Comparison of TID Effects in Space-Like Variable Dose Rates and Constant Dose Rates

NASA Technical Reports Server (NTRS)

Harris, Richard D.; McClure, Steven S.; Rax, Bernard G.; Evans, Robin W.; Jun, Insoo

2008-01-01

The degradation of the LM193 dual voltage comparator has been studied at different TID dose rate profiles, including several different constant dose rates and a variable dose rate that simulates the behavior of a solar flare. A comparison of results following constant dose rate vs. variable dose rates is made to explore how well the constant dose rates used for typical part testing predict the performance during a simulated space-like mission. Testing at a constant dose rate equal to the lowest dose rate seen during the simulated flare provides an extremely conservative estimate of the overall amount of degradation. A constant dose rate equal to the average dose rate is also more conservative than the variable rate. It appears that, for this part, weighting the dose rates by the amount of total dose received at each rate (rather than the amount of time at each dose rate) results in an average rate that produces an amount of degradation that is a reasonable approximation to that received by the variable rate.

UV-induced photocatalytic degradation of aqueous acetaminophen: the role of adsorption and reaction kinetics.

PubMed

Basha, Shaik; Keane, David; Nolan, Kieran; Oelgemöller, Michael; Lawler, Jenny; Tobin, John M; Morrissey, Anne

2015-02-01

Nanostructured titania supported on activated carbon (AC), termed as integrated photocatalytic adsorbents (IPCAs), were prepared by ultrasonication and investigated for the photocatalytic degradation of acetaminophen (AMP), a common analgesic and antipyretic drug. The IPCAs showed high affinity towards AMP (in dark adsorption studies), with the amount adsorbed proportional to the TiO2 content; the highest adsorption was at 10 wt% TiO2. Equilibrium isotherm studies showed that the adsorption followed the Langmuir model, indicating the dependence of the reaction on an initial adsorption step, with maximum adsorption capacity of 28.4 mg/g for 10 % TiO2 IPCA. The effects of initial pH, catalyst amount and initial AMP concentration on the photocatalytic degradation rates were studied. Generally, the AMP photodegradation activity of the IPCAs was better than that of bare TiO2. Kinetic studies on the photocatalytic degradation of AMP under UV suggest that the degradation followed Langmuir-Hinshelwood (L-H) kinetics, with an adsorption rate constant (K) that was considerably higher than the photocatalytic rate constant (k r), indicating that the photocatalysis of AMP is the rate-determining step during the adsorption/photocatalysis process.

On determining dose rate constants spectroscopically

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodriguez, M.; Rogers, D. W. O.

2013-01-15

Purpose: To investigate several aspects of the Chen and Nath spectroscopic method of determining the dose rate constants of {sup 125}I and {sup 103}Pd seeds [Z. Chen and R. Nath, Phys. Med. Biol. 55, 6089-6104 (2010)] including the accuracy of using a line or dual-point source approximation as done in their method, and the accuracy of ignoring the effects of the scattered photons in the spectra. Additionally, the authors investigate the accuracy of the literature's many different spectra for bare, i.e., unencapsulated {sup 125}I and {sup 103}Pd sources. Methods: Spectra generated by 14 {sup 125}I and 6 {sup 103}Pd seedsmore » were calculated in vacuo at 10 cm from the source in a 2.7 Multiplication-Sign 2.7 Multiplication-Sign 0.05 cm{sup 3} voxel using the EGSnrc BrachyDose Monte Carlo code. Calculated spectra used the initial photon spectra recommended by AAPM's TG-43U1 and NCRP (National Council of Radiation Protection and Measurements) Report 58 for the {sup 125}I seeds, or TG-43U1 and NNDC(2000) (National Nuclear Data Center, 2000) for {sup 103}Pd seeds. The emitted spectra were treated as coming from a line or dual-point source in a Monte Carlo simulation to calculate the dose rate constant. The TG-43U1 definition of the dose rate constant was used. These calculations were performed using the full spectrum including scattered photons or using only the main peaks in the spectrum as done experimentally. Statistical uncertainties on the air kerma/history and the dose rate/history were Less-Than-Or-Slanted-Equal-To 0.2%. The dose rate constants were also calculated using Monte Carlo simulations of the full seed model. Results: The ratio of the intensity of the 31 keV line relative to that of the main peak in {sup 125}I spectra is, on average, 6.8% higher when calculated with the NCRP Report 58 initial spectrum vs that calculated with TG-43U1 initial spectrum. The {sup 103}Pd spectra exhibit an average 6.2% decrease in the 22.9 keV line relative to the main peak

Adsorption kinetics of ion of Pb2+ using Tricalcium Phosphate particles

NASA Astrophysics Data System (ADS)

Fadli, A.; Yenti, S. R.; Akbar, F.; Maihendra; Mawarni, F.

2018-04-01

One of the heavy metals that can pollute water is Pb2+. The concentration of ion Pb2+ can be removed using the adsorption method. The purpose of this research is to determine the adsorption kinetics model of ions Pb2+ using tricalcium phosphate (TCP) particles with variation of the temperature and adsorbent dosage. Five hundred mililiter Pb2+ solution with of 3 mg/L were added 0,5 gr, 1 gr and 1,5 gr of TCP in a glass beaker and stirred with rate of 300 rpm at a temperature of 30 °C, 40 °C and 50 °C. Pb2+ concentration in solution was analyzed by AAS (Atomic Adsorption Spectroscopy). The results showed that the rate of adsorption increased with the increasing of the temperature and adsorbent dosage. Minimum constant value of adsorption kinetic was 1,720 g/mg.min obtained at temperature of 30 °C and adsorbent dosageof 0,5 gr. The maximum value of adsorption kinetic constant was 9,755 g/mg.min obtained at temperature of 50 °C and adsorbent dosage of 1,5 gr. The appropriate model for adsorption kinetics followed the pseudo second order.

On the validity of specific rate constants (kSA) in Fe0/H2O systems.

PubMed

Noubactep, C

2009-05-30

The validity of the specific reaction rate constants (k(SA)) in modelling contaminant removal in Fe(0)/H(2)O systems is questioned. It is shown that the current k(SA)-model does not consider the large reactive surface area provided by the in-situ formed oxide film, and thus the adsorptive interactions between contaminants and film materials. Furthermore, neither the dynamic nature of film formation nor the fact that the Fe(0) surface is shielded by the film is considered. Suggestions are made how the k(SA)-model could be further developed to meet its original goal.

Novel three-stage kinetic model for aqueous benzene adsorption on activated carbon.

PubMed

Choi, Jae-Woo; Choi, Nag-Choul; Lee, Soon-Jae; Kim, Dong-Ju

2007-10-15

We propose a novel kinetic model for adsorption of aqueous benzene onto both granular activated carbon (GAC) and powdered activated carbon (PAC). The model is based on mass conservation of benzene coupled with three-stage adsorption: (1) the first portion for an instantaneous stage or external surface adsorption, (2) the second portion for a gradual stage with rate-limiting intraparticle diffusion, and (3) the third portion for a constant stage in which the aqueous phase no longer interacts with activated carbon. An analytical solution of the kinetic model was validated with the kinetic data obtained from aqueous benzene adsorption onto GAC and PAC in batch experiments with two different solution concentrations (C(0)=300 mg L(-1), 600 mg L(-1)). Experimental results revealed that benzene adsorption for the two concentrations followed three distinct stages for PAC but two stages for GAC. The analytical solution could successfully describe the kinetic adsorption of aqueous benzene in the batch reaction system, showing a fast instantaneous adsorption followed by a slow rate-limiting adsorption and a final long constant adsorption. Use of the two-stage model gave incorrect values of adsorption coefficients in the analytical solution due to inability to describe the third stage.

Measurements of VOC adsorption/desorption characteristics of typical interior building materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

An, Y.; Zhang, J.S.; Shaw, C.Y.

2000-07-01

The adsorption/desorption of volatile organic compounds (VOCs) on interior building material surfaces (i.e., the sink effect) can affect the VOC concentrations in a building, and thus need to be accounted for an indoor air quality (IAQ) prediction model. In this study, the VOC adsorption/desorption characteristics (sink effect) were measured for four typical interior building materials including carpet, vinyl floor tile, painted drywall, and ceiling tile. The VOCs tested were ethylbenzene, cyclohexanone, 1,4-dichlorobenzene, benzaldehyde, and dodecane. These five VOCs were selected because they are representative of hydrocarbons, aromatics, ketones, aldehydes, and chlorine substituted compounds. The first order reversible adsorption/desorption model wasmore » based on the Langmuir isotherm was used to analyze the data and to determine the equilibrium constant of each VOC-material combination. It was found that the adsorption/desorption equilibrium constant, which is a measure of the sink capacity, increased linearly with the inverse of the VOC vapor pressure. For each compound, the adsorption/desorption equilibrium constant, and the adsorption rate constant differed significantly among the four materials tested. A detailed characterization of the material structure in the micro-scale would improve the understanding and modeling of the sink effect in the future. The results of this study can be used to estimate the impact of sink effect on the VOC concentrations in buildings.« less

Monte Carlo Simulations of the Kinetics of Protein Adsorption

NASA Astrophysics Data System (ADS)

Zhdanov, V. P.; Kasemo, B.

The past decade has been characterized by rapid progress in Monte Carlo simulations of protein folding in a solution. This review summarizes the main results obtained in the field, as a background to the major topic, namely corresponding advances in simulations of protein adsorption kinetics at solid-liquid interfaces. The latter occur via diffusion in the liquid towards the interface followed by actual adsorption, and subsequent irreversible conformational changes, resulting in more or less pronounced denaturation of the native protein structure. The conventional kinetic models describing these steps are based on the assumption that the denaturation transitions obey the first-order law with a single value of the denaturation rate constant kr. The validity of this assumption has been studied in recent lattice Monte Carlo simulations of denaturation of model protein-like molecules with different types of the monomer-monomer interactions. The results obtained indicate that, due to trapping in metastable states, (i) the transition of a molecule to the denatured state is usually nonexponential in time, i.e. it does not obey the first-order law, and (ii) the denaturation transitions of an ensemble of different molecules are characterized by different time scales, i.e. the denaturation process cannot be described by a single rate constant kr. One should, rather, introduce a distribution of values of this rate constant (physically, different values of kr reflect the fact that the transitions to the altered state occurs via different metastable states). The phenomenological kinetics of irreversible adsorption of proteins with and without a distribution of the denaturation rate constant values have been calculated in the limits where protein diffusion in the solution is, respectively, rapid or slow. In both cases, the adsorption kinetics with a distribution of kr are found to be close to those with a single-valued rate constant kr, provided that the average value of kr in

Hydrogel covered bimetallic Co:Ni magnetic nano alloy for protein adsorption in biomedical application

NASA Astrophysics Data System (ADS)

Rajar, Kausar; Alveroglu, Esra

2017-10-01

In this study, polyacrylamide (PAAm) hydrogel covered CoNi magnetic nanoalloys with various Co/Ni molar ratio (from 1/4 to 4/1) were synthesized, characterized and used for adsorption of Bovine Serum Albumin (BSA). XRD, EDS, VSM, SEM, AFM, Automated Gas Sorption Analyzer and Fluorescence measurements were used for characterizations and adsorption studies. The results confirm that all the synthesized nanoalloys have soft ferromagnetic nature and particles size were determined to be in the range of 8.60-12.19 nm. Adsorption performances of magnetic nanoalloys were investigated on bovine serum albumin (BSA) as a model protein. The results showed that prepared CoNi:PAAm composites have multistage adsorption kinetics for BSA and increasing Ni content in the CoNi nanoalloys enhance the adsorption rate constant and the rate constant can be tuned between 0.003 s-1 and 0.009 s-1 and between 0.01 s-1 and 0.60 s-1 for the first order adsorption and the second order adsorption stages, respectively. These results show that CoNi:PAAm composites can open new pathways for preparing a special composite material which has specific adsorption kinetic for bio-separation technology.

The Rate Constant for Fluorescence Quenching

ERIC Educational Resources Information Center

Legenza, Michael W.; Marzzacco, Charles J.

1977-01-01

Describes an experiment that utilizes fluorescence intensity measurements from a Spectronic 20 to determine the rate constant for the fluorescence quenching of various aromatic hydrocarbons by carbon tetrachloride in an ethanol solvent. (MLH)

Equilibrium and kinetic adsorption study of a cationic dye by a natural adsorbent--silkworm pupa.

PubMed

Noroozi, B; Sorial, G A; Bahrami, H; Arami, M

2007-01-02

In this work the use of silkworm pupa, which is the waste of silk spinning industries has been investigated as an adsorbent for the removal of C.I. Basic Blue 41. The amino acid nature of the pupa provided a reasonable capability for dye removal. Equilibrium adsorption isotherms and kinetics were investigated. The adsorption equilibrium data were analyzed by using various adsorption isotherm models and the results have shown that adsorption behavior of the dye could be described reasonably well by either Langmuir or Freundlich models. The characteristic parameters for each isotherm have been determined. The monolayer adsorption capacity was determined to be 555 mg/g. Kinetic studies indicated that the adsorption follows pseudo-second-order kinetics with a rate constant of 0.0434 and 0.0572 g/min mg for initial dye concentration of 200 mg/l at 20 and 40 degrees C, respectively. Kinetic studies showed that film diffusion and intra-particle diffusion were simultaneously operating during the adsorption process. The rate constant for intra-particle diffusion was estimated to be 1.985 mg/g min(0.5).

Estimation of hydrolysis rate constants for carbamates ...

EPA Pesticide Factsheets

Cheminformatics based tools, such as the Chemical Transformation Simulator under development in EPA’s Office of Research and Development, are being increasingly used to evaluate chemicals for their potential to degrade in the environment or be transformed through metabolism. Hydrolysis represents a major environmental degradation pathway; unfortunately, only a small fraction of hydrolysis rates for about 85,000 chemicals on the Toxic Substances Control Act (TSCA) inventory are in public domain, making it critical to develop in silico approaches to estimate hydrolysis rate constants. In this presentation, we compare three complementary approaches to estimate hydrolysis rates for carbamates, an important chemical class widely used in agriculture as pesticides, herbicides and fungicides. Fragment-based Quantitative Structure Activity Relationships (QSARs) using Hammett-Taft sigma constants are widely published and implemented for relatively simple functional groups such as carboxylic acid esters, phthalate esters, and organophosphate esters, and we extend these to carbamates. We also develop a pKa based model and a quantitative structure property relationship (QSPR) model, and evaluate them against measured rate constants using R square and root mean square (RMS) error. Our work shows that for our relatively small sample size of carbamates, a Hammett-Taft based fragment model performs best, followed by a pKa and a QSPR model. This presentation compares three comp

Instanton rate constant calculations close to and above the crossover temperature.

PubMed

McConnell, Sean; Kästner, Johannes

2017-11-15

Canonical instanton theory is known to overestimate the rate constant close to a system-dependent crossover temperature and is inapplicable above that temperature. We compare the accuracy of the reaction rate constants calculated using recent semi-classical rate expressions to those from canonical instanton theory. We show that rate constants calculated purely from solving the stability matrix for the action in degrees of freedom orthogonal to the instanton path is not applicable at arbitrarily low temperatures and use two methods to overcome this. Furthermore, as a by-product of the developed methods, we derive a simple correction to canonical instanton theory that can alleviate this known overestimation of rate constants close to the crossover temperature. The combined methods accurately reproduce the rate constants of the canonical theory along the whole temperature range without the spurious overestimation near the crossover temperature. We calculate and compare rate constants on three different reactions: H in the Müller-Brown potential, methylhydroxycarbene → acetaldehyde and H 2  + OH → H + H 2 O. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Rate constants measured for hydrated electron reactions with peptides and proteins

NASA Technical Reports Server (NTRS)

Braams, R.

1968-01-01

Effects of ionizing radiation on the amino acids of proteins and the reactivity of the protonated amino group depends upon the pK subscript a of the group. Estimates of the rate constants for reactions involving the amino acid side chains are presented. These rate constants gave an approximate rate constant for three different protein molecules.

[Effect of SO2 volume fraction in flue gas on the adsorption behaviors adsorbed by ZL50 activated carbon and kinetic analysis].

PubMed

Gao, Ji-xian; Wang, Tie-feng; Wang, Jin-fu

2010-05-01

The influence of SO2 dynamic adsorption behaviors using ZL50 activated carbon for flue gas desulphurization and denitrification under different SO2 volume fraction was investigated experimentally, and the kinetic analysis was conducted by kinetic models. With the increase of SO2 volume fraction in flue gas, the SO2 removal ratio and the activity ratio of ZL50 activated carbon decreased, respectively, and SO2 adsorption rate and capacity increased correspondingly. The calculated results indicate that Bangham model has the best prediction effect, the chemisorption processes of SO2 was significantly affected by catalytic oxidative reaction. The adsorption rate constant of Lagergren's pseudo first order model increased with the increase of inlet SO, volume fraction, which indicated that catalytic oxidative reaction of SO2 adsorbed by ZL50 activated carbon may be the rate controlling step in earlier adsorption stage. The Lagergren's and Bangham's initial adsorption rate were deduced and defined, respectively. The Ho's and Elovich's initial adsorption rate were also deduced in this paper. The Bangham's initial adsorption rate values were defined in good agreement with those of experiments. The defined Bangham's adsorptive reaction kinetic model can describe the SO2 dynamic adsorption rate well. The studied results indicated that the SO2 partial order of initial reaction rate was one or adjacent to one, while the O2 and water vapor partial order of initial reaction rate were constants ranging from 0.15-0.20 and 0.45-0.50, respectively.

Relationship between reaction rate constants of organic pollutants and their molecular descriptors during Fenton oxidation and in situ formed ferric-oxyhydroxides.

PubMed

Jia, Lijuan; Shen, Zhemin; Su, Pingru

2016-05-01

Fenton oxidation is a promising water treatment method to degrade organic pollutants. In this study, 30 different organic compounds were selected and their reaction rate constants (k) were determined for the Fenton oxidation process. Gaussian09 and Material Studio software sets were used to carry out calculations and obtain values of 10 different molecular descriptors for each studied compound. Ferric-oxyhydroxide coagulation experiments were conducted to determine the coagulation percentage. Based upon the adsorption capacity, all of the investigated organic compounds were divided into two groups (Group A and Group B). The percentage adsorption of organic compounds in Group A was less than 15% (wt./wt.) and that in the Group B was higher than 15% (wt./wt.). For Group A, removal of the compounds by oxidation was the dominant process while for Group B, removal by both oxidation and coagulation (as a synergistic process) took place. Results showed that the relationship between the rate constants (k values) and the molecular descriptors of Group A was more pronounced than for Group B compounds. For the oxidation-dominated process, EHOMO and Fukui indices (f(0)x, f(-)x, f(+)x) were the most significant factors. The influence of bond order was more significant for the synergistic process of oxidation and coagulation than for the oxidation-dominated process. The influences of all other molecular descriptors on the synergistic process were weaker than on the oxidation-dominated process. Copyright © 2015. Published by Elsevier B.V.

Real-Time Monitoring of Azo Dye Interfacial Adsorption at Silica-Water Interface by Total Internal Reflection-Induced Surface Evanescent Wave.

PubMed

Xiong, Yan; Wang, Qing; Duan, Ming; Tan, Jun; Fang, Shenwen; Wu, Jiayi

2018-06-19

An interface research method based on total internal reflection induced evanescent wave (TIR-EW) is developed to monitor the adsorption behavior of azo dye at the silica-water interface. The monitoring system is constructed by employing silica optical fiber (SOF) as both charged substrate for dye adsorption and light transmission waveguide for evanescent wave production. According to the change of evanescent wave intensity and followed by Beer's law, the methylene blue (MB) adsorption behavior can be real-time monitored at the silica-water interface. Langmuir adsorption model and pseudo-first-order model are applied to obtain the related thermodynamic and kinetic data. The adsorption equilibrium constant ( K ads ) and adsorption free energy (Δ G) of MB at the silica-water interface are determined to be (3.3 ± 0.5) × 10 4 M -1 and -25.7 ± 1.7 kJ mol -1 . Meanwhile, this method is highlighted to isolate elementary processes of adsorption and desorption under steady-state conditions, and gives adsorption rate constant ( k a ) and desorption rate constant ( k d ) of 8585 ± 19.8 min -1 and 0.26 ± 0.0006 min -1 for 15 r/min flow rate. The surface interaction process is revealed and adsorption mechanism is proposed, indicating MB first adsorbed on Si-O - sites through electrostatic attraction and then on Si-OH sites through hydrogen bond with increasing MB concentrations. Our findings from this study provided molecular-level interpretation of azo dye adsorption at silica-water interface, and the results provide important insight into how MB adsorption can be controlled at the interface.

Rate constant for reaction of atomic hydrogen with germane

NASA Technical Reports Server (NTRS)

Nava, David F.; Payne, Walter A.; Marston, George; Stief, Louis J.

1990-01-01

Due to the interest in the chemistry of germane in the atmospheres of Jupiter and Saturn, and because previously reported kinetic reaction rate studies at 298 K gave results differing by a factor of 200, laboratory measurements were performed to determine the reaction rate constant for H + GeH4. Results of the study at 298 K, obtained via the direct technique of flash photolysis-resonance fluorescence, yield the reaction rate constant, k = (4.08 + or - 0.22) x 10(exp -12) cu cm/s.

The vibrational dependence of dissociative recombination: Rate constants for N{sub 2}{sup +}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guberman, Steven L., E-mail: slg@sci.org

Dissociative recombination rate constants are reported with electron temperature dependent uncertainties for the lowest 5 vibrational levels of the N{sub 2}{sup +} ground state. The rate constants are determined from ab initio calculations of potential curves, electronic widths, quantum defects, and cross sections. At 100 K electron temperature, the rate constants overlap with the exception of the third vibrational level. At and above 300 K, the rate constants for excited vibrational levels are significantly smaller than that for the ground level. It is shown that any experimentally determined total rate constant at 300 K electron temperature that is smaller thanmore » 2.0 × 10{sup −7} cm{sup 3}/s is likely to be for ions that have a substantially excited vibrational population. Using the vibrational level specific rate constants, the total rate constant is in very good agreement with that for an excited vibrational distribution found in a storage ring experiment. It is also shown that a prior analysis of a laser induced fluorescence experiment is quantitatively flawed due to the need to account for reactions with unknown rate constants. Two prior calculations of the dissociative recombination rate constant are shown to be inconsistent with the cross sections upon which they are based. The rate constants calculated here contribute to the resolution of a 30 year old disagreement between modeled and observed N{sub 2}{sup +} ionospheric densities.« less

Kinetics of Adsorption of Diethylene-triaminomethylated Polyacrylamide on Dispersed Kaolin Accompanied by Flocculation.

PubMed

Kislenko; Verlinskaya

1999-08-01

The kinetics of the adsorption of diethylene-triaminomethylated polyacrylamide on kaolin dispersed in water has been investigated. An influence of the flocculation of kaolin dispersion on polymer adsorption has been found. The kinetics of particle aggregation under the influence of dissolved polymer has been studied. Polymer adsorption and particle aggregation proceed simultaneously, accompanied by a steady decrease in the amount of adsorbed polymer per unit mass of kaolin. A mathematical model of the adsorption process, consistent with the experimental data, is described. The rate constants and their ratios have been determined. Copyright 1999 Academic Press.

Precisely and Accurately Inferring Single-Molecule Rate Constants

PubMed Central

Kinz-Thompson, Colin D.; Bailey, Nevette A.; Gonzalez, Ruben L.

2017-01-01

The kinetics of biomolecular systems can be quantified by calculating the stochastic rate constants that govern the biomolecular state versus time trajectories (i.e., state trajectories) of individual biomolecules. To do so, the experimental signal versus time trajectories (i.e., signal trajectories) obtained from observing individual biomolecules are often idealized to generate state trajectories by methods such as thresholding or hidden Markov modeling. Here, we discuss approaches for idealizing signal trajectories and calculating stochastic rate constants from the resulting state trajectories. Importantly, we provide an analysis of how the finite length of signal trajectories restrict the precision of these approaches, and demonstrate how Bayesian inference-based versions of these approaches allow rigorous determination of this precision. Similarly, we provide an analysis of how the finite lengths and limited time resolutions of signal trajectories restrict the accuracy of these approaches, and describe methods that, by accounting for the effects of the finite length and limited time resolution of signal trajectories, substantially improve this accuracy. Collectively, therefore, the methods we consider here enable a rigorous assessment of the precision, and a significant enhancement of the accuracy, with which stochastic rate constants can be calculated from single-molecule signal trajectories. PMID:27793280

Evaluation of BTEX and phenol removal from aqueous solution by multi-solute adsorption onto smectite organoclay.

PubMed

Carvalho, M N; da Motta, M; Benachour, M; Sales, D C S; Abreu, C A M

2012-11-15

The removal process of BTEX and phenol was evaluated. The smectite organoclay for single-solute system reached removal was evaluated by adsorption on smectite organoclay adsorbent by kinetic and equilibrium efficiencies between 55 and 90% while was reached between 30 and 90% for multi-solute system at 297 K and pH 9. The Langmuir-Freundlich model was used to fit the experimental data with correlation coefficient between 0.98 and 0.99 providing kinetic and equilibrium parameter values. Phenol and ethylbenzene presented high maximum adsorbed amount, 8.28 and 6.67 mg/g, respectively, compared to the other compounds for single-solute. Toluene and p-xylene presented high values of adsorption constant which indicates a high adsorption affinity of compounds to organoclay surface and high binding energy of adsorption. Phenol presented low kinetic adsorption constant value indicating slow rate of adsorption. Copyright © 2012 Elsevier B.V. All rights reserved.

Predicting heavy metals' adsorption edges and adsorption isotherms on MnO2 with the parameters determined from Langmuir kinetics.

PubMed

Hu, Qinghai; Xiao, Zhongjin; Xiong, Xinmei; Zhou, Gongming; Guan, Xiaohong

2015-01-01

Although surface complexation models have been widely used to describe the adsorption of heavy metals, few studies have verified the feasibility of modeling the adsorption kinetics, edge, and isotherm data with one pH-independent parameter. A close inspection of the derivation process of Langmuir isotherm revealed that the equilibrium constant derived from the Langmuir kinetic model, KS-kinetic, is theoretically equivalent to the adsorption constant in Langmuir isotherm, KS-Langmuir. The modified Langmuir kinetic model (MLK model) and modified Langmuir isotherm model (MLI model) incorporating pH factor were developed. The MLK model was employed to simulate the adsorption kinetics of Cu(II), Co(II), Cd(II), Zn(II) and Ni(II) on MnO2 at pH3.2 or 3.3 to get the values of KS-kinetic. The adsorption edges of heavy metals could be modeled with the modified metal partitioning model (MMP model), and the values of KS-Langmuir were obtained. The values of KS-kinetic and KS-Langmuir are very close to each other, validating that the constants obtained by these two methods are basically the same. The MMP model with KS-kinetic constants could predict the adsorption edges of heavy metals on MnO2 very well at different adsorbent/adsorbate concentrations. Moreover, the adsorption isotherms of heavy metals on MnO2 at various pH levels could be predicted reasonably well by the MLI model with the KS-kinetic constants. Copyright © 2014. Published by Elsevier B.V.

Determination of kinetic and equilibrium parameters of the batch adsorption of Mn(II), Co(II), Ni(II) and Cu(II) from aqueous solution by black carrot (Daucus carota L.) residues.

PubMed

Güzel, Fuat; Yakut, Hakan; Topal, Giray

2008-05-30

In this study, the effect of temperature on the adsorption of Mn(II), Ni(II), Co(II) and Cu(II) from aqueous solution by modified carrot residues (MCR) was investigated. The equilibrium contact times of adsorption process for each heavy metals-MCR systems were determined. Kinetic data obtained for each heavy metal by MCR at different temperatures were applied to the Lagergren equation, and adsorption rate constants (kads) at these temperatures were determined. These rate constants related to the adsorption of heavy metal by MCR were applied to the Arrhenius equation, and activation energies (Ea) were determined. In addition, the isotherms for adsorption of each heavy metal by MCR at different temperatures were also determined. These isothermal data were applied to linear forms of isotherm equations that they fit the Langmuir adsorption isotherm, and the Langmuir constants (qm and b) were calculated. b constants determined at different temperatures were applied to thermodynamic equations, and thermodynamic parameters such as enthalpy (Delta H), free energy (Delta G), and entropy (Delta S) were calculated and these values show that adsorption of heavy metal on MCR was an endothermic process and process of adsorption was favoured at high temperatures.

High-Temperature Slow Crack Growth of Silicon Carbide Determined by Constant-Stress-Rate and Constant-Stress Testing

NASA Technical Reports Server (NTRS)

Choi, Sung H.; Salem, J. A.; Nemeth, N. N.

1998-01-01

High-temperature slow-crack-growth behaviour of hot-pressed silicon carbide was determined using both constant-stress-rate ("dynamic fatigue") and constant-stress ("static fatigue") testing in flexure at 1300 C in air. Slow crack growth was found to be a governing mechanism associated with failure of the material. Four estimation methods such as the individual data, the Weibull median, the arithmetic mean and the median deviation methods were used to determine the slow crack growth parameters. The four estimation methods were in good agreement for the constant-stress-rate testing with a small variation in the slow-crack-growth parameter, n, ranging from 28 to 36. By contrast, the variation in n between the four estimation methods was significant in the constant-stress testing with a somewhat wide range of n= 16 to 32.

Effects of Motility and Adsorption Rate Coefficient on Transport of Bacteria through Saturated Porous Media

PubMed Central

Camper, Anne K.; Hayes, Jason T.; Sturman, Paul J.; Jones, Warren L.; Cunningham, Alfred B.

1993-01-01

Three strains of Pseudomonas fluorescens with different motility rates and adsorption rate coefficients were injected into porous-medium reactors packed with l-mm-diameter glass spheres. Cell breakthrough, time to peak concentration, tailing, and cell recovery were measured at three interstitial pore velocities (higher than, lower than, and much lower than the maximal bacterial motility rate). All experiments were done with distilled water to reduce the effects of growth and chemotaxis. Contrary to expectations, motility did not result in either early breakthrough or early time to peak concentration at flow velocities below the motility rate. Bacterial size exclusion effects were shown to affect breakthrough curve shape at the very low flow velocity, but no such effect was seen at the higher flow velocity. The tendency of bacteria to adsorb to porous-medium surfaces, as measured by adsorption rate coefficients, profoundly influenced transport characteristics. Cell recoveries were shown to be correlated with the ratio of advective to adsorptive transport in the reactors. Adsorption rate coefficients were found to be better predictors of microbial transport phenomena than individual characteristics, such as size, motility, or porous-medium hydrodynamics. PMID:16349075

Computer Calculation of First-Order Rate Constants

ERIC Educational Resources Information Center

Williams, Robert C.; Taylor, James W.

1970-01-01

Discusses the computer program used to calculate first-order rate constants. Discussion includes data preparation, weighting options, comparison techniques, infinity point adjustment, least-square fit, Guggenheim calculation, and printed outputs. Exemplifies the utility of the computer program by two experiments: (1) the thermal decomposition of…

Synthesis of Magnesium Ferrites for the Adsorption of Congo Red from Aqueous Solution Using Batch Studies

NASA Astrophysics Data System (ADS)

Erdawati, E.; Darsef, D.

2018-04-01

A sol gel method with citric acid as an anionic surfactant was used to fabricate nano magnesium ferrites (MgFe2O4) under different calcination temperatures for 2h, respectively. The microstructure and surface morphology of magnesium ferrite powder were characterized by FTIR, XRD, SEM, and BET. The results of this study are useful for adsorption Congo red. The results showed that increasing solution pH and extending contact time are favorable for improving adsorption efficiency. with initial Congo red concentration of 50 mg/L and 100 mg/L. Adsorption data fits well with the Langmuir isotherm models with a maximum adsorption capacity (qm) and a Langmuir adsorption equilibrium constant (K) of 65.1 mg/g and 0.090 L/mg, respectively. The adsorption kinetic agrees well with pseudo second order model with the pseudo second rate constants (K2) of 0.0468 and0.00189 g/mg/min for solutions with initial congo red of 50 and 100 mg/L, respectively

The rate constant of a quantum-diffusion-controlled bimolecular reaction

NASA Astrophysics Data System (ADS)

Bondarev, B. V.

1986-04-01

A quantum-mechanical equation is derived in the tight-bond approximation which describes the motion and chemical interaction of a pair of species A and B when their displacement in the matrix is caused by tunnelling. Within the framework of the discrete model of random walks, definitions are given of the probability and rate constant of a reaction A + B → P (products) proceeding in a condensed medium. A method is suggested for calculating the rate constant of a quantum-diffusion-controlled bimolecular reaction. By this method, an expression is obtained for the rate constant in the stationary spherically symmetrical case. An equation for the density matrix is also proposed which describes the motion and chemical interaction of a pair of species when the quantum and classical diffusion are competitive.

BTEX and MTBE adsorption onto raw and thermally modified diatomite.

PubMed

Aivalioti, Maria; Vamvasakis, Ioannis; Gidarakos, Evangelos

2010-06-15

The removal of BTEX (benzene, toluene, ethyl-benzene and xylenes) and MTBE (methyl tertiary butyl ether) from aqueous solution by raw (D(R)) and thermally modified diatomite at 550, 750 and 950 degrees C (D(550), D(750) and D(950) respectively) was studied. Physical characteristics of both raw and modified diatomite such as specific surface, pore volume distribution, porosity and pH(solution) were determined, indicating important structural changes in the modified diatomite, due to exposure to high temperatures. Both adsorption kinetic and isotherm experiments were carried out. The kinetics data proved a closer fit to the pseudo-second order model. Maximum values for the rate constant, k(2), were obtained for MTBE and benzene (48.9326 and 18.0996 g mg(-1)h(-1), respectively) in sample D(550). The isotherm data proved to fit the Freundlich model more closely, which produced values of the isotherm constant 1/n higher than one, indicating unfavorable adsorption. The highest adsorption capacity, calculated through the values of the isotherm constant k(F), was obtained for MTBE (48.42 mg kg(-1) (mg/L)(n)) in sample D(950). Copyright 2010 Elsevier B.V. All rights reserved.

Influences of brain tissue poroelastic constants on intracranial pressure (ICP) during constant-rate infusion.

PubMed

Li, Xiaogai; von Holst, Hans; Kleiven, Svein

2013-01-01

A 3D finite element (FE) model has been developed to study the mean intracranial pressure (ICP) response during constant-rate infusion using linear poroelasticity. Due to the uncertainties in the poroelastic constants for brain tissue, the influence of each of the main parameters on the transient ICP infusion curve was studied. As a prerequisite for transient analysis, steady-state simulations were performed first. The simulated steady-state pressure distribution in the brain tissue for a normal cerebrospinal fluid (CSF) circulation system showed good correlation with experiments from the literature. Furthermore, steady-state ICP closely followed the infusion experiments at different infusion rates. The verified steady-state models then served as a baseline for the subsequent transient models. For transient analysis, the simulated ICP shows a similar tendency to that found in the experiments, however, different values of the poroelastic constants have a significant effect on the infusion curve. The influence of the main poroelastic parameters including the Biot coefficient α, Skempton coefficient B, drained Young's modulus E, Poisson's ratio ν, permeability κ, CSF absorption conductance C(b) and external venous pressure p(b) was studied to investigate the influence on the pressure response. It was found that the value of the specific storage term S(ε) is the dominant factor that influences the infusion curve, and the drained Young's modulus E was identified as the dominant parameter second to S(ε). Based on the simulated infusion curves from the FE model, artificial neural network (ANN) was used to find an optimised parameter set that best fit the experimental curve. The infusion curves from both the FE simulation and using ANN confirmed the limitation of linear poroelasticity in modelling the transient constant-rate infusion.

18 CFR 806.12 - Constant-rate aquifer testing.

Code of Federal Regulations, 2014 CFR

2014-04-01

... withdraw or increase a withdrawal of groundwater shall perform a constant-rate aquifer test in accordance... groundwater availability analysis to determine the availability of water during a 1-in-10-year recurrence...

18 CFR 806.12 - Constant-rate aquifer testing.

Code of Federal Regulations, 2012 CFR

2012-04-01

... withdraw or increase a withdrawal of groundwater shall perform a constant-rate aquifer test in accordance... groundwater availability analysis to determine the availability of water during a 1-in-10-year recurrence...

18 CFR 806.12 - Constant-rate aquifer testing.

Code of Federal Regulations, 2011 CFR

2011-04-01

... withdraw or increase a withdrawal of groundwater shall perform a constant-rate aquifer test in accordance... groundwater availability analysis to determine the availability of water during a 1-in-10-year recurrence...

18 CFR 806.12 - Constant-rate aquifer testing.

Code of Federal Regulations, 2013 CFR

2013-04-01

... withdraw or increase a withdrawal of groundwater shall perform a constant-rate aquifer test in accordance... groundwater availability analysis to determine the availability of water during a 1-in-10-year recurrence...

Rate constant for the reaction of atomic chlorine with methane

NASA Technical Reports Server (NTRS)

Lin, C. L.; Leu, M. T.; Demore, W. B.

1978-01-01

The rate constant and temperature dependence of the Cl + CH4 reaction have been investigated by the techniques of competitive chlorination of CH4/C2H6 mixtures and by discharge-flow/mass spectroscopy. The objectives were to determine an accurate value for the rate constant for use in stratospheric modeling, and to clarify discrepancies in results previously obtained by different techniques. The results deduced from the competitive chlorination study are in good agreement with the absolute values measured by the mass spectrometric method, and at temperatures above 300 K are in good agreement with measurements by other techniques based on resonance fluorescence detection of atomic chlorine. However, in the 220-300 K region, the competitive experiments indicate lower rate constants than those obtained by resonance fluorescence methods, and do not reproduce the curved Arrhenius plots seen in some of those studies.

Biodegradation testing of chemicals with high Henry's constants - Separating mass and effective concentration reveals higher rate constants.

PubMed

Birch, Heidi; Andersen, Henrik R; Comber, Mike; Mayer, Philipp

2017-05-01

During simulation-type biodegradation tests, volatile chemicals will continuously partition between water phase and headspace. This study addressed how (1) this partitioning affects test results and (2) can be accounted for by combining equilibrium partition and dynamic biodegradation models. An aqueous mixture of 9 (semi)volatile chemicals was first generated using passive dosing and then diluted with environmental surface water producing concentrations in the ng/L to μg/L range. After incubation for 2 h to 4 weeks, automated Headspace Solid Phase Microextraction (HS-SPME) was applied directly on the test systems to measure substrate depletion by biodegradation relatively to abiotic controls. HS-SPME was also applied to determine air to water partitioning ratios. Biodegradation rate constants relating to the chemical in the water phase, k water , were generally a factor 1 to 11 times higher than biodegradation rate constants relating to the total mass of chemical in the test system, k system , with one exceptional factor of 72 times for a long chain alkane. True water phase degradation rate constants were found (i) more appropriate for risk assessment than test system rate constants, (ii) to facilitate extrapolation to other air-water systems and (iii) to be better defined input parameters for aquatic exposure and fate models. Copyright © 2017 Elsevier Ltd. All rights reserved.

ESTIMATION OF PHOSPHATE ESTER HYDROLYSIS RATE CONSTANTS - ALKALINE HYDROLYSIS

EPA Science Inventory

SPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to allow the calculation of alkaline hydrolysis rate constants of phosphate esters in water. The rate is calculated from the energy difference between the initial and transition state...

Utilization of powdered waste sludge (PWS) for removal of textile dyestuffs from wastewater by adsorption.

PubMed

Ozmihci, Serpil; Kargi, Fikret

2006-11-01

Acid pre-treated powdered waste sludge (PWS) was used for removal of textile dyestuffs from aqueous medium by adsorption as an alternative to the use of powdered activated carbon (PAC). The rate and extent of dysetuff removals were determined for four different dyestuffs at different PWS concentrations varying between 1 and 6 gl(-1). Biosorbed dyestuff concentrations at equilibrium decreased with increasing PWS concentration for all dyestuffs tested. PWS was more effective for adsorption of Remazol red RR and Chrisofonia direct yellow 12 as compared to the other dyestuffs tested. More than 80% percent dyestuff removal was obtained for all dyestuffs at PWS concentrations above 4 gl(-1) after 6h of incubation. Similar to percent dyestuff removal, the rate of adsorption was maximum at a PWS concentration of 4 gl(-1). Kinetics of adsorption of dyestuffs was investigated by using the first- and second-order kinetic models and the kinetic constants were determined. Second-order kinetics was found to fit the experimental data better than the first-order model for all dyestuffs tested. Adsorption isotherms were established for all dyestuffs used and the isotherm constants were determined by using the experimental data. Langmuir and the generalized adsorption isotherms were found to be more suitable than the Freundlich isotherm for correlation of equilibrium adsorption data. Acid pre-treated PWS was proven to be an effective adsorbent for dyestuff removal as compared to the other adsorbents reported in literature studies.

Rate Constant and Temperature Dependence for the Reaction of Hydroxyl Radicals with 2-Flouropropane (FC-281ea) and Comparison with an Estimated Rate Constant

NASA Technical Reports Server (NTRS)

DeMore, W.; Wilson, E., Jr.

1998-01-01

Relative rate experiments were used to measure the rate constant and temperature dependence of the reaction of OH radicals with 2-fluoropropane (HFC-281ea), using ethane, propane, ethyl chloride as reference standards.

Flame Chemiluminescence Rate Constants for Quantitative Microgravity Combustion Diagnostics

NASA Technical Reports Server (NTRS)

Luque, Jorge; Smith, Gregory P.; Jeffries, Jay B.; Crosley, David R.; Weiland, Karen (Technical Monitor)

2001-01-01

Absolute excited state concentrations of OH(A), CH(A), and C2(d) were determined in three low pressure premixed methane-air flames. Two dimensional images of chemiluminescence from these states were recorded by a filtered CCD camera, processed by Abel inversion, and calibrated against Rayleigh scattering, Using a previously validated 1-D flame model with known chemistry and excited state quenching rate constants, rate constants are extracted for the reactions CH + O2 (goes to) OH(A) + CO and C2H + O (goes to) CH(A) + CO at flame temperatures. Variations of flame emission intensities with stoichiometry agree well with model predictions.

ESTIMATION OF CARBOXYLIC ACID ESTER HYDROLYSIS RATE CONSTANTS

EPA Science Inventory

SPARC chemical reactivity models were extended to calculate hydrolysis rate constants for carboxylic acid esters from molecular structure. The energy differences between the initial state and the transition state for a molecule of interest are factored into internal and external...

Adsorption of catechol and comparative solutes on hydroxyapatite.

PubMed

Chirdon, William M; O'Brien, William J; Robertson, Richard E

2003-08-15

Contemporary medical and dental adhesives often have difficulty sticking to wet surfaces or weaken with long-term exposure to water. Substantial research has been dedicated to finding a means of achieving adhesion in an aqueous environment. A study evaluates the adsorption of catechol relative to other chemical groups as means of gauging how effective they may be as adsorptive groups in adhesives. Contact angle and surface-tension measurements of solutions of catechols and other chemical groups were used to determine their works of adhesion. Adsorption isotherms were also constructed to ascertain Langmuir constants. Solutes containing catechol groups were compared to solutes containing other polar groups to see how well catechol adsorbs to hydroxyapatite, the mineral component of bones and teeth, relative to other chemical groups found in adhesives. The results of this study show that catechol and molecules containing catechol groups have higher rates and energies of adsorption to hydroxyapatite than do groups such as alcohols, amines, and carboxylic acids. Copyright 2003 Wiley Periodicals, Inc.

Modeling the effect of adsorption on the degradation rate of propiconazole in profiles of Polish Luvisols.

PubMed

Paszko, Tadeusz; Jankowska, Monika

2018-06-18

Laboratory adsorption and degradation studies were carried out to determine the effect of time-dependent adsorption on propiconazole degradation rates in samples from three Polish Luvisols. Strong propiconazole adsorption (organic carbon normalized adsorption coefficients K oc in the range of 1217-7777 mL/g) was observed in batch experiments, with a typical biphasic mechanism with a fast initial step followed by the time-dependent step, which finished within 48 h in the majority of soils. The time-dependent step observed in incubation experiments was longer (duration from 5 to 23 d), and its contribution to total adsorption was from 20% to 34%. The half-lives obtained at 25 °C and 40% maximum water holding capacity of soil, were in the range of 34.7-112.9 d in the Ap horizon and in the range of 42.3-448.8 d for subsoils. The very strong correlations, between degradation rates in pore water and soil organic carbon and soil microbial activity, indicated that microbial degradation of propiconazole was most likely the only significant process responsible for the decay of this compound under aerobic conditions for the whole of the examined soil profiles. Modeling of the processes showed that only models coupling adsorption and degradation were able to correctly describe the experimental data. The analysis of the bioavailability factor values showed that degradation was not limited by the rate of propiconazole desorption from soil, but sorption affected the degradation rate by decreasing its availability for microorganisms. Copyright © 2018. Published by Elsevier Inc.

Breakthrough Adsorption Study of Crude Oil Removal Using Buffing Dust

NASA Astrophysics Data System (ADS)

Setyaningsih, L. W. N.; Yuliansyah, A. T.; Prasetyo, A.; Arimanintan, S. K.; Putri, D. R.

2018-05-01

The utilization of leather industry solid waste as adsorbent to separate oil from water emulsions of surfactant flooding process is a solution that is relatively inexpensive. This study was conducted aiming to obtain a mathematical model that is appropriate for the adsorption process of crude oil by buffing dust in emulsion phase with a continuous adsorption method. Variations in the column adsorption experiments were carried out, such as: flow rate of feed of water-crude oil-surfactant, the concentration of crude oil in the feed, and mass of adsorbent used. Data were evaluated using three models: Adams Bohart, Thomas and Yan. Best results are obtained on the following conditions, the feed flow rate of 60 mL/minute, the crude oil concentration in feed is 1.5% volume and the mass of adsorbent used was 10 g. The values of kinetic constant and adsorption capacity obtained from Yan Model was 21.7774 mL/mg/minute and 220.9581 mg/g with the relative error obtained is 5.4424%.

Rationalizing 5000-Fold Differences in Receptor-Binding Rate Constants of Four Cytokines

PubMed Central

Pang, Xiaodong; Qin, Sanbo; Zhou, Huan-Xiang

2011-01-01

The four cytokines erythropoietin (EPO), interleukin-4 (IL4), human growth hormone (hGH), and prolactin (PRL) all form four-helix bundles and bind to type I cytokine receptors. However, their receptor-binding rate constants span a 5000-fold range. Here, we quantitatively rationalize these vast differences in rate constants by our transient-complex theory for protein-protein association. In the transient complex, the two proteins have near-native separation and relative orientation, but have yet to form the short-range specific interactions of the native complex. The theory predicts the association rate constant as ka=ka0exp(−ΔGel∗/kBT) where ka0 is the basal rate constant for reaching the transient complex by random diffusion, and the Boltzmann factor captures the rate enhancement due to electrostatic attraction. We found that the vast differences in receptor-binding rate constants of the four cytokines arise mostly from the differences in charge complementarity among the four cytokine-receptor complexes. The basal rate constants (ka0) of EPO, IL4, hGH, and PRL were similar (5.2 × 105 M−1s−1, 2.4 × 105 M−1s−1, 1.7 × 105 M−1s−1, and 1.7 × 105 M−1s−1, respectively). However, the average electrostatic free energies (ΔGe1∗) were very different (−4.2 kcal/mol, −2.4 kcal/mol, −0.1 kcal/mol, and −0.5 kcal/mol, respectively, at ionic strength = 160 mM). The receptor-binding rate constants predicted without adjusting any parameters, 6.2 × 108 M−1s−1, 1.3 × 107 M−1s−1, 2.0 × 105 M−1s−1, and 7.6 × 104 M−1s−1, respectively, for EPO, IL4, hGH, and PRL agree well with experimental results. We uncover that these diverse rate constants are anticorrelated with the circulation concentrations of the cytokines, with the resulting cytokine-receptor binding rates very close to the limits set by the half-lives of the receptors, suggesting that these binding rates are functionally relevant and perhaps evolutionarily

Theoretical Evaluation of the Transient Response of Constant Head and Constant Flow-Rate Permeability Tests

USGS Publications Warehouse

Zhang, M.; Takahashi, M.; Morin, R.H.; Esaki, T.

1998-01-01

A theoretical analysis is presented that compares the response characteristics of the constant head and the constant flowrate (flow pump) laboratory techniques for quantifying the hydraulic properties of geologic materials having permeabilities less than 10-10 m/s. Rigorous analytical solutions that describe the transient distributions of hydraulic gradient within a specimen are developed, and equations are derived for each method. Expressions simulating the inflow and outflow rates across the specimen boundaries during a constant-head permeability test are also presented. These solutions illustrate the advantages and disadvantages of each method, including insights into measurement accuracy and the validity of using Darcy's law under certain conditions. The resulting observations offer practical considerations in the selection of an appropriate laboratory test method for the reliable measurement of permeability in low-permeability geologic materials.

Water adsorption on goethite: Application of multilayer adsorption models

NASA Astrophysics Data System (ADS)

Hatch, C. D.; Tumminello, R.; Meredith, R.

2016-12-01

Adsorbed water on the surface of atmospheric mineral dust has recently been shown to significantly affect the ability of mineral dust aerosol to act as cloud condensation nuclei. We have studied water adsorption as a function of relative humidity (RH) on goethite (α-FeO(OH)), a common component of atmospheric mineral dust. The goethite surface area and particle size was determined using BET analysis and with N2 as an adsorbate and scanning electron microscopy, respectively. Water adsorption on the sample was monitored using horizontal attenuated total reflectance Fourier transform infrared (HATR-FTIR) spectroscopy equipped with a flow cell. Water content was determined using Beer's law and the optical constants for bulk water. The results were analyzed using Type II adsorption isotherms to model multilayer adsorption, including BET (Brunauer, Emmet and Teller), FHH (Frenkel, Halsey and Hill) and Freundlich. BET fits to experimental data provide parameters of monolayer coverage, while the FHH and Freundlich isotherms provide insights into multilayer adsorption mechanisms. Results indicate that goethite contains 5% H2O by mass at 50% RH, which increases to 12% by mass at 90% RH. Adsorption parameters and experimental results will be presented.

18 CFR 806.12 - Constant-rate aquifer testing.

Code of Federal Regulations, 2010 CFR

2010-04-01

... groundwater availability analysis to determine the availability of water during a 1-in-10-year recurrence... 18 Conservation of Power and Water Resources 2 2010-04-01 2010-04-01 false Constant-rate aquifer testing. 806.12 Section 806.12 Conservation of Power and Water Resources SUSQUEHANNA RIVER BASIN...

[Adsorption characteristics of acetone and butanone onto honeycomb ZSM-5 molecular sieve].

PubMed

Du, Juan; Luan, Zhi-Qiang; Xie, Qiang; Ye, Ping-Wei; Li, Kai; Wang, Xi-Qin

2013-12-01

Adsorption capacity of acetone and acetone-butanone mixture onto honeycomb ZSM-5 molecular sieve was measured in this paper, and the influences of relative humidity, initial adsorbate concentration and airflow velocity on the adsorption process were investigated. Besides, adsorption performance parameters were calculated by Wheeler's equation. The results showed that relative humidity had no obvious influence on the acetone adsorption performance, which suggests that this material has good hydrophobic ability; in the low concentration range, the dynamic saturated adsorption capacity of acetone increased with the increase of initial concentration, but in the occasion of high concentration of acetone gas (more than 9 mg x L(-1)), the dynamic saturated adsorption capacity maintained at a certain level and did not vary with the increase of initial concentration; the increase of air flow velocity resulted in significant increase of acetone adsorption rate constant, at the same time the critical layer thickness of the adsorbent bed also increased significantly. In the cases of acetone-butanone mixture, the adsorption capacity of butanone onto ZSM-5 was clearly higher than that of acetone.

ESTIMATION OF PHOSPHATE ESTER HYDROLYSIS RATE CONSTANTS. I. ALKALINE HYDROLYSIS

EPA Science Inventory

SPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to allow the calculation of alkaline hydrolysis rate constants of phosphate esters in water. The rate is calculated from the energy difference between the initial and transition state...

MICROBIAL TRANSFORMATION RATE CONSTANTS OF STRUCTURALLY DIVERSE MAN-MADE CHEMICALS

EPA Science Inventory

To assist in estimating microbially mediated transformation rates of man-made chemicals from their chemical structures, all second order rate constants that have been measured under conditions that make the values comparable have been extracted from the literature and combined wi...

Experimental and Estimated Rate Constants for the Reactions of Hydroxyl Radicals with Several Halocarbons

NASA Technical Reports Server (NTRS)

DeMore, W.B.

1996-01-01

Relative rate experiments are used to measure rate constants and temperature dependencies of the reactions of OH with CH3F (41), CH2FCl (31), CH2BrCl (30B1), CH2Br2 (3OB2), CHBr3 (2OB3), CF2BrCHFCl (123aBl(alpha)), and CF2ClCHCl2 (122). Rate constants for additional compounds of these types are estimated using an empirical rate constant estimation method which is based on measured rate constants for a wide range of halocarbons. The experimental data are combined with the estimated and previously reported rate constants to illustrate the effects of F, Cl, and Br substitution on OH rate constants for a series of 19 halomethanes and 25 haloethanes. Application of the estimation technique is further illustrated for some higher hydrofluorocarbons (HFCs), including CHF2CF2CF2CF2H (338pcc), CF3CHFCHFCF2CF3 (43-10mee), CF3CH2CH2CF3 (356ffa), CF3CH2CF2CH2CF3 (458mfcf), CF3CH2CHF2 (245fa), and CF3CH2CF2CH3 (365mfc). The predictions are compared with literature data for these compounds.

Higher success rate with transcranial electrical stimulation of motor-evoked potentials using constant-voltage stimulation compared with constant-current stimulation in patients undergoing spinal surgery.

PubMed

Shigematsu, Hideki; Kawaguchi, Masahiko; Hayashi, Hironobu; Takatani, Tsunenori; Iwata, Eiichiro; Tanaka, Masato; Okuda, Akinori; Morimoto, Yasuhiko; Masuda, Keisuke; Tanaka, Yuu; Tanaka, Yasuhito

2017-10-01

During spine surgery, the spinal cord is electrophysiologically monitored via transcranial electrical stimulation of motor-evoked potentials (TES-MEPs) to prevent injury. Transcranial electrical stimulation of motor-evoked potential involves the use of either constant-current or constant-voltage stimulation; however, there are few comparative data available regarding their ability to adequately elicit compound motor action potentials. We hypothesized that the success rates of TES-MEP recordings would be similar between constant-current and constant-voltage stimulations in patients undergoing spine surgery. The objective of this study was to compare the success rates of TES-MEP recordings between constant-current and constant-voltage stimulation. This is a prospective, within-subject study. Data from 100 patients undergoing spinal surgery at the cervical, thoracic, or lumbar level were analyzed. The success rates of the TES-MEP recordings from each muscle were examined. Transcranial electrical stimulation with constant-current and constant-voltage stimulations at the C3 and C4 electrode positions (international "10-20" system) was applied to each patient. Compound muscle action potentials were bilaterally recorded from the abductor pollicis brevis (APB), deltoid (Del), abductor hallucis (AH), tibialis anterior (TA), gastrocnemius (GC), and quadriceps (Quad) muscles. The success rates of the TES-MEP recordings from the right Del, right APB, bilateral Quad, right TA, right GC, and bilateral AH muscles were significantly higher using constant-voltage stimulation than those using constant-current stimulation. The overall success rates with constant-voltage and constant-current stimulations were 86.3% and 68.8%, respectively (risk ratio 1.25 [95% confidence interval: 1.20-1.31]). The success rates of TES-MEP recordings were higher using constant-voltage stimulation compared with constant-current stimulation in patients undergoing spinal surgery. Copyright © 2017

Modelling the arsenic (V) and (III) adsorption

NASA Astrophysics Data System (ADS)

Rau, I.; Meghea, A.; Peleanu, I.; Gonzalo, A.; Valiente, M.; Zaharescu, M.

2003-01-01

Arsenic has gained great notoriety historically for its toxic properties. In aquatic environment, arsenic can exist in several oxidation states, as both inorganic and organometallic species. As (V) is less toxic than As (III). Most research has been directed to the control of arsenic pollution of potable water. Various techniques such as precipitation with iron and aluminium hydroxides, ion exchange, reverse osmosis, and adsorption are used for As (V) removal from surface and waste waters. Because of the easy handling of sludge, its free operation and regeneration capability, the adsorption technique has secured a place as one of the advanced methods of arsenic removal. A study of As (III) and As (V) sorption onto some different adsorbents (Fe (III) — iminodiacetate resin, nanocomposite materials, Fe(III) — forager sponge) referring to kinetic considerations and modelling of the process will be presented. All the systems studied are better described by Freundlich-Langmuir isotherm and the rate constant evaluation shows a sub-unitary order for the adsorption process.

Adsorption of β-galactosidase on silica and aluminosilicate adsorbents

NASA Astrophysics Data System (ADS)

Atyaksheva, L. F.; Dobryakova, I. V.; Pilipenko, O. S.

2015-03-01

It is shown that adsorption of β-galactosidase of Aspergillus oryzae fungi on mesoporous and biporous silica and aluminosilicate adsorbents and the rate of the process grow along with the diameter of the pores of the adsorbent. It is found that the shape of the adsorption isotherms changes as well, depending on the texture of the adsorbent: the Michaelis constant rises from 0.3 mM for the enzyme in solution to 0.4-0.5 mM for the enzyme on a surface in the hydrolysis of o-nitrophenyl-β-D-galactopyranoside. It is concluded that β-galactosidase displays its maximum activity on the surface of biporous adsorbents.

