tap water samples. The new-generation adsorbent can be used for the removal and simultaneous preconcentration of As(III) and As(V) from water samples successfully. The adsorbent removal for As(III) is better than As(V).

  4. Benchmarking the thermodynamic analysis of water molecules around a model beta sheet.

    PubMed

    Huggins, David J

    2012-06-05

    Water molecules play a vital role in biological and engineered systems by controlling intermolecular interactions in the aqueous phase. Inhomogeneous fluid solvation theory provides a method to quantify solvent thermodynamics from molecular dynamics or Monte Carlo simulations and provides an insight into intermolecular interactions. In this study, simulations of TIP4P-2005 and TIP5P-Ewald water molecules around a model beta sheet are used to investigate the orientational correlations and predicted thermodynamic properties of water molecules at a protein surface. This allows the method to be benchmarked and provides information about the effect of a protein on the thermodynamics of nearby water molecules. The results show that the enthalpy converges with relatively little sampling, but the entropy and thus the free energy require considerably more sampling to converge. The two water models yield a very similar pattern of hydration sites, and these hydration sites have very similar thermodynamic properties, despite notable differences in their orientational preferences. The results also predict that a protein surface affects the free energy of water molecules to a distance of approximately 4.0 Å, which is in line with previous work. In addition, all hydration sites have a favorable free energy with respect to bulk water, but only when the water-water entropy term is included. A new technique for calculating this term is presented and its use is expected to be very important in accurately calculating solvent thermodynamics for quantitative application.

  5. Amino-functionalized mesoporous MCM-41 silica as an efficient adsorbent for water treatment: batch and fixed-bed column adsorption of the nitrate anion

    NASA Astrophysics Data System (ADS)

    Ebrahimi-Gatkash, Mehdi; Younesi, Habibollah; Shahbazi, Afsaneh; Heidari, Ava

    2015-11-01

    In the present study, amino-functionalized Mobil Composite Material No. 41 (MCM-41) was used as an adsorbent to remove nitrate anions from aqueous solutions. Mono-, di- and tri-amino functioned silicas (N-MCM-41, NN-MCM-41 and NNN-MCM-41) were prepared by post-synthesis grafting method. The samples were characterized by means of X-ray powder diffraction, FTIR spectroscopy, thermogravimetric analysis, scanning electron microscopy and nitrogen adsorption-desorption. The effects of pH, initial concentration of anions, and adsorbent loading were examined in batch adsorption system. Results of adsorption experiments showed that the adsorption capacity increased with increasing adsorbent loading and initial anion concentration. It was found that the Langmuir mathematical model indicated better fit to the experimental data than the Freundlich. According to the constants of the Langmuir equation, the maximum adsorption capacity for nitrate anion by N-MCM-41, NN-MCM-41 and NNN-MCM-41 was found to be 31.68, 38.58 and 36.81 mg/g, respectively. The adsorption kinetics were investigated with pseudo-first-order and pseudo-second-order model. Adsorption followed the pseudo-second-order rate kinetics. The coefficients of determination for pseudo-second-order kinetic model are >0.99. For continuous adsorption experiments, NNN-MCM-41 adsorbent was used for the removal of nitrate anion from solutions. Breakthrough curves were investigated at different bed heights, flow rates and initial nitrate anion concentrations. The Thomas and Yan models were utilized to calculate the kinetic parameters and to predict the breakthrough curves of different bed height. Results from this study illustrated the potential utility of these adsorbents for nitrate removal from water solution.

  6. Work function variation of MoS{sub 2} atomic layers grown with chemical vapor deposition: The effects of thickness and the adsorption of water/oxygen molecules

    SciTech Connect

    Kim, Jong Hun; Kim, Jae Hyeon; Park, Jeong Young E-mail: jeongypark@kaist.ac.kr; Lee, Jinhwan; Hwang, C. C.; Lee, Changgu E-mail: jeongypark@kaist.ac.kr

    2015-06-22

    The electrical properties of two-dimensional atomic sheets exhibit remarkable dependences on layer thickness and surface chemistry. Here, we investigated the variation of the work function properties of MoS{sub 2} films prepared with chemical vapor deposition (CVD) on SiO{sub 2} substrates with the number of film layers. Wafer-scale CVD MoS{sub 2} films with 2, 4, and 12 layers were fabricated on SiO{sub 2}, and their properties were evaluated by using Raman and photoluminescence spectroscopies. In accordance with our X-ray photoelectron spectroscopy results, our Kelvin probe force microscopy investigation found that the surface potential of the MoS{sub 2} films increases by ∼0.15 eV when the number of layers is increased from 2 to 12. Photoemission spectroscopy (PES) with in-situ annealing under ultra high vacuum conditions was used to directly demonstrate that this work function shift is associated with the screening effects of oxygen or water molecules adsorbed on the film surface. After annealing, it was found with PES that the surface potential decreases by ∼0.2 eV upon the removal of the adsorbed layers, which confirms that adsorbed species have a role in the variation in the work function.

  7. Quasielastic neutron scattering investigation of motion of water molecules in n-propyl alcohol-water mixture.

    PubMed

    Nakada, Masaru; Maruyama, Kenji; Yamamuro, Osamu; Misawa, Masakatsu

    2009-02-21

    The dynamics of water molecules in the n-propyl alcohol-water mixtures is investigated by using quasielastic neutron scattering measurements. The dynamic structure factor S(Q,E) obtained from incoherent scattering of hydrogen atoms of water is fitted with jump diffusion and relaxing cage models. The diffusion constant obtained from the relaxing cage model, which gives better fitting with S(Q,E), shows better agreement to the experimental value than that of jump diffusion model. The dependence of translational relaxation time tau(T)(Q) and stretched exponent beta(T)(Q) on the fraction of hydrophobic hydrating water molecules in the solution is discussed.

  8. Quasielastic neutron scattering investigation of motion of water molecules in n-propyl alcohol-water mixture

    NASA Astrophysics Data System (ADS)

    Nakada, Masaru; Maruyama, Kenji; Yamamuro, Osamu; Misawa, Masakatsu

    2009-02-01

    The dynamics of water molecules in the n-propyl alcohol-water mixtures is investigated by using quasielastic neutron scattering measurements. The dynamic structure factor S(Q,E) obtained from incoherent scattering of hydrogen atoms of water is fitted with jump diffusion and relaxing cage models. The diffusion constant obtained from the relaxing cage model, which gives better fitting with S(Q,E), shows better agreement to the experimental value than that of jump diffusion model. The dependence of translational relaxation time τT(Q) and stretched exponent βT(Q) on the fraction of hydrophobic hydrating water molecules in the solution is discussed.

  9. MTBE adsorption on alternative adsorbents and packed bed adsorber performance.

    PubMed

    Rossner, Alfred; Knappe, Detlef R U

    2008-04-01

    Widespread use of the fuel additive methyl tertiary-butyl ether (MTBE) has led to frequent MTBE detections in North American and European drinking water sources. The overall objective of this research was to evaluate the effectiveness of a silicalite zeolite, a carbonaceous resin, and a coconut-shell-based granular activated carbon (GAC) for the removal of MTBE from water. Isotherm and short bed adsorber tests were conducted in ultrapure water and river water to obtain parameters describing MTBE adsorption equilibria and kinetics and to quantify the effect of natural organic matter (NOM) on MTBE adsorption. Both the silicalite zeolite and the carbonaceous resin exhibited larger MTBE adsorption uptakes than the tested GAC. Surface diffusion coefficients describing intraparticle MTBE mass transfer rates were largest for the GAC and smallest for the carbonaceous resin. Pilot tests were conducted to verify MTBE breakthrough curve predictions obtained with the homogeneous surface diffusion model and to evaluate the effect of NOM preloading on packed bed adsorber performance. Results showed that GAC was the most cost-competitive adsorbent when considering adsorbent usage rate only; however, the useful life of an adsorber containing silicalite zeolite was predicted to be approximately 5-6 times longer than that of an equally sized adsorber containing GAC. Pilot column results also showed that NOM preloading did not impair the MTBE removal efficiency of the silicalite zeolite. Thus, it may be possible to regenerate spent silicalite with less energy-intensive methods than those required to regenerate GAC.

  10. Synthesis of an attapulgite clay@carbon nanocomposite adsorbent by a hydrothermal carbonization process and their application in the removal of toxic metal ions from water.

    PubMed

    Chen, Li-Feng; Liang, Hai-Wei; Lu, Yang; Cui, Chun-Hua; Yu, Shu-Hong

    2011-07-19

    A new kind of attapulgite clay@carbon (ATP@C) nanocomposite adsorbent has been synthesized by a one-pot hydrothermal carbonization process under mild conditions using two cheap, ecofriendly materials (i.e., attapulgite clay (ATP), which is a magnesium aluminum silicate that is abundant in nature, and glucose, which is a green chemical obtained from biomass). Compared to carbon-based materials, this new ATP@C nanocomposite exhibits a high adsorption ability for Cr(VI) and Pb(II) ions with maximum adsorption capacities of 177.74 and 263.83 mg·g(-1), respectively. The results demonstrate that this nanocomposite is an exceptionally promising candidate as a low-cost, sustainable, and effective adsorbent for the removal of toxic ions from water.

  11. The role of water molecules in stereoselectivity of glucose/galactose-binding protein

    NASA Astrophysics Data System (ADS)

    Kim, Minsup; Cho, Art E.

    2016-11-01

    Using molecular dynamics (MD) simulation methods, we attempted to explain the experimental results on ligand specificity of glucose/galactose-binding protein (GGBP) to β-D-glucose and β-D-galactose. For the simulation, a three-dimensional structure of GGBP was prepared, and homology modeling was performed to generate variant structures of GGBP with mutations at Asp14. Then, docking was carried out to find a reasonable β-D-glucose and β-D-galactose binding conformations with GGBP. Subsequent molecular dynamics simulations of β-D-glucose–GGBP and β-D-galactose–GGBP complexes and estimation of the orientation and stability of water molecules at the binding site revealed how water molecules influence ligand specificity. In our simulation, water molecules mediated interactions of β-D-glucose or β-D-galactose with residue 14 of GGBP. In this mechanism, the Phe16Ala mutant leaves both sugar molecules free to move, and the specific role of water molecules were eliminated, while the wild type, Asp14Asn mutant, and Asp14Glu mutant make hydrogen bond interactions with β-D-glucose more favorable. Our results demonstrate that bound water molecules at the binding site of GGBP are related to localized conformational change, contributing to ligand specificity of GGBP for β-D-glucose over β-D-galactose.

  12. Preparation, characterization and application of Saussurea tridactyla Sch-Bip as green adsorbents for preconcentration of rare earth elements in environmental water samples

    NASA Astrophysics Data System (ADS)

    Zhang, Qiangying; He, Man; Chen, Beibei; Hu, Bin

    2016-07-01

    This paper deals with preparation, characterization and application of the Saussurea tridactyla Sch-Bip (STSB) as a new green adsorbent for separation of matrix elements and preconcentration of rare earth elements (REEs) in environmental water samples. The pretreated STSB adsorbent with 2 mol L- 1 NaOH is characterized with higher surface area and adsorption capacities in comparison with a raw STSB material. The new adsorbent was used for the development of on-line solid phase extraction (SPE) for the determination of REEs by radial viewing 27 MHz inductively coupled plasma optical emission spectrometry (ICP-OES). Various parameters affecting the adsorption/desorption procedure were optimized. The adsorption capacities for the STSB were found to be 62.2 (Y)-153 mg g- 1 (Tm). Under the optimized conditions, the limits of detection (LODs, 3σ) for REEs were in the range of 0.06 (Yb)-8.77 (Sm) ng mL- 1. The relative standard deviations (RSDs) for 7 replicate determinations of target REEs at low concentration level ranged from 2.4 (Yb) to 8.9 (Sm)%. The adsorption isotherm fitted Langmuir model and the adsorption kinetics fitted well with both Pseudo-first order and Pseudo-second order models. The predominant adsorption mechanism is ion exchange. The STSB pretreated with 2 mol L- 1 NaOH has been demonstrated to be low cost, green and environment friendly adsorbent, featuring with high adsorption capacity, wide pH range, and fast adsorption/desorption kinetics for target REEs with long lifetime. The proposed method was applied to the determination of REEs in East Lake, Yangtze River and rain water samples.

  13. Sulfate-doped Fe3O4/Al2O3 nanoparticles as a novel adsorbent for fluoride removal from drinking water.

    PubMed

    Chai, Liyuan; Wang, Yunyan; Zhao, Na; Yang, Weichun; You, Xiangyu

    2013-08-01

    A novel adsorbent of sulfate-doped Fe3O4/Al2O3 nanoparticles with magnetic separability was developed for fluoride removal from drinking water. The nanosized adsorbent was characterized and its performance in fluoride removal was evaluated. Kinetic data reveal that the fluoride adsorption was rapid in the beginning followed by a slower adsorption process, nearly 90% adsorption can be achieved within 20 min and only 10-15% additional removal occurred in the following 8 h. The fluoride adsorption isotherm was well described by Elovich model. The calculated adsorption capacity of this nanoadsorbent for fluoride by two-site Langmuir model was 70.4 mg/g at pH 7.0. Moreover, this nanoadsorbent performed well over a considerable wide pH range of 4-10, and the fluoride removal efficiencies reached up to 90% and 70% throughout the pH range of 4-10 with initial fluoride concentrations of 10 mg/L and 50 mg/L, respectively. The observed sulfate-fluoride displacement and decreased sulfur content on the adsorbent surface reveal that anion exchange process was an important mechanism for fluoride adsorption by the sulfate-doped Fe3O4/Al2O3 nanoparticles. Moreover, a shift of the pH of zero point charge (pHPZC) of the nanoparticles and surface analysis based on X-ray photoelectron spectroscopy (XPS) suggest the formation of inner-sphere fluoride complex at the aluminum center as another adsorption mechanism. With the exception of PO4(3-), other co-existing anions (NO3(-), Cl(-) and SO4(2-)) did not evidently inhibit fluoride removal by the nanoparticles. Findings of this study demonstrate the potential utility of the nanoparticles as an effective adsorbent for fluoride removal from drinking water.

  14. Uptake of CO2, SO2, HNO3 and HCl on calcite (CaCO3) at 300 K: mechanism and the role of adsorbed water.

    PubMed

    Santschi, Ch; Rossi, M J

    2006-06-01

    All experimental observations of the uptake of the four title compounds on calcite are consistent with the presence of a reactive bifunctional surface intermediate Ca(OH)(HCO3) that has been proposed in the literature. The uptake of CO2 and SO2 occurs on specific adsorption sites of crystalline CaCO3(s) rather than by dissolution in adsorbed water, H2O(ads). SO2 primarily interacts with the bicarbonate moiety whereas CO2, HNO3 and HCl all react first with the hydroxyl group of the surface intermediate. Subsequently, the latter two react with the bicarbonate group to presumably form Ca(NO3)2 and CaCl2.2H2O. The effective equilibrium constant of the interaction of CO2 with calcite in the presence of H2O(ads) is kappa = deltaCO2/(H2O(ads)[CO2]) = 1.62 x 10(3) bar(-1), where CO2 is the quantity of CO2 adsorbed on CaCO3. The reaction mechanism involves a weakly bound precursor species that is reversibly adsorbed and undergoes rate-controlling concurrent reactions with both functionalities of the surface intermediate. The initial uptake coefficients gamma0 on calcite powder depend on the abundance of H2O(ads) under the present experimental conditions and are on the order of 10(-4) for CO2 and 0.1 for SO2, HNO3 and HCl, with gamma(ss) being significantly smaller than gamma0 for HNO3 and HCl, thus indicating partial saturation of the uptake. At 33% relative humidity and 300 K there are 3.5 layers of H2O adsorbed on calcite that reduce to a fraction of a monolayer of weakly and strongly bound water upon pumping and/or heating.

  15. Enhanced Raman spectroscopy of molecules adsorbed on carbon-doped TiO₂ obtained from titanium carbide: a visible-light-assisted renewable substrate.

    PubMed

    Kiran, Vankayala; Sampath, Srinivasan

    2012-08-01

    Titanium carbide (TiC) is an electrically conducting material with favorable electrochemical properties. In the present studies, carbon-doped TiO(2) (C-TiO(2)) has been synthesized from TiC particles, as well as TiC films coated on stainless steel substrate via thermal annealing under various conditions. Several C-TiO(2) substrates are synthesized by varying experimental conditions and characterized by UV-visible spectroscopy, photoluminescence, X-ray diffraction, and X-ray photoelectron spectroscopic techniques. C-TiO(2) in the dry state (in powder form as well as in film form) is subsequently used as a substrate for enhancing Raman signals corresponding to 4-mercaptobenzoic acid and 4-nitrothiophenol by utilizing chemical enhancement based on charge-transfer interactions. Carbon, a nonmetal dopant in TiO(2), improves the intensities of Raman signals, compared to undoped TiO(2). Significant dependence of Raman intensity on carbon doping is observed. Ameliorated performance obtained using C-TiO(2) is attributed to the presence of surface defects that originate due to carbon as a dopant, which, in turn, triggers charge transfer between TiO(2) and analyte. The C-TiO(2) substrates are subsequently regenerated for repetitive use by illuminating an analyte-adsorbed substrate with visible light for a period of 5 h.

  16. Desorption of Hot Molecules from Photon Irradiated Interstellar Ices

    NASA Astrophysics Data System (ADS)

    Thrower, J. D.; Burke, D. J.; Collings, M. P.; Dawes, A.; Holtom, P. D.; Jamme, F.; Kendall, P.; Brown, W. A.; Clark, I. P.; Fraser, H. J.; McCoustra, M. R. S.; Mason, N. J.; Parker, A. W.

    2008-02-01

    We present experimental measurements of photodesorption from ices of astrophysical relevance. Layers of benzene and water ice were irradiated with a laser tuned to an electronic transition in the benzene molecule. The translational energy of desorbed molecules was measured by time-of-flight (ToF) mass spectrometry. Three distinct photodesorption processes were identified: a direct adsorbate-mediated desorption producing benzene molecules with a translational temperature of around 1200 K, an indirect adsorbate-mediated desorption resulting in water molecules with a translational temperature of around 450 K, and a substrate-mediated desorption of both benzene and water producing molecules with translational temperatures of around 530 and 450 K, respectively. The translational temperature of each population of desorbed molecules is well above the temperature of the ice matrix. The implications for gas-phase chemistry in the interstellar medium are discussed.

  17. Density functional study of adsorptions of CO2, NO2 and SO2 molecules on Zn(0002) surfaces

    NASA Astrophysics Data System (ADS)

    Nugraha; Saputro, A. G.; Agusta, M. K.; Yuliarto, B.; Dipojono, H. K.; Maezono, R.

    2016-08-01

    We report on a theoretical study of adsorptions of CO2, NO2 and SO2 molecules on ZnO(0002) surfaces using density functional theory-based (DFT-based) calculations. These adsorptions are done on perfect and defective ZnO(0002) surfaces. We find that all of these molecules are chemically adsorbed on the perfect ZnO(0002) surface. In the presence of Zn vacancy, we find that the surface is only active toward SO2 molecule. On the hydroxylated ZnO(0002) surfaces, CO2 and SO2 molecules can react with the preadsorbed OH molecule to form various adsorbates such as: carboxyl (COOH), bicarbonate (CO3H), sulfonyl hydroxide (SO3H), SO3 and water. However, NO2 molecule cannot react with the pre-adsorbed OH molecule and only physically adsorbed on the surface.

  18. Identification of intrinsic catalytic activity for electrochemical reduction of water molecules to generate hydrogen.

    PubMed

    Shinagawa, Tatsuya; Takanabe, Kazuhiro

    2015-06-21

    Insufficient hydronium ion activities at near-neutral pH and under unbuffered conditions induce diffusion-limited currents for hydrogen evolution, followed by a reaction with water molecules to generate hydrogen at elevated potentials. The observed constant current behaviors at near neutral pH reflect the intrinsic electrocatalytic reactivity of the metal electrodes for water reduction.

  19. Adsorbate Diffusion on Transition Metal Nanoparticles

    DTIC Science & Technology

    2015-01-01

    systematically studied adsorption and diffusion of atomic and diatomic species (H, C, N, O, CO, and NO) on nanometer-sized Pt and Cu nanoparticles with...species and two diatomic molecules (H, C, N, O, CO, and NO) as adsorbates and study the adsorption and diffusion of these adsorbates across the edges

  20. Incipient ferroelectricity of water molecules confined to nano-channels of beryl

    PubMed Central

    Gorshunov, B. P.; Torgashev, V. I.; Zhukova, E. S.; Thomas, V. G.; Belyanchikov, M. A.; Kadlec, C.; Kadlec, F.; Savinov, M.; Ostapchuk, T.; Petzelt, J.; Prokleška, J.; Tomas, P. V.; Pestrjakov, E. V.; Fursenko, D. A.; Shakurov, G. S.; Prokhorov, A. S.; Gorelik, V. S.; Kadyrov, L. S.; Uskov, V. V.; Kremer, R. K.; Dressel, M.

    2016-01-01

    Water is characterized by large molecular electric dipole moments and strong interactions between molecules; however, hydrogen bonds screen the dipole–dipole coupling and suppress the ferroelectric order. The situation changes drastically when water is confined: in this case ordering of the molecular dipoles has been predicted, but never unambiguously detected experimentally. In the present study we place separate H2O molecules in the structural channels of a beryl single crystal so that they are located far enough to prevent hydrogen bonding, but close enough to keep the dipole–dipole interaction, resulting in incipient ferroelectricity in the water molecular subsystem. We observe a ferroelectric soft mode that causes Curie–Weiss behaviour of the static permittivity, which saturates below 10 K due to quantum fluctuations. The ferroelectricity of water molecules may play a key role in the functioning of biological systems and find applications in fuel and memory cells, light emitters and other nanoscale electronic devices. PMID:27687693

  1. Incipient ferroelectricity of water molecules confined to nano-channels of beryl

    NASA Astrophysics Data System (ADS)

    Gorshunov, B. P.; Torgashev, V. I.; Zhukova, E. S.; Thomas, V. G.; Belyanchikov, M. A.; Kadlec, C.; Kadlec, F.; Savinov, M.; Ostapchuk, T.; Petzelt, J.; Prokleška, J.; Tomas, P. V.; Pestrjakov, E. V.; Fursenko, D. A.; Shakurov, G. S.; Prokhorov, A. S.; Gorelik, V. S.; Kadyrov, L. S.; Uskov, V. V.; Kremer, R. K.; Dressel, M.

    2016-09-01

    Water is characterized by large molecular electric dipole moments and strong interactions between molecules; however, hydrogen bonds screen the dipole-dipole coupling and suppress the ferroelectric order. The situation changes drastically when water is confined: in this case ordering of the molecular dipoles has been predicted, but never unambiguously detected experimentally. In the present study we place separate H2O molecules in the structural channels of a beryl single crystal so that they are located far enough to prevent hydrogen bonding, but close enough to keep the dipole-dipole interaction, resulting in incipient ferroelectricity in the water molecular subsystem. We observe a ferroelectric soft mode that causes Curie-Weiss behaviour of the static permittivity, which saturates below 10 K due to quantum fluctuations. The ferroelectricity of water molecules may play a key role in the functioning of biological systems and find applications in fuel and memory cells, light emitters and other nanoscale electronic devices.

  2. Incipient ferroelectricity of water molecules confined to nano-channels of beryl.

    PubMed

    Gorshunov, B P; Torgashev, V I; Zhukova, E S; Thomas, V G; Belyanchikov, M A; Kadlec, C; Kadlec, F; Savinov, M; Ostapchuk, T; Petzelt, J; Prokleška, J; Tomas, P V; Pestrjakov, E V; Fursenko, D A; Shakurov, G S; Prokhorov, A S; Gorelik, V S; Kadyrov, L S; Uskov, V V; Kremer, R K; Dressel, M

    2016-09-30

    Water is characterized by large molecular electric dipole moments and strong interactions between molecules; however, hydrogen bonds screen the dipole-dipole coupling and suppress the ferroelectric order. The situation changes drastically when water is confined: in this case ordering of the molecular dipoles has been predicted, but never unambiguously detected experimentally. In the present study we place separate H2O molecules in the structural channels of a beryl single crystal so that they are located far enough to prevent hydrogen bonding, but close enough to keep the dipole-dipole interaction, resulting in incipient ferroelectricity in the water molecular subsystem. We observe a ferroelectric soft mode that causes Curie-Weiss behaviour of the static permittivity, which saturates below 10 K due to quantum fluctuations. The ferroelectricity of water molecules may play a key role in the functioning of biological systems and find applications in fuel and memory cells, light emitters and other nanoscale electronic devices.

  3. Auger spectrum of a water molecule after single and double core ionization.

    PubMed

    Inhester, L; Burmeister, C F; Groenhof, G; Grubmüller, H

    2012-04-14

    The high intensity of free electron lasers opens up the possibility to perform single-shot molecule scattering experiments. However, even for small molecules, radiation damage induced by absorption of high intense x-ray radiation is not yet fully understood. One of the striking effects which occurs under intense x-ray illumination is the creation of double core ionized molecules in considerable quantity. To provide insight into this process, we have studied the dynamics of water molecules in single and double core ionized states by means of electronic transition rate calculations and ab initio molecular dynamics (MD) simulations. From the MD trajectories, photoionization and Auger transition rates were computed based on electronic continuum wavefunctions obtained by explicit integration of the coupled radial Schrödinger equations. These rates served to solve the master equations for the populations of the relevant electronic states. To account for the nuclear dynamics during the core hole lifetime, the calculated electron emission spectra for different molecular geometries were incoherently accumulated according to the obtained time-dependent populations, thus neglecting possible interference effects between different decay pathways. We find that, in contrast to the single core ionized water molecule, the nuclear dynamics for the double core ionized water molecule during the core hole lifetime leaves a clear fingerprint in the resulting electron emission spectra. The lifetime of the double core ionized water was found to be significantly shorter than half of the single core hole lifetime.

  4. Auger spectrum of a water molecule after single and double core ionization

    SciTech Connect

    Inhester, L.; Burmeister, C. F.; Groenhof, G.; Grubmueller, H.

    2012-04-14

    The high intensity of free electron lasers opens up the possibility to perform single-shot molecule scattering experiments. However, even for small molecules, radiation damage induced by absorption of high intense x-ray radiation is not yet fully understood. One of the striking effects which occurs under intense x-ray illumination is the creation of double core ionized molecules in considerable quantity. To provide insight into this process, we have studied the dynamics of water molecules in single and double core ionized states by means of electronic transition rate calculations and ab initio molecular dynamics (MD) simulations. From the MD trajectories, photoionization and Auger transition rates were computed based on electronic continuum wavefunctions obtained by explicit integration of the coupled radial Schroedinger equations. These rates served to solve the master equations for the populations of the relevant electronic states. To account for the nuclear dynamics during the core hole lifetime, the calculated electron emission spectra for different molecular geometries were incoherently accumulated according to the obtained time-dependent populations, thus neglecting possible interference effects between different decay pathways. We find that, in contrast to the single core ionized water molecule, the nuclear dynamics for the double core ionized water molecule during the core hole lifetime leaves a clear fingerprint in the resulting electron emission spectra. The lifetime of the double core ionized water was found to be significantly shorter than half of the single core hole lifetime.

  5. Vibrational states of a water molecule in a nano-cavity of beryl crystal lattice.

    PubMed

    Zhukova, Elena S; Torgashev, Victor I; Gorshunov, Boris P; Lebedev, Vladimir V; Shakurov, Gil'man S; Kremer, Reinhard K; Pestrjakov, Efim V; Thomas, Victor G; Fursenko, Dimitry A; Prokhorov, Anatoly S; Dressel, Martin

    2014-06-14

    Low-energy excitations of a single water molecule are studied when confined within a nano-size cavity formed by the ionic crystal lattice. Optical spectra are measured of manganese doped beryl single crystal Mn:Be3Al2Si6O18, that contains water molecules individually isolated in 0.51 nm diameter voids within the crystal lattice. Two types of orientation are distinguished: water-I molecules have their dipole moments aligned perpendicular to the c axis and dipole moments of water-II molecules are parallel to the c-axis. The optical conductivity σ(ν) and permittivity ɛ'(ν) spectra are recorded in terahertz and infrared ranges, at frequencies from several wavenumbers up to ν = 7000 cm(-1), at temperatures 5-300 K and for two polarizations, when the electric vector E of the radiation is parallel and perpendicular to the c-axis. Comparative experiments on as-grown and on dehydrated samples allow to identify the spectra of σ(ν) and ɛ'(ν) caused exclusively by water molecules. In the infrared range, well-known internal modes ν1, ν2, and ν3 of the H2O molecule are observed for both polarizations, indicating the presence of water-I and water-II molecules in the crystal. Spectra recorded below 1000 cm(-1) reveal a rich set of highly anisotropic features in the low-energy response of H2O molecule in a crystalline nano-cavity. While for E∥c only two absorption peaks are detected, at ~90 cm(-1) and ~160 cm(-1), several absorption bands are discovered for E⊥c, each consisting of narrower resonances. The bands are assigned to librational (400-500 cm(-1)) and translational (150-200 cm(-1)) vibrations of water-I molecule that is weakly coupled to the nano-cavity "walls." A model is presented that explains the "fine structure" of the bands by a splitting of the energy levels due to quantum tunneling between the minima in a six-well potential relief felt by a molecule within the cavity.

  6. Vibrational states of a water molecule in a nano-cavity of beryl crystal lattice

    NASA Astrophysics Data System (ADS)

    Zhukova, Elena S.; Torgashev, Victor I.; Gorshunov, Boris P.; Lebedev, Vladimir V.; Shakurov, Gil'man S.; Kremer, Reinhard K.; Pestrjakov, Efim V.; Thomas, Victor G.; Fursenko, Dimitry A.; Prokhorov, Anatoly S.; Dressel, Martin

    2014-06-01

    Low-energy excitations of a single water molecule are studied when confined within a nano-size cavity formed by the ionic crystal lattice. Optical spectra are measured of manganese doped beryl single crystal Mn:Be3Al2Si6O18, that contains water molecules individually isolated in 0.51 nm diameter voids within the crystal lattice. Two types of orientation are distinguished: water-I molecules have their dipole moments aligned perpendicular to the c axis and dipole moments of water-II molecules are parallel to the c-axis. The optical conductivity σ(ν) and permittivity ɛ'(ν) spectra are recorded in terahertz and infrared ranges, at frequencies from several wavenumbers up to ν = 7000 cm-1, at temperatures 5-300 K and for two polarizations, when the electric vector E of the radiation is parallel and perpendicular to the c-axis. Comparative experiments on as-grown and on dehydrated samples allow to identify the spectra of σ(ν) and ɛ'(ν) caused exclusively by water molecules. In the infrared range, well-known internal modes ν1, ν2, and ν3 of the H2O molecule are observed for both polarizations, indicating the presence of water-I and water-II molecules in the crystal. Spectra recorded below 1000 cm-1 reveal a rich set of highly anisotropic features in the low-energy response of H2O molecule in a crystalline nano-cavity. While for E∥c only two absorption peaks are detected, at ˜90 cm-1 and ˜160 cm-1, several absorption bands are discovered for E⊥c, each consisting of narrower resonances. The bands are assigned to librational (400-500 cm-1) and translational (150-200 cm-1) vibrations of water-I molecule that is weakly coupled to the nano-cavity "walls." A model is presented that explains the "fine structure" of the bands by a splitting of the energy levels due to quantum tunneling between the minima in a six-well potential relief felt by a molecule within the cavity.

  7. Water and Small-Molecule Permeation of Dormant Bacillus subtilis Spores

    PubMed Central

    Cermak, Nathan; Feijó Delgado, Francisco; Setlow, Barbara; Setlow, Peter

    2015-01-01

    ABSTRACT We use a suspended microchannel resonator to characterize the water and small-molecule permeability of Bacillus subtilis spores based on spores' buoyant mass in different solutions. Consistent with previous results, we found that the spore coat is not a significant barrier to small molecules, and the extent to which small molecules may enter the spore is size dependent. We have developed a method to directly observe the exchange kinetics of intraspore water with deuterium oxide, and we applied this method to wild-type spores and a panel of congenic mutants with deficiencies in the assembly or structure of the coat. Compared to wild-type spores, which exchange in approximately 1 s, several coat mutant spores were found to have relatively high water permeability with exchange times below the ∼200-ms temporal resolution of our assay. In addition, we found that the water permeability of the spore correlates with the ability of spores to germinate with dodecylamine and with the ability of TbCl3 to inhibit germination with l-valine. These results suggest that the structure of the coat may be necessary for maintaining low water permeability. IMPORTANCE Spores of Bacillus species cause food spoilage and disease and are extremely resistant to standard decontamination methods. This hardiness is partly due to spores' extremely low permeability to chemicals, including water. We present a method to directly monitor the uptake of molecules into B. subtilis spores by weighing spores in fluid. The results demonstrate the exchange of core water with subsecond resolution and show a correlation between water permeability and the rate at which small molecules can initiate or inhibit germination in coat-damaged spores. The ability to directly measure the uptake of molecules in the context of spores with known structural or genetic deficiencies is expected to provide insight into the determinants of spores' extreme resistance. PMID:26483518

  8. Magnetic metal-organic framework-titanium dioxide nanocomposite as adsorbent in the magnetic solid-phase extraction of fungicides from environmental water samples.

    PubMed

    Su, Hao; Lin, Yunliang; Wang, Zhenhua; Wong, Y-L Elaine; Chen, Xiangfeng; Chan, T-W Dominic

    2016-09-30

    In this work, a core-shell Fe3O4@SiO2@MOF/TiO2 nanocomposite was synthesized and used to as adsorbent for magnetic solid-phase extraction (MSPE) of triazole fungicides from environmental water samples. Five triazole fungicides, namely, triadimenol, hexaconazole, diniconazole, myclobutanil, and tebuconazole, were selected as target analytes for MSPE. These analytes were quantitatively adsorbed on microspheres, and the sorbents were separated from the solution by using a magnet. The analytes were desorbed by methanol and determined through liquid-chromatography coupled with tandem mass spectrometry. The extraction parameters affecting the extraction efficiency were optimized through response surface methodology. The limits of detection and limits of quantification for the selected fungicides were 0.19-1.20ngL(-1) and 0.61-3.62ngL(-1), respectively. The proposed method was applied to determine the concentration of fungicides in actual environmental water samples. The accuracy of the proposed method was evaluated by measuring the recovery of the spiked samples. The satisfying recoveries of the four water samples ranged from 90.2% to 104.2%. Therefore, the magnetic metal-organic framework/TiO2 nanocomposite based MSPE is a potential approach to analyze fungicides in actual water samples.

  9. Adsorptive Removal of Pharmaceuticals and Personal Care Products from Water with Functionalized Metal-organic Frameworks: Remarkable Adsorbents with Hydrogen-bonding Abilities

    PubMed Central

    Seo, Pill Won; Bhadra, Biswa Nath; Ahmed, Imteaz; Khan, Nazmul Abedin; Jhung, Sung Hwa

    2016-01-01

    Adsorption of typical pharmaceuticals and personal care products (PPCPs) (such as naproxen, ibuprofen and oxybenzone) from aqueous solutions was studied by using the highly porous metal-organic framework (MOF) MIL-101 with and without functionalization. Adsorption results showed that MIL-101s with H-donor functional groups such as –OH and –NH2 were very effective for naproxen adsorption, despite a decrease in porosity, probably because of H-bonding between O atoms on naproxen and H atoms on the adsorbent. For this reason, MIL-101 with two functional groups capable of H-bonding (MIL-101-(OH)2) exhibited remarkable adsorption capacity based on adsorbent surface area. The favorable contributions of –OH and –(OH)2 on MIL-101 in the increased adsorption of ibuprofen and oxybenzone (especially based on porosity) confirmed again the importance of H-bonding mechanism. The adsorbent with the highest adsorption capacity, MIL-101-OH, was very competitive when compared with carbonaceous materials, mesoporous materials, and pristine MIL-101. Moreover, the MIL-101-OH could be recycled several times by simply washing with ethanol, suggesting potential application in the adsorptive removal of PPCPs from water. PMID:27695005

  10. Wide pH range for fluoride removal from water by MHS-MgO/MgCO₃ adsorbent: kinetic, thermodynamic and mechanism studies.

    PubMed

    Zhang, Kaisheng; Wu, Shibiao; Wang, Xuelong; He, Junyong; Sun, Bai; Jia, Yong; Luo, Tao; Meng, Fanli; Jin, Zhen; Lin, Dongyue; Shen, Wei; Kong, Lingtao; Liu, Jinhuai

    2015-05-15

    A novel environment friendly adsorbent, micro-nano hierarchical structured flower-like MgO/MgCO3 (MHS-MgO/MgCO3), was developed for fluoride removal from water. The adsorbent was characterized and its defluoridation properties were investigated. Adsorption kinetics fitted well the pseudo-second-order model. Kinetic data revealed that the fluoride adsorption was rapid, more than 83-90% of fluoride could be removed within 30 min, and the adsorption equilibrium was achieved in the following 4 h. The fluoride adsorption isotherm was well described by Freundlich model. The maximum adsorption capacity was about 300 mg/g at pH=7. Moreover, this adsorbent possessed a very wide available pH range of 5-11, and the fluoride removal efficiencies even reached up to 86.2%, 83.2% and 76.5% at pH=11 for initial fluoride concentrations of 10, 20 and 30 mg/L, respectively. The effects of co-existing anions indicated that the anions had less effect on adsorption of fluoride except phosphate. In addition, the adsorption mechanism analysis revealed that the wide available pH range toward fluoride was mainly resulted from the exchange of the carbonate and hydroxyl groups on the surface of the MHS-MgO/MgCO3 with fluoride anions.

  11. Adsorptive Removal of Pharmaceuticals and Personal Care Products from Water with Functionalized Metal-organic Frameworks: Remarkable Adsorbents with Hydrogen-bonding Abilities

    NASA Astrophysics Data System (ADS)

    Seo, Pill Won; Bhadra, Biswa Nath; Ahmed, Imteaz; Khan, Nazmul Abedin; Jhung, Sung Hwa

    2016-10-01

    Adsorption of typical pharmaceuticals and personal care products (PPCPs) (such as naproxen, ibuprofen and oxybenzone) from aqueous solutions was studied by using the highly porous metal-organic framework (MOF) MIL-101 with and without functionalization. Adsorption results showed that MIL-101s with H-donor functional groups such as –OH and –NH2 were very effective for naproxen adsorption, despite a decrease in porosity, probably because of H-bonding between O atoms on naproxen and H atoms on the adsorbent. For this reason, MIL-101 with two functional groups capable of H-bonding (MIL-101-(OH)2) exhibited remarkable adsorption capacity based on adsorbent surface area. The favorable contributions of –OH and –(OH)2 on MIL-101 in the increased adsorption of ibuprofen and oxybenzone (especially based on porosity) confirmed again the importance of H-bonding mechanism. The adsorbent with the highest adsorption capacity, MIL-101-OH, was very competitive when compared with carbonaceous materials, mesoporous materials, and pristine MIL-101. Moreover, the MIL-101-OH could be recycled several times by simply washing with ethanol, suggesting potential application in the adsorptive removal of PPCPs from water.

  12. Hydroxyl and water molecule orientations in trypsin: Comparison to molecular dynamics structures

    SciTech Connect

    McDowell, R.S.; Kossiakoff, A.A.

    1994-12-31

    A comparison is presented of experimentally observed hydroxyl and water hydrogens in trypsin determined from neutron density maps with the results of a 140ps molecular dynamics (MD) simulation. Experimental determination of hydrogen and deuterium atom positions in molecules as large as proteins is a unique capability of neutron diffraction. The comparison addresses the degree to which a standard force-field approach can adequately describe the local electrostatic and van der Waals forces that determine the orientations of these hydrogens. Neutron densities, derived from 2.1{Angstrom} D{sub 2}O-H{sub 2}O difference Fourier maps, provide a database of 27 well-ordered hydroxyl hydrogens. Most of the simulated hydroxyl orientations are within a standard deviation of the experimentally-observed positions, including several examples in which both the simulation and the neutron density indicate that a hydroxyl group is shifted from a {open_quote}standard{close_quote} rotamer. For the most highly ordered water molecules, the hydrogen distributions calculated from the trajectory were in good agreement with neutron density; simulated water molecules that displayed multiple hydrogen bonding networks had correspondingly broadened neutron density profiles. This comparison was facilitated by development of a method to construct a pseudo 2{Angstrom} density map based on the hydrogen atom distributions from the simulation. The degree of disorder of internal water molecules is shown to result primarily from the electrostatic environment surrounding that water molecule as opposed to the cavity size available to the molecule. A method is presented for comparing the discrete observations sampled in a dynamics trajectory with the time- averaged data obtained from X-ray or neutron diffraction studies. This method is particularly useful for statically-disordered water molecules, in which the average location assigned from a trajectory may represent a site of relatively low occupancy.

  13. Effect of Amine Surface Coverage on the Co-Adsorption of CO2 and Water: Spectral Deconvolution of Adsorbed Species.

    PubMed

    Didas, Stephanie A; Sakwa-Novak, Miles A; Foo, Guo Shiou; Sievers, Carsten; Jones, Christopher W

    2014-12-04

    Three primary amine materials functionalized onto mesoporous silica with low, medium, and high surface amine coverages are prepared and evaluated for binary CO2/H2O adsorption under dilute conditions. Enhancement of amine efficiency due to humid adsorption is most pronounced for low surface amine coverage materials. In situ FT-IR spectra of adsorbed CO2 on these materials suggest this enhancement may be associated with the formation of bicarbonate species during adsorption on materials with low surface amine coverage, though such species are not observed on high surface coverage materials. On the materials with the lowest amine loading, bicarbonate is observed on longer time scales of adsorption, but only after spectral contributions from rapidly forming alkylammonium carbamate species are removed. This is the first time that direct evidence for bicarbonate formation, which is known to occur in liquid aqueous amine solutions, has been presented for CO2 adsorption on solid amine adsorbents.

  14. Heat transfer to the adsorbent in solar adsorption cooling device

    NASA Astrophysics Data System (ADS)

    Pilat, Peter; Patsch, Marek; Papucik, Stefan; Vantuch, Martin

    2014-08-01

    The article deals with design and construction of solar adsorption cooling device and with heat transfer problem in adsorber. The most important part of adsorption cooling system is adsorber/desorber containing adsorbent. Zeolith (adsorbent) type was chosen for its high adsorption capacity, like a coolant was used water. In adsorber/desorber occur, at heating of adsorbent, to heat transfer from heat change medium to the adsorbent. The time required for heating of adsorber filling is very important, because on it depend flexibility of cooling system. Zeolith has a large thermal resistance, therefore it had to be adapted the design and construction of adsorber. As the best shows the tube type of adsorber with double coat construction. By this construction is ensured thin layer of adsorbent and heating is quick in all volume of adsorbent. The process of heat transfer was experimentally measured, but for comparison simulated in ANSYS, too.

  15. Giant pumping of single-file water molecules in a carbon nanotube.

    PubMed

    Wang, Y; Zhao, Y J; Huang, J P

    2011-11-17

    Achieving a fast, unidirectional flow of single-file water molecules (UFSWM) across nanochannels is important for membrane-based water purification or seawater desalination. For this purpose, electro-osmosis methods are recognized as a very promising approach and have been extensively discussed in the literature. Utilizing molecular dynamics simulations, here we propose a design for pumping water molecules in a single-walled carbon nanotube in the presence of a linearly gradient electric (GE) field. Such a GE field is inspired by GE fields generated from charged ions located adjacent to biological membrane water nanochannels that can conduct water in and out of cells and can be experimentally achieved by using the charged tip of an atomic force microscope. As a result, the maximum speed of the UFSWM can be 1 or 2 orders of magnitude larger than that in a uniform electric (UE) field. Also, inverse transportation of water molecules does not exist in case of the GE field but can appear for the UE field. Thus, the GE field yields a much more efficient UFSWM than the UE field. The giant pumping ability as revealed is attributed to the nonzero net electrostatic force acting on each water molecule confined in the nanotube. These observations have significance for the design of nanoscale devices for readily achieving controllable UFSWM at high speed.