Metal adsorption onto bacterial surfaces: development of a predictive approach

NASA Astrophysics Data System (ADS)

Fein, Jeremy B.; Martin, Aaron M.; Wightman, Peter G.

2001-12-01

Aqueous metal cation adsorption onto bacterial surfaces can be successfully modeled by means of a surface complexation approach. However, relatively few stability constants for metal-bacterial surface complexes have been measured. In order to determine the bacterial adsorption behavior of cations that have not been studied in the laboratory, predictive techniques are required that enable estimation of the stability constants of bacterial surface complexes. In this study, we use a linear free-energy approach to compare previously measured stability constants for Bacillus subtilis metal-carboxyl surface complexes with aqueous metal-organic acid anion stability constants. The organic acids that we consider are acetic, oxalic, citric, and tiron. We add to this limited data set by conducting metal adsorption experiments onto Bacillus subtilis, determining bacterial surface stability constants for Co, Nd, Ni, Sr, and Zn. The adsorption behavior of each of the metals studied here was described well by considering metal-carboxyl bacterial surface complexation only, except for the Zn adsorption behavior, which required carboxyl and phosphoryl complexation to obtain a suitable fit to the data. The best correlation between bacterial carboxyl surface complexes and aqueous organic acid anion stability constants was obtained by means of metal-acetate aqueous complexes, with a linear correlation coefficient of 0.97. This correlation applies only to unhydrolyzed aqueous cations and only to carboxyl binding of those cations, and it does not predict the binding behavior under conditions where metal binding to other bacterial surface site types occurs. However, the relationship derived in this study permits estimation of the carboxyl site adsorption behavior of a wide range of aqueous metal cations for which there is an absence of experimental data. This technique, coupled with the observation of similar adsorption behaviors across bacterial species (Yee and Fein, 2001), enables

Calculation of the acid-base equilibrium constants at the alumina/electrolyte interface from the ph dependence of the adsorption of singly charged ions (Na+, Cl-)

NASA Astrophysics Data System (ADS)

Gololobova, E. G.; Gorichev, I. G.; Lainer, Yu. A.; Skvortsova, I. V.

2011-05-01

A procedure was proposed for the calculation of the acid-base equilibrium constants at an alumina/electrolyte interface from experimental data on the adsorption of singly charged ions (Na+, Cl-) at various pH values. The calculated constants (p K {1/0}= 4.1, p K {2/0}= 11.9, p K {3/0}= 8.3, and p K {4/0}= 7.7) are shown to agree with the values obtained from an experimental pH dependence of the electrokinetic potential and the results of potentiometric titration of Al2O3 suspensions.

Steady-State Computation of Constant Rotational Rate Dynamic Stability Derivatives

NASA Technical Reports Server (NTRS)

Park, Michael A.; Green, Lawrence L.

2000-01-01

Dynamic stability derivatives are essential to predicting the open and closed loop performance, stability, and controllability of aircraft. Computational determination of constant-rate dynamic stability derivatives (derivatives of aircraft forces and moments with respect to constant rotational rates) is currently performed indirectly with finite differencing of multiple time-accurate computational fluid dynamics solutions. Typical time-accurate solutions require excessive amounts of computational time to complete. Formulating Navier-Stokes (N-S) equations in a rotating noninertial reference frame and applying an automatic differentiation tool to the modified code has the potential for directly computing these derivatives with a single, much faster steady-state calculation. The ability to rapidly determine static and dynamic stability derivatives by computational methods can benefit multidisciplinary design methodologies and reduce dependency on wind tunnel measurements. The CFL3D thin-layer N-S computational fluid dynamics code was modified for this study to allow calculations on complex three-dimensional configurations with constant rotation rate components in all three axes. These CFL3D modifications also have direct application to rotorcraft and turbomachinery analyses. The modified CFL3D steady-state calculation is a new capability that showed excellent agreement with results calculated by a similar formulation. The application of automatic differentiation to CFL3D allows the static stability and body-axis rate derivatives to be calculated quickly and exactly.

A new approach using coagulation rate constant for evaluation of turbidity removal

NASA Astrophysics Data System (ADS)

Al-Sameraiy, Mukheled

2017-06-01

Coagulation-flocculation-sedimentation processes for treating three levels of bentonite synthetic turbid water using date seeds (DS) and alum (A) coagulants were investigated in the previous research work. In the current research, the same experimental results were used to adopt a new approach on a basis of using coagulation rate constant as an investigating parameter to identify optimum doses of these coagulants. Moreover, the performance of these coagulants to meet (WHO) turbidity standard was assessed by introducing a new evaluating criterion in terms of critical coagulation rate constant (kc). Coagulation rate constants (k2) were mathematically calculated in second order form of coagulation process for each coagulant. The maximum (k2) values corresponded to doses, which were obviously to be considered as optimum doses. The proposed criterion to assess the performance of coagulation process of these coagulants was based on the mathematical representation of (WHO) turbidity guidelines in second order form of coagulation process stated that (k2) for each coagulant should be ≥ (kc) for each level of synthetic turbid water. For all tested turbid water, DS coagulant could not satisfy it. While, A coagulant could satisfy it. The results obtained in the present research are exactly in agreement with the previous published results in terms of finding optimum doses for each coagulant and assessing their performances. On the whole, it is recommended considering coagulation rate constant to be a new approach as an indicator for investigating optimum doses and critical coagulation rate constant to be a new evaluating criterion to assess coagulants' performance.

CO2/H2O adsorption equilibrium and rates on metal-organic frameworks: HKUST-1 and Ni/DOBDC.

PubMed

Liu, Jian; Wang, Yu; Benin, Annabelle I; Jakubczak, Paulina; Willis, Richard R; LeVan, M Douglas

2010-09-07

Metal-organic frameworks (MOFs) have recently attracted intense research interest because of their permanent porous structures, huge surface areas, and potential applications as novel adsorbents and catalysts. In order to provide a basis for consideration of MOFs for removal of carbon dioxide from gases containing water vapor, such as flue gas, we have studied adsorption equilibrium of CO(2), H(2)O vapor, and their mixtures and also rates of CO(2) adsorption in two MOFs: HKUST-1 (CuBTC) and Ni/DOBDC (CPO-27-Ni or Ni/MOF-74). The MOFs were synthesized via solvothermal methods, and the as-synthesized products were solvent exchanged and regenerated before experiments. Pure component adsorption equilibria and CO(2)/H(2)O binary adsorption equilibria were studied using a volumetric system. The effects of H(2)O adsorption on CO(2) adsorption for both MOF samples were determined, and the results for 5A and NaX zeolites were included for comparison. The hydrothermal stabilities for the two MOFs over the course of repetitive measurements of H(2)O and CO(2)/H(2)O mixture equilibria were also studied. CO(2) adsorption rates from helium for the MOF samples were investigated by using a unique concentration-swing frequency response (CSFR) system. Mass transfer into the MOFs is rapid with the controlling resistance found to be macropore diffusion, and rate parameters were established for the mechanism.

Adsorption of Safranin-T from wastewater using waste materials- activated carbon and activated rice husks.

PubMed

Gupta, Vinod K; Mittal, Alok; Jain, Rajeev; Mathur, Megha; Sikarwar, Shalini

2006-11-01

Textile effluents are major industrial polluters because of high color content, about 15% unfixed dyes and salts. The present paper is aimed to investigate and develop cheap adsorption methods for color removal from wastewater using waste materials activated carbon and activated rice husk-as adsorbents. The method was employed for the removal of Safranin-T and the influence of various factors such as adsorbent dose, adsorbate concentration, particle size, temperature, contact time, and pH was studied. The adsorption of the dye over both the adsorbents was found to follow Langmuir and Freundlich adsorption isotherm models. Based on these models, different useful thermodynamic parameters have been evaluated for both the adsorption processes. The adsorption of Safranin-T over activated carbon and activated rice husks follows first-order kinetics and the rate constants for the adsorption processes decrease with increase in temperature.

Accelerating Gas Adsorption on 3D Percolating Carbon Nanotubes.

PubMed

Li, Hui; Wen, Chenyu; Zhang, Youwei; Wu, Dongping; Zhang, Shi-Li; Qiu, Zhi-Jun

2016-02-18

In the field of electronic gas sensing, low-dimensional semiconductors such as single-walled carbon nanotubes (SWCNTs) can offer high detection sensitivity owing to their unprecedentedly large surface-to-volume ratio. The sensitivity and responsivity can further improve by increasing their areal density. Here, an accelerated gas adsorption is demonstrated by exploiting volumetric effects via dispersion of SWCNTs into a percolating three-dimensional (3D) network in a semiconducting polymer. The resultant semiconducting composite film is evaluated as a sensing membrane in field effect transistor (FET) sensors. In order to attain reproducible characteristics of the FET sensors, a pulsed-gate-bias measurement technique is adopted to eliminate current hysteresis and drift of sensing baseline. The rate of gas adsorption follows the Langmuir-type isotherm as a function of gas concentration and scales with film thickness. This rate is up to 5 times higher in the composite than only with an SWCNT network in the transistor channel, which in turn results in a 7-fold shorter time constant of adsorption with the composite. The description of gas adsorption developed in the present work is generic for all semiconductors and the demonstrated composite with 3D percolating SWCNTs dispersed in functional polymer represents a promising new type of material for advanced gas sensors.

Kinetics of Molybdenum Adsorption and Desorption in Soils.

PubMed

Sun, Wenguang; Selim, H Magdi

2018-05-01

Much uncertainty exists in mechanisms and kinetics controlling the adsorption and desorption of molybdenum (Mo) in the soil environment. To investigate the characteristics of Mo adsorption and desorption and predict Mo behavior in the vadose zone, kinetic batch experiments were performed using three soils: Webster loam, Windsor sand and Mahan sand. Adsorption isotherms for Mo were strongly nonlinear for all three soils. Strong kinetic adsorption of Mo by all soils was also observed, where the rate of retention was rapid initially and was followed by slow retention behavior with time. The time-dependent Mo sorption rate was not influenced when constant pH was maintained. Desorption or release results indicated that there were significant fractions of Mo that appeared to be irreversible or slowly reversibly sorbed by Windsor and Mahan. X-ray absorption near edge structure (XANES) analysis for Windsor and Mahan soils indicated that most of Mo had been bound to kaolinite, whereas Webster had similar XANES features to those of Mo sorbed to montmorillonite. A sequential extraction procedure provided evidence that a significant amount of Mo was irreversibly sorbed. A multireaction model (MRM) with nonlinear equilibrium and kinetic sorption parameters was used to describe the adsorption-desorption kinetics of Mo on soils. Our results demonstrated that a formulation of MRM with two sorption sites (equilibrium and reversible) successfully described Mo adsorption-desorption data for Webster loam, and an additional irreversible reaction phase was recommended to describe Mo desorption or release with time for Windsor and Mahan soils. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Semiclassical Calculation of Reaction Rate Constants for Homolytical Dissociations

NASA Technical Reports Server (NTRS)

Cardelino, Beatriz H.

2002-01-01

There is growing interest in extending organometallic chemical vapor deposition (OMCVD) to III-V materials that exhibit large thermal decomposition at their optimum growth temperature, such as indium nitride. The group III nitrides are candidate materials for light-emitting diodes and semiconductor lasers operating into the blue and ultraviolet regions. To overcome decomposition of the deposited compound, the reaction must be conducted at high pressures, which causes problems of uniformity. Microgravity may provide the venue for maintaining conditions of laminar flow under high pressure. Since the selection of optimized parameters becomes crucial when performing experiments in microgravity, efforts are presently geared to the development of computational OMCVD models that will couple the reactor fluid dynamics with its chemical kinetics. In the present study, we developed a method to calculate reaction rate constants for the homolytic dissociation of III-V compounds for modeling OMCVD. The method is validated by comparing calculations with experimental reaction rate constants.

Kinetic and thermodynamic studies on the adsorption of anionic surfactant on quaternary ammonium cationic cellulose.

PubMed

Zhang, Yuanzhang; Shi, Wenjian; Zhou, Hualan; Fu, Xing; Chen, Xuan

2010-06-01

Removal of anionic surfactants from aqueous solutions by adsorption onto quaternary ammonium cationic cellulose (QACC) was investigated. The effects of solution acidity, initial concentration, adsorption time, and temperature on the adsorption of sodium dodecyl-benzene sulfonate (SDBS), sodium lauryl sulfate (SLS), and sodium dodecyl sulfonate (SDS) were studied. The kinetic experimental data fit well with the pseudo-second-order model; the rate constant of the adsorption increased with temperature. The values of apparent activation energy for the adsorption were calculated as ranging from 10.2 to 17.4 kJ/ mol. The adsorption isotherm can be described by the Langmuir isotherm. The values of thermodynamic parameters (deltaH0, deltaS0, and deltaG0) for the adsorption indicated that this process was spontaneous and endothermic. At 318 K, the saturated adsorption capacities of QACC for SDBS, SLS, and SDS were 1.75, 1.53, and 1.39 mmol/g, respectively. The adsorption process was mainly chemisorption and partially physisorption. The results show that QACC is effective for the removal of anionic surfactants.

Effective rate constants for nanostructured heterogeneous catalysts

NASA Astrophysics Data System (ADS)

Hendy, Shaun; Gaston, Nicola; Zhang, Philip; Lund, Nat

2012-02-01

There is currently a high level of interest in the use of nanostructured materials for catalysis. For instance, gold, which is largely inert in the bulk, can exhibit strong catalytic activity when in nanoparticle form. With precious metal catalysts such as Pt and Pd in high demand, the use of these materials in nanoparticle form can also substantially reduce costs by exposure of more surface area for the same volume of material. When reactants are plentiful, the effective activity of a nanoparticulate catalyst will increase roughly with its surface area. However, under diffusion-limited conditions, the reactant must diffuse to active sites on the catalyst, so a high surface area and a high density of active sites may bring diminishing returns if reactant is consumed faster than it arrives. Here we apply a mathematical homogenisation approach to derive simple expressions for the effective reactivity of a nanostructured catalyst under diffusion limited conditions that relate the intrinsic rate constants of the surfaces presented by the catalyst to an effective rate constant. When highly active catalytic sites, such as step edges or other defects are present, we show that distinct limiting cases emerge depending on the degree of overlap of the reactant depletion zone about each site. In gases, the size of this depletion zone is approximately the mean free path, so the effective reactivity will depend on the structure of the catalyst on that scale. We discuss implications for the optimal design of nanoparticle catalysts.

Kinetic rate constant prediction supports the conformational selection mechanism of protein binding.

PubMed

Moal, Iain H; Bates, Paul A

2012-01-01

The prediction of protein-protein kinetic rate constants provides a fundamental test of our understanding of molecular recognition, and will play an important role in the modeling of complex biological systems. In this paper, a feature selection and regression algorithm is applied to mine a large set of molecular descriptors and construct simple models for association and dissociation rate constants using empirical data. Using separate test data for validation, the predicted rate constants can be combined to calculate binding affinity with accuracy matching that of state of the art empirical free energy functions. The models show that the rate of association is linearly related to the proportion of unbound proteins in the bound conformational ensemble relative to the unbound conformational ensemble, indicating that the binding partners must adopt a geometry near to that of the bound prior to binding. Mirroring the conformational selection and population shift mechanism of protein binding, the models provide a strong separate line of evidence for the preponderance of this mechanism in protein-protein binding, complementing structural and theoretical studies.

Carbon dioxide adsorption in Brazilian coals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jose Luciano Soares; Andre L.B. Oberziner; Humberto J. Jose

Carbon dioxide (CO{sub 2}) is one of the most important greenhouse gases. In the period between 1980 and 1998, CO{sub 2} emissions increased more than 21% and projections suggest that the emissions will continue to increase globally by 2.2% between 2000 and 2020 and 3.3% in the developed countries. The sequestration of CO{sub 2} in deep unminable coal beds is one of the more promising of several methods of geological sequestration that are currently being investigated. CO{sub 2} can adsorb onto coal, and there are several studies demonstrating that CO{sub 2} dissolves in coals and swells them. At very lowmore » pressures (P {lt} 1 bar), CO{sub 2} dissolution does not seem to be a problem; however, high pressures are necessary for CO{sub 2} sequestration (P {gt} 50 bar). In this study, we evaluated the kinetics and equilibrium of sorption of CO{sub 2} on Brazilian coals at low pressures. The adsorption equilibrium isotherm at room temperature (30{sup o}C) was measured through the static method. The results showed that the Freundlich model or the Langmuir model is suitable to describe the equilibrium experimental results. The CO{sub 2} adsorption capacity of Brazilian coals are in the range of 0.089-0.186 mmol CO{sub 2}/g, which are typical values for coals with high ash content. The dynamics of adsorption in a fixed-bed column that contains granular coal (particle sizes of 0.8, 2.4, and 4.8 mm) showed that the adsorption rate is fast and a mathematical model was developed to describe the CO{sub 2} dynamics of the adsorption in a fixed-bed column. The linear driving force (LDF) was used to describe the rate of adsorption and the mass-transfer constants of the LDF model (K{sub s}) are in the range of 1.0-2.0 min{sup -1}. 29 refs., 5 figs., 3 tabs.« less

HO + CO reaction rates and H/D kinetic isotope effects: master equation models with ab initio SCTST rate constants.

PubMed

Weston, Ralph E; Nguyen, Thanh Lam; Stanton, John F; Barker, John R

2013-02-07

Ab initio microcanonical rate constants were computed using Semi-Classical Transition State Theory (SCTST) and used in two master equation formulations (1D, depending on active energy with centrifugal corrections, and 2D, depending on total energy and angular momentum) to compute temperature-dependent rate constants for the title reactions using a potential energy surface obtained by sophisticated ab initio calculations. The 2D master equation was used at the P = 0 and P = ∞ limits, while the 1D master equation with centrifugal corrections and an empirical energy transfer parameter could be used over the entire pressure range. Rate constants were computed for 75 K ≤ T ≤ 2500 K and 0 ≤ [He] ≤ 10(23) cm(-3). For all temperatures and pressures important for combustion and for the terrestrial atmosphere, the agreement with the experimental rate constants is very good, but at very high pressures and T ≤ 200 K, the theoretical rate constants are significantly smaller than the experimental values. This effect is possibly due to the presence in the experiments of dimers and prereactive complexes, which were not included in the model calculations. The computed H/D kinetic isotope effects are in acceptable agreement with experimental data, which show considerable scatter. Overall, the agreement between experimental and theoretical H/D kinetic isotope effects is much better than in previous work, and an assumption of non-RRKM behavior does not appear to be needed to reproduce experimental observations.

Phototransformation rate constants of PAHs associated with soot particles.

PubMed

Kim, Daekyun; Young, Thomas M; Anastasio, Cort

2013-01-15

Photodegradation is a key process governing the residence time and fate of polycyclic aromatic hydrocarbons (PAHs) in particles, both in the atmosphere and after deposition. We have measured photodegradation rate constants of PAHs in bulk deposits of soot particles illuminated with simulated sunlight. The photodegradation rate constants at the surface (k(p)(0)), the effective diffusion coefficients (D(eff)), and the light penetration depths (z(0.5)) for PAHs on soot layers of variable thickness were determined by fitting experimental data with a model of coupled photolysis and diffusion. The overall disappearance rates of irradiated low molecular weight PAHs (with 2-3 rings) on soot particles were influenced by fast photodegradation and fast diffusion kinetics, while those of high molecular weight PAHs (with 4 or more rings) were apparently controlled by either the combination of slow photodegradation and slow diffusion kinetics or by very slow diffusion kinetics alone. The value of z(0.5) is more sensitive to the soot layer thickness than the k(p)(0) value. As the thickness of the soot layer increases, the z(0.5) values increase, but the k(p)(0) values are almost constant. The effective diffusion coefficients calculated from dark experiments are generally higher than those from the model fitting method for illumination experiments. Due to the correlation between k(p)(0) and z(0.5) in thinner layers, D(eff) should be estimated by an independent method for better accuracy. Despite some limitations of the model used in this study, the fitted parameters were useful for describing empirical results of photodegradation of soot-associated PAHs. Copyright © 2012 Elsevier B.V. All rights reserved.

Phototransformation Rate Constants of PAHs Associated with Soot Particles

PubMed Central

Kim, Daekyun; Young, Thomas M.; Anastasio, Cort

2013-01-01

Photodegradation is a key process governing the residence time and fate of polycyclic aromatic hydrocarbons (PAHs) in particles, both in the atmosphere and after deposition. We have measured photodegradation rate constants of PAHs in bulk deposits of soot particles illuminated with simulated sunlight. The photodegradation rate constants at the surface (k0p), the effective diffusion coefficients (Deff), and the light penetration depths (z0.5) for PAHs on soot layers of variable thickness were determined by fitting experimental data with a model of coupled photolysis and diffusion. The overall disappearance rates of irradiated low molecular weight PAHs (with 2-3 rings) on soot particles were influenced by fast photodegradation and fast diffusion kinetics, while those of high molecular weight PAHs (with 4 or more rings) were apparently controlled by either the combination of slow photodegradation and slow diffusion kinetics or by very slow diffusion kinetics alone. The value of z0.5 is more sensitive to the soot layer thickness than the k0p value. As the thickness of the soot layer increases, the z0.5 values increase, but the k0p values are almost constant. The effective diffusion coefficients calculated from dark experiments are generally higher than those from the model fitting method for illumination experiments. Due to the correlation between k0p and z0.5 in thinner layers, Deff should be estimated by an independent method for better accuracy. Despite some limitations of the model used in this study, the fitted parameters were useful for describing empirical results of photodegradation of soot-associated PAHs. PMID:23247292

Theoretical rate constants of super-exchange hole transfer and thermally induced hopping in DNA.

PubMed

Shimazaki, Tomomi; Asai, Yoshihiro; Yamashita, Koichi

2005-01-27

Recently, the electronic properties of DNA have been extensively studied, because its conductivity is important not only to the study of fundamental biological problems, but also in the development of molecular-sized electronics and biosensors. We have studied theoretically the reorganization energies, the activation energies, the electronic coupling matrix elements, and the rate constants of hole transfer in B-form double-helix DNA in water. To accommodate the effects of DNA nuclear motions, a subset of reaction coordinates for hole transfer was extracted from classical molecular dynamics (MD) trajectories of DNA in water and then used for ab initio quantum chemical calculations of electron coupling constants based on the generalized Mulliken-Hush model. A molecular mechanics (MM) method was used to determine the nuclear Franck-Condon factor. The rate constants for two types of mechanisms of hole transfer-the thermally induced hopping (TIH) and the super-exchange mechanisms-were determined based on Marcus theory. We found that the calculated matrix elements are strongly dependent on the conformations of the nucleobase pairs of hole-transferable DNA and extend over a wide range of values for the "rise" base-step parameter but cluster around a particular value for the "twist" parameter. The calculated activation energies are in good agreement with experimental results. Whereas the rate constant for the TIH mechanism is not dependent on the number of A-T nucleobase pairs that act as a bridge, the rate constant for the super-exchange process rapidly decreases when the length of the bridge increases. These characteristic trends in the calculated rate constants effectively reproduce those in the experimental data of Giese et al. [Nature 2001, 412, 318]. The calculated rate constants were also compared with the experimental results of Lewis et al. [Nature 2000, 406, 51].

Impact of uncertainties in inorganic chemical rate constants on tropospheric composition and ozone radiative forcing

NASA Astrophysics Data System (ADS)

Newsome, Ben; Evans, Mat

2017-12-01

Chemical rate constants determine the composition of the atmosphere and how this composition has changed over time. They are central to our understanding of climate change and air quality degradation. Atmospheric chemistry models, whether online or offline, box, regional or global, use these rate constants. Expert panels evaluate laboratory measurements, making recommendations for the rate constants that should be used. This results in very similar or identical rate constants being used by all models. The inherent uncertainties in these recommendations are, in general, therefore ignored. We explore the impact of these uncertainties on the composition of the troposphere using the GEOS-Chem chemistry transport model. Based on the Jet Propulsion Laboratory (JPL) and International Union of Pure and Applied Chemistry (IUPAC) evaluations we assess the influence of 50 mainly inorganic rate constants and 10 photolysis rates on tropospheric composition through the use of the GEOS-Chem chemistry transport model. We assess the impact on four standard metrics: annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime. Uncertainty in the rate constants for NO2 + OH →M HNO3 and O3 + NO → NO2 + O2 are the two largest sources of uncertainty in these metrics. The absolute magnitude of the change in the metrics is similar if rate constants are increased or decreased by their σ values. We investigate two methods of assessing these uncertainties, addition in quadrature and a Monte Carlo approach, and conclude they give similar outcomes. Combining the uncertainties across the 60 reactions gives overall uncertainties on the annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime of 10, 11, 16 and 16 %, respectively. These are larger than the spread between models

Adsorption interactions of humic acids with biocides

NASA Astrophysics Data System (ADS)

Mal'Tseva, E. V.; Ivanov, A. A.; Yudina, N. V.

2009-11-01

The chemical composition of humic acids from brown coal (Aldrich) was determined by element analysis, 13C NMR spectroscopy, and potentiometric titration. The adsorption ability of humic acids with different biocides (cyproconasol, propiconasol, tebuconasol, irgarol 1051, and DCOIT) was studied. The adsorption ability of a mixture of biocides in aqueous solutions was higher than that of the individual components. The limiting concentration of humic acids at which adsorption of biocides was maximum was determined. Adsorption constants were calculated by the Freundlich equation for each biocide in aqueous solution.

Modeling experimental stable isotope results from CO2 adsorption and diffusion experiments

NASA Astrophysics Data System (ADS)

Larson, T. E.

2012-12-01

Transport of carbon dioxide through porous media can be affected by diffusion, advection and adsorption processes. Developing new tools to understand which of these processes dominates migration of CO2 or other gases in the subsurface is important to a wide range of applications including CO2 storage. Whereas advection rates are not affected by isotope substitution in CO2, adsorption and diffusion constants are. For example, differences in the binary diffusion constant calculated between C12O2-He and C13O2-He results in a carbon isotope fractionation whereby the front of the chromatographic peak is enriched in carbon-12 and the tail of the peak is enriched in carbon-13. Interestingly, adsorption is shown to have an opposite, apparent inverse affect whereby the lighter isotopologues of CO2 are preferentially retained by the chromatographic column and the heavier isotopologues are eluted first. This apparent inverse chromatographic effect has been ascribed to Van der Waals dispersion forces. Smaller molar volumes of the heavier isotopologues resulting from increased bond strength (shorter bond length) effectively decreases Van der Waals forces in heavier isotopologues compared to lighter isotopologues. Here we discuss the possible application of stable isotope values measured across chromatographic peaks to differentiate diffusion-dominated from adsorption-dominated transport processes for CO2. Separate 1-dimensional flow-through columns were packed with quartz and illite, and one remained empty. Dry helium was used as a carrier gas. Constant flow rate, temperature and column pressure were maintained. After background CO2 concentrations were minimized and constant, a sustained pulse of CO2 was injected at the head of the column and the effluent was sampled at 4 minute intervals for CO2 concentration, and carbon and oxygen isotope ratios. The quartz-sand packed and empty columns resulted in similar trends in concentration and isotope ratios whereby CO2 concentrations

Impact of transverse and longitudinal dispersion on first-order degradation rate constant estimation

NASA Astrophysics Data System (ADS)

Stenback, Greg A.; Ong, Say Kee; Rogers, Shane W.; Kjartanson, Bruce H.

2004-09-01

A two-dimensional analytical model is employed for estimating the first-order degradation rate constant of hydrophobic organic compounds (HOCs) in contaminated groundwater under steady-state conditions. The model may utilize all aqueous concentration data collected downgradient of a source area, but does not require that any data be collected along the plume centerline. Using a least squares fit of the model to aqueous concentrations measured in monitoring wells, degradation rate constants were estimated at a former manufactured gas plant (FMGP) site in the Midwest U.S. The estimated degradation rate constants are 0.0014, 0.0034, 0.0031, 0.0019, and 0.0053 day -1 for acenaphthene, naphthalene, benzene, ethylbenzene, and toluene, respectively. These estimated rate constants were as low as one-half those estimated with the one-dimensional (centerline) approach of Buscheck and Alcantar [Buscheck, T.E., Alcantar, C.M., 1995. Regression techniques and analytical solutions to demonstrate intrinsic bioremediation. In: Hinchee, R.E., Wilson, J.T., Downey, D.C. (Eds.), Intrinsic Bioremediation, Battelle Press, Columbus, OH, pp. 109-116] which does not account for transverse dispersivity. Varying the transverse and longitudinal dispersivity values over one order of magnitude for toluene data obtained from the FMGP site resulted in nearly a threefold variation in the estimated degradation rate constant—highlighting the importance of reliable estimates of the dispersion coefficients for obtaining reasonable estimates of the degradation rate constants. These results have significant implications for decision making and site management where overestimation of a degradation rate may result in remediation times and bioconversion factors that exceed expectations. For a complex source area or non-steady-state plume, a superposition of analytical models that incorporate longitudinal and transverse dispersion and time may be used at sites where the centerline method would not be

Charring rate of wood exposed to a constant heat flux

Treesearch

R. H. White; H. C. Tran

1996-01-01

A critical factor in the fire endurance of a wood member is its rate of charring. Most available charring rate data have been obtained using the time-temperature curves of the standard fire resistance tests (ASTM E 119 and ISO 834) to define the fire exposure. The increased use of heat release calorimeters using exposures of constant heat flux levels has broadened the...

Study on improving the turbidity measurement of the absolute coagulation rate constant.

PubMed

Sun, Zhiwei; Liu, Jie; Xu, Shenghua

2006-05-23

The existing theories dealing with the evaluation of the absolute coagulation rate constant by turbidity measurement were experimentally tested for different particle-sized (radius = a) suspensions at incident wavelengths (lambda) ranging from near-infrared to ultraviolet light. When the size parameter alpha = 2pi a/lambda > 3, the rate constant data from previous theories for fixed-sized particles show significant inconsistencies at different light wavelengths. We attribute this problem to the imperfection of these theories in describing the light scattering from doublets through their evaluation of the extinction cross section. The evaluations of the rate constants by all previous theories become untenable as the size parameter increases and therefore hampers the applicable range of the turbidity measurement. By using the T-matrix method, we present a robust solution for evaluating the extinction cross section of doublets formed in the aggregation. Our experiments show that this new approach is effective in extending the applicability range of the turbidity methodology and increasing measurement accuracy.

Relationship of compressive stress-strain response of engineering materials obtained at constant engineering and true strain rates

DOE PAGES

Song, Bo; Sanborn, Brett

2018-05-07

In this paper, a Johnson–Cook model was used as an example to analyze the relationship of compressive stress-strain response of engineering materials experimentally obtained at constant engineering and true strain rates. There was a minimal deviation between the stress-strain curves obtained at the same constant engineering and true strain rates. The stress-strain curves obtained at either constant engineering or true strain rates could be converted from one to the other, which both represented the intrinsic material response. There is no need to specify the testing requirement of constant engineering or true strain rates for material property characterization, provided that eithermore » constant engineering or constant true strain rate is attained during the experiment.« less

Relationship of compressive stress-strain response of engineering materials obtained at constant engineering and true strain rates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Bo; Sanborn, Brett

In this paper, a Johnson–Cook model was used as an example to analyze the relationship of compressive stress-strain response of engineering materials experimentally obtained at constant engineering and true strain rates. There was a minimal deviation between the stress-strain curves obtained at the same constant engineering and true strain rates. The stress-strain curves obtained at either constant engineering or true strain rates could be converted from one to the other, which both represented the intrinsic material response. There is no need to specify the testing requirement of constant engineering or true strain rates for material property characterization, provided that eithermore » constant engineering or constant true strain rate is attained during the experiment.« less

Adsorption of tobacco-specific nitrosamine 4-(methylnitrosamino) -1- (3-pyridyl)-1-butanone from aqueous solution with graphene aerogel

NASA Astrophysics Data System (ADS)

Xu, T. G.; Shi, R.; Lu, N.; Zhang, J.; Bai, R. S.; Yang, Z. D.; Zhou, J.

2018-03-01

The adsorption behavior of graphene aerogel in the 4-(Methylnitrosamino)-1-(3-pryidyl)-1-butanone (NNK) aqueous solution was studied. The adsorption kinetics fitted pseudo-second-order model with the rate constant (k2) of 0.154 g/mg·h. The adsorption isotherm was investigated and fitted Langmuir and Freundlich models well, and the maximum adsorption capacity (qm) was 59.66 mg/g estimated from Langmuir isotherm. Thermodynamic result indicated that the process of adsorption of NNK onto graphene aerogel was spontaneous and exothermic. Higher pH solution was favorable for NNK adsorption on graphene aerogel. The adsorption for NNK on graphene aerogel arose from the π-π interaction between them, and the high adsorption efficiency was resulted from the -NO2 functional groups. The capability of graphene aerogel was maintained after repeated absorption-desorption cycles, which was benefit for convenient separating and recycling of graphene aerogel.

The characterization of the adsorption of cadmium from aqueous solution using natural fibers treated with nanoparticles

NASA Astrophysics Data System (ADS)

Rediske, Nicole M.

The objective of this research was to characterize natural carbon fibers from coconut husks, both bare and impregnated with metallic nanoparticles, in removing cadmium from aqueous media. The adsorbent load, kinetics, isotherm parameters, removal efficiencies, desorption capacity and possible contaminant removal mechanisms were evaluated. It was found that the fibers treated with metallic nanoparticles performed better than the bare fibers in removing cadmium from water. The ideal conditions were found to be neutral pH with low initial cadmium concentrations. Through the kinetic analyses, the adsorption process was first thought to be pseudo first order with two separate adsorption mechanisms apparent. Upon further analysis, it was seen that the first mechanism does not follow the pseudo first order kinetics model. An increase in calcium and magnesium concentrations was observed as the cadmium concentrations decreases. This increase corresponds with first mechanism. This suggests the cadmium removal in the first mechanism is due to ion exchange. The second mechanism's rate constant was consistently lower than the first mechanisms rate constant by an order of magnitude. This led to the hypothesis that the second mechanism is controlled by van de Waals forces, specifically ion-induced dipole interactions, and physical adsorption. It was also found that the cadmium does not effectively desorb from the wasted fibers in DI water. Keywords: Adsorption; kinetics; pseudo first order; cadmium; metallic nanoparticles; natural fibers; removal efficiencies; ion exchange.

The temperature dependence of the rate constant for the reaction of hydroxyl radicals with nitric acid

NASA Technical Reports Server (NTRS)

Kurylo, M. J.; Cornett, K. D.; Murphy, J. L.

1982-01-01

The rate constant for the reaction of hydroxyl radicals with nitric acid in the 225-443 K temperature range has been measured by means of the flash photolysis resonance fluorescence technique. Above 300 K, the rate constant levels off in a way that can only be explained by the occurrence of two reaction channels, of which one, operative at low temperatures, proceeds through the formation of an adduct intermediate. The implications of these rate constant values for stratospheric reaction constants is discussed.

Quantitative Prediction of Rate Constants for Aqueous Racemization To Avoid Pointless Stereoselective Syntheses

PubMed Central

Ballard, Andrew; Ahmad, Hiwa O.; Narduolo, Stefania; Rosa, Lucy; Chand, Nikki; Cosgrove, David A.; Varkonyi, Peter; Asaad, Nabil; Tomasi, Simone

2017-01-01

Abstract Racemization has a large impact upon the biological properties of molecules but the chemical scope of compounds with known rate constants for racemization in aqueous conditions was hitherto limited. To address this remarkable blind spot, we have measured the kinetics for racemization of 28 compounds using circular dichroism and 1H NMR spectroscopy. We show that rate constants for racemization (measured by ourselves and others) correlate well with deprotonation energies from quantum mechanical (QM) and group contribution calculations. Such calculations thus provide predictions of the second‐order rate constants for general‐base‐catalyzed racemization that are usefully accurate. When applied to recent publications describing the stereoselective synthesis of compounds of purported biological value, the calculations reveal that racemization would be sufficiently fast to render these expensive syntheses pointless. PMID:29072355

A first-passage scheme for determination of overall rate constants for non-diffusion-limited suspensions

NASA Astrophysics Data System (ADS)

Lu, Shih-Yuan; Yen, Yi-Ming

2002-02-01

A first-passage scheme is devised to determine the overall rate constant of suspensions under the non-diffusion-limited condition. The original first-passage scheme developed for diffusion-limited processes is modified to account for the finite incorporation rate at the inclusion surface by using a concept of the nonzero survival probability of the diffusing entity at entity-inclusion encounters. This nonzero survival probability is obtained from solving a relevant boundary value problem. The new first-passage scheme is validated by an excellent agreement between overall rate constant results from the present development and from an accurate boundary collocation calculation for the three common spherical arrays [J. Chem. Phys. 109, 4985 (1998)], namely simple cubic, body-centered cubic, and face-centered cubic arrays, for a wide range of P and f. Here, P is a dimensionless quantity characterizing the relative rate of diffusion versus surface incorporation, and f is the volume fraction of the inclusion. The scheme is further applied to random spherical suspensions and to investigate the effect of inclusion coagulation on overall rate constants. It is found that randomness in inclusion arrangement tends to lower the overall rate constant for f up to the near close-packing value of the regular arrays because of the inclusion screening effect. This screening effect turns stronger for regular arrays when f is near and above the close-packing value of the regular arrays, and consequently the overall rate constant of the random array exceeds that of the regular array. Inclusion coagulation too induces the inclusion screening effect, and leads to lower overall rate constants.

Material design of two-phase-coexisting niobate dielectrics by electrostatic adsorption

NASA Astrophysics Data System (ADS)

Fuchigami, Teruaki; Yoshida, Katsuya; Kakimoto, Ken-ichi

2017-10-01

A material design process using electrostatic adsorption was proposed to synthesize composite ceramics with a two-phase-coexisting structure. Supported particles were fabricated by the electrostatic adsorption of (Na,K)NbO3-SrTiO3 (NKN-ST) nanoparticles on (Na,K)NbO3-Ba2NaNb5O15 (NKN-BNN) particles. NKN-ST and NKN-BNN were well dispersed with no aggregate in NKN-ST/NKN-BNN ceramics synthesized using the supported particles in comparison with ceramics synthesized using a mixture obtained by simply mixing NKN-ST and NKN-BNN powder. The temperature dependence of dielectric constant is closely related to the composite structure and the dielectric constant was stable in a wide temperature range from room temperature to 400 °C. Capacitance for DC bias was also insensitive to temperature in the range of 0-2 kV/mm, and the change rate of the capacitance was within ±5% in the temperature range from room temperature to 200 °C.

Application of the compensated Arrhenius formalism to explain the dielectric constant dependence of rates for Menschutkin reactions.

PubMed

Petrowsky, Matt; Glatzhofer, Daniel T; Frech, Roger

2013-11-21

The dependence of the reaction rate on solvent dielectric constant is examined for the reaction of trihexylamine with 1-bromohexane in a series of 2-ketones over the temperature range 25-80 °C. The rate constant data are analyzed using the compensated Arrhenius formalism (CAF), where the rate constant assumes an Arrhenius-like equation that also contains a dielectric constant dependence in the exponential prefactor. The CAF activation energies are substantially higher than those obtained using the simple Arrhenius equation. A master curve of the data is observed by plotting the prefactors against the solvent dielectric constant. The master curve shows that the reaction rate has a weak dependence on dielectric constant for values approximately less than 10 and increases more rapidly for dielectric constant values greater than 10.

Electron-ion dissociative recombination rate constants relevant to the Titan atmosphere and the Interstellar Medium

NASA Astrophysics Data System (ADS)

Osborne, David; Lawson, Patrick; Adams, Nigel

2014-01-01

Following the arrival of Cassini at Titan in 2004, the Titan atmosphere has been shown to contain large complex polycyclic-aromatic hydrocarbons. Since Cassini has provided a great deal of data, there exists a need for kinetic rate data to help with modeling this atmosphere. One type of kinetic data needed is electron-ion dissociative recombination (e-IDR) rate constants. These data are not readily available for larger compounds, such as naphthalene, or oxygen containing compounds, such as 1,4 dioxane or furan. Here, the rate constants for naphthalene, 1,4 dioxane, and furan have been measured and their temperature dependencies are determined when possible, using the University of Georgia's Variable Temperature Flowing Afterglow. The rate constants are compared with those previously published for other compounds; these show trends which illustrate the effects which multi-rings and oxygen heteroatoms substitutions have upon e-IDR rate constants.

Rate constant for the reaction SO + BrO yields SO2 + Br

NASA Technical Reports Server (NTRS)

Brunning, J.; Stief, L.

1986-01-01

The rate of the radical-radical reaction SO + BrO yields SO2 + Br has been determined at 298 K in a discharge flow system near 1 torr pressure with detection of SO and BrO via collision-free sampling mass spectrometry. The rate constant was determined using two different methods: measuring the decay of SO radicals in the presence of an excess of BrO and measuring the decay of BrO radicals in excess SO. The results from the two methods are in reasonable agreement and the simple mean of the two values gives the recommended rate constant at 298 K, k = (5.7 + or - 2.0) x 10 to the -11th cu cm/s. This represents the first determination of this rate constant and it is consistent with a previously derived lower limit based on SO2 formation. Comparison is made with other radical-radical reactions involving SO or BrO. The reaction SO + BrO yields SO2 + Br is of interest for models of the upper atmosphere of the earth and provides a potential coupling between atmospheric sulfur and bromine chemistry.

Effects of Alloyed Metal on the Catalysis Activity of Pt for Ethanol Partial Oxidation: Adsorption and Dehydrogenation on Pt3M (M=Pt, Ru, Sn, Re, Rh, and Pd)

PubMed Central

Xu, Zhen-Feng; Wang, Yixuan

2011-01-01

The adsorption and dehydrogenation reactions of ethanol over bimetallic clusters, Pt3M (M = Pt, Ru, Sn, Re, Rh, and Pd), have been extensively investigated with density functional theory. Both the α-hydrogen and hydroxyl adsorptions on Pt as well as on the alloyed transition metal M sites of PtM were considered as initial reaction steps. The adsorptions of ethanol on Pt and M sites of some PtM via the α-hydrogen were well established. Although the α-hydrogen adsorption on Pt site is weaker than the hydroxyl, the potential energy profiles show that the dehydrogenation via the α-hydrogen path has much lower energy barrier than that via the hydroxyl path. Generally for the α-hydrogen path the adsorption is a rate-determining-step because of rather low dehydrogenation barrier for the α-hydrogen adsorption complex (thermodynamic control), while the hydroxyl path is determined by its dehydrogenation step (kinetic control). The effects of alloyed metal on the catalysis activity of Pt for ethanol partial oxidation, including adsorption energy, energy barrier, electronic structure, and eventually rate constant were discussed. Among all of the alloyed metals only Sn enhances the rate constant of the dehydrogenation via the α-hydrogen path on the Pt site of Pt3Sn as compared with Pt alone, which interprets why the PtSn is the most active to the oxidation of ethanol. PMID:22102920

QSPR prediction of the hydroxyl radical rate constant of water contaminants.

PubMed

Borhani, Tohid Nejad Ghaffar; Saniedanesh, Mohammadhossein; Bagheri, Mehdi; Lim, Jeng Shiun

2016-07-01

In advanced oxidation processes (AOPs), the aqueous hydroxyl radical (HO) acts as a strong oxidant to react with organic contaminants. The hydroxyl radical rate constant (kHO) is important for evaluating and modelling of the AOPs. In this study, quantitative structure-property relationship (QSPR) method is applied to model the hydroxyl radical rate constant for a diverse dataset of 457 water contaminants from 27 various chemical classes. The constricted binary particle swarm optimization and multiple-linear regression (BPSO-MLR) are used to obtain the best model with eight theoretical descriptors. An optimized feed forward neural network (FFNN) is developed to investigate the complex performance of the selected molecular parameters with kHO. Although the FFNN prediction results are more accurate than those obtained using BPSO-MLR, the application of the latter is much more convenient. Various internal and external validation techniques indicate that the obtained models could predict the logarithmic hydroxyl radical rate constants of a large number of water contaminants with less than 4% absolute relative error. Finally, the above-mentioned proposed models are compared to those reported earlier and the structural factors contributing to the AOP degradation efficiency are discussed. Copyright © 2016 Elsevier Ltd. All rights reserved.

Electron-ion dissociative recombination rate constants relevant to the Titan atmosphere and the Interstellar Medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osborne, David; Lawson, Patrick; Adams, Nigel, E-mail: ngadams@uga.edu

Following the arrival of Cassini at Titan in 2004, the Titan atmosphere has been shown to contain large complex polycyclic-aromatic hydrocarbons. Since Cassini has provided a great deal of data, there exists a need for kinetic rate data to help with modeling this atmosphere. One type of kinetic data needed is electron-ion dissociative recombination (e-IDR) rate constants. These data are not readily available for larger compounds, such as naphthalene, or oxygen containing compounds, such as 1,4 dioxane or furan. Here, the rate constants for naphthalene, 1,4 dioxane, and furan have been measured and their temperature dependencies are determined when possible,more » using the University of Georgia's Variable Temperature Flowing Afterglow. The rate constants are compared with those previously published for other compounds; these show trends which illustrate the effects which multi-rings and oxygen heteroatoms substitutions have upon e-IDR rate constants.« less

Cadmiun and Zinc Adsorption by Acric Soils

NASA Astrophysics Data System (ADS)

da Silva, Luiz Gabriel; Colato, Alexandre; Casagrande, José Carlos; Soares, Marcio Roberto

2017-04-01

Acrodox soils are very weathered soils, characterized by having buildup of iron and aluminum oxides and hydroxides. These soils are present in extensive productive regions in the state of São Paulo. This work aimed at verifying the adequacy of constant capacitance model in describing the adsorption of cadmium and zinc in Anionic Rhodic Acrudox, Anionic Xanthic Acrudox and Rhodic Hapludalf. The chemical, mineralogical and physical attributes of these soils were determined in the layers 0-20 cm and 20-40 cm. Adsorption data of cadmium and zinc were also previously determined for samples of both layers of each soil. Were applied 5 mg dm-3 of cadmium and zinc to 2,0 g of soil to ample pH range (3 to 10) to build the adsorption envelops to three ionic strength. The constant capacitance model was adequate to simulate the adsorption of zinc and cadmium. It was not possible to make appropriate distinctions between measurements and simulations for two soil layers studied, neither between the three concentrations of background electrolyte.

Rate constant for the fraction of atomic chlorine with formaldehyde from 200 to 500K

NASA Technical Reports Server (NTRS)

Michael, J. V.; Nava, D. F.; Payne, W. A.; Stief, L. J.

1978-01-01

A flash photolysis - resonance fluorescence technique was used to measure rate constant. The results were independent of substantial variations in H2CO, total pressure (Ar), and flash intensity (i.e., initial Cl). The rate constant was shown to be invariant with temperature, the best representation for this temperature range being K = (7.48 + or - 0.50) x 10 to the minus 11 power cu cm molecule-1 s-1 where the error is one standard deviation. The rate constant is theoretically discussed and the potential importance of the reaction in stratospheric chemistry is considered.

Surface complexation modeling of proton and Cd adsorption onto an algal cell wall.

PubMed

Kaulbach, Emily S; Szymanowski, Jennifer E S; Fein, Jeremy B

2005-06-01

This study quantifies Cd adsorption onto the cell wall of the algal species Pseudokirchneriella subcapitata by applying a surface complexation approach to model the observed adsorption behavior. We use potentiometric titrations to determine deprotonation constants and site concentrations for the functional groups on the algal cell wall. Adsorption and desorption kinetics experiments illustrate that adsorption of Cd onto the cell wall is rapid and reversible, except under low pH conditions. Adsorption experiments conducted as a function of pH and total Cd concentration yield the stoichiometry and site-specific stability constants for the important Cd-algal surface complexes. We model the acid/base properties of the algal cell wall by invoking four discrete surface functional group types, with pKa values of 3.9 +/- 0.3, 5.4 +/- 0.1, 7.6 +/- 0.3, and 9.6 +/- 0.4. The results of the Cd adsorption experiments indicate that the first, third, and fourth sites contribute to Cd adsorption under the experimental conditions, with calculated log stability constant values of 4.1 +/- 0.5, 5.4 +/- 0.5, and 6.1 +/- 0.4, respectively. Our results suggest that the stabilities of the Cd-surface complexes are high enough for algal adsorption to affect the fate and transport of Cd under some conditions and that on a per gram basis, algae and bacteria exhibit broadly similar extents of Cd adsorption.

Rate constants for proteins binding to substrates with multiple binding sites using a generalized forward flux sampling expression

NASA Astrophysics Data System (ADS)

Vijaykumar, Adithya; ten Wolde, Pieter Rein; Bolhuis, Peter G.

2018-03-01

To predict the response of a biochemical system, knowledge of the intrinsic and effective rate constants of proteins is crucial. The experimentally accessible effective rate constant for association can be decomposed in a diffusion-limited rate at which proteins come into contact and an intrinsic association rate at which the proteins in contact truly bind. Reversely, when dissociating, bound proteins first separate into a contact pair with an intrinsic dissociation rate, before moving away by diffusion. While microscopic expressions exist that enable the calculation of the intrinsic and effective rate constants by conducting a single rare event simulation of the protein dissociation reaction, these expressions are only valid when the substrate has just one binding site. If the substrate has multiple binding sites, a bound enzyme can, besides dissociating into the bulk, also hop to another binding site. Calculating transition rate constants between multiple states with forward flux sampling requires a generalized rate expression. We present this expression here and use it to derive explicit expressions for all intrinsic and effective rate constants involving binding to multiple states, including rebinding. We illustrate our approach by computing the intrinsic and effective association, dissociation, and hopping rate constants for a system in which a patchy particle model enzyme binds to a substrate with two binding sites. We find that these rate constants increase as a function of the rotational diffusion constant of the particles. The hopping rate constant decreases as a function of the distance between the binding sites. Finally, we find that blocking one of the binding sites enhances both association and dissociation rate constants. Our approach and results are important for understanding and modeling association reactions in enzyme-substrate systems and other patchy particle systems and open the way for large multiscale simulations of such systems.

Complexes of DOTA-bisphosphonate conjugates: probes for determination of adsorption capacity and affinity constants of hydroxyapatite.

PubMed

Vitha, Tomas; Kubícek, Vojtech; Hermann, Petr; Kolar, Zvonimir I; Wolterbeek, Hubert Th; Peters, Joop A; Lukes, Ivan

2008-03-04

The adsorption on hydroxyapatite of three conjugates of a bisphosphonate and a macrocycle having C1, C2, and C3 spacers and their terbium complexes was studied by the radiotracer method using 160Tb as the label. The radiotracer-containing complex of the conjugate with the C3 spacer was used as a probe for the determination of the adsorption parameters of other bisphosphonates that lack a DOTA unit. A physicochemical model describing the competitive adsorption was successfully applied in the fitting of the obtained data. The maximum adsorption capacity of bisphosphonates containing bulky substituents is determined mainly by their size. For bisphosphonates having no DOTA moiety, the maximum adsorption capacity is determined by the electrostatic repulsion between negatively charged bisphosphonate groups. Compounds with a hydroxy or amino group attached to the alpha-carbon atom show higher affinities. Macrocyclic compounds containing a short spacer between the different bisphosphonic acid groups and the macrocyclic unit exhibit high affinities, indicating a synergic effect of the bisphosphonic and the macrocyclic groups during adsorption. The competition method described uses a well-characterized complex and allows a simple evaluation of the adsorption behavior of bisphosphonates. The application of the macrocycle-bisphosphonate conjugates allows easy radiolabeling via complexation of a suitable metal isotope.

Prediction of Chain Propagation Rate Constants of Polymerization Reactions in Aqueous NIPAM/BIS and VCL/BIS Systems.

PubMed

Kröger, Leif C; Kopp, Wassja A; Leonhard, Kai

2017-04-06

Microgels have a wide range of possible applications and are therefore studied with increasing interest. Nonetheless, the microgel synthesis process and some of the resulting properties of the microgels, such as the cross-linker distribution within the microgels, are not yet fully understood. An in-depth understanding of the synthesis process is crucial for designing tailored microgels with desired properties. In this work, rate constants and reaction enthalpies of chain propagation reactions in aqueous N-isopropylacrylamide/N,N'-methylenebisacrylamide and aqueous N-vinylcaprolactam/N,N'-methylenebisacrylamide systems are calculated to identify the possible sources of an inhomogeneous cross-linker distribution in the resulting microgels. Gas-phase reaction rate constants are calculated from B2PLYPD3/aug-cc-pVTZ energies and B3LYPD3/tzvp geometries and frequencies. Then, solvation effects based on COSMO-RS are incorporated into the rate constants to obtain the desired liquid-phase reaction rate constants. The rate constants agree with experiments within a factor of 2-10, and the reaction enthalpies deviate less than 5 kJ/mol. Further, the effect of rate constants on the microgel growth process is analyzed, and it is shown that differences in the magnitude of the reaction rate constants are a source of an inhomogeneous cross-linker distribution within the resulting microgel.

Adsorption of antimony onto iron oxyhydroxides: adsorption behavior and surface structure.

PubMed

Guo, Xuejun; Wu, Zhijun; He, Mengchang; Meng, Xiaoguang; Jin, Xin; Qiu, Nan; Zhang, Jing

2014-07-15

Antimony is detected in soil and water with elevated concentration due to a variety of industrial applications and mining activities. Though antimony is classified as a pollutant of priority interest by the United States Environmental Protection Agency (USEPA) and Europe Union (EU), very little is known about its environmental behavior and adsorption mechanism. In this study, the adsorption behaviors and surface structure of antimony (III/V) on iron oxides were investigated using batch adsorption techniques, surface complexation modeling (SCM), X-ray photon spectroscopy (XPS) and extended X-ray absorption fine structure spectroscopy (EXAFS). The adsorption isotherms and edges indicated that the affinity of Sb(V) and Sb(III) toward the iron oxides depended on the Sb species, solution pH, and the characteristics of iron oxides. Sb(V) adsorption was favored at acidic pH and decreased dramatically with increasing pH, while Sb(III) adsorption was constant over a broad pH range. When pH is higher than 7, Sb(III) adsorption by goethite and hydrous ferric oxide (HFO) was greater than Sb(V). EXAFS analysis indicated that the majority of Sb(III), either adsorbed onto HFO or co-precipitated by FeCl3, was oxidized into Sb(V) probably due to the involvement of O2 in the long duration of sample preservation. Only one Sb-Fe subshell was filtered in the EXAFS spectra of antimony adsorption onto HFO, with the coordination number of 1.0-1.9 attributed to bidentate mononuclear edge-sharing ((2)E) between Sb and HFO. Copyright © 2014 Elsevier B.V. All rights reserved.

Adsorption characteristics of siloxanes in landfill gas by the adsorption equilibrium test.

PubMed

Nam, Sangchul; Namkoong, Wan; Kang, Jeong-Hee; Park, Jin-Kyu; Lee, Namhoon

2013-10-01

Due to the increase in energy cost by constantly high oil prices and the obligation to reduce greenhouse effect gases, landfill gas is frequently used as an alternative energy source for producing heat and electricity. Most of landfill gas utility facilities, however, are experiencing problems controlling siloxanes from landfill gas as their catalytic oxidizers are becoming fouled by silicon dioxide dust. To evaluate adsorption characteristics of siloxanes, an adsorption equilibrium test was conducted and parameters in the Freundlich and Langmuir isotherms were analyzed. Coconut activated carbon (CA1), coal activated carbon (CA2), impregnated activated carbon (CA3), silicagel (NCA1), and activated alumina (NCA2) were used for the adsorption of the mixed siloxane which contained hexamethyldisiloxane (L2), octamethylcyclotetrasiloxane (D4), and decamethylcyclopentasiloxane (D5). L2 had higher removal efficiency in noncarbon adsorbents compared to carbon adsorbents. The application of Langmuir and Freundlich adsorption isotherm demonstrated that coconut based CA1 and CA3 provided higher adsorption capacity on L2. And CA2 and NCA1 provided higher adsorption capacity on D4 and D5. Based on the experimental results, L2, D4, and D5 were converted by adsorption and desorption in noncarbon adsorbents. Adsorption affinity of siloxane is considered to be affect by the pore size distribution of the adsorbents and by the molecular size of each siloxane. Copyright © 2013 Elsevier Ltd. All rights reserved.

Effect of bacterial growth rate on bacteriophage population growth rate.

PubMed

Nabergoj, Dominik; Modic, Petra; Podgornik, Aleš

2018-04-01

It is important to understand how physiological state of the host influence propagation of bacteriophages (phages), due to the potential higher phage production needs in the future. In our study, we tried to elucidate the effect of bacterial growth rate on adsorption constant (δ), latent period (L), burst size (b), and bacteriophage population growth rate (λ). As a model system, a well-studied phage T4 and Escherichia coli K-12 as a host was used. Bacteria were grown in a continuous culture operating at dilution rates in the range between 0.06 and 0.98 hr -1 . It was found that the burst size increases linearly from 8 PFU·cell -1 to 89 PFU·cell -1 with increase in bacteria growth rate. On the other hand, adsorption constant and latent period were both decreasing from 2.6∙10 -9  ml·min -1 and 80 min to reach limiting values of 0.5 × 10 -9  ml·min -1 and 27 min at higher growth rates, respectively. Both trends were mathematically described with Michaelis-Menten based type of equation and reasons for such form are discussed. By applying selected equations, a mathematical equation for prediction of bacteriophage population growth rate as a function of dilution rate was derived, reaching values around 8 hr -1 at highest dilution rate. Interestingly, almost identical description can be obtained using much simpler Monod type equation and possible reasons for this finding are discussed. © 2017 The Authors. MicrobiologyOpen published by John Wiley & Sons Ltd.