  16. Water molecules inside protein structure affect binding of monosaccharides with HIV-1 antibody 2G12.

    PubMed

    Ueno-Noto, Kaori; Takano, Keiko

    2016-10-05

    Water molecules inside biomolecules constitute integral parts of their structure and participate in the functions of the proteins. Some of the X-ray crystallographic data are insufficient for analyzing a series of ligand-protein complexes in the same condition. We theoretically investigated antibody binding abilities of saccharide ligands and the effects of the inner water molecules of ligand-antibody complexes. Classical molecular dynamics and quantum chemical simulations using a model with possible water molecules inside the protein were performed with saccharide ligands and Human Immunodeficiency Virus 1 neutralizing antibody 2G12 complexes to estimate how inner water molecules of the protein affect the dynamics of the complexes as well as the ligand-antibody interaction. Our results indicate the fact that d-fructose's strong affinity to the antibody was partly due to the good retentiveness of solvent water molecules of the ligand and its stability of the ligand's conformation and relative position in the active site. © 2016 Wiley Periodicals, Inc.

  17. Electrical-driven transport of endohedral fullerene encapsulating a single water molecule.

    PubMed

    Xu, Baoxing; Chen, Xi

    2013-04-12

    Encapsulating a single water molecule inside an endohedral fullerene provides an opportunity for manipulating the H2O@C60 through the encapsulated polar H2O molecule. Using molecular dynamic simulations, we propose a strategy of electrical-driven transport of H2O@C60 inside a channel, underpinned by the unique behavior of a water molecule free from a hydrogen-bonding environment. When an external electrical field is applied along the channel's axial direction, steady-state transport of H2O@C60 can be reached. The transport direction and rate depend on the applied electrical intensity as well as the polar orientation of the encapsulated H2O molecule.

  18. Molecules, water, and radiant energy: new clues for the origin of life.

    PubMed

    Pollack, Gerald H; Figueroa, Xavier; Zhao, Qing

    2009-03-27

    We here examine the putative first step in the origin of life: the coalescence of dispersed molecules into a more condensed, organized state. Fresh evidence implies that the driving energy for this coalescence may come in a manner more direct than previously thought. The sun's radiant energy separates charge in water, and this free charge demonstrably induces condensation. This condensation mechanism puts water as a central protagonist in life rather than as an incidental participant, and thereby helps explain why life requires water.

  19. Interactions of carbon nanotubes with the nitromethane-water mixture governing selective adsorption of energetic molecules from aqueous solution.

    PubMed

    Liu, Yingzhe; Lai, Weipeng; Yu, Tao; Kang, Ying; Ge, Zhongxue

    2015-03-14

    The structure and dynamics of the nitromethane-water (NM-WT) binary mixture surrounding single walled carbon nanotubes (SWNTs) have been investigated by molecular dynamics simulations. The simulation trajectories show that the NM molecules can be selectively adsorbed both outside the surface and inside the cavity of SWNTs mainly dominated by van der Waals attractions because SWNTs have a higher binding affinity for NM than WT. The binding energies of SWNTs with NM and WT obtained from electronic structure calculations at the M06-2X/6-31+G* level are 15.31 and 5.51 kcal mol(-1), respectively. Compared with the SWNT exterior, the selective adsorption of NM is preferentially occurred in the SWNT interior due to the hydrophobic interactions and the dipole-dipole interactions, which induces the decrease of the hydrogen-bond number of NM with WT and ordered structures of NM with preferred intermolecular orientation in the SWNT cavity. Furthermore, the selective adsorption dynamics of NM from the aqueous solution is regardless of the chirality and radius of SWNTs. The SWNT radius plays a negligible role in the mass density distributions of NM outside the SWNTs, while the mass density of NM in the SWNT interior decreases gradually as the SWNT radius increases. The structural arrangements and intermolecular orientations of NM in the SWNT cavity are greatly dependent on the SWNT radius due to the size effect.

  20. Water-mediated influence of a crowded environment on internal vibrations of a protein molecule.

    PubMed

    Kuffel, Anna; Zielkiewicz, Jan

    2016-02-14

    The influence of crowding on the protein inner dynamics is examined by putting a single protein molecule close to one or two neighboring protein molecules. The presence of additional molecules influences the amplitudes of protein fluctuations. Also, a weak dynamical coupling of collective velocities of surface atoms of proteins separated by a layer of water is detected. The possible mechanisms of these phenomena are described. The cross-correlation function of the collective velocities of surface atoms of two proteins was decomposed into the Fourier series. The amplitude spectrum displays a peak at low frequencies. Also, the results of principal component analysis suggest that the close presence of an additional protein molecule influences the high-amplitude, low-frequency modes in the most prominent way. This part of the spectrum covers biologically important protein motions. The neighbor-induced changes in the inner dynamics of the protein may be connected with the changes in the velocity power spectrum of interfacial water. The additional protein molecule changes the properties of solvation water and in this way it can influence the dynamics of the second protein. It is suggested that this phenomenon may be described, at first approximation, by a damped oscillator driven by an external random force. This model was successfully applied to conformationally rigid Choristoneura fumiferana antifreeze protein molecules.

  1. Influence of Aromatic Molecules on the Structure and Spectroscopy of Water Clusters

    NASA Astrophysics Data System (ADS)

    Tabor, Daniel P.; Sibert, Edwin; Walsh, Patrick S.; Zwier, Timothy S.

    2016-06-01

    Isomer-specific resonant ion-dip infrared spectra are presented for benzene-(water)_n, 1-2-diphenoxyethane-(water)_n, and tricyclophane-(water)_n clusters. The IR spectra are modeled with a local mode Hamiltonian that was originally formulated for the analysis of benzene-(water)_n clusters with up to seven waters. The model accounts for stretch-bend Fermi coupling, which can complicate the IR spectra in the 3150-3300 cm-1 region. When the water clusters interact with each of the solutes, the hydrogen bond lengths between the water molecules change in a characteristic way, reflecting the strength of the solute-water interaction. These structural effects are also reflected spectroscopically in the shifts of the local mode OH stretch frequencies. When diphenoxyethane is the solute, the water clusters distort more significantly than when bound to benzene. Tricyclophane's structure provides an aromatic-rich binding pocket for the water clusters. The local mode model is used to extract Hamiltonians for individual water molecules. These monomer Hamiltonians divide into groups based on their local H-bonding architecture, allowing for further classification of the wide variety of water environments encountered in this study.

  2. Interaction of water molecules with hexagonal 2D systems. A DFT study

    NASA Astrophysics Data System (ADS)

    Rojas, Ángela; Rey, Rafael

    Over the years water sources have been contaminated with many chemical agents, becoming issues that affect health of the world population. The advances of the nanoscience and nanotechnology in the development new materials constitute an alternative for design molecular filters with great efficiencies and low cost for water treatment and purification. In the nanoscale, the process of filtration or separation of inorganic and organic pollutants from water requires to study interactions of these atoms or molecules with different nano-materials. Specifically, it is necessary to understand the role of these interactions in physical and chemical properties of the nano-materials. In this work, the main interest is to do a theoretical study of interaction between water molecules and 2D graphene-like systems, such as silicene (h-Si) or germanene (h-Ge). Using Density Functional Theory we calculate total energy curves as function of separation between of water molecules and 2D systems. Different spatial configurations of water molecules relative to 2D systems are considered. Structural relaxation effects and changes of electronic charge density also are reported. Universidad Nacional de Colombia.

  3. Chemical interaction of water molecules with framework Al in acid zeolites: a periodic ab initio study on H-clinoptilolite.

    PubMed

    Valdiviés-Cruz, Karell; Lam, Anabel; Zicovich-Wilson, Claudio M

    2015-09-28

    Periodic quantum-chemistry methods as implemented in the CRYSTAL14 code were considered to analyse the interaction of acid clinoptilolite with water. Initially adsorbed molecules hydrolyse the Al-O bonds, giving rise to defective dealuminated materials. A suitable and representative periodic model of the partially disordered hydrated H-zeolite is the primitive cell (18 T sites) of a decahydrated trialuminated structure of HEU topology. The water distribution inside the material cavities was initially investigated. The model considered for further dealumination was the most stable one from those generated through a combined force field Monte Carlo and ab initio optimization strategy. Optimizations and energy estimations were made at the hybrid DFT level of theory (PBE0 functional) with an atomic basis set of VDZP quality. The energetics of the different pathways involved in the dealumination process was addressed by considering the Gibbs free energy with thermal and zero-point corrections through phonon analysis. It arises that hydrated models exhibit protonated water clusters stabilized by different kinds of H-bonds. The first Al extraction is slightly more energetically favourable from T3 than T2 sites, but at the same time the latter is more probable owing to its larger Al population. However, concerning the second dealumination step, it is more favourable removing the Al atom from both remaining sites after a starting abstraction from T2 rather than T3. These facts determine that the most probable overall pathways go through a first Al removal from T2. The agreement with experimental results is discussed.

  4. Auger spectrum of a water molecule after single and double core ionization

    NASA Astrophysics Data System (ADS)

    Inhester, Ludger; Burmeister, Carl F.; Groenhof, Gerrit; Grubmueller, Helmut

    2012-06-01

    The high intensity of Free Electron Lasers (FEL) opens up the possibility to perform single-shot molecule scattering experiments. However, even for small molecules radiation damage induced by absorption of intense x-ray radiation is not yet fully understood. To provide insight into this process, we have studied the dynamics of water molecules in single and double core ionized states by means of electronic transition rate calculations and ab initio molecular dynamics (MD) simulations. From MD trajectories photoionization and Auger transition rates were computed based on electronic continuum wavefunctions obtained by explicit integration of the coupled radial Schr"odinger equations. To account for the nuclear dynamics during the core hole lifetime, the calculated electron emission spectra for different molecular geometries were accumulated according to the obtained time-dependent populations. We find that, in contrast to the single core ionized water molecule, the nuclear dynamics for the double core ionized water molecule during the core hole lifetime leaves a clear fingerprint on the electron emission spectra. In addition, the lifetime of the double core ionized water was found to be significantly shorter than half of the single core hole lifetime.

  5. Femtosecond mid-infrared study of the dynamics of water molecules in water-acetone and water-dimethyl sulfoxide mixtures.

    PubMed

    Lotze, S; Groot, C C M; Vennehaug, C; Bakker, H J

    2015-04-23

    We study the vibrational relaxation dynamics and the reorientation dynamics of HDO molecules in binary water-dimethyl sulfoxide (DMSO) and water-acetone mixtures with polarization-resolved femtosecond mid-infrared spectroscopy. For low solute concentrations we observe a slowing down of the reorientation of part of the water molecules that hydrate the hydrophobic methyl groups of DMSO and acetone. For water-DMSO mixtures the fraction of slowed-down water molecules rises much steeper with solute concentration than for water-acetone mixtures, showing that acetone molecules show significant aggregation already at low concentrations. At high solute concentrations, the vibrational and reorientation dynamics of both water-DMSO and water-acetone mixtures show a clear distinction between the dynamics of water molecules donating hydrogen bonds to other water molecules and the dynamics of water donating a hydrogen bond to the S═O/C═O group of the solute. For water-DMSO mixtures both types of water molecules show a very slow reorientation. The water molecules forming hydrogen bonds to the S═O group reorient with a time constant that decreases from 46 ± 14 ps at XDMSO = 0.33 to 13 ± 2 ps at XDMSO = 0.95. The water molecules forming hydrogen bonds to the C═O group of acetone show a much faster reorientation with a time constant that decreases from 6.1 ± 0.2 ps at Xacet = 0.3 to 2.96 ± 0.05 ps at Xacet = 0.9. The large difference in reorientation time constant of the solute-bound water for DMSO and acetone can be explained from the fact that the hydrogen bond between water and the S═O group of DMSO is much stronger than the hydrogen bond between water and the C═O group of acetone. We attribute the strongly different behavior of water in DMSO-rich and acetone-rich mixtures to their difference in molecular shape.

  6. Photo-active and dynamical properties of hematite (Fe2O3)-water interfaces: an experimental and theoretical study.

    PubMed

    English, Niall J; Rahman, Mahfujur; Wadnerkar, Nitin; MacElroy, J M D

    2014-07-28

    The dynamical properties of physically and chemically adsorbed water molecules at pristine hematite-(001) surfaces have been studied by means of equilibrium Born-Oppenheimer molecular dynamics (BOMD) in the NVT ensemble at 298 K. The dissociation of water molecules to form chemically adsorbed species was scrutinised, in addition to 'hopping' or swapping events of protons between water molecules. Particular foci have been dynamical properties of the adsorbed water molecules and OH(-) and H3O(+) ions, the hydrogen bonds between protons in water molecules and the bridging oxygen atoms at the hematite surface, as well as the interactions between oxygen atoms in adsorbed water molecules and iron atoms at the hematite surface. Experimental results for photoelectrical current generation complement simulation findings of water dissociation.

  7. Molecular mimicry of substrate oxygen atoms by water molecules in the beta-amylase active site.

    PubMed

    Pujadas, G; Palau, J

    2001-08-01

    Soybean beta-amylase (EC 3.2.1.2) has been crystallized both free and complexed with a variety of ligands. Four water molecules in the free-enzyme catalytic cleft form a multihydrogen-bond network with eight strategic residues involved in enzyme-ligand hydrogen bonds. We show here that the positions of these four water molecules are coincident with the positions of four potential oxygen atoms of the ligands within the complex. Some of these waters are displaced from the active site when the ligands bind to the enzyme. How many are displaced depends on the shape of the ligand. This means that when one of the four positions is not occupied by a ligand oxygen atom, the corresponding water remains. We studied the functional/structural role of these four waters and conclude that their presence means that the conformation of the eight side chains is fixed in all situations (free or complexed enzyme) and preserved from unwanted or forbidden conformational changes that could hamper the catalytic mechanism. The water structure at the active pocket of beta-amylase is therefore essential for providing the ligand recognition process with plasticity. It does not affect the protein active-site geometry and preserves the overall hydrogen-bonding network, irrespective of which ligand is bound to the enzyme. We also investigated whether other enzymes showed a similar role for water. Finally, we discuss the potential use of these results for predicting whether water molecules can mimic ligand atoms in the active center.

  8. Molecularly Imprinted Filtering Adsorbents for Odor Sensing

    PubMed Central

    Shinohara, Sho; Chiyomaru, You; Sassa, Fumihiro; Liu, Chuanjun; Hayashi, Kenshi

    2016-01-01

    Versatile odor sensors that can discriminate among huge numbers of environmental odorants are desired in many fields, including robotics, environmental monitoring, and food production. However, odor sensors comparable to an animal’s nose have not yet been developed. An animal’s olfactory system recognizes odor clusters with specific molecular properties and uses this combinatorial information in odor discrimination. This suggests that measurement and clustering of odor molecular properties (e.g., polarity, size) using an artificial sensor is a promising approach to odor sensing. Here, adsorbents composed of composite materials with molecular recognition properties were developed for odor sensing. The selectivity of the sensor depends on the adsorbent materials, so specific polymeric materials with particular solubility parameters were chosen to adsorb odorants with various properties. The adsorption properties of the adsorbents could be modified by mixing adsorbent materials. Moreover, a novel molecularly imprinted filtering adsorbent (MIFA), composed of an adsorbent substrate covered with a molecularly imprinted polymer (MIP) layer, was developed to improve the odor molecular recognition ability. The combination of the adsorbent and MIP layer provided a higher specificity toward target molecules. The MIFA thus provides a useful technique for the design and control of adsorbents with adsorption properties specific to particular odor molecules. PMID:27886070

  9. Effects of water molecules on binding kinetics of peptide receptor on a piezoelectric microcantilever

    NASA Astrophysics Data System (ADS)

    Hui Kim, Sang; Kyoung Yoo, Yong; Chae, Myung-Sic; Yoon Kang, Ji; Song Kim, Tae; Seon Hwang, Kyo; Hoon Lee, Jeong

    2012-12-01

    The use of highly selective reversible peptide receptors is essential for cantilever-based electronic nose systems. Here, we present the effects of water molecules on the binding kinetics of 2,4-dinitrotoluene (DNT) molecules with DNT selective peptide receptors linked with a tri(ethylene glycol)-based (TEG) self-assembled monolayer (SAM) in a gas phase in a piezoelectric microcantilever sensor. We observed 1.5-times faster reaction kinetics in wet conditions compared with dry conditions. In a dissociation step, distinctive differences in the recovery time were observed in wet conditions, which could be attributed to water retention efficiency of TEG-linkers for the conformation of biomolecules.

  10. Water, UV shielding, and Organic Molecules in the Terrestrial Planet Region of Disks

    NASA Astrophysics Data System (ADS)

    Najita, Joan; Carr, John

    2015-08-01

    Water vapor is abundant in the inner few AU of protoplanetary disks, as shown by the common detection of mid-infrared emission lines of warm water in T Tauri disk atmospheres. Simple organic molecules are also abundant. The properties of the water and organic molecule emission (column densities and abundances) hint at an active disk chemistry and the synthesis of complex organic molecules. Because T Tauri disks have experienced significant grain growth and settling, the water in the disk atmosphere is expected to be a significant UV opacity source. Recent models of disk atmospheres show that the absorption of stellar FUV photons by water and other molecules not only heats the disk atmosphere but also shields the disk midplane from UV radiation. The properties of the molecular layers synthesized in the models are in good agreement with the observed infrared molecular emission from T Tauri stars. In addition to describing these model results, we will present direct observational evidence for the photodissociation of water and its role in shielding T Tauri disks. Detailed study of the mid-infrared OH emission spectrum reveals the signature of a photochemical origin for the OH, i.e., OH production through photodissociation of water by FUV photons at 1150-1400 A, most likely dominated by Lyman alpha. The nearly ubiquitous presence of rotationally hot OH emission in classical T Tauri stars implies that photodissociation of water is common in the terrestrial planet region of the disk. The resulting UV shielding by water could be important in facilitating a rich organic chemistry in the disk midplane.

  11. Impact of temperature and electrical potentials on the stability and structure of collagen adsorbed on the gold electrode

    NASA Astrophysics Data System (ADS)

    Meiners, Frank; Ahlers, Michael; Brand, Izabella; Wittstock, Gunther

    2015-01-01

    The morphology and structure of collagen type I adsorbed on gold electrodes were studied as a function of electrode potential and temperature by means of capacitance measurements, polarization modulation infrared reflection-absorption spectroscopy and scanning force microscopy at temperatures of 37 °C, 43 °C and 50 °C. The selected temperatures corresponded to the normal body temperature, temperature of denaturation of collagen molecules and denaturation of collagen fibrils, respectively. Independently of the solution temperature, collagen was adsorbed on gold electrodes in the potential range - 0.7 V < E < 0.4 V vs. Ag/AgCl, where the protein film was very stable. Fragments of collagen molecules made a direct contact to the gold surface and water was present in the film. Protein molecules were oriented preferentially with their long axis towards the gold surface. Collagen molecules in the adsorbed state preserved their native triple helical structure even at temperatures corresponding to collagen denaturation in aqueous solutions. Application of E < - 0.75 V vs. Ag/AgCl leads to the swelling of the protein film by water and desorption from the electrode surface. IR spectra provided no evidence of the thermal denaturation of adsorbed collagen molecules. A temperature increase to 50 °C leads to a distortion of the collagen film. The processes of aggregation and fibrilization were preferred over thermal denaturation for collagen adsorbed on the electrode surface and exposed to changing potentials.

  12. Local lateral environment of the molecules at the surface of DMSO-water mixtures

    NASA Astrophysics Data System (ADS)

    Fábián, Balázs; Idrissi, Abdenacer; Marekha, Bogdan; Jedlovszky, Pál

    2016-10-01

    Molecular dynamics simulations of the liquid-vapour interface of dimethyl sulphoxide (DMSO)-water mixtures of 11 different compositions, including two neat systems are performed on the canonical (N, V, T) ensemble at 298 K. The molecules constituting the surface layer of these systems are selected by means of the identification of the truly interfacial molecules (ITIM) method, and their local lateral environment at the liquid surface is investigated by performing Voronoi analysis. The obtained results reveal that both molecules prefer to be in a mixed local environment, consisting of both kinds of molecules, at the liquid surface, and this preference is even stronger here than in the bulk liquid phase. Neat-like patches, in which a molecule is surrounded by like neighbours, are not found. However, vacancies that are surrounded solely by water molecules are observed at the liquid surface. Our results show that strongly hydrogen bonded DMSO·H2O complexes, known to exist in the bulk phase of these mixtures, are absent from the liquid surface.

  13. Proton transfer in hydrogen-bonded network of phenol molecules: intracluster formation of water.

    PubMed

    Lengyel, Jozef; Gorejová, Radka; Herman, Zdeněk; Fárník, Michal

    2013-11-07

    Electron ionization and time-of-flight mass spectrometry was used to investigate the phenol clusters (PhOH)n of different size from single molecule to large clusters: in coexpansion with He, the dimers n = 2 are mostly generated; in Ar, large species of n ≥ 10 also occur. Besides [(PhOH)n](+•) cluster ion series, hydrated phenol cluster ions [(PhOH)n·xH2O](+•) with up to x = 3 water molecules and dehydrated phenol clusters [(PhOH)n-H2O](+•) were observed. The hydrated phenol series exhibits minima and maxima that are interpreted as evidence for proton transfer between the hydrogen bonded cluster ions of cyclic structures. The proton transfer leads to a water generation within the clusters, and subsequent elimination of the diphenyl ether molecule(s) from the cluster yields the hydrated phenol cluster ions. Alternatively, a water molecule release yields a series of dehydrated phenols, among which the diphenyl ether ion [PhOPh](+•) (n = 2) constitutes the maximum.