Preparation of steam activated carbon from rubberwood sawdust (Hevea brasiliensis) and its adsorption kinetics.

PubMed

Prakash Kumar, B G; Shivakamy, K; Miranda, Lima Rose; Velan, M

2006-08-25

Activated carbon was produced from a biowaste product, rubberwood sawdust (RWSD) using steam in a high temperature fluidized bed reactor. Experiments were carried out to investigate the influence of various process parameters such as activation time, activation temperature, particle size and fluidising velocity on the quality of the activated carbon. The activated carbon was characterized based on its iodine number, methylene blue number, Brauner Emmet Teller (BET) surface area and surface area obtained using the ethylene glycol mono ethyl ether (EGME) retention method. The best quality activated carbon was obtained at an activation time and temperature of 1h and 750 degrees C for an average particle size of 0.46 mm. The adsorption kinetics shows that pseudo-second-order rate fitted the adsorption kinetics better than pseudo-first-order rate equation. The adsorption capacity of carbon produced from RWSD was found to be 1250 mg g(-1) for the Bismark Brown dye. The rate constant and diffusion coefficient for intraparticle transport were determined for steam activated carbon. The characteristic of the prepared activated carbon was found comparable to the commercial activated carbon.

The effects of surface chemistry of mesoporous silica materials and solution pH on kinetics of molsidomine adsorption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dolinina, E.S.; Parfenyuk, E.V., E-mail: terrakott37@mail.ru

2014-01-15

Adsorption kinetics of molsidomine on mesoporous silica material (UMS), the phenyl- (PhMS) and mercaptopropyl-functionalized (MMS) derivatives from solution with different pH and 298 K was studied. The adsorption kinetics was found to follow the pseudo-second-order kinetic model for all studied silica materials and pH. Effects of surface functional groups and pH on adsorption efficiency and kinetic adsorption parameters were investigated. At all studied pH, the highest molsidomine amount is adsorbed on PhMS due to π–π interactions and hydrogen bonding between surface groups of PhMS and molsidomine molecules. An increase of pH results in a decrease of the amounts of adsorbedmore » molsidomine onto the silica materials. Furthermore, the highest adsorption rate kinetically evaluated using a pseudo-second-order model, is observed onto UMS and it strongly depends on pH. The mechanism of the adsorption process was determined from the intraparticle diffusion and Boyd kinetic film–diffusion models. The results showed that the molsidomine adsorption on the silica materials is controlled by film diffusion. Effect of pH on the diffusion parameters is discussed. - Graphical abstract: The kinetic study showed that the k{sub 2} value, the rate constant of pseudo-second order kinetic model, is the highest for molsidomine adsorption on UMS and strongly depends on pH because it is determined by availability and accessibility of the reaction sites of the adsorbents molsidomine binding. Display Omitted - Highlights: • The adsorption capacities of UMS, PhMS and MMS were dependent on the pH. • At all studied pH, the highest molsidomine amount is adsorbed on PhMS. • The highest adsorption rate, k{sub 2}, is observed onto UMS and strongly depends on pH. • Film diffusion was the likely rate-limiting step in the adsorption process.« less

Removal of Congo Red from Aqueous Solution by Anion Exchange Membrane (EBTAC): Adsorption Kinetics and Themodynamics.

PubMed

Khan, Muhammad Imran; Akhtar, Shahbaz; Zafar, Shagufta; Shaheen, Aqeela; Khan, Muhammad Ali; Luque, Rafael; Rehman, Aziz Ur

2015-07-08

The adsorption behavior of anionic dye congo red (CR) from aqueous solutions using an anion exchange membrane (EBTAC) has been investigated at room temperature. The effect of several factors including contact time, membrane dosage, ionic strength and temperature were studied. Kinetic models, namely pseudo-first-order and pseudo-second-order, liquid film diffusion and Elovich models as well as Bangham and modified freundlich Equations, were employed to evaluate the experimental results. Parameters such as adsorption capacities, rate constant and related correlation coefficients for every model were calculated and discussed. The adsorption of CR on anion exchange membranes followed pseudo-second-order Kinetics. Thermodynamic parameters, namely changes in Gibbs free energy ( ∆G° ), enthalpy ( ∆H° ) and entropy ( ∆S° ) were calculated for the adsorption of congo red, indicating an exothermic process.

Removal of Congo Red from Aqueous Solution by Anion Exchange Membrane (EBTAC): Adsorption Kinetics and Themodynamics

PubMed Central

Khan, Muhammad Imran; Akhtar, Shahbaz; Zafar, Shagufta; Shaheen, Aqeela; Khan, Muhammad Ali; Luque, Rafael; ur Rehman, Aziz

2015-01-01

The adsorption behavior of anionic dye congo red (CR) from aqueous solutions using an anion exchange membrane (EBTAC) has been investigated at room temperature. The effect of several factors including contact time, membrane dosage, ionic strength and temperature were studied. Kinetic models, namely pseudo-first-order and pseudo-second-order, liquid film diffusion and Elovich models as well as Bangham and modified freundlich Equations, were employed to evaluate the experimental results. Parameters such as adsorption capacities, rate constant and related correlation coefficients for every model were calculated and discussed. The adsorption of CR on anion exchange membranes followed pseudo-second-order Kinetics. Thermodynamic parameters, namely changes in Gibbs free energy (∆G°), enthalpy (∆H°) and entropy (∆S°) were calculated for the adsorption of congo red, indicating an exothermic process. PMID:28793430

Binary gaseous mixture and single component adsorption of methane and argon on exfoliated graphite

NASA Astrophysics Data System (ADS)

Russell, Brice Adam

Exfoliated graphite was used as a substrate for adsorption of argon and methane. Adsorption experiments were conducted for both equal parts mixtures of argon and methane and for each gas species independently. The purpose of this was to compare mixture adsorption to single component adsorption and to investigate theoretical predictions concerning the kinetics of adsorption made by Burde and Calbi.6 In particular, time to reach pressure equilibrium of a single dose at a constant temperature for the equal parts mixture was compared to time of adsorption for each species by itself. It was shown that mixture adsorption is a much more complex and time consuming process than single component adsorption and requires a much longer amount of time to reach equilibrium. Information about the composition evolution of the mixture during the times when pressure was going toward equilibrium was obtained using a quadrupole mass spectrometer. Evidence for initial higher rate of adsorption for the weaker binding energy species (argon) was found as well as overall composition change which clearly indicated a higher coverage of methane on the graphite sample by the time equilibration was reached. Effective specific surface area of graphite for both argon and methane was also determined using the Point-B method.2

Molecular Simulations of Adsorption and Diffusion in Silicalite.

NASA Astrophysics Data System (ADS)

Snurr, Randall Quentin

The adsorption and diffusion of hydrocarbons in the zeolite silicalite have been studied using molecular simulations. The simulations use an atomistic description of zeolite/sorbate interactions and are based on principles of statistical mechanics. Emphasis was placed on developing new simulation techniques to allow complex systems relevant to industrial applications in catalysis and separations processes to be studied. Adsorption isotherms and heats of sorption for methane in silicalite were calculated from grand canonical Monte Carlo (GCMC) simulations and also from molecular dynamics (MD) simulations accompanied by Widom test particle insertions. Good agreement with experimental data from the literature was found. The adsorption thermodynamics of aromatic species in silicalite at low loading was predicted by direct evaluation of the configurational integrals. Good agreement with experiment was obtained for the Henry's constants and the heats of adsorption. Molecules were predicted to be localized in the channel intersections at low loading. At higher loading, conventional GCMC simulations were found to be infeasible. Several variations of the GCMC technique were developed incorporating biased insertion moves. These new techniques are much more efficient than conventional GCMC and allow for the prediction of adsorption isotherms of tightly-fitting aromatic molecules in silicalite. Our simulations when combined with experimental evidence of a phase change in the zeolite structure at intermediate loading provide an explanation of the characteristic steps seen in the experimental isotherms. A hierarchical atomistic/lattice model for studying these systems was also developed. The hierarchical model is more than an order of magnitude more efficient computationally than direct atomistic simulation. Diffusion of benzene in silicalite was studied using transition-state theory (TST). Such an approach overcomes the time-scale limitations of using MD simulations for

Application of surface complexation models to anion adsorption by natural materials.

PubMed

Goldberg, Sabine

2014-10-01

Various chemical models of ion adsorption are presented and discussed. Chemical models, such as surface complexation models, provide a molecular description of anion adsorption reactions using an equilibrium approach. Two such models, the constant capacitance model and the triple layer model, are described in the present study. Characteristics common to all the surface complexation models are equilibrium constant expressions, mass and charge balances, and surface activity coefficient electrostatic potential terms. Methods for determining parameter values for surface site density, capacitances, and surface complexation constants also are discussed. Spectroscopic experimental methods of establishing ion adsorption mechanisms include vibrational spectroscopy, nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, X-ray absorption spectroscopy, and X-ray reflectivity. Experimental determinations of point of zero charge shifts and ionic strength dependence of adsorption results and molecular modeling calculations also can be used to deduce adsorption mechanisms. Applications of the surface complexation models to heterogeneous natural materials, such as soils, using the component additivity and the generalized composite approaches are described. Emphasis is on the generalized composite approach for predicting anion adsorption by soils. Continuing research is needed to develop consistent and realistic protocols for describing ion adsorption reactions on soil minerals and soils. The availability of standardized model parameter databases for use in chemical speciation-transport models is critical. Published 2014 Wiley Periodicals Inc. on behalf of SETAC. This article is a US Government work and as such, is in the public domain in the in the United States of America.

A simple method relating specific rate constants k(E,J) and Thermally averaged rate constants k(infinity)(T) of unimolecular bond fission and the reverse barrierless association reactions.

PubMed

Troe, J; Ushakov, V G

2006-06-01

This work describes a simple method linking specific rate constants k(E,J) of bond fission reactions AB --> A + B with thermally averaged capture rate constants k(cap)(T) of the reverse barrierless combination reactions A + B --> AB (or the corresponding high-pressure dissociation or recombination rate constants k(infinity)(T)). Practical applications are given for ionic and neutral reaction systems. The method, in the first stage, requires a phase-space theoretical treatment with the most realistic minimum energy path potential available, either from reduced dimensionality ab initio or from model calculations of the potential, providing the centrifugal barriers E(0)(J). The effects of the anisotropy of the potential afterward are expressed in terms of specific and thermal rigidity factors f(rigid)(E,J) and f(rigid)(T), respectively. Simple relationships provide a link between f(rigid)(E,J) and f(rigid)(T) where J is an average value of J related to J(max)(E), i.e., the maximum J value compatible with E > or = E0(J), and f(rigid)(E,J) applies to the transitional modes. Methods for constructing f(rigid)(E,J) from f(rigid)(E,J) are also described. The derived relationships are adaptable and can be used on that level of information which is available either from more detailed theoretical calculations or from limited experimental information on specific or thermally averaged rate constants. The examples used for illustration are the systems C6H6+ <==> C6H5+ + H, C8H10+ --> C7H7+ + CH3, n-C9H12+ <==> C7H7+ + C2H5, n-C10H14+ <==> C7H7+ + C3H7, HO2 <==> H + O2, HO2 <==> HO + O, and H2O2 <==> 2HO.

The characteristics of phosphorus adsorption and desorption in gray desert soil of Xinjiang, China

NASA Astrophysics Data System (ADS)

Wang, B.; Sun, J. S.; Liu, H.; Ma, Y. B.

2017-07-01

The characteristics of phosphorus (P) adsorption and desorption in Xinjiang gray desert soil (0 - 200 mm) of China in the long-term fertilization condition is affected by the level of soil P content which studied through an isothermal adsorption and desorption experiments of P. The results stated that within the experimental concentration range, with the increase of the amount of outer-source phosphorus, P adsorption, desorption and desorption rate increased and adsorption rate decreased gradually in different Olsen-P levels of gray desert soil in Xinjiang, China. Olsen-P content is significantly correlated with the P adsorption saturation (DPS) of gray desert soil. The maximum adsorption capacity (Xm ) of the treatments followed an extremely significant decreasing order of CK>NPK≈NPKM>PK≈NPKS. The maximum buffer capacity (MBC) and adsorption constant (K) of the NPK treatment was much higher than NPKM, NPKS, PK and CK treatments. And, MBC value of CK treatment was extremely higher than NPKS and PK, however, the differences between NPKM and CK, NPKS and PK were not significant. The comparison between NPKM, NPKS, PK and CK treatments showed no significant difference in K value, but these four showed significantly lower than NPK treatments. The value of soil easy desorption P (RDP) of NPKS and NPKM was significantly higher than NPK and PK, and the chemical fertilizer with organic fertilizer was a best way to release the phosphorus for Xinjiang agricultural production, China.

Assessing changes in the physico-chemical properties and fluoride adsorption capacity of activated alumina under varied conditions

USGS Publications Warehouse

Craig, Laura; Stillings, Lisa; Decker, David L.

2017-01-01

Adsorption using activated alumina is a simple method for removing fluoride from drinking water, but to be cost effective the adsorption capacity must be high and effective long-term. The intent of this study was to assess changes in its adsorption capacity under varied conditions. This was determined by evaluating the physico-chemical properties, surface charge, and fluoride (F−) adsorption capacity and rate of activated alumina under conditions such as hydration period, particle size, and slow vs. fast titrations. X-ray diffraction and scanning electron microscopy analyses show that the mineralogy of activated alumina transformed to boehmite, then bayerite with hydration period and a corresponding reduction in adsorption capacity was expected; while surface area analyses show no notable changes with hydration period or particle size. The pH dependent surface charge was three times higher using slow potentiometric titrations as compared to fast titrations (due largely to diffusion into pore space), with the surface acidity generally unaffected by hydration period. Results from batch adsorption experiments similarly show no change in fluoride adsorption capacity with hydration period. There was also no notable difference in fluoride adsorption capacity between the particle size ranges of 0.5–1.0 mm and 0.125–0.250 mm, or with hydration period. However, adsorption rate increased dramatically with the finer particle sizes: at an initial F− concentration of 0.53 mmol L−1 (10 mg L−1), 90% was adsorbed in the 0.125–0.250 mm range after 1 h, while the 0.5–1.0 mm range required 24 h to achieve 90% adsorption. Also, the pseudo-second-order adsorption rate constants for the finer vs. larger particle sizes were 3.7 and 0.5 g per mmol F− per min respectively (24 h); and the initial intraparticle diffusion rate of the former was 2.6 times faster than the latter. The results show that adsorption capacity of activated alumina remains consistent and

Mechanisms for the adsorption of substituted nitrobenzenes by smectite clays.

PubMed

Boyd, S A; Sheng, G; Teppen, B J; Johnston, C T

2001-11-01

To more fully understand the potential for transport of nitroaromatic compounds in soils and subsoils,the adsorption of a series of para- and meta-substituted nitrobenzenes (SNBs) by K-smectite clay was measured. Adsorption isotherms were fit to the Freundlich equation, and the resultant Freundlich adsorption coefficients (log(Kf) were positively correlated with the Hammett substituent constant (r2 = 0.80). This relationship and a positive reaction constant (p = 1.15) indicate that the adsorption reaction is favored by electron-withdrawing substituents. These results are consistent with an electron donor (smectite)-acceptor (substituted nitrobenzene) mechanism offered previously. However, quantum calculations did not reveal any systematic relationship between the Hammett constant and the electron density on the aromatic ring, which would explain a donor-acceptor relationship. Rather, electron density donated by a second substituent on nitrobenzene appears to be appropriated by the nitro group leaving ring electron density unchanged. Fourier transform infrared spectroscopy revealed shifts in the -NO2 vibrational modes of 1,3,5-trinitrobenzene (TNB) upon adsorption to K+-smectite that were consistent with the complexation of K+ by -NO2 groups. Such TNB vibrational shifts were not observed for SWy-1 saturated with more strongly hydrated cations (i.e., Na+, Mg2+, Ca2+, and Ba2+). The simultaneous interaction of multiple -NO2 groups with exchangeable K+ was indicated by molecular dynamic simulations. Adsorption of SNBs by smectite clays appears to result from the additive interactions of -NO2 groups and secondary substituents with interlayer K+ ions. Adsorption occurs to a greater or lesser extent depending on the abilities of substituents to complex additional interlayer cations and the water solubilities of SNBs. We conclude that the adsorption trends of SNBs on K-SAz-1 can be explained without recourse to hypothetical electron donor-acceptor complexes.

Arrhenius Rate: constant volume burn

DOE Office of Scientific and Technical Information (OSTI.GOV)

Menikoff, Ralph

A constant volume burn occurs for an idealized initial state in which a large volume of reactants at rest is suddenly raised to a high temperature and begins to burn. Due to the uniform spatial state, there is no fluid motion and no heat conduction. This reduces the time evolu tion to an ODE for the reaction progress variable. With an Arrhenius reaction rate, two characteristics of thermal ignition are illustrated: induction time and thermal runaway. The Frank-Kamenetskii approximation then leads to a simple expression for the adiabatic induction time. For a first order reaction, the analytic solution is derivedmore » and used to illustrate the effect of varying the activation temperature; in particular, on the induction time. In general, the ODE can be solved numerically. This is used to illustrate the effect of varying the reaction order. We note that for a first order reaction, the time evolution of the reaction progress variable has an exponential tail. In contrast, for a reaction order less than one, the reaction completes in a nite time. The reaction order also affects the induction time.« less

Cd and proton adsorption onto bacterial consortia grown from industrial wastes and contaminated geologic settings.

PubMed

Borrok, David M; Fein, Jeremy B; Kulpa, Charles F

2004-11-01

To model the effects of bacterial metal adsorption in contaminated environments, results from metal adsorption experiments involving individual pure stains of bacteria must be extrapolated to systems in which potentially dozens of bacterial species are present. This extrapolation may be made easier because bacterial consortia from natural environments appear to exhibit similar metal binding properties. However, bacteria that thrive in highly perturbed contaminated environments may exhibit significantly different adsorptive behavior. Here we measure proton and Cd adsorption onto a range of bacterial consortia grown from heavily contaminated industrial wastes, groundwater, and soils. We model the results using a discrete site surface complexation approach to determine binding constants and site densities for each consortium. The results demonstrate that bacterial consortia from different contaminated environments exhibit a range of total site densities (approximately a 3-fold difference) and Cd-binding constants (approximately a 10-fold difference). These ranges for Cd binding constants may be small enough to suggest that bacteria-metal adsorption in contaminated environments can be described using relatively few "averaged" bacteria-metal binding constants (in conjunction with the necessary binding constants for competing surfaces and ligands). However, if additional precision is necessary, modeling parameters must be developed separately for each contaminated environment of interest.

Propagation rate constants for the peroxidation of sterols on the biosynthetic pathway to cholesterol.

PubMed

Lamberson, Connor R; Muchalski, Hubert; McDuffee, Kari B; Tallman, Keri A; Xu, Libin; Porter, Ned A

2017-10-01

The free radical chain autoxidation of cholesterol and the oxidation products formed, i.e. oxysterols, have been the focus of intensive study for decades. The peroxidation of sterol precursors to cholesterol such as 7-dehydrocholesterol (7-DHC) and desmosterol as well as their oxysterols has received less attention. The peroxidation of these sterol precursors can become important under circumstances in which genetic conditions or exposures to small molecules leads to an increase of these biosynthetic intermediates in tissues and fluids. 7-DHC, for example, has a propagation rate constant for peroxidation some 200 times that of cholesterol and this sterol is found at elevated levels in a devastating human genetic condition, Smith-Lemli-Opitz syndrome (SLOS). The propagation rate constants for peroxidation of sterol intermediates on the biosynthetic pathway to cholesterol were determined by a competition kinetic method, i.e. a peroxyl radical clock. In this work, propagation rate constants for lathosterol, zymostenol, desmosterol, 7-dehydrodesmosterol and other sterols in the Bloch and Kandutsch-Russell pathways are assigned and these rate constants are related to sterol structural features. Furthermore, potential oxysterols products are proposed for sterols whose oxysterol products have not been determined. Copyright © 2017 Elsevier B.V. All rights reserved.

GROUND WATER ISSUE - CALCULATION AND USE OF FIRST-ORDER RATE CONSTANTS FOR MONITORED NATURAL ATTENUATION STUDIES

EPA Science Inventory

This issue paper explains when and how to apply first-order attenuation rate constant calculations in monitored natural attenuation (MNA) studies. First-order attenuation rate constant calculations can be an important tool for evaluating natural attenuation processes at ground-wa...

Binding Rate Constants Reveal Distinct Features of Disordered Protein Domains.

PubMed

Dogan, Jakob; Jonasson, Josefin; Andersson, Eva; Jemth, Per

2015-08-04

Intrinsically disordered proteins (IDPs) are abundant in the proteome and involved in key cellular functions. However, experimental data about the binding kinetics of IDPs as a function of different environmental conditions are scarce. We have performed an extensive characterization of the ionic strength dependence of the interaction between the molten globular nuclear co-activator binding domain (NCBD) of CREB binding protein and five different protein ligands, including the intrinsically disordered activation domain of p160 transcriptional co-activators (SRC1, TIF2, ACTR), the p53 transactivation domain, and the folded pointed domain (PNT) of transcription factor ETS-2. Direct comparisons of the binding rate constants under identical conditions show that the association rate constant, kon, for interactions between NCBD and disordered protein domains is high at low salt concentrations (90-350 × 10(6) M(-1) s(-1) at 4 °C) but is reduced significantly (10-30-fold) with an increasing ionic strength and reaches a plateau around physiological ionic strength. In contrast, the kon for the interaction between NCBD and the folded PNT domain is only 7 × 10(6) M(-1) s(-1) (4 °C and low salt) and displays weak ionic strength dependence, which could reflect a distinctly different association that relies less on electrostatic interactions. Furthermore, the basal rate constant (in the absence of electrostatic interactions) is high for the NCBD interactions, exceeding those typically observed for folded proteins. One likely interpretation is that disordered proteins have a large number of possible collisions leading to a productive on-pathway encounter complex, while folded proteins are more restricted in terms of orientation. Our results highlight the importance of electrostatic interactions in binding involving IDPs and emphasize the significance of including ionic strength as a factor in studies that compare the binding properties of IDPs to those of ordered proteins.

Adsorption of asymmetric rigid rods or heteronuclear diatomic moleculeson homogeneous surfaces

NASA Astrophysics Data System (ADS)

Engl, W.; Courbin, L.; Panizza, P.

2004-10-01

We treat the adsorption on homogeneous surfaces of asymmetric rigid rods (like for instance heteronuclear diatomic molecules). We show that the n→0 vector spin formalism is well suited to describe such a problem. We establish an isomorphism between the coupling constants of the magnetic Hamiltonian and the adsorption parameters of the rigid rods. By solving this Hamiltonian within a mean-field approximation, we obtain analytical expressions for the densities of the different rod’s configurations, both isotherm and isobar adsorptions curves. The most probable configurations of the molecules (normal or parallel to the surface) which depends on temperature and energy parameters are summarized in a diagram. We derive that the variation of Qv , the heat of adsorption at constant volume, with the temperature is a direct signature of the adsorbed molecules configuration change. We show that this formalism can be generalized to more complicated problems such as for instance the adsorption of symmetric and asymmetric rigid rods mixtures in the presence or not of interactions.

Adsorptive removal of organics from aqueous phase by acid-activated coal fly ash: preparation, adsorption, and Fenton regenerative valorization of "spent" adsorbent.

PubMed

Wang, Nannan; Hao, Linlin; Chen, Jiaqing; Zhao, Qiang; Xu, Han

2018-05-01

Raw coal fly ash was activated to an adsorbent by sulfuric acid impregnation. The activation condition, the adsorption capacity, and the regenerative valorization of the adsorbent were studied. The results show that the optimal preparation conditions of the adsorbent are [H 2 SO 4 ] = 1 mol L -1 , activation time = 30 min, the ratio of coal fly ash to acid = 1:20 (g:mL), calcination temperature = 100 °C. The adsorption of p-nitrophenol on the adsorbent accords with the pseudo-second-order kinetic equation and the adsorption rate constant is 0.089 g mg -1  min -1 . The adsorption on this adsorbent can be considered enough after 35 min, when the corresponding adsorption capacity is 1.07 mg g -1 (85.6% of p-nitrophenol removal). Compared with raw coal fly ash, the adsorbent has a stable adsorption performance at low pH range (pH = 1-6) and the adsorption of p-nitrophenol is an exothermic process. Ninety minutes is required for the regenerative valorization of saturated adsorbent by Fenton process. The regenerative valorization for this saturated adsorbent can reach 89% under the optimal proposed conditions (30 °C, pH = 3, [H 2 O 2 ] = 5.0 mmol L -1 , [Fe 2+ ] = 5.5 mmol L -1 ). Within 15 experimental runs, the adsorbent has a better and better stability with the increase of experimental runs. Finally, the mechanism of activating coal fly ash is proposed, being verified by the results of the SEM and BET test.

Kinetics and thermodynamics of Pb(II) adsorption onto modified spent grain from aqueous solutions

NASA Astrophysics Data System (ADS)

Li, Qingzhu; Chai, Liyuan; Yang, Zhihui; Wang, Qingwei

2009-01-01

Spent grain, a main by-product of the brewing industry, is available in large quantities, but its main application has been limited to animal feeding. Nevertheless, in this study, spent grain modified with 1 M NaCl solution as a novel adsorbent has been used for the adsorption of Pb(II) in aqueous solutions. Isotherms, kinetics and thermodynamics of Pb(II) adsorption onto modified spent grain were studied. The equilibrium data were well fitted with Langmuir, Freundlich and Dubinin-Radushkevick (D-R) isotherm models. The kinetics of Pb(II) adsorption followed pseudo-second-order model, using the rate constants of pseudo-second-order model, the activation energy ( Ea) of Pb(II) adsorption was determined as 12.33 kJ mol -1 according to the Arrhenius equation. Various thermodynamic parameters such as Δ Gads, Δ Hads and Δ Sads were also calculated. Thermodynamic results indicate that Pb(II) adsorption onto modified spent grain is a spontaneous and endothermic process. Therefore, it can be concluded that modified spent grain as a new effective adsorbent has potential for Pb(II) removal from aqueous solutions.

Adsorption of Pb2+ on Thiol-functionalized Mesoporous Silica, SH-MCM-48

NASA Astrophysics Data System (ADS)

Taba, P.; Mustafa, R. D. P.; Ramang, L. M.; Kasim, A. H.

2018-03-01

Modification of mesoporous silica, MCM-48, by using 3- mercaptopropyltrimethoxysilane has been successfully conducted. MCM-48 and SH-MCM-48 were characterized using XRD and FTIR. SH-MCM-48 was used as an adsorbent of Pb2+ ions from solution. A number of Pb2+ ions adsorbed were studied as the function of time, pH, and concentration. The concentration of the ions after adsorption was determined by an Atomic Absorption Spectrophotometer. The removal of the adsorbed ions from the SH-MCM-48 was also studied using several desorbing agents. The result showed that the optimum time was 20 minutes and optimum pH was 4. The adsorption of Pb(II) ion followed the pseudo-second-order with the rate constant of 0,2632 g•mg-1•min-1. Adsorption of Pb(II) ion fitted the Langmuir isotherm with the adsorption capacity of 0,1088 mmol/g. The best desorbing agent to remove the adsorbed ion from SH-MCM-48 was 0.3 M HCl solution with the desorption percentage of 58.6%.

Adsorption and separation of proteins by collagen fiber adsorbent.

PubMed

Li, Juan; Liao, Xue-pin; Zhang, Qi-xian; Shi, Bi

2013-06-01

The separation of proteins is a key step in biomedical and pharmaceutical industries. In the present investigation, the collagen fiber adsorbent (CFA) was exploited as column packing material to separate proteins. Bovine serum albumin (BSA), bovine hemoglobin (Hb) and lysozyme (LYS) that have different isoelectric points (pIs) were selected as model proteins to investigate the separation ability of CFA to proteins. In batch adsorption, the adsorption behaviors of these proteins on CFA under different pHs and ionic strengths indicated that the electrostatic interaction plays a predominant role in the adsorption of proteins on CFA. CFA exhibited high adsorption capacity to Hb and LYS. In column separation, the proteins were completely separated by adjusting pH and ionic strength of the eluent. The increase of flow rate could reduce the separation time with no influence on the recovery of protein in the experimental range. The protein recovery was higher than 90% even when the CFA column was re-used for 4 times in separation of BSA and LYS, and the retention time of BSA or LYS was almost constant during the repeated applications. In addition, as a practical application, LYS was successfully separated from chicken egg white powder by CFA column. Copyright © 2013 Elsevier B.V. All rights reserved.

Method and means for dynamic measurement of rates of adsorption from solutions

DOEpatents

Slomka, Bogdan J.; Buttermore, William H.

1992-05-05

A method and apparatus for dynamic measurement of rates of absorption from solutions. The method has the advantage of avoiding the use of solvent normally used to establish a baseline. The method involves pre-evacuating the adsorbent contained in an adsorbent cell and thereafter rapidly contacting the adsorbent with analytical solution, all without prior exposure of adsorbent to pure solvent. The result is a sharp characteristic adsorption line.

Likelihood inference of non-constant diversification rates with incomplete taxon sampling.

PubMed

Höhna, Sebastian

2014-01-01

Large-scale phylogenies provide a valuable source to study background diversification rates and investigate if the rates have changed over time. Unfortunately most large-scale, dated phylogenies are sparsely sampled (fewer than 5% of the described species) and taxon sampling is not uniform. Instead, taxa are frequently sampled to obtain at least one representative per subgroup (e.g. family) and thus to maximize diversity (diversified sampling). So far, such complications have been ignored, potentially biasing the conclusions that have been reached. In this study I derive the likelihood of a birth-death process with non-constant (time-dependent) diversification rates and diversified taxon sampling. Using simulations I test if the true parameters and the sampling method can be recovered when the trees are small or medium sized (fewer than 200 taxa). The results show that the diversification rates can be inferred and the estimates are unbiased for large trees but are biased for small trees (fewer than 50 taxa). Furthermore, model selection by means of Akaike's Information Criterion favors the true model if the true rates differ sufficiently from alternative models (e.g. the birth-death model is recovered if the extinction rate is large and compared to a pure-birth model). Finally, I applied six different diversification rate models--ranging from a constant-rate pure birth process to a decreasing speciation rate birth-death process but excluding any rate shift models--on three large-scale empirical phylogenies (ants, mammals and snakes with respectively 149, 164 and 41 sampled species). All three phylogenies were constructed by diversified taxon sampling, as stated by the authors. However only the snake phylogeny supported diversified taxon sampling. Moreover, a parametric bootstrap test revealed that none of the tested models provided a good fit to the observed data. The model assumptions, such as homogeneous rates across species or no rate shifts, appear to be

Frost heave susceptibility of saturated soil under constant rate of freezing

NASA Astrophysics Data System (ADS)

Ryokai, K.; Iguro, M.; Yoneyama, K.

Introduced are the results of experiments carried out to quantitatively obtain the frost heave pressure and displacement of soil subjected to artificial freezing or freezing around in-ground liquefied natural gas storage tanks. This experiment is conducted to evaluate the frost heave susceptibility of saturated soil under overconsolidation. In other words, this experiment was carried out to obtain the relation of the over-burden pressure and freezing rate to the frost heave ratio by observing the frost heave displacement and freezing time of specimens by freezing the specimens at a constant freezing rate under a constant overburden pressure, while letting water freely flow in and out of the system. Introduced are the procedures for frost heave test required to quantitatively obtain the frost heave displacement and pressure of soil. Furthermore, the relation between the frost heave susceptibility and physical properties of soil obtained by this test is reported.

[Effects of soil trituration size on adsorption of oxytetracycline on soils].

PubMed

Qi, Rui-Huan; Li, Zhao-Jun; Long, Jian; Fan, Fei-Fei; Liang, Yong-Chao

2011-02-01

In order to understand the effects of soil trituration size on adsorption of oxytetracycline (OTC) on soils, two contrasting soils including moisture soil and purplish soil were selected to investigate adsorption of OTC on these soils, at the scales of no more than 0.20 mm, 0.84 mm, 0.25 mm and 0.15 mm, using the method of batch equilibrium experiments respectively. The results presented as the following: (1) Adsorption amount of OTC on moisture soil and purplish soil increased with the sampling time, and reached to equilibration at 24 h. First-order kinetic model, second-order kinetic model, parabolic-diffusion kinetic model, Elovich kinetic model, and two-constant kinetic model could be used to fit the changes in adsorption on soils with sampling time. Adsorption of OTC on two soils consisted of two processes such as quick adsorption and slow adsorption. Quick adsorption process happened during the period of 0-0.5 h. The adsorption rates of OTC on soils were higher at the small trituration size than those at the large trituration size, and at the same trituration size, the k(f) of purplish soil was about two times higher than those of moisture soil. (2) Adsorption isotherms of OTC on two soils with different trituration sizes were deviated from the linear model. The data were fitted well to Freundlich and Langmuir models, with the correlation coefficients between 0.956 and 0.999. The values of k(f) and q(m) for purplish soil were higher than those for moisture soil. At the same soil, adsorption amount of OTC increased with the decreases of soil trituration size. The results suggested that it is important to select the appropriate trituration size, based on the physical and chemical properties such as soil particle composition and so on, when the fate of antibiotics on soils was investigated.

Constant-load versus heart rate-targeted exercise - Responses of systolic intervals

NASA Technical Reports Server (NTRS)

Lance, V. Q.; Spodick, D. H.

1975-01-01

Various systolic intervals were measured prior to and during heart rate-targeted bicycle ergometer exercise. There were striking similarities within each matched exercise set for Q-Im, isovolumetric contraction time, preejection period (PEP), and PEP/left ventricular ejection time (LVET). LVET was significantly shorter for rate-targeted exercise. It is concluded that either constant-load or rate-targeted bicycle ergometry may be used with the choice of method determined by the purpose of the protocol, and that systolic intervals (except LVET) should not be much altered owing to the method chosen.

Rate constants for the reactions of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br

NASA Technical Reports Server (NTRS)

Hsu, K.-J.; Demore, W. B.

1994-01-01

Rate constants for the reactions of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br have been measured by a relative rate technique in which the reaction rate of each compound was compared to that of HFC-152a (CH3CHF2) and (for CH2Cl2) HFC-161 (CH3CH2F). Using absolute rate constants for HFC-152a and HFC-161, which we have determined relative to those for CH4, CH3CCl3, and C2H6, temperature dependent rate constants of both compounds were derived. The derived rate constant for CH3Br is in good agreement with recent absolute measurements. However, for the chloromethanes all the rate constants are lower at atmospheric temperatures than previously reported, especially for CH2Cl2 where the present rate constant is about a factor of 1.6 below the JPL 92-20 value. The new rate constant appears to resolve a discrepancy between the observed atmospheric concentrations and those calculated from the previous rate constant and estimated release rates.

Method and means for dynamic measurement of rates of adsorption from solutions

DOEpatents

Slomka, B.J.; Buttermore, W.H.

1992-05-05

A method and apparatus are described for the dynamic measurement of rates of absorption from solutions. The method has the advantage of avoiding the use of solvent normally used to establish a baseline. The method involves pre-evacuating the adsorbent contained in an adsorbent cell and thereafter rapidly contacting the adsorbent with analytical solution, all without prior exposure of adsorbent to pure solvent. The result is a sharp characteristic adsorption line. 5 figs.

RELATIVE RATE CONSTANTS OF CONTAMINANT CANDIDATE LIST PESTICIDES WITH HYDROXYL RADICALS

EPA Science Inventory

The objective of this study was to establish the rate constants for the reactions of selected pesticides listed on the US EPA Contaminant Candidate List, with UV and hydroxyl radicals (·OH). Batch experiments were conducted in phosphate buffered solution at pH 7. All pestici...

Activated Carbon Preparation and Modification for Adsorption

NASA Astrophysics Data System (ADS)

Cao, Yuhe

compared to charcoal-based commercial AC (143.8 mg g -1). Based on the adsorption experiments of butanol vapor, we found the chemical properties of the AC surface play an important role in adsorbing molecules. The adsorption of creatinine on active carbons was also studied, which is a toxic compound generated by human. High levels of creatinine in the blood stream is normally caused by malfunction or failure of the kidneys. Activated carbons is taken by the patients orally to reduce creatinine level. In order to figure out whether chemical modification could increase the adsorption capacity of creatinine, AC samples modified by nitric acid hydrothermal modification were assessed for their ability to adsorb creatinine. The pore structure and surface properties of the AC samples were characterized by N 2 adsorption, temperature programmed desorption (TPD), Fourier Transform Infrared spectroscopy (FTIR), and X-ray photoelectron spectrometer (XPS). It indicated that 4M HNO3 hydrothermal modification with 180 °C was an efficient method in improvement of the creatinine adsorption. The improved adsorption capacity can be attributed mainly to an increase in the acidic oxygen-containing functional groups. The adsorption of creatinine over AC may involve an interaction with the acidic oxygen-containing groups on AC. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherm and isotherm constants. Equilibrium data fitted very well to the Freundlich model in the entire saturation range (3.58-59.08 mg L-1 ). The maximum adsorption capacities of AC modified with 180 °C is 62.5 mg g-1 according to the Langmuir model. Pseudo first-order and second-order kinetic models were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted well to the second-order kinetic model, which indicates that the chemical adsorption was the rate-limiting step, instead of mass transfer. (Abstract shortened by ProQuest.).

Adsorption of DDT and PCB by Nanomaterials from Residual Soil.

PubMed

Taha, Mohd Raihan; Mobasser, Shariat

2015-01-01

This paper presents the findings of a study on adsorption of dichlorodiphenythreechloroethen (DDT) and polychlorinated biphenyls (PCBs) on three nanomaterials including Multi walled Carbon Nanotube (MWNT), nano-clay and nano-alumina. DDT and PCBs are of significant concern due their high toxicity and long environmental half-lives. Experiments were conducted using batch adsorption procedures at different DDT and PCBs concentrations, from 10 to 60 mg/L. The amounts of MWNT, nano-clay and Nano-alumina used were 0.25%, 0.50%, 0.75%, 1%, 2% and 10%. The adsorption of PCBs solution onto the MWNT, nano-clay and nano-alumina was characterized by an initial rapid adsorption which eventually became constant within 22, 20, and 17 hours, respectively. The adsorption of DDT solution onto the MWNT, nano-clay and nano-alumina was also characterized by an initial rapid adsorption which gradually became constant within 22, 22 and 16 hours, respectively. Results of this study indicated that MWNT was a better adsorbent material compared to nano-clay and nano-alumina for both contaminants in this study. While at 10% of MWNT 88.9% and 77% of DDT and PCB were removed by MWNT, respectively. The effect of pH and temperature were also investigated.

Adsorption of DDT and PCB by Nanomaterials from Residual Soil

PubMed Central

Taha, Mohd Raihan; Mobasser, Shariat

2015-01-01

This paper presents the findings of a study on adsorption of dichlorodiphenythreechloroethen (DDT) and polychlorinated biphenyls (PCBs) on three nanomaterials including Multi walled Carbon Nanotube (MWNT), nano-clay and nano-alumina. DDT and PCBs are of significant concern due their high toxicity and long environmental half-lives. Experiments were conducted using batch adsorption procedures at different DDT and PCBs concentrations, from 10 to 60 mg/L. The amounts of MWNT, nano-clay and Nano-alumina used were 0.25%, 0.50%, 0.75%, 1%, 2% and 10%. The adsorption of PCBs solution onto the MWNT, nano-clay and nano-alumina was characterized by an initial rapid adsorption which eventually became constant within 22, 20, and 17 hours, respectively. The adsorption of DDT solution onto the MWNT, nano-clay and nano-alumina was also characterized by an initial rapid adsorption which gradually became constant within 22, 22 and 16 hours, respectively. Results of this study indicated that MWNT was a better adsorbent material compared to nano-clay and nano-alumina for both contaminants in this study. While at 10% of MWNT 88.9% and 77% of DDT and PCB were removed by MWNT, respectively. The effect of pH and temperature were also investigated. PMID:26659225

Development of a constant surface pressure penetration langmuir balance based on axisymmetric drop shape analysis.

PubMed

Wege, H A; Holgado-Terriza, J A; Cabrerizo-Vílchez, M A

2002-05-15

A new constant pressure pendant-drop penetration surface balance has been developed combining a pendant-drop surface balance, a rapid-subphase-exchange technique, and a fuzzy logic control algorithm. Beside the determination of insoluble monolayer compression-expansion isotherms, it allows performance of noninvasive kinetic studies of the adsorption of surfactants added to the new subphase onto the free surface and of the adsorption/penetration/reaction of the former onto/into/with surface layers, respectively. The interfacial pressure pi is a fundamental parameter in these studies: by working at constant pi one controls the height of the energy barrier to adsorption/penetration and can select different regimes and steps of the adsorption/penetration process. In our device a solution drop is formed at the tip of a coaxial double capillary, connected to a double microinjector. Drop profiles are extracted from digital drop micrographs and fitted to the equation of capillarity, yielding pi, the drop volume V, and the interfacial area A. pi is varied changing V (and hence A) with the microinjector. Control is based on a case-adaptable modulated fuzzy-logic PID algorithm able to maintain constant pi (or A) under a wide range of experimental conditions. The drop subphase liquid can be exchanged quantitatively by the coaxial capillaries. The adsorption/penetration/reaction kinetics at constant pi are then studied monitoring A(t), i.e., determining the relative area change necessary at each instant to compensate the pressure variation due to the interaction of the surfactant in the subsurface with the surface layer. A fully Windows-integrated program manages the whole setup. Examples of experimental protein adsorption and monolayer penetration kinetics are presented.

Influence of clay on the adsorption of heavy metals like copper and cadmium on chitosan.

PubMed

Prakash, Nagan; Latha, Srinivasan; Sudha, Persu N; Renganathan, N Gopalan

2013-02-01

The influence of clay on the adsorption of heavy metals like copper and cadmium on chitosan from simulated industrial wastewater is evaluated. Chitosan-clay blend with ratio of (1:1), (1:2), and (2:1) have been prepared, and these were used as membranes to remove copper and cadmium ions from synthetic industrial wastewater. The chemical parameters for quantities of adsorption of heavy metal contamination have been done, and the kinetics of adsorption has also been carried out. Clay provides enough absorbable sites to overcome mass transfer limitations. The number of absorbable sites for cadmium is more compared to copper, and thus the rate of recovery of cadmium is faster than copper, and the percentage removal of cadmium is more than copper at all times on clay over nylon 6. This difference indicates the influence of clay in the adsorption of heavy metals in comparison to synthetic polymer nylon 6. Rate constant for first-order kinetics of adsorption, k (1), for copper and cadmium is less than that of clay, which clearly indicates that clay, which is a natural polymer, is more kinetically favored compared to synthetic polymer. The difference in the intraparticle diffusion in both the natural and synthetic polymer is not much, and it suggests that the particle diffusion mechanism is the same in both cases. Copper and cadmium recovery is parallel at all times. The percentage of removal of copper increased with an increase in pH from 3 to 5. In the case of cadmium containing wastewater, the maximum removal of metal occurred at pH 5. The uptake amount of Cu(2+) ions on chitosan increased rapidly with increasing the contact time from 0 to 360 min and then reaches equilibrium after 360 min, and the equilibrium constant for copper and cadmium ions are more or less the same for the adsorption reaction. There are more adsorption sites for cadmium in the presence of clay and mass transfer limitation is avoided without resorting to rotation, which is the highlight of the

Application of surface complexation models to anion adsorption by natural materials

USDA-ARS?s Scientific Manuscript database

Various chemical models of ion adsorption will be presented and discussed. Chemical models, such as surface complexation models, provide a molecular description of anion adsorption reactions using an equilibrium approach. Two such models, the constant capacitance model and the triple layer model w...

Multi-target QSPR modeling for simultaneous prediction of multiple gas-phase kinetic rate constants of diverse chemicals

NASA Astrophysics Data System (ADS)

Basant, Nikita; Gupta, Shikha

2018-03-01

The reactions of molecular ozone (O3), hydroxyl (•OH) and nitrate (NO3) radicals are among the major pathways of removal of volatile organic compounds (VOCs) in the atmospheric environment. The gas-phase kinetic rate constants (kO3, kOH, kNO3) are thus, important in assessing the ultimate fate and exposure risk of atmospheric VOCs. Experimental data for rate constants are not available for many emerging VOCs and the computational methods reported so far address a single target modeling only. In this study, we have developed a multi-target (mt) QSPR model for simultaneous prediction of multiple kinetic rate constants (kO3, kOH, kNO3) of diverse organic chemicals considering an experimental data set of VOCs for which values of all the three rate constants are available. The mt-QSPR model identified and used five descriptors related to the molecular size, degree of saturation and electron density in a molecule, which were mechanistically interpretable. These descriptors successfully predicted three rate constants simultaneously. The model yielded high correlations (R2 = 0.874-0.924) between the experimental and simultaneously predicted endpoint rate constant (kO3, kOH, kNO3) values in test arrays for all the three systems. The model also passed all the stringent statistical validation tests for external predictivity. The proposed multi-target QSPR model can be successfully used for predicting reactivity of new VOCs simultaneously for their exposure risk assessment.

Real-time association rate constant measurement using combination tapered fiber-optic biosensor (CTFOB) dip-probes

NASA Astrophysics Data System (ADS)

Simmonds, Boris; Wang, Chun-Wei; Kapoor, Rakesh

2010-02-01

This document reports a novel method of measuring association rate constant (ka) for antibody-antigen interaction using evanescent wave-based combination tapered fiber-optic biosensor (CTFOB) dip-probes. The method was demonstrated by measuring association rate constant for bovine serum albumin (BSA) and anti-BSA antibody interaction. "Direct method" was used for detection; goat anti-BSA "capture" antibodies were immobilized on the probe surfaces while the antigen (BSA) was directly labeled with Alexa 488 dye. The probes were subsequently submerged in 3nM Labeled BSA in egg albumin (1 mg/ml). The fluorescence signal recorded was proportional to BSA anti-BSA conjugates and continuous signal was acquired suing a fiber optic spectrometer (Ocean Optics, Inc.). A 476 nm diode laser was use as an excitation source. Association constant was estimated from a plot of signal as a function of time. Measured association rate constant ka for the binding of BSA with anti-BSA at room temperature is (8.33 +/- 0.01) x 104 M-1s-1.

A new analytical method for estimating lumped parameter constants of linear viscoelastic models from strain rate tests

NASA Astrophysics Data System (ADS)

Mattei, G.; Ahluwalia, A.

2018-04-01

We introduce a new function, the apparent elastic modulus strain-rate spectrum, E_{app} ( \\dot{ɛ} ), for the derivation of lumped parameter constants for Generalized Maxwell (GM) linear viscoelastic models from stress-strain data obtained at various compressive strain rates ( \\dot{ɛ}). The E_{app} ( \\dot{ɛ} ) function was derived using the tangent modulus function obtained from the GM model stress-strain response to a constant \\dot{ɛ} input. Material viscoelastic parameters can be rapidly derived by fitting experimental E_{app} data obtained at different strain rates to the E_{app} ( \\dot{ɛ} ) function. This single-curve fitting returns similar viscoelastic constants as the original epsilon dot method based on a multi-curve global fitting procedure with shared parameters. Its low computational cost permits quick and robust identification of viscoelastic constants even when a large number of strain rates or replicates per strain rate are considered. This method is particularly suited for the analysis of bulk compression and nano-indentation data of soft (bio)materials.

Adsorption of calcitonin to glass.

PubMed

Law, S L; Shih, C L

1999-02-01

Surface adsorption of calcitonin on soda lime silica glass was investigated. An attempt was also made to examine the effect of additives on the inhibition of calcitonin adsorption. Results showed that the adsorption isotherms were of the Langmuir and Freundlich type, depending on pH. Less adsorption was found for calcitonin at pH 4.3. The addition of nonionic surfactants such as Pluronic F68 and Tween 80 to the calcitonin solutions demonstrated inhibition of absorption and reduction of adsorption rate. The addition of chlorobutanol also showed the effect of minimizing adsorption.

Investigation into adsorption and photocatalytic degradation of gaseous benzene in an annular fluidized bed photocatalytic reactor.

PubMed

Geng, Qijin; Tang, Shankang; Wang, Lintong; Zhang, Yunchen

2015-01-01

The adsorption and photocatalytic degradation of gaseous benzene were investigated considering the operating variables and kinetic mechanism using nano-titania agglomerates in an annular fluidized bed photocatalytic reactor (AFBPR) designed. The special adsorption equilibrium constant, adsorption active sites, and apparent reaction rate coefficient of benzene were determined by linear regression analysis at various gas velocities and relative humidities (RH). Based on a series of photocatalytic degradation kinetic equations, the influences of operating variables on degradation efficiency, apparent reaction rate coefficient and half-life were explored. The findings indicated that the operating variables have obviously influenced the adsorption/photocatalytic degradation and corresponding kinetic parameters. In the photocatalytic degradation process, the relationship between photocatalytic degradation efficiency and RH indicated that water molecules have a dual-function which was related to the structure characteristics of benzene. The optimal operating conditions for photocatalytic degradation of gaseous benzene in AFBPR were determined as the fluidization number at 1.9 and RH required related to benzene concentration. This investigation highlights the importance of controlling RH and benzene concentration in order to obtain the desired synergy effect in photocatalytic degradation processes.

Adsorption Properties of Tetracycline onto Graphene Oxide: Equilibrium, Kinetic and Thermodynamic Studies

PubMed Central

Ghadim, Ehsan Ezzatpour; Manouchehri, Firouzeh; Soleimani, Gholamreza; Hosseini, Hadi; Kimiagar, Salimeh; Nafisi, Shohreh

2013-01-01

Graphene oxide (GO) nanoparticle is a high potential effective absorbent. Tetracycline (TC) is a broad-spectrum antibiotic produced, indicated for use against many bacterial infections. In the present research, a systematic study of the adsorption and release process of tetracycline on GO was performed by varying pH, sorption time and temperature. The results of our studies showed that tetracycline strongly loads on the GO surface via π–π interaction and cation–π bonding. Investigation of TC adsorption kinetics showed that the equilibrium was reached within 15 min following the pseudo-second-order model with observed rate constants of k2 = 0.2742–0.5362 g/mg min (at different temperatures). The sorption data has interpreted by the Langmuir model with the maximum adsorption of 323 mg/g (298 K). The mean energy of adsorption was determined 1.83 kJ/mol (298 K) based on the Dubinin–Radushkevich (D–R) adsorption isotherm. Moreover, the thermodynamic parameters such as ΔH°, ΔS° and ΔG° values for the adsorption were estimated which indicated the endothermic and spontaneous nature of the sorption process. The electrochemistry approved an ideal reaction for the adsorption under electrodic process. Simulation of GO and TC was done by LAMMPS. Force studies in z direction showed that tetracycline comes close to GO sheet by C8 direction. Then it goes far and turns and again comes close from amine group to the GO sheet. PMID:24302989

Adsorption properties of tetracycline onto graphene oxide: equilibrium, kinetic and thermodynamic studies.

PubMed

Ghadim, Ehsan Ezzatpour; Manouchehri, Firouzeh; Soleimani, Gholamreza; Hosseini, Hadi; Kimiagar, Salimeh; Nafisi, Shohreh

2013-01-01

Graphene oxide (GO) nanoparticle is a high potential effective absorbent. Tetracycline (TC) is a broad-spectrum antibiotic produced, indicated for use against many bacterial infections. In the present research, a systematic study of the adsorption and release process of tetracycline on GO was performed by varying pH, sorption time and temperature. The results of our studies showed that tetracycline strongly loads on the GO surface via π-π interaction and cation-π bonding. Investigation of TC adsorption kinetics showed that the equilibrium was reached within 15 min following the pseudo-second-order model with observed rate constants of k2 = 0.2742-0.5362 g/mg min (at different temperatures). The sorption data has interpreted by the Langmuir model with the maximum adsorption of 323 mg/g (298 K). The mean energy of adsorption was determined 1.83 kJ/mol (298 K) based on the Dubinin-Radushkevich (D-R) adsorption isotherm. Moreover, the thermodynamic parameters such as ΔH°, ΔS° and ΔG° values for the adsorption were estimated which indicated the endothermic and spontaneous nature of the sorption process. The electrochemistry approved an ideal reaction for the adsorption under electrodic process. Simulation of GO and TC was done by LAMMPS. Force studies in z direction showed that tetracycline comes close to GO sheet by C8 direction. Then it goes far and turns and again comes close from amine group to the GO sheet.

Carboxylate-containing chelating agent interactions with amorphous chromium hydroxide: Adsorption and dissolution

NASA Astrophysics Data System (ADS)

Carbonaro, Richard F.; Gray, Benjamin N.; Whitehead, Charles F.; Stone, Alan T.

2008-07-01

Anthropogenic chelating agents and biological chelating agents produced by indigenous organisms may dissolve Cr III (hydr)oxides in soils and sediments. The resulting dissolved Cr III-chelating agent complexes are more readily transported through porous media, thereby spreading contamination. With this work, we examine chelating agent-assisted dissolution of amorphous chromium hydroxide (ACH) by the (amino)carboxylate chelating agents iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), tricarballylic acid (TCA), citric acid (CIT), ethylenediaminetetraacetic acid (EDTA), trans-1,2-cyclohexanediaminetetraacetic acid (CDTA), and trimethylenediaminetetraacetic acid (TMDTA). The extent of chelating agent adsorption onto ACH increased quickly over the first few hours, and then increased more gradually until a constant extent was attained. The extent of chelating agent adsorption versus pH followed "ligand-like" behavior. All chelating agents with the exception of TCA and IDA effectively dissolved significant amounts of ACH within 10 days from pH 4.0 to 9.4. IDA dissolved ACH below pH 6.5 and above pH 7.5. Rates of ACH dissolution normalized to the extent of chelating agent adsorption were pH dependent. IDA, NTA, CIT, and CDTA exhibited an increase in normalized dissolution rate with decreasing pH. EDTA and TMDTA exhibited a maximum in normalized dissolution rate near pH 8.5. Use of acetic acid as a pH buffer in experiments decreased the extent of chelating agent adsorption for IDA, NTA, and CIT but increased normalized rates of chelating agent-assisted dissolution for all chelating agents except EDTA. The results from this study provide the necessary information to calculate the extents and time scales of ACH dissolution in the presence of (amino)carboxylate chelating agents.

Studies of the water adsorption on Lampung’s natural zeolite of Indonesia for cooling application

NASA Astrophysics Data System (ADS)

Wulandari, D. A.; Nasruddin; Lemington

2018-03-01

Part of minerals that originally formed from volcanic rock and ash layers reacting further with alkaline groundwater is called natural zeolite, where its sources are not always available in all countries. Indonesia is located in the ring of fire which have a huge sources of zeolite, one of the area is Lampung, South Sumatra. Natural zeolite has been considered as one of potential heat adsorbent medium which can contribute to the energy consumption and reduce air pollution in the using of cooling application. The characteristic of this Lampung natural zeolite such as adsorption kinetics, adsorption water uptake, and adsorption capacity were test with ASAP 2020 system. Sorption kinetics by this experiment of zeolite samples were carried out in a constant temperature and humidity chamber. The chamber can supply constant air condition with deviations of ±0.5 °C for temperature and ±3% for relative humidity. The data based on rate of adsorption and the defined working condition was set as 20°C and 70% RH. Pore volume is a significant parameter for determining the limitation of water uptake, which can describe the saturated condition of zeolite. Sorption isotherm models used to describe sorption phenomena are commonly deduced from the Polanyi potential theory were investigated. The water adsorption quantity increased with the increase of relative pressure. To sum up, this pure zeolite has a less heat and mass transfer performance so its need to be activated before using in cooling application to get their great potential and by being coated in a desiccant heat exchanger systems.

Annealed importance sampling with constant cooling rate

NASA Astrophysics Data System (ADS)

Giovannelli, Edoardo; Cardini, Gianni; Gellini, Cristina; Pietraperzia, Giangaetano; Chelli, Riccardo

2015-02-01

Annealed importance sampling is a simulation method devised by Neal [Stat. Comput. 11, 125 (2001)] to assign weights to configurations generated by simulated annealing trajectories. In particular, the equilibrium average of a generic physical quantity can be computed by a weighted average exploiting weights and estimates of this quantity associated to the final configurations of the annealed trajectories. Here, we review annealed importance sampling from the perspective of nonequilibrium path-ensemble averages [G. E. Crooks, Phys. Rev. E 61, 2361 (2000)]. The equivalence of Neal's and Crooks' treatments highlights the generality of the method, which goes beyond the mere thermal-based protocols. Furthermore, we show that a temperature schedule based on a constant cooling rate outperforms stepwise cooling schedules and that, for a given elapsed computer time, performances of annealed importance sampling are, in general, improved by increasing the number of intermediate temperatures.

Adsorption, desorption, and removal of polymeric nanomedicine on and from cellulose surfaces: effect of size.

PubMed

Zhang, Ming; Akbulut, Mustafa

2011-10-18

The increased production and commercial use of nanoparticulate drug delivery systems combined with a lack of regulation to govern their disposal may result in their introduction to soils and ultimately into groundwater systems. To better understand how such particles interact with environmentally significant interfaces, we study the adsorption, desorption, and removal behavior of poly(ethylene glycol)-based nanoparticulate drug delivery systems on and from cellulose, which is the most common organic compound on Earth. It is shown that such an adsorption process is only partially reversible, and most of the adsorbate particles do not desorb from the cellulose surface even upon rinsing with a large amount of water. The rate constant of adsorption decreases with increasing particle size. Furthermore, hydrodynamic forces acting parallel to the surfaces are found to be of great importance in the context of particle dynamics near the cellulose surface, and ultimately responsible for the removal of some fraction of particles via rolling or sliding. As the particle size increases, the removal rates of the particles increase for a given hydrodynamical condition. © 2011 American Chemical Society

Adsorption and desorption characteristics of endosulfan in two typical agricultural soils in Southwest China.

PubMed

Qian, Sheng; Zhu, Heng; Xiong, Bailian; Zheng, Guocan; Zhang, Jinzhong; Xu, Weihong

2017-04-01

Endosulfan is an organochlorine pesticide widely used in Southwest China. In this paper, the adsorption and desorption characteristics of endosulfan in two typical agricultural soils (latosol and lateritic red soil) in this area were studied. The results showed that Langmuir isothermal equation could well describe the adsorption thermodynamic characteristics of endosulfan in latosol and lateritic red soil, and the maximum adsorption capacities of α-endosulfan were 0.186 and 0.209 mg/g, while those of β-endosulfan were 0.140 and 0.148 mg/g, respectively. Endosulfan adsorption in the two soils was an exothermic physicochemical process, but dominated by physical process. The adsorption kinetic characteristics of endosulfan in the two soils could be well described by second-order kinetic equation, and the initial rate constants were 0.228 and 0.325 mg/(g min) for α-endosulfan, while those were 0.119 and 0.125 mg/(g min) for β-endosulfan, respectively. The adsorbed endosulfan in the two soils was difficult to be desorbed into the liquid phase, and showed weak desorption hysteresis. These results implied that endosulfan could be firmly adsorbed by the two soils, and their adsorption and desorption abilities may be related to the contents of soil clay and organic matter.

On the ambiguity of the reaction rate constants in multivariate curve resolution for reversible first-order reaction systems.

PubMed

Schröder, Henning; Sawall, Mathias; Kubis, Christoph; Selent, Detlef; Hess, Dieter; Franke, Robert; Börner, Armin; Neymeyr, Klaus

2016-07-13

If for a chemical reaction with a known reaction mechanism the concentration profiles are accessible only for certain species, e.g. only for the main product, then often the reaction rate constants cannot uniquely be determined from the concentration data. This is a well-known fact which includes the so-called slow-fast ambiguity. This work combines the question of unique or non-unique reaction rate constants with factor analytic methods of chemometrics. The idea is to reduce the rotational ambiguity of pure component factorizations by considering only those concentration factors which are possible solutions of the kinetic equations for a properly adapted set of reaction rate constants. The resulting set of reaction rate constants corresponds to those solutions of the rate equations which appear as feasible factors in a pure component factorization. The new analysis of the ambiguity of reaction rate constants extends recent research activities on the Area of Feasible Solutions (AFS). The consistency with a given chemical reaction scheme is shown to be a valuable tool in order to reduce the AFS. The new methods are applied to model and experimental data. Copyright © 2016 Elsevier B.V. All rights reserved.

Temperature-Dependent Rate Constants and Substituent Effects for the Reactions of Hydroxyl Radicals With Three Partially Fluorinated Ethers

NASA Technical Reports Server (NTRS)

Hsu, K.-J.; DeMore, W. B.

1995-01-01

Rate constants and temperature dependencies for the reactions of OH with CF3OCH3 (HFOC-143a), CF2HOCF2H (HFOC-134), and CF3OCF2H (HFOC-125) were studied using a relative rate technique in the temperature range 298-393 K. The following absolute rate constants were derived: HFOC-143a, 1.9E-12 exp(-1555/T); HFOC-134, 1.9E-12 exp(-2006/T); HFOC-125, 4.7E-13 exp(-2095/T). Units are cm(exp 3)molecule(exp -1) s(exp -1). Substituent effects on OH abstraction rate constants are discussed, and it is shown that the CF3O group has an effect on the OH rate constants similar to that of a fluorine atom. The effects are related to changes in the C-H bond energies of the reactants (and thereby the activation energies) rather than changes in the preexponential factors. On the basis of a correlation of rate constants with bond energies, the respective D(C-H) bond strengths in the three ethers are found to be 102, 104, and 106 kcal/mol, with an uncertainty of about 1 kcal/mol.

[Influence of Three Low-Molecular-Weight Organic Acids on the Adsorption of Phenanthrene in Purple Soil].

PubMed

Xie, Li; Chen, Ben-shou; Zhang, Jin-zhong; Lu, Song; Jiang, Tao

2016-03-15

The effects of three low-molecular-weight organic acids (citric acid, malic acid and oxalic acid) on the adsorption of phenanthrene in purple soil were studied by static adsorption experiment. The results showed that the adsorption kinetic process of phenanthrene in purple soil could be described by the second-order kinetic model, and the adsorption rate constant would significantly decrease in the presence of the three low-molecular-weight organic acids ( LMWOAs). The adsorption thermodynamic process could be well described by linear adsorption model, which was dominated by distribution role. The three LMWOAs could promote the adsorption of phenantherene in purple soil when their concentrations were less than 5 mmol · L⁻¹, whereas inhibit the adsorption when their concentrations were more than 10 mmol · L⁻¹, and the inhibition would increase with increasing concentrations. Moreover, the inhibitory ability displayed a decreasing order of citric acid, oxalic acid, and malic acid when their concentrations were 20 mmol · L⁻¹, which is related to the molecular structure and acidity of the three LMWOAs. Compared with the control, the content of dissolved organic matter (DOM) released from purple soil showed a trend of first decrease and then increase with increasing LMWOAs concentration, and the adsorption capacity of phenanthrene in purple soil was negatively related to DOM content.

Adsorption of xenon and krypton on shales

NASA Technical Reports Server (NTRS)

Podosek, F. A.; Bernatowicz, T. J.; Kramer, F. E.

1981-01-01

A method that uses a mass spectrometer as a manometer is employed in the measurement of Xe and Kr adsorption parameters on shales and related samples, where gas partial pressures were lower than 10 to the -11th atm, corresponding adsorption coverages are only small fractions of a monolayer, and Henry's Law behavior is expected and observed. Results show heats of adsorption in the 2-7 kcal/mol range, and Henry constants at 0-25 C of 1 cu cm STP/g per atmosphere are extrapolated. Although the adsorption properties obtained are variable by sample, the range obtained suggests that shales may be capable of an equilibrium adsorption with modern air high enough to account for a significant fraction of the atmospheric inventory of Xe, and perhaps even of Kr. This effect will nevertheless not account for the factor-of-25 defficiency of atmospheric Xe, in comparison with the planetary gas patterns observed in meteorites.

Modeling crystal growth from solution with molecular dynamics simulations: approaches to transition rate constants.

PubMed

Reilly, Anthony M; Briesen, Heiko

2012-01-21

The feasibility of using the molecular dynamics (MD) simulation technique to study crystal growth from solution quantitatively, as well as to obtain transition rate constants, has been studied. The dynamics of an interface between a solution of Lennard-Jones particles and the (100) face of an fcc lattice comprised of solute particles have been studied using MD simulations, showing that MD is, in principle, capable of following growth behavior over large supersaturation and temperature ranges. Using transition state theory, and a nearest-neighbor approximation growth and dissolution rate constants have been extracted from equilibrium MD simulations at a variety of temperatures. The temperature dependence of the rates agrees well with the expected transition state theory behavior. © 2012 American Institute of Physics

Protein adsorption to poly(ethylenimine)-modified Sepharose FF: VI. Partial charge neutralization drastically increases uptake rate.

PubMed

Zhao, Yangyang; Dong, Xiaoyan; Yu, Linling; Sun, Yan

2016-01-04

The adsorption and elution behaviors of bovine serum albumin (BSA) on poly(ethylenimine) (PEI)-grafted Sepharose FF resins were recently studied and a critical ionic capacity (cIC; 600 mmol/L) was found, above which the uptake rate increased drastically due to the occurrence of significant "chain delivery" effect. Moreover, above the cIC value, higher salt concentrations were required for protein elution due to the high charge density of the resins. In this work, we have reduced the charge density on the PEI chains of a PEI-grafted resin by neutralization of the amine groups with sodium acetate. PEI-modified resin with IC of 740 mmol/L (FF-PEI-L740, IC>cIC) was chosen as the starting material, and three resins with residual IC values of 660, 560 and 440 mmol/L (FF-PEI-R440) were obtained. The adsorption and chromatographic behaviors of these resins for BSA were investigated. It was found that, with IC decreasing from 740 to 440 mmol/L, the adsorption capacity kept almost unchanged; the effective protein diffusivity (De) also showed negligible variations as IC decreased from 740 to 560 mmol/L (De/D0=0.38 ± 0.04). However, it was interesting to observe a three-fold increase of the De value for FF-PEI-R440 (De/D0=1.23 ± 0.08). It is considered that the occurrence of the drastic uptake rate increase in FF-PEI-R440 was attributed to the decreased available binding sites for protein molecule, which led to the decrease of binding strength, thus facilitated the happenings of "chain delivery" effect of bound proteins. Besides, a study on the effect of ionic strength clarified that the lower the IC value, the higher the sensitivity of protein binding to salt concentration due to the easily screened electrostatic interactions at low surface charge densities. The ionic strength at the elution peak also decreased with decreasing IC in accordance with the salt sensitivity order. Column breakthrough studies demonstrated that the dynamic adsorption capacity of FF-PEI-R440 was

ESTIMATION OF PHOSPHATE ESTER HYDROLYSIS RATE CONSTANTS. II. ACID AND GENERAL BASE CATALYZED HYDROLYSIS

EPA Science Inventory

SPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to calculate acid and neutral hydrolysis rate constants of phosphate esters in water. The rate is calculated from the energy difference between the initial and transition states of a ...

Laser Measurements of the H Atom + Ozone Rate Constant at Atmospheric Temperatures

NASA Astrophysics Data System (ADS)

Liu, Y.; Smith, G. P.; Peng, J.; Reppert, K. J.; Callahan, S. L.

2015-12-01

The exothermic H + O3 reaction produces OH(v) Meinel band emissions, used to derive mesospheric H concentrations and chemical heating rates. We have remeasured its rate constant to reduce resulting uncertainties and the measurement extend to lower mesospheric temperatures using modern laser techniques. H atoms are produced by pulsed ultraviolet laser trace photolysis of O3, followed by reaction of O(D) with added H2. A second, delayed, frequency-mixed dye laser measures the reaction decay rate with the remaining ozone by laser induced fluorescence. We monitor either the H atom decay by 2 photon excitation at 205 nm and detection of red fluorescence, or the OH(v=9) product time evolution with excitation of the B-X (0,9) band at 237 nm and emission in blue B-A bands. By cooling the enclosed low pressure flow cell we obtained measurements from 146-305 K. Small kinetic modeling corrections are made for secondary regeneration of H atoms. The results fully confirm the current NASA JPL recommendation for this rate constant, and establish its extrapolation down to the lower temperatures of the mesosphere. This work was supported by the NSF Aeronomy Program and an NSF Physics summer REU student grant.

Free Radical Chemistry of Disinfection Byproducts 2: Rate Constants and Degradation Mechanism of Trichloronitromethane (Chloropicrin)

DOE Office of Scientific and Technical Information (OSTI.GOV)

B. J. Mincher; S. K. Cole; W. J. Cooper

2007-02-01

Absolute rate constants for the free-radical-induced degradation of trichloronitromethane (TCNM, chloropicrin) were determined using electron pulse radiolysis and transient absorption spectroscopy. Rate constants for hydroxyl radical, OH, and hydrated electron, eaq-, reactions were (4.97 ± 0.28) × 107 M-1 s-1 and (2.13 ± 0.03) × 1010 M-1 s-1, respectively. It appears that the OH adds to the nitro-group, while the eaq- reacts via dissociative electron attachment to give two carbon centered radicals. The mechanisms of these free radical reactions with TCNM were investigated, using 60Co gamma irradiation at various absorbed doses, measuring the disappearance of TCNM and the appearance ofmore » the product nitrate and chloride ions. The rate constants and mechanistic data were combined in a kinetic computer model that was used to describe the major free radical pathways for the destruction of TCNM in solution. These data are applicable to other advanced oxidation/reduction processes.« less

Unsteady flow past an airfoil pitched at constant rate

NASA Technical Reports Server (NTRS)

Lourenco, L.; Vandommelen, L.; Shib, C.; Krothapalli, A.

1992-01-01

The unsteady flow past a NACA 0012 airfoil that is undertaking a constant-rate pitching up motion is investigated experimentally by the PIDV technique in a water towing tank. The Reynolds number is 5000, based upon the airfoil's chord and the free-stream velocity. The airfoil is pitching impulsively from 0 to 30 deg. with a dimensionless pitch rate alpha of 0.131. Instantaneous velocity and associated vorticity data have been acquired over the entire flow field. The primary vortex dominates the flow behavior after it separates from the leading edge of the airfoil. Complete stall emerges after this vortex detaches from the airfoil and triggers the shedding of a counter-rotating vortex near the trailing edge. A parallel computational study using the discrete vortex, random walk approximation has also been conducted. In general, the computational results agree very well with the experiment.

Linear free energy relationships between aqueous phase hydroxyl radical reaction rate constants and free energy of activation.

PubMed

Minakata, Daisuke; Crittenden, John

2011-04-15

The hydroxyl radical (HO(•)) is a strong oxidant that reacts with electron-rich sites on organic compounds and initiates complex radical chain reactions in aqueous phase advanced oxidation processes (AOPs). Computer based kinetic modeling requires a reaction pathway generator and predictions of associated reaction rate constants. Previously, we reported a reaction pathway generator that can enumerate the most important elementary reactions for aliphatic compounds. For the reaction rate constant predictor, we develop linear free energy relationships (LFERs) between aqueous phase literature-reported HO(•) reaction rate constants and theoretically calculated free energies of activation for H-atom abstraction from a C-H bond and HO(•) addition to alkenes. The theoretical method uses ab initio quantum mechanical calculations, Gaussian 1-3, for gas phase reactions and a solvation method, COSMO-RS theory, to estimate the impact of water. Theoretically calculated free energies of activation are found to be within approximately ±3 kcal/mol of experimental values. Considering errors that arise from quantum mechanical calculations and experiments, this should be within the acceptable errors. The established LFERs are used to predict the HO(•) reaction rate constants within a factor of 5 from the experimental values. This approach may be applied to other reaction mechanisms to establish a library of rate constant predictions for kinetic modeling of AOPs.

Perfluorooctane sulfonate adsorption on powder activated carbon: Effect of phosphate (P) competition, pH, and temperature.

PubMed

Qian, Jin; Shen, Mengmeng; Wang, Peifang; Wang, Chao; Li, Kun; Liu, Jingjing; Lu, Bianhe; Tian, Xin

2017-09-01

Powdered activated carbon (PAC), as an adsorbent, was applied to remove perfluorooctane sulfonate (PFOS) from aqueous solution. Laboratory batch experiments were performed to investigate the influences of phosphate (P) competition, temperature, and pH for PFOS adsorption onto PAC. The results showed that higher temperature favored PFOS adsorption in single and binary systems. The kinetic data fitted very well to the pseudo second-order kinetic model. Thermodynamically, the endothermic enthalpy of the PFOS adsorption in single and binary systems were 125.07 and 21.25 kJ mol -1 , respectively. The entropy of the PFOS adsorption in single and binary systems were 0.479 and 0.092 kJ mol -1  K -1 , respectively. And the Gibbs constants were negative. These results indicated that the adsorption processes were spontaneous. The adsorption isotherms of PFOS agreed well with the Langmuir model. In the single system, PFOS adsorption decreased with increased pH value. The difference in the amount of PFOS adsorption between the single and binary systems increased at higher pH. Frustrated total internal reflection (FTIR) demonstrated that P competition increased the hydrophilicity of the PAC and the electrostatic repulsion between PFOS and PAC, then the PFOS adsorption amount decreased. It also demonstrated that, at higher temperature, increased PFOS adsorption was mainly due to the higher diffusion rate of PFOS molecules and greater number of active sites opened on the PAC surface. Copyright © 2017 Elsevier Ltd. All rights reserved.

Constant growth rate can be supported by decreasing energy flux and increasing aerobic glycolysis.

PubMed

Slavov, Nikolai; Budnik, Bogdan A; Schwab, David; Airoldi, Edoardo M; van Oudenaarden, Alexander

2014-05-08

Fermenting glucose in the presence of enough oxygen to support respiration, known as aerobic glycolysis, is believed to maximize growth rate. We observed increasing aerobic glycolysis during exponential growth, suggesting additional physiological roles for aerobic glycolysis. We investigated such roles in yeast batch cultures by quantifying O2 consumption, CO2 production, amino acids, mRNAs, proteins, posttranslational modifications, and stress sensitivity in the course of nine doublings at constant rate. During this course, the cells support a constant biomass-production rate with decreasing rates of respiration and ATP production but also decrease their stress resistance. As the respiration rate decreases, so do the levels of enzymes catalyzing rate-determining reactions of the tricarboxylic-acid cycle (providing NADH for respiration) and of mitochondrial folate-mediated NADPH production (required for oxidative defense). The findings demonstrate that exponential growth can represent not a single metabolic/physiological state but a continuum of changing states and that aerobic glycolysis can reduce the energy demands associated with respiratory metabolism and stress survival. Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.

Microfabricated microengine with constant rotation rate

DOEpatents

Romero, Louis A.; Dickey, Fred M.

1999-01-01

A microengine uses two synchronized linear actuators as a power source and converts oscillatory motion from the actuators into constant rotational motion via direct linkage connection to an output gear or wheel. The microengine provides output in the form of a continuously rotating output gear that is capable of delivering drive torque at a constant rotation to a micromechanism. The output gear can have gear teeth on its outer perimeter for directly contacting a micromechanism requiring mechanical power. The gear is retained by a retaining means which allows said gear to rotate freely. The microengine is microfabricated of polysilicon on one wafer using surface micromachining batch fabrication.

Rate Constants for the Reactions of Hydroxyl Radical with Several Alkanes, Cycloalkanes, and Dimethyl Ether

NASA Technical Reports Server (NTRS)

DeMore, W.; Bayes, K.

1998-01-01

Relative rate experiements were used to measure rate constants and temperature denpendencies of the reactions of OH with propane, n-butane, n-pentane, n-hexane, cyclopropane, cyclobutane, cyclopentane, and dimethyl ether.

Rapid estimation of glucosinolate thermal degradation rate constants in leaves of Chinese kale and broccoli (Brassica oleracea) in two seasons.

PubMed

Hennig, Kristin; Verkerk, Ruud; Bonnema, Guusje; Dekker, Matthijs

2012-08-15

Kinetic modeling was used as a tool to quantitatively estimate glucosinolate thermal degradation rate constants. Literature shows that thermal degradation rates differ in different vegetables. Well-characterized plant material, leaves of broccoli and Chinese kale plants grown in two seasons, was used in the study. It was shown that a first-order reaction is appropriate to model glucosinolate degradation independent from the season. No difference in degradation rate constants of structurally identical glucosinolates was found between broccoli and Chinese kale leaves when grown in the same season. However, glucosinolate degradation rate constants were highly affected by the season (20-80% increase in spring compared to autumn). These results suggest that differences in glucosinolate degradation rate constants can be due to variation in environmental as well as genetic factors. Furthermore, a methodology to estimate rate constants rapidly is provided to enable the analysis of high sample numbers for future studies.

Kafirin adsorption on ion-exchange resins: isotherm and kinetic studies.

PubMed

Kumar, Prashant; Lau, Pei Wen; Kale, Sandeep; Johnson, Stuart; Pareek, Vishnu; Utikar, Ranjeet; Lali, Arvind

2014-08-22

Kafirin is a natural, hydrophobic and celiac safe prolamin protein obtained from sorghum seeds. Today kafirin is found to be useful in designing delayed delivery systems and coatings of pharmaceuticals and nutraceuticals where its purity is important and this can be obtained by adsorptive chromatography. This study is the first scientific insight into the isotherm and kinetic studies of kafirin adsorption on anion- and cation-exchange resins for practical applications in preparative scale chromatography. Adsorption isotherms of kafirin were determined for five anion- and two cation-exchange resins in batch systems. Isotherm parameters such as maximum binding capacity and dissociation constant were determined from Langmuir isotherm, and adsorptive capacity and affinity constant from Freundlich isotherm. Langmuir isotherm was found to fit the adsorption equilibrium data well. Batch uptake kinetics for kafirin adsorption on these resins was also carried out and critical parameters including the diffusion coefficient, film mass transfer coefficient, and Biot number for film-pore diffusion model were calculated. Both the isotherm and the kinetic parameters were considered for selection of appropriate resin for kafirin purification. UNOsphere Q (78.26 mg/ml) and Toyopearl SP-650M (57.4 mg/ml) were found to offer better kafirin binding capacities and interaction strength with excellent uptake kinetics under moderate operating conditions. With these adsorbents, film diffusion resistance was found to be major governing factor for adsorption (Bi<10 and δ<1). Based on designer objective function, UNOsphere Q was found be best adsorbent for binding of kafirin. The data presented is valuable for designing large scale preparative adsorptive chromatographic kafirin purification systems. Copyright © 2014 Elsevier B.V. All rights reserved.

Kinetic characteristics of Cu (II) adsorption on nano(poly)-cumulene

NASA Astrophysics Data System (ADS)

Babkin, Alexander; Neskoromnaya, Elena; Burakova, Irina; Kucherova, Ananstasia; Burakov, Alexander; Mkrtchyan, Elina

2017-11-01

The present paper considers the possibility of using a new type of nanocarbon materials for sorption - polycumulene modified with "Taunit-M" carbon nanotubes or graphene nanoplatelets. To evaluate the efficiency of these novel nanomodified materials as sorbents, the following studies were carried out: 1) determination of the optimum pH value to perform static batch sorption experiments, 2) identification of the onset of equilibrium for the adsorption of heavy metal ions (on the example of Cu(II) ions), and 3) elucidation of kinetic adsorption mechanisms. As a result of implementation of kinetic models such as external and internal diffusion, as well as pseudo-first- and pseudo-second-order and Elovich (to determine the contribution of chemisorption), rate constants for the Cu(II) adsorption were estimated. It was noted that the absorption process occurs in a mixed-diffusion mode with the influence of the limiting factor - "sorbate-sorbate" chemical interaction. The equilibrium time was found to be 45 min at the sorption capacity values of about 30.71 mg g-1 (in the case of the material containing carbon nanotubes) and about 24.7 mg g-1 (in the case of the material containing graphene nanoplatelets).

Effects of Humidity Swings on Adsorption Columns for Air Revitalization: Modeling and Experiments

NASA Technical Reports Server (NTRS)

LeVan, M. Douglas; Finn, John E.

1997-01-01

Air purification systems are necessary to provide clean air in the closed environments aboard spacecraft. Trace contaminants are removed using adsorption. One major factor concerning the removal of trace contaminants is relative humidity. Water can reduce adsorption capacity and, due to constant fluctuations, its presence is difficult to incorporate into adsorption column designs. The purpose of the research was to allow for better design techniques in trace contaminant adsorption systems, especially for feeds with water present. Experiments and mathematical modeling research on effects of humidity swings on adsorption columns for air revitalization were carried out.

A modified Poisson-Boltzmann equation applied to protein adsorption.

PubMed

Gama, Marlon de Souza; Santos, Mirella Simões; Lima, Eduardo Rocha de Almeida; Tavares, Frederico Wanderley; Barreto, Amaro Gomes Barreto

2018-01-05

Ion-exchange chromatography has been widely used as a standard process in purification and analysis of protein, based on the electrostatic interaction between the protein and the stationary phase. Through the years, several approaches are used to improve the thermodynamic description of colloidal particle-surface interaction systems, however there are still a lot of gaps specifically when describing the behavior of protein adsorption. Here, we present an improved methodology for predicting the adsorption equilibrium constant by solving the modified Poisson-Boltzmann (PB) equation in bispherical coordinates. By including dispersion interactions between ions and protein, and between ions and surface, the modified PB equation used can describe the Hofmeister effects. We solve the modified Poisson-Boltzmann equation to calculate the protein-surface potential of mean force, treated as spherical colloid-plate system, as a function of process variables. From the potential of mean force, the Henry constants of adsorption, for different proteins and surfaces, are calculated as a function of pH, salt concentration, salt type, and temperature. The obtained Henry constants are compared with experimental data for several isotherms showing excellent agreement. We have also performed a sensitivity analysis to verify the behavior of different kind of salts and the Hofmeister effects. Copyright © 2017 Elsevier B.V. All rights reserved.

Synthesis of Large-Pore Stabilized MIL-53(Al) Compounds with Increased CO2 Adsorption and Decreased Water Adsorption

DTIC Science & Technology

2014-01-01

increase in the quadrupolar coupling constant upon saturation with DMF for sDMF220, 8.4~10.1, and sDMF120, 8.2~10.1 compared to the increase in CQ...nonpolar methane . The CH4 adsorption isotherms for sH2O and sDMF220 shown in Fig. 5 also exhibit Type I behaviour. The CO2 adsorption isotherm for sH2O...Am. Chem. Soc., 2002, 124, 13519-13526. 15. T. Loiseau, C. Serre, C. Huguenard, G. Fink, F. Taulelle, M. Henry , T. Bataille and G. Ferey, Chem-Eur J

Absolute rate constant for the O plus NO chemiluminescence in the near infrared

NASA Technical Reports Server (NTRS)

Golde, M. F.; Roche, A. E.; Kaufman, F.

1973-01-01

Infrared chemiluminescence from the process O + NO (+M) NO2 + hv (+M) has been studied between 1.3 and 4.1 micrometer. The wavelength dependence of the continuum between 1.3 and 3.3 micrometer is in fair agreement with previous studies and the measured radiative rate constant at 1.51 micrometer establishes the NO-O glow in this spectral range as a secondary emission standard. Comparison with previous studies of the visible region of the glow implies that the overall radiative rate constant lies in the range (9.4 to 11.2) x 10 to the minus 17 power cu cm sec/1. In the region 3.3 to 4.1 micrometer, the previously observed broad band, peaking at 3.7 micrometer, shows a complex kinetic dependence on O and M.

Determination of acidity constants of curcumin in aqueous solution and apparent rate constant of its decomposition

NASA Astrophysics Data System (ADS)

Bernabé-Pineda, Margarita; Ramírez-Silva, María. Teresa; Romero-Romo, Mario; González-Vergara, Enrique; Rojas-Hernández, Alberto

2004-04-01

The stability of curcumin (H 3Cur) in aqueous media is improved when the systems in which it is present are at high pH values (higher than 11.7), fitting a model describable by a pseudo-zero order with a rate constant k' for the disappearance of the Cur 3- species of 1.39 (10 -9) M min -1. There were three acidity constants measured for the curcumin as follows: p KA3=10.51±0.01 corresponding to the equilibrium HCur 2-=Cur 3-+H +, a p KA2=9.88±0.02 corresponding to the equilibrium H 2Cur -=HCur -2+H +. These p KA values were attributed to the hydrogen of the phenol part of the curcumin, while the p KA1=8.38±0.04 corresponds to the equilibrium H 3Cur=H 2Cur -+H + and is attributed the acetylacetone type group. Formation of quinoid structures play an important role in the tautomeric forms of the curcumin in aqueous media, which makes the experimental values differ from the theoretically calculated ones, depending on the conditions adopted in the study.

Toward an understanding of the turbidity measurement of heterocoagulation rate constants of dispersions containing particles of different sizes.

PubMed

Liu, Jie; Xu, Shenghua; Sun, Zhiwei

2007-11-06

Our previous studies have shown that the determination of coagulation rate constants by turbidity measurement becomes impossible for a certain operating wavelength (that is, its blind point) because at this wavelength the change in the turbidity of a dispersion completely loses its response to the coagulation process. Therefore, performing the turbidity measurement in the wavelength range near the blind point should be avoided. In this article, we demonstrate that the turbidity measurement of the rate constant for coagulation of a binary dispersion containing particles of two different sizes (heterocoagulation) presents special difficulties because the blind point shifts with not only particle size but also with the component fraction. Some important aspects of the turbidity measurement for the heterocoagulation rate constant are discussed and experimentally tested. It is emphasized that the T-matrix method can be used to correctly evaluate extinction cross sections of doublets formed during the heterocoagulation process, which is the key data determining the rate constant from the turbidity measurement, and choosing the appropriate operating wavelength and component fraction are important to achieving a more accurate rate constant. Finally, a simple scheme in experimentally determining the sensitivity of the turbidity changes with coagulation over a wavelength range is proposed.

A kinetic model for beta-amyloid adsorption at the air/solution interface and its implication to the beta-amyloid aggregation process.

PubMed

Jiang, Dianlu; Dinh, Kim Lien; Ruthenburg, Travis C; Zhang, Yi; Su, Lei; Land, Donald P; Zhou, Feimeng

2009-03-12

At the air/buffer solution interface the kinetics of adsorption of amyloid beta peptide, Abeta(1-42), whose bulk concentration (submicromolar) is more than 2 orders of magnitude lower than that typically used in other in vitro aggregation studies, has been studied using a Langmuir-Blodgett trough. The pressure-time curves exhibit a lag phase, wherein the surface pressure essentially remains at zero, and a rising phase, corresponding to the Abeta adsorption at the interface. The duration of the lag phase was found to be highly dependent on both the Abeta bulk concentration and the solution temperature. A large activation energy (62.2 +/- 4.1 KJ/mol) was determined and the apparent adsorption rate constant was found to be linearly dependent on the Abeta bulk concentration. Attenuated total reflection-IR spectra of the adsorbed Abeta transferred to a solid substrate and circular dichroism measurements of Abeta in the solution layer near the interface reveal that the natively unstructured Abeta in the bulk undergo a conformation change (folding) to mainly the alpha-helical structure. The results suggest that, prior to the adsorption step, an equilibrium between Abeta conformations is established within the subsurface. The kinetic equation derived from this model confirms that the overall Abeta adsorption is kinetically controlled and the apparent rate constant is proportional to the Abeta bulk concentration. This model also indicates that interfaces such as cell membranes and lipid bilayers may facilitate Abeta aggregation/ fibrillation by providing a thin hydrophobic layer adjacent to the interface for the initial A/beta conformation change (misfolding) and accumulation. Such a preconcentration effect offers a plausible explanation of the fact that Abeta fibrillation occurs in vivo at nanomolar concentrations. Another important biological implication from our work is that Abeta misfolding may occur before its adsorption onto a cell membrane. This general kinetic model

A Kinetic Model for β-Amyloid Adsorption at the Air/Solution Interface and Its Implication to the β-Amyloid Aggregation Process

PubMed Central

Jiang, Dianlu; Dinh, Kim Lien; Ruthenburg, Travis; Zhang, Yi; Su, Lei; Land, Donald; Zhou, Feimeng

2011-01-01

The kinetics of adsorption at the air/buffer solution interface of amyloid beta peptide, Aβ(1–42), whose bulk concentration (submicromolar) is more than two orders of magnitude lower than that typically used in other in vitro aggregation studies, has been studied using a Langmuir-Blodgett trough. The pressure–time curves exhibit a lag phase, wherein the surface pressure essentially remains at zero, and a rising phase, corresponding to the Aβ adsorption at the interface. The duration of the lag phase was found to be highly dependent on both the Aβ bulk concentration and the solution temperature. A large activation energy (62.2 ± 4.1 KJ/mol) was determined and the apparent adsorption rate constant was found to be linearly dependent on the Aβ bulk concentration. Attenuated total reflection-IR spectra of the adsorbed Aβ transferred to a solid substrate and circular dichroism measurements of Aβ in the solution layer near the interface reveal that the natively unstructured Aβ in the bulk undergo a conformation change (folding) to mainly the α-helical structure. The results suggest that, prior to the adsorption step, an equilibrium between Aβ conformations is established within the subsurface. The kinetic equation derived from this model confirms that the overall Aβ adsorption is kinetically controlled and the apparent rate constant is proportional to the Aβ bulk concentration. This model also indicates that interfaces such as cell membranes and lipid bilayers may facilitate Aβ aggregation/fibrillation by providing a thin hydrophobic layer adjacent to the interface for the initial Aβ conformation change (misfolding) and accumulation. Such a preconcentration effect offers a plausible explanation of the fact that Aβ fibrillation occurs in vivo at nanomolar concentrations. Another important biological implication from our work is that Aβ misfolding may occur before its adsorption onto a cell membrane. This general kinetic model should also find

The Rate Constant for the Reaction H + C2H5 at T = 295 - 150K

NASA Technical Reports Server (NTRS)

Pimentel, Andre S.; Payne, Walter A.; Nesbitt, Fred L.; Cody, Regina J.; Stief, Louis J.

2004-01-01

The reaction between the hydrogen atom and the ethyl (C2H3) radical is predicted by photochemical modeling to be the most important loss process for C2H5 radicals in the atmospheres of Jupiter and Saturn. This reaction is also one of the major sources for the methyl radicals in these atmospheres. These two simplest hydrocarbon radicals are the initial species for the synthesis of larger hydrocarbons. Previous measurements of the rate constant for the H + C2H5 reaction varied by a factor of five at room temperature, and some studies showed a dependence upon temperature while others showed no such dependence. In addition, the previous studies were at higher temperatures and generally higher pressures than that needed for use in planetary atmospheric models. The rate constant for the reaction H + C2H5 has been measured directly at T = 150, 202 and 295 K and at P = 1.0 Torr He for all temperatures and additionally at P = 0.5 and 2.0 Torr He at T = 202 K. The measurements were performed in a discharge - fast flow system. The decay of the C2H5 radical in the presence of excess hydrogen was monitored by low-energy electron impact mass spectrometry under pseudo-first order conditions. H atoms and C2H5 radicals were generated rapidly and simultaneously by the reaction of fluorine atoms with H2 and C2H6, respectively. The total rate constant was found to be temperature and pressure independent. The measured total rate constant at each temperature are: k(sub 1)(295K) = (1.02+/-0.24)x10(exp -10), k(sub 1)(202K) = (1.02+/-0.22)x10(exp -10) and k(sub 1)(150K) = (0.93+/-0.21)x10(exp -10), all in units of cu cm/molecule/s. The total rate constant derived from all the combined measurements is k(sub 1) = (l.03+/-0.17)x10(exp -10) cu cm/molecule/s. At room temperature our results are about a factor of two higher than the recommended rate constant and a factor of three lower than the most recently published study.

Prediction of Rate Constant for Supramolecular Systems with Multiconfigurations.

PubMed

Guo, Tao; Li, Haiyan; Wu, Li; Guo, Zhen; Yin, Xianzhen; Wang, Caifen; Sun, Lixin; Shao, Qun; Gu, Jingkai; York, Peter; Zhang, Jiwen

2016-02-25

The control of supramolecular systems requires a thorough understanding of their dynamics, especially on a molecular level. It is extremely difficult to determine the thermokinetic parameters of supramolecular systems, such as drug-cyclodextrin complexes with fast association/dissociation processes by experimental techniques. In this paper, molecular modeling combined with novel mathematical relationships integrating the thermodynamic/thermokinetic parameters of a series of isomeric multiconfigurations to predict the overall parameters in a range of pH values have been employed to study supramolecular dynamics at the molecular level. A suitable form of Eyring's equation was derived and a two-stage model was introduced. The new approach enabled accurate prediction of the apparent dissociation/association (k(off)/k(on)) and unbinding/binding (k-r/kr) rate constants of the ubiquitous multiconfiguration complexes of the supramolecular system. The pyronine Y (PY) was used as a model system for the validation of the presented method. Interestingly, the predicted k(off) value ((40 ± 1) × 10(5) s(-1), 298 K) of PY is largely in agreement with that previously determined by fluorescence correlation spectroscopy ((5 ± 3) × 10(5) s(-1), 298 K). Moreover, the k(off)/k(on) and k-r/kr for flurbiprofen-β-cylcodextrin and ibuprofen-β-cyclodextrin systems were also predicted and suggested that the association processes are diffusion-controlled. The methodology is considered to be especially useful in the design and selection of excipients for a supramolecular system with preferred association and dissociation rate constants and understanding their mechanisms. It is believed that this new approach could be applicable to a wide range of ligand-receptor supramolecular systems and will surely help in understanding their complex mechanism.

Rate constants and temperature dependences for the reactions of hydroxyl radical with several halogenated methanes, ethanes, and propanes by relative rate measurements

NASA Technical Reports Server (NTRS)

Hsu, K.-J.; DeMore, W. B.

1995-01-01

Rate constants of 15 OH reactions with halogen-substituted alkanes, C1 to C3, were studied using a relative rate technique in the temperature range 283-403 K. Compounds studied were CHF2Cl (22), CHF2Br (22B), CH3F (41), CH2F2 (32), CHF3 (23), CHClFCCl2F (122a), CHCl2CF3 (123), CHClFCF3 (124), CH3CF3 (143a), CH3CH2F (161), CF3CHFCF3 (227ea), CF3CH2CF3 (236fa), CF3CHFCHF2 (236ea), and CHF2CF2CH2F (245ca). Using CH4, CH3CCl3, CF3CF2H, and C2H6 as primary reference standards (JPL 92-20 rate constants), absolute rate constants are derived. Results are in good agreement with previous experimental results for six of the compounds studied, including CHF2Cl, CHF2Br, CH2F2, CH3CF3, CHFClCFCl2, and CF3CHFCF3. For the remainder the relative rate constants are lower than those derived from experiments in which OH loss was used to measure the reaction rate. Comparisons of the derived Arrhenius A factors with previous literature transition-state calculations show order of magnitude agreement in most cases. However, the experimental A factors show a much closer proportionality to the number of H atoms in the molecule than is evident from the transition state calculations. For most of the compounds studied, an A factor of (8 +/- 3)E-13 cm(exp 3)/(molecule s) per C-H bond is observed. A new measurement of the ratio k(CH3CCl3)/k(CH4) is reported that is in good agreement with previous data.

Biotransformation of trace organic chemicals during groundwater recharge: How useful are first-order rate constants?

PubMed

Regnery, J; Wing, A D; Alidina, M; Drewes, J E

2015-08-01

This study developed relationships between the attenuation of emerging trace organic chemicals (TOrC) during managed aquifer recharge (MAR) as a function of retention time, system characteristics, and operating conditions using controlled laboratory-scale soil column experiments simulating MAR. The results revealed that MAR performance in terms of TOrC attenuation is primarily determined by key environmental parameters (i.e., redox, primary substrate). Soil columns with suboxic and anoxic conditions performed poorly (i.e., less than 30% attenuation of moderately degradable TOrC) in comparison to oxic conditions (on average between 70-100% attenuation for the same compounds) within a residence time of three days. Given this dependency on redox conditions, it was investigated if key parameter-dependent rate constants are more suitable for contaminant transport modeling to properly capture the dynamic TOrC attenuation under field-scale conditions. Laboratory-derived first-order removal kinetics were determined for 19 TOrC under three different redox conditions and rate constants were applied to MAR field data. Our findings suggest that simplified first-order rate constants will most likely not provide any meaningful results if the target compounds exhibit redox dependent biotransformation behavior or if the intention is to exactly capture the decline in concentration over time and distance at field-scale MAR. However, if the intention is to calculate the percent removal after an extended time period and subsurface travel distance, simplified first-order rate constants seem to be sufficient to provide a first estimate on TOrC attenuation during MAR. Copyright © 2015 Elsevier B.V. All rights reserved.

Evaluation of Adsorption Characteristics of a Fibrous Adsorbent Containing Zwitter-Ionic Functional Group, Targeting Organic Acids.

PubMed

Nakazawa, Akira; Tang, Ning; Inoue, Yoshinori; Kamichatani, Waka; Katoh, Toshifumi; Saito, Mitsuru; Obara, Kenji; Toriba, Akira; Hayakawa, Kazuichi

2017-01-01

Diallylamine-maleic acid copolymer (DAM)-nonwoven fabric (DAM-f), a fibrous adsorbent, contains DAM with zwitter-ionic functional groups and forms a hydration layer on the surface. The aim of this report was to evaluate the adsorption selectivity of DAM-f to semi-volatile organic acid (C1-C5). In the aqueous phase, formic acid dissolved in the hydration layer bound to the imino group of DAM-f due to anion exchange interaction. In the gas phase, the adsorption amounts of organic acids increased with the exposure time. Moreover, the adsorption rate constants correlated with the air/water partition coefficients (log K aw ) for formic acid, propionic acid, butyric acid, valeric acid and isovaleric acid, except for acetic acid. These results indicate that DAM-f is highly selective to hydrophilic compounds which easily move from the air to the hydration layer of DAM-f.

Preparation of highly ordered cubic NaA zeolite from halloysite mineral for adsorption of ammonium ions.

PubMed

Zhao, Yafei; Zhang, Bing; Zhang, Xiang; Wang, Jinhua; Liu, Jindun; Chen, Rongfeng

2010-06-15

Well-ordered cubic NaA zeolite was first synthesized using natural halloysite mineral with nanotubular structure as source material by hydro-thermal method. SEM and HRTEM images indicate that the synthesized NaA zeolite is cubic-shaped crystal with planar surface, well-defined edges and symmetrical and uniform pore channels. The adsorption behavior of ammonium ions (NH(4)(+)) from aqueous solution onto NaA zeolite was investigated as a function of parameters such as equilibrium time, pH, initial NH(4)(+) concentration, temperature and competitive cations. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. A maximum adsorption capacity of 44.3 mg g(-1) of NH(4)(+) was achieved. The regeneration and reusable ability of this adsorbent was evaluated, and the results indicated that the recovered adsorbent could be used again for NH(4)(+) removal with nearly constant adsorption capacity. Thermodynamic parameters such as change in free energy (DeltaG(0)), enthalpy (DeltaH(0)) and entropy (DeltaS(0)) were also determined, which indicated that the adsorption was a spontaneous and exothermic process at ambient conditions. Compared with other adsorbents, the as-synthesized NaA zeolite displays a faster adsorption rate and higher adsorption capacity, which implies potential application for removing NH(4)(+) pollutants from wastewaters. Copyright 2010 Elsevier B.V. All rights reserved.

Accurate acceleration of kinetic Monte Carlo simulations through the modification of rate constants.

PubMed

Chatterjee, Abhijit; Voter, Arthur F

2010-05-21

We present a novel computational algorithm called the accelerated superbasin kinetic Monte Carlo (AS-KMC) method that enables a more efficient study of rare-event dynamics than the standard KMC method while maintaining control over the error. In AS-KMC, the rate constants for processes that are observed many times are lowered during the course of a simulation. As a result, rare processes are observed more frequently than in KMC and the time progresses faster. We first derive error estimates for AS-KMC when the rate constants are modified. These error estimates are next employed to develop a procedure for lowering process rates with control over the maximum error. Finally, numerical calculations are performed to demonstrate that the AS-KMC method captures the correct dynamics, while providing significant CPU savings over KMC in most cases. We show that the AS-KMC method can be employed with any KMC model, even when no time scale separation is present (although in such cases no computational speed-up is observed), without requiring the knowledge of various time scales present in the system.

Volatile organic compound adsorption in a gas-solid fluidized bed.

PubMed

Ng, Y L; Yan, R; Tsen, L T S; Yong, L C; Liu, M; Liang, D T

2004-01-01

Fluidization finds many process applications in the areas of catalytic reactions, drying, coating, combustion, gasification and microbial culturing. This work aims to compare the dynamic adsorption characteristics and adsorption rates in a bubbling fluidized bed and a fixed bed at the same gas flow-rate, gas residence time and bed height. Adsorption with 520 ppm methanol and 489 ppm isobutane by the ZSM-5 zeolite of different particle size in the two beds enabled the differentiation of the adsorption characteristics and rates due to bed type, intraparticle mass transfer and adsorbate-adsorbent interaction. Adsorption of isobutane by the more commonly used activated carbon provided the comparison of adsorption between the two adsorbent types. With the same gas residence time of 0.79 seconds in both the bubbling bed and fixed bed of the same bed size of 40 mm diameter and 48 mm height, the experimental results showed a higher rate of adsorption in the bubbling bed as compared to the fixed bed. Intraparticle mass transfer and adsorbent-adsorbate interaction played significant roles in affecting the rate of adsorption, with intraparticle mass transfer being more dominant. The bubbling bed was observed to have a steeper decline in adsorption rate with respect to increasing outlet concentration compared to the fixed bed. The adsorption capacities of zeolite for the adsorbates studied were comparatively similar in both beds; fluidizing, and using smaller particles in the bubbling bed did not increase the adsorption capacity of the ZSM-5 zeolite. The adsorption capacity of activated carbon for isobutane was much higher than the ZSM-5 zeolite for isobutane, although at a lower adsorption rate. Fourier transform infra-red (FTIR) spectroscopy was used as an analytical tool for the quantification of gas concentration. Calibration was done using a series of standards prepared by in situ dilution with nitrogen gas, based on the ideal gas law and relating partial pressure to gas

Acoustic emission of rock mass under the constant-rate fluid injection

NASA Astrophysics Data System (ADS)

Shadrin Klishin, AV, VI

2018-03-01

The authors study acoustic emission in coal bed and difficult-to-cave roof under injection of fluid by pumps at a constant rate. The functional connection between the roof hydrofracture length and the total number of AE pulses is validated, it is also found that the coal bed hydroloosening time, injection rate and time behavior of acoustic emission activity depend on the fluid injection volume required until the fluid breakout in a roadway through growing fractures. In the formulas offered for the practical application, integral parameters that characterize permeability and porosity of rock mass and process parameters of the technology are found during test injection.

Application of an Artificial Neural Network to the Prediction of OH Radical Reaction Rate Constants for Evaluating Global Warming Potential.

PubMed

Allison, Thomas C

2016-03-03

Rate constants for reactions of chemical compounds with hydroxyl radical are a key quantity used in evaluating the global warming potential of a substance. Experimental determination of these rate constants is essential, but it can also be difficult and time-consuming to produce. High-level quantum chemistry predictions of the rate constant can suffer from the same issues. Therefore, it is valuable to devise estimation schemes that can give reasonable results on a variety of chemical compounds. In this article, the construction and training of an artificial neural network (ANN) for the prediction of rate constants at 298 K for reactions of hydroxyl radical with a diverse set of molecules is described. Input to the ANN consists of counts of the chemical bonds and bends present in the target molecule. The ANN is trained using 792 (•)OH reaction rate constants taken from the NIST Chemical Kinetics Database. The mean unsigned percent error (MUPE) for the training set is 12%, and the MUPE of the testing set is 51%. It is shown that the present methodology yields rate constants of reasonable accuracy for a diverse set of inputs. The results are compared to high-quality literature values and to another estimation scheme. This ANN methodology is expected to be of use in a wide range of applications for which (•)OH reaction rate constants are required. The model uses only information that can be gathered from a 2D representation of the molecule, making the present approach particularly appealing, especially for screening applications.

Enhanced removal of azo dye using modified PAN nanofibrous membrane Fe complexes with adsorption/visible-driven photocatalysis bifunctional roles

NASA Astrophysics Data System (ADS)

Li, Fu; Dong, Yongchun; Kang, Weimin; Cheng, Bowen; Cui, Guixin

2017-05-01

A series of polyacrylonitrile (PAN) nanofibrous membrane Fe complexes as the Fenton heterogeneous catalysts were fabricated through surface modification with different ratio of hydrazine hydrate (HH) and hydroxylamine (HA) and subsequent coordination with Fe3+ ions for the synergistic removal of a typical azo dye, Reactive Red 195 (RR 195) via adsorption and visible-driven photocatalytic oxidation. Effect of molar ratio of HH and HA on surface structure characteristics of the resulting complexes were examined. Their adsorptive or photocatalytic activity was also compared by changing molar ratio of HH and HA. The results indicated that three PAN nanofibrous membrane Fe complexes prepared with simultaneous modification of HA and HH exhibited much higher adsorption and visible photocatalytic activities than the complex modified solely with HA or HH due to their distinctive surface structures containing more active sites. Their adsorption and visible photocatalytic kinetics of RR 195 followed pseudo-second-order model equation. Their high photocatalytic rate constant and large amount of dye adsorption were regarded as the main reasons for better dye removal efficiency and durability in cyclic reuse by means of the synergistic adsorption-photocatalysis process.

Kinetics of heavy metal adsorption and desorption in soil: Developing a unified model based on chemical speciation

NASA Astrophysics Data System (ADS)

Peng, Lanfang; Liu, Paiyu; Feng, Xionghan; Wang, Zimeng; Cheng, Tao; Liang, Yuzhen; Lin, Zhang; Shi, Zhenqing

2018-03-01

Predicting the kinetics of heavy metal adsorption and desorption in soil requires consideration of multiple heterogeneous soil binding sites and variations of reaction chemistry conditions. Although chemical speciation models have been developed for predicting the equilibrium of metal adsorption on soil organic matter (SOM) and important mineral phases (e.g. Fe and Al (hydr)oxides), there is still a lack of modeling tools for predicting the kinetics of metal adsorption and desorption reactions in soil. In this study, we developed a unified model for the kinetics of heavy metal adsorption and desorption in soil based on the equilibrium models WHAM 7 and CD-MUSIC, which specifically consider metal kinetic reactions with multiple binding sites of SOM and soil minerals simultaneously. For each specific binding site, metal adsorption and desorption rate coefficients were constrained by the local equilibrium partition coefficients predicted by WHAM 7 or CD-MUSIC, and, for each metal, the desorption rate coefficients of various binding sites were constrained by their metal binding constants with those sites. The model had only one fitting parameter for each soil binding phase, and all other parameters were derived from WHAM 7 and CD-MUSIC. A stirred-flow method was used to study the kinetics of Cd, Cu, Ni, Pb, and Zn adsorption and desorption in multiple soils under various pH and metal concentrations, and the model successfully reproduced most of the kinetic data. We quantitatively elucidated the significance of different soil components and important soil binding sites during the adsorption and desorption kinetic processes. Our model has provided a theoretical framework to predict metal adsorption and desorption kinetics, which can be further used to predict the dynamic behavior of heavy metals in soil under various natural conditions by coupling other important soil processes.

Adsorption of a reactive dye on chemically modified activated carbons--influence of pH.

PubMed

Orfão, J J M; Silva, A I M; Pereira, J C V; Barata, S A; Fonseca, I M; Faria, P C C; Pereira, M F R

2006-04-15

The surface chemistry of a commercial activated carbon with a slightly basic nature was modified by appropriate treatments in order to obtain two additional samples, respectively with acidic and basic properties, without changing its textural parameters significantly. Different techniques (N2 adsorption at 77 K, temperature programmed desorption, and determination of acidity, basicity, and pH at the point of zero charge) were used to characterize the adsorbents. Kinetic and equilibrium adsorption data of a selected textile reactive dye (Rifafix Red 3BN, C.I. reactive red 241) on the mentioned materials were obtained at the pH values of 2, 7, and 12. The kinetic curves are fitted using the second-order model. The respective rate constants seem to diminish progressively with the initial concentration for the more diluted solutions tested, reaching a constant value at higher concentrations, which depends on the experimental system under consideration (adsorbent and pH). In general, the Langmuir model provides the best fit for the equilibrium data. The different uptakes obtained are discussed in relation to the surface chemical properties of the adsorbents. It is shown that the adsorption of the reactive (anionic) dye on the basic sample (prepared by thermal treatment under H2 flow at 700 degrees C) is favored. This conclusion is explained on the basis of the dispersive and electrostatic interactions involved. Moreover, it is also shown that the optimal adsorption condition for all the activated carbons tested corresponds to solution pH values not higher than the pH(pzc) of the adsorbents, which may be interpreted by taking into account the electrostatic forces present.

Nonparametric change point estimation for survival distributions with a partially constant hazard rate.

PubMed

Brazzale, Alessandra R; Küchenhoff, Helmut; Krügel, Stefanie; Schiergens, Tobias S; Trentzsch, Heiko; Hartl, Wolfgang

2018-04-05

We present a new method for estimating a change point in the hazard function of a survival distribution assuming a constant hazard rate after the change point and a decreasing hazard rate before the change point. Our method is based on fitting a stump regression to p values for testing hazard rates in small time intervals. We present three real data examples describing survival patterns of severely ill patients, whose excess mortality rates are known to persist far beyond hospital discharge. For designing survival studies in these patients and for the definition of hospital performance metrics (e.g. mortality), it is essential to define adequate and objective end points. The reliable estimation of a change point will help researchers to identify such end points. By precisely knowing this change point, clinicians can distinguish between the acute phase with high hazard (time elapsed after admission and before the change point was reached), and the chronic phase (time elapsed after the change point) in which hazard is fairly constant. We show in an extensive simulation study that maximum likelihood estimation is not robust in this setting, and we evaluate our new estimation strategy including bootstrap confidence intervals and finite sample bias correction.

Rate constants for reactions of ClO/x/ of atmospheric interest

NASA Technical Reports Server (NTRS)

Watson, R. T.

1977-01-01

Chemical kinetics measurements on 82 gas phase reactions of chlorine containing species are reviewed. Recommended rate constants are given. The principal species of interest are Cl, Cl2, ClO, Cl2O, ClOO, OClO, CINO, HCl and halo derivatives of methane and ethane. Absorption spectra are given for 21 species. In addition the chemical kinetics methods used to obtain these data are discussed with regard to their applicability and reliability.

Temperature and pressure dependence of the absolute rate constant for the reactions of NH2 radicals with acetylene and ethylene

NASA Technical Reports Server (NTRS)

Bosco, S. R.; Nava, D. F.; Brobst, W. D.; Stief, L. J.

1984-01-01

The absolute rate constants for the reaction between the NH2 free radical and acetylene and ethylene is measured experimentally using a flash photolysis technique. The constant is considered to be a function of temperature and pressure. At each temperature level of the experiment, the observed pseudo-first-order rate constants were assumed to be independent of flash intensity. The results of the experiment indicate that the bimolecular rate constant for the NH2 + C2H2 reaction increases with pressure at 373 K and 459 K but not at lower temperatures. Results near the pressure limit conform to an Arrhenius expression of 1.11 (+ or -) 0.36 x 10 to the -13th over the temperature range from 241 to 459 K. For the reaction NH2 + C2H4, a smaller rate of increase in the bimolecular rate constant was observed over the temperature range 250-465 K. The implications of these results for current theoretical models of NH2 + C2H2 (or H4) reactions in the atmospheres of Jupiter and Saturn are discussed.

Degradation and adsorption of selected pharmaceuticals and personal care products (PPCPs) in agricultural soils.

PubMed

Xu, Jian; Wu, Laosheng; Chang, Andrew C

2009-11-01

Pharmaceuticals and personal care products (PPCPs) are emerging contaminants in the environment, which have drawn popular concerns recently. Most studies on the environmental fate of PPCPs have focused on their behaviors during wastewater treatment processes, in aquatic environments, and in the sludge, however, little is known about their behavior in agricultural soils. In this study, adsorption and degradation of six selected PPCPs, including clofibric acid, ibuprofen, naproxen, triclosan, diclofenac and bisphenol A have been investigated in the laboratory using four US agricultural soils associated with reclaimed wastewater reuse. Adsorption test using a batch equilibrium method demonstrated that adsorption of all tested chemicals in soils could be well described with Freundlich equation, and their adsorption affinity on soil followed the order of triclosan>bisphenol A>clofibric acid>naproxen>diclofenac>ibuprofen. Retardation factor (R(F)) suggested that ibuprofen had potential to move downward with percolating water, while triclosan and bisphenol A were readily retarded in soils. Degradation of selected PPCPs in soils generally followed first-order exponential decay kinetics, with half-lives ranging from 0.81 to 20.44 d. Degradation of PPCPs in soils appeared to be influenced by the soil organic matter and clay contents. Sterilization generally decreased the degradation rates, indicating microbial activity played a significant role in the degradation in soils. The degradation rate constant decreased with increasing initial chemical concentrations in soil, implying that the microbial activity was inhibited with high chemical loading levels.

Enhancement of the dissolution rate and bioavailability of fenofibrate by a melt-adsorption method using supercritical carbon dioxide

PubMed Central

Cha, Kwang-Ho; Cho, Kyung-Jin; Kim, Min-Soo; Kim, Jeong-Soo; Park, Hee Jun; Park, Junsung; Cho, Wonkyung; Park, Jeong-Sook; Hwang, Sung-Joo

2012-01-01

Background: The aim of this study was to enhance the bioavailability of fenofibrate, a poorly water-soluble drug, using a melt-adsorption method with supercritical CO2. Methods: Fenofibrate was loaded onto Neusilin® UFL2 at different weight ratios of fenofibrate to Neusilin UFL2 by melt-adsorption using supercritical CO2. For comparison, fenofibrate-loaded Neusilin UFL2 was prepared by solvent evaporation and hot melt-adsorption methods. The fenofibrate formulations prepared were characterized by differential scanning calorimetry, powder x-ray diffractometry, specific surface area, pore size distribution, scanning electron microscopy, and energy-dispersive x-ray spectrometry. In vitro dissolution and in vivo bioavailability were also investigated. Results: Fenofibrate was distributed into the pores of Neusilin UFL2 and showed reduced crystal formation following adsorption. Supercritical CO2 facilitated the introduction of fenofibrate into the pores of Neusilin UFL2. Compared with raw fenofibrate, fenofibrate from the prepared powders showed a significantly increased dissolution rate and better bioavailability. In particular, the area under the drug concentration-time curve and maximal serum concentration of the powders prepared using supercritical CO2 were 4.62-fold and 4.52-fold greater than the corresponding values for raw fenofibrate. Conclusion: The results of this study highlight the usefulness of the melt-adsorption method using supercritical CO2 for improving the bioavailability of fenofibrate. PMID:23118538

Protein adsorption in microengraving immunoassays.