  14. Preparation and characterization of polar polymeric adsorbents with high surface area for the removal of phenol from water.

    PubMed

    Zeng, Xiaowei; Yu, Tingjun; Wang, Peng; Yuan, Ronghua; Wen, Qing; Fan, Yunge; Wang, Chunhong; Shi, Rongfu

    2010-05-15

    Preparation of methyl methacrylate (MMA)/divinylbenzene (DVB) and ethylene glycol dimethacrylate (EGDMA)/DVB copolymers via suspension polymerization yielded precursors which possess residual vinyl groups. Post-crosslinking of appropriate dichloroethane swollen precursors without external crosslinking agent in the presence of anhydrous ferric chloride (FeCl(3)) yielded post-crosslinked resins with high surface area and suitable polarity. FT-IR spectrum indicated that increasing the proportion of MMA or EGDMA in monomer mixtures notably reduces the amount of the pendant vinyl groups onto the matrix of the precursors. Furthermore, the pendant vinyl groups of precursors were almost absent when the content of MMA and EGDMA increased to 40 mol% and 20 mol% in the monomers, respectively. The specific surface areas and pore volumes of copolymers showed a remarkable increase after post-crosslinking. Experimental results showed that isotherms of phenol adsorption onto these polymeric adsorbents could be represented by Freundlich model and Langmuir model reasonably. PDE-5 pc exhibited higher adsorption capacity of phenol than other adsorbents, which resulted from synergistic effect of larger specific surface area and polar groups onto the network. Column adsorption/desorption dynamic curves suggested that PDE-5 pc is a potential candidate for treatment of chemical effluent containing phenol and phenolic pollutants.

  15. Arsenic Re-Mobilization in Water Treatment Adsorbents Under Reducing Conditions: Part II, XAS and Modeling Study

    SciTech Connect

    Liu,S.; Jing, C.; Meng, X.

    2008-01-01

    The mechanism of arsenic re-mobilization in spent adsorbents under reducing conditions was studied using X-ray absorption spectroscopy and surface complexation model calculations. X-ray absorption near edge structure (XANES) spectroscopy demonstrated that As(V) was partially reduced to As(III) in spent granular ferric hydroxide (GFH), titanium dioxide (TiO2), activated alumina (AA) and modified activated alumina (MAA) adsorbents after 2 years of anaerobic incubation. As(V) was completely reduced to As(III) in spent granular ferric oxide (GFO) under 2-year incubation. The extended X-ray absorption fine structure (EXAFS) spectroscopy analysis showed that As(III) formed bidentate binuclear surface complexes on GFO as evidenced by an average As(III)-O bond distance of 1.78 Angstroms and As(III)-Fe distance of 3.34 Angstroms . The release of As from the spent GFO and TiO2 was simulated using the charge distribution multi-site complexation (CD-MUSIC) model. The observed redox ranges for As release and sulfate mobility were described by model calculations.

  16. Sum Frequency Generation Vibrational Spectroscopy of Adsorbed Amino Acids, Peptides and Proteins of Hydrophilic and Hydrophobic Solid-Water Interfaces

    SciTech Connect

    Holinga IV, George Joseph

    2010-09-01

    Sum frequency generation (SFG) vibrational spectroscopy was used to investigate the interfacial properties of several amino acids, peptides, and proteins adsorbed at the hydrophilic polystyrene solid-liquid and the hydrophobic silica solid-liquid interfaces. The influence of experimental geometry on the sensitivity and resolution of the SFG vibrational spectroscopy technique was investigated both theoretically and experimentally. SFG was implemented to investigate the adsorption and organization of eight individual amino acids at model hydrophilic and hydrophobic surfaces under physiological conditions. Biointerface studies were conducted using a combination of SFG and quartz crystal microbalance (QCM) comparing the interfacial structure and concentration of two amino acids and their corresponding homopeptides at two model liquid-solid interfaces as a function of their concentration in aqueous solutions. The influence of temperature, concentration, equilibration time, and electrical bias on the extent of adsorption and interfacial structure of biomolecules were explored at the liquid-solid interface via QCM and SFG. QCM was utilized to quantify the biological activity of heparin functionalized surfaces. A novel optical parametric amplifier was developed and utilized in SFG experiments to investigate the secondary structure of an adsorbed model peptide at the solid-liquid interface.

  17. DFTr optimization and DFTr-MD studies of glucose, ten explicit water molecules enclosed by an implicit solvent, COSMO

    Technology Transfer Automated Retrieval System (TEKTRAN)

    DFTr optimization studies are carried out on alpha/beta-glucose surrounded by ten explicit water molecules and the glucose/water super-molecule completely enclosed by an implicit solvation model, COSMO. Twenty one starting configurations of the explicit waters were first optimized empirically with t...

  18. Evaluation of the use of performance reference compounds in an oasis-HLB adsorbent based passive sampler for improving water concentration estimates of polar herbicides in freshwater

    USGS Publications Warehouse

    Mazzella, N.; Lissalde, S.; Moreira, S.; Delmas, F.; Mazellier, P.; Huckins, J.N.

    2010-01-01

    Passive samplers such as the Polar Organic Chemical Integrative Sampler (POCIS) are useful tools for monitoring trace levels of polar organic chemicals in aquatic environments. The use of performance reference compounds (PRC) spiked into the POCIS adsorbent for in situ calibration may improve the semiquantitative nature of water concentration estimates based on this type of sampler. In this work, deuterium labeled atrazine-desisopropyl (DIA-d5) was chosen as PRC because of its relatively high fugacity from Oasis HLB (the POCIS adsorbent used) and our earlier evidence of its isotropic exchange. In situ calibration of POCIS spiked with DIA-d5was performed, and the resulting time-weighted average concentration estimates were compared with similar values from an automatic sampler equipped with Oasis HLB cartridges. Before PRC correction, water concentration estimates based on POCIS data sampling ratesfrom a laboratory calibration exposure were systematically lower than the reference concentrations obtained with the automatic sampler. Use of the DIA-d5 PRC data to correct POCIS sampling rates narrowed differences between corresponding values derived from the two methods. Application of PRCs for in situ calibration seems promising for improving POCIS-derived concentration estimates of polar pesticides. However, careful attention must be paid to the minimization of matrix effects when the quantification is performed by HPLC-ESI-MS/MS. ?? 2010 American Chemical Society.

  19. Graphene-modified TiO2 nanotube arrays as an adsorbent in micro-solid phase extraction for determination of carbamate pesticides in water samples.

    PubMed

    Zhou, Qingxiang; Fang, Zhi

    2015-04-15

    Graphene is a good adsorbent for organic pollutants, especially for compounds containing benzene rings. When used in TiO2 nanotube arrays for micro-solid phase extraction (μ-SPE), the combination of graphene's strong adsorptive properties with its good separation capabilities results in excellent sample preconcentration performance. In the present study, graphene-modified TiO2 nanotube arrays were prepared by electrodeposition using a cyclic voltammetric reduction method. Four carbamate pesticides, including metolcarb, carbaryl, isoprocarb, and diethofencarb, were used as model analytes to validate the enrichment properties of the prepared adsorbent in μ-SPE. Factors affecting the enrichment efficiency of the μ-SPE procedure were optimized and included sample pH, elution solvents, salting-out effect, adsorption time and desorption time. Under optimal conditions, graphene-modified TiO2 nanotube arrays exhibited excellent enrichment efficiency for carbamate pesticides. The detection limits of these carbamate pesticides ranged from 2.27 to 3.26 μg L(-1). The proposed method was validated using four environmental water samples, and yields of pesticides recovered from spiked test samples of the four analytes were in the range of 83.9-108.8%. These results indicate that graphene-modified TiO2 nanotube arrays exhibit good adsorption to the target pollutants, and the method described in this work could be used as a faster and easier alternative procedure for routine analysis of carbamate pesticides in real water samples.

  20. Determination of triazine herbicides in environmental water samples by high-performance liquid chromatography using graphene-coated magnetic nanoparticles as adsorbent.

    PubMed

    Zhao, Guangying; Song, Shuangju; Wang, Chun; Wu, Qiuhua; Wang, Zhi

    2011-12-05

    In this paper, a graphene-based Fe(3)O(4) magnetic nanoparticles (G-Fe(3)O(4) MNPs) was used as the adsorbent for the magnetic solid-phase extraction of some triazine herbicides (atrazine, prometon, propazine and prometryn) in environmental water samples followed by high performance liquid chromatography-diode array detection (HPLC-DAD). After the extraction, the adsorbent can be conveniently separated from the aqueous samples by an external magnet. The main factors influencing the extraction efficiency including the amount of the MNPs, the extraction time, the pH of sample solution, and desorption conditions were studied and optimized. Under the optimized experimental conditions, a good linearity was observed in the range of 0.1-50.0 ng mL(-1) for all the analytes, with the correlation coefficients (r) ranging from 0.9996 to 0.9999. The limits of detection of the method ranged between 0.025 and 0.040 ng mL(-1). Good reproducibility was obtained with the relative standard deviations below 5.2%. The developed method was applied to the analysis of the triazine herbicides in different water samples (lake, river and reservoir). The recoveries of the method were in the range between 89.0% and 96.2%.

  1. Magnetized graphene layers synthesized on the carbon nanofibers as novel adsorbent for the extraction of polycyclic aromatic hydrocarbons from environmental water samples.

    PubMed

    Rezvani-Eivari, Mostafa; Amiri, Amirhassan; Baghayeri, Mehdi; Ghaemi, Ferial

    2016-09-23

    The application of magnetized graphene (G) layers synthesized on the carbon nanofibers (CNFs) (m-G/CNF) was investigated as novel adsorbent for the magnetic solid-phase extraction (MSPE) of polycyclic aromatic hydrocarbons (PAHs) in water samples followed by gas chromatography-flame ionization detector (GC-FID). Six important parameters, affecting the extraction efficiency of PAHs, including: amount of adsorbent, adsorption and desorption times, type and volume of the eluent solvent and salt content of the sample were evaluated. The optimum extraction conditions were obtained as: 5min for extraction time, 20mg for sorbent amount, dichloromethane as desorption solvent, 1mL for desorption solvent volume, 5min for desorption time and 15% (w/v) for NaCl concentration. Good performance data were obtained at the optimized conditions. The calibration curves were linear over the concentration ranges from 0.012 to 100ngmL(-1) with correlation coefficients (r) between 0.9950 and 0.9967 for all the analytes. The limits of detection (LODs, S/N=3) of the proposed method for the studied PAHs were 0.004-0.03ngmL(-1). The relative standard deviations (RSDs) for five replicates at two concentration levels (0.1 and 50ngmL(-1)) of PAHs were ranged from 3.4 to 5.7%. Appropriate relative recovery values, in the range of 95.5-99.9%, were also obtained for the real water sample analysis.

  2. Study of the betulin molecule in a water environment; ab initio and molecular simulation calculations.

    PubMed

    Pospíšil, Miroslav; Kovář, Petr; Vácha, Robert; Svoboda, Michal

    2012-01-01

    Ab initio and molecular simulation methods were used in calculations of the neutral individual betulin molecule, and molecular simulations were used to optimize the betulin molecule immersed in various amounts of water. Individual betulin was optimized in different force fields to find the one exhibiting best agreement with ab initio calculations obtained in the Gaussian03 program. Dihedral torsions of active groups of betulin were determined for both procedures, and related calculated structures were compared successfully. The selected force field was used for subsequent optimization of betulin in a water environment, and a conformational search was performed using quench molecular dynamics. The total energies of betulin and its interactions in water bulk were calculated, and the influence of water on betulin structure was investigated.

  3. Molecular Water Lilies: Orienting Single Molecules in a Polymer Film by Solvent Vapor Annealing.

    PubMed

    Würsch, Dominik; Hofmann, Felix J; Eder, Theresa; Aggarwal, A Vikas; Idelson, Alissa; Höger, Sigurd; Lupton, John M; Vogelsang, Jan

    2016-11-17

    The microscopic orientation and position of photoactive molecules is crucial to the operation of optoelectronic devices such as OLEDs and solar cells. Here, we introduce a shape-persistent macrocyclic molecule as an excellent fluorescent probe to simply measure (i) its orientation by rotating the excitation polarization and recording the strength of modulation in photoluminescence (PL) and (ii) its position in a film by analyzing the overall PL brightness at the molecular level. The unique shape, the absorption and the fluorescence properties of this probe yield information on molecular orientation and position. We control orientation and positioning of the probe in a polymer film by solvent vapor annealing (SVA). During the SVA process the molecules accumulate at the polymer/air interface, where they adopt a flat orientation, much like water lilies on the surface of a pond. The results are potentially significant for OLED fabrication and single-molecule spectroscopy (SMS) in general.

  4. An interpretation of the enhancement of the water dipole moment due to the presence of other water molecules.

    PubMed

    Kemp, Daniel D; Gordon, Mark S

    2008-06-05

    The dipole moment of the gas phase water monomer is 1.85 D. When solvated in bulk water, the dipole moment of an individual water molecule is observed to be enhanced to the much larger value of 2.9 +/- 0.6 D. To understand the origin of this dipole moment enhancement, the effective fragment potential (EFP) method is used to solvate an ab initio water molecule to predict the dipole moments for various cluster sizes. The dipole moment as a function of cluster size, nH 2O, is investigated [for n = 6-20 (even n), 26, 32, 41, and 50]. Localized charge distributions are used in conjunction with localized molecular orbitals to interpret the dipole moment enhancement. These calculations suggest that the enhancement of the dipole moment originates from the decrease of the angle between the dipole vectors of the lone pairs on oxygen as the number of hydrogen bonds to that oxygen increases. Thus, the decreased angle, and the consequent increase in water dipole moment, is most likely to occur in environments with a larger number of hydrogen bonds, such as the center of a cluster of water molecules.

  5. In vivo diffusion MRS investigation of non-water molecules in biological tissues.

    PubMed

    Cao, Peng; Wu, Ed X

    2017-03-01

    Diffusion MRS of non-water molecules offers great potential in directly revealing various tissue microstructures and physiology at both cellular and subcellular levels. In brain, (1) H diffusion MRS has been demonstrated as a new tool for probing normal tissue microstructures and their pathological changes. In skeletal muscle, (1) H diffusion MRS could characterize slow and restricted intramyocellular lipid diffusion, providing a sensitive marker for metabolic alterations, while (31) P diffusion MRS can measure ATP and PCr diffusion, which may reflect the capacity of cellular energy transport, complementing the information from frequently used (31) P MRS in muscle. In intervertebral disk, (1) H diffusion MRS can directly monitor extracellular matrix integrity by quantifying the mobility of macromolecules such as proteoglycans and collagens. In tumor tissue, (13) C diffusion MRS could probe intracellular glycolytic metabolism, while (1) H diffusion MRS may separate the spectrally overlapped lactate and lipid resonances. In this review, recent diffusion MRS studies of these biologically relevant non-water molecules under normal and diseased conditions will be presented. Technical considerations for diffusion MRS experiments will be discussed. With advances in MRI hardware and diffusion methodology, diffusion MRS of non-water molecules is expected to provide increasingly valuable and biologically specific information on tissue microstructures and physiology, complementing the traditional diffusion MRI of small and ubiquitous water molecules. Copyright © 2016 John Wiley & Sons, Ltd.

  6. Contribution of water molecules in the spontaneous release of protein by graphene sheets.

    PubMed

    Liang, Li-Jun; Wang, Qi; Wu, Tao; Sun, Tian-Yang; Kang, Yu

    2013-09-16

    Applications of graphene sheets in the fields of biosensors and biomedical devices are limited by the aqueous solubility of graphene. Consequently, understanding the role of water molecules in the aggregation or dispersion of graphene in aqueous solution with a biomolecule is of vital importance to its application. Herein, protein is spontaneously released by the layer-to-layer aggregation of two single-layer graphene sheets due to van der Waals force between the sheets. The properties of water molecules, including density and dynamics, are discussed in detail. The dynamic behavior of aggregation of graphene sheets is triggered by the dynamics of water molecules. To stabilize dispersed graphene sheets in aqueous solution, the density of water molecules between the graphene sheets should be larger than 0.83 g cm(-3), and graphene modified by hydroxyl groups could be a good choice. The stability of a model protein on the graphene sheet is studied to investigate the biological compatibility of graphene sheets. To be a material with good biocompatibility, graphene should be functionalized by hydrophilic groups. The results presented herein could be helpful in the research and application of graphene sheets in the fields of biomaterials, biosensors, and biomedical devices.

  7. Size, separation, structural order, and mass density of molecules packing in water and ice.

    PubMed

    Huang, Yongli; Zhang, Xi; Ma, Zengsheng; Li, Wen; Zhou, Yichun; Zhou, Ji; Zheng, Weitao; Sun, Chang Q

    2013-10-21

    The structural symmetry and molecular separation in water and ice remain uncertain. We present herewith a solution to unifying the density, the structure order and symmetry, the size (H-O length dH), and the separation (d(OO) = d(L) + d(H) or the O:H length d(L)) of molecules packing in water and ice in terms of statistic mean. This solution reconciles: i) the d(L) and the d(H) symmetrization of the O:H-O bond in compressed ice, ii) the d(OO) relaxation of cooling water and ice and, iii) the d(OO) expansion of a dimer and between molecules at water surface. With any one of the d(OO), the density ρ(g·cm⁻³), the d(L), and the d(H), as a known input, one can resolve the rest quantities using this solution that is probing conditions or methods independent. We clarified that: i) liquid water prefers statistically the mono-phase of tetrahedrally-coordinated structure with fluctuation, ii) the low-density phase (supersolid phase as it is strongly polarized with even lower density) exists only in regions consisting molecules with fewer than four neighbors and, iii) repulsion between electron pairs on adjacent oxygen atoms dictates the cooperative relaxation of the segmented O:H-O bond, which is responsible for the performance of water and ice.

  8. Thermodynamics of hydrogen bond patterns in supramolecular assemblies of water molecules.

    PubMed

    Henry, Marc

    2002-07-02

    The PACHA (Partial Atomic Charges and Hardnesses Analysis) formalism is applied to various supramolecular assemblies of water molecules. After a detailed study of all available crystal structures for ice polymorphs, we shown that the hydrogen bond strength is roughly constant below 1 GPa and considerably weakened above that value. New hydrogen bond patterns are proposed for ice IV, V, and VI after (EB) (electrostatic balance) minimization. For other polymorphs, there is an almost perfect coincidence between experimental and predicted hydrogen bond patterns. The evolution of hydrogen bond energy as a function of molecular geometry in water clusters with up to 280 water molecules and in large supramolecular compounds is quantitatively described. Intermolecular hydrogen bonds are found to lie between -9 and -32 kJ mol-1, the stronger interaction occurs within the spherical fully disordered water droplet buried at the heart of Müller's superfullerene keplerate. The weakest one occurs in a chiral molecular snub cube built from six calix[4]resorcinarene and eight water molecules. Intramolecular hydrogen bonds are found in the range -10-100 kJ mol-1 and can thus be considerably stronger than intermolecular bonds. Finally, through the investigation of a clathrate type I compound, it was possible to obtain a deep insight of the host-guest interactions and self-assembly rules of water cages in these materials.

  9. Conserved water molecules in family 1 glycosidases: a DXMS and molecular dynamics study.

    PubMed

    Teze, David; Hendrickx, Johann; Dion, Michel; Tellier, Charles; Woods, Virgil L; Tran, Vinh; Sanejouand, Yves-Henri

    2013-08-27

    By taking advantage of the wealth of structural data available for family 1 glycoside hydrolases, a study of the conservation of internal water molecules found in this ubiquitous family of enzymes was undertaken. Strikingly, seven water molecules are observed in more than 90% of the known structures. To gain insight into their possible function, the water dynamics inside Thermus thermophilus β-glycosidase was probed using deuterium exchange mass spectroscopy, allowing the pinpointing of peptide L117-A125, which exchanges most of its amide hydrogens quickly in spite of the fact that it is for the most part buried in the crystal structure. To help interpret this result, a molecular dynamics simulation was performed whose analysis suggests that two water channels are involved in the process. The longest one (∼16 Å) extends between the protein surface and W120, whose side chain interacts with E164 (the acid-base residue involved in the catalytic mechanism), whereas the other channel allows for the exchange with the bulk of the highly conserved water molecules belonging to the hydration shell of D121, a deeply buried residue. Our simulation also shows that another chain of highly conserved water molecules, going from the protein surface to the bottom of the active site cleft close to the nucleophile residue involved in the catalytic mechanism, is able to exchange with the bulk on the nanosecond time scale. It is tempting to speculate that at least one of these three water channels could be involved in the function of family 1 glycoside hydrolases.

  10. Water/carbonate stripping for CO.sub.2 capture adsorber regeneration and CO.sub.2 delivery to photoautotrophs

    DOEpatents

    Chance, Ronald; Koros, William J.; McCool, Benjamin; Noel, James

    2015-08-11

    The invention provides systems and methods for the delivery of carbon to photoautotrophs. The invention utilizes low energy regeneration of adsorbent for CO.sub.2 capture and provides for effective CO.sub.2 loading into liquids useful for photoautotroph growth and/or production of photosynthetic products, such as biofuels, via photoautotrophic culture media. The inventive system comprises a fluid/membrane/fluid contactor that provides selective transfer of molecular CO.sub.2 via a dense (non-porous) membrane from a carbonate-based CO.sub.2 snipping solution to a culture medium where the CO.sub.2 is consumed by a photoautotroph for the production of biofuels, biofuel precursors or other commercial products.

  11. Simultaneous removal of multiple pesticides from water: effect of organically modified clays as coagulant aid and adsorbent in coagulation-flocculation process.

    PubMed

    Shabeer, T P Ahammed; Saha, Ajoy; Gajbhiye, V T; Gupta, Suman; Manjaiah, K M; Varghese, Eldho

    2014-01-01

    Contamination of drinking water sources with agrochemical residues became a major concern in the twenty-first century. Coagulation-flocculation is the most widely used water-treatment process, but the efficiency to remove pesticides and other organic pollutants are limited compared to adsorption process. Thus, simultaneous action of adsorption on normal bentonite or organo-modified montmorillonite clays [modified with octadecylamine (ODA-M) and octadecylamine + amino-propyltriethoxysilane (ODAAPS-M)] followed by coagulation-flocculation by alum and poly aluminium chloride has been evaluated for removal of 10 different pesticides, namely atrazine, lindane, metribuzin, aldrin, chlorpyriphos, pendimethalin, alpha-endosulphan, beta-endosulphan, p,p'-DDT, cypermethrin and two of its metabolites, endosulphan sulphate and p,p'-DDE, from water. The coagulation without integration of adsorption was less effective (removal % varies from 12 to 49) than the adsorption-coagulation integrated system (removal % varies from 71 to 100). Further, coagulation integrated with adsorption was more effective when organically modified montmorillonite was used as adsorbent compared to normal bentonite. The removal efficiency of organic clay depends upon the concentration of pesticides, doses of clay minerals, and efficiency was more for ODAAPS-M as compared to ODA-M. The combination of ODAAPS-M-clay with coagulants was also used efficiently for the removal of pesticides from natural and fortified natural water collected and the results exhibit the usefulness of this remediation technique for application in water decontamination and in treatment of industrial and agricultural waste waters.

  12. Hydrogen bonding changes of internal water molecules in rhodopsin during metarhodopsin I and metarhodopsin II formation.

    PubMed Central

    Rath, P; Delange, F; Degrip, W J; Rothschild, K J

    1998-01-01

    Rhodopsin is a 7-helix, integral membrane protein found in the rod outer segments, which serves as the light receptor in vision. Light absorption by the retinylidene chromophore of rhodopsin triggers an 11-cis-->all-trans isomerization, followed by a series of protein conformational changes, which culminate in the binding and activation of the G-protein transducin by the metarhodopsin II (Meta II) intermediate. Fourier transform IR difference spectroscopy has been used to investigate the structural changes that water, as well as other OH- and NH-containing groups, undergo during the formation of the metarhodopsin I (Meta I) and Meta II intermediates. Bands associated with the OH stretch modes of water are identified by characteristic downshifts upon substitution of H2(18)O for H2O. Compared with earlier work, several negative bands associated with water molecules in unphotolysed rhodopsin were detected, which shift to lower frequencies upon formation of the Meta I and Meta II intermediates. These data indicate that at least one water molecule undergoes an increase in hydrogen bonding upon formation of the Meta I intermediate, while at least one other increases its hydrogen bonding during Meta II formation. Amino acid residue Asp-83, which undergoes a change in its hydrogen bonding during Meta II formation, does not appear to interact with any of the structurally active water molecules. Several NH and/or OH groups, which are inaccessible to hydrogen/deuterium exchange, also undergo alterations during Meta I and Meta II formation. PMID:9445403

  13. Neuroscience of water molecules: a salute to professor Linus Carl Pauling.

    PubMed

    Nakada, Tsutomu

    2009-04-01

    More than 35 years ago double Nobel laureate Linus Carl Pauling published a powerful model of the molecular mechanism of general anesthesia, generally referred to as the hydrate-microcrystal (aqueous-phase) theory. This hypothesis, based on the molecular behavior of water molecules, did not receive serious attention during Pauling's life time, when scientific tools for examining complex systems such as the brain were still in their infancy. The situation has since drastically changed, and, now, in the twenty first century, many scientific tools are available for examining different types of complex systems. The discovery of aquaporin-4, a subtype of water channel abundantly expressed in glial systems, further highlighted the concept that the dynamics of water molecules in the cerebral cortex play an important role in important physiological brain functions including consciousness and information processing.

  14. A novel fiber-based adsorbent technology

    SciTech Connect

    Reynolds, T.A.

    1997-10-01

    In this Phase I Small Business Innovation Research program, Chemica Technologies, Inc. is developing an economical, robust, fiber-based adsorbent technology for removal of heavy metals from contaminated water. The key innovation is the development of regenerable adsorbent fibers and adsorbent fiber cloths that have high capacity and selectivity for heavy metals and are chemically robust. The process has the potential for widespread use at DOE facilities, mining operations, and the chemical process industry.

  15. Rotational excitation of water by hydrogen molecules: comparison of results from classical and quantum mechanics.

    PubMed

    Faure, Alexandre; Wiesenfeld, Laurent; Wernli, Michael; Valiron, Pierre

    2006-06-07

    Quasiclassical trajectory calculations are carried out for rotational excitation of water by hydrogen molecules. State-to-state rate coefficients are determined at 100 K and are compared to available quantum results. A good agreement between classical and quantum rates is observed for downward transitions, with an average accuracy of classical results better than a factor of 2. It is thus found that the ambiguities described by Faure and Wiesenfeld [J. Chem. Phys. 121, 6771 (2004)] can be solved in the particular case of waterlike asymmetric-top molecules.

  16. Monte Carlo simulation of several biologically relevant molecules and zwitterions in water

    NASA Astrophysics Data System (ADS)

    Patuwo, Michael Y.; Bettens, Ryan P. A.

    2012-02-01

    In this work, we study the hydration free energies of butane, zwitterionic alanine, valine, serine, threonine, and asparagine, and two neuraminidase inhibitors by means of Monte Carlo (MC) simulation. The solute molecule, represented in the form of distributed multipoles and modified 6-12 potential, was varied from a non-interacting 'ghost' molecule to its full potential functions in TIP4P water. Intermediate systems with soft-core solute-solvent interaction potentials are simulated separately and then subjected to Bennett's Acceptance ratio (BAR) for the free energy calculation. Hydration shells surrounding the solute particles were used to assess the quality of potential functions.

  17. A 2D-g-C3N4 nanosheet as an eco-friendly adsorbent for various environmental pollutants in water.

    PubMed

    Cai, Xingguo; He, Junyong; Chen, Liang; Chen, Kai; Li, Yulian; Zhang, Kaisheng; Jin, Zhen; Liu, Jinyun; Wang, Chengming; Wang, Xuguang; Kong, Lingtao; Liu, Jinhuai

    2017-03-01

    A novel graphitic carbon nitride (g-C3N4) nanosheet adsorbent with a large surface area, remarkable hydrophilicity and high adsorption capacity, was presented for the removal of cadmium ions (Cd(2+)) and methylene blue (MB) from aqueous solution. Adsorption measurements were conducted systematically to study the influences of the contact time, initial concentrations of Cd(2+) and MB, temperature, and pH value. The maximum adsorption capacities of g-C3N4 towards Cd(2+) and MB were 94.4 and 42.1 mg g(-1), respectively, at 318.5 K when the initial concentrations of Cd(2+) and MB were 200 and 20 mg L(-1), respectively. The adsorption kinetics fit a pseudo-second-order model. The high adsorption performance of the g-C3N4 adsorbent can be attributed to the multiple adsorption sites on g-C3N4, including the π-π conjugate interactions and electrostatic attractions with pollutants in water. In addition, it is significant to achieve high adsorption performance of g-C3N4 nanosheets by efficiently exposing the adsorption sites by adjusting the microstructure surface properties and dispersity in solution.

  18. INTERSTELLAR ICES AS WITNESSES OF STAR FORMATION: SELECTIVE DEUTERATION OF WATER AND ORGANIC MOLECULES UNVEILED

    SciTech Connect

    Cazaux, S.; Spaans, M.; Caselli, P.

    2011-11-10

    Observations of star-forming environments revealed that the abundances of some deuterated interstellar molecules are markedly larger than the cosmic D/H ratio of 10{sup -5}. Possible reasons for this pointed to grain surface chemistry. However, organic molecules and water, which are both ice constituents, do not enjoy the same deuteration. For example, deuterated formaldehyde is very abundant in comets and star-forming regions, while deuterated water rarely is. In this paper, we explain this selective deuteration by following the formation of ices (using the rate equation method) in translucent clouds, as well as their evolution as the cloud collapses to form a star. Ices start with the deposition of gas-phase CO and O onto dust grains. While reaction of oxygen with atoms (H or D) or molecules (H{sub 2}) yields H{sub 2}O (HDO), CO only reacts with atoms (H and D) to form H{sub 2}CO (HDCO, D{sub 2}CO). As a result, the deuteration of formaldehyde is sensitive to the gas D/H ratio as the cloud undergoes gravitational collapse, while the deuteration of water strongly depends on the dust temperature at the time of ice formation. These results reproduce well the deuterium fractionation of formaldehyde observed in comets and star-forming regions and can explain the wide spread of deuterium fractionation of water observed in these environments.

  19. Hydrophobic molecules slow down the hydrogen-bond dynamics of water.

    PubMed

    Bakulin, Artem A; Pshenichnikov, Maxim S; Bakker, Huib J; Petersen, Christian

    2011-03-17

    We study the spectral and orientational dynamics of HDO molecules in solutions of tertiary-butyl-alcohol (TBA), trimethyl-amine-oxide (TMAO), and tetramethylurea (TMU) in isotopically diluted water (HDO:D(2)O and HDO:H(2)O). The spectral dynamics are studied with femtosecond two-dimensional infrared spectroscopy and the orientational dynamics with femtosecond polarization-resolved vibrational pump-probe spectroscopy. We observe a strong slowing down of the spectral diffusion around the central part of the absorption line that increases with increasing solute concentration. At low concentrations, the fraction of water showing slow spectral dynamics is observed to scale with the number of methyl groups, indicating that this effect is due to slow hydrogen-bond dynamics in the hydration shell of the methyl groups of the solute molecules. The slowing down of the vibrational frequency dynamics is strongly correlated with the slowing down of the orientational mobility of the water molecules. This correlation indicates that these effects have a common origin in the effect of hydrophobic molecular groups on the hydrogen-bond dynamics of water.

  20. H^- and D^- channels of Dissociative Electron Attachment to water molecules

    NASA Astrophysics Data System (ADS)

    Adaniya, Hidehito; Rudek, Benedikt; Osipov, Timur; Lee, Sun; Weber, Thorsten; Hertlein, Marcus; Schoeffler, Markus; Prior, Mike; Belkacem, Ali

    2009-05-01

    A COLTRIM technique is modified to measure the kinetic energy and angular distribution of H^- and D^- ions arising from dissociative electron attachment to water and heavy water molecules. A low energy pulsed electron, an effusive water target, a pulsed extraction plate are used in combination with the COLTRIMS spectrometer. The spectrometer carries an electrostatic lens system to compensate the effusiveness of the target. This technique is applied to study the H^- and D^- channels in the three Feshbach resonances of water and heavy water anion. The measured kinetic energy release will give the energy partitioning among the fragments, and the means to identify the two-body and three-body breakup channels. The angular distribution of the H^-(D^-) ions with respect to the electron beam is found to reflect well the breakup dynamics of the H2O^- at the dissociation. The experimental results are compared with the theoretical predictions.

  1. Temperature dependence of local solubility of hydrophobic molecules in the liquid-vapor interface of water.

    PubMed

    Abe, Kiharu; Sumi, Tomonari; Koga, Kenichiro

    2014-11-14

    One important aspect of the hydrophobic effect is that solubility of small, nonpolar molecules in liquid water decreases with increasing temperature. We investigate here how the characteristic temperature dependence in liquid water persists or changes in the vicinity of the liquid-vapor interface. From the molecular dynamics simulation and the test-particle insertion method, the local solubility Σ of methane in the liquid-vapor interface of water as well as Σ of nonpolar solutes in the interface of simple liquids are calculated as a function of the distance z from the interface. We then examine the temperature dependence of Σ under two conditions: variation of Σ at fixed position z and that at fixed local solvent density around the solute molecule. It is found that the temperature dependence of Σ at fixed z depends on the position z and the system, whereas Σ at fixed local density decreases with increasing temperature for all the model solutions at any fixed density between vapor and liquid phases. The monotonic decrease of Σ under the fixed-density condition in the liquid-vapor interface is in accord with what we know for the solubility of nonpolar molecules in bulk liquid water under the fixed-volume condition but it is much robust since the solvent density to be fixed can be anything between the coexisting vapor and liquid phases. A unique feature found in the water interface is that there is a minimum in the local solubility profile Σ(z) on the liquid side of the interface. We find that with decreasing temperature the minimum of Σ grows and at the same time the first peak in the oscillatory density profile of water develops. It is likely that the minimum of Σ is due to the layering structure of the free interface of water.

  2. Picosecond adsorbate dynamics at condensed phase interfaces

    SciTech Connect

    Scott, T.W.; Chang, Y.J.; Martorell, J.

    1993-12-31

    Picosecond surface second harmonic generation has been used to probe a variety of elementary adsorbate reactions at liquid-solid interfaces. Electron transfer reactions at semiconductor-liquid junctions, geminate recombination of photogenerated free radical pairs and the orientational dynamics of dipolar adsorbates have all been explored in varying degrees of detail. These kinetic studies have led to a detailed analysis of adsorbate detection on the surface of non-centrosymmetric substrates as well as the use of total internal reflection geometries for signal enhancement from optically absorbing liquids. Particular emphasis has been placed on the static and dynamic characterization of adsorbate orientational distribution functions and how these are determined from the torque exerted on adsorbates by the angular part of the molecule-surface interaction potential.

  3. Nanovalved Adsorbents for CH4 Storage.

    PubMed

    Song, Zhuonan; Nambo, Apolo; Tate, Kirby L; Bao, Ainan; Zhu, Minqi; Jasinski, Jacek B; Zhou, Shaojun J; Meyer, Howard S; Carreon, Moises A; Li, Shiguang; Yu, Miao

    2016-05-11

    A novel concept of utilizing nanoporous coatings as effective nanovalves on microporous adsorbents was developed for high capacity natural gas storage at low storage pressure. The work reported here for the first time presents the concept of nanovalved adsorbents capable of sealing high pressure CH4 inside the adsorbents and storing it at low pressure. Traditional natural gas storage tanks are thick and heavy, which makes them expensive to manufacture and highly energy-consuming to carry around. Our design uses unique adsorbent pellets with nanoscale pores surrounded by a coating that functions as a valve to help manage the pressure of the gas and facilitate more efficient storage and transportation. We expect this new concept will result in a lighter, more affordable product with increased storage capacity. The nanovalved adsorbent concept demonstrated here can be potentially extended for the storage of other important gas molecules targeted for diverse relevant functional applications.

  4. Structure and dynamics of water and lipid molecules in charged anionic DMPG lipid bilayer membranes

    NASA Astrophysics Data System (ADS)

    Rønnest, A. K.; Peters, G. H.; Hansen, F. Y.; Taub, H.; Miskowiec, A.

    2016-04-01

    Molecular dynamics simulations have been used to investigate the influence of the valency of counter-ions on the structure of freestanding bilayer membranes of the anionic 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) lipid at 310 K and 1 atm. At this temperature, the membrane is in the fluid phase with a monovalent counter-ion and in the gel phase with a divalent counter-ion. The diffusion constant of water as a function of its depth in the membrane has been determined from mean-square-displacement calculations. Also, calculated incoherent quasielastic neutron scattering functions have been compared to experimental results and used to determine an average diffusion constant for all water molecules in the system. On extrapolating the diffusion constants inferred experimentally to a temperature of 310 K, reasonable agreement with the simulations is obtained. However, the experiments do not have the sensitivity to confirm the diffusion of a small component of water bound to the lipids as found in the simulations. In addition, the orientation of the dipole moment of the water molecules has been determined as a function of their depth in the membrane. Previous indirect estimates of the electrostatic potential within phospholipid membranes imply an enormous electric field of 108-109 V m-1, which is likely to have great significance in controlling the conformation of translocating membrane proteins and in the transfer of ions and molecules across the membrane. We have calculated the membrane potential for DMPG bilayers and found ˜1 V (˜2 ṡ 108 V m-1) when in the fluid phase with a monovalent counter-ion and ˜1.4 V (˜2.8 ṡ 108 V m-1) when in the gel phase with a divalent counter-ion. The number of water molecules for a fully hydrated DMPG membrane has been estimated to be 9.7 molecules per lipid in the gel phase and 17.5 molecules in the fluid phase, considerably smaller than inferred experimentally for 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine (DMPC

  5. Local thermodynamics of the water molecules around single- and double-stranded DNA studied by grid inhomogeneous solvation theory

    NASA Astrophysics Data System (ADS)

    Nakano, Miki; Tateishi-Karimata, Hisae; Tanaka, Shigenori; Tama, Florence; Miyashita, Osamu; Nakano, Shu-ichi; Sugimoto, Naoki

    2016-09-01

    Thermodynamic properties of water molecules around single- and double-stranded DNAs (ssDNAs and dsDNAs) with different sequences were investigated using grid inhomogeneous solvation theory. Free energies of water molecules solvating the minor groove of dsDNAs are lower than those near ssDNAs, while water molecules should be released during the formation of dsDNA. Free energies of water molecules around dsDNA are lower than those around ssDNA even in the second and third hydration shells. Our findings will help to clarify the role of water molecules in the formation of dsDNA from ssDNAs, thus facilitating the designs of drugs or nanomaterials using DNA.

  6. Understanding the site selectivity in small-sized neutral and charged Al(n) (4 ≤ N ≤ 7) clusters using density functional theory based reactivity descriptors: a validation study on water molecule adsorption.

    PubMed

    Das, Susanta; Pal, Sourav; Krishnamurty, Sailaja

    2013-09-12

    Aluminum clusters are now technologically important due to their high catalytic activity. Our present study on the small-sized aluminum clusters applies density functional theory (DFT)-based reactivity descriptors to identify potential sites for adsorption and eventual chemical reaction. Depending on symmetry, susceptibility of various type of reactive sites within a cluster toward an impending electrophilic and/or nucleophilic attack is predicted using the reactivity descriptors. In addition, the study devises general rules as to how the size, shape, and charge of the cluster influences the number of available sites for an electrophilic and/or nucleophilic attack. The predictions by reactivity descriptors are validated by performing an explicit adsorption of water molecule on Al clusters with four atoms. The adsorption studies demonstrate that the most stable water-cluster complex is obtained when the molecule is adsorbed through an oxygen atom on the site with the highest relative electrophilicity.

  7. Double ionization of single oriented water molecules by electron impact: Second-order Born description

    SciTech Connect

    Dal Cappello, C.; Champion, C.; Kada, I.; Mansouri, A.

    2011-06-15

    The double ionization of isolated water molecules fixed in space is investigated within a theoretical approach based on the second-order Born approximation. Electron angular distributions have been studied for specific kinematical conditions. The three usual mechanisms, the shake-off and the two two-step mechanisms, have been identified. A significant contribution of the two-step mechanism is clearly visible for some particular kinematics.

  8. Effects of water molecules of Ar-Cs MHD disk generator operated with strong MHD interaction

    SciTech Connect

    Ishikawa, M.; Kosugi, A.; Inui, Y.; Kabashima, S.

    1998-07-01

    Effects of water molecule impurity are studied on performance of a disk type MHD generator operated with Ar-Cs weakly ionized plasma. To reveal phenomena for a wide range of operation conditions, time-dependent one-dimensional analyses are carried out, where an up-wind, second order Chakravarthy TVD scheme is applied for the gasdynamics, while a Galerkin FEM is used for the electrodynamics. A simplified model is used for the water molecule impurity, where total effects of nonelastic collision between electrons and water molecules are estimated by the collision loss factor of electrons and also the electron momentum-transfer collision frequency is taken into account. The collision loss factor of electrons and the electron momentum-transfer collision frequency are taken from references, and the loss factor is assumed to be 700 independently of the electron temperature. On the Fuji-1 facilities at Tokyo Institute Technology, Japan, series of experiment A4105 were carried out with the Disk F-4 generator. Ar was heated with the heat-exchanger heated by the natural gas-air combustion and the metal cesium was used as the seeding material, while SCM maintained the magnetic field of 4.7 T at the center of disk and the very strong MHD interaction was realized. The thermal input was about 3 MW, the electrical output was about 500 kW with the enthalpy extraction ratio of about 17%. The numerical analyses have shown that the water molecule enhances the ionization instability at the low voltage loading because of insufficient Joule heating for electrons. The generator performance is degraded and the strong MHD interaction between the unstable plasma and the flow field induces slow and fast moving shock waves, leading to the very complicated flow field. The fast and slow moving shocks collide with each other, merge into a sharp shock moving downward, and then the shock front moves back slightly to maintain the pressure balance, collides again with another weak moving shock, and

  9. Influence of Organic Chemicals on Water Molecule Bridges in Soil Organic Matter of a Sapric Histosol.

    PubMed

    Ondruch, Pavel; Kučerík, Jiri; Steinmetz, Zacharias; Schaumann, Gabriele E

    2017-03-02

    Water molecules in soil organic matter (SOM) can form clusters bridging neighboring molecular segments (water molecule bridges; WaMB). WaMB are hypothesized to enhance physical entrapment of organic chemicals and to control the rigidity of the SOM supramolecular structure. However, the understanding of WaMB dynamics in SOM is still limited. We investigated the relation between WaMB stability and the physicochemical properties of their environment by treating a sapric histosol with various solvents and organic chemicals. Based on predictions from molecular modeling, we hypothesized that the stability of WaMB, measured by differential scanning calorimetry, increases with decreasing ability of a chemical to interact with water molecules of the WaMB. The interaction ability between WaMB and the chemicals was characterized by linear solvation energy relationships. WaMB stability in solvent-treated samples was found to decrease with increasing ability of a solvent to undergo H-donor/acceptor interactions. Spiking with an organic chemical stabilized (naphthalene) or destabilized (phenol) the WaMB. WaMB stability and matrix rigidity were generally reduced strongly and fast when hydrophilic chemicals entered the soil. The physicochemical aging following this destabilization is slow, but leads to a successive WaMB stabilization and matrix stiffening.

  10. WaterLOGSY NMR experiments in conjunction with molecular-dynamics simulations identify immobilized water molecules that bridge peptide mimic MDWNMHAA to anticarbohydrate antibody SYA/J6.