PubMed

Song, Qing

2015-10-16

Microengraving is a novel immunoassay for characterizing multiple protein secretions from single cells. During the immunoassay, characteristic diffusion and kinetic time scales  and  determine the time for molecular diffusion of proteins secreted from the activated single lymphocytes and subsequent binding onto the glass slide surface respectively. Our results demonstrate that molecular diffusion plays important roles in the early stage of protein adsorption dynamics which shifts to a kinetic controlled mechanism in the later stage. Similar dynamic pathways are observed for protein adsorption with significantly fast rates and rapid shifts in transport mechanisms when  is increased a hundred times from 0.313 to 31.3. Theoretical adsorption isotherms follow the trend of experimentally obtained data. Adsorption isotherms indicate that amount of proteins secreted from individual cells and subsequently captured on a clean glass slide surface increases monotonically with time. Our study directly validates that protein secretion rates can be quantified by the microengraving immunoassay. This will enable us to apply microengraving immunoassays to quantify secretion rates from 10⁴-10⁵ single cells in parallel, screen antigen-specific cells with the highest secretion rate for clonal expansion and quantitatively reveal cellular heterogeneity within a small cell sample.

Protein Adsorption in Microengraving Immunoassays

PubMed Central

Song, Qing

2015-01-01

Microengraving is a novel immunoassay forcharacterizing multiple protein secretions from single cells. During the immunoassay, characteristic diffusion and kinetic time scales τD and τK determine the time for molecular diffusion of proteins secreted from the activated single lymphocytes and subsequent binding onto the glass slide surface respectively. Our results demonstrate that molecular diffusion plays important roles in the early stage of protein adsorption dynamics which shifts to a kinetic controlled mechanism in the later stage. Similar dynamic pathways are observed for protein adsorption with significantly fast rates and rapid shifts in transport mechanisms when C0* is increased a hundred times from 0.313 to 31.3. Theoretical adsorption isotherms follow the trend of experimentally obtained data. Adsorption isotherms indicate that amount of proteins secreted from individual cells and subsequently captured on a clean glass slide surface increases monotonically with time. Our study directly validates that protein secretion rates can be quantified by the microengraving immunoassay. This will enable us to apply microengraving immunoassays to quantify secretion rates from 104–105 single cells in parallel, screen antigen-specific cells with the highest secretion rate for clonal expansion and quantitatively reveal cellular heterogeneity within a small cell sample. PMID:26501282

Investigation of Dynamic Oxygen Adsorption in Molten Solder Jetting Technology

NASA Technical Reports Server (NTRS)

Megaridis, Constantine M.; Bellizia, Giulio; McNallan, Michael; Wallace, David B.

2003-01-01

Surface tension forces play a critical role in fluid dynamic phenomena that are important in materials processing. The surface tension of liquid metals has been shown to be very susceptible to small amounts of adsorbed oxygen. Consequently, the kinetics of oxygen adsorption can influence the capillary breakup of liquid-metal jets targeted for use in electronics assembly applications, where low-melting-point metals (such as tin-containing solders) are utilized as an attachment material for mounting of electronic components to substrates. By interpreting values of surface tension measured at various surface ages, adsorption and diffusion rates of oxygen on the surface of the melt can be estimated. This research program investigates the adsorption kinetics of oxygen on the surface of an atomizing molten-metal jet. A novel oscillating capillary jet method has been developed for the measurement of dynamic surface tension of liquids, and in particular, metal melts which are susceptible to rapid surface degradation caused by oxygen adsorption. The experimental technique captures the evolution of jet swells and necks continuously along the jet propagation axis and is used in conjunction with an existing linear, axisymmetric, constant-property model to determine the variation of the instability growth rate, and, in turn, surface tension of the liquid as a function of surface age measured from the exit orifice. The conditions investigated so far focus on a time window of 2-4ms from the jet orifice. The surface properties of the eutectic 63%Sn-37%Pb solder alloy have been investigated in terms of their variation due to O2 adsorption from a N2 atmosphere containing controlled amounts of oxygen (from 8 ppm to 1000 ppm). The method performed well for situations where the oxygen adsorption was low in that time window. The value of surface tension for the 63Sn-37Pb solder in pure nitrogen was found to be 0.49 N/m, in good agreement with previously published work. A characteristic

Competitive adsorption/desorption of tetracycline, oxytetracycline and chlortetracycline on two acid soils: Stirred flow chamber experiments.

PubMed

Fernández-Calviño, David; Bermúdez-Couso, Alipio; Arias-Estévez, Manuel; Nóvoa-Muñoz, Juan Carlos; Fernández-Sanjurjo, Maria J; Álvarez-Rodríguez, Esperanza; Núñez-Delgado, Avelino

2015-09-01

The objective of this work was to study the competitive adsorption/desorption of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) on two acid soils. We used the stirred flow chamber technique to obtain experimental data on rapid kinetic processes affecting the retention/release of the antibiotics. Both adsorption and desorption were higher on soil 1 (which showed the highest carbon, clay and Al and Fe oxides content) than on soil 2. Moreover, hysteresis affected the adsorption/desorption processes. Experimental data were fitted to a pseudo-first order equation, resulting qamax (adsorption maximum) values that were higher for soil 1 than for soil 2, and indicating that CTC competed with TC more intensely than OTC in soil 1. Regarding soil 2, the values corresponding to the adsorption kinetics constants (ka) and desorption kinetics constants for fast sites (kd1), followed a trend inverse to qamax and qdmax respectively. In conclusion, competition affected adsorption/desorption kinetics for the three antibiotics assayed, and thus retention/release and subsequent transport processes in soil and water environments. Copyright © 2015 Elsevier Ltd. All rights reserved.

Adsorption of crystal violet onto functionalised multi-walled carbon nanotubes: Equilibrium and kinetic studies.

PubMed

Sabna, V; Thampi, Santosh G; Chandrakaran, S

2016-12-01

Synthetic dyes present in effluent from textile, paper and paint industries contain crystal violet (CV), a known carcinogenic agent. This study investigates the modification of multiwalled carbon nanotubes by acid reflux method and equilibrium and kinetic behaviour of adsorption of CV onto functionalized multi-walled carbon nanotubes (fMWNTs) in batch system. High stability of the fMWNTs suspension in water indicates the hydrophilicity of fMWNTs induced due to the formation of functional groups that make hydrogen bonds with water molecules. fMWNTs were characterized by Fourier Transform Infra Red (FTIR) spectroscopy and the functional groups present on the fMWNTs were confirmed. Characteristic variation was observed in the FTIR spectra of fMWNTs after adsorption of crystal violet onto it. Adsorption characteristics were evaluated as a function of system variables such as contact time, dosage of fMWNTs and initial concentration and pH of the crystal violet solution. Adsorption capacity of fMWNTs and percentage removal of the dye increased with increase in contact time, adsorbent dosage and pH but declined with increase in initial concentration of the dye. fMWNTs showed higher adsorption capacity compared to that of pristine MWNTs. Data showed good fit with the Langmuir and Freundlich isotherm models and the pseudo-second order kinetic model; the maximum adsorption capacity was 90.52mg/g. Kinetic parameters such as rate constants, equilibrium adsorption capacities and regression coefficients were estimated. Results indicate that fMWNTs are an effective adsorbent for the removal of crystal violet from aqueous solution. Copyright © 2015 Elsevier Inc. All rights reserved.

Pseudo-extravasation rate constant of dynamic susceptibility contrast-MRI determined from pharmacokinetic first principles.

PubMed

Li, Xin; Varallyay, Csanad G; Gahramanov, Seymur; Fu, Rongwei; Rooney, William D; Neuwelt, Edward A

2017-11-01

Dynamic susceptibility contrast-magnetic resonance imaging (DSC-MRI) is widely used to obtain informative perfusion imaging biomarkers, such as the relative cerebral blood volume (rCBV). The related post-processing software packages for DSC-MRI are available from major MRI instrument manufacturers and third-party vendors. One unique aspect of DSC-MRI with low-molecular-weight gadolinium (Gd)-based contrast reagent (CR) is that CR molecules leak into the interstitium space and therefore confound the DSC signal detected. Several approaches to correct this leakage effect have been proposed throughout the years. Amongst the most popular is the Boxerman-Schmainda-Weisskoff (BSW) K 2 leakage correction approach, in which the K 2 pseudo-first-order rate constant quantifies the leakage. In this work, we propose a new method for the BSW leakage correction approach. Based on the pharmacokinetic interpretation of the data, the commonly adopted R 2 * expression accounting for contributions from both intravascular and extravasating CR components is transformed using a method mathematically similar to Gjedde-Patlak linearization. Then, the leakage rate constant (K L ) can be determined as the slope of the linear portion of a plot of the transformed data. Using the DSC data of high-molecular-weight (~750 kDa), iron-based, intravascular Ferumoxytol (FeO), the pharmacokinetic interpretation of the new paradigm is empirically validated. The primary objective of this work is to empirically demonstrate that a linear portion often exists in the graph of the transformed data. This linear portion provides a clear definition of the Gd CR pseudo-leakage rate constant, which equals the slope derived from the linear segment. A secondary objective is to demonstrate that transformed points from the initial transient period during the CR wash-in often deviate from the linear trend of the linearized graph. The inclusion of these points will have a negative impact on the accuracy of the leakage

Application of physical adsorption thermodynamics to heterogeneous chemistry on polar stratospheric clouds

NASA Technical Reports Server (NTRS)

Elliott, Scott; Turco, Richard P.; Toon, Owen B.; Hamill, Patrick

1991-01-01

Laboratory isotherms for the binding of several nonheterogeneously active atmospheric gases and for HCl to water ice are translated into adsorptive equilibrium constants and surface enthalpies. Extrapolation to polar conditions through the Clausius Clapeyron relation yields coverage estimates below the percent level for N2, Ar, CO2, and CO, suggesting that the crystal faces of type II stratospheric cloud particles may be regarded as clean with respect to these species. For HCl, and perhaps HF and HNO3, estimates rise to several percent, and the adsorbed layer may offer acid or proton sources alternate to the bulk solid for heterogeneous reactions with stratospheric nitrates. Measurements are lacking for many key atmospheric molecules on water ice, and almost entirely for nitric acid trihydrate as substrate. Adsorptive equilibria enter into gas to particle mass flux descriptions, and the binding energy determines rates for desorption of, and encounter between, potential surface reactants.

Headgroup effects of template monolayers on the adsorption behavior and conformation of glucose oxidase adsorbed at air/liquid interfaces.

PubMed

Wang, Ke-Hsuan; Syu, Mei-Jywan; Chang, Chien-Hsiang; Lee, Yuh-Lang

2011-06-21

Stearic acid (SA) and octadecylamine (ODA) monolayers at the air/liquid interface were used as template layers to adsorb glucose oxidase (GOx) from aqueous solution. The effect of the template monolayers on the adsorption behavior of GOx was studied in terms of the variation of surface pressure, the evolution of surface morphology observed by BAM and AFM, and the conformation of adsorbed GOx. The results show that the presence of a template monolayer can enhance the adsorption rate of GOx; furthermore, ODA has a higher ability, compared to SA, to adsorb GOx, which is attributed to the electrostatic attractive interaction between ODA and GOx. For adsorption performed on a bare surface or on an SA monolayer, the surface pressure approaches an equilibrium value (ca. 8 mN/m) after 2 to 3 h of adsorption and remains nearly constant in the following adsorption process. For the adsorption on an ODA monolayer, the surface pressure will increase further 1 to 2 h after approaching the first equilibrium pressure, which is termed the second adsorption stage. The measurement of circular dichroism (CD) spectroscopy indicates that the Langmuir-Blodgett films of adsorbed GOx transferred at the first equilibrium state (π = 8 mN/m) have mainly a β-sheet conformation, which is independent of the type of template monolayers. However, the ODA/GOx LB film transferred at the second adsorption stage has mainly an α-helix conformation. It is concluded that the specific interaction between ODA and GOx not only leads to a higher adsorption rate and adsorbed amount of GOx but also induces a conformation change in adsorbed GOx from β-sheet to α-helix. The present results indicate that is possible to control the conformation of adsorbed protein by selecting the appropriate template monolayer. © 2011 American Chemical Society

Efficient quantum-classical method for computing thermal rate constant of recombination: application to ozone formation.

PubMed

Ivanov, Mikhail V; Babikov, Dmitri

2012-05-14

Efficient method is proposed for computing thermal rate constant of recombination reaction that proceeds according to the energy transfer mechanism, when an energized molecule is formed from reactants first, and is stabilized later by collision with quencher. The mixed quantum-classical theory for the collisional energy transfer and the ro-vibrational energy flow [M. Ivanov and D. Babikov, J. Chem. Phys. 134, 144107 (2011)] is employed to treat the dynamics of molecule + quencher collision. Efficiency is achieved by sampling simultaneously (i) the thermal collision energy, (ii) the impact parameter, and (iii) the incident direction of quencher, as well as (iv) the rotational state of energized molecule. This approach is applied to calculate third-order rate constant of the recombination reaction that forms the (16)O(18)O(16)O isotopomer of ozone. Comparison of the predicted rate vs. experimental result is presented.

Rate constant for OH with selected large alkanes : shock-tube measurements and an improved group scheme.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sivaramakrishnan, R.; Michael, J. V.; Chemical Sciences and Engineering Division

High-temperature rate constant experiments on OH with the five large (C{sub 5}-C{sub 8}) saturated hydrocarbons n-heptane, 2,2,3,3-tetramethylbutane (2,2,3,3-TMB), n-pentane, n-hexane, and 2,3-dimethylbutane (2,3-DMB) were performed with the reflected-shock-tube technique using multipass absorption spectrometric detection of OH radicals at 308 nm. Single-point determinations at {approx}1200 K on n-heptane, 2,2,3,3-TMB, n-hexane, and 2,3-DMB were previously reported by Cohen and co-workers; however, the present work substantially extends the database to both lower and higher temperature. The present experiments span a wide temperature range, 789-1308 K, and represent the first direct measurements of rate constants at T > 800 K for n-pentane. The presentmore » work utilized 48 optical passes corresponding to a total path length of {approx}4.2 m. As a result of this increased path length, the high OH concentration detection sensitivity permitted pseudo-first-order analyses for unambiguously measuring rate constants.« less

Determining the folding and unfolding rate constants of nucleic acids by biosensor. Application to telomere G-quadruplex.

PubMed

Zhao, Yong; Kan, Zhong-yuan; Zeng, Zhi-xiong; Hao, Yu-hua; Chen, Hua; Tan, Zheng

2004-10-20

Nucleic acid molecules may fold into secondary structures, and the formation of such structures is involved in many biological processes and technical applications. The folding and unfolding rate constants define the kinetics of conformation interconversion and the stability of these structures and is important in realizing their functions. We developed a method to determine these kinetic parameters using an optical biosensor based on surface plasmon resonance. The folding and unfolding of a nucleic acid is coupled with a hybridization reaction by immobilization of the target nucleic acid on a sensor chip surface and injection of a complementary probe nucleic acid over the sensor chip surface. By monitoring the time course of duplex formation, both the folding and unfolding rate constants for the target nucleic acid and the association and dissociation rate constants for the target-probe duplex can all be derived from the same measurement. We applied this method to determine the folding and unfolding rate constants of the G-quadruplex of human telomere sequence (TTAGGG)(4) and its association and dissociation rate constants with the complementary strand (CCCTAA)(4). The results show that both the folding and unfolding occur on the time scale of minutes at physiological concentration of K(+). We speculate that this property might be important for telomere elongation. A complete set of the kinetic parameters for both of the structures allows us to study the competition between the formation of the quadruplex and the duplex. Calculations indicate that the formation of both the quadruplex and the duplex is strand concentration-dependent, and the quadruplex can be efficiently formed at low strand concentration. This property may provide the basis for the formation of the quadruplex in vivo in the presence of a complementary strand.

Estimate Of The Decay Rate Constant of Hydrogen Sulfide Generation From Landfilled Drywall

EPA Science Inventory

Research was conducted to investigate the impact of particle size on H2S gas emissions and estimate a decay rate constant for H2S gas generation from the anaerobic decomposition of drywall. Three different particle sizes of regular drywall and one particle size of paperless drywa...

Kinetics and thermodynamics studies on the BMP-2 adsorption onto hydroxyapatite surface with different multi-morphological features.

PubMed

Lu, Zhiwei; Huangfu, Changxin; Wang, Yanying; Ge, Hongwei; Yao, Yao; Zou, Ping; Wang, Guangtu; He, Hua; Rao, Hanbing

2015-01-01

The effect of the surface topography on protein adsorption process is of great significance for designing hydroxyapatite (HA) ceramic material surfaces. In this work, three different topographies of HA materials HA-sheet, HA-rod, and HA-whisker were synthesized and testified by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Brunauer-Emmett-Teller (BET) and a field emission scanning electron microscopy (FE-SEM). We have systematically investigated the adsorption kinetics and thermodynamics of bone morphogenetic proteins (BMP-2) on the three different topography surfaces of HA, respectively. The results showed that the maximum adsorption capacities of HA-sheet, HA-rod and HA-whisker were (219.96 ± 10.18), (247.13 ± 12.35), and (354.67 ± 17.73) μg · g(-1), respectively. Kinetic parameters, rate constants, equilibrium adsorption capacities and related correlation coefficients, for each kinetic model were calculated as well as discussed. It demonstrated that the adsorption of BMP-2 onto HA could be described by the pseudo second-order equation. Adsorption of BMP-2 onto HA followed the Langmuir isotherm. It confirmed that compared with other samples HA-whisker had more adsorption sites for its high specific surface area which could provide more opportunities for protein molecules. The adsorption processes were endothermic (ΔH > 0), spontaneous (ΔG < 0) and entropy increasing (ΔS > 0). A possible adsorption mechanism has been proposed. In addition, the BMP-2 could be adsorbed to the surface which existed slight conformational changes by FT-IR. Copyright © 2015 Elsevier B.V. All rights reserved.

Comparative study on pharmaceuticals adsorption in reclaimed water desalination concentrate using biochar: Impact of salts and organic matter.

PubMed

Lin, Lu; Jiang, Wenbin; Xu, Pei

2017-12-01

The synergistic impact of salts and organic matter on adsorption of ibuprofen and sulfamethoxazole by three types of biochar and an activated carbon was investigated using reclaimed water reverse osmosis (RO) concentrate and synthetic solutions spiked with target organic compounds and non-target water constituents (e.g., Na + , Ca 2+ , Mg 2+ , K + , Cl - , SO 4 2- , alkalinity, humic acid (HA), and bovine serum albumin (BSA)). Kinetic modeling was used to better understand the adsorption process between the carbon adsorbents and pharmaceuticals and to elucidate the impact of water chemistry on pharmaceuticals adsorption. The adsorption capacity of pharmaceuticals by biochar was affected by their physicochemical properties including ash content, specific surface area, charge, pore volume, as well as hydrophobicity, π-energy, and speciation of pharmaceuticals. The adsorption of pharmaceuticals in concentrate was pH-dependent, the kinetic rate constant increased with deceasing pH due to the electrical interactions between pharmaceutical molecules and adsorbents. High salinity and electrolyte ions in RO concentrate improved adsorption, whereas the presence of carbonate species, HA, and BSA hindered the removal of ibuprofen and sulfamethoxazole. This study revealed the correlation of concentrate water quality on adsorption of pharmaceuticals by biochar and activated carbon. Biochar provides a promising alternative to activated carbon for removal of organic contaminants of emerging concerns in various wastewater and concentrate streams. Copyright © 2017 Elsevier B.V. All rights reserved.

Adsorption of pharmaceuticals onto trimethylsilylated mesoporous SBA-15.

PubMed

Bui, Tung Xuan; Pham, Viet Hung; Le, Son Thanh; Choi, Heechul

2013-06-15

The adsorption of a complex mixture of 12 selected pharmaceuticals to trimethylsilylated mesoporous SBA-15 (TMS-SBA-15) has been investigated by batch adsorption experiments. The adsorption of pharmaceuticals to TMS-SBA-15 was highly dependent on the solution pH and pharmaceutical properties (i.e., hydrophobicity (logKow) and acidity (pKa)). Good log-log linear relationships between the adsorption (Kd) and pH-dependent octanol-water coefficients (Kow(pH)) were then established among the neutral, anionic, and cationic compounds, suggesting hydrophobic interaction as a primary driving force in the adsorption. In addition, the neutral species of each compound accounted for a major contribution to the overall compound adsorption onto TMS-SBA-15. The adsorption kinetics of pharmaceuticals was evaluated by the nonlinear first-order and pseudo-second-order models. The first-order model gave a better fit for five pharmaceuticals with lower adsorption capacity, whereas the pseudo-second-order model fitted better for seven pharmaceuticals having higher adsorption capacity. In the same group of properties, pharmaceuticals having higher adsorption capacity exhibited faster adsorption rates. The rate-limiting steps for adsorption of pharmaceuticals onto TMS-SBA-15 are boundary layer diffusion and intraparticle diffusion including diffusion in mesopores and micropores. In addition, the adsorption of pharmaceuticals to TMS-SBA-15 was not influenced by the change of initial pharmaceutical concentration (10-100μgL(-1)) and the presence of natural organic matter. Copyright © 2013 Elsevier B.V. All rights reserved.

The adsorption of HCl on volcanic ash

NASA Astrophysics Data System (ADS)

Gutiérrez, Xochilt; Schiavi, Federica; Keppler, Hans

2016-03-01

Understanding the interaction between volcanic gases and ash is important to derive gas compositions from ash leachates and to constrain the environmental impact of eruptions. Volcanic HCl could potentially damage the ozone layer, but it is unclear what fraction of HCl actually reaches the stratosphere. The adsorption of HCl on volcanic ash was therefore studied from -76 to +150 °C to simulate the behavior of HCl in the dilute parts of a volcanic plume. Finely ground synthetic glasses of andesitic, dacitic, and rhyolitic composition as well as a natural obsidian from Vulcano (Italy) served as proxies for fresh natural ash. HCl adsorption is an irreversible process and appears to increase with the total alkali content of the glass. Adsorption kinetics follow a first order law with rate constants of 2.13 ṡ10-6 s-1 to 1.80 ṡ10-4 s-1 in the temperature range investigated. For dacitic composition, the temperature and pressure dependence of adsorption can be described by the equation ln ⁡ c = 1.26 + 0.27 ln ⁡ p - 715.3 / T, where c is the surface concentration of adsorbed HCl in mg/m2, T is temperature in Kelvin, and p is the partial pressure of HCl in mbar. A comparison of this model with a large data set for the composition of volcanic ash suggests that adsorption of HCl from the gas phase at relatively low temperatures can quantitatively account for the majority of the observed Cl concentrations. The model implies that adsorption of HCl on ash increases with temperature, probably because of the increasing number of accessible adsorption sites. This temperature dependence is opposite to that observed for SO2, so that HCl and SO2 are fractionated by the adsorption process and the fractionation factor changes by four orders of magnitude over a temperature range of 250 K. The assumption of equal adsorption of different species is therefore not appropriate for deriving volcanic gas compositions from analyses of adsorbates on ash. However, with the experimental

Adsorption energies and prefactor determination for CH3OH adsorption on graphite.

PubMed

Doronin, M; Bertin, M; Michaut, X; Philippe, L; Fillion, J-H

2015-08-28

In this paper, we have studied adsorption and thermal desorption of methanol CH3OH on graphite surface, with the specific aim to derive from experimental data quantitative parameters that govern the desorption, namely, adsorption energy Eads and prefactor ν of the Polanyi-Wigner law. In low coverage regime, these two values are interconnected and usually the experiments can be reproduced with any couple (Eads, ν), which makes intercomparison between studies difficult since the results depend on the extraction method. Here, we use a method for determining independently the average adsorption energy and a prefactor value that works over a large range of incident methanol coverage, from a limited set of desorption curves performed at different heating rates. In the low coverage regime the procedure is based on a first order kinetic law, and considers an adsorption energy distribution which is not expected to vary with the applied heating rate. In the case of CH3OH multilayers, Eads is determined as 430 meV with a prefactor of 5 × 10(14) s(-1). For CH3OH submonolayers on graphite, adsorption energy of 470 ± 30 meV and a prefactor of (8 ± 3) × 10(16) s(-1) have been found. These last values, which do not change between 0.09 ML and 1 ML initial coverage, suggest that the methanol molecules form island-like structure on the graphite even at low coverage.

A chemical equilibrium model for metal adsorption onto bacterial surfaces

NASA Astrophysics Data System (ADS)

Fein, Jeremy B.; Daughney, Christopher J.; Yee, Nathan; Davis, Thomas A.

1997-08-01

This study quantifies metal adsorption onto cell wall surfaces of Bacillus subtilis by applying equilibrium thermodynamics to the specific chemical reactions that occur at the water-bacteria interface. We use acid/base titrations to determine deprotonation constants for the important surface functional groups, and we perform metal-bacteria adsorption experiments, using Cd, Cu, Pb, and Al, to yield site-specific stability constants for the important metal-bacteria surface complexes. The acid/base properties of the cell wall of B. subtilis can best be characterized by invoking three distinct types of surface organic acid functional groups, with pK a values of 4.82 ± 0.14, 6.9 ± 0.5, and 9.4 ± 0.6. These functional groups likely correspond to carboxyl, phosphate, and hydroxyl sites, respectively, that are displayed on the cell wall surface. The results of the metal adsorption experiments indicate that both the carboxyl sites and the phosphate sites contribute to metal uptake. The values of the log stability constants for metal-carboxyl surface complexes range from 3.4 for Cd, 4.2 for Pb, 4.3 for Cu, to 5.0 for Al. These results suggest that the stabilities of the metal-surface complexes are high enough for metal-bacterial interactions to affect metal mobilities in many aqueous systems, and this approach enables quantitative assessment of the effects of bacteria on metal mobilities.

Surface complexation modeling calculation of Pb(II) adsorption onto the calcined diatomite

NASA Astrophysics Data System (ADS)

Ma, Shu-Cui; Zhang, Ji-Lin; Sun, De-Hui; Liu, Gui-Xia

2015-12-01

Removal of noxious heavy metal ions (e.g. Pb(II)) by surface adsorption of minerals (e.g. diatomite) is an important means in the environmental aqueous pollution control. Thus, it is very essential to understand the surface adsorptive behavior and mechanism. In this work, the Pb(II) apparent surface complexation reaction equilibrium constants on the calcined diatomite and distributions of Pb(II) surface species were investigated through modeling calculations of Pb(II) based on diffuse double layer model (DLM) with three amphoteric sites. Batch experiments were used to study the adsorption of Pb(II) onto the calcined diatomite as a function of pH (3.0-7.0) and different ionic strengths (0.05 and 0.1 mol L-1 NaCl) under ambient atmosphere. Adsorption of Pb(II) can be well described by Freundlich isotherm models. The apparent surface complexation equilibrium constants (log K) were obtained by fitting the batch experimental data using the PEST 13.0 together with PHREEQC 3.1.2 codes and there is good agreement between measured and predicted data. Distribution of Pb(II) surface species on the diatomite calculated by PHREEQC 3.1.2 program indicates that the impurity cations (e.g. Al3+, Fe3+, etc.) in the diatomite play a leading role in the Pb(II) adsorption and dominant formation of complexes and additional electrostatic interaction are the main adsorption mechanism of Pb(II) on the diatomite under weak acidic conditions.

Modeling of fixed-bed column studies for the adsorption of cadmium onto novel polymer-clay composite adsorbent.

PubMed

Unuabonah, Emmanuel I; Olu-Owolabi, Bamidele I; Fasuyi, Esther I; Adebowale, Kayode O

2010-07-15

Kaolinite clay was treated with polyvinyl alcohol to produce a novel water-stable composite called polymer-clay composite adsorbent. The modified adsorbent was found to have a maximum adsorption capacity of 20,400+/-13 mg/L (1236 mg/g) and a maximum adsorption rate constant of approximately = 7.45x10(-3)+/-0.0002 L/(min mg) at 50% breakthrough. Increase in bed height increased both the breakpoint and exhaustion point of the polymer-clay composite adsorbent. The time for the movement of the Mass Transfer Zone (delta) down the column was found to increase with increasing bed height. The presence of preadsorbed electrolyte and regeneration were found to reduce this time. Increased initial Cd(2+) concentration, presence of preadsorbed electrolyte, and regeneration of polymer-clay composite adsorbent reduced the volume of effluent treated. Premodification of polymer-clay composite adsorbent with Ca- and Na-electrolytes reduced the rate of adsorption of Cd(2+) onto polymer-clay composite and lowered the breakthrough time of the adsorbent. Regeneration and re-adsorption studies on the polymer-clay composite adsorbent presented a decrease in the bed volume treated at both the breakpoint and exhaustion points of the regenerated bed. Experimental data were observed to show stronger fits to the Bed Depth Service Time (BDST) model than the Thomas model. 2010 Elsevier B.V. All rights reserved.

Atmospheric fate of a series of carbonyl nitrates: photolysis frequencies and OH-oxidation rate constants.

PubMed

Suarez-Bertoa, R; Picquet-Varrault, B; Tamas, W; Pangui, E; Doussin, J-F

2012-11-20

Multifunctional organic nitrates are potential NO(x) reservoirs whose atmospheric chemistry is somewhat little known. They could play an important role in the spatial distribution of reactive nitrogen species and consequently in ozone formation and distribution in remote areas. In this work, the rate constants for the reaction with OH radical and the photolysis frequencies of α-nitrooxyacetone, 3-nitrooxy-2-butanone, and 3-methyl-3-nitrooxy-2-butanone have been determined at room temperature at 1000 mbar total pressure of synthetic air. The rate constants for the OH oxidation were measured using the relative rate technique, with methanol as reference compound. The following rate constants were obtained for the reaction with OH: k(OH) = (6.7 ± 2.5) × 10(-13) cm(3) molecule(-1) s(-1) for α-nitrooxyacetone, (10.6 ± 4.1) × 10(-13) cm(3) molecule(-1) s(-1) for 3-nitrooxy-2-butanone, and (2.6 ± 0.9) × 10(-13) cm(3) molecule(-1) s(-1) for 3-methyl-3-nitrooxy-2-butanone. The corresponding photolysis frequencies extrapolated to typical atmospheric conditions for July first at noon at 40° latitude North were (4.8 ± 0.3) × 10(-5) s(-1), (5.7 ± 0.3) × 10(-5) s(-1), and (7.4 ± 0.2) × 10(-5) s(-1), respectively. The data show that photolysis is a major atmospheric sink for these organic nitrates.

Methane steam reforming rates over Pt, Rh and Ni(111) accounting for H tunneling and for metal lattice vibrations

NASA Astrophysics Data System (ADS)

German, Ernst D.; Sheintuch, Moshe

2017-02-01

Microkinetic models of methane steam reforming (MSR) over bare platinum and rhodium (111) surfaces are analyzed in present work using calculated rate constants. The individual rate constants are classified into three different sets: (i) rate constants of adsorption and desorption steps of CH4, H2O, CO and of H2; (ii) rate constants of dissociation and formation of A-H bonds (A = C, O, and H), and (iii) rate constants of dissociation and formation of C-O bond. The rate constants of sets (i) and (iii) are calculated using transition state theory and published thermochemical data. The rate constants of H-dissociation reactions (set (ii)) are calculated in terms of a previously-developed approach that accounts for thermal metal lattice vibrations and for H tunneling through a potential barrier of height which depends on distance of AH from a surface. Pre-exponential factors of several group (ii) steps were calculated to be usually lower than the traditional kBT/h due to tunneling effect. Surface composition and overall MSR rates over platinum and rhodium surfaces are compared with those over nickel surface showing that operating conditions strongly affect on the activity order of the catalysts.

Adsorption of Cu(II) Ions in Aqueous Solutions by HCl Activated Carbon of Oil Palm

NASA Astrophysics Data System (ADS)

Muslim, A.; Syamsuddin, Y.; Salamun, A.; Abubakar; Ramadhan, D.; Peiono, D.

2017-06-01

Activated carbon was prepared from oil palm empty fruit bunch (OPEFB) by pyrolysis at 873.15 K in a furnace and chemical activation using 0.01 M HCl. Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy and BET (Brunauer, Emmett and Teller) surface area analyses were taken into account to investigate the chemical functional group, to characterise the surface morphology and to determine total surface area the OPEFB AC, respectively. Experiments in batch mode were conducted to investigate Cu(II) adsorption capacity by the OPEFB AC whereas the system consisted of 1 g the OPEFB AC in 100 mL Cu(II) aqueous solution with initial concentration in the range of 10-70 mg/L, magnetic stirring at 75 rpm, room temperature of 300.15 K (± 2 K), at 1 atm and neutral pH over contact time in the range of 0-150 min. As the result, Cu(II) adsorption capacity increased exponentially over contact time and initial concentration. The Cu(II) adsorption kinetics followed the pseudo second order kinetics with the correlation coefficients (R 2), kinetics rate constant and equilibrium adsorption capacity being 0.98, 4.81 mg/g and 0.15/min, respectively for initial Cu(II) concentration being 58.71 mg/L. In addition, Cu(II) adsorption isotherm followed the Langmuir equation with the R2 value, the mono-layer and over-all adsorption capacity being 0.99, 5.92 mg/g and 0.17 L/mg, respectively.

Extension of the master sintering curve for constant heating rate modeling

NASA Astrophysics Data System (ADS)

McCoy, Tammy Michelle

The purpose of this work is to extend the functionality of the Master Sintering Curve (MSC) such that it can be used as a practical tool for predicting sintering schemes that combine both a constant heating rate and an isothermal hold. Rather than just being able to predict a final density for the object of interest, the extension to the MSC will actually be able to model a sintering run from start to finish. Because the Johnson model does not incorporate this capability, the work presented is an extension of what has already been shown in literature to be a valuable resource in many sintering situations. A predicted sintering curve that incorporates a combination of constant heating rate and an isothermal hold is more indicative of what is found in real-life sintering operations. This research offers the possibility of predicting the sintering schedule for a material, thereby having advanced information about the extent of sintering, the time schedule for sintering, and the sintering temperature with a high degree of accuracy and repeatability. The research conducted in this thesis focuses on the development of a working model for predicting the sintering schedules of several stabilized zirconia powders having the compositions YSZ (HSY8), 10Sc1CeSZ, 10Sc1YSZ, and 11ScSZ1A. The compositions of the four powders are first verified using x-ray diffraction (XRD) and the particle size and surface area are verified using a particle size analyzer and BET analysis, respectively. The sintering studies were conducted on powder compacts using a double pushrod dilatometer. Density measurements are obtained both geometrically and using the Archimedes method. Each of the four powders is pressed into ¼" diameter pellets using a manual press with no additives, such as a binder or lubricant. Using a double push-rod dilatometer, shrinkage data for the pellets is obtained over several different heating rates. The shrinkage data is then converted to reflect the change in relative

Adsorption of selenium by amorphous iron oxyhydroxide and manganese dioxide

USGS Publications Warehouse

Balistrieri, L.S.; Chao, T.T.

1990-01-01

is reflected in decreasing equilibrium constants for selenite with increasing adsorption density and both experimental observations and modeling results suggest that manganese dioxide has fewer sites of higher energy for selenite adsorption than amorphous iron oxyhydroxide. Modeling and interpreting the adsorption of phosphate, molybdate, and silicate on the oxides are made difficult by the lack of constraint in choosing surface species and the fact that equally good fits can be obtained with different surface species. Finally, predictions of anion competition using the model results from single adsorbate systems are not very successful because the model does not account for surface site heterogeneity. Selenite adsorption data from a multi-adsorbate system could be fit if the equilibrium constant for selenite is decreased with increasing anion adsorption density. ?? 1990.

Comparative study on kinetic adsorption of Cu(II), Cd(II) and Ni(II) ions from aqueous solutions using activated sludge and dried sludge

NASA Astrophysics Data System (ADS)

Ong, Soon-An; Toorisaka, Eiichi; Hirata, Makoto; Hano, Tadashi

2013-03-01

The adsorption of Cu(II), Cd(II) and Ni(II) ions from aqueous solutions by activated sludge and dried sludge was investigated under laboratory conditions to assess its potential in removing metal ions. The adsorption behavior of metal ions onto activated sludge and dried sludge was analyzed with Weber-Morris intra-particle diffusion model, Lagergren first-order model and pseudo second-order model. The rate constant of intra-particle diffusion on activated sludge and dried sludge increased in the sequence of Cu(II) > Ni(II) > Cd(II). According to the regression coefficients, it was observed that the kinetic adsorption data can fit better by the pseudo second-order model compared to the first-order Lagergren model with R 2 > 0.997. The adsorption capacities of metal ions onto activated sludge and dried sludge followed the sequence Ni(II) ≈ Cu(II) > Cd(II) and Cu(II) > Ni(II) > Cd(II).

Adsorptive removal of bisphenol A using synthesized magnetite nanoparticles

NASA Astrophysics Data System (ADS)

Orimolade, B. O.; Adekola, F. A.; Adebayo, G. B.

2018-03-01

Bisphenol A (BPA) is an organic compound which is often used as plasticizer and has been reported to be hazardous to man. In this research the efficiency of removal of BPA from water by magnetite through adsorption process was studied. The magnetite was synthesized using reverse co-precipitation method and fully characterized. Various physicochemical parameters affecting the adsorption of BPA using magnetite were studied as well. The optimum time for the adsorption process was found to be 60 min at pH of 6, adsorbent dose of 0.2 g and 50 ppm of BPA. The adsorption data were fitted by the Langmuir adsorption isotherm best with a regression value of 0.957. The R L value was 0.179 which revealed that the process is favorable. The Freundlich constant n which was 1.901 also revealed that the adsorption is normal and favorable. The data were in agreement with the pseudo-second-order kinetics with regression value of 0.98. From the thermodynamic studies, the process was found to be exothermic and the Gibb's free energy value which was negative showed that the adsorption was spontaneous. The synthesized magnetite therefore offers great potential for the remediation of bisphenol A-contaminated media.

Nonadiabatic effects on the charge transfer rate constant: A numerical study of a simple model system

NASA Astrophysics Data System (ADS)

Shin, Seokmin; Metiu, Horia

1995-06-01

We use a minimal model to study the effects of the upper electronic states on the rate of a charge transfer reaction. The model consists of three ions and an electron, all strung on a line. The two ions at the ends of the structure are held fixed, but the middle ion and the electron are allowed to move in one dimension, along the line joining them. The system has two bound states, one in which the electron ties the movable ion to the fixed ion at the left, and the other in which the binding takes place to the fixed ion at the right. The transition between these bound states is a charge transfer reaction. We use the flux-flux correlation function theory to perform two calculations of the rate constant for this reaction. In one we obtain numerically the exact rate constant. In the other we calculate the exact rate constant for the case when the reaction proceeds exclusively on the ground adiabatic state. The difference between these calculations gives the magnitude of the nonadiabatic effects. We find that the nonadiabatic effects are fairly large even when the gap between the ground and the excited adiabatic state substantially exceeds the thermal energy. The rate in the nonadiabatic theory is always smaller than that of the adiabatic one. Both rate constants satisfy the Arrhenius formula. Their activation energies are very close but the nonadiabatic one is always higher. The nonadiabatic preexponential is smaller, due to the fact that the upper electronic state causes an early recrossing of the reactive flux. The description of this reaction in terms of two diabatic states, one for reactants and one for products, is not always adequate. In the limit when nonadiabaticity is small, we need to use a third diabatic state, in which the electron binds to the moving ion as the latter passes through the transition state; this is an atom transfer process. The reaction changes from an atom transfer to an electron transfer, as nonadiabaticity is increased.

Rate constants for chemical reactions in high-temperature nonequilibrium air

NASA Technical Reports Server (NTRS)

Jaffe, R. L.

1986-01-01

In the nonequilibrium atmospheric chemistry regime that will be encountered by the proposed Aeroassisted Orbital Transfer Vehicle in the upper atmosphere, where air density is too low for thermal and chemical equilibrium to be maintained, the detailed high temperature air chemistry plays a critical role in defining radiative and convective heating loads. Although vibrational and electronic temperatures remain low (less than 15,000 K), rotational and translational temperatures may reach 50,000 K. Attention is presently given to the effects of multiple temperatures on the magnitudes of various chemical reaction rate constants, for the cases of both bimolecular exchange reactions and collisional excitation and dissociation reactions.

Adsorption of humic acids and trace metals in natural waters

NASA Technical Reports Server (NTRS)

Leung, W. H.

1982-01-01

Studies concerning the interactions between suspended hydrous iron oxide and dissolved humic acids and trace metals are reported. As a major component of dissolved organic matters and its readiness for adsorption at the solid/water interface, humic acids may play a very important role in the organometallic geochemistry of suspended sediments and in determining the fate and distribution of trace metals, pesticides and anions in natural water systems. Most of the solid phases in natural waters contain oxides and hydroxides. The most simple promising theory to describe the interactions of hydrous iron oxide interface is the surface complex formation model. In this model, the adsorptions of humic acids on hydrous iron oxide may be interpreted as complex formation of the organic bases (humic acid oxyanions) with surface Fe ions. Measurements on adsorptions were made in both fresh water and seawater. Attempts have been made to fit our data to Langmuir adsorption isotherm. Adsorption equilibrium constants were determined.

DISSOCIATION OF ARSENITE-PEPTIDE COMPLEXES: TRIPHASIC NATURE, RATE CONSTANTS, HALF LIVES AND BIOLOGICAL IMPORTANCE

EPA Science Inventory

We determined the number and the dissociation rate constants of different complexes formed from arsenite and two peptides containing either one (RV AVGNDYASGYHYGV for peptide 20) or three cysteines (LE AWQGK VEGTEHLYSMK K for peptide 10) via radioactive 73As labeled arsenite and ...

Applying constraints on model-based methods: Estimation of rate constants in a second order consecutive reaction

NASA Astrophysics Data System (ADS)

Kompany-Zareh, Mohsen; Khoshkam, Maryam

2013-02-01

This paper describes estimation of reaction rate constants and pure ultraviolet/visible (UV-vis) spectra of the component involved in a second order consecutive reaction between Ortho-Amino benzoeic acid (o-ABA) and Diazoniom ions (DIAZO), with one intermediate. In the described system, o-ABA was not absorbing in the visible region of interest and thus, closure rank deficiency problem did not exist. Concentration profiles were determined by solving differential equations of the corresponding kinetic model. In that sense, three types of model-based procedures were applied to estimate the rate constants of the kinetic system, according to Levenberg/Marquardt (NGL/M) algorithm. Original data-based, Score-based and concentration-based objective functions were included in these nonlinear fitting procedures. Results showed that when there is error in initial concentrations, accuracy of estimated rate constants strongly depends on the type of applied objective function in fitting procedure. Moreover, flexibility in application of different constraints and optimization of the initial concentrations estimation during the fitting procedure were investigated. Results showed a considerable decrease in ambiguity of obtained parameters by applying appropriate constraints and adjustable initial concentrations of reagents.

Powdered activated carbon adsorption of two fishy odorants in water: Trans,trans-2,4-heptadienal and trans,trans-2,4-decadienal.

PubMed

Li, Xin; Wang, Jun; Zhang, Xiaojian; Chen, Chao

2015-06-01

Powdered activated carbon (PAC) adsorption of two fishy odorants, trans,trans-2,4-heptadienal (HDE) and trans,trans-2,4-decadienal (DDE), was investigated. Both the pseudo first-order and the pseudo second-order kinetic models well described the kinetics curves, and DDE was more readily removed by PAC. In isotherm tests, both Freundlich and Modified Freundlich isotherms fitted the experimental data well. PAC exhibited a higher adsorption capacity for DDE than for HDE, which could be ascribed to the difference in their hydrophobicity. The calculated thermodynamic parameters (ΔG0, ΔH0, and ΔS0) indicated an exothermic and spontaneous adsorption process. PAC dosage, pH, and natural organic matter (NOM) presence were found to influence the adsorption process. With increasing PAC dosage, the pseudo first-order and pseudo second-order rate constants both increased. The value of pH had little influence on HDE or DDE molecules but altered the surface charge of PAC, and the maximum adsorption capacity occurred at pH9. The presence of NOM, especially the fraction with molecular weight less than 1k Dalton, hindered the adsorption. The study showed that preloaded NOM impaired the adsorption capacity of HDE or DDE more severely than simultaneously fed NOM did. Copyright © 2015. Published by Elsevier B.V.

Absolute rate constants of alkoxyl radical reactions in aqueous solution. [Tert-butyl hydroperoxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erben-Russ, M.; Michel, C.; Bors, W.

1987-04-23

The pulse radiolysis technique was used to generate the alkoxyl radical derived from tert-butyl hydroperoxide (/sup t/BuOOH) in aqueous solution. The reactions of this radical with 2,2'-azinobis(3-ethyl-6-benzothiazolinesulfonate) (ABTS) and promethazine were monitored by kinetic spectroscopy. The unimolecular decay rate constant of the tert-butoxyl radical (/sup t/BuO) was determined to be 1.4 x 10/sup 6/ s/sup -1/. On the basis of this value, the rate constants for /sup t/BuO attack on quercetin, crocin, crocetin, ascorbate, isoascorbate, trolox c, glutathione, thymidine, adenosine, guanosine, and unsaturated fatty acids were determined. In addition, the reaction of /sup t/BuO with the polyunsaturated fatty acids (PUFA)more » was observed by directly monitoring the formation of the fatty acid pentadienyl radicals. Interestingly, the attack of /sup t/BuO on PUFA was found to be faster by about one order of magnitude as compared to the same reaction in a nonpolar solvent.« less

Physicochemical factors affecting ethanol adsorption by activated carbon.

PubMed

Bradley, K J; Hamdy, M K; Toledo, R T

1987-03-01

Powder and granular activated charcoal were evaluated for ethanol adsorptivity from aqueous mixtures using an adsorption isotherm. Ethanol adsorption capacity was more pronounced at 25 degrees C as compared to 5, 15, and 40 degrees C. When pH of the ethanol-buffer mixture (0.09 ionic strength) was changed from acidic (2.3) to neutral and then to alkaline (11.2), ethanol adsorption was decreased. Increasing ionic strength of the ethanol-buffer mixtures from 0.05 to 0.09 enhanced ethanol adsorption but a further increase to 0.14 showed no significant effect. Ethanol adsorption was more efficient from an aqueous ethanol mixture as compared to semidefined and nondefined fermentation worts, respectively. Heating granular charcoal to 400 degrees C for 1 h and 600 degrees C for 3 h in N(2) increased ethanol adsorptivity and heating to 1000 degrees C (1 h) in CO(2) decreased it when ethanol was removed from dilute solutions by simple pass adsorption in a carbon packed column. Granular charcoal was superior to powdered charcoal and an inverse relationship was noted between the weight of the granular carbon bed in the column and ethanol adsorbed/g carbon. Decreasing the column feed flow rate from 7.5 to 2.0 L aqueous ethanol/min increased the adsorption rate.

Accelerated Testing Methodology in Constant Stress-Rate Testing for Advanced Structural Ceramics: A Preloading Technique

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.; Huebert, Dean; Bartlett, Allen; Choi, Han-Ho

2001-01-01

Preloading technique was used as a means of an accelerated testing methodology in constant stress-rate ('dynamic fatigue') testing for two different brittle materials. The theory developed previously for fatigue strength as a function of preload was further verified through extensive constant stress-rate testing for glass-ceramic and CRT glass in room temperature distilled water. The preloading technique was also used in this study to identify the prevailing failure mechanisms at elevated temperatures, particularly at lower test rate in which a series of mechanisms would be associated simultaneously with material failure, resulting in significant strength increase or decrease. Two different advanced ceramics including SiC whisker-reinforced composite silicon nitride and 96 wt% alumina were used at elevated temperatures. It was found that the preloading technique can be used as an additional tool to pinpoint the dominant failure mechanism that is associated with such a phenomenon of considerable strength increase or decrease.

Accelerated Testing Methodology in Constant Stress-Rate Testing for Advanced Structural Ceramics: A Preloading Technique

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.; Huebert, Dean; Bartlett, Allen; Choi, Han-Ho

2001-01-01

Preloading technique was used as a means of an accelerated testing methodology in constant stress-rate (dynamic fatigue) testing for two different brittle materials. The theory developed previously for fatigue strength as a function of preload was further verified through extensive constant stress-rate testing for glass-ceramic and CRT glass in room temperature distilled water. The preloading technique was also used in this study to identify the prevailing failure mechanisms at elevated temperatures, particularly at lower test rates in which a series of mechanisms would be associated simultaneously with material failure, resulting in significant strength increase or decrease. Two different advanced ceramics including SiC whisker-reinforced composite silicon nitride and 96 wt% alumina were used at elevated temperatures. It was found that the preloading technique can be used as an additional tool to pinpoint the dominant failure mechanism that is associated with such a phenomenon of considerable strength increase or decrease.

Dose equivalent rate constants and barrier transmission data for nuclear medicine facility dose calculations and shielding design.

PubMed

Kusano, Maggie; Caldwell, Curtis B

2014-07-01

A primary goal of nuclear medicine facility design is to keep public and worker radiation doses As Low As Reasonably Achievable (ALARA). To estimate dose and shielding requirements, one needs to know both the dose equivalent rate constants for soft tissue and barrier transmission factors (TFs) for all radionuclides of interest. Dose equivalent rate constants are most commonly calculated using published air kerma or exposure rate constants, while transmission factors are most commonly calculated using published tenth-value layers (TVLs). Values can be calculated more accurately using the radionuclide's photon emission spectrum and the physical properties of lead, concrete, and/or tissue at these energies. These calculations may be non-trivial due to the polyenergetic nature of the radionuclides used in nuclear medicine. In this paper, the effects of dose equivalent rate constant and transmission factor on nuclear medicine dose and shielding calculations are investigated, and new values based on up-to-date nuclear data and thresholds specific to nuclear medicine are proposed. To facilitate practical use, transmission curves were fitted to the three-parameter Archer equation. Finally, the results of this work were applied to the design of a sample nuclear medicine facility and compared to doses calculated using common methods to investigate the effects of these values on dose estimates and shielding decisions. Dose equivalent rate constants generally agreed well with those derived from the literature with the exception of those from NCRP 124. Depending on the situation, Archer fit TFs could be significantly more accurate than TVL-based TFs. These results were reflected in the sample shielding problem, with unshielded dose estimates agreeing well, with the exception of those based on NCRP 124, and Archer fit TFs providing a more accurate alternative to TVL TFs and a simpler alternative to full spectral-based calculations. The data provided by this paper should assist

Growth rate and trapping efficacy of nematode-trapping fungi under constant and fluctuating temperatures.

PubMed

Fernández, A S; Larsen, M; Wolstrup, J; Grønvold, J; Nansen, P; Bjørn, H

1999-08-01

The effect of temperature on radial growth and predatory activity of different isolates of nematode-trapping fungi was assessed. Four isolates of Duddingtonia flagrans and one isolate of Arthrobotrys oligospora were inoculated on petri dishes containing either cornmeal agar (CMA) or faecal agar and then incubated for 14 days under three different constant and fluctuating temperature regimes. The radial growth was similar on the two substrates at each temperature regime. All fungal isolates showed a higher growth rate at a constant 20 degrees C. At 10 degrees and 15 degrees C, all D. flagrans isolates showed very similar patterns of radial growth at both constant and fluctuating temperatures. At 20 degrees C, they grew significantly faster at constant than at fluctuating temperatures. A. oligospora grew significantly faster than all D. flagrans isolates except when incubated at a fluctuating 20 degrees C. Spores of each fungal isolate were added to faecal cultures containing eggs of Cooperia oncophora at a concentration of 6250 spores/g faeces. The cultures were incubated for 14 days at the same temperature regimes described above. Control faeces (without fungal material) were also cultured. More larvae were recovered from the fungus-treated cultures incubated at a constant 10 degrees or 15 degrees C than from those incubated at the respective fluctuating temperatures, except for one D. flagrans isolate. Incubation at 20 degrees C showed the opposite effect. The general reduction observed in the number of nematode larvae due to fungal trapping was 18-25% and 48-80% for a constant and fluctuating 10 degrees C, 70-96% and 93-95% for a constant and fluctuating 15 degrees C, and 63-98% and 0-25% for a constant and fluctuating 20 degrees C, respectively.

The Accelerated Late Adsorption of Pulmonary Surfactant

PubMed Central

2011-01-01

Adsorption of pulmonary surfactant to an air−water interface lowers surface tension (γ) at rates that initially decrease progressively, but which then accelerate close to the equilibrium γ. The studies here tested a series of hypotheses concerning mechanisms that might cause the late accelerated drop in γ. Experiments used captive bubbles and a Wilhelmy plate to measure γ during adsorption of vesicles containing constituents from extracted calf surfactant. The faster fall in γ reflects faster adsorption rather than any feature of the equation of state that relates γ to surface concentration (Γ). Adsorption accelerates when γ reaches a critical value rather than after an interval required to reach that γ. The hydrophobic surfactant proteins (SPs) represent key constituents, both for reaching the γ at which the acceleration occurs and for producing the acceleration itself. The γ at which rates of adsorption increase, however, is unaffected by the Γ of protein in the films. In the absence of the proteins, a phosphatidylethanolamine, which, like the SPs, induces fusion of the vesicles with the interfacial film, also causes adsorption to accelerate. Our results suggest that the late acceleration is characteristic of adsorption by fusion of vesicles with the nascent film, which proceeds more favorably when the Γ of the lipids exceeds a critical value. PMID:21417351

pH-Dependence of Binding Constants and Desorption Rates of Phosphonate- and Hydroxamate-Anchored [Ru(bpy)3]2+ on TiO2 and WO3.

PubMed

Esarey, Samuel L; Bartlett, Bart M

2018-04-17

The binding constants and rate constants for desorption of the modified molecular dye [Ru(bpy) 3 ] 2+ anchored by either phosphonate or hydroxamate on the bipyridine ligand to anatase TiO 2 and WO 3 have been measured. In aqueous media at pH 1-10, repulsive electrostatic interactions between the negatively charged anchor and the negatively charged surface govern phosphonate desorption under neutral and basic conditions for TiO 2 anatase due to the high acidity of phosphonic acid (p K a,4 = 5.1). In contrast, the lower acidity of hydroxamate (p K a,1 = 6.5, p K a,2 = 9.1) leads to little change in adsorption/desorption properties as a function of pH from 1 to 7. The binding constant for hydroxamate is 10 3 in water, independent of pH in this range. These results are true for WO 3 as well, but are not reported at pH > 4 due to its Arrhenius acidity. Kinetics for desorption as a function of pH are reported, with a proposed mechanism for phosphonate desorption at high pH being the electrostatic repulsion of negative charges between the surface and the anionic anchor. Further, the hydroxamic acid anchor itself is likely the site of quasi-reversible redox activity in [Ru(bpy) 2 (2,2'-bpy-4,4'-(C(O)N(OH)) 2 )] 2+ , which does not lead to any measurable deterioration of the complex within 2 h of dark cyclic voltammogram scans in aqueous media. These results posit phosphonate as the preferred anchoring group under acidic conditions and hydroxamate for neutral/basic conditions.

Generalized adsorption isotherms for molecular and dissociative adsorption of a polar molecular species on two polar surface geometries: Perovskite (100) (Pm-3m) and fluorite (111) (Fm-3m)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Danielson, Thomas; Hin, Celine; Savara, Aditya

Lattice based kinetic Monte Carlo (KMC) simulations have been used to determine a functional form for the second order adsorption isotherms on two commonly investigated crystal surfaces: the (111) fluorite surface and the (100) perovskite surface which has the same geometric symmetry as the NaCl (100) surface. The functional form is generalized to be applicable to all values of the equilibrium constant by a shift along the pressure axis. Functions have been determined for estimating the pressure at which a desired coverage would be achieved and for estimating the coverage at a certain pressure. The generalized form has been calculatedmore » by investigating the surface adsorbate coverage across a range of thermodynamic equilibrium constants that span the range 10-26 to 1013. Finally, the equations have been shown to be general for any value of the adsorption equilibrium constant.« less

Generalized adsorption isotherms for molecular and dissociative adsorption of a polar molecular species on two polar surface geometries: Perovskite (100) (Pm-3m) and fluorite (111) (Fm-3m)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Danielson, Thomas; Hin, Celine; Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061

Lattice based kinetic Monte Carlo simulations have been used to determine a functional form for the second order adsorption isotherms on two commonly investigated crystal surfaces: the (111) fluorite surface and the (100) perovskite surface which has the same geometric symmetry as the NaCl (100) surface. The functional form is generalized to be applicable to all values of the equilibrium constant by a shift along the pressure axis. Functions have been determined for estimating the pressure at which a desired coverage would be achieved and, conversely, for estimating the coverage at a certain pressure. The generalized form has been calculatedmore » by investigating the surface adsorbate coverage across a range of thermodynamic equilibrium constants that span the range 10{sup −26} to 10{sup 13}. The equations have been shown to be general for any value of the adsorption equilibrium constant.« less

Generalized adsorption isotherms for molecular and dissociative adsorption of a polar molecular species on two polar surface geometries: Perovskite (100) (Pm-3m) and fluorite (111) (Fm-3m)

DOE PAGES

Danielson, Thomas; Hin, Celine; Savara, Aditya

2016-08-10

Lattice based kinetic Monte Carlo (KMC) simulations have been used to determine a functional form for the second order adsorption isotherms on two commonly investigated crystal surfaces: the (111) fluorite surface and the (100) perovskite surface which has the same geometric symmetry as the NaCl (100) surface. The functional form is generalized to be applicable to all values of the equilibrium constant by a shift along the pressure axis. Functions have been determined for estimating the pressure at which a desired coverage would be achieved and for estimating the coverage at a certain pressure. The generalized form has been calculatedmore » by investigating the surface adsorbate coverage across a range of thermodynamic equilibrium constants that span the range 10-26 to 1013. Finally, the equations have been shown to be general for any value of the adsorption equilibrium constant.« less

Adsorption of phenolic compound by aged-refuse.