    PubMed

    Szczepina, Monica G; Bleile, Dustin W; Müllegger, Johannes; Lewis, Andrew R; Pinto, B Mario

    2011-10-04

    X-ray crystallographic data of the carbohydrate mimic MDWNMHAA when bound to an anti-Shigella flexneri Y mAb SYA/J6 indicate the immobilization of water molecules, that is, the presence of "bound" waters, in the active site. Water Ligand Observed via Gradient Spectroscopy (WaterLOGSY) was used in conjunction with saturation transfer difference (STD)-NMR spectroscopy to probe the existence of immobilized water molecules in the complex of MDWNMHAA 1 bound to mAb SYA/J6. Molecular dynamics simulations using the ZymeCAD Molecular Dynamics platform were then used to specify the likely locations of these water molecules. Of note, those waters involved in providing complementarity between the peptide and mAb SYA/J6 remained throughout the course of the simulation. Together, the experimental and computational protocols have been used to identify the bound water molecules present in the antibody-peptide complex.

  11. How strongly do hydrogen and water molecules stick to carbon nanomaterials?

    NASA Astrophysics Data System (ADS)

    Al-Hamdani, Yasmine S.; Alfè, Dario; Michaelides, Angelos

    2017-03-01

    The interaction strength of molecular hydrogen and water to carbon nanomaterials is relevant to, among many applications, hydrogen storage, water treatment, and water flow. However, accurate interaction energies for hydrogen and water with carbon nanotubes (CNTs) remain scarce despite the importance of having reliable benchmark data to inform experiments and to validate computational models. Here, benchmark fixed-node diffusion Monte Carlo (DMC) interaction energies are provided for hydrogen and water monomers inside and outside a typical zigzag CNT. The DMC interaction energies provide valuable insight into molecular interactions with CNTs in general and are also expected to be particularly relevant to gas uptake studies on CNTs. In addition, a selection of density functional theory (DFT) exchange-correlation (xc) functionals and force field potentials that ought to be suitable for these systems is compared. An unexpected variation is found in the performance of DFT van der Waals (vdW) models in particular. An analysis of the peculiar discrepancy between different vdW models indicates that medium-range correlation (at circa 3 to 5 Å) plays a key role inside CNTs and is poorly predicted by some vdW models. Using accurate reference information, this work reveals which xc functionals and force fields perform well for molecules interacting with CNTs. The findings will be valuable to future work on these and related systems that involve molecules interacting with low-dimensional systems.

  12. Adsorption of water molecules on selected charged sodium-chloride clusters.

    PubMed

    Bradshaw, James A; Gordon, Sidney L; Leavitt, Andrew J; Whetten, Robert L

    2012-01-12

    The adsorption of water molecules (H(2)O) on sodium chloride cluster cations and anions was studied at 298 K over a mass range of 100-1200 amu using a custom-built laser desorption ionization reactor and mass spectrometer. Under the conditions used, the cations Na(3)Cl(2)(+) and Na(4)Cl(3)(+) bind up to three water molecules, whereas the larger cations, Na(5)Cl(4)(+) to Na(19)Cl(18)(+), formed hydrates with one or two only. The overall trend is a decrease in hydration with increasing cluster size, with an abrupt drop occurring at the closed-shell Na(14)Cl(13)(+). As compared to the cluster cations, the cluster anions showed almost no adsorption. Among smaller clusters, a weak adsorption of one water molecule was observed for the cluster anions Na(6)Cl(7)(-) and Na(7)Cl(8)(-). In the higher mass region, a substantial adsorption of one water molecule was observed for Na(14)Cl(15)(-). Density functional theory (DFT) computations were carried out for the adsorption of one molecule of H(2)O on the cations Na(n)Cl(n-1)(+), for n = 2-8, and the anions Na(n)Cl(n+1)(-), for n = 1-7. For each ion, the structure of the hydrate, the hydration energy, and the standard-state enthalpy, entropy, and Gibbs energy of hydration at 298 K were computed. In addition, it was useful to compute the distortion energy, defined as the electronic energy lost due to weakening of the Na-Cl bonds upon adsorption of H(2)O. The results show that strong adsorption of a H(2)O molecule occurs for the linear cations only at an end Na ion and for the nonlinear cations only at a corner Na ion bonded to two Cl ions. An unexpected result of the theoretical investigation for the anions is that certain low-energy isomers of Na(6)Cl(7)(-) and Na(7)Cl(8)(-) bind H(2)O strongly enough to produce the observed weak adsorption. The possible implications of these results for the initial hydration of extended NaCl surfaces are discussed.

  13. Influences of Dilute Organic Adsorbates on the Hydration of Low-Surface-Area Silicates.

    PubMed

    Sangodkar, Rahul P; Smith, Benjamin J; Gajan, David; Rossini, Aaron J; Roberts, Lawrence R; Funkhouser, Gary P; Lesage, Anne; Emsley, Lyndon; Chmelka, Bradley F

    2015-07-01

    Competitive adsorption of dilute quantities of certain organic molecules and water at silicate surfaces strongly influence the rates of silicate dissolution, hydration, and crystallization. Here, we determine the molecular-level structures, compositions, and site-specific interactions of adsorbed organic molecules at low absolute bulk concentrations on heterogeneous silicate particle surfaces at early stages of hydration. Specifically, dilute quantities (∼0.1% by weight of solids) of the disaccharide sucrose or industrially important phosphonic acid species slow dramatically the hydration of low-surface-area (∼1 m(2)/g) silicate particles. Here, the physicochemically distinct adsorption interactions of these organic species are established by using dynamic nuclear polarization (DNP) surface-enhanced solid-state NMR techniques. These measurements provide significantly improved signal sensitivity for near-surface species that is crucial for the detection and analysis of dilute adsorbed organic molecules and silicate species on low-surface-area particles, which until now have been infeasible to characterize. DNP-enhanced 2D (29)Si{(1)H}, (13)C{(1)H}, and (31)P{(1)H} heteronuclear correlation and 1D (29)Si{(13)C} rotational-echo double-resonance NMR measurements establish hydrogen-bond-mediated adsorption of sucrose at distinct nonhydrated and hydrated silicate surface sites and electrostatic interactions with surface Ca(2+) cations. By comparison, phosphonic acid molecules are found to adsorb electrostatically at or near cationic calcium surface sites to form Ca(2+)-phosphonate complexes. Although dilute quantities of both types of organic molecules effectively inhibit hydration, they do so by adsorbing in distinct ways that depend on their specific architectures and physicochemical interactions. The results demonstrate the feasibility of using DNP-enhanced NMR techniques to measure and assess dilute adsorbed molecules and their molecular interactions on low

  14. The interaction of Al atoms with water molecules: A theoretical study.

    PubMed

    Alvarez-Barcia, S; Flores, J R

    2009-11-07

    The interaction of individual Al atoms with water molecules has been studied from the point of view of the energy by means of ab initio and DFT calculations in order to find the pathways for the generation of HAlOH(H(2)O)(n) or AlOH(H(2)O)(n)+H. The potential energy surface of the Al(H(2)O)(n+1) (n=0-3) systems has been explored for local minima and the relevant saddle points. The interaction of Al and several water molecules tends to produce low-lying local minima in which (for n=2-3) Al is "inserted" into relatively compact structures of water molecules, so typically a ring is formed containing an AlOH(2) moiety. Isomerization of such moiety into HAlOH(H(2)O)(n) may take place through saddle points of the "relay" type; however those saddle points lie very close to AlOH(2)(H(2)O)(n-1)+H(2)O, which means that such isomerization process has to compete with a water-elimination process. Larger systems Al(H(2)O)(n+1) (n=4-7) have also been computed by means of a DFT method, as a first step to predict the behavior of isolated Al atoms in even larger clusters or in the bulk. Finally, an effective fragment potential method has been employed to simulate those large clusters together with a polarizable continuum model to take into account the effect of the bulk. Our results suggest that the reaction should take place in inert matrices and in the bulk. We also conclude that HAlOH(H(2)O)(n) and AlOH(H(2)O)(n) could be the intermediates involved in the generation of hydrogen by the interaction of Al atoms with water, so their production would be the critical step of such process.

  15. Morphological changes in adsorbed protein films at the air-water interface subjected to large area variations, as observed by brewster angle microscopy.

    PubMed

    Xu, Rong; Dickinson, Eric; Murray, Brent S

    2007-04-24

    Adsorbed films of proteins at the air-water interface have been imaged using Brewster angle microscopy (BAM). The proteins beta-lactoglobulin (beta-L) and ovalbumin (OA) were studied at a range of protein concentrations and surface ages at 25.0 degrees C and two pH values (7 and 5) in a Langmuir trough. The adsorbed films were periodically subjected to compression and expansion cycles such that the film area was typically varied between 125% and 50% of the original film area. With beta-L on its own, no structural changes were observable at pH 7. When a low-area fraction (less than 0.01%) of 20 mum polystyrene latex particles was spread at the interface before adsorption of beta-L, the particles became randomly distributed throughout the interface, but after protein adsorption and compression/expansion, the particles highlighted notable structural features not visible in their absence. Such features included the appearance of long (several hundred micrometers or more) folds and cracks in the films, generally oriented at right angles to the direction of compression, and also aggregates of protein and/or particles. Such structuring was more visible the longer the film was aged or at higher initial protein concentrations for shorter adsorption times. At pH 5, close to the isoelectric pH of beta-L, such features were just noticeable in the absence of particles but were much more pronounced than at pH 7 in the presence of particles. Similar experiments with OA revealed even more pronounced structural features, both in the absence and presence of particles, particularly at pH 5 (close to the isoelectric pH of OA also), producing striking stripelike and meshlike domains. Changes in the dilatational elasticity of the films could be correlated with the variations in the structural integrity of the films as observed via BAM. The results indicate that interfacial area changes of this type, typical of those that occur in food colloid processing, will lead to highly

  16. Assessment of carbon nanotubes and silver nanoparticles loaded clays as adsorbents for removal of bacterial contaminants from water sources.

    PubMed

    Hassouna, M E M; ElBably, M A; Mohammed, Asmaa N; Nasser, M A G

    2017-02-01

    This work evaluated the antimicrobial efficacy of kaolin clay and its loaded forms with carbon nanotubes (CNTs) and silver nanoparticles (AgNPs) against bacterial isolates from different water supplies (tap, underground and surface water) in addition to wastewater. A total of 160 water samples were collected from different water sources in the investigated districts. Samples were cultured for isolation and serological identification of pathogenic bacteria. AgNPs were synthesized by a typical one-step synthesis protocol, where CNTs were carried out in a reactor employing the double bias-assisted hot filament chemical vapor deposition method. Both were characterized using transmission electron microscopy, infrared and X-ray fluorescence (XRF) spectroscopy. The antimicrobial efficacy of each of natural kaolin clay, AgNPs- and CNTs-loaded clays were evaluated by their application in four concentrations (0.01, 0.03, 0.05 and 0.1 ppm) at different contact times (5 min, 15 min, 30 min and 2 h). AgNPs-loaded clays at concentrations of 0.05 and 0.1 mg/l for 2 h contact time exhibited a higher bactericidal efficacy on Escherichia coli and Salmonella spp. (70, 70, 80 and 90%, respectively) compared to CNTs-loaded clay. Concluding, the application of AgNPs-loaded clay for removal of water bacterial contaminants at a concentration of 0.1 ppm for 2 h contact times resulted in highly effective removals.

  17. Nitrogen cycling between sediment and the shallow-water column in the transition zone of the Potomac River and Estuary. II. The role of wind-driven resuspension and adsorbed ammonium

    USGS Publications Warehouse

    Simon, N.S.

    1989-01-01

    During periods of sediment resuspension, desorption of ammonium from sediment solids can be the major pathway for enriching the water column with the ammonium that is produced by bacterial degradation of organic matter in the bottom material. This hyopthesis is based on a three-year study of diffusive flux in the transition zone of the Potomac River at a site 35 m from the Virginia shore where the average water-column depth is approximately 1 m over sandy sediment. A diffusion-controlled sampler was used to collect water samples at the interface between the water column and sediment and at several tens of centimeters into the sediment. Interstitial water concentration gradients showed that diffusive flux of ammonium from the sandy shallow-water sediments was approximately 1% of the diffusive flux of ammonium from the silty channel sediments in the same zone of the Potomac River. Organic nitrogen and bound or adsorbed ammonium were the predominant nitrogen forms in the sediment. Adsorbed ammonium concentrations ranged from nondetectable to 3??7 ??mol g-1 of sediment. Concentrations of adsorbed ammonium per gram of sediment were one to three orders of magnitude more than interstitial water ammonium concentrations. Desorption of ammonium from sediment solids appeared to be the controlling factor in the degree of water-column ammonium enrichment. In laboratory experiments that simulated sediment resuspension, 40-80% of the adsorbed ammonium predicted to desorb did so after approximately 30 min of mixing. Based on calculations for 1 m2 to a depth of 4 cm, one resuspenion event lasting minutes could mix more ammonium into the water column from desorption of ammonium from sediment solids than could be delivered to the water column by diffusive flux from shallow-water sediments in 10-1000 days and would be comparable to enrichment by ammonium diffusive flux for 5-50 days from channel sediments in the same river zone. ?? 1989.

  18. Reactions of water and C1 molecules on carbide and metal-modified carbide surfaces.

    PubMed

    Wan, Weiming; Tackett, Brian M; Chen, Jingguang G

    2017-02-23

    The formation of carbides can significantly modify the physical and chemical properties of the parent metals. In the current review, we summarize the general trends in the reactions of water and C1 molecules over transition metal carbide (TMC) and metal-modified TMC surfaces and thin films. Although the primary focus of the current review is on the theoretical and experimental studies of reactions of C1 molecules (CO, CO2, CH3OH, etc.), the reactions of water will also be reviewed because water plays an important role in many of the C1 transformation reactions. This review is organized by discussing separately thermal reactions and electrochemical reactions, which provides insights into the application of TMCs in heterogeneous catalysis and electrocatalysis, respectively. In thermal reactions, we discuss the thermal decomposition of water and methanol, as well as the reactions of CO and CO2 over TMC surfaces. In electrochemical reactions, we summarize recent studies in the hydrogen evolution reaction, electrooxidation of methanol and CO, and electroreduction of CO2. Finally, future research opportunities and challenges associated with using TMCs as catalysts and electrocatalysts are also discussed.

  19. Single-Molecule Imaging of DNAs with Sticky Ends at Water/Fused Silica Interface

    SciTech Connect

    Isailovic, Slavica

    2005-01-01

    Total internal reflection fluorescence microscopy (TIRFM) was used to study intermolecular interactions of DNAs with unpaired (sticky) ends of different lengths at water/fused silica interface at the single-molecule level. Evanescent field residence time, linear velocity and adsorption/desorption frequency were measured in a microchannel for individual DNA molecules from T7, Lambda, and PSP3 phages at various pH values. The longest residence times and the highest adsorption/desorption frequencies at the constant flow at pH 5.5 were found for PSP3 DNA, followed by lower values for Lambda DNA, and the lowest values for T7 DNA. Since T7, Lambda, and PSP3 DNA molecules contain none, twelve and nineteen unpaired bases, respectively, it was concluded that the affinity of DNAs for the surface increases with the length of the sticky ends. This confirms that hydrophobic and hydrogen-bonding interactions between sticky ends and fused-silica surface are driving forces for DNA adsorption at the fused-silica surface. Described single-molecule methodology and results therein can be valuable for investigation of interactions in liquid chromatography, as well as for design of DNA hybridization sensors and drug delivery systems.

  20. Dangling OH Vibrations of Water Molecules in Aqueous Solutions of Aprotic Polar Compounds Observed in the Near-Infrared Regime.

    PubMed

    Sagawa, Naoya; Shikata, Toshiyuki

    2015-06-25

    Near-infrared (NIR) absorption spectrum measurements over a frequency range from 4000 to 12000 cm(-1) were employed to investigate the effects of the presence of solute compounds to vibrational modes of water molecules in aqueous solutions of some aprotic hydroneutral polar compounds with large dipole moments, such as nitro compounds and nitriles. The obtained NIR spectra for the aqueous solutions were decomposed into three components: free water, solute, and water molecules affected by the presence of solutes. Newly determined NIR spectra of affected water molecules were well-described with at least four absorption modes observed at 7040, 6850, 6450, and 5640 cm(-1) for both the nitro compounds and nitriles. The highest frequency mode at 7040 cm(-1) possessing the strongest intensity was assigned to the first stretching overtone of affected water hydroxy (O-H) groups, which are nonhydrogen bonded to other water molecules and dangling. The second highest frequency mode at 6850 cm(-1) was assigned to the first stretching overtone of affected water O-H groups hydrated to other (free) water molecules. The third mode at 6400 cm(-1) was attributed to a combination mode of the fundamental stretching of O-H and the first overtone of the O-H bending mode of the affected water molecules. The lowest frequency mode at 5640 cm(-1) was assigned to the combination mode of the fundamental O-H stretching mode, the fundamental O-H bending mode, and the hindered rotational (libration) mode of the affected water molecules. Because absorption intensities of the third and lowest frequency modes for water molecules affected by the solutes depended on the sizes of alkyl groups of polar solutes, these two modes possibly result from the contribution of hydrophobic hydration effects.

  1. Effects of a single water molecule on the OH + H2O2 reaction.

    PubMed

    Buszek, Robert J; Torrent-Sucarrat, Miquel; Anglada, Josep M; Francisco, Joseph S

    2012-06-21

    The effect of a single water molecule on the reaction between H(2)O(2) and HO has been investigated by employing MP2 and CCSD(T) theoretical approaches in connection with the aug-cc-PVDZ, aug-cc-PVTZ, and aug-cc-PVQZ basis sets and extrapolation to an ∞ basis set. The reaction without water has two elementary reaction paths that differ from each other in the orientation of the hydrogen atom of the hydroxyl radical moiety. Our computed rate constant, at 298 K, is 1.56 × 10(-12) cm(3) molecule(-1) s(-1), in excellent agreement with the suggested value by the NASA/JPL evaluation. The influence of water vapor has been investigated by considering either that H(2)O(2) first forms a complex with water that reacts with hydroxyl radical or that H(2)O(2) reacts with a previously formed H(2)O·OH complex. With the addition of water, the reaction mechanism becomes much more complex, yielding four different reaction paths. Two pathways do not undergo the oxidation reaction but an exchange reaction where there is an interchange between H(2)O(2)·H(2)O and H(2)O·OH complexes. The other two pathways oxidize H(2)O(2), with a computed total rate constant of 4.09 × 10(-12) cm(3) molecule(-1) s(-1) at 298 K, 2.6 times the value of the rate constant of the unassisted reaction. However, the true effect of water vapor requires taking into account the concentration of the prereactive bimolecular complex, namely, H(2)O(2)·H(2)O. With this consideration, water can actually slow down the oxidation of H(2)O(2) by OH between 1840 and 20.5 times in the 240-425 K temperature range. This is an example that demonstrates how water could be a catalyst in an atmospheric reaction in the laboratory but is slow under atmospheric conditions.

  2. Identification and characterization of the motion of water molecules in normal and deuterated pyromellitic acid dihydrate

    NASA Astrophysics Data System (ADS)

    Schajor, W.; Haeberlen, U.; Tegenfeldt, T.

    Proton wide-line, multiple-pulse, T1 and T1 ϱ measurements on single crystals of PMADH, and deuteron EFG measurements and bandshape analyses of spectra recorded from deuterated crystals of PMADH are reported. The wide-line and multiple-pulse proton results indicate that the water molecules in PMADH are flipping about their twofold symmetry axes. Both T1 and T1 ϱ were measured as a function of crystal orientation and temperature. Comparison of the experimental data with model calculations for T1 ϱ based on the established flipping motions of the water molecules shows that {1}/{T 1ϱ} is dominated by this process whereas {1}/{T 1} is not. The T1 ϱ data thus enable determination of the rate of the H 2O flips as a function of temperature. EFGs of the water deuterons in deuterated PMADH, measured at low and high temperatures, confirm the occurrence of the flips for D 2O in PMADH. The flips constitute an exchange process for the water deuterons. Bandshape analyses of single-crystal deuteron spectra recorded at temperatures covering the full range of exchange rates allowed determination of the flip rates of the D 2O molecules. The activation energies for the H 2O and D 2O flips are the same, Ea = 10 kcal/mol, within the limits of accuracy of the experiments. The frequency factors in the Arrhenius relation are 8.3 X 10 13 sec -1 (H 2O) and 2.6 X 10 13 sec -1 (D 2O).

  3. Effects of multivalent hexacyanoferrates and their ion pairs on water molecule dynamics measured with terahertz spectroscopy.

    PubMed

    DiTucci, Matthew J; Böhm, Fabian; Schwaab, Gerhard; Williams, Evan R; Havenith, Martina

    2017-02-27

    The valency of aqueous solutes plays a large role in determining the extent of ion-water dynamics, which can greatly influence the chemical and physical properties of solutions. In these experiments, broadband Fourier transform terahertz spectroscopy is used to probe perturbations to the low-frequency dynamics of water molecules by three different multivalent hexacyanoferrate salts. K3Fe(CN)6, K4Fe(CN)6 and Na4Fe(CN)6 were investigated as a function of concentration up to their solubility limits using spectral subtractions and fitting with damped harmonic lineshapes. Regions with subtle nonlinearities in amplitude with respect to solute concentration provide insight into ion-pairing events. The extent of nonlinearity suggests that ion pairs are major constituents in solution for all concentrations measured and is consistent with ion-pairing observed at millimolar concentrations by potentiometric and spectroscopic measurements. A lower estimate for the number of water molecules that are influenced by each ion is obtained from the damped harmonic fits. Values of 19, 28 and 25 water molecules with perturbed dynamics are obtained for KFe(CN)6(2-), KFe(CN)6(3-) and NaFe(CN)6(3-) ion pairs, respectively. These values represent dynamical perturbations into a second solvation shell and are consistent with the long-range structural effects observed in recent aqueous nanodrop spectroscopy experiments. Furthermore, the spectral absorptions for hexacyanoferrates are in agreement with a wide range of solutes studied previously using the developing methodology for interpreting terahertz spectra.