PubMed

Xiaoli, Chai; Youcai, Zhao

2006-09-01

The adsorption of phenol, 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol by aged-refuse has been studied. Adsorption isotherms have been determined for phenol, 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol and the data fits well to the Freundlich equation. The chlorinated phenols are absorbed more strongly than the phenol and the adsorption capacity has an oblivious relationship with the numbers and the position of chlorine subsistent. The experiment data suggests that both the partition function and the chemical adsorption involve in the adsorption process. Pseudo-first-order and pseudo-second-order model were applied to investigate the kinetics of the adsorption and the results show that it fit the pseudo-second-order model. More than one step involves in the adsorption process and the overall rate of the adsorption process appears to be controlled by the chemical reaction. The thermodynamic analysis indicates that the adsorption is spontaneous and endothermic.

Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soudackov, Alexander V.; Hammes-Schiffer, Sharon

2015-11-21

Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at highmore » temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to

Estimation of Anaerobic Debromination Rate Constants of PBDE Pathways Using an Anaerobic Dehalogenation Model.

PubMed

Karakas, Filiz; Imamoglu, Ipek

2017-04-01

This study aims to estimate anaerobic debromination rate constants (k m ) of PBDE pathways using previously reported laboratory soil data. k m values of pathways are estimated by modifying a previously developed model as Anaerobic Dehalogenation Model. Debromination activities published in the literature in terms of bromine substitutions as well as specific microorganisms and their combinations are used for identification of pathways. The range of estimated k m values is between 0.0003 and 0.0241 d -1 . The median and maximum of k m values are found to be comparable to the few available biologically confirmed rate constants published in the literature. The estimated k m values can be used as input to numerical fate and transport models for a better and more detailed investigation of the fate of individual PBDEs in contaminated sediments. Various remediation scenarios such as monitored natural attenuation or bioremediation with bioaugmentation can be handled in a more quantitative manner with the help of k m estimated in this study.

Adsorption, sedimentation, and inactivation of E. coli within wastewater treatment wetlands.

PubMed

Boutilier, L; Jamieson, R; Gordon, R; Lake, C; Hart, W

2009-09-01

Bacteria fate and transport within constructed wetlands must be understood if engineered wetlands are to become a reliable form of wastewater treatment. This study investigated the relative importance of microbial treatment mechanisms in constructed wetlands treating both domestic and agricultural wastewater. Escherichia coli (E. coli) inactivation, adsorption, and settling rates were measured in the lab within two types of wastewater (dairy wastewater lagoon effluent and domestic septic tank effluent). In situ E. coli inactivation was also measured within a domestic wastewater treatment wetland and the adsorption of E. coli was also measured within the wetland effluent. Inactivation of E. coli appears to be the most significant contributor to E. coli removal within the wastewaters and wetland environments examined in this study. E. coli survived longer within the dairy wastewater (DW) compared to the domestic wastewater treatment wetland water (WW). First order rate constants for E. coli inactivation within the WW in the lab ranged from 0.09 day(-1) (d(-1)) at 7.6 degrees C to 0.18d(-1) at 22.8 degrees C. The average in situ rate constant observed within the domestic wetland ranged from 0.02 d(-1) to 0.03 d(-1) at an average water temperature of 17 degrees C. First order rate constants for E. coli inactivation within the DW ranged from 0.01 d(-1) at 7.7 degrees C to 0.04 d(-1) at 24.6 degrees C. Calculated distribution coefficients (K(d)) were 19,000 mL g(-1), 324,000 mL g(-1), and 293 mL g(-1) for E. coli with domestic septic tank effluent (STE), treated wetland effluent (WLE), and DW, respectively. Approximately 50%, 20%, and 90% of E. coli were "free floating" or associated with particles <5 microm in size within the STE, WLE, and DW respectively. Although 10-50% of E. coli were found to associate with particles >5 microm within both the STE and DW, settling did not appear to contribute to E. coli removal within sedimentation experiments, indicating that the

Adsorption and Exchange Kinetics of Hydrophilic and Hydrophobic Phosphorus Ligands on Gold Surface

NASA Astrophysics Data System (ADS)

Zhuge, X. Q.; Bian, Z. C.; Luo, Z. H.; Mu, Y. Y.; Luo, K.

2017-02-01

The adsorption kinetics process of hydrophobic ligand (triphenylphosphine, PPh3) and hydrophilic ligand (tris(hydroxymethyl)phosphine oxide, THPO) on the surface of gold electrode were estimated by using electrical double layer capacitance (EDLC). Results showed that the adsorption process of both ligands included fast and slow adsorption processes, and the fast adsorption process could fit the first order kinetic equation of Langmuir adsorption isotherm. During the slow adsorption process, the surface coverage (θ) of PPh3 was higher than that of THPO due to the larger adsorption kinetic constant of PPh3 than that of THPO, which implied that PPh3 could replace THPO on the gold electrode. The exchange process of both ligands on the surface of gold electrode proved that PPh3 take the place of THPO by testing the variation of EDLC which promote the preparation of Janus gold, and the theoretic simulation explained the reason of ligands exchange from the respect of energy..

Human serum albumin adsorption study on 62-MHz miniaturized quartz gravimetric sensors.

PubMed

Kao, Ping; Patwardhan, Ashish; Allara, David; Tadigadapa, Srinivas

2008-08-01

We have designed and fabricated 25-microm-thick quartz resonators operating at a fundamental resonance frequency of approximately 62 MHz. The results show a substantial increase in the mass sensitivity compared to single monolithic commercial resonators operating at lower frequencies in the approximately 5-10-MHz range. The overall performance of the micromachined resonators is demonstrated for the example of human serum albumin protein adsorption from aqueous buffer solutions onto gold electrodes functionalized with self-assembled monolayers. The results show a saturation adsorption frequency change of 6.8 kHz as opposed to 40 Hz for a commercial approximately 5-MHz sensor under identical loading conditions. From the analysis of the adsorption isotherm, the equilibrium adsorption constant of the adsorption of the protein layer was found to be K = 8.03 x 10(6) M(-1), which is in agreement with the values reported in the literature. The high sensitivity of the miniaturized QCM devices can be a significant advantage in both vapor and solution adsorption analyses.

Mechanism and kinetics of uranium adsorption onto soil around coal-fired power plant

NASA Astrophysics Data System (ADS)

Yasim, Nurzulaifa Shaheera Erne Mohd; Ariffin, Nik Azlin Nik; Mohammed, Noradila; Ayob, Syafina

2017-11-01

Coal is the largest source of energy in Malaysia providing approximately 80 % of all entire power needs. The combustion of coal concentrates a high content of heavy metals and radioactive elements in the ashes and sludge. Hazardous emissions from coal combustion were deposited into the soil and most likely transported into the groundwater system. The presence of radioactive materials in the ground water system can cause a wide range of environmental impacts and adverse health effects like cancer, impairment of neurological function and cardiovascular disease. However, the soil has a natural capability in adsorption of radioactive materials. Thus, this study was evaluated the adsorption capacity of Uranium onto the soil samples collected nearby the coal-fired power plants. In the batch experiment, parameters that were set constant include pH, the amount of soil and contact time. Various initial concentrations of radionuclides elements in the range of 2 mg/L - 10 mg/L were used. The equilibrium adsorption data was analyzed by the Freundlich isotherm and Langmuir isotherms. Then, the influences of solution pH, contact time and temperature on the adsorption process were investigated. The kinetics of radioactive materials was discussed by pseudo-first-order and pseudo-second-order rate equation. Thus, the data from this study could provide information about the potentiality of soil in sorption of radioactive materials that can be leached into groundwater. Besides that, this study could also be used as baseline data for future reference in the development of adsorption modeling in the calculation of distribution coefficient.

Characterization of metal adsorption variability in a sand and gravel aquifer, Cape Cod, Massachusetts, U.S.A

USGS Publications Warehouse

Fuller, C.C.; Davis, J.A.; Coston, J.A.; Dixon, E.

1996-01-01

Several geochemical properties of an aquifer sediment that control metal-ion adsorption were investigated to determine their potential use as indicators of the spatial variability of metal adsorption. Over the length of a 4.5-m-long core from a sand and gravel aquifer, lead (Pb2+) and zinc (Zn2+) adsorption at constant chemical conditions (pH 5.3) varied by a factor of 2 and 4, respectively. Pb2+ and Zn2+ were adsorbed primarily by Fe- and Al-oxide coatings on quartz-grain surfaces. Per unit surface area, both Pb2+ and Zn2+ adsorption were significantly correlated with the amount of Fe and Al that dissolved from the aquifer material in a partial chemical extraction. The variability in conditional binding constants for Pb2+ and Zn2+ adsorption (log KADS) derived from a simple non-electrostatic surface complexation model were also predicted by extracted Fe and Al normalized to surface area. Because the abundance of Fe- and Al-oxide coatings that dominate adsorption does not vary inversely with grain size by a simple linear relationship, only a weak, negative correlation was found between the spatial variability of Pb2+ adsorption and grain size in this aquifer. The correlation between Zn2+ adsorption and grain size was not significant. Partial chemical extractions combined with surface-area measurements have potential use for estimating metal adsorption variability in other sand and gravel aquifers of negligible carbonate and organic carbon content.

Cell wall reactivity of acidophilic and alkaliphilic bacteria determined by potentiometric titrations and Cd adsorption experiments.

PubMed

Kenney, Janice P L; Fein, Jeremy B

2011-05-15

In this study, we used potentiometric titrations and Cd adsorption experiments to determine the binding capacities of two acidophilic (A. cryptum and A. acidophilum) and two alkaliphilic (B. pseudofirmus and B. circulans) bacterial species in order to determine if any consistent trends could be observed relating bacterial growth environment to proton and Cd binding properties and to compare those binding behaviors to those of neutrophilic bacteria. All of the bacterial species studied exhibited significant proton buffering over the pH range in this study, with the alkaliphiles exhibiting significantly higher acidity constants than the acidophiles as well as the neutrophilic bacterial consortia. The calculated average site concentrations for each of the bacteria in this study are within 2σ experimental error of each other, with the exception of A. cryptum, which has a significantly higher Site 2 concentration than the other species. Despite differing acidity constants between the acidophiles and alkaliphiles, all bacteria except A. cryptum exhibited remarkably similar Cd adsorption behavior to each other, and the observed extent of adsorption was also similar to that predicted from a generalized model derived using neutrophilic bacterial consortia. This study demonstrates that bacteria that grow under extreme conditions exhibit similar proton and metal adsorption behavior to that of previously studied neutrophilic species and that a single set of proton and metal binding constants can be used to model the behavior of bacterial adsorption under a wide range of environmental conditions.

Neptunium(V) Adsorption to Bacteria at Low and High Ionic Strength

NASA Astrophysics Data System (ADS)

Ams, D.; Swanson, J. S.; Reed, D. T.

2010-12-01

Np(V) is expected to be the predominant oxidation state of neptunium in aerobic natural waters. Np(V), as the NpO2+ aquo and associated complexed species, is readily soluble, interacts weakly with geologic media, and has a high redox stability under a relatively wide range of subsurface conditions. These chemical properties, along with a long half-life make it a primary element of concern regarding long-term nuclear waste storage and subsurface containment. The fate and transport of neptunium in the environment may be influenced by adsorption onto bacterial surfaces. The adsorption of neptunium to bacterial surfaces ties the mobility of the contaminant to the mobility of the bacterium. In this study, the adsorption of the neptunyl (NpO2+) ion was evaluated at low ionic strength on a common soil bacterium and at high ionic strength on a halophilic bacterium isolated from a briny groundwater near the Waste Isolation Pilot Plant (WIPP) in southeast New Mexico. Adsorption experiments were performed in batch reactors as a function of pH, ionic strength, and bacteria/Np mass ratio. Np(V) adsorption was modeled using a surface complexation approach with the mathematical program FITEQL to determine functional group specific binding constants. The data from acid and base titrations of the bacteria used were also modeled to estimate the concentrations and deprotonation constants of discrete bacterial surface functional groups. Bacterial functional group characteristics and Np(V) adsorption behavior between the soil bacterium and the halophilic bacterium were compared. These results highlight key similarities and differences in actinide adsorption behavior in environments of significantly different ionic strength. The observed adsorption behavior may be linked to similarities and differences in the characteristics of the moieties between the cell walls of common gram-negative soil and halophilic bacteria. Moreover, differences in adsorption behavior may also reflect ionic

Adsorption of Nanoplastics on Algal Photosynthesis

NASA Astrophysics Data System (ADS)

Turner, James; Bhattacharya, Priyanka; Lin, Sijie; Ke, Pu Chun

2010-03-01

The rapid accumulation of disposed plastics in the environment, especially in the Pacific Ocean, has become a global concern in recent years. Photo, chemical and physical degradations constantly fragment these plastics into a wide array of macroscopic to microscopic particles. As a result, marine organisms such as algae may be exposed to plastic particles through ingestion, adsorption and other forms of uptake. Such interactions, currently little understood, could potentially impact on the health state of the entire food chain. Here we report on polystyrene-algae interaction and its impact on algal photosynthesis. We first investigated the adsorption of polystyrene beads (20 nm) on a cellulose film coated on a 96-well plate. We derived a supralinear increase of the adsorption with the beads concentration for both positively and negatively charged polystyrene beads, with a saturation observed for the negatively charged polystyrene beads of concentration above 1.6 mg/mL. Using a bicarbonate indicator we discovered decreased carbon dioxide depletion due to polystyrene-algae binding. Since polystyrene beads also mediated algae aggregation, nanoplastics may alternatively be harnessed for waste water treatment.

Kinetic Analysis for the Multistep Profiles of Organic Reactions: Significance of the Conformational Entropy on the Rate Constants of the Claisen Rearrangement.

PubMed

Sumiya, Yosuke; Nagahata, Yutaka; Komatsuzaki, Tamiki; Taketsugu, Tetsuya; Maeda, Satoshi

2015-12-03

The significance of kinetic analysis as a tool for understanding the reactivity and selectivity of organic reactions has recently been recognized. However, conventional simulation approaches that solve rate equations numerically are not amenable to multistep reaction profiles consisting of fast and slow elementary steps. Herein, we present an efficient and robust approach for evaluating the overall rate constants of multistep reactions via the recursive contraction of the rate equations to give the overall rate constants for the products and byproducts. This new method was applied to the Claisen rearrangement of allyl vinyl ether, as well as a substituted allyl vinyl ether. Notably, the profiles of these reactions contained 23 and 84 local minima, and 66 and 278 transition states, respectively. The overall rate constant for the Claisen rearrangement of allyl vinyl ether was consistent with the experimental value. The selectivity of the Claisen rearrangement reaction has also been assessed using a substituted allyl vinyl ether. The results of this study showed that the conformational entropy in these flexible chain molecules had a substantial impact on the overall rate constants. This new method could therefore be used to estimate the overall rate constants of various other organic reactions involving flexible molecules.

Phage adsorption to Lactobacillus plantarum: influence of physiological and environmental factors.

PubMed

Marcó, M Briggiler; Reinheimer, J A; Quiberoni, A

2010-04-15

Bacteriophage infection of lactic acid bacteria (LAB) constitutes one of the major problems in the dairy industry, causing economic losses and a constant risk of low quality and/or unsafe foods. The first step in the phage biology is the adsorption on the host cell surface. In a previous study, a remarkable thermal, chemical and photocatalytic resistance was demonstrated by four phages of Lactobacillus plantarum (ATCC 8014-B1, ATCC 8014-B2, FAGK1 and FAGK2). In the present work, these phages were used to characterize the adsorption process on L. plantarum ATCC 8014. Clearly, the characterization of this process could increase the possibilities of design useful strategies in order to prevent phage infections. The influence of Ca(2+), temperature, pH and physiological cell state on phage adsorption was investigated. Burst sizes of phages ATCC 8014-B1 and ATCC 8014-B2 were 60 and 83 PFU/infective centre, respectively. The four phages exhibited a high infectivity even at pH 4 and pH 11. Calcium or magnesium ions were not indispensable for cell lysis and plaque formation, and more than 99% of phage particles were adsorbed either in the presence or absence of Ca(2+), after 15 min at 37 degrees C. Phage adsorption was only partially affected at 50 degrees C, while reached its maximum between 30 and 42 degrees C. The highest adsorption values (99.9%) were observed from pH 5 to 7, after 30 min at 37 degrees C. Adsorption rates decreased after the thermal inactivation of cells, though, when 20 microg/ml of chloramphenicol was used, adsorption values were similar on treated and untreated cells. All these results showed that the adsorption process was only partially affected by a few conditions: thermally killed host cells, an incubation temperature of 50 degrees C and pH values of 9 and 10. Nevertheless, and unfortunately, those conditions are not commonly applied during fermented food manufacturing, thus restricting highly the application of strategies currently available to

Theoretical Discussion of Electron Transport Rate Constant at TCNQ / Ge and TiO2 System

NASA Astrophysics Data System (ADS)

Al-agealy, Hadi J. M.; Alshafaay, B.; Hassooni, Mohsin A.; Ashwiekh, Ahmed M.; Sadoon, Abbas K.; Majeed, Raad H.; Ghadhban, Rawnaq Q.; Mahdi, Shatha H.

2018-05-01

We have been studying and estimation the electronic transport constant at TCNQ / Ge and Tio2 interface by means of tunneling potential (TP), transport energy reorientation (TER), driving transition energy DTE and coupling coefficient constant. A simple quantum model for the transition processes was adapted to estimation and analysis depending on the quantum state for donor state |α D > and acceptor stated |α A > and assuming continuum levels of the system. Evaluation results were performed for the surfaces of Ge and Tio2 as best as for multilayer TCNQ. The results show an electronic transfer feature for electronic TCNQ density of states and a semiconductor behavior. The electronic rate constant result for both systems shows a good tool to election system in applied devices. All these results indicate the

Characterization of Adsorption Enthalpy of Novel Water-Stable Zeolites and Metal-Organic Frameworks

NASA Astrophysics Data System (ADS)

Kim, Hyunho; Cho, H. Jeremy; Narayanan, Shankar; Yang, Sungwoo; Furukawa, Hiroyasu; Schiffres, Scott; Li, Xiansen; Zhang, Yue-Biao; Jiang, Juncong; Yaghi, Omar M.; Wang, Evelyn N.

2016-01-01

Water adsorption is becoming increasingly important for many applications including thermal energy storage, desalination, and water harvesting. To develop such applications, it is essential to understand both adsorbent-adsorbate and adsorbate-adsorbate interactions, and also the energy required for adsorption/desorption processes of porous material-adsorbate systems, such as zeolites and metal-organic frameworks (MOFs). In this study, we present a technique to characterize the enthalpy of adsorption/desorption of zeolites and MOF-801 with water as an adsorbate by conducting desorption experiments with conventional differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA). With this method, the enthalpies of adsorption of previously uncharacterized adsorbents were estimated as a function of both uptake and temperature. Our characterizations indicate that the adsorption enthalpies of type I zeolites can increase to greater than twice the latent heat whereas adsorption enthalpies of MOF-801 are nearly constant for a wide range of vapor uptakes.

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

2017-07-01

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.

Reaction rate constants and mean population percentage for nitrifiers in an alternating oxidation ditch system.

PubMed

Mantziaras, I D; Katsiri, A

2011-01-01

This paper presents a methodology for the determination of reaction rate constants for nitrifying bacteria and their mean population percentage in biomass in an alternating oxidation ditch system. The method used is based on the growth rate equations of the ASM1 model (IWA) (Henze et al. in Activated sludge models ASM1, ASM2, ASM2d, and ASM3. IWA Scientific and Technical Report no. 9, IWA Publishing, London, UK, 2000) and the application of mass balance equations for nitrifiers and ammonium nitrogen in an operational cycle of the ditch system. The system consists of two ditches operating in four phases. Data from a large-scale oxidation ditch pilot plant with a total volume of 120 m(3) within an experimental period of 8 months was used. Maximum specific growth rate for autotrophs (μ(A)) and the half-saturation constant for ammonium nitrogen (K(NH)) were found to be 0.36 day(-1) and 0.65 mgNH(4)-N/l, respectively. Additionally, the average population percentage of the nitrifiers in the biomass was estimated to be around 3%.

Adsorptive removal of ascertained and suspected endocrine disruptors from aqueous solution using plant-derived materials.

PubMed

Loffredo, Elisabetta; Taskin, Eren

2017-08-01

The present study deals with the use of low-cost plant-derived materials, namely a biochar, spent coffee grounds, spent tea leaves, and a compost humic acid, for the adsorptive removal from water of two estrogens, 4-tert-octylphenol (OP) and 17-β-estradiol (E2), and two pesticides, carbaryl and fenuron, each spiked at a concentration of 1 mg L -1 . Kinetics and adsorption isotherms have been performed using a batch equilibrium method to measure the sorption capacities of the adsorbents towards the four molecules. Adsorption constants were calculated using the linear, Freundlich, and Langmuir models. Kinetics data obtained evidenced a rapid adsorption of each compound onto both biochar and coffee grounds with the attainment of a steady-state equilibrium in less than 4 h. Significant differences among the adsorbents and the compounds were found regarding the model and the extent of adsorption. In general, the estrogens were adsorbed more quickly and in greater amounts than the less hydrophobic pesticides, following the order: OP > E2 > carbaryl > fenuron. The ranges of Freundlich constants obtained for OP, E2, carbaryl, and fenuron onto the sorbents were 5049-2253, 3385-206, 2491-79, and 822-24 L kg -1 , respectively. The maximum values of constants were obtained for biochar, except for OP that was more adsorbed by spent coffee grounds. Adsorption kinetic data followed a pseudo-second-order model, thus indicating the occurrence of chemical interactions between the compounds and the substrates. The remarkable sorption capacities of all adsorbents towards the four molecules suggest the valuable exploitation of these materials for decontamination purposes, such as the treatment of wastewater before a feasible recycle in soil.

Theory for rates, equilibrium constants, and Brønsted slopes in F1-ATPase single molecule imaging experiments

PubMed Central

Volkán-Kacsó, Sándor; Marcus, Rudolph A.

2015-01-01

A theoretical model of elastically coupled reactions is proposed for single molecule imaging and rotor manipulation experiments on F1-ATPase. Stalling experiments are considered in which rates of individual ligand binding, ligand release, and chemical reaction steps have an exponential dependence on rotor angle. These data are treated in terms of the effect of thermodynamic driving forces on reaction rates, and lead to equations relating rate constants and free energies to the stalling angle. These relations, in turn, are modeled using a formalism originally developed to treat electron and other transfer reactions. During stalling the free energy profile of the enzymatic steps is altered by a work term due to elastic structural twisting. Using biochemical and single molecule data, the dependence of the rate constant and equilibrium constant on the stall angle, as well as the Børnsted slope are predicted and compared with experiment. Reasonable agreement is found with stalling experiments for ATP and GTP binding. The model can be applied to other torque-generating steps of reversible ligand binding, such as ADP and Pi release, when sufficient data become available. PMID:26483483

The uncertainty of biodegradation rate constants of emerging organic compounds in soil and groundwater - A compilation of literature values for 82 substances.

PubMed

Greskowiak, Janek; Hamann, Enrico; Burke, Victoria; Massmann, Gudrun

2017-12-01

The present study reports on biodegradation rate constants of emerging organic compounds (EOCs) in soil and groundwater available in the literature. The major aim of this compilation was to provide an assessment of the uncertainty of hydrological models with respect to the fate of EOCs. The literature search identified a total number of 82 EOCs for which 1st-order rate constants could be derived. It was found that for the majority of compounds degradation rate constants vary over more than three orders of magnitude. Correlation to factors that are well known to affect the degradation rate, such as temperature or redox condition was weak. No correlation at all was found with results from available quantitative structure-activity relationship models. This suggests that many unknown site specific or experimentally specific factors influence the degradation behavior of EOCs in the environment. Thus, local and catchment scale predictive models to estimate EOC concentration at receptors, e.g., receiving waters or drinking water wells, need to consider the large uncertainty in 1st-order rate constants. As a consequence, applying rate constants that were derived from one experiment or field site investigation to other experiments or field sites should be done with extreme caution. Copyright © 2017 Elsevier Ltd. All rights reserved.

Co-adsorption of Trichloroethylene and Arsenate by Iron-Impregnated Granular Activated Carbon.

PubMed

Deng, Baolin; Kim, Eun-Sik

2016-05-01

Co-adsorption of trichloroethylene (TCE) and arsenate [As(V)] was investigated using modified granular activated carbons (GAC): untreated, sodium hypochlorite-treated (NaClO-GAC), and NaClO with iron-treated GAC (NaClO/Fe-GAC). Batch experiments of single- [TCE or As(V)] and binary- [TCE and As(V)] components solutions are evaluated through Langmuir and Freundlich isotherm models and adsorption kinetic tests. In the single-component system, the adsorption capacity of As(V) was increased by the NaClO-GAC and the NaClO/Fe-GAC. The untreated GAC showed a low adsorption capacity for As(V). Adsorption of TCE by the NaClO/Fe-GAC was maximized, with an increased Freundlich constant. Removal of TCE in the binary-component system was decreased 15% by the untreated GAC, and NaClO- and NaClO/Fe-GAC showed similar efficiency to the single-component system because of the different chemical status of the GAC surfaces. Results of the adsorption isotherms of As(V) in the binary-component system were similar to adsorption isotherms of the single-component system. The adsorption affinities of single- and binary-component systems corresponded with electron transfer, competitive adsorption, and physicochemical properties.

Tunneling Rate Constants for H2CO+H on Amorphous Solid Water Surfaces

NASA Astrophysics Data System (ADS)

Song, Lei; Kästner, Johannes

2017-12-01

Formaldehyde (H2CO) is one of the most abundant molecules observed in the icy mantle covering interstellar grains. Studying its evolution can contribute to our understanding of the formation of complex organic molecules in various interstellar environments. In this work, we investigated the hydrogenation reactions of H2CO yielding CH3O, CH2OH, and the hydrogen abstraction resulting in H2+HCO on an amorphous solid water (ASW) surface using a quantum mechanics/molecular mechanics (QM/MM) model. The binding energies of H2CO on the ASW surface vary broadly, from 1000 to 9370 K. No correlation was found between binding energies and activation energies of hydrogenation reactions. Combining instanton theory with QM/MM modeling, we calculated rate constants for the Langmuir-Hinshelwood and the Eley-Rideal mechanisms for the three product channels of H+H2CO surface reactions down to 59 K. We found that the channel producing CH2OH can be ignored, owing to its high activation barrier leading to significantly lower rates than the other two channels. The ASW surface influences the reactivity in favor of formation of CH3O (branching ratio ˜80%) and hinders the H2CO dissociation into H2+HCO. In addition, kinetic isotope effects are strong in all reaction channels and vary strongly between the channels. Finally, we provide fits of the rate constants to be used in astrochemical models.

Adsorption kinetics of SO2 on powder activated carbon

NASA Astrophysics Data System (ADS)

Li, Bing; Zhang, Qilong; Ma, Chunyuan

2018-02-01

The flue gas SO2 adsorption removal by powder activated carbon is investigated based on a fixed bed reactor. The effect of SO2 inlet concentration on SO2 adsorption is investigated and the adsorption kinetics is analyzed. The results indicated that the initial SO2 adsorption rate and the amount of SO2 adsorbed have increased with increased in SO2 inlet concentration. Gas diffusion, surface adsorption and catalytic oxidation reaction are involved in SO2 adsorption on powder activated carbon, which play a different role in different stage. The Bangham kinetics model can be used to predict the kinetics of SO2 adsorption on powder activated carbon.

[Key physical parameters of hawthorn leaf granules by stepwise regression analysis method].

PubMed

Jiang, Qie-Ying; Zeng, Rong-Gui; Li, Zhe; Luo, Juan; Zhao, Guo-Wei; Lv, Dan; Liao, Zheng-Gen

2017-05-01

The purpose of this study was to investigate the effect of key physical properties of hawthorn leaf granule on its dissolution behavior. Hawthorn leaves extract was utilized as a model drug. The extract was mixed with microcrystalline cellulose or starch with the same ratio by using different methods. Appropriate amount of lubricant and disintegrating agent was added into part of the mixed powder, and then the granules were prepared by using extrusion granulation and high shear granulation. The granules dissolution behavior was evaluated by using equilibrium dissolution quantity and dissolution rate constant of the hypericin as the indicators. Then the effect of physical properties on dissolution behavior was analyzed through the stepwise regression analysis method. The equilibrium dissolution quantity of hypericin and adsorption heat constant in hawthorn leaves were positively correlated with the monolayer adsorption capacity and negatively correlated with the moisture absorption rate constant. The dissolution rate constants were decreased with the increase of Hausner rate, monolayer adsorption capacity and adsorption heat constant, and were increased with the increase of Carr index and specific surface area. Adsorption heat constant, monolayer adsorption capacity, moisture absorption rate constant, Carr index and specific surface area were the key physical properties of hawthorn leaf granule to affect its dissolution behavior. Copyright© by the Chinese Pharmaceutical Association.

Adsorption of Cd (II) on Modified Granular Activated Carbons: Isotherm and Column Study.

PubMed

Rodríguez-Estupiñán, Paola; Erto, Alessandro; Giraldo, Liliana; Moreno-Piraján, Juan Carlos

2017-12-20

In this work, equilibrium and dynamic adsorption tests of cadmium Cd (II) on activated carbons derived from different oxidation treatments (with either HNO₃, H₂O₂, or NaOCl, corresponding to GACoxN, GACoxP, and GACoxCl samples) are presented. The oxidation treatments determined an increase in the surface functional groups (mainly the acidic ones) and a decrease in the pH PZC (except for the GACoxCl sample). A slight alteration of the textural parameters was also observed, which was more significant for the GACoxCl sample, in terms of a decrease of both Brunauer-Emmett-Teller ( BET ) surface area and micropore volume. Adsorption isotherms were determined for all the adsorbents and a significant increase in the adsorption performances of the oxidized samples with respect to the parent material was observed. The performances ranking was GACoxCl > GACoxP > GACoxN > GAC, likely due to the chemical surface properties of the adsorbents. Dynamic tests in a fixed bed column were carried out in terms of breakthrough curves at constant Cd inlet concentration and flow rate. GACoxCl and GACoxN showed a significantly higher value of the breakpoint time, likely due to the higher adsorption capacity. Finally, the dynamic tests were analyzed in light of a kinetic model. In the adopted experimental conditions, the results showed that mass transfer is controlled by internal pore diffusion, in which surface diffusion plays a major role.

A Unified Kinetics and Equilibrium Experiment: Rate Law, Activation Energy, and Equilibrium Constant for the Dissociation of Ferroin

ERIC Educational Resources Information Center

Sattar, Simeen

2011-01-01

Tris(1,10-phenanthroline)iron(II) is the basis of a suite of four experiments spanning 5 weeks. Students determine the rate law, activation energy, and equilibrium constant for the dissociation of the complex ion in acid solution and base dissociation constant for phenanthroline. The focus on one chemical system simplifies a daunting set of…

Rate constant for reaction of vitamin C with protein radicals in γ-irradiated aqueous albumin solution at 295 K

NASA Astrophysics Data System (ADS)

Miyazaki, Tetsuo; Yoshimura, Toru; Mita, Kazuya; Suzuki, Keiji; Watanabe, Masami

1995-02-01

When an aqueous solution of albumin (0.1 kg dm -3) is irradiated by γ-rays at 295 K, albumin radicals with a long lifetime are observed by ESR. The reaction of vitamin C with the albumin radicals has been studied at 295 K in the albumin solution, which is considered as a model of cells. The rate constant for the reaction of vitamin C with the albumin radicals was measured as 0.014 dm 3 mol -1 s -1, which is much smaller than the reported rate constants (10 6-10 10 dm 3 mol -1 s -1) for the reaction of vitamin C with radicals in a dilute aqueous solution. The small rate constant for the reaction of vitamin C is ascribed to the reaction in polymer coils in the albumin solution, since vitamin C and albumin radicals diffuse very slowly in the coils.

Thermodynamic characteristics of the adsorption of organic molecules on modified MCM-41 adsorbents

NASA Astrophysics Data System (ADS)

Gus'kov, V. Yu.; Sukhareva, D. A.; Salikhova, G. R.; Karpov, S. I.; Kudasheva, F. Kh.; Roessner, F.; Borodina, E. V.

2017-07-01

The adsorption of a number of organic molecules on samples of MCM-41 adsorbent modified with dichloromethylphenylsilane and subsequently treated with sulfuric acid (MDCS) and N-trimethoxysilylpropyl- N, N, N-trimethylammonium chloride (MNM) is studied. Specific retention volumes equal to the Henry constant are determined by means of inverse gas chromatography at infinite dilution. The thermodynamic characteristics of adsorption, the dispersive and specific components of the Helmholtz energy of adsorption, and the increment of the methyl group to the heat of adsorption are calculated. It is shown that the grafting of aminosilane and phenylsilane groups enhances the forces of dispersion and reduces specific interactions. A greater drop in polarity is observed for MDCS than for MNM, due to the stronger polarity of amoinosilane; the enthalpy factor makes the main contribution to the adsorption of organic compounds on the investigated adsorbents. It is found that the MNM sample is capable of the irreversible adsorption of alcohols.

Characterization of Adsorption Enthalpy of Novel Water-Stable Zeolites and Metal-Organic Frameworks

PubMed Central

Kim, Hyunho; Cho, H. Jeremy; Narayanan, Shankar; Yang, Sungwoo; Furukawa, Hiroyasu; Schiffres, Scott; Li, Xiansen; Zhang, Yue-Biao; Jiang, Juncong; Yaghi, Omar M.; Wang, Evelyn N.

2016-01-01

Water adsorption is becoming increasingly important for many applications including thermal energy storage, desalination, and water harvesting. To develop such applications, it is essential to understand both adsorbent-adsorbate and adsorbate-adsorbate interactions, and also the energy required for adsorption/desorption processes of porous material-adsorbate systems, such as zeolites and metal-organic frameworks (MOFs). In this study, we present a technique to characterize the enthalpy of adsorption/desorption of zeolites and MOF-801 with water as an adsorbate by conducting desorption experiments with conventional differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA). With this method, the enthalpies of adsorption of previously uncharacterized adsorbents were estimated as a function of both uptake and temperature. Our characterizations indicate that the adsorption enthalpies of type I zeolites can increase to greater than twice the latent heat whereas adsorption enthalpies of MOF-801 are nearly constant for a wide range of vapor uptakes. PMID:26796523

Comparative studies on adsorptive removal of heavy metal ions by biosorbent, bio-char and activated carbon obtained from low cost agro-residue.

PubMed

Kırbıyık, Çisem; Pütün, Ayşe Eren; Pütün, Ersan

2016-01-01

In this study, Fe(III) and Cr(III) metal ion adsorption processes were carried out with three adsorbents in batch experiments and their adsorption performance was compared. These adsorbents were sesame stalk without pretreatment, bio-char derived from thermal decomposition of biomass, and activated carbon which was obtained from chemical activation of biomass. Scanning electron microscopy and Fourier transform-infrared techniques were used for characterization of adsorbents. The optimum conditions for the adsorption process were obtained by observing the influences of solution pH, adsorbent dosage, initial solution concentration, contact time and temperature. The optimum adsorption efficiencies were determined at pH 2.8 and pH 4.0 for Fe(III) and Cr(III) metal ion solutions, respectively. The experimental data were modelled by different isotherm models and the equilibriums were well described by the Langmuir adsorption isotherm model. The pseudo-first-order, pseudo-second-order kinetic, intra-particle diffusion and Elovich models were applied to analyze the kinetic data and to evaluate rate constants. The pseudo-second-order kinetic model gave a better fit than the others. The thermodynamic parameters, such as Gibbs free energy change ΔG°, standard enthalpy change ΔH° and standard entropy change ΔS° were evaluated. The thermodynamic study showed the adsorption was a spontaneous endothermic process.

Determination of equilibrium and rate constants for complex formation by fluorescence correlation spectroscopy supplemented by dynamic light scattering and Taylor dispersion analysis.

PubMed

Zhang, Xuzhu; Poniewierski, Andrzej; Jelińska, Aldona; Zagożdżon, Anna; Wisniewska, Agnieszka; Hou, Sen; Hołyst, Robert

2016-10-04

The equilibrium and rate constants of molecular complex formation are of great interest both in the field of chemistry and biology. Here, we use fluorescence correlation spectroscopy (FCS), supplemented by dynamic light scattering (DLS) and Taylor dispersion analysis (TDA), to study the complex formation in model systems of dye-micelle interactions. In our case, dyes rhodamine 110 and ATTO-488 interact with three differently charged surfactant micelles: octaethylene glycol monododecyl ether C 12 E 8 (neutral), cetyltrimethylammonium chloride CTAC (positive) and sodium dodecyl sulfate SDS (negative). To determine the rate constants for the dye-micelle complex formation we fit the experimental data obtained by FCS with a new form of the autocorrelation function, derived in the accompanying paper. Our results show that the association rate constants for the model systems are roughly two orders of magnitude smaller than those in the case of the diffusion-controlled limit. Because the complex stability is determined by the dissociation rate constant, a two-step reaction mechanism, including the diffusion-controlled and reaction-controlled rates, is used to explain the dye-micelle interaction. In the limit of fast reaction, we apply FCS to determine the equilibrium constant from the effective diffusion coefficient of the fluorescent components. Depending on the value of the equilibrium constant, we distinguish three types of interaction in the studied systems: weak, intermediate and strong. The values of the equilibrium constant obtained from the FCS and TDA experiments are very close to each other, which supports the theoretical model used to interpret the FCS data.

Rate Constant and Reaction Coordinate of Trp-Cage Folding in Explicit Water

PubMed Central

Juraszek, Jarek; Bolhuis, Peter G.

2008-01-01

We report rate constant calculations and a reaction coordinate analysis of the rate-limiting folding and unfolding process of the Trp-cage mini-protein in explicit solvent using transition interface sampling. Previous transition path sampling simulations revealed that in this (un)folding process the protein maintains its compact configuration, while a (de)increase of secondary structure is observed. The calculated folding rate agrees reasonably with experiment, while the unfolding rate is 10 times higher. We discuss possible origins for this mismatch. We recomputed the rates with the forward flux sampling method, and found a discrepancy of four orders of magnitude, probably caused by the method's higher sensitivity to the choice of order parameter with respect to transition interface sampling. Finally, we used the previously computed transition path-sampling ensemble to screen combinations of many order parameters for the best model of the reaction coordinate by employing likelihood maximization. We found that a combination of the root mean-square deviation of the helix and of the entire protein was, of the set of tried order parameters, the one that best describes the reaction coordination. PMID:18676648

Development of parthenium based activated carbon and its utilization for adsorptive removal of p-cresol from aqueous solution.

PubMed

Singh, Ravi Kant; Kumar, Shashi; Kumar, Surendra; Kumar, Arinjay

2008-07-15

The activated carbon was prepared from carbonaceous agriculture waste Parthenium hysterophorous by chemical activation using concentrated H2SO4 at 130+/-5 degrees C. The prepared activated carbon was characterized and was found as an effective adsorbent material. In order to test the efficacy of parthenium based activated carbon (PAC), batch experiments were performed to carryout the adsorption studies on PAC for the removal of highly toxic pollutant p-cresol from aqueous solution. The p-cresol adsorption studies were also carried out on commercial grade activated carbon (AC) to facilitate comparison between the adsorption capabilities of PAC and AC. For PAC and AC, the predictive capabilities of two types of kinetic models and six types of adsorption equilibrium isotherm models were examined. The effect of pH of solution, adsorbent dose and initial p-cresol concentration on adsorption behaviour was investigated, as well. The adsorption on PAC and on AC was found to follow pseudo-first order kinetics with rate constant 0.0016 min(-1) and 0.0050 min(-1), respectively. The highest adsorptive capacity of PAC and AC for p-cresol solution was attained at pH 6.0. Further, as an adsorbent PAC was found to be as good as AC for removal of p-cresol upto a concentration of 500 mg/l in aqueous solution. Freundlich, Redlich-Peterson, and Fritz-Schlunder models were found to be appropriate isotherm models for PAC while Toth, Radke-Prausnitz and Fritz-Schlunder were suitable models for AC to remove p-cresol from aqueous solution.

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

Adsorption of various antimicrobial agents to endotoxin removal polymyxin-B immobilized fiber (Toraymyxin®). Part 2: Adsorption of two drugs to Toraymyxin PMX-20R cartridges.

PubMed

Shimokawa, Ken-ichi; Takakuwa, Ryotaro; Wada, Yuko; Yamazaki, Noriko; Ishii, Fumiyoshi

2013-01-01

In our previous study, the degree of adsorption of 9 representative antimicrobial agents to Toraymyxin(®) PMX-F sheets was quantitatively evaluated. As a result, the adsorption rate was 22.1% for Linezolid in the presence of serum. Therefore, we investigated whether two types of antimicrobial agents (Ciprofroxacin and Linezolid) can be better adsorbed on PMX-F sheets. When the number of PMX-F sheets was increased in a step wise manner, specifically 2, 4, 6, 8 and 12, the adsorption rate increased linearly. In addition, the adsorption to polymyxin-B immobilized fiber (Toraymyxin(®) PMX-20R) cartridges, widely used to remove endotoxins from circulating blood in the treatment of sepsis, was quantitatively evaluated. As a result, in the presence of serum, Linezolid showed adsorption to PMX-20R, and the adsorption rate after 2h was 54.5%, and that after 4h was 65.8%. The results of this study suggest the necessity of monitoring blood antimicrobial concentration during treatment for sepsis with Linezolid, which showed adsorption to PMX-20R in an environment close to a clinical environment. Copyright © 2012 Elsevier B.V. All rights reserved.

Estimation of rate constants of PCB dechlorination reactions using an anaerobic dehalogenation model.

PubMed

Karakas, Filiz; Imamoglu, Ipek

2017-02-15

This study aims to estimate anaerobic dechlorination rate constants (k m ) of reactions of individual PCB congeners using data from four laboratory microcosms set up using sediment from Baltimore Harbor. Pathway k m values are estimated by modifying a previously developed model as Anaerobic Dehalogenation Model (ADM) which can be applied to any halogenated hydrophobic organic (HOC). Improvements such as handling multiple dechlorination activities (DAs) and co-elution of congeners, incorporating constraints, using new goodness of fit evaluation led to an increase in accuracy, speed and flexibility of ADM. DAs published in the literature in terms of chlorine substitutions as well as specific microorganisms and their combinations are used for identification of pathways. The best fit explaining the congener pattern changes was found for pathways of Phylotype DEH10, which has the ability to remove doubly flanked chlorines in meta and para positions, para flanked chlorines in meta position. The range of estimated k m values is between 0.0001-0.133d -1 , the median of which is found to be comparable to the few available published biologically confirmed rate constants. Compound specific modelling studies such as that performed by ADM can enable monitoring and prediction of concentration changes as well as toxicity during bioremediation. Copyright © 2016 Elsevier B.V. All rights reserved.

An optimal policy for deteriorating items with time-proportional deterioration rate and constant and time-dependent linear demand rate

NASA Astrophysics Data System (ADS)

Singh, Trailokyanath; Mishra, Pandit Jagatananda; Pattanayak, Hadibandhu

2017-12-01

In this paper, an economic order quantity (EOQ) inventory model for a deteriorating item is developed with the following characteristics: (i) The demand rate is deterministic and two-staged, i.e., it is constant in first part of the cycle and linear function of time in the second part. (ii) Deterioration rate is time-proportional. (iii) Shortages are not allowed to occur. The optimal cycle time and the optimal order quantity have been derived by minimizing the total average cost. A simple solution procedure is provided to illustrate the proposed model. The article concludes with a numerical example and sensitivity analysis of various parameters as illustrations of the theoretical results.

Removal of lead(II) by adsorption using treated granular activated carbon: batch and column studies.

PubMed

Goel, Jyotsna; Kadirvelu, Krishna; Rajagopal, Chitra; Kumar Garg, Vinod

2005-10-17

In the present study, a deeper understanding of adsorption behavior of Pb(II) from aqueous systems onto activated carbon and treated activated carbon has been attempted via static and column mode studies under various conditions. It probes mainly two adsorbents that is, activated carbon (AC) and modified activated carbon (AC-S). Characterization of both the adsorbents was one of the key focal areas of the present study. This has shown a clear change or demarcation in the various physical and chemical properties of the modified adsorbent from its precursor activated carbon. Both the adsorbents are subjected to static mode adsorption studies and then after a comparison based on isotherm analysis; more efficient adsorbent is screened for column mode adsorption studies. The lead removal increased for sample of treated carbon. The extent of Pb(II) removal was found to be higher in the treated activated carbon. The aim of carrying out the continuous-flow studies was to assess the effect of various process variables, viz., of bed height, hydraulic loading rate and initial feed concentration on breakthrough time and adsorption capacity. This has helped in ascertaining the practical applicability of the adsorbent. Breakthrough curves were plotted for the adsorption of lead on the adsorbent using continuous-flow column operation by varying different operating parameters like hydraulic loading rate (3.0-10.5 m3/(hm2)), bed height (0.3-0.5 m) and feed concentrations (2.0-6.0 mg/l). At the end, an attempt has also been made to model the data generated from column studies using the empirical relationship based on Bohart-Adams model. This model has provided an objective framework to the subjective interpretation of the adsorption system and the model constant obtained here can be used to achieve the ultimate objective of our study that is, up scaling and designing of adsorption process at the pilot plant scale level. AC-S column regeneration using 0.5 and 1.0M concentration of

(In)validity of the constant field and constant currents assumptions in theories of ion transport.

PubMed Central

Syganow, A; von Kitzing, E

1999-01-01

Constant electric fields and constant ion currents are often considered in theories of ion transport. Therefore, it is important to understand the validity of these helpful concepts. The constant field assumption requires that the charge density of permeant ions and flexible polar groups is virtually voltage independent. We present analytic relations that indicate the conditions under which the constant field approximation applies. Barrier models are frequently fitted to experimental current-voltage curves to describe ion transport. These models are based on three fundamental characteristics: a constant electric field, negligible concerted motions of ions inside the channel (an ion can enter only an empty site), and concentration-independent energy profiles. An analysis of those fundamental assumptions of barrier models shows that those approximations require large barriers because the electrostatic interaction is strong and has a long range. In the constant currents assumption, the current of each permeating ion species is considered to be constant throughout the channel; thus ion pairing is explicitly ignored. In inhomogeneous steady-state systems, the association rate constant determines the strength of ion pairing. Among permeable ions, however, the ion association rate constants are not small, according to modern diffusion-limited reaction rate theories. A mathematical formulation of a constant currents condition indicates that ion pairing very likely has an effect but does not dominate ion transport. PMID:9929480

Quantum calculations of the rate constant for the O(3P)+HCl reaction on new ab initio 3A″ and 3A' surfaces

NASA Astrophysics Data System (ADS)

Xie, Tiao; Bowman, Joel M.; Peterson, K. A.; Ramachandran, B.

2003-11-01

We report the thermal rate constant of the O(3P)+HCl→OH+Cl reaction calculated from 200 to 3200 K, using new fits to extensive ab initio calculations [B. Ramachandran and K. A. Peterson, J. Chem. Phys. 119, 9590 (2003), preceding paper]. The rate constants are obtained for both the 3A″ and 3A' surfaces using exact quantum reactive scattering calculations for selected values of the total angular momentum and the J-shifting approximation for both the 3A″ and 3A' surfaces. The results are compared with the ICVT/μOMT rate constants calculated by the POLYRATE program and all available experimental data. Other related high-energy reaction channels are also studied qualitatively for their contribution to the total thermal rate constant at high temperature.

The effect of high ionic strength on neptunium (V) adsorption to a halophilic bacterium

NASA Astrophysics Data System (ADS)

Ams, David A.; Swanson, Juliet S.; Szymanowski, Jennifer E. S.; Fein, Jeremy B.; Richmann, Michael; Reed, Donald T.

2013-06-01

capacity to previously studied non-halophilic bacteria. The titration data were used to determine the number of types, concentrations, and associated deprotonation constants of functional groups on the bacterial surface; the neptunium adsorption measurements were used to constrain binding constant values for the important neptunium (V)-bacterial surface species. Together, these results can be incorporated into geochemical speciation models to aid in the prediction of neptunium (V) mobility in complex bacteria-bearing geochemical systems.

Study of adsorption of Neon on open Carbon nanohorns aggregates

NASA Astrophysics Data System (ADS)

Ziegler, Carl Andrew

Adsorption isotherms can be used to determine surface area of a substrate and the heat released when adsorption occurs. Our measurements are done determining the equilibrium pressures corresponding to a given amount of gas adsorbed on a substrate at constant temperature. The adsorption studies were done on aggregates of open dahlia-like carbon nanohorns. The nanohorns were oxidized for 9 hours at 550 °C to open them up and render their interior space accessible for adsorption. Volumetric adsorption measurements of Ne were performed at twelve different temperatures between 19 K and 48 K. The isotherms showed two substeps. The first substep corresponds to adsorption on the high energy binding sites in the interior of the nanohorns, near the tip. The second substep corresponds to low energy binding sites both on the outside of the nanotubes and inside the nanotube away from the tip. The isosteric heat measurements obtained from the isotherm data also shows these two distinct substeps. The effective surface area of the open nanotubes was determined from the isotherms using the point-B method. The isosteric heat and surface area data for neon on open nanohorns were compared to two similar experiments of neon adsorbed on aggregates of closed nanohorns.

Adsorption of surfactant ions and binding of their counterions at an air/water interface.

PubMed

Tagashira, Hiroaki; Takata, Youichi; Hyono, Atsushi; Ohshima, Hiroyuki

2009-01-01

An expression for the surface tension of an aqueous mixed solution of surfactants and electrolyte ions in the presence of the common ions was derived from the Helmholtz free energy of an air/water surface. By applying the equation to experimental data for the surface tension, the adsorption constant of surfactant ions onto the air/water interface, the binding constant of counterions on the surfactants, and the surface potential and surface charge density of the interface were estimated. The adsorption constant and binding constant were dependent on the species of surfactant ion and counterion, respectively. Taking account of the dependence of surface potential and surface charge density on the concentration of electrolyte, it was suggested that the addition of electrolyte to the aqueous surfactant solution brings about the decrease in the surface potential, the increase in the surface density of surfactant ions, and consequently, the decrease in the surface tension. Furthermore, it was found that the configurational entropy plays a predominant role for the surface tension, compared to the electrical work.

Effect of Micellization on the Adsorption Kinetics of Polymeric Surfactants to the Solid/Water Interface

NASA Astrophysics Data System (ADS)

Toomey, Ryan; Tirrell, Matthew

2002-03-01

We have studied the adsorption kinetics of two classes of hydrophobic/ionic diblock copolymer surfactants in aqueous environments to understand the role that micellization plays in the adsorption process. The two systems studied were poly(t-butyl styrene)-block-poly(styrene sulfonate) (PtBS-b-PSS) and polystyrene-block-poly(acrylic acid) (PS-b-PAA). It is found that by changing the hydrophobicity of the adsorbing surface, micelle adsorption can be turned on or off. When micelle adsorption occurs, the initial adsorption rate is always slower than the supply rate of micelles to the surface, indicating “reaction-limited” adsorption. Since these micelles have essentially frozen cores, the adsorption cannot be explained by the release of unimers from the micelles. Rather, micelles directly adsorb, and they have to overcome the potential barrier imposed by their corona. Due to micellization, the adsorption rate can also be a complex function of ionic strength. A regime was found where the initial adsorption rate decreased with increasing ionic strength. This anomaly can be explained by the onset of micellization. As the salt concentration is increased, more micelles are formed. However micelles adsorb roughly an order of magnitude slower than free chains. Therefore, if increasing the ionic strength produces more micelles, the adsorption rate will simultaneously decrease.

USE OF ROUGH SETS AND SPECTRAL DATA FOR BUILDING PREDICTIVE MODELS OF REACTION RATE CONSTANTS

EPA Science Inventory

A model for predicting the log of the rate constants for alkaline hydrolysis of organic esters has been developed with the use of gas-phase min-infrared library spectra and a rule-building software system based on the mathematical theory of rough sets. A diverse set of 41 esters ...

Modeling the effects of variable groundwater chemistry on adsorption of molybdate

USGS Publications Warehouse

Stollenwerk, Kenneth G.

1995-01-01

Laboratory experiments were used to identify and quantify processes having a significant effect on molybdate (MoO42−) adsorption in a shallow alluvial aquifer on Cape Cod, assachusetts. Aqueous chemistry in the aquifer changes as a result of treated sewage effluent mixing with groundwater. Molybdate adsorption decreased as pH, ionic strength, and the concentration of competing anions increased. A diffuse-layer surface complexation model was used to simulate adsorption of MoO42−, phosphate (PO43−), and sulfate (SO42−) on aquifer sediment. Equilibrium constants for the model were calculated by calibration to data from batch experiments. The model was then used in a one-dimensional solute transport program to successfully simulate initial breakthrough of MoO42− from column experiments. A shortcoming of the solute transport program was the inability to account for kinetics of physical and chemical processes. This resulted in a failure of the model to predict the slow rate of desorption of MoO42− from the columns. The mobility of MoO42− ncreased with ionic strength and with the formation of aqueous complexes with calcium, magnesium, and sodium. Failure to account for MoO42− speciation and ionic strength in the model resulted in overpredicting MoO42− adsorption. Qualitatively, the laboratory data predicted the observed behavior of MoO42− in the aquifer, where retardation of MoO42− was greatest in uncontaminated roundwater having low pH, low ionic strength, and low concentrations of PO43− and SO42−.

Adsorption and structure of the adsorbed layer of ionic surfactants.

PubMed

Ivanov, Ivan B; Ananthapadmanabhan, Kavssery P; Lips, Alex

2006-11-16

Our goal in this study was to investigate theoretically and experimentally the adsorption of ionic surfactants and the role of different factors in the mechanism of adsorption, the adsorption parameters and the structure of the adsorbed layer. We used available literature data for the interfacial tension, sigma, vs. concentration, C(s), for sodium dodecyl sulfate (SDS) in three representative systems with Air/Water (A/W), Oil/Water (O/W) and Oil/Water + 0.1 M NaCl (O/WE) interfaces. We derived 6 new adsorption isotherms and 6 new equations of state (EOS) based on the adsorption isotherms for non-ionic surfactants of Langmuir, Volmer and Helfand-Frisch-Lebowitz (HFL) with interaction term betatheta2/2 in the EOS, theta=alphaGamma being the degree of coverage, with Gamma--adsorption and alpha--minimum area per molecule. We applied Gouy equation for high surface potentials and modified it to account for partial penetration of the counterions in the adsorbed layer. The equations were written in terms of the effective concentration C=[C(s)(C(s)+C(el))](1/2), where C(s) and C(el) are, respectively concentrations of the surfactant and the electrolyte. We showed that the adsorption constant K was model independent and derived an equation for the effective thickness of the adsorbed layer, delta(s). We found also that the minimum area per molecule, alpha, is larger than the true area, alpha(0), which depends on the adsorption model and is a function of the adsorption Gamma. The interaction term betatheta2/2 in the Langmuir EOS was found to be exact for small beta<1, but for the Volmer EOS it turned out to be only a crude approximation. Semi-quantitative considerations about the interaction between adsorbed discrete charges revealed that at A/W interface part of the adsorbed surfactant molecules are partially immersed in water, which leads to decreased repulsion and increased adsorption Gamma. At O/W the larger adsorption energy keeps the surfactant molecules on the surface

Adsorption of diastase over natural halloysite nanotubes (HNTs)

NASA Astrophysics Data System (ADS)

Twaiq, F.; Chang, K. X.; Ling, J. Y. W.

2017-06-01

Adsorption of diastase over natural halloysite nanotubes is studied in order to evaluate the adsorption capacity of diastase. The halloysite surface characteristics were assessed using nitrogen adsorption, x-ray diffraction (XRD), thermal gravimetric analysis (TGA) and Fourier transformed infrared (FTIR). The surface area of the natural halloysite is found to be 51 m2·g-1, with total pore volume of 0.106 cm3·g-1. The natural halloysite has a basal spacing (d001) of 10 Å confirming the structure of the natural halloysite material. TGA results indicated that halloysite loses its interlayer water in the range of 30 to 105 °C and the dehydration in the structural layer above 150 °C. The dehydroxylation of halloysite has occurred at approximately 460 °C. The FTIR result of the thermally treated halloysite sample indicated that the bands observed are assigned to Si-O and Al-O bonds. The effects of solution pH and temperature were studied on the adsorption capacity and percent removal of diastase from the solution. The adsorption kinetic found to fit well with both the Pseudo first-order and Pseudo second-order models, and the values of the kinetic constant were found to be 0.173 min-1 and 0.00018 g·mg-1·min-1 respectively. The Langmuir isotherm model is found to fit well to the adsorption data and a kinetic value is found to be 0.00059 m3·g-1. The maximum adsorption capacity was found to be 370 mg·g-1, indicating the potential for applications of the natural nanostructured halloysite material as an effective adsorbent for diastase.