  4. Interfacial water molecules in SH3 interactions: a revised paradigm for polyproline recognition.

    PubMed

    Martin-Garcia, Jose M; Ruiz-Sanz, Javier; Luque, Irene

    2012-03-01

    In spite of its biomedical relevance, polyproline recognition is still not fully understood. The disagreement between the current description of SH3 (Src homology 3) complexes and their thermodynamic behaviour calls for a revision of the SH3-binding paradigm. Recently, Abl-SH3 was demonstrated to recognize its ligands by a dual binding mechanism involving a robust network of water-mediated hydrogen bonds that complements the canonical hydrophobic interactions. The systematic analysis of the SH3 structural database in the present study reveals that this dual binding mode is universal to SH3 domains. Tightly bound buried-interfacial water molecules were found in all SH3 complexes studied mediating the interaction between the peptide ligand and the domain. Moreover, structural waters were also identified in a high percentage of the free SH3 domains. A detailed analysis of the pattern of water-mediated interactions enabled the identification of conserved hydration sites in the polyproline-recognition region and the establishment of relationships between hydration profiles and the sequence of both ligands and SH3 domains. Water-mediated interactions were also systematically observed in WW (protein-protein interaction domain containing two conserved tryptophan residues), UEV (ubiquitin-conjugating enzyme E2 variant) and EVH-1 [Ena/VASP (vasodilator-stimulated phosphoprotein) homology 1] structures. The results of the present study clearly indicate that the current description of proline-rich sequence recognition by protein-protein interaction modules is incomplete and insufficient for a correct understanding of these systems. A new binding paradigm is required that includes interfacial water molecules as relevant elements in polyproline recognition.

  5. Effects of Disaccharide Sugars on Dynamics of Water Molecules: Dynamic Light Scattering and Dielectric Loss Spectroscopy Studies

    NASA Astrophysics Data System (ADS)

    Seo, Jeong-Ah; Kwon, Hyun-Joung; Kim, Hyung Kook; Hwang, Yoon-Hwae

    2008-02-01

    We studied the effects of disaccharide sugars (trehalose, sucrose, and maltose) on the dynamics of water molecules in sugar-water mixtures. We measured the acoustic phonons in sugar-water mixtures with different sugar contents by using a Sandercock Tandem 6-pass Febry-Petor interferometer and found that the Brillouin peak positions shifted to higher frequencies as the sugar concentration increased. We also measured the dielectric loss of hydrogen bonds in water molecules in sugar-water mixtures by using a Network analyzer with different sugar contents. The loss peak position in the dielectric loss spectra moved to lower frequencies as the sugar contents increased. The trehalose-water mixture showed the largest Brillouin peak shift and relaxation time change with increasing sugar content among three disaccharides indicating that the effect of trehalose on the dynamics of water molecules is the strongest. This unique property of trehalose sugar might be the origin of the superior bio-protection ability of trehalose.

  6. Spectrophotometric determination of basic fuchsin from various water samples after vortex assisted solid phase extraction using reduced graphene oxide as an adsorbent.

    PubMed

    Tokalıoğlu, Şerife; Yavuz, Emre; Aslantaş, Ayşe; Şahan, Halil; Taşkın, Ferhat; Patat, Şaban

    2015-01-01

    In this study, a fast and simple vortex assisted solid phase extraction method was developed for the separation/preconcentration of basic fuchsin in various water samples. The determination of basic fuchsin was carried out at a wavelength of 554 nm by spectrophotometry. Reduced graphene oxide which was used as a solid phase extractor was synthesized and characterized by X-ray diffraction, scanning electron microscopy and the Brunauer, Emmett and Teller. The optimum conditions are as follows: pH 2, contact times for adsorption and elution of 30 s and 90 s, respectively, 10 mg adsorbent, and eluent (ethanol) volume of 1 mL. The effects of some interfering ions and dyes were investigated. The method was linear in the concentration range of 50-250 μg L(-1). The adsorption capacity was 34.1 mg g(-1). The preconcentration factor, limit of detection and precision (RSD, %) of the method were found to be 400, 0.07 μg L(-1) and 1.2%, respectively. The described method was validated by analyzing basic fuchsin spiked certified reference material (SPS-WW1 Batch 114-Wastewater) and spiked real water samples.

  7. Influence of the water molecules near surface of viral protein on virus activation process

    NASA Astrophysics Data System (ADS)

    Shepelenko, S. O.; Salnikov, A. S.; Rak, S. V.; Goncharova, E. P.; Ryzhikov, A. B.

    2009-06-01

    The infection of a cell with influenza virus comprises the stages of receptor binding to the cell membrane, endocytosis of virus particle, and fusion of the virus envelope and cell endosome membrane, which is determined by the conformational changes in hemagglutinin, a virus envelope protein, caused by pH decrease within the endosome. The pH value that induces conformation rearrangements of hemagglutinin molecule considerably varies for different influenza virus strains, first and foremost, due to the differences in amino acid structure of the corresponding proteins. The main goal of this study was to construct a model making it possible to assess the critical pH value characterizing the fusogenic activity of influenza virus hemagglutinin from the data on hemagglutinin structure and experimental verification of this model. Under this model, we assume that when the electrostatic force between interacting hemagglutinin molecules in the virus envelop exceeds a certain value, the hemagglutinin HA1 subunits are arranged so that they form a cavity sufficient for penetration of water molecules. This event leads to an irreversible hydration of the inner fragments of hemagglutinin molecule in a trimer and to the completion of conformational changes. The geometry of electrostatic field in hemagglutinin trimer was calculated taking into account the polarization effects near the interface of two dielectrics, aqueous medium and protein macromolecule. The critical pH values for the conformational changes in hemagglutinin were measured by the erythrocyte hemolysis induced by influenza virus particles when decreasing pH. The critical pH value conditionally separating the pH range into the regions with and without the conformational changes was calculated for several influenza virus H1N1 and H3N2 strains based on the data on the amino acid structure of the corresponding hemagglutinin molecules. Comparison of the theoretical and experimental values of critical pH values for

  8. 35 Years of Marine Natural Product Research in Sweden: Cool Molecules and Models from Cold Waters.

    PubMed

    Bohlin, Lars; Cárdenas, Paco; Backlund, Anders; Göransson, Ulf

    2017-01-01

    Currents efforts in marine biodiscovery have essentially focused on temperate to tropical shallow water organisms. With more than 6000 species of marine plants and animals, the Kosterfjord area has the richest marine biodiversity in Swedish waters, but it remains understudied. The overall objective of our marine pharmacognosy research is to explore and reveal the pharmacological potential of organisms from this poorly explored region. More generally, we wish to understand aspects of structure-activity relationships of chemical interactions in cold-water marine environment (shallow and deep). Our strategy is based on ecologically guided search for compounds through studies of physiology and organism interactions coupled to identification of bioactive molecules guided by especially in vivo assays. The research programme originated in the beginning of the 1980s with a broad screening of Swedish marine organisms using both in vitro and in vivo assays, resulting in isolation and identification of several different bioactive molecules. Two congenerous cyclopeptides, i.e. barettin and 8,9-dihydrobarettin, were isolated from the deep-sea sponge Geodia barretti, and structurally elucidated, guided by their antifouling activity and their affinity to a selection of human serotonin receptors. To optimize the activity a number of analogues of barettin were synthezised and tested for antifouling activity. Within the EU project BlueGenics, two larger homologous peptides, barrettides A and B, were isolated from G. baretti. Also, metabolic fingerprinting combined with sponge systematics was used to further study deep-sea natural product diversity in the genus Geodia. Finally, the chemical property space model 'ChemGPS-NP' has been developed and used in our research group, enabling a more efficient use of obtained compounds and exploration of possible biological activities and targets. Another approach is the broad application of phylogenetic frameworks, which can be used in

  9. Detection of water molecules in inert gas based plasma by the ratios of atomic spectral lines

    NASA Astrophysics Data System (ADS)

    Bernatskiy, A. V.; Ochkin, V. N.

    2017-01-01

    A new approach is considered to detect the water leaks in inert plasma-forming gas present in the reactor chamber. It is made up of the intensity ratio of D α and H α spectral lines in combination with O, Ar and Xe lines intensity. The concentrations of H2O, O, H and D particles have been measured with high sensitivity. At the D2 admixture pressure {{p}{{\\text{D}\\text{2}}}}   =  0.025 mbar, we used the acquisition time of 10 s to measure the rate of water molecules injected from the outside, Γ0  =  1.4 · 10-9 mbar · m3 · s-1, and the incoming water molecules to plasma, Γ  =  5 ·10-11 mbar · m3 · s-1. The scaling proves that at small D2 admixtures (10-4 mbar), the leaks with the rates Γ0  ≈  6 · 10-12 mbar · m3 · s-1 and Γ  ≈  2 · 10-13 mbar · m3 · s-1 can be detected and measured. The difference between Γ0 and Γ values is due to the high degree of H2O dissociation, which can be up to 97-98%.

  10. The Effect of Water Molecules on Mechanical Properties of Bamboo Microfibrils

    NASA Astrophysics Data System (ADS)

    Rahbar, Nima

    Bamboo fibers have higher strength-to-weight ratios than steel and concrete. The unique properties of bamboo fibers come from their natural composite structures that comprise mainly cellulose nanofibrils in a matrix of intertwined hemicellulose and lignin called lignin-carbohydrate complex (LCC). Here, we have utilized atomistic simulations to investigate the mechanical properties and mechanisms of interactions between these materials, in the presence of water molecules. Our results suggest that hemicellulose exhibits better mechanical properties and lignin shows greater tendency to adhere to cellulose nanofibrils. Consequently, the role of hemicellulose found to be enhancing the mechanical properties and lignin found to be providing the strength of bamboo fibers. The abundance of Hbonds in hemicellulose chains is responsible for improving the mechanical behavior of LCC. The strong van der Waals forces between lignin molecules and cellulose nanofibrils is responsible for higher adhesion energy between LCC/cellulose nanofibrils. We also found out that the amorphous regions of cellulose nanofibrils is the weakest interface in bamboo Microfibrils. In presence of water, the elastic modulus of lignin increases at low water content (less than 10 NSF CAREER Grant No. 1261284.

  11. Intramolecular cyclization of aspartic acid residues assisted by three water molecules: a density functional theory study

    NASA Astrophysics Data System (ADS)

    Takahashi, Ohgi; Kirikoshi, Ryota

    2014-01-01

    Aspartic acid (Asp) residues in peptides and proteins (l-Asp) are known to undergo spontaneous nonenzymatic reactions to form l-β-Asp, d-Asp, and d-β-Asp residues. The formation of these abnormal Asp residues in proteins may affect their three-dimensional structures and hence their properties and functions. Indeed, the reactions have been thought to contribute to aging and pathologies. Most of the above reactions of the l-Asp residues proceed via a cyclic succinimide intermediate. In this paper, a novel three-water-assisted mechanism is proposed for cyclization of an Asp residue (forming a gem-diol precursor of the succinimide) by the B3LYP/6-31 + G(d,p) density functional theory calculations carried out for an Asp-containing model compound (Ace-Asp-Nme, where Ace = acetyl and Nme = NHCH3). The three water molecules act as catalysts by mediating ‘long-range’ proton transfers. In the proposed mechanism, the amide group on the C-terminal side of the Asp residue is first converted to the tautomeric iminol form (iminolization). Then, reorientation of a water molecule and a conformational change occur successively, followed by the nucleophilic attack of the iminol nitrogen on the carboxyl carbon of the Asp side chain to form the gem-diol species. A satisfactory agreement was obtained between the calculated and experimental energetics.

  12. Prussian blue caged in alginate/calcium beads as adsorbents for removal of cesium ions from contaminated water.

    PubMed

    Vipin, Adavan Kiliyankil; Hu, Baiyang; Fugetsu, Bunshi

    2013-08-15

    Prussian blue encapsulated in alginate beads reinforced with highly dispersed carbon nanotubes were prepared for the safe removal of cesium ions from aqueous solutions. Equilibrium and kinetic studies were conducted using different models and the goodness of mathematical fitting of the experimental data on the adsorption isotherms was in the order Langmuir>Freundlich, and that of the kinetic models were in the order of pseudo second order>pseudo first order. Fixed bed adsorption column analysis indicated that the beads can be used for large scale treatment of cesium contaminated water.

  13. Continuum Navier-Stokes modelling of water flow past fullerene molecules

    NASA Astrophysics Data System (ADS)

    Walther, J. H.; Popadic, A.; Koumoutsakos, P.; Praprotnik, M.

    2015-11-01

    We present continuum simulations of water flow past fullerene molecules. The governing Navier-Stokes equations are complemented with the Navier slip boundary condition with a slip length that is extracted from related molecular dynamics simulations. We find that several quantities of interest as computed by the present model are in good agreement with results from atomistic and atomistic-continuum simulations at a fraction of the computational cost. We simulate the flow past a single fullerene and an array of fullerenes and demonstrate that such nanoscale flows can be computed efficiently by continuum flow solvers, allowing for investigations into spatiotemporal scales inaccessible to atomistic simulations.

  14. Spectral properties of mixtures of montmorillonite and dark grains - Implications for remote sensing minerals containing chemically and physically adsorbed water

    NASA Technical Reports Server (NTRS)

    Clark, R. N.

    1983-01-01

    The spectral properties from 0.4 to 3 microns of montmorillonite plus dark carbon grains (called opaques) of various sizes are studied as a function of the weight fraction of opaques present. The reflectance level and band depths of the 1.4-, 1.9-, 2.2-, and 2.8-micron water and/or OH absorption features are analyzed using derived empirical relationships and scattering theory. It is found that the absorption band depths and reflectance level are a very nonlinear function of the weight fraction of opaques present but can be predicted in many cases by simple scattering theory. The 2.8-micron bound water fundamental band is the most difficult absorption feature to suppress. The overtone absorptions are suppressed a greater amount than the fundamental but are still apparent even when 10-20 wt pct opaques are present. The relationships observed and the simple scattering theory presented show that quantitative compositional remote sensing studies are feasible for surfaces containing complex mineral mixtures.

  15. Explicit Consideration of Water Molecules to Study Vibrational Circular DICHROÎSM of Monosaccharide's

    NASA Astrophysics Data System (ADS)

    Moussi, Sofiane; Ouamerali, Ourida

    2014-06-01

    Carbohydrates have multiples roles in biological systems. It has been found that the glycoside bond is fundamentally important in many aspects of chemistry and biology and forms the basis of carbohydrate chemistry. That means the stereochemical information, namely, glycosidic linkages α or β, gives an significant features of the carbohydrate glycosidation position of the glycosylic acceptor. For these reasons, much effort was made for the synthesis and analysis of the glycoside bond. Vibrational circular dichroism VCD has some advantages over conventional electronic circular dichroism (ECD) due to the applicability to all organic molecules and the reliability of ab initio quantum calculation. However, for a molecule with many chiral centers such as carbohydrates, determination of the absolute configuration tends to be difficult because the information from each stereochemical center is mixed and averaged over the spectrum. In the CH stretching region, only two VCD studies on carbohydrates have been reported and spectra--structure correlation, as determined for the glycoside band, remains to be investigated. T. Taniguchi and collaborators report that methyl glycosides exhibit a characteristic VCD peak, the sign of which solely reflects the C-1 absolute configuration. This work is a theoretical contribution to study the behaviour of VCD spectrum's of the monosaccharides when the water molecules are taken explicitly. This study is focused on six different monosaccharides in theirs absolute configuration R and S. We used the method of density functional theory DFT by means of the B3LYP hybrid functional and 6-31G * basis set.

  16. [Extraction of triazine herbicides from environmental water samples with magnetic graphene nanoparticles as the adsorbent followed by determination using gas chromatography-mass spectrometry].

    PubMed

    Zhang, Guijiang; Zang, Xiaohuan; Zhou, Xin; Wang, Lu; Wang, Chun; Wang, Zhi

    2013-11-01

    A novel method was developed for the determination of seven triazine herbicides in environmental water samples by magnetic solid-phase extraction with graphene-based magnetic nanoparticles (G-Fe3O4 MNPs) as the adsorbent coupled with gas chromatography-mass spectrometry detection. The main factors influencing the extraction efficiency including the amount of G-Fe3O4, the extraction time, the pH and the ionic strength of sample solution and the desorption conditions were optimized. Under the optimized experimental conditions, the enrichment factors of the method for the analytes were in the range from 574 to 968; the linearities of the method ranged from 0.01 to 10.0 microg/L for simazine, propazine, metribuzin, simetryn and cyanazine, from 0.05 to 10.0 microg/L for atrazine and from 0.01 to 8.0 microg/L for prometryn, with the correlation coefficients (r) ranging from 0.996 8 to 0.999 8. The limits of detection were in the range between 1.0 and 5.0 ng/L. Good reproducibilities were obtained with the relative standard deviations below 10.5%. The developed method was applied to the analysis of the triazine herbicides in different water samples (lake, well and tap). The recoveries of the method were in the range from 79.8% to 118.3% at the spiked levels of 0.5 microg/L and 2.0 microg/L. The results indicated that the developed method can be used as a simple and efficient technique for the determination of the triazine herbicides in environmental water samples.

  17. Cassava root husks powder as green adsorbent for the removal of Cu(II) from natural river water

    NASA Astrophysics Data System (ADS)

    Jorgetto, A. O.; Silva, R. I. V.; Saeki, M. J.; Barbosa, R. C.; Martines, M. A. U.; Jorge, S. M. A.; Silva, A. C. P.; Schneider, J. F.; Castro, G. R.

    2014-01-01

    Through a series of simple processes, cassava root husks were turned into a fine powder of controlled particle size (63-75 μm). FTIR spectrum demonstrated the existence of alcohol, amine and carboxylic groups; and elemental analysis confirmed the presence of elements of interest such as sulphur, nitrogen and oxygen. Cross-polarized {1H}sbnd 13C NMR technique indicated the existence of methionine and thiamine through the signals observed at 55 ppm and 54 ppm, respectively, and the point of zero charge (pHpzc) was achieved at pH 5.2. The material was applied in solid-phase extraction of Cu(II) via batch experiments. Optimum adsorption pH was found to be in range of 3-6 and in the kinetic experiment the equilibrium was attained in 1 min. The highest adsorption capacity was 0.14 mmol g-1. The adsorption data were fit to the modified Langmuir equation, and the maximum amount of metal species extracted from the solution, Ns, was determined to be ∼0.14 mmol g-1, which is an indicative that the main adsorption mechanism is through chemisorption. Under optimized conditions, the material was utilized in preconcentration experiments, which culminated in an enrichment factor of 41.3-fold. With the aid of the enrichment factor, experiments were carried out to determine the Cu(II) content in tap water and natural water. Preconcentration method was also applied to a certified reference material (1643e) and the concentration found was 23.03 ± 0.79 μg L-1, whereas the specified Cu(II) concentration was 22.7 ± 0.31 μg L-1.

  18. Energy deposition model based on electron scattering cross section data from water molecules

    NASA Astrophysics Data System (ADS)

    Muñoz, A.; Oiler, J. C.; Blanco, F.; Gorfinkiel, J. D.; Limão-Vieira, P.; Maira-Vidal, A.; Borge, M. J. G.; Tengblad, O.; Huerga, C.; Téllez, M.; García, G.

    2008-10-01

    A complete set of electrons scattering cross sections by water molecules over a broad energy range, from the me V to the Me V ranges, is presented in this study. These data have been obtained by combining experiments and calculations and cover most relevant processes, both elastic and inelastic, which can take place in the considered energy range. A new Monte Carlo simulation programme has been developed using as input parameter these cross sectional data as well as experimental energy loss spectra. The simulation procedure has been applied to obtain electron tracks and energy deposition plots in water when irradiated by a Ru-106 plaque as those used for brachyteraphy of ocular tumours. Finally, the low energy electron tracks provided by the present model have been compared with those obtained with other codes available in the literature

  19. Water and complex organic molecules in the warm inner regions of solar-type protostars

    NASA Astrophysics Data System (ADS)

    Coutens, A.; Jørgensen, J. K.; Persson, M. V.; Lykke, J. M.; Taquet, V.; van Dishoeck, E. F.; Vastel, C.; Wampfler, S. F.

    2015-12-01

    Water and complex organic molecules play an important role in the emergence of Life. They have been detected in different types of astrophysical environments (protostars, prestellar cores, outflows, protoplanetary disks, comets, etc). In particular, they show high abundances towards the warm inner regions of protostars, where the icy grain mantles thermally desorb. Can a part of the molecular content observed in these regions be preserved during the star formation process and incorporated into asteroids and comets, that can deliver it to planetary embryos through impacts? By comparison with cometary studies, interferometric observations of solar-type protostars can help to address this important question. We present recent results obtained with the Plateau de Bure interferometer about water deuteration, glycolaldehyde and ethylene glycol towards the low-mass protostar NGC 1333 IRAS2A.

  20. Development and characterization of activated hydrochars from orange peels as potential adsorbents for emerging organic contaminants.

    PubMed

    Fernandez, M E; Ledesma, B; Román, S; Bonelli, P R; Cukierman, A L

    2015-05-01

    Activated hydrochars obtained from the hydrothermal carbonization of orange peels (Citrus sinensis) followed by various thermochemical processing were assessed as adsorbents for emerging contaminants in water. Thermal activation under flows of CO2 or air as well as chemical activation with phosphoric acid were applied to the hydrochars. Their characteristics were analyzed and related to their ability to uptake three pharmaceuticals (diclofenac sodium, salicylic acid and flurbiprofen) considered as emerging contaminants. The hydrothermal carbonization and subsequent activations promoted substantial chemical transformations which affected the surface properties of the activated hydrochars; they exhibited specific surface areas ranging from 300 to ∼620 m(2)/g. Morphological characterization showed the development of coral-like microspheres dominating the surface of most hydrochars. Their ability to adsorb the three pharmaceuticals selected was found largely dependent on whether the molecules were ionized or in their neutral form and on the porosity developed by the new adsorbents.