Evaluation and comparison of diffusion MR methods for measuring apparent transcytolemmal water exchange rate constant

NASA Astrophysics Data System (ADS)

Tian, Xin; Li, Hua; Jiang, Xiaoyu; Xie, Jingping; Gore, John C.; Xu, Junzhong

2017-02-01

Two diffusion-based approaches, CG (constant gradient) and FEXI (filtered exchange imaging) methods, have been previously proposed for measuring transcytolemmal water exchange rate constant kin, but their accuracy and feasibility have not been comprehensively evaluated and compared. In this work, both computer simulations and cell experiments in vitro were performed to evaluate these two methods. Simulations were done with different cell diameters (5, 10, 20 μm), a broad range of kin values (0.02-30 s-1) and different SNR's, and simulated kin's were directly compared with the ground truth values. Human leukemia K562 cells were cultured and treated with saponin to selectively change cell transmembrane permeability. The agreement between measured kin's of both methods was also evaluated. The results suggest that, without noise, the CG method provides reasonably accurate estimation of kin especially when it is smaller than 10 s-1, which is in the typical physiological range of many biological tissues. However, although the FEXI method overestimates kin even with corrections for the effects of extracellular water fraction, it provides reasonable estimates with practical SNR's and more importantly, the fitted apparent exchange rate AXR showed approximately linear dependence on the ground truth kin. In conclusion, either CG or FEXI method provides a sensitive means to characterize the variations in transcytolemmal water exchange rate constant kin, although the accuracy and specificity is usually compromised. The non-imaging CG method provides more accurate estimation of kin, but limited to large volume-of-interest. Although the accuracy of FEXI is compromised with extracellular volume fraction, it is capable of spatially mapping kin in practice.

Determination of Bimolecular Rate Constants for Reactions of Hydroxyl Radical with Pharmaceutical and Cosmetics Chemicals - Implications to the Fate in the Aquatic Environment

NASA Astrophysics Data System (ADS)

Nakajima, H.; Arakaki, T.; Anastasio, C.

2008-12-01

Large organic compounds such as hyaluronic acid and chondroitin sulfate are often used in pharmaceutical and cosmetics products, but their chemical degradation pathways are not well understood. To better elucidate their fate in the aquatic environment, we initiated a study to determine bimolecular rate constants between these organic compounds and hydroxyl radical (OH), which is a potent oxidant in the environment. The lifetimes of many organic compounds are determined by reactions with OH radicals, and the lifetime of OH is often controlled by reactions with organic compounds. To determine these bimolecular rate constants we used a competition kinetics technique with either hydrogen peroxide or nitrate as a source of OH and benzoate as the competing sink. Since the molecular weights of some of the large organic compounds we studied were not known, we used dissolved organic carbon (DOC) concentrations to determine mole-carbon based bimolecular rate constants, instead of the commonly used molar-based bimolecular rate constants. We will report the mole-carbon based bimolecular rate constants of OH, determined at room temperature, with hyaluronic acid, chondroitin sulfate and some other large organic compounds.

Slow Crack Growth Analysis of Brittle Materials with Finite Thickness Subjected to Constant Stress-Rate Flexural Loading

NASA Technical Reports Server (NTRS)

Chio, S. R.; Gyekenyesi, J. P.

1999-01-01

A two-dimensional, numerical analysis of slow crack growth (SCG) was performed for brittle materials with finite thickness subjected to constant stress-rate ("dynamic fatigue") loading in flexure. The numerical solution showed that the conventional, simple, one-dimensional analytical solution can be used with a maximum error of about 5% in determining the SCG parameters of a brittle material with the conditions of a normalized thickness (a ratio of specimen thickness to initial crack size) T > 3.3 and of a SCG parameter n > 10. The change in crack shape from semicircular to elliptical configurations was significant particularly at both low stress rate and low T, attributed to predominant difference in stress intensity factor along the crack front. The numerical solution of SCG parameters was supported within the experimental range by the data obtained from constant stress-rate flexural testing for soda-lime glass microslides at ambient temperature.

Constant Flux Proxies and Pleistocene Sediment Accumulation Rates on the Juan de Fuca Ridge in the Northeast Pacific

NASA Astrophysics Data System (ADS)

Middleton, J. L.; Mukhopadhyay, S.; Langmuir, C. H.; Costa, K.; McManus, J. F.; d'Almeida, M.; Huybers, P. J.; Winckler, G.

2016-12-01

Mass accumulation rates of marine sediments are often employed to constrain deposition rates of important proxies such as terrigenous dust, carbonate, and biogenic opal to quantitatively examine variations in continental aridity, atmospheric transport, and biologic productivity across changing climatic conditions. However, deposition rates that are estimated using traditional mass accumulation rates calculated from sediment core age models can be subject to bias from lateral sediment transport and limited age model resolution. Constant flux proxies, such as extraterrestrial helium-3 (3HeET) and excess thorium-230 (230ThXS), can be used to calculate vertical sediment accumulation rates that are independent of age model uncertainties and the effects of lateral sediment transport. While a short half-life limits analyses of 230ThXS to the past 500 ka, 3HeET is stable and could be used to constrain sedimentary fluxes during much of the Cenozoic. Despite the vast paleoceanographic potential of constant flux proxies, few studies have directly compared the behavior of 230ThXS and 3HeET using measurements from the same samples. Sediment grain size fractionation and local scavenging effects may differentially bias one or both proxy systems and complicate the interpretation of 230ThXS or 3HeET data. We will present a new record of vertical sediment accumulation rates spanning the past 600 ka in the Northeast Pacific constrained using analyses of both 3HeET and 230ThXS in two sediment cores from cruise AT26-19 on the Juan de Fuca Ridge. Such a record allows for intercomparison of both constant flux proxies in the mid-ocean ridge environment and examination of sedimentary behavior across multiple glacial cycles. The 230ThXS-derived accumulation rates typically range from 0.5 to 2 g cm-2 ka-1 over the past 450 ka, with periods of maximum deposition coinciding with glacial maxima. Preliminary results of samples analyzed with both 3HeET and 230ThXS indicate relative consistency

Behaviors and kinetics of toluene adsorption-desorption on activated carbons with varying pore structure.

PubMed

Yang, Xi; Yi, Honghong; Tang, Xiaolong; Zhao, Shunzheng; Yang, Zhongyu; Ma, Yueqiang; Feng, Tiecheng; Cui, Xiaoxu

2018-05-01

This work was undertaken to investigate the behaviors and kinetics of toluene adsorption and desorption on activated carbons with varying pore structure. Five kinds of activated carbon from different raw materials were selected. Adsorption isotherms and breakthrough curves for toluene were measured. Langmuir and Freundlich equations were fitted to the equilibrium data, and the Freundlich equation was more suitable for simulating toluene adsorption. The process consisted of monolayer, multilayer and partial active site adsorption types. The effect of the pore structure of the activated carbons on toluene adsorption capacity was investigated. The quasi-first-order model was more suitable for describing the process than the quasi-second-order model. The adsorption data was also modeled by the internal particle diffusion model and it was found that the adsorption process could be divided into three stages. In the external surface adsorption process, the rate depended on the specific surface area. During the particle diffusion stage, pore structure and volume were the main factors affecting adsorption rate. In the final equilibrium stage, the rate was determined by the ratio of meso- and macro-pores to total pore volume. The rate over the whole adsorption process was dominated by the toluene concentration. The desorption behavior of toluene on activated carbons was investigated, and the process was divided into heat and mass transfer parts corresponding to emission and diffusion mechanisms, respectively. Physical adsorption played the main role during the adsorption process. Copyright © 2017. Published by Elsevier B.V.

Rate constants for OH with selected large alkanes : shock-tube measurements and an improved group scheme.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sivaramakrishnan, R.; Michael, J. V.; Chemical Sciences and Engineering Division

High-temperature rate constant experiments on OH with the five large (C{sub 5}-C{sub 8}) saturated hydrocarbons n-heptane, 2,2,3,3-tetramethylbutane (2,2,3,3-TMB), n-pentane, n-hexane, and 2,3-dimethylbutane (2,3-DMB) were performed with the reflected-shock-tube technique using multipass absorption spectrometric detection of OH radicals at 308 nm. Single-point determinations at {approx}1200 K on n-heptane, 2,2,3,3-TMB, n-hexane, and 2,3-DMB were previously reported by Cohen and co-workers; however, the present work substantially extends the database to both lower and higher temperature. The present experiments span a wide temperature range, 789-1308 K, and represent the first direct measurements of rate constants at T > 800 K for n-pentane. The presentmore » work utilized 48 optical passes corresponding to a total path length of {approx}4.2 m. As a result of this increased path length, the high OH concentration detection sensitivity permitted pseudo-first-order analyses for unambiguously measuring rate constants. The experimental results can be expressed in Arrhenius form in units of cm{sup 3} molecule{sup -1} s{sup -1} as follows: K{sub OH+n-heptane} = (2.48 {+-} 0.17) x 10{sup -10} exp[(-1927 {+-} 69 K)/T] (838-1287 K); k{sub OH+2,2,3,3-TMB} = (8.26 {+-} 0.89) x 10{sup -11} exp[(-1337 {+-} 94 K)/T] (789-1061 K); K{sub OH+n-pentane} = (1.60 {+-} 0.25) x 10{sup -10} exp[(-1903 {+-} 146 K)/T] (823-1308 K); K{sub OH+n-hexane} = (2.79 {+-} 0.39) x 10{sup -10} exp[(-2301 {+-} 134 K)/T] (798-1299 K); and k{sub OH+2,3-DMB} = (1.27 {+-} 0.16) x 10{sup -10} exp[(-1617 {+-} 118 K)/T] (843-1292 K). The available experimental data, along with lower-T determinations, were used to obtain evaluations of the experimental rate constants over the temperature range from {approx}230 to 1300 K for most of the title reactions. These extended-temperature-range evaluations, given as three-parameter fits, are as follows: k{sub OH+n-heptane} = 2.059 x 10{sup -5}T{sup 1.401} exp(33 K

Non-steady state mass action dynamics without rate constants: dynamics of coupled reactions using chemical potentials

NASA Astrophysics Data System (ADS)

Cannon, William R.; Baker, Scott E.

2017-10-01

Comprehensive and predictive simulation of coupled reaction networks has long been a goal of biology and other fields. Currently, metabolic network models that utilize enzyme mass action kinetics have predictive power but are limited in scope and application by the fact that the determination of enzyme rate constants is laborious and low throughput. We present a statistical thermodynamic formulation of the law of mass action for coupled reactions at both steady states and non-stationary states. The formulation uses chemical potentials instead of rate constants. When used to model deterministic systems, the method corresponds to a rescaling of the time dependent reactions in such a way that steady states can be reached on the same time scale but with significantly fewer computational steps. The relationships between reaction affinities, free energy changes and generalized detailed balance are central to the discussion. The significance for applications in systems biology are discussed as is the concept and assumption of maximum entropy production rate as a biological principle that links thermodynamics to natural selection.

Comparison of cation adsorption by isostructural rutile and cassiterite.

PubMed

Machesky, Michael; Wesolowski, David; Rosenqvist, Jörgen; Předota, Milan; Vlcek, Lukas; Ridley, Moira; Kohli, Vaibhav; Zhang, Zhan; Fenter, Paul; Cummings, Peter; Lvov, Serguei; Fedkin, Mark; Rodriguez-Santiago, Victor; Kubicki, James; Bandura, Andrei

2011-04-19

Macroscopic net proton charging curves for powdered rutile and cassiterite specimens with the (110) crystal face predominant, as a function of pH in RbCl and NaCl solutions, trace SrCl(2) in NaCl, and trace ZnCl(2) in NaCl and Na Triflate solutions, are compared to corresponding molecular-level information obtained from static DFT optimizations and classical MD simulations, as well as synchrotron X-ray methods. The similarities and differences in the macroscopic charging behavior of rutile and cassiterite largely reflect the cation binding modes observed at the molecular level. Cation adsorption is primarily inner-sphere on both isostructural (110) surfaces, despite predictions that outer-sphere binding should predominate on low bulk dielectric constant oxides such as cassiterite (ε(bulk) ≈ 11). Inner-sphere adsorption is also significant for Rb(+) and Na(+) on neutral surfaces, whereas Cl(-) binding is predominately outer-sphere. As negative surface charge increases, relatively more Rb(+), Na(+), and especially Sr(2+) are bound in highly desolvated tetradentate fashion on the rutile (110) surface, largely accounting for enhanced negative charge development relative to cassiterite. Charging curves in the presence of Zn(2+) are very steep but similar for both oxides, reflective of Zn(2+) hydrolysis (and accompanying proton release) during the adsorption process, and the similar binding modes for ZnOH(+) on both surfaces. These results suggest that differences in cation adsorption between high and low bulk dielectric constant oxides are more subtly related to the relative degree of cation desolvation accompanying inner-sphere binding (i.e., more tetradentate binding on rutile), rather than distinct inner- and outer-sphere adsorption modes. Cation desolvation may be favored at the rutile (110) surface in part because inner-sphere water molecules are bound further from and less tightly than on the cassiterite (110) surface. Hence, their removal upon inner

High-level theoretical study of the reaction between hydroxyl and ammonia: Accurate rate constants from 200 to 2500 K

NASA Astrophysics Data System (ADS)

Nguyen, Thanh Lam; Stanton, John F.

2017-10-01

Hydrogen abstraction from NH3 by OH to produce H2O and NH2—an important reaction in combustion of NH3 fuel—was studied with a theoretical approach that combines high level quantum chemistry and advanced chemical kinetics methods. Thermal rate constants calculated from first principles agree well (within 5%-20%) with available experimental data over a temperature range that extends from 200 to 2500 K. Quantum mechanical tunneling effects were found to be important; they lead to a decided curvature and non-Arrhenius behavior for the rate constant.

High-level theoretical study of the reaction between hydroxyl and ammonia: Accurate rate constants from 200 to 2500 K.

PubMed

Nguyen, Thanh Lam; Stanton, John F

2017-10-21

Hydrogen abstraction from NH 3 by OH to produce H 2 O and NH 2 -an important reaction in combustion of NH 3 fuel-was studied with a theoretical approach that combines high level quantum chemistry and advanced chemical kinetics methods. Thermal rate constants calculated from first principles agree well (within 5%-20%) with available experimental data over a temperature range that extends from 200 to 2500 K. Quantum mechanical tunneling effects were found to be important; they lead to a decided curvature and non-Arrhenius behavior for the rate constant.

High-level theoretical study of the reaction between hydroxyl and ammonia: Accurate rate constants from 200 to 2500 K

DOE PAGES

Nguyen, Thanh Lam; Stanton, John F.

2017-06-02

Hydrogen abstraction from NH 3 by OH to produce H 2O and NH 2 — an important reaction in combustion of NH 3 fuel — was studied with a theoretical approach that combines high level quantum chemistry and advanced chemical kinetics methods. Thermal rate constants calculated from first principles agree well (within 5 to 20%) with available experimental data over a temperature range that extends from 200 to 2500 K. Here, quantum mechanical tunneling effects were found to be important; they lead to a decided curvature and non-Arrhenius behavior for the rate constant.

Decrease in zinc adsorption onto soil in the presence of EPS-rich and EPS-poor Pseudomonas aureofaciens.

PubMed

Drozdova, O Yu; Pokrovsky, O S; Lapitskiy, S A; Shirokova, L S; González, A G; Demin, V V

2014-12-01

The adsorption of Zn onto the humic and illuvial horizons of the podzol soil in the presence of soil bacteria was studied using a batch-reactor technique as a function of the pH (from 2 to 9) and the Zn concentration in solution (from 0.076mM to 0.760mM). Exopolysaccharides-forming aerobic heterotrophs Pseudomonas aureofaciens were added at 0.1 and 1.0gwetL(-1) concentrations to two different soil horizons, and Zn adsorption was monitored as a function of the pH and the dissolved-Zn concentration. The pH-dependent adsorption edge demonstrated more efficient Zn adsorption by the humic horizon than the mineral horizon at otherwise similar soil concentrations. The Zn adsorption onto the EPS-poor strain was on slightly lower than that onto EPS-rich bacteria. Similar differences in the adsorption capacities between the soil and bacteria were also detected by "langmuirian" constant-pH experiments conducted in soil-Zn and bacteria-Zn binary systems. The addition of 0.1gwetL(-1)P. aureofaciens to a soil-bacteria system (4gdryL(-1)soil) resulted in statistically significant decrease in the adsorption yield, which was detectable from both the pH-dependent adsorption edge and the constant-pH isotherm experiments. Increasing the amount of added bacteria to 1gwetL(-1) further decreased the overall adsorption in the full range of the pH. This decrease was maximal for the EPS-rich bacteria and minimal for the EPS-poor bacteria (a factor of 2.8 and 2.2 at pH=6.9, respectively). These observations in binary and ternary systems were further rationalized by linear-programming modeling of surface equilibria that revealed the systematic differences in the number of binding sites and the surface-adsorption constant of zinc onto the two soil horizons with and without bacteria. The main finding of this work is that the adsorption of Zn onto the humic soil-bacteria system is lower than that in pure, bacteria-free soil systems. This difference is statistically significant (p<0.05). As such

Surface Complexation Modeling of Fluoride Adsorption by Soil and the Role of Dissolved Aluminum on Adsorption

NASA Astrophysics Data System (ADS)

Padhi, S.; Tokunaga, T.

2017-12-01

Adsorption of fluoride (F) on soil can control the mobility of F and subsequent contamination of groundwater. Hence, accurate evaluation of adsorption equilibrium is a prerequisite for understanding transport and fate of F in the subsurface. While there have been studies for the adsorption behavior of F with respect to single mineral constituents based on surface complexation models (SCM), F adsorption to natural soil in the presence of complexing agents needs much investigation. We evaluated the adsorption processes of F on a natural granitic soil from Tsukuba, Japan, as a function of initial F concentration, ionic strength, and initial pH. A SCM was developed to model F adsorption behavior. Four possible surface complexation reactions were postulated with and without including dissolved aluminum (Al) and Al-F complex sorption. Decrease in F adsorption with the increase in initial pH was observed in between the initial pH range of 4 to 9, and a decrease in the rate of the reduction of adsorbed F with respect to the increase in the initial pH was observed in the initial pH range of 5 to 7. Ionic strength variation in the range of 0 to 100mM had insignificant effect on F removal. Changes in solution pH were observed by comparing the solution before and after F adsorption experiments. At acidic pH, the solution pH increased, whereas at alkaline pH, the solution pH decreased after equilibrium. The SCM including dissolved Al and the adsorption of Al-F complex can simulate the experimental results quite successfully. Also, including dissolved Al and the adsorption of Al-F complex to the model explained the change in solution pH after F adsorption.

Effect of pH on the adsorption and photocatalytic degradation of sulfadimidine in Vis/g-C3N4 progress.

PubMed

Yang, Bin; Mao, Xuhui; Pi, Liu; Wu, Yixiao; Ding, Huijun; Zhang, Weihao

2017-03-01

In this study, g-C 3 N 4 was synthesized by thermal polycondensation of melamine and was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, UV-visible diffuse reflection spectroscopy, and scanning electron microscopy. Results showed that g-C 3 N 4 degraded sulfadimidine (SMD) under visible light, in which the adsorption and photocatalytic degradation was influenced by pH. The maximum adsorption capacity was achieved at approximately pH 5. The highest degradation rate constant was obtained at strong acid and alkali. In addition, the degradation mechanism of g-C 3 N 4 was evaluated with the help of quencher agents. The intermediates, degradation pathways, and mineralization of SMD were also determined to evaluate the degradation and oxidation ability of g-C 3 N 4 .

Photochemical parameters of atmospheric source gases: accurate determination of OH reaction rate constants over atmospheric temperatures, UV and IR absorption spectra

NASA Astrophysics Data System (ADS)

Orkin, V. L.; Khamaganov, V. G.; Martynova, L. E.; Kurylo, M. J.

2012-12-01

The emissions of halogenated (Cl, Br containing) organics of both natural and anthropogenic origin contribute to the balance of and changes in the stratospheric ozone concentration. The associated chemical cycles are initiated by the photochemical decomposition of the portion of source gases that reaches the stratosphere. Reactions with hydroxyl radicals and photolysis are the main processes dictating the compound lifetime in the troposphere and release of active halogen in the stratosphere for a majority of halogen source gases. Therefore, the accuracy of photochemical data is of primary importance for the purpose of comprehensive atmospheric modeling and for simplified kinetic estimations of global impacts on the atmosphere, such as in ozone depletion (i.e., the Ozone Depletion Potential, ODP) and climate change (i.e., the Global Warming Potential, GWP). The sources of critically evaluated photochemical data for atmospheric modeling, NASA/JPL Publications and IUPAC Publications, recommend uncertainties within 10%-60% for the majority of OH reaction rate constants with only a few cases where uncertainties lie at the low end of this range. These uncertainties can be somewhat conservative because evaluations are based on the data from various laboratories obtained during the last few decades. Nevertheless, even the authors of the original experimental works rarely estimate the total combined uncertainties of the published OH reaction rate constants to be less than ca. 10%. Thus, uncertainties in the photochemical properties of potential and current atmospheric trace gases obtained under controlled laboratory conditions still may constitute a major source of uncertainty in estimating the compound's environmental impact. One of the purposes of the presentation is to illustrate the potential for obtaining accurate laboratory measurements of the OH reaction rate constant over the temperature range of atmospheric interest. A detailed inventory of accountable sources of

Absolute rate constants for the reaction of OH with cyclopentane and cycloheptane from 233 to 351 K.

PubMed

Gennaco, Michael A; Huang, Yi-wen; Hannun, Reem A; Dransfield, Timothy J

2012-12-27

Absolute rate constant measurements for the reactions of OH with cyclopentane and cycloheptane in the gas phase in 6-8 Torr of nitrogen from 233 to 351 K in the Harvard University High-Pressure Flow System (HPFS) are reported. Hydroxyl concentrations were measured using laser-induced fluorescence, and alkane concentrations were measured using Fourier transform infrared spectroscopy. Results were fit to a modified Arrhenius equation based on transition state theory (ignoring tunneling): k(T) = B e(-E(a)/T)/T(1 - e(-1.44ν(1)/T))(2)(1 - e(-1.44ν(2)/T)), with ν(1) and ν(2) bending frequencies set to 280 and 500 cm(-1) . Results were as follows for E(a) (K) and k (298) (10(-12) cm(3) s(-1)): cyclopentane, 460 ± 32, 4.85; cycloheptane, 319 ± 36, 9.84. This work represents the second absolute temperature-dependent rate constant measurement reported for cycloheptane, and the third absolute temperature-dependent rate constant measurement reported near room temperature for the reaction of OH and cyclopentane. For the title reactions, the reaction barriers reported here are in agreement with the reaction barrier previously reported for cyclohexane and considerably higher than the barrier previously reported for cyclo-octane, a result that is not predicted by our current understanding of hydrocarbon reactivity.

Adsorption dynamics of methyl violet onto granulated mesoporous carbon: Facile synthesis and adsorption kinetics.

PubMed

Kim, Yohan; Bae, Jiyeol; Park, Hosik; Suh, Jeong-Kwon; You, Young-Woo; Choi, Heechul

2016-09-15

A new and facile one-step synthesis method for preparing granulated mesoporous carbon (GMC) with three-dimensional spherical mesoporous symmetry is prepared to remove large molecular weight organic compounds in aqueous phase. GMC is synthesized in a single step using as-synthesized mesoporous carbon particles and organic binders through a simple and economical synthesis approach involving a simultaneous calcination and carbonization process. Characterization results obtained from SEM, XRD, as well as surface and porosity analysis indicate that the synthesized GMC has similar physical properties to those of the powdered mesoporous carbon and maintains the Brunauer-Emmett-Teller (BET) surface area and pore volume because the new synthesis method prevents the collapse of the pores during the granulation process. Batch adsorption experiments revealed GMC showed a substantial adsorption capacity (202.8 mg/g) for the removal of methyl violet as a target large molecular contaminant in aqueous phase. The mechanisms and dynamics modeling of GMC adsorption were also fully examined, which revealed that surface diffusion was rate limiting step on adsorption process of GMC. Adsorption kinetics of GMC enables 3 times faster than that of granular activated carbon in terms of surface diffusion coefficient. This is the first study, to the best of our knowledge, to synthesize GMC as an adsorbent for water purification by using facile granulation method and to investigate the adsorption kinetics and characteristics of GMC. This study introduces a new and simple method for the synthesis of GMC and reveals its adsorption characteristics for large molecular compounds in a water treatment. Copyright © 2016 Elsevier Ltd. All rights reserved.

First-principles calculation of photo-induced electron transfer rate constants in phthalocyanine-C60 organic photovoltaic materials: Beyond Marcus theory

NASA Astrophysics Data System (ADS)

Lee, Myeong H.; Dunietz, Barry D.; Geva, Eitan

2014-03-01

Classical Marcus theory is commonly adopted in solvent-mediated charge transfer (CT) process to obtain the CT rate constant, but it can become questionable when the intramolecular vibrational modes dominate the CT process as in OPV devices because Marcus theory treats these modes classically and therefore nuclear tunneling is not accounted for. We present a computational scheme to obtain the electron transfer rate constant beyond classical Marcus theory. Within this approach, the nuclear vibrational modes are treated quantum-mechanically and a short-time approximation is avoided. Ab initio calculations are used to obtain the basic parameters needed for calculating the electron transfer rate constant. We apply our methodology to phthalocyanine(H2PC)-C60 organic photovoltaic system where one C60 acceptor and one or two H2PC donors are included to model the donor-acceptor interface configuration. We obtain the electron transfer and recombination rate constants for all accessible charge transfer (CT) states, from which the CT exciton dynamics is determined by employing a master equation. The role of higher lying excited states in CT exciton dynamics is discussed. This work is pursued as part of the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the US Department of Energy Office of Science, Office of Basic Energy Sciences under 390 Award No. DE-SC0000957.

KABAM Version 1.0 User's Guide and Technical Documentation - Appendix H - Methods for Estimating Metabolism Rate Constant

EPA Pesticide Factsheets

Appendix H of KABAM Version 1.0 documentation related to estimating the metabolism rate constant. KABAM is a simulation model used to predict pesticide concentrations in aquatic regions for use in exposure assessments.

Immobilization of Acetobacter aceti on cellulose ion exchangers: adsorption isotherms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bar, R.; Gainer, J.L.; Kirwan, D.J.

1986-08-01

The adsorptive behavior of cells of Acetobacter aceti, ATCC 23746, on DEAE-, TEAE-, and DEHPAE-cellulose ion exchangers in a modified Hoyer's medium at 30 degrees Centigrade was investigated. The maximum observed adsorption capacities varied from 46 to 64 mg dry wt/g resin. The Langmuir isotherm form was used to fit the data, since the cells formed a monolayer on the resin and exhibited saturation. The equilibrium constant in the Langmuir expression was qualitatively correlated with the surface charge density of the resin. The adsorption was also ''normalized'' by considering the ionic capacities of the resins. The exceptionally high normalized adsorptionmore » capacity of ECTEOLA-cellulose, 261 mg dry/meq, may be explained by an interaction between the cell wall and the polyglyceryl chains of the exchanging groups in addition to the electrostatic effects. The effect of pH on the bacterial adsorption capacity of ECTEOLA-, TEAE-, and phosphate-cellulose resins was studied and the pH of the bacteria was estimated to be 3.0. 17 references.« less

Adsorption of trichloroethylene and benzene vapors onto hypercrosslinked polymeric resin.

PubMed

Liu, Peng; Long, Chao; Li, Qifen; Qian, Hongming; Li, Aimin; Zhang, Quanxing

2009-07-15

In this research, the adsorption equilibria of trichloroethylene (TCE) and benzene vapors onto hypercrosslinked polymeric resin (NDA201) were investigated by the column adsorption method in the temperature range from 303 to 333 K and pressures up to 8 kPa for TCE, 12 kPa for benzene. The Toth and Dubinin-Astakov (D-A) equations were tested to correlate experimental isotherms, and the experimental data were found to fit well by them. The good fits and characteristic curves of D-A equation provided evidence that a pore-filling phenomenon was involved during the adsorption of TCE and benzene onto NDA-201. Moreover, thermodynamic properties such as the Henry's constant and the isosteric enthalpy of adsorption were calculated. The isosteric enthalpy curves varied with the surface loading for each adsorbate, indicating that the hypercrosslinked polymeric resin has an energetically heterogeneous surface. In addition, a simple mathematic model developed by Yoon and Nelson was applied to investigate the breakthrough behavior on a hypercrosslinked polymeric resin column at 303 K and the calculated breakthrough curves were in high agreement with corresponding experimental data.

Protein Adsorption to Titanium and Zirconia Using a Quartz Crystal Microbalance Method

PubMed Central

Kusakawa, You

2017-01-01

Protein adsorption onto titanium (Ti) or zirconia (ZrO2) was evaluated using a 27 MHz quartz crystal microbalance (QCM). As proteins, fibronectin (Fn), a cell adhesive protein, and albumin (Alb), a cell adhesion-inhibiting protein, were evaluated. The Ti and ZrO2 sensors for QCM were characterized by atomic force microscopy and electron probe microanalysis observation, measurement of contact angle against water, and surface roughness. The amounts of Fn and Alb adsorbed onto the Ti and ZrO2 sensors and apparent reaction rate were obtained using QCM measurements. Ti sensor showed greater adsorption of Fn and Alb than the ZrO2 sensor. In addition, amount of Fn adsorbed onto the Ti or ZrO2 sensors was higher than that of Alb. The surface roughness and hydrophilicity of Ti or ZrO2 may influence the adsorption of Fn or Alb. With regard to the adsorption rate, Alb adsorbed more rapidly than Fn onto Ti. Comparing Ti and ZrO2, Alb adsorption rate to Ti was faster than that to ZrO2. Fn adsorption will be effective for cell activities, but Alb adsorption will not. QCM method could simulate in vivo Fn and Alb adsorption to Ti or ZrO2. PMID:28246591

Competitive adsorption behaviors of carbon dioxide and n-dodecane mixtures in 13X molecular sieve

NASA Astrophysics Data System (ADS)

Zhu, Chaofan; Dong, Mingzhe; Gong, Houjian

2018-01-01

The CO2 cyclic injection has been proven to be effective to enhance tight oil recovery under constant reservoir temperature and down hole pressure conditions. However, the enhance tight oil recovery mechanism was unclear, especially the adsorption of the CO2 and alkane in the surface. Therefore, it is great important to study the adsorption mechanism of CO2 and alkane mixtures in tight oil. In this study, a new experimental method and apparatus have been designed to test the change of the mole fraction of CO2 and n-C12 before and after the adsorption equilibrium. Then, the adsorption amount of CO2 and n-C12 was obtained by a mathematical method. Moreover, the adsorption character of CO2 and n-C12 mixtures in 13X molecular sieve and the effect of pressure on the adsorption and amount were studied. The results show that the adsorption of CO2 and the desorption of n-C12 follow the Langmuir adsorption. This study provides a straightforward method to experimentally determine the adsorption properties of the tight oil, which can be used to evaluate enhanced tight oil recovery by CO2 injection.

Adsorption of aqueous copper on peanut hulls

NASA Astrophysics Data System (ADS)

Davis, Kanika Octavia

A method was established for measuring the adsorption of Cu(II) from aqueous solution to unmodified and modified peanut hulls at constant temperature and pH. Modification of the hulls was performed by oxidation with alkaline hydrogen peroxide. During the modification process, the hydrogen peroxide solubilizes the lignin component, making the surface more porous which increases the availability of binding sites, while simultaneously oxidizing the cellulose. The oxidation of alcohol groups creates more binding sites by creating functional groups such as COO-, which increases chelation to metal ions. Fourier transform infrared spectroscopy confirms delignification of the peanut hulls by the disappearance of carboxyl peaks of the modified hulls, which were originally produced from the lignin content. Although, oxidation is not fully confirmed, it is not ruled out because the expected carboxylate peak (1680 cm-1) maybe overshadowed by a broad peak due to OH bending of water adsorbed to the hulls. Hulls adsorbed copper from solutions in the concentration range of 50-1000 ppm of CuCl2. Concentrations of pre- and post-adsorption solutions were determined using inductively coupled plasma optical emission spectroscopy. The adsorption isotherms were fit to known two and three-parameter models, evaluated and the binding mechanism was inferred. Maximum surface coverage was 3.5 +/- 0.6 mg Cu2+ /g hull for unmodified hulls and 11 +/- 1 mg Cu2+/g hull for modified hulls. The adsorption for the hulls is best described by the Langmuir model, suggesting monolayer, homogeneous adsorption. With a free energy of adsorption of 10.5 +/- 0.9 kJ/mol for unmodified hulls and 14.5 +/-0.4 kJ/mol for modified hulls, the process is categorized as chemisorption for both types of hulls. The adsorption for both hulls is also described by the Redlich-Peterson model, giving beta nearer to 1 than 0, which further suggests homogeneous adsorption described by the Langmuir model. After rinsing the hulls

A fundamental study of the impact of pressure on the adsorption mechanism in reversed-phase liquid chromatography.

PubMed

Åsberg, Dennis; Samuelsson, Jörgen; Fornstedt, Torgny

2016-07-29

A fundamental investigation of the pressure effect on individual adsorption sites was undertaken based on adsorption energy distribution and adsorption isotherm measurements. For this purpose, we measured adsorption equilibrium data at pressures ranging from 100 to 1000bar at constant flow and over a wide concentration range for three low-molecular-weight solutes, antipyrine, sodium 2-naphthalenesulfonate, and benzyltriethylammonium chloride, on an Eternity C18 stationary phase. The adsorption energy distribution was bimodal for all solutes, remaining clearly so at all pressures. The bi-Langmuir model best described the adsorption in these systems and two types of adsorption sites were identified, one with a low and another with a high energy of interaction. Evidence exists that the low-energy interactions occur at the interface between the mobile and stationary phases and that the high-energy interactions occur nearer the silica surface, deeper in the C18 layer. The contribution of each type of adsorption site to the retention factor was calculated and the change in solute molar volume from the mobile to stationary phase during the adsorption process was estimated for each type of site. The change in solute molar volume was 2-4 times larger at the high-energy site, likely because of the greater loss of solute solvation layer when penetrating deeper into the C18 layer. The association equilibrium constant increased with increasing pressure while the saturation capacity of the low-energy site remained almost unchanged. The observed increase in saturation capacity for the high-energy site did not affect the column loading capacity, which was almost identical at 50- and 950-bar pressure drops over the column. Copyright © 2016 Elsevier B.V. All rights reserved.

Comparison of rate constants for (PO3-) transfer by the Mg(II), Cd(II), and Li(I) forms of phosphoglucomutase.

PubMed

Ray, W J; Post, C B; Puvathingal, J M

1989-01-24

Net rate constants that define the steady-state rate through a sequence of steps and the corresponding effective energy barriers for two (PO3-)-transfer steps in the phosphoglucomutase reaction were compared as a function of metal ion, M, where M = Mg2+ and Cd2+. These steps involve the reaction of either the 1-phosphate or the 6-phosphate of glucose 1,6-bisphosphate (Glc-P2) bound to the dephosphoenzyme (ED) to produce the phosphoenzyme (EP) and the free monophosphates, glucose 1-phosphate (Glc-1-P) or glucose 6-phosphate (Glc-6-P): EP.M + Glc-1-P----ED.M.Glc-P2----EP.M.Glc-6-P6. Before this comparison was made, net rate constants for the Cd2+ enzyme, obtained at high enzyme concentration via 31P NMR saturation-transfer studies [Post, C. B., Ray, W. J., Jr., & Gorenstein, D. G. (1989) Biochemistry (preceding paper in this issue)], were appropriately scaled by using the observed constants to calculate both the expected isotope-transfer rate at equilibrium and the steady-state rate under initial velocity conditions and comparing the calculated values with those measured in dilute solution. For the Mg2+ enzyme, narrow limits on possible values of the corresponding net rate constants were imposed on the basis of initial velocity rate constants for the forward and reverse directions plus values for the equilibrium distribution of central complexes, since direct measurement is not feasible. The effective energy barriers for both the Mg2+ and Cd2+ enzymes, calculated from the respective net rate constants, together with previously values for the equilibrium distribution of complexes in both enzymic systems [Ray, W. J., Jr., & Long, J. W. (1976) Biochemistry 15, 4018-4025], show that the 100-fold decrease in the kappa cat for the Cd2+ relative to the Mg2+ enzyme is caused by two factors: the increased stability of the intermediate bisphosphate complex and the decreased ability to cope with the phosphate ester involving the 1-hydroxyl group of the glucose ring. In fact, it

Kinetics of adsorption of whey proteins and hydroxypropyl-methyl-cellulose mixtures at the air-water interface.

PubMed

Pérez, Oscar E; Carrera Sánchez, Cecilio; Pilosof, Ana M R; Rodríguez Patino, Juan M

2009-08-15

The aim of this research is to quantify the competitive adsorption of a whey protein concentrate (WPC) and hydroxypropyl-methyl-cellulose (HPMC so called E4M, E50LV and F4M) at the air-water interface by means of dynamic surface tensiometry and Brewster angle microscopy (BAM). These biopolymers are often used together in many food applications. The concentration of both protein and HPMC, and the WPC/HPMC ratio in the aqueous bulk phase were variables, while pH (7), the ionic strength (0.05 M) and temperature (20 degrees C) were kept constant. The differences observed between mixed systems were in accordance with the relative bulk concentration of these biopolymers (C(HPMC) and C(WPC)) and the molecular structure of HPMC. At short adsorption times, the results show that under conditions where both WPC and HPMC could saturate the air-water interface on their own or when C(HPMC) > or = C(WPC), the polysaccharide dominates the surface. At concentrations where none of the biopolymers was able to saturate the interface, a synergistic behavior was observed for HPMC with lower surface activity (E50LV and F4M), while a competitive adsorption was observed for E4M (the HPMC with the highest surface activity). At long-term adsorption the rate of penetration controls the adsorption of mixed components. The results reflect complex competitive/synergistic phenomena under conditions of thermodynamic compatibility or in the presence of a "depletion mechanism". Finally, the order in which the different components reach the interface will influence the surface composition and the film properties.

Adsorption of saturated fatty acid in urea complexation: Kinetics and equilibrium studies

NASA Astrophysics Data System (ADS)

Setyawardhani, Dwi Ardiana; Sulistyo, Hary; Sediawan, Wahyudi Budi; Fahrurrozi, Mohammad

2018-02-01

Urea complexation is fractionation process for concentrating poly-unsaturated fatty acids (PUFAs) from vegetable oil or animal fats. For process design and optimization in commercial industries, it is necessary to provide kinetics and equilibrium data. Urea inclusion compounds (UICs) as the product is a unique complex form which one molecule (guest) is enclosed within another molecule (host). In urea complexation, the guest-host bonding exists between saturated fatty acids (SFAs) and crystalline urea. This research studied the complexation is analogous to an adsorption process. The Batch adsorption process was developed to obtain the experimental data. The ethanolic urea solution was mixed with SFA in certain compositions and adsorption times. The mixture was heated until it formed homogenous and clear solution, then it cooled very slowly until the first numerous crystal appeared. Adsorption times for the kinetic data were determined since the crystal formed. The temperature was maintained constant at room temperature. Experimental sets of data were observed with adsorption kinetics and equilibrium models. High concentration of saturated fatty acid (SFA) was used to represent adsorption kinetics and equilibrium parameters. Kinetic data were examined with pseudo first-order, pseudo second-order and intra particle diffusion models. Linier, Freundlich and Langmuir isotherm were used to study the equilibrium model of this adsorption. The experimental data showed that SFA adsorption in urea crystal followed pseudo second-order model. The compatibility of the data with Langmuir isotherm showed that urea complexation was a monolayer adsorption.

Adsorption of reovirus to clay minerals: effects of cation-exchange capacity, cation saturation, and surface area.

PubMed Central

Lipson, S M; Stotzky, G

1983-01-01

The adsorption of reovirus to clay minerals has been reported by several investigators, but the mechanisms defining this association have been studied only minimally. The purpose of this investigation was to elucidate the mechanisms involved with this interaction. More reovirus type 3 was adsorbed, in both distilled and synthetic estuarine water, by low concentrations of montmorillonite than by comparable concentrations of kaolinite containing a mixed complement of cations on the exchange complex. Adsorption to the clays was essentially immediate and was correlated with the cation-exchange capacity of the clays, indicating that adsorption was primarily to negatively charged sites on the clays. Adsorption was greater with low concentrations of clays in estuarine water than in distilled water, as the higher ionic strength of the estuarine water reduced the electrokinetic potential of both clay and virus particles. The addition of cations (as chloride salts) to distilled water enhanced adsorption, with divalent cations being more effective than monovalent cations and 10(-2) M resulting in more adsorption than 10(-3) M. Potassium ions suppressed reovirus adsorption to montmorillonite, probably by collapsing the clay lattices and preventing the expression of the interlayer-derived cation-exchange capacity. More virus was adsorbed by montmorillonite made homoionic to various mono-, di-, and trivalent cations (except by montmorillonite homoionic to potassium) than by comparable concentrations of kaolinite homoionic to the same cations. The sequence of the amount of adsorption to homoionic montmorillonite was Al greater than Ca greater than Mg greater than Na greater than K; the sequence of adsorption to kaolinite was Na greater than Al greater than Ca greater than Mg greater than K. The constant partition-type adsorption isotherms obtained when the clay concentration was maintained constant and the virus concentration was varied indicated that a fixed proportion of the

Study on Adsorption of Chromium (VI) by Activated Carbon from Cassava Sludge

NASA Astrophysics Data System (ADS)

Yang, Jinhui; Li, Chuanshu; Yang, Bin; Kang, Sijun; Zhang, Zhen

2018-03-01

In this paper, a new type of adsorbent prepared by waste sludge from alcohol production industry was used to adsorb Cr (VI) in activated carbon from cassava sludge. A series of static adsorption experiments were carried out on the initial concentration of solution Cr (VI), pH value of solution, adsorption time and dosage of adsorbent. The results of single factor experiments show that the removal rate of Cr (VI) increases with the initial concentration of Cr(VI), while the adsorption amount is opposite. When the pH value of the solution is low, the adsorption effect of activated carbon is better.The adsorption time should be controlled within 40-60min. When the activated carbon dosage is increased, the removal rate increases but the adsorption capacity decreases.

Pulse gas chromatographic study of adsorption of substituted aromatics and heterocyclic molecules on MIL-47 at zero coverage.

PubMed

Duerinck, Tim; Couck, Sarah; Vermoortele, Frederik; De Vos, Dirk E; Baron, Gino V; Denayer, Joeri F M

2012-10-02

The low coverage adsorptive properties of the MIL-47 metal organic framework toward aromatic and heterocyclic molecules are reported in this paper. The effect of molecular functionality and size on Henry adsorption constants and adsorption enthalpies of alkyl and heteroatom functionalized benzene derivates and heterocyclic molecules was studied using pulse gas chromatography. By means of statistical analysis, experimental data was analyzed and modeled using principal component analysis and partial least-squares regression. Structure-property relationships were established, revealing and confirming several trends. Among the molecular properties governing the adsorption process, vapor pressure, mean polarizability, and dipole moment play a determining role.

Zinc adsorption effects on arsenite oxidation kinetics at the birnessite-water interface

USGS Publications Warehouse

Power, L.E.; Arai, Y.; Sparks, D.L.

2005-01-01

Arsenite is more toxic and mobile than As(V) in soil and sediment environments, and thus it is advantageous to explore factors that enhance oxidation of As(III) to As(V). Previous studies showed that manganese oxides, such as birnessite (??-MnO2), directly oxidized As(III). However, these studies did not explore the role that cation adsorption has on As(III) oxidation. Accordingly, the effects of adsorbed and nonadsorbed Zn on arsenite (As(III)) oxidation kinetics at the birnessite-water interface were investigated using batch adsorption experiments (0.1 g L-1; pH 4.5 and 6.0; I = 0.01 M NaCl). Divalent Zn adsorption on synthetic ??-MnO 2 in the absence of As(III) increased with increasing pH and caused positive shifts in electrophoretic mobility values at pH 4-6, indirectly suggesting inner-sphere Zn adsorption mechanisms. Arsenite was readily oxidized on birnessite in the absence of Zn. The initial As(III) oxidation rate constant decreased with increasing pH from 4.5 to 6.0 and initial As(III) concentrations from 100 to 300 ??M. Similar pH and initial As(III) concentration effects were observed in systems when Zn was present (i.e., presorbed Zn prior to As(III) addition and simultaneously added Zn-As(III) systems), but As(III) oxidation reactions were suppressed compared to the respective control systems. The suppression was more pronounced when Zn was presorbed on the ??-MnO 2 surfaces as opposed to added simultaneously with As(III). This study provides further understanding of As(III) oxidation reactions on manganese oxide surfaces under environmentally applicable conditions where metals compete for reactive sites.

Effect of Phenol Molecular Structure on Bacterial Transformation Rate Constants in Pond and River Samples

PubMed Central

Paris, Doris F.; Wolfe, N. Lee; Steen, William C.; Baughman, George L.

1983-01-01

Microbial transformation rate constants for a series of phenols were correlated with a property of the substituents, van der Waal's radius. Transformation products were the corresponding catechols, with the exception of p-hydroxybenzoic acid, the product of p-acetylphenol. A different product suggested a different pathway; p-acetylphenol, therefore, was deleted from the data base. PMID:16346236

Characteristics and mechanisms of nickel adsorption on biochars produced from wheat straw pellets and rice husk.

PubMed

Shen, Zhengtao; Zhang, Yunhui; McMillan, Oliver; Jin, Fei; Al-Tabbaa, Abir

2017-05-01

The adsorption characteristics and mechanisms of Ni 2+ on four-standard biochars produced from wheat straw pellets (WSP550, WSP700) and rice husk (RH550, RH700) at 550 and 700 °C, respectively, were investigated. The kinetic results show that the adsorption of Ni 2+ on the biochars reached an equilibrium within 5 min. The increase of the solid to liquid ratio resulted in an increase of Ni 2+ removal percentage but a decrease of the adsorbed amount of Ni 2+ per weight unit of biochar. The Ni 2+ removal percentage increased with the increasing of initial solution pH values at the range of 2-4, was relatively constant at the pH range of 4-8, and significantly increased to ≥98% at pH 9 and stayed constantly at the pH range of 9-10. The calculated maximum adsorption capacities of Ni 2+ for the biochars follow the order of WSP700 > WSP550 > RH700 > RH550. Both cation exchange capacity and pH of biochar can be a good indicator of the maximum adsorption capacity for Ni 2+ showing a positively linear and exponential relationship, respectively. This study also suggests that a carefully controlled standardised production procedure can make it reliable to compare the adsorption capacities between different biochars and investigate the mechanisms involved.

The role of particle-size soil fractions in the adsorption of heavy metals

NASA Astrophysics Data System (ADS)

Mandzhieva, Saglara; Minkina, Tatiana; Pinsky, David; Batukaev, Abdulmalik; Kalinitchenko, Valeriy; Sushkova, Svetlana; Chaplygin, Viktor; Dikaev, Zaurbek; Startsev, Viktor; Bakoev, Serojdin

2014-05-01

Ion-exchange adsorption phenomena are important in the immobilization of heavy metals (HMs) by soils. Numerous works are devoted to the study of this problem. However, the interaction features of different particle-size soil fractions and their role in the immobilization of HMs studied insufficiently. Therefore, the assessment of the effect of the particle-size distribution on the adsorption properties of soils is a vital task. The parameters of Cu2+, Pb2+ and Zn2+ adsorption by chernozems of the south of Russia and their particle-size fractions were studied. In the particle-size fractions separated from the soils, the concentrations of Cu2+, Pb2+, and Zn2 decreased with the decreasing particle size. The parameters of the adsorption values of k (the constant of the affinity)and Cmax.(the maximum adsorption of the HMs) characterizing the adsorption of HMs by the southern chernozem and its particle-size fractions formed the following sequence: silt > clay > entire soil. The adsorption capacity of chernozems for Cu2+, Pb2+, and Zn2+ depending on the particle-size distribution decreased in the following sequence: clay loamy ordinary chernozem clay loamy southern chernozem> loamy southern chernozem> loamy sandy southern chernozem. According to the parameters of the adsorption by the different particle-size fractions, the heavy metal cations form a sequence analogous to that obtained for the entire soils: Cu2+ ≥ Pb2+ > Zn2+. The parameters of the heavy metal adsorption by similar particle-size fractions separated from different soils decreased in the following order: clay loamy chernozem> loamy chernozem> loamy sandy chernozem. The analysis of the changes in the parameters of the Cu2+, Pb2+, and Zn2+ adsorption by the studied soils and their particle-size fractions showed that the extensive adsorption characteristic - the maximum adsorption (Cmax.) - is a less sensitive parameter characterizing the adsorption capacity of the soils than the intensive characteristic of

The Adsorption of Bromide Ion at Mercury from Propylene Carbonate Solutions of Constant Ionic Strength

DTIC Science & Technology

1991-05-20

Chemistry University of California Davis, CA 95616 * To whom correspondence should be addressed. t Permanent address: Instituto de Fisica e Quimica ...I]. In the case of Br- ion adsorption at Hg, studies have been carried out in water [2-4] and N- methylformamide solutions [5,6] of both varying and...discussed with respect to current theoretical developments. 4 Experimental Differential capacity against potential data were obtained for the mercury

Optimization of High-Throughput Sequencing Kinetics for determining enzymatic rate constants of thousands of RNA substrates

PubMed Central

Niland, Courtney N.; Jankowsky, Eckhard; Harris, Michael E.

2016-01-01

Quantification of the specificity of RNA binding proteins and RNA processing enzymes is essential to understanding their fundamental roles in biological processes. High Throughput Sequencing Kinetics (HTS-Kin) uses high throughput sequencing and internal competition kinetics to simultaneously monitor the processing rate constants of thousands of substrates by RNA processing enzymes. This technique has provided unprecedented insight into the substrate specificity of the tRNA processing endonuclease ribonuclease P. Here, we investigate the accuracy and robustness of measurements associated with each step of the HTS-Kin procedure. We examine the effect of substrate concentration on the observed rate constant, determine the optimal kinetic parameters, and provide guidelines for reducing error in amplification of the substrate population. Importantly, we find that high-throughput sequencing, and experimental reproducibility contribute their own sources of error, and these are the main sources of imprecision in the quantified results when otherwise optimized guidelines are followed. PMID:27296633

Rate constants of agonist binding to muscarinic receptors in rat brain medulla. Evaluation by competition kinetics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schreiber, G.; Henis, Y.I.; Sokolovsky, M.

The method of competition kinetics, which measures the binding kinetics of an unlabeled ligand through its effect on the binding kinetics of a labeled ligand, was employed to investigate the kinetics of muscarinic agonist binding to rat brain medulla pons homogenates. The agonists studied were acetylcholine, carbamylcholine, and oxotremorine, with N-methyl-4-(TH)piperidyl benzilate employed as the radiolabeled ligand. Our results suggested that the binding of muscarinic agonists to the high affinity sites is characterized by dissociation rate constants higher by 2 orders of magnitude than those of antagonists, with rather similar association rate constants. Our findings also suggest that isomerization ofmore » the muscarinic receptors following ligand binding is significant in the case of antagonists, but not of agonists. Moreover, it is demonstrated that in the medulla pons preparation, agonist-induced interconversion between high and low affinity bindings sites does not occur to an appreciable extent.« less

Scaling trace organic contaminant adsorption capacity by granular activated carbon.

PubMed

Corwin, Christopher J; Summers, R Scott

2010-07-15

The role of particle size on the reduction of granular activated carbon (GAC) adsorption capacity for trace organic contaminants by dissolved organic matter (DOM) is examined and applied to performance scale-up. The adsorption capacity reduction, termed fouling, must be scalable in order to use bench scale tests, such as the rapid small-scale column test (RSSCT) to predict full-scale breakthrough. Equilibrium adsorption capacity tests with GAC preloaded with DOM and RSSCT breakthrough curves at three different GAC particle sizes indicate that GAC adsorption capacity is dependent on GAC particle size when DOM is present. Thus, the RSSCT cannot be expected to match full-scale results regardless of which RSSCT design approach is used (constant or proportional diffusivity), unless a scaling factor is applied to the results. Proportional diffusivity RSSCT breakthrough curves demonstrate that surface concentration of DOM is not a good measure of fouling. It is hypothesized that pore blockage is the mechanism responsible for the dependence on particle size. As GAC particle size increases, the microporous surface area behind a constricted pore also increases. The result is lower adsorption capacity per mass of adsorbent in the larger GAC particles. A scaling methodology for equilibrium and breakthrough data is presented that accounts for the dependence of NOM preloading effects on GAC particle diameter.

Determination of rate constants and branching ratios for TCE degradation by zero-valent iron using a chain decay multispecies model.

PubMed

Hwang, Hyoun-Tae; Jeen, Sung-Wook; Sudicky, Edward A; Illman, Walter A

2015-01-01

The applicability of a newly-developed chain-decay multispecies model (CMM) was validated by obtaining kinetic rate constants and branching ratios along the reaction pathways of trichloroethene (TCE) reduction by zero-valent iron (ZVI) from column experiments. Changes in rate constants and branching ratios for individual reactions for degradation products over time for two columns under different geochemical conditions were examined to provide ranges of those parameters expected over the long-term. As compared to the column receiving deionized water, the column receiving dissolved CaCO3 showed higher mean degradation rates for TCE and all of its degradation products. However, the column experienced faster reactivity loss toward TCE degradation due to precipitation of secondary carbonate minerals, as indicated by a higher value for the ratio of maximum to minimum TCE degradation rate observed over time. From the calculated branching ratios, it was found that TCE and cis-dichloroethene (cis-DCE) were dominantly dechlorinated to chloroacetylene and acetylene, respectively, through reductive elimination for both columns. The CMM model, validated by the column test data in this study, provides a convenient tool to determine simultaneously the critical design parameters for permeable reactive barriers and natural attenuation such as rate constants and branching ratios. Copyright © 2015 Elsevier B.V. All rights reserved.

Characterization of N3 dye adsorption on TiO2 using quartz-crystal microbalance with dissipation monitoring

NASA Astrophysics Data System (ADS)

Wayment-Steele, Hannah K.; Johnson, Lewis E.; Dixon, Matthew C.; Johal, Malkiat S.

2013-09-01

Understanding the kinetics of dye adsorption on semiconductors is crucial for designing dye-sensitized solar cells (DSSCs) with enhanced efficiency. Harms et al. recently applied the Quartz-Crystal Microbalance with Dissipation Monitoring (QCM-D) to study in situ dye adsorption on flat TiO2 surfaces. QCM-D measures adsorption in real time and therefore allows one to determine the kinetics of the process. In this work, we characterize the adsorption of N3, a commercial RuBipy dye, using the native oxide layer of a titanium sensor to simulate the TiO2 substrate of a DSSC. We report equilibrium constants that are in agreement with previous absorbance studies of N3 adsorption, and therefore demonstrate the native oxide layer of a titanium sensor as a valid and readily available planar TiO2 morphology to study dye adsorption.

Adsorption Isotherms and Surface Reaction Kinetics

ERIC Educational Resources Information Center

Lobo, L. S.; Bernardo, C. A.

1974-01-01

Explains an error that occurs in calculating the conditions for a maximum value of a rate expression for a bimolecular reaction. The rate expression is derived using the Langmuir adsorption isotherm to relate gas pressures and corresponding surface coverages. (GS)

Absolute protein-protein association rate constants from flexible, coarse-grained Brownian dynamics simulations: the role of intermolecular hydrodynamic interactions in barnase-barstar association.

PubMed

Frembgen-Kesner, Tamara; Elcock, Adrian H

2010-11-03

Theory and computation have long been used to rationalize the experimental association rate constants of protein-protein complexes, and Brownian dynamics (BD) simulations, in particular, have been successful in reproducing the relative rate constants of wild-type and mutant protein pairs. Missing from previous BD studies of association kinetics, however, has been the description of hydrodynamic interactions (HIs) between, and within, the diffusing proteins. Here we address this issue by rigorously including HIs in BD simulations of the barnase-barstar association reaction. We first show that even very simplified representations of the proteins--involving approximately one pseudoatom for every three residues in the protein--can provide excellent reproduction of the absolute association rate constants of wild-type and mutant protein pairs. We then show that simulations that include intermolecular HIs also produce excellent estimates of association rate constants, but, for a given reaction criterion, yield values that are decreased by ∼35-80% relative to those obtained in the absence of intermolecular HIs. The neglect of intermolecular HIs in previous BD simulation studies, therefore, is likely to have contributed to the somewhat overestimated absolute rate constants previously obtained. Consequently, intermolecular HIs could be an important component to include in accurate modeling of the kinetics of macromolecular association events. Copyright © 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Constant strain accumulation rate between major earthquakes on the North Anatolian Fault.

PubMed

Hussain, Ekbal; Wright, Tim J; Walters, Richard J; Bekaert, David P S; Lloyd, Ryan; Hooper, Andrew

2018-04-11

Earthquakes are caused by the release of tectonic strain accumulated between events. Recent advances in satellite geodesy mean we can now measure this interseismic strain accumulation with a high degree of accuracy. But it remains unclear how to interpret short-term geodetic observations, measured over decades, when estimating the seismic hazard of faults accumulating strain over centuries. Here, we show that strain accumulation rates calculated from geodetic measurements around a major transform fault are constant for its entire 250-year interseismic period, except in the ~10 years following an earthquake. The shear strain rate history requires a weak fault zone embedded within a strong lower crust with viscosity greater than ~10 20  Pa s. The results support the notion that short-term geodetic observations can directly contribute to long-term seismic hazard assessment and suggest that lower-crustal viscosities derived from postseismic studies are not representative of the lower crust at all spatial and temporal scales.