  1. Dynamics and mass accommodation of HCl molecules on sulfuric acid-water surfaces.

    PubMed

    Behr, P; Scharfenort, U; Ataya, K; Zellner, R

    2009-09-28

    A molecular beam technique has been used to study the dynamics and mass accommodation of HCl molecules in collision with sulfuric acid-water surfaces. The experiments were performed by directing a nearly mono-energetic beam of HCl molecules onto a continuously renewed liquid film of 54-76 wt% sulfuric acid at temperatures between 213 K and 243 K. Deuterated sulfuric acid was used to separate sticking but non-reactive collisions from those that involved penetration through the phase boundary followed by dissociation and recombination with D+. The results indicate that the mass accommodation of HCl on sulfuric acid-water surfaces decreases sharply with increasing acidity over the concentration range 54-76 wt%. Using the capillary wave theory of mass accommodation this effect is explained by a change of the surface dynamics. Regarding the temperature dependence it is found that the mass accommodation of HCl increases with increasing temperature and is limited by the bulk phase viscosity and driven by the restoring forces of the surface tension. These findings imply that under atmospheric conditions the uptake of HCl from the gas phase depends crucially on the bulk phase parameters of the sulfuric acid aerosol.

  2. Conserved hydrogen bonds and water molecules in MDR HIV-1 protease substrate complexes.

    PubMed

    Liu, Zhigang; Wang, Yong; Yedidi, Ravikiran S; Dewdney, Tamaria G; Reiter, Samuel J; Brunzelle, Joseph S; Kovari, Iulia A; Kovari, Ladislau C

    2013-01-18

    The success of highly active antiretroviral therapy (HAART) in anti-HIV therapy is severely compromised by the rapidly developing drug resistance. HIV-1 protease inhibitors, part of HAART, are losing their potency and efficacy in inhibiting the target. Multi-drug resistant (MDR) 769 HIV-1 protease (resistant mutations at residues 10, 36, 46, 54, 62, 63, 71, 82, 84, 90) was selected for the present study to understand the binding to its natural substrates. The nine crystal structures of MDR769 HIV-1 protease substrate hepta-peptide complexes were analyzed in order to reveal the conserved structural elements for the purpose of drug design against MDR HIV-1 protease. Our structural studies demonstrated that highly conserved hydrogen bonds between the protease and substrate peptides, together with the conserved crystallographic water molecules, played a crucial role in the substrate recognition, substrate stabilization and protease stabilization. In addition, the absence of the key flap-ligand bridging water molecule might imply a different catalytic mechanism of MDR769 HIV-1 protease compared to that of wild type (WT) HIV-1 protease.

  3. Conserved hydrogen bonds and water molecules in MDR HIV-1 protease substrate complexes

    SciTech Connect

    Liu, Zhigang; Wang, Yong; Yedidi, Ravikiran S.; Dewdney, Tamaria G.; Reiter, Samuel J.; Brunzelle, Joseph S.; Kovari, Iulia A.; Kovari, Ladislau C.

    2012-12-19

    Success of highly active antiretroviral therapy (HAART) in anti-HIV therapy is severely compromised by the rapidly developing drug resistance. HIV-1 protease inhibitors, part of HAART, are losing their potency and efficacy in inhibiting the target. Multi-drug resistant (MDR) 769 HIV-1 protease (resistant mutations at residues 10, 36, 46, 54, 62, 63, 71, 82, 84, 90) was selected for the present study to understand the binding to its natural substrates. The nine crystal structures of MDR769 HIV-1 protease substrate hepta-peptide complexes were analyzed in order to reveal the conserved structural elements for the purpose of drug design against MDR HIV-1 protease. Our structural studies demonstrated that highly conserved hydrogen bonds between the protease and substrate peptides, together with the conserved crystallographic water molecules, played a crucial role in the substrate recognition, substrate stabilization and protease stabilization. Additionally, the absence of the key flap-ligand bridging water molecule might imply a different catalytic mechanism of MDR769 HIV-1 protease compared to that of wild type (WT) HIV-1 protease.

  4. Investigations on humic acid removal from water using surfactant-modified zeolite as adsorbent in a fixed-bed reactor

    NASA Astrophysics Data System (ADS)

    Elsheikh, Awad F.; Ahmad, Umi Kalthom; Ramli, Zainab

    2016-12-01

    Natural organic matter (NOM) is ubiquitous in aquatic environments and has recently become an issue of worldwide concern in drinking water treatment. The major component of NOM is humic acids (HA). In this study, a natural zeolite (mordenite) was modified employing hexadecyltrimethylammonium bromide (HDTMA) to enhance greater efficient sites for sorption of HA. The natural zeolite and surfactant-modified zeolite (SMZ) were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectrometer (FT-IR), N2 Adsorption-desorption isotherms and BET-specific surface area, thermographic analysis, derivative thermographic analysis (TGA-DTA) and Field emission scanning electron microscopy (FESEM). A fixed-bed reactor was used for the removal of HA and the effects of different experimental parameters such as HDTMA loading levels, HA solution flow rate, solution pH and eluent concentration were investigated. The results indicated that the SMZ bed with HDTMA loading of 75% of external cation exchange capacity (ECEC) at a flow rate of 2 BV/h and pH of 10 showed the greatest enhanced removal efficiency of HA while ethanol solutions (25%v/v) with feed flow rate of 2 BV/h were sufficient for complete regeneration of SMZ and desorption of HA. Measurements of surface area of SMZ indicated that a monolayer formation of the surfactant at those conditions allowed the optimum removal of HA.

  5. Photophysical studies of a new water soluble indocarbocyanine dye adsorbed onto microcrystalline cellulose and β-cyclodextrin.

    PubMed

    El-Shishtawy, Reda M; Oliveira, Anabela S; Almeida, Paulo; Ferreira, Diana P; Conceição, David S; Ferreira, Luis F Vieira

    2013-05-15

    A water-soluble indocarbocyanine dye was synthesized and its photophysics were studied for the first time on two solid hosts, microcrystalline cellulose and b-cyclodextrin, as well as in homogeneous media. The inclusion of the indocarbocyanine moiety onto microcrystalline cellulose increased the dye aggregation with both H and J aggregates being formed. Adsorption on b-cyclodextrin enhanced aggregation in a similar way. The fluorescence quantum yields were determined for the powdered samples of the cyanine dye on the two hosts and a significant increase was observed relative to homogeneous solution. A remarkable concentration dependence was also detected in both cases. A lifetime distribution analysis has shown that the indocarbocyanine dye mainly occupies the amorphous part of cellulose and is not entrapped in the crystalline part of this host. In the b-CD case, the adsorption occurs outside the host cavity. In both hosts a strong concentration quenching effect is observed and only monomers emit. Both adsorptions may be explained by stereochemical constraints imposed by the two long sulphoethyl tails linked to nitrogen atoms of the indocarbocyanine dye.

  6. Carbon nanotube sponges as a solid-phase extraction adsorbent for the enrichment and determination of polychlorinated biphenyls at trace levels in environmental water samples.

    PubMed

    Wang, Lei; Wang, Xia; Zhou, Jia-Bin; Zhao, Ru-Song

    2016-11-01

    Carbon nanotube (CNT) sponges has recently attracted considerable attention in numerous fields because of its excellent properties, such as high porosity, light weight, and large surface area. The potential of CNT sponges for the solid-phase extraction (SPE) of organic pollutants at trace levels was investigated in this study for the first time. Seven polychlorinated biphenyls (PCBs) were selected as analytes, and gas chromatography-tandem mass spectrometry was employed for the detection. We optimized important parameters that may influence the efficiency of SPE, including the kind and volume of elution solvent, sample pH, and sample flow rate and volume. Under optimized conditions, low limits of detection (0.72-1.98ngL(-1)), wide range of linearity (10-1000ngL(-1)) and good repeatability (2.69-6.85%, n=5) were obtained. CNT sponges exhibited higher extraction performance than other adsorbent materials under the optimized conditions. Real environmental water samples were analyzed, and satisfactory recoveries (81.1-119.1%) were achieved. All these results demonstrated that CNT sponges are suitable SPE material for the enrichment and sensitive determination of PCBs at trace levels.

  7. One pot synthesis of magnetic graphene/carbon nanotube composites as magnetic dispersive solid-phase extraction adsorbent for rapid determination of oxytetracycline in sewage water.

    PubMed

    Sun, Yunyun; Tian, Jing; Wang, Lu; Yan, Hongyuan; Qiao, Fengxia; Qiao, Xiaoqiang

    2015-11-27

    A simple and time-saving one pot synthesis of magnetic graphene/carbon nanotube composites (M-G/CNTs) was developed that could avoid the tedious drying process of graphite oxide, and G/CNTs were modified by Fe3O4 nanoparticles in the reduction procedure. It contributed to a shorten duration of the synthesis process of M-G/CNTs. The obtained M-G/CNTs were characterized and the results indicated that CNTs and Fe3O4 nanoparticles were served as spacer distributing to the layers of graphene, which was beneficial for enlarging surface area and improving extraction efficiency. Moreover, M-G/CNTs showed good magnetic property and outstanding thermal stability. Then M-G/CNTs were applied as adsorbent of magnetic dispersive solid-phase extraction for rapid extraction and determination of oxytetracycline in sewage water. Under the optimum conditions, good linearity was obtained in the range of 20-800ngmL(-1) and the recoveries were ranged from 95.5% to 112.5% with relative standard deviations less than 5.8%.

  8. A simple and efficient method to characterize bonded water molecules in aqueous solutions of electrolytes: Application to sodium sulphate decahydrate

    NASA Astrophysics Data System (ADS)

    Fargeot, Carole; Bebon, C.; Colson, D.; Klein, J.-P.; Blandin, A.-F.; Bossoutrot, J.-M.

    2007-09-01

    During a study on crystallization in viscous media, an unexpected relevant theoretical and experimental result about the organization of water molecules in salt solutions has been obtained. Experimental results obtained during measurement of viscosity of saccharose and water solutions demonstrate that the salt dissolved in saccharose solution has the capacity to catch the solvent, namely water, from the solvated substance, here saccharose, which induces a quite large viscosity gap. There is a certain mutual electrolyte-water attraction; it may be pushed on by stronger water-salt than water-saccharose interactions. Determination of the binding of water with the salt in the solution can be done directly from measured viscosity. The number of water molecules withdrawn by Na 2SO 4 in solution is computable from viscosity values. Significance of the results obtained is a relevant demonstration that the 10 water molecules of Na 2SO 4·10H 2O are already organised around the solute before the crystallization. The phenomenon observed here questions theoretical predictions that rely on solvent organization and salt effect in solution. Novelty of this study may thus encourage further experimental work in order to elucidate and test the validity of such investigational method to determine the number of water molecules withdrawn by salt in solution.

  9. Control of unidirectional transport of single-file water molecules through carbon nanotubes in an electric field.

    PubMed

    Su, Jiaye; Guo, Hongxia

    2011-01-25

    The transport of water molecules through nanopores is not only crucial to biological activities but also useful for designing novel nanofluidic devices. Despite considerable effort and progress that has been made, a controllable and unidirectional water flow is still difficult to achieve and the underlying mechanism is far from being understood. In this paper, using molecular dynamics simulations, we systematically investigate the effects of an external electric field on the transport of single-file water molecules through a carbon nanotube (CNT). We find that the orientation of water molecules inside the CNT can be well-tuned by the electric field and is strongly coupled to the water flux. This orientation-induced water flux is energetically due to the asymmetrical water-water interaction along the CNT axis. The wavelike water density profiles are disturbed under strong field strengths. The frequency of flipping for the water dipoles will decrease as the field strength is increased, and the flipping events vanish completely for the relatively large field strengths. Most importantly, a critical field strength E(c) related to the water flux is found. The water flux is increased as E is increased for E ≤ E(c), while it is almost unchanged for E > E(c). Thus, the electric field offers a level of governing for unidirectional water flow, which may have some biological applications and provides a route for designing efficient nanopumps.

  10. The binding energies of one and two water molecules to the first transition-row metal positive ions. II

    NASA Technical Reports Server (NTRS)

    Rosi, Marzio; Bauschlicher, Charles W., Jr.

    1990-01-01

    The present investigation of H2O's binding energy to transition-metal ions proceeds from the D(2h) structure and bends the two water molecules out of plane. The molecule is constrained to have C(2v) symmetry, so that each water molecule and metal ion lies on a plane. The ground states are bent only for Mn(H2O)2(+) and Zn(H2O)2(+), where only 4s4p hybridization is energetically favorable; 4s4p hybridization reduces repulsion.

  11. [Interactions of DNA bases with individual water molecules. Molecular mechanics and quantum mechanics computation results vs. experimental data].

    PubMed

    Gonzalez, E; Lino, J; Deriabina, A; Herrera, J N F; Poltev, V I

    2013-01-01

    To elucidate details of the DNA-water interactions we performed the calculations and systemaitic search for minima of interaction energy of the systems consisting of one of DNA bases and one or two water molecules. The results of calculations using two force fields of molecular mechanics (MM) and correlated ab initio method MP2/6-31G(d, p) of quantum mechanics (QM) have been compared with one another and with experimental data. The calculations demonstrated a qualitative agreement between geometry characteristics of the most of local energy minima obtained via different methods. The deepest minima revealed by MM and QM methods correspond to water molecule position between two neighbor hydrophilic centers of the base and to the formation by water molecule of hydrogen bonds with them. Nevertheless, the relative depth of some minima and peculiarities of mutual water-base positions in' these minima depend on the method used. The analysis revealed insignificance of some differences in the results of calculations performed via different methods and the importance of other ones for the description of DNA hydration. The calculations via MM methods enable us to reproduce quantitatively all the experimental data on the enthalpies of complex formation of single water molecule with the set of mono-, di-, and trimethylated bases, as well as on water molecule locations near base hydrophilic atoms in the crystals of DNA duplex fragments, while some of these data cannot be rationalized by QM calculations.

  12. Development of an element-selective monitoring system for adsorbable organic halogens (AOX) with plasma emission spectrometric detection for quasi-continuous waste-water analysis.

    PubMed

    Twiehaus, T; Evers, S; Buscher, W; Cammann, K

    2001-11-01

    An automated quasi-continuously-operating monitor has been developed for element-selective analysis of adsorbable organic halogens (AOX) in water. After extensive optimization the automatic method was applied to the analysis of standard solutions and real waste water samples to prove its analytical applicability. The new instrument is based on the element-selective analysis of halogens by means of a spectroscopic detection system consisting of a microwave-induced helium plasma excitation source (TM010-type; developed in this laboratory) and the plasma emission detector (PED) which operates with oscillating narrow-band interference filters. After enriching the organic components on activated charcoal and pyrolysis in an oxygen stream at 950 degrees C, in accordance with DIN/EN 38409,H14/1485, interfering CO2 and H2O gas generated during combustion is removed from the analytes in the so-called ELSA-system (element-selective AOX-analyzer). For focused injection into the plasma excitation source the analytes (hydrogen halides) are trapped in a deactivated fused silica capillary at -180 degrees C; this is followed by identification and quantification on the basis of element-specific emission of radiation in the VIS and NIR-region (chlorine 837.6 nm, fluorine 685.6 nm). Bromine and iodine could not be detected with satisfactory inter-element selectivity, because of spectral interferences caused by matrix elements, and so results from the respective single-element investigations for determination of AOBr and AOI are not presented. The procedure has been validated and the analytical performance has been examined by calibration with p-chlorophenol and p-fluorophenol. The limit of detection was 1.1 microg (absolute) for chlorine and 6.6 microg (absolute) for fluorine.

  13. Evaluation of heavy crude oil from a water-oil model system as starting material for the preparation of adsorbents type NaY zeolite-templated carbon.

    PubMed

    Elles-Pérez, Cindy J; Muñoz-Acevedo, Amner; Guzmán, Andrés; Camargo, Hernando; Henao, José

    2017-03-22

    In this work, NaY zeolite is explored as a possible "template" to obtain porous materials type ZTC from the adsorption of heavy crude oil in a water-oil model system (emulsion). In order to produce the adsorbents, a cationic surfactant is selected to facilitate the adsorption of the crude oil into the pores of the zeolite and to get the composite, which was activated with controlled thermal treatments (T: 700-800 °C and t: 0.5-1 h) in inert conditions (N2 gaseous). The starting materials, composite and porous carbons were characterized using structural/surface analysis techniques (API Gravity, SARA, IR, XRD, XRF, TGA, Langmuir isotherms, BET and SEM). The results showed that four types of mesoporous carbons were produced with specific surface areas between 70 ± 1 m(2)/g and 220 ± 3 m(2)/g, average pore volumes between 0.144 cm(3)/g and 0.40 cm(3)/g and average pore widths between 4.9 nm and 8.3 nm. The activation conditions of 800 °C and 1 h allowed to make the carbonaceous material with the best surface characteristics (220 ± 3 m(2)/g, 0.27 cm(3)/g, and 4.9 nm). Therefore, it is concluded that under assay conditions employed, the heavy crude oil, as a mixed model (water-oil), from an aqueous environment is a starting material suitable for preparation of "mesoporous" carbons.

  14. Cation effects on rotational dynamics of anions and water molecules in alkali (Li+, Na+, K+, Cs+) thiocyanate (SCN-) aqueous solutions.

    PubMed

    Bian, Hongtao; Chen, Hailong; Zhang, Qiang; Li, Jiebo; Wen, Xiewen; Zhuang, Wei; Zheng, Junrong

    2013-07-03

    Waiting time dependent rotational anisotropies of SCN(-) anions and water molecules in alkali thiocyanate (XSCN, X = Li, Na, K, Cs) aqueous solutions at various concentrations were measured with ultrafast infrared spectroscopy. It was found that cations can significantly affect the reorientational motions of both water molecules and SCN(-) anions. The dynamics are slower in a solution with a smaller cation. The reorientational time constants follow the order of Li(+) > Na(+) > K(+) ~/= Cs(+). The changes of rotational time constants of SCN(-) at various concentrations scale almost linearly with the changes of solution viscosity, but those of water molecules do not. In addition, the concentration-dependent amplitudes of dynamical changes are much more significant in the Li(+) and Na(+) solutions than those in the K(+) and Cs(+) solutions. Further investigations on the systems with the ultrafast vibrational energy exchange method and molecular dynamics simulations provide an explanation for the observations: the observed rotational dynamics are the balanced results of ion clustering and cation/anion/water direct interactions. In all the solutions at high concentrations (>5 M), substantial amounts of ions form clusters. The structural inhomogeneity in the solutions leads to distinct rotational dynamics of water and anions. The strong interactions of Li(+) and Na(+) because of their relatively large charge densities with water molecules and SCN(-) anions, in addition to the likely geometric confinements because of ion clustering, substantially slow down the rotations of SCN(-) anions and water molecules inside the ion clusters. The interactions of K(+) and Cs(+) with water or SCN(-) are much weaker. The rotations of water molecules inside ion clusters of K(+) and Cs(+) solutions are not significantly different from those of other water species so that the experimentally observed rotational relaxation dynamics are only slightly affected by the ion concentrations.

  15. Effects of water molecules on rearrangements of formamide on the kaolinite basal (001) surface.

    PubMed

    Nguyen, Huyen Thi; Nguyen, Minh Tho

    2014-08-28

    The effects of kaolinite mineral surfaces on the unimolecular rearrangements of formamide (FM) were investigated using periodic density functional theory in conjunction with pseudopotential plane-wave approach. Surface hydroxyl groups covering the octahedral surface of kaolinite were found to play the role of catalysts in the transformations of FM. They induce a reduction of 31 kcal/mol on the energy barrier for formation of its isomer aminohydroxymethylene (AHM), which is close to the reduction amount calculated for water-catalyzed reactions. This suggests that the kaolinite octahedral surface exerts a catalytic effect similar to that of the water molecule. As the tetrahedral surface does not contain catalytic surface hydroxyl groups, only water-assisted FM transformation was therefore studied on this surface whose energy barrier amounts to ∼17 kcal/mol. The combined effect of both water and kaolinite on FM rearrangements via triple hydrogen transfer reactions does not significantly lower the energy barriers, as compared to those of double hydrogen transfer reactions. The triple hydrogen transfer energy barriers amount to ∼20 and ∼36 kcal/mol, and the double ones are ∼21 and ∼40 kcal/mol for formation of formimic acid and AHM isomers, respectively. However, the energies of the systems in water-catalyzed channels lie below the available energies of the original reactants, and thus these channels are more favored than the water-free ones. With its multiple functions as both a supporting plate-form and a catalyst for FM reactions, kaolinite can thus be regarded as an important natural catalyst for prebiotic synthesis.

  16. Unintended consequences? Water molecules at biological and crystallographic protein-protein interfaces.

    PubMed

    Ahmed, Mostafa H; Habtemariam, Mesay; Safo, Martin K; Scarsdale, J Neel; Spyrakis, Francesca; Cozzini, Pietro; Mozzarelli, Andrea; Kellogg, Glen E

    2013-12-01

    The importance of protein-protein interactions (PPIs) is becoming increasingly appreciated, as these interactions lie at the core of virtually every biological process. Small molecule modulators that target PPIs are under exploration as new therapies. One of the greatest obstacles faced in crystallographically determining the 3D structures of proteins is coaxing the proteins to form "artificial" PPIs that lead to uniform crystals suitable for X-ray diffraction. This work compares interactions formed naturally, i.e., "biological", with those artificially formed under crystallization conditions or "non-biological". In particular, a detailed analysis of water molecules at the interfaces of high-resolution (≤2.30 Å) X-ray crystal structures of protein-protein complexes, where 140 are biological protein-protein complex structures and 112 include non-biological protein-protein interfaces, was carried out using modeling tools based on the HINT forcefield. Surprisingly few and relatively subtle differences were observed between the two types of interfaces: (i) non-biological interfaces are more polar than biolog