Rate Constants and Activation Energies for Gas-Phase Reactions of Three Cyclic Volatile Methyl Siloxanes with the Hydroxyl Radical.

PubMed

Safron, Andreas; Strandell, Michael; Kierkegaard, Amelie; Macleod, Matthew

2015-07-01

Reaction with hydroxyl radicals (OH) is the major pathway for removal of cyclic volatile methyl siloxanes (cVMS) from air. We present new measurements of second-order rate constants for reactions of the cVMS octamethylcyclotetrasiloxane (D 4 ), decamethylcyclopentasiloxane (D 5 ), and dodecamethylcyclohexasiloxane (D 6 ) with OH determined at temperatures between 313 and 353 K. Our measurements were made using the method of relative rates with cyclohexane as a reference substance and were conducted in a 140-mL gas-phase reaction chamber with online mass spectrometry analysis. When extrapolated to 298 K, our measured reaction rate constants of D 4 and D 5 with the OH radical are 1.9 × 10 -12 (95% confidence interval (CI): (1.7-2.2) × 10 -12 ) and 2.6 × 10 -12 (CI: (2.3-2.9) × 10 -12 ) cm 3 molecule -1 s -1 , respectively, which are 1.9× and 1.7× faster than previous measurements. Our measured rate constant for D 6 is 2.8 × 10 -12 (CI: (2.5-3.2) × 10 -12 ) cm 3 molecule -1 s -1 and to our knowledge there are no comparable laboratory measurements in the literature. Reaction rates for D 5 were 33% higher than for D 4 (CI: 30-37%), whereas the rates for D 6 were only 8% higher than for D 5 (CI: 5-10%). The activation energies of the reactions of D 4 , D 5 , and D 6 with OH were not statistically different and had a value of 4300 ± 2800 J/mol.

Simultaneous measurement of the maximum oscillation amplitude and the transient decay time constant of the QCM reveals stiffness changes of the adlayer.

PubMed

Marxer, C Galli; Coen, M Collaud; Bissig, H; Greber, U F; Schlapbach, L

2003-10-01

Interpretation of adsorption kinetics measured with a quartz crystal microbalance (QCM) can be difficult for adlayers undergoing modification of their mechanical properties. We have studied the behavior of the oscillation amplitude, A(0), and the decay time constant, tau, of quartz during adsorption of proteins and cells, by use of a home-made QCM. We are able to measure simultaneously the frequency, f, the dissipation factor, D, the maximum amplitude, A(0), and the transient decay time constant, tau, every 300 ms in liquid, gaseous, or vacuum environments. This analysis enables adsorption and modification of liquid/mass properties to be distinguished. Moreover the surface coverage and the stiffness of the adlayer can be estimated. These improvements promise to increase the appeal of QCM methodology for any applications measuring intimate contact of a dynamic material with a solid surface.

Fixed-bed adsorption study of methylene blue onto pyrolytic tire char

NASA Astrophysics Data System (ADS)

Makrigianni, Vassiliki; Giannakas, Aris; Papadaki, Maria; Albanis, Triantafyllos; Konstantinou, Ioannis

2016-04-01

In this work, the adsorption efficiency of acid treated pyrolytic tire char to cationic methylene blue (MB) dye adsorption from aqueous solutions was investigated by fixed-bed adsorption column experiments. The effects of the initial dye concentration (10 - 40 mg L-1) and feed flow rate (50 - 150 mL min -1) with a fixed bed height (15 cm) were studied in order to determine the breakthrough characteristics of the adsorption system. The Adams-Bohart, Yoon-Nelson and Thomas model were applied to the adsorption of MB onto char at different operational conditions to predict the breakthrough curves and to determine the characteristic parameters of the column. The results showed that the maximum adsorbed quantities decreased with increasing flow rate and increased with increasing initial MB concentration. Breakthrough time and exhaustion time increased with decreasing inlet dye concentration and flow rate. In contrast with Adams-Bohart model, Yoon-Nelson model followed by Thomas model were found more suitable to describe the fixed-bed adsorption of methylene blue by char. The correlation coefficient values R2 for both models at different operating conditions are higher than 0.9 and the low average relative error values provided very good fittings of experimental data at different operating conditions. Higher adsorption capacity of 3.85 mg g -1 was obtained at 15 cm of adsorbent bed height, flow rate of 100 mL min -1and initial MB concentration of 40 mg L-1. Although that activated carbons exhibited higher adsorption capacities in the literature, acid-treated pyrolytic tire char was found to be considerably efficient adsorbent for the removal of MB dye column taking into account the advantages of the simpler production process compared to activated carbons, as well as, the availability of waste tire feedstock and concurrent waste tire management.

Atypical transitions in material response during constant strain rate, hot deformation of austenitic steel

NASA Astrophysics Data System (ADS)

Borah, Utpal; Aashranth, B.; Samantaray, Dipti; Kumar, Santosh; Davinci, M. Arvinth; Albert, Shaju K.; Bhaduri, A. K.

2017-10-01

Work hardening, dynamic recovery and dynamic recrystallization (DRX) occurring during hot working of austenitic steel have been extensively studied. Various empirical models describe the nature and effects of these phenomena in a typical framework. However, the typical model is sometimes violated following atypical transitions in deformation mechanisms of the material. To ascertain the nature of these atypical transitions, researchers have intentionally introduced discontinuities in the deformation process, such as interrupting the deformation as in multi-step rolling and abruptly changing the rate of deformation. In this work, we demonstrate that atypical transitions are possible even in conventional single-step, constant strain rate deformation of austenitic steel. Towards this aim, isothermal, constant true strain rate deformation of austenitic steel has been carried out in a temperature range of 1173-1473 K and strain rate range of 0.01-100 s-1. The microstructural response corresponding to each deformation condition is thoroughly investigated. The conventional power-law variation of deformation grain size (D) with peak stress (σp) during DRX is taken as a typical model and experimental data is tested against it. It is shown that σp-D relations exhibit an atypical two-slope linear behaviour rather than a continuous power law relation. Similarly, the reduction in σp with temperature (T) is found to consist of two discrete linear segments. In practical terms, the two linear segments denote two distinct microstructural responses to deformation. As a consequence of this distinction, the typical model breaks down and is unable to completely relate microstructural evolution to flow behaviour. The present work highlights the microstructural mechanisms responsible for this atypical behavior and suggests strategies to incorporate the two-slope behaviour in the DRX model.

SU-G-201-06: Directional Low-Dose Rate Brachytherapy: Determination of the TG-43 Dose-Rate Constant Analog for a New Pd-103 Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aima, M; Culberson, W; Hammer, C

Purpose: The aim of this work is to determine the TG-43 dose-rate constant analog for a new directional low-dose rate brachytherapy source based on experimental methods and comparison to Monte Carlo simulations. The CivaSheet™ is a new commercially available planar source array comprised of a variable number of discrete directional source elements called “CivaDots”. Given the directional nature and non-conventional design of the source, modifications to the AAPM TG-43 protocol for dosimetry are required. As a result, various parameters of the TG-43 dosimetric formalism have to be adapted to accommodate this source. This work focuses on the dose-rate constant analogmore » determination for a CivaDot. Methods: Dose to water measurements of the CivaDot were performed in a polymethyl methacrylate phantom (20×20×12 cm{sup 3}) using thermoluminescent dosimeters (TLDs) and Gafchromic EBT3 film. The source was placed in the center of the phantom, and nine TLD micro-cubes were irradiated along its central axis at a distance of 1 cm. For the film measurements, the TLDs were substituted by a (3×3) cm{sup 2} EBT3 film. Primary air-kerma strength measurements of the source were performed using a variable-aperture free-air chamber. Finally, the source was modeled using the Monte Carlo N-Particle Transport Code 6. Results: Dose-rate constant analog observed for a total of eight CivaDots using TLDs and five CivaDots using EBT3 film was within ±7.0% and ±2.9% of the Monte Carlo predicted value respectively. The average difference observed was −4.8% and −0.1% with a standard deviation of 1.7% and 2.1% for the TLD and the film measurements respectively, which are both within the comparison uncertainty. Conclusion: A preliminary investigation to determine the doserate constant analog for a CivaDot was conducted successfully with good agreement between experimental and Monte Carlo based methods. This work will aid in the eventual realization of a clinically

Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soudackov, Alexander; Hammes-Schiffer, Sharon

2015-11-17

Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency regimes for the proton donor-acceptor vibrational mode. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term does not significantly impact the rate constants derived using the cumulant expansion approachmore » in any of the regimes studied. The effects of the quadratic term may become significant when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant, however, particularly at high temperatures and for proton transfer interfaces with extremely soft proton donor-acceptor modes that are associated with extraordinarily weak hydrogen bonds. Even with the thermal averaging procedure, the effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances, and the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton transfer and proton-coupled electron transfer in chemical and biological processes. We are grateful for support from National Institutes of Health Grant GM056207 (applications to enzymes) and the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of

Analysis of mercury adsorption at the gibbsite-water interface using the CD-MUSIC model.

PubMed

Park, Chang Min

2018-05-22

Mercury (Hg), one of the most toxic substances in nature, has long been released during the anthropogenic activity. A correct description of the adsorptive behavior of mercury is important to gain a better insight into its fate and transport in natural mineral surfaces, which will be a prerequisite for the development of surface complexation model for the adsorption processes. In the present study, simulation experiments on macroscopic Hg(II) sorption by gibbsite (α-Al(OH) 3 ), a representative aluminum (hydr)oxide mineral, were performed using the charge distribution and multi-site complexation (CD-MUSIC) approach with 1-pK triple plane model (TPM). For this purpose, several data sets which had already been reported in the literature were employed to analyze the effect of pH, ionic strength, and co-exisiting ions (NO 3 - and Cl - ) on the Hg(II) adsorption onto gibbsite. Sequential optimization approach was used to determine the acidity and asymmetric binding constants for electrolyte ions and the affinity constants of the surface species through the model simulation using FITEQLC (a modified code of FITEQL 4.0). The model successfully incorporated the presence of inorganic ligands at the dominant edge (100) face of gibbsite with consistent surface species, which was evidenced by molecular scale analysis. The model was verified with an independent set of Hg(II) adsorption data incorporating carbonate binding species in an open gibbsite-water system.

Adsorption and photodegradation of methylene blue by iron oxide impregnated on granular activated carbons in an oxalate solution

NASA Astrophysics Data System (ADS)

Kadirova, Zukhra C.; Katsumata, Ken-ichi; Isobe, Toshihiro; Matsushita, Nobuhiro; Nakajima, Akira; Okada, Kiyoshi

2013-11-01

The photocatalytic adsorbents BAU-OA, BAU-CL and BAU-HA with varying iron oxide content (9-10 mass%) were prepared by heat treatment at 250 °C from commercial activated carbon (BAU) impregnated with iron oxalate, chloride, tris-benzohydroxamate, respectively. The XRD patterns showed amorphous structure in the BAU-CL sample (SBET 50 m2/g) and low crystallinity (as FeOOH and Fe2O3 phases) in the BAU-HA and BAU-OA samples (SBET 4 and 111 m2/g, respectively). The methylene blue adsorption capacities was decreased in order of BAU-OA < BAU-CL < BAU-HA sample and the adsorption followed Langmuir model. The apparent MB photodegradation rate constant (kapp) was increased in same order BAU-HA < BAU-CL < BAU-OA under the standard experimental conditions (initial MB concentrations 0.015-0.025 mM; sample content - 10 mg/l; initial oxalic acid concentration - 0.43 mM; pH 3-4; UV illumination). The process included high efficiency combination of adsorption, heterogeneous and homogeneous catalysis under UV and solar lights illumination without addition of hydrogen peroxide. The detoxification of water sample containing organic dyes was confirmed after combined sorption-photocatalytic treatment.

Post-combustion CO2 capture with activated carbons using fixed bed adsorption

NASA Astrophysics Data System (ADS)

Al Mesfer, Mohammed K.; Danish, Mohd; Fahmy, Yasser M.; Rashid, Md. Mamoon

2018-03-01

In the current work, the capturing of carbon dioxide from flue gases of post combustion emission using fixed bed adsorption has been carried out. Two grades of commercial activated carbon (sorbent-1 and sorbent-2) were used as adsorbent. Feed consisting of CO2 and N2 mixture was used for carrying out the adsorption. The influence of bed temperature, feed rate, equilibrium partial pressure and initial % CO2 in feed were considered for analyzing adsorption-desorption process. It was found that the total adsorption-desorption cycle time decreases with increased column temperature and feed rates. The time required to achieve the condition of bed saturation decreases with increased bed temperature and feed rates. The amount of CO2 adsorbed/Kg of the adsorbent declines with increased bed temperature with in studied range for sorbent-1 and sorbent-2. It was suggested that the adsorption capacity of the both the sorbents increases with increased partial pressure of the gas.

Effect of Humid Aging on the Oxygen Adsorption in SnO₂ Gas Sensors.

PubMed

Suematsu, Koichi; Ma, Nan; Watanabe, Ken; Yuasa, Masayoshi; Kida, Tetsuya; Shimanoe, Kengo

2018-01-16

To investigate the effect of aging at 580 °C in wet air (humid aging) on the oxygen adsorption on the surface of SnO₂ particles, the electric properties and the sensor response to hydrogen in dry and humid atmospheres for SnO₂ resistive-type gas sensors were evaluated. The electric resistance in dry and wet atmospheres at 350 °C was strongly increased by humid aging. From the results of oxygen partial pressure dependence of the electric resistance, the oxygen adsorption equilibrium constants ( K ₁; for O - adsorption, K ₂; for O 2- adsorption) were estimated on the basis of the theoretical model of oxygen adsorption. The K ₁ and K ₂ in dry and wet atmospheres at 350 °C were increased by humid aging at 580 °C, indicating an increase in the adsorption amount of both O - and O 2- . These results suggest that hydroxyl poisoning on the oxygen adsorption is suppressed by humid aging. The sensor response to hydrogen in dry and wet atmosphere at 350 °C was clearly improved by humid aging. Such an improvement of the sensor response seems to be caused by increasing the oxygen adsorption amount. Thus, the humid aging offers an effective way to improve the sensor response of SnO₂ resistive-type gas sensors in dry and wet atmospheres.

Mechanism of tyramine adsorption on Ca-montmorillonite.

PubMed

Chang, Po-Hsiang; Jiang, Wei-Teh; Li, Zhaohui

2018-06-10

Tyramine (TY) adsorption on a Ca-montmorillonite (SAz-2) was investigated with batch experiments and complementary analyses utilizing ultra-high performance liquid chromatography, ion chromatography, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetry (TG). The adsorption reached equilibrium in 8 h, complying with the pseudo-second-order rate equation, and came to an adsorption capacity of 682 mmol kg -1 at pH 6-8.1, utilizing the Langmuir isotherm model. The adsorption of TY and desorption of exchangeable cations exhibited a linear relationship with a slope of 0.9, implying that the adsorption was largely influenced by a cation exchange mechanism. The effective adsorption was further verified by the characteristic TY bands in the FTIR spectra and the signals of mass loss due to TY decomposition in the TG measurements of the clay after adsorption experiments. Intercalation of hydrated TY into the clay interlayer was confirmed by XRD and TG analyses of the heated samples loaded with TY. The adsorption reached only 0.57 cation exchange capacity of the clay which was probably limited by the low charge density of TY as compared to the negative charge density of the clay surface and by the steric effects arising from the hydration of TY that increased its molecular size. Adsorption of TY on montmorillonite can make TY more resistant to thermal decomposition and possibly better preserved in aquatic and soil environments. Copyright © 2018 Elsevier B.V. All rights reserved.

Carbon composite lignin-based adsorbents for the adsorption of dyes.

PubMed

Wang, Xiaohong; Jiang, Chenglong; Hou, Bingxia; Wang, Yingying; Hao, Chen; Wu, Jingbo

2018-05-10

Carbon composite lignin-based adsorbent were prepared through hydrothermal method with glucose as carbon source, calcium lignosulfonate and triethylene tetramine as raw materials, respectively. The optimum synthesis conditions were determined by investigating the addition of carbon and triethylene tetramine. The adsorbent was used for the adsorption of azo dyes Congo red and Eriochrome blue black R, and the five factors affecting the adsorption were discussed, including pH of dyes, initial concentration, adsorption time, adsorption temperature and adsorbent dosage. The corresponding adsorption mechanism such as pseudo first order kinetics, pseudo second order kinetics, intraparticle diffusion, Langmuir adsorption isotherm, Freundlich isotherm, Temkin isotherm, Dubinin-Radushkevich adsorption isotherm, thermodynamics were also studied. When the dye concentration is 40 mg L -1 , Congo red and Eriochrome blue black R dye removal rates reach 99%. Moreover, the adsorption process of two kinds of dyes follow the pseudo second order kinetics and the Langmuir adsorption isotherm. Copyright © 2018 Elsevier Ltd. All rights reserved.

Synergic mechanism of adsorption and metal-free catalysis for phenol degradation by N-doped graphene aerogel.

PubMed

Ren, Xiaohua; Guo, Huanhuan; Feng, Jinkui; Si, Pengchao; Zhang, Lin; Ci, Lijie

2018-01-01

3D porous N-doped reduced graphene oxide (N-rGO) aerogels were synthesized by a hydrothermal reduction of graphene oxide (GO) with urea and following freeze-drying process. N-rGO aerogels have a high BET surface of 499.70 m 2 /g and a high N doping content (5.93-7.46 at%) including three kinds of N (graphitic, pyridinic and pyrrolic). Their high catalytic performance for phenol oxidation in aqueous solution was investigated by catalytic activation of persulfate (PS). We have demonstrated that N-rGO aerogels are promising metal-free catalysts for phenol removal. Kinetics studies indicate that phenol degradation follows first-order reaction kinetics with the reaction rate constant of 0.16799 min -1 for N-rGO-A(1:30). Interestingly, the comparison of direct catalytic oxidation with adsorption-catalytic oxidation experiments indicates that adsorption plays an important role in the catalytic oxidation of phenol by decreasing the phenol degradation time. Spin density and adsorption modeling demonstrates that graphitic N in N-rGO plays the most important role for the catalytic performance by inducing high positive charge densities to adjacent carbon atoms and facilitating phenol adsorption on these carbon sites. Furthermore, the activation mechanism of persulfate (PS) on N-rGO was first investigated by DFT method and PS can be activated to generate strongly oxidative radical (SO 4 · - ) by transferring electrons to N-rGO. Copyright © 2017 Elsevier Ltd. All rights reserved.

Rate constants and mechanisms for the crystallization of Al nano-goethite under environmentally relevant conditions

NASA Astrophysics Data System (ADS)

Bazilevskaya, Ekaterina; Archibald, Douglas D.; Martínez, Carmen Enid

2012-07-01

Mobile inorganic and organic nanocolloidal particles originate-from and interact-with bulk solid phases in soil and sediment environments, and as such, they contribute to the dynamic properties of environmental systems. In particular, ferrihydrite and (nano)goethite are the most abundant of nanocolloidal Fe oxy(hydr)oxides in these environments. We therefore investigated the ferrihydrite to goethite phase transformation using experimental reaction conditions that mimicked environmental conditions where the formation of nanocolloidal Fe oxy(hydr)oxides may occur: slow titration of dilute solutions to pH 5 at 25 °C with and without 2 mol% Al. Subsequently, the rate constants from 54-d nano-goethite aging/crystallization experiments at 50 °C were determined using aliquots pulled for vibrational spectroscopy (including multivariate curve resolution, MCR, analyses of infrared spectra) and synchrotron-based X-ray diffraction (XRD). We also present a mechanistic model that accounts for the nano-goethite crystallization observed by the aforementioned techniques, and particle structural characteristics observed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). In contrast to the common assumption that metastable ferrihydrite precipitates first, before it transforms to goethite, the presence of characteristic infrared bands in freshly synthesized nanoparticle suspensions indicate goethite can precipitate directly from solution under environmentally relevant conditions: low Fe concentration, ambient temperature, and pH maintained at 5. However, the presence of 2 mol% Al prevented direct goethite precipitation. Rate constants obtained by fitting the contributions from the MCR-derived goethite-like component to the OH-stretching region were (7.4 ± 1.1) × 10-7 s-1 for 0% Al and (4.2 ± 0.4) × 10-7 s-1 for 2 mol% Al suspensions. Rate constants derived from intensities of OH-bending infrared vibrations (795 and 895 cm-1) showed similar values

Ice-surface adsorption enhanced colligative effect of antifreeze proteins in ice growth inhibition

NASA Astrophysics Data System (ADS)

Mao, Yougang; Ba, Yong

2006-09-01

This Communication describes a mechanism to explain antifreeze protein's function to inhibit the growth of ice crystals. We propose that the adsorption of antifreeze protein (AFP) molecules on an ice surface induces a dense AFP-water layer, which can significantly decrease the mole fraction of the interfacial water and, thus, lower the temperature for a seed ice crystal to grow in a super-cooled AFP solution. This mechanism can also explain the nearly unchanged melting point for the ice crystal due to the AFP's ice-surface adsorption. A mathematical model combining the Langmuir theory of adsorption and the colligative effect of thermodynamics has been proposed to find the equilibrium constants of the ice-surface adsorptions, and the interfacial concentrations of AFPs through fitting the theoretical curves to the experimental thermal hysteresis data. This model has been demonstrated by using the experimental data of serial size-mutated beetle Tenebrio molitor (Tm) AFPs. It was found that the AFP's ice-surface adsorptions could increase the interfacial AFP's concentrations by 3 to 4 orders compared with those in the bulk AFP solutions.

Adsorption kinetic and desorption studies of Cd2+ on Multi-Carboxylic-Functionalized Silica Gel

NASA Astrophysics Data System (ADS)

Li, Min; Wei, Jian; Meng, Xiaojing; Wu, Zhuqiang; Liang, Xiuke

2018-01-01

In the present study, the adsorption behavior of cadmium (II) ion from aqueous solution onto multi-carboxylic-functionalized silica gel (SG-MCF) has been investigated in detail by means of batch and column experiments. Batch experiments were performed to evaluate the effects of contact time on adsorption capacity of cadmium (II) ion. The kinetic data were analyzed on the basis of the pseudo-first-order kinetic and the pseudo-second-order kinetic models and consequently, the pseudo-second-order kinetic can better describe the adsorption process than the pseudo-first-order kinetic model. And the adsorption mechanism of the process was studied by intra-particle and film diffusion, it was found out that the adsorption rate was governed primarily by film diffusion to the adsorption onto the SG-MCF. In addition, column experiments were conducted to assess the effects initial inlet concentration and the flow rate on breakthrough time and adsorption capacity ascertaining the practical applicability of the adsorbent. The results suggest that the total amount of adsorbed cadmium (II) ion increased with declined flow rate and increased the inlet concentration. The adsorption-desorption experiment confirmed that adsorption capacity of cadmium (II) ion didn’t present an obvious decrease after five cycles.

Adsorption kinetic and desorption studies of Cu2+ on Multi-Carboxylic-Functionalized Silica Gel

NASA Astrophysics Data System (ADS)

Li, Min; Meng, Xiaojing; Liu, Yushuang; Hu, Xinju; Liang, Xiuke

2018-01-01

In the present study, the adsorption behavior of copper (II) ion from aqueous solution onto multi-carboxylic-functionalized silica gel (SG-MCF) has been investigated in detail by means of batch and column experiments. Batch experiments were performed to evaluate the effects of contact time on adsorption capacity of copper (II) ion. The kinetic data were analyzed on the basis of the pseudo-first-order kinetic and the pseudo-second-order kinetic models and consequently, the pseudo-second-order kinetic can better describe the adsorption process than the pseudo-first-order kinetic model. And the adsorption mechanism of the process was studied by intra-particle and film diffusion, it was found out that the adsorption rate was governed primarily by film diffusion to the adsorption onto the SG-MCF. In addition, column experiments were conducted to assess the effects initial inlet concentration and the flow rate on breakthrough time and adsorption capacity ascertaining the practical applicability of the adsorbent. The results suggest that the total amount of adsorbed copper (II) ion increased with declined flow rate and increased the inlet concentration. The adsorption-desorption experiment confirmed that adsorption capacity of copper (II) ion didn’t present an obvious decrease after five cycles.

An exploration of the relationship between adsorption and bioavailability of pesticides in soil to earthworm.

PubMed

Yu, Yun Long; Wu, Xiao Mao; Li, Shao Nan; Fang, Hua; Zhan, Hai Yan; Yu, Jing Quan

2006-06-01

A study was conducted to determine the adsorption/desorption of butachlor, myclobutanil and chlorpyrifos on five soils using a batch equilibration technique and to study the relationship between bioavailability to Allolobophora caliginosa and the adsorption/desorption of these three pesticides. The results showed that the adsorption/desorption processes of the tested compounds were mainly controlled by soil organic matter content (OM) and octanol/water-partitioning coefficient (K(ow)), and that the bioavailability of the pesticides was dependent on characteristics of pesticides, properties of soils, and uptake routes of earthworms. Bioconcentration of butachlor and myclobutanil was negatively correlated with Freundlich adsorption constant K(af) and K(df). However, only a slightly positive correlation between bioconcentration and K(af) and K(df) was observed for chlorpyrifos due to its high affinity onto soil.

Study of Adsorption Mechanism of Congo Red on Graphene Oxide/PAMAM Nanocomposite

PubMed Central

Rafi, Mohammad; Samiey, Babak; Cheng, Chil-Hung

2018-01-01

Graphene oxide/poly(amidoamine) (GO/PAMAM) nanocomposite adsorbed high quantities of congo red (CR) anionic dye in 0.1 M NaCl solution, with the maximum adsorption capacity of 198 mg·g−1. The kinetics and thermodynamics of adsorption were investigated to elucidate the effects of pH, temperature, shaking rate, ionic strength, and contact time. Kinetic data were analyzed by the KASRA model and the KASRA, ISO, and pore-diffusion equations. Adsorption adsorption isotherms were studied by the ARIAN model and the Henry, Langmuir, and Temkin equations. It was shown that adsorption sites of GO/PAMAM at experimental conditions were phenolic hydroxyl groups of GO sheets and terminal amine groups of PAMAM dendrimer. Analysis of kinetic data indicated that amine sites were located on the surface, and that hydroxyl sites were placed in the pores of adsorbent. CR molecules interacted with the adsorption sites via hydrogen bonds. The molecules were adsorbed firstly on the amine sites, and then on the internal hydroxyl sites. Adsorption kinetic parameters indicated that the interaction of CR to the –NH3+ sites was the rate-controlling step of adsorption of CR on this site and adsorption activation energies calculated for different parts of this step. On the other hand, kinetic parameters showed that the intraparticle diffusion was the rate-controlling step during the interaction of CR molecules to –OH sites and activation energy of this step was not calculable. Finally, the used GO/PAMAM was completely regenerated by using ethylenediamine. PMID:29587463

Simulation of methylene blue adsorption by salts-treated beech sawdust in batch and fixed-bed systems.

PubMed

Batzias, F A; Sidiras, D K

2007-10-01

Batch and column kinetics of methylene blue adsorption on calcium chloride, zinc chloride, magnesium chloride and sodium chloride treated beech sawdust were simulated, using untreated beech sawdust as control, in order to explore its potential use as a low-cost adsorbent for wastewater dye removal. The adsorption capacity, estimated according to Freundlich's model, the Langmuir constant K(L) and the adsorption capacity coefficient values, determined using the Bohart and Adams' bed depth service model indicate that salts treatment enhanced the adsorption properties of the original material. Since sawdust is an industrial waste/byproduct and the salts used can be recovered as spent liquids from various chemical operations, this process of adsorbent upgrading/modification might be considered to take place within an 'Industrial Ecology' framework.

Estimation of uptake rate constants for PCB congeners accumulated by semipermeable membrane devices and brown treat (Salmo trutta)

USGS Publications Warehouse

Meadows, J.C.; Echols, K.R.; Huckins, J.N.; Borsuk, F.A.; Carline, R.F.; Tillitt, D.E.

1998-01-01

The triolein-filled semipermeable membrane device (SPMD) is a simple and effective method of assessing the presence of waterborne hydrophobic chemicals. Uptake rate constants for individual chemicals are needed to accurately relate the amounts of chemicals accumulated by the SPMD to dissolved water concentrations. Brown trout and SPMDs were exposed to PCB- contaminated groundwater in a spring for 28 days to calculate and compare uptake rates of specific PCB congeners by the two matrixes. Total PCB congener concentrations in water samples from the spring were assessed and corrected for estimated total organic carbon (TOC) sorption to estimate total dissolved concentrations. Whole and dissolved concentrations averaged 4.9 and 3.7 ??g/L, respectively, during the exposure. Total concentrations of PCBs in fish rose from 0.06 to 118.3 ??g/g during the 28-day exposure, while concentrations in the SPMD rose from 0.03 to 203.4 ??g/ g. Uptake rate constants (k1) estimated for SPMDs and brown trout were very similar, with k1 values for SPMDs ranging from one to two times those of the fish. The pattern of congener uptake by the fish and SPMDs was also similar. The rates of uptake generally increased or decreased with increasing K(ow), depending on the assumption of presence or absence of TOC.The triolein-filled semipermeable membrane device (SPMD) is a simple and effective method of assessing the presence of waterborne hydrophobic chemicals. Uptake rate constants for individual chemicals are needed to accurately relate the amounts of chemicals accumulated by the SPMB to dissolved water concentrations. Brown trout and SPMDs were exposed to PCB-contaminated groundwater in a spring for 28 days to calculate and compare uptake rates of specific PCB congeners by the two matrixes. Total PCB congener concentrations in water samples from the spring were assessed and corrected for estimated total organic carbon (TOC) sorption to estimate total dissolved concentrations. Whole and

Rate constants for the quenching of metastable O2 (1Sigma g +) molecules

NASA Technical Reports Server (NTRS)

Kwang, Y. C.; Leu, M.-T.

1985-01-01

The O2 (1Sigma g +) rates for CO2, H2, N2, Cl2, CO, O3, and 2,3 DMB-2 are determined by monitoring the 762-nm emission in a fast-flow-discharge chemiluminescence detection system (Leu, 1984; Leu and Smith, 1981). The results are presented in tables and graphs and briefly characterized. The rate constants (in cu cm/s x 10 to the -16th) are 4600 + or - 500 for CO2, 7000 + or - 300 for H2, 17 + or - 1 for N2, 4.5 + or - 0.8 for Cl2, 45 + or - 5 for CO, 220,000 + or - 30,000 for O3, and 6000 + or - 100 for 2,3 DMB-2. The temperature dependence of the CO2 and O3 quenching reactions at 245-362 K is found to be negligible.

The Langmuir isotherm: a commonly applied but misleading approach for the analysis of protein adsorption behavior.

PubMed

Latour, Robert A

2015-03-01

The Langmuir adsorption isotherm provides one of the simplest and most direct methods to quantify an adsorption process. Because isotherm data from protein adsorption studies often appear to be fit well by the Langmuir isotherm model, estimates of protein binding affinity have often been made from its use despite that fact that none of the conditions required for a Langmuir adsorption process may be satisfied for this type of application. The physical events that cause protein adsorption isotherms to often provide a Langmuir-shaped isotherm can be explained as being due to changes in adsorption-induced spreading, reorientation, clustering, and aggregation of the protein on a surface as a function of solution concentration in contrast to being due to a dynamic equilibrium adsorption process, which is required for Langmuir adsorption. Unless the requirements of the Langmuir adsorption process can be confirmed, fitting of the Langmuir model to protein adsorption isotherm data to obtain thermodynamic properties, such as the equilibrium constant for adsorption and adsorption free energy, may provide erroneous values that have little to do with the actual protein adsorption process, and should be avoided. In this article, a detailed analysis of the Langmuir isotherm model is presented along with a quantitative analysis of the level of error that can arise in derived parameters when the Langmuir isotherm is inappropriately applied to characterize a protein adsorption process. © 2014 Wiley Periodicals, Inc.

Sedative and cardiorespiratory effects of detomidine constant rate infusion in sheep.

PubMed

de Moura, Rauane Sousa; Bittar, Isabela Plazza; da Silva, Luiz Henrique; Villela, Ana Carolina Vasquez; Dos Santos Júnior, Marcelo Borges; Borges, Naida Cristina; Franco, Leandro Guimarães

2018-02-01

The use of sheep in experiments is widespread and is increasing worldwide, and so is the need to develop species-specific anaesthetic techniques to ensure animal safety. Previous studies have mentioned several protocols involving the administration of alpha-2 adrenergic agonists in sheep; however, assessment of the efficacy and safety of these infusion techniques is still relatively new. Thus, the aim of the present study is to assess the effectiveness of detomidine constant rate infusion (CRI) in sheep by measuring the cardiovascular and respiratory parameters, blood gas variables and sedation scores. Eight adult female Santa Inês sheep received 20 µg/kg of detomidine hydrochloride intravenously as a bolus loading dose, followed by an infusion rate of 60 µg/kg/h. The heart rates and respiratory rates changed continuously during the CRI period. No arrhythmias were observed. The reduction in arterial partial pressure of oxygen (PaO 2 ) was not significant, but one animal showed signs of hypoxaemia (minimum PaO 2 of 66.9 mmHg). The arterial partial pressure of carbon dioxide (PaCO 2 ) increased, but the animals did not become hypercapnic. The bicarbonate (HCO 3- ), pH and base excess (BE) tended towards metabolic alkalosis. The cardiac output (CO), stroke volume (SV), cardiac index (CI) and ejection fraction (EF%) showed no significant changes. The fractional shortening (FS%) decreased slightly, starting at T 45min . Sedation scores varied between 3 (0/10) after sedation and during recovery and 7 (0/10) during CRI. We concluded that administering detomidine at an infusion rate of 60 µg/kg/h in Santa Inês sheep is a simple technique that produces satisfactory sedation for minimally invasive procedures.

Removal Rate of Organic Matter Using Natural Cellulose via Adsorption Isotherm and Kinetic Studies.

PubMed

Din, Mohd Fadhil Md; Ponraj, Mohanadoss; Low, Wen-Pei; Fulazzaky, Mohamad Ali; Iwao, Kenzo; Songip, Ahmad Rahman; Chelliapan, Shreeshivadasan; Ismail, Zulhilmi; Jamal, Mohamad Hidayat

2016-02-01

In this study, the removal of natural organic matter (NOM) using coconut fiber (CF) and palm oil fiber (POF) was investigated. Preliminary analysis was performed using a jar test for the selection of optimal medium before the fabricated column model experiment. The equilibrium studies on isotherms and kinetic models for NOM adsorption were analyzed using linearized correlation coefficient. Results showed that the equilibrium data were fitted to Langmuir isotherm model for both CF and POF. The most suitable adsorption model was the pseudo-first-order kinetic model for POF and pseudo-second-order kinetic model for CF. The adsorption capacities achieved by the CF and POF were 15.67 and 30.8 mg/g respectively. Based on this investigation, it can be concluded that the POF is the most suitable material for the removal of NOM in semi polluted river water.

The Influence of Uncompensated Solution Resistance on the Determination and Standard Electrochemical Rate Constants Using Cyclic Voltammetry, and Some Comparisons with AC Voltammetry.

DTIC Science & Technology

1987-09-25

rate constants, k2r using cyclic voltametry . The res tss are expressed in terms of systematic deviations oP sapparent measured" rate constants, k~b(app...concentration was taken to be lum unless otherwise noted. The voltammetric sweep rate was set at 20 V sŕ unless specified otherwise. The general procedure...peaks for the negative- and positive-going potential sweeps have opposite signs, the measured cathodic-anodic peak separation, AEp, will clearly be

The elimination of siloxanes from the biogas of a wastewater treatment plant by means of an adsorption process.

PubMed

Trapote, Arturo; García, Mariano; Prats, Daniel

2016-12-01

Siloxanes present in the biogas produced during anaerobic digestion in wastewater treatment plants (WWTPs) can damage the mechanism of cogeneration heat engines and obstruct the process of energy valorization. The objective of this research is to detect the presence of siloxanes in the biogas and evaluate a procedure for their elimination. A breakthrough curve of a synthetic decamethylcyclopentasiloxane on an experimental bed of activated carbon was modeled and the theoretical mathematical model of the adsorption process was adjusted. As a result, the constants of the model were obtained: the mass transfer constant, Henry's equilibrium constant, and the Eddy diffusion. The procedure developed allows the adsorption equilibrium of siloxanes on activated carbon to be predicted, and makes it possible to lay the basis for the design of an appropriate activated carbon module for the elimination of siloxanes in a WWTP.

Kinetic and mechanism studies of the adsorption of lead onto waste cow bone powder (WCBP) surfaces.

PubMed

Cha, Jihoon; Cui, Mingcan; Jang, Min; Cho, Sang-Hyun; Moon, Deok Hyun; Khim, Jeehyeong

2011-01-01

This study examines the adsorption isotherms, kinetics and mechanisms of Pb²(+) sorption onto waste cow bone powder (WCBP) surfaces. The concentrations of Pb²(+) in the study range from 10 to 90 mg/L. Although the sorption data follow the Langmuir and Freundlich isotherm, a detailed examination reveals that surface sorption or complexation and co-precipitation are the most important mechanisms, along with possibly ion exchange and solid diffusion also contributing to the overall sorption process. The co-precipitation of Pb²(+) with the calcium hydroxyapatite (Ca-HAP) is implied by significant changes in Ca²(+) and PO₄³⁻ concentrations during the metal sorption processes. The Pb²(+) sorption onto the WCBP surface by metal complexation with surface functional groups such as ≡ POH. The major metal surface species are likely to be ≡ POPb(+). The sorption isotherm results indicated that Pb²(+) sorption onto the Langmuir and Freundlich constant q(max) and K( F ) is 9.52 and 8.18 mg g⁻¹, respectively. Sorption kinetics results indicated that Pb²(+) sorption onto WCBP was pseudo-second-order rate constants K₂ was 1.12 g mg⁻¹ h⁻¹. The main mechanism is adsorption or surface complexation (≡POPb(+): 61.6%), co-precipitation or ion exchange [Ca₃(.)₉₃ Pb₁(.)₀₇ (PO₄)₃ (OH): 21.4%] and other precipitation [Pb 50 mg L⁻¹ and natural pH: 17%). Sorption isotherms showed that WCBP has a much higher Pb²(+) removal rate in an aqueous solution; the greater capability of WCBP to remove aqueous Pb²(+) indicates its potential as another promising way to remediate Pb²(+)-contaminated media.

Reduction of Iron-Oxide-Carbon Composites: Part I. Estimation of the Rate Constants

NASA Astrophysics Data System (ADS)

Halder, S.; Fruehan, R. J.

2008-12-01

A new ironmaking concept using iron-oxide-carbon composite pellets has been proposed, which involves the combination of a rotary hearth furnace (RHF) and an iron bath smelter. This part of the research focuses on studying the two primary chemical kinetic steps. Efforts have been made to experimentally measure the kinetics of the carbon gasification by CO2 and wüstite reduction by CO by isolating them from the influence of heat- and mass-transport steps. A combined reaction model was used to interpret the experimental data and determine the rate constants. Results showed that the reduction is likely to be influenced by the chemical kinetics of both carbon oxidation and wüstite reduction at the temperatures of interest. Devolatilized wood-charcoal was observed to be a far more reactive form of carbon in comparison to coal-char. Sintering of the iron-oxide at the high temperatures of interest was found to exert a considerable influence on the reactivity of wüstite by virtue of altering the internal pore surface area available for the reaction. Sintering was found to be predominant for highly porous oxides and less of an influence on the denser ores. It was found using an indirect measurement technique that the rate constants for wüstite reduction were higher for the porous iron-oxide than dense hematite ore at higher temperatures (>1423 K). Such an indirect mode of measurement was used to minimize the influence of sintering of the porous oxide at these temperatures.

Determination of Chemical Kinetic Rate Constants of a Model for Carbothermal Processing of Lunar Regolith Simulant Using Methane

NASA Technical Reports Server (NTRS)

Balasubramaniam, R; Gokoglu, S.; Hegde, U.

2009-01-01

We have previously developed a chemical conversion model of the carbothermal processing of lunar regolith using methane to predict the rate of production of carbon monoxide. In this carbothermal process, gaseous methane is pyrolyzed as it flows over the hot surface of a molten zone of lunar regolith and is converted to carbon and hydrogen. Hydrogen is carried away by the exiting stream of gases and carbon is deposited on the melt surface. The deposited carbon mixes with the melt and reacts with the metal oxides in it to produce carbon monoxide that bubbles out of the melt. In our model, we assume that the flux of carbon deposited is equal to the product of the surface reaction rate constant gamma and the concentration of methane adjacent to the melt surface. Similarly, the rate of consumption of carbon per unit volume in the melt is equal to the product of the melt reaction rate constant k and the concentrations of carbon and metal oxide in the melt. In this paper, we describe our effort to determine gamma and k by comparison of the predictions from our model with test data obtained by ORBITEC (Orbital Technologies Corporation). The concentration of methane adjacent to the melt surface is a necessary input to the model. It is inferred from the test data by a mass balance of methane, adopting the usual assumptions of the continuously-stirred-tank-reactor model, whereby the average concentration of a given gaseous species equals its exit concentration. The reaction rates gamma and k have been determined by a non-linear least-squares fit to the test data for the production of carbon monoxide and the fraction of the incoming methane that is converted. The comparison of test data with our model predictions using the determined chemical kinetic rate constants provides a consistent interpretation of the process over the full range of temperatures, pressures, and methane flow rates used in the tests, thereby increasing our confidence to use the model for scale-up purposes.

Creatine kinase rate constant in the human heart measured with 3D‐localization at 7 tesla

PubMed Central

Robson, Matthew D.; Neubauer, Stefan; Rodgers, Christopher T.

2016-01-01

Purpose We present a new Bloch‐Siegert four Angle Saturation Transfer (BOAST) method for measuring the creatine kinase (CK) first‐order effective rate constant kf in human myocardium at 7 tesla (T). BOAST combines a variant of the four‐angle saturation transfer (FAST) method using amplitude‐modulated radiofrequency pulses, phosphorus Bloch‐Siegert B1+‐mapping to determine the per‐voxel flip angles, and nonlinear fitting to Bloch simulations for postprocessing. Methods Optimal flip angles and repetition time parameters were determined from Monte Carlo simulations. BOAST was validated in the calf muscle of two volunteers at 3T and 7T. The myocardial CK forward rate constant was then measured in 10 volunteers at 7T in 82 min (after 1H localization). Results BOAST kfCK values were 0.281 ± 0.002 s−1 in the calf and 0.35 ± 0.05 s−1 in myocardium. These are consistent with literature values from lower fields. Using a literature values for adenosine triphosphate concentration, we computed CK flux values of 4.55 ± 1.52 mmol kg−1 s−1. The sensitive volume for BOAST depends on the B1 inhomogeneity of the transmit coil. Conclusion BOAST enables measurement of the CK rate constant in the human heart at 7T, with spatial localization in three dimensions to 5.6 mL voxels, using a 10‐cm loop coil. Magn Reson Med 78:20–32, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. PMID:27579566

Adsorption interaction in the molecular hydrogen-aluminophosphate AlPO-5 zeolite system

NASA Astrophysics Data System (ADS)

Grenev, I. V.; Gavrilov, V. Yu.

2015-03-01

The adsorption interaction between molecular hydrogen and atoms forming the lattice of AlPO-5 zeolite is studied. The potential of intramolecular interaction is calculated by summing the potentials of individual pairwise H2-O(Al, P) interactions in a fragment of the zeolite structure with a volume of ˜32 nm3. Isopotential surfaces are constructed that allow determination of the shape of zeolite microchannels and the places of the preferential localization of sorbate molecules in the porous space. The calculated and experimental values of the Henry constant of H2 adsorption on AlPO-5 at 77 K are compared.

Rate Constants and Activation Energies for Gas‐Phase Reactions of Three Cyclic Volatile Methyl Siloxanes with the Hydroxyl Radical

PubMed Central

Safron, Andreas; Strandell, Michael; Kierkegaard, Amelie

2015-01-01

ABSTRACT Reaction with hydroxyl radicals (OH) is the major pathway for removal of cyclic volatile methyl siloxanes (cVMS) from air. We present new measurements of second‐order rate constants for reactions of the cVMS octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) with OH determined at temperatures between 313 and 353 K. Our measurements were made using the method of relative rates with cyclohexane as a reference substance and were conducted in a 140‐mL gas‐phase reaction chamber with online mass spectrometry analysis. When extrapolated to 298 K, our measured reaction rate constants of D4 and D5 with the OH radical are 1.9 × 10−12 (95% confidence interval (CI): (1.7–2.2) × 10−12) and 2.6 × 10−12 (CI: (2.3–2.9) × 10−12) cm3 molecule−1 s−1, respectively, which are 1.9× and 1.7× faster than previous measurements. Our measured rate constant for D6 is 2.8 × 10−12 (CI: (2.5–3.2) × 10−12) cm3 molecule−1 s−1 and to our knowledge there are no comparable laboratory measurements in the literature. Reaction rates for D5 were 33% higher than for D4 (CI: 30–37%), whereas the rates for D6 were only 8% higher than for D5 (CI: 5–10%). The activation energies of the reactions of D4, D5, and D6 with OH were not statistically different and had a value of 4300 ± 2800 J/mol. PMID:27708500

A Thermodynamic Description of the Adsorption of Simple Water-Soluble Peptoids to Silica.

PubMed

Calkins, Anna L; Yin, Jennifer; Rangel, Jacenda L; Landry, Madeleine R; Fuller, Amelia A; Stokes, Grace Y

2016-11-08

The first report of a water-soluble peptoid adsorbed to silica monitored by second harmonic generation (SHG) at the liquid/solid interface is presented here. The molecular insights gained from these studies will inform the design and preparation of novel peptoid coatings. Simple 6- and 15-residue peptoids were dissolved in phosphate buffered saline and adsorbed to bare silica surfaces. Equilibrium binding constants and relative surface concentrations of adsorbed peptoids were determined from fits to the Langmuir model. Complementary fluorescence spectroscopy studies were used to quantify the maximum surface excess. Binding constants, determined here by SHG, were comparable to those previously reported for cationic proteins and small molecules. Enthalpies and free energies of adsorption were determined to elucidate thermodynamic driving forces. Circular dichroism spectra confirm that minimal conformational changes occur when peptoids are adsorbed to silica while pH studies indicate that electrostatic interactions impact adsorption.

Rate constant for the reaction of OH with CH3CCl2F (HCFC-141b) determined by relative rate measurements with CH4 and CH3CCl3

NASA Technical Reports Server (NTRS)

Huder, Karin; Demore, William B.

1993-01-01

Determination of accurate rate constants for OH abstraction is of great importance for the calculation of lifetimes for HCFCs and their impact on the atmosphere. For HCFC-141b there has been some disagreement in the literature for absolute measurements of this rate constant. In the present work rate constant ratios for HCFC-141b were measured at atmospheric pressure in the temperature range of 298-358 K, with CH4 and CH3CCl3 as reference gases. Ozone was photolyzed at 254 nm in the presence of water vapor to produce OH radicals. Relative depletions of 141b and the reference gases were measured by FTIR. Arrhenius expressions for 141b were derived from each reference gas and found to be in good agreement with each other. The combined expression for HCFC-141b which we recommend is 1.4 x 10 exp -12 exp(-1630/T) with k at 298 K being 5.9 x 10 exp -15 cu cm/molec-s. This value is in excellent agreement with the JPL 92-20 recommendation.

Determination of the strong coupling constant from jet rates in deep inelastic scattering

NASA Astrophysics Data System (ADS)

Ahmed, T.; Aid, S.; Andreev, V.; Andrieu, B.; Appuhn, R.-D.; Arpagaus, M.; Babaev, A.; Baehr, J.; Bán, J.; Baranov, P.; Barrelet, E.; Bartel, W.; Barth, M.; Bassler, U.; Beck, H. P.; Behrend, H.-J.; Belousov, A.; Berger, Ch.; Bergstein, H.; Bernardi, G.; Bernet, R.; Bertrand-Coremans, G.; Besançon, M.; Beyer, R.; Biddulph, P.; Bizot, J. C.; Blobel, V.; Borras, K.; Botterweck, F.; Boudry, V.; Braemer, A.; Brasse, F.; Braunschweig, W.; Brisson, V.; Bruncko, D.; Brune, C.; Buchholz, R.; Büngener, L.; Bürger, J.; Büsser, F. W.; Buniatian, A.; Burke, S.; Buschhorn, G.; Campbell, A. J.; Carli, T.; Charles, F.; Clarke, D.; Clegg, A. B.; Clerbaux, B.; Colombo, M.; Contreras, J. G.; Cormack, C.; Coughlan, J. A.; Courau, A.; Coutures, Ch.; Cozzika, G.; Criegee, L.; Cussans, D. G.; Cvach, J.; Dagoret, S.; Dainton, J. B.; Danilov, M.; Dau, W. D.; Daum, K.; David, M.; Deffur, E.; Delcourt, B.; Del Buono, L.; De Roeck, A.; De Wolf, E. A.; Di Nezza, P.; Dollfus, C.; Dowell, J. D.; Dreis, H. B.; Droutskoi, A.; Duboc, J.; Düllmann, D.; Dünger, O.; Duhm, H.; Ebert, J.; Ebert, T. R.; Eckerlin, G.; Efremenko, V.; Egli, S.; Ehrlichmann, H.; Eichenberger, S.; Eichler, R.; Eisele, F.; Eisenhandler, E.; Ellison, R. J.; Elsen, E.; Erdmann, M.; Erdmann, W.; Evrard, E.; Favart, L.; Fedotov, A.; Feeken, D.; Felst, R.; Feltesse, J.; Ferencei, J.; Ferrarotto, F.; Flamm, K.; Fleischer, M.; Flieser, M.; Flügge, G.; Fomenko, A.; Fominykh, B.; Forbush, M.; Formánek, J.; Foster, J. M.; Franke, G.; Fretwurst, E.; Gabathuler, E.; Gabathuler, K.; Gamerdinger, K.; Garvey, J.; Gayler, J.; Gebauer, M.; Gellrich, A.; Genzel, H.; Gerhards, R.; Goerlach, U.; Goerlich, L.; Gogitidze, N.; Goldberg, M.; Goldner, D.; Gonzalez-Pineiro, B.; Gorelov, I.; Goritchev, P.; Grab, C.; Grässler, H.; Grässler, R.; Greenshaw, T.; Grindhammer, G.; Gruber, A.; Gruber, C.; Haack, J.; Haidt, D.; Hajduk, L.; Hamon, O.; Hampel, M.; Hanlon, E. M.; Hapke, M.; Haynes, W. J.; Heatherington, J.; Heinzelmann, G.; Henderson, R. C. W.; Henschel, H.; Herma, R.; Herynek, I.; Hess, M. F.; Hildesheim, W.; Hill, P.; Hill, K. H.; Hilton, C. D.; Hladký, J.; Hoeger, K. C.; Höppner, M.; Horisberger, R.; Huet, Ph.; Hufnagel, H.; Ibbotson, M.; Itterbeck, H.; Jabiol, M.-A.; Jacholkowska, A.; Jacobsson, C.; Jaffre, M.; Janoth, J.; Jansen, T.; Jönsson, L.; Johannsen, K.; Johnson, D. P.; Johnson, L.; Jung, H.; Kalmus, P. I. P.; Kant, D.; Kaschowitz, R.; Kasselmann, P.; Kathage, U.; Kaufmann, H. H.; Kazarian, S.; Kenyon, I. R.; Kermiche, S.; Keuler, C.; Kiesling, C.; Klein, M.; Kleinwort, C.; Knies, G.; Ko, W.; Köhler, T.; Köhne, J. H.; Kolanoski, H.; Kole, F.; Kolya, S. D.; Korbel, V.; Korn, M.; Kostka, P.; Kotelnikov, S. K.; Krämerkämper, T.; Krasny, M. W.; Krehbiel, H.; Krücker, D.; Krüger, U.; Krüner-Marquis, U.; Kubenka, J. P.; Küster, H.; Kuhlen, M.; Kurča, T.; Kurzhöfer, J.; Kuznik, B.; Lacour, D.; Lamarche, F.; Lander, R.; Landon, M. P. J.; Lange, W.; Lanius, P.; Laporte, J.-F.; Lebedev, A.; Leverenz, C.; Levonian, S.; Ley, Ch.; Lindner, A.; Lindström, G.; Linsel, F.; Lipinski, J.; List, B.; Loch, P.; Lohmander, H.; Lopez, G. C.; Lubimov, V.; Lüke, D.; Magnussen, N.; Malinovski, E.; Mani, S.; Maraček, R.; Marage, P.; Marks, J.; Marshall, R.; Martens, J.; Martin, R.; Martyn, H.-U.; Martyniak, J.; Masson, S.; Mavroidis, T.; Maxfield, S. J.; McMahon, S. J.; Mehta, A.; Meier, K.; Mercer, D.; Merz, T.; Meyer, C. A.; Meyer, H.; Meyer, J.; Mikocki, S.; Milstead, D.; Moreau, F.; Morris, J. V.; Müller, G.; Müller, K.; Murín, P.; Nagovizin, V.; Nahnhauer, R.; Naroska, B.; Naumann, Th.; Newman, P. R.; Newton, D.; Neyret, D.; Nguyen, H. K.; Niebergall, F.; Niebuhr, C.; Nisius, R.; Nowak, G.; Noyes, G. W.; Nyberg-Werther, M.; Oakden, M.; Oberlack, H.; Obrock, U.; Olsson, J. E.; Panaro, E.; Panitch, A.; Pascaud, C.; Patel, G. D.; Peppel, E.; Perez, E.; Phillips, J. P.; Pichler, Ch.; Pitzl, D.; Pope, G.; Prell, S.; Prosi, R.; Rädel, G.; Raupach, F.; Reimer, P.; Reinshagen, S.; Ribarics, P.; Rick, H.; Riech, V.; Riedlberger, J.; Riess, S.; Rietz, M.; Robertson, S. M.; Robmann, P.; Roloff, H. E.; Roosen, R.; Rosenbauer, K.; Rostovtsev, A.; Rouse, F.; Royon, C.; Rüter, K.; Rusakov, S.; Rybicki, K.; Rylko, R.; Sahlmann, N.; Sanchez, E.; Sankey, D. P. C.; Savitsky, M.; Schacht, P.; Schiek, S.; Schleper, P.; von Schlippe, W.; Schmidt, C.; Schmidt, D.; Schmidt, G.; Schöning, A.; Schröder, V.; Schuhmann, E.; Schwab, B.; Schwind, A.; Seehausen, U.; Sefkow, F.; Seidel, M.; Sell, R.; Semenov, A.; Shekelyan, V.; Sheviakov, I.; Shooshtari, H.; Shtarkov, L. N.; Siegmon, G.; Siewert, U.; Sirois, Y.; Skillicorn, I. O.; Smirnov, P.; Smith, J. R.; Soloviev, Y.; Spitzer, H.; Starosta, R.; Steenbock, M.; Steffen, P.; Steinberg, R.; Stella, B.; Stephens, K.; Stier, J.; Stiewe, J.; Stösslein, U.; Strachota, J.; Straumann, U.; Struczinski, W.; Sutton, J. P.; Tapprogge, S.; Taylor, R. E.; Tchernyshov, V.; Thiebaux, C.; Thompson, G.; Truöl, P.; Turnau, J.; Tutas, J.; Uelkes, P.; Usik, A.; Valkár, S.; Valkárová, A.; Vallée, C.; Van Esch, P.; Van Mechelen, P.; Vartapetian, A.; Vazdik, Y.; Vecko, M.; Verrecchia, P.; Villet, G.; Wacker, K.; Wagener, A.; Wagener, M.; Walker, I. W.; Walther, A.; Weber, G.; Weber, M.; Wegener, D.; Wegner, A.; Wellisch, H. P.; West, L. R.; Willard, S.; Winde, M.; Winter, G.-G.; Wright, A. E.; Wünsch, E.; Wulff, N.; Yiou, T. P.; Žáček, J.; Zarbock, D.; Zhang, Z.; Zhokin, A.; Zimmer, M.; Zimmermann, W.; Zomer, F.; Zuber, K.; H1 Collaboration

1995-02-01

Jet rates in deep inelastic electron proton scattering are studied with the H1 detector at HERA for momentum transfers squared between 10 and 4000 GeV 2. It is shown that they can be quantitatively described by perturbative QCD in next to leading order making use of the parton densities of the proton and with the strong coupling constant αs as a free parameter. The measured value, αs( MZ2) = 0.123 ± 0.018, is in agreement both with determinations from e+e- annihilation at LEP using the same observable and with the world average.

Rate constant for the reaction NH2 + NO from 216 to 480 K

NASA Technical Reports Server (NTRS)

Stief, L. J.; Brobst, W. D.; Nava, D. F.; Borkowski, R. P.; Michael, J. V.

1982-01-01

The absolute rate constant was measured by the technique of flash photolysis-laser induced fluorescence (FP-LIF). NH2 radicals were produced by the flash photolysis of ammonia and the fluorescent NH2 photons were measured by multiscaling techniques. At each temperature, the results were independent of variations in total pressure, and flash intensity. The results are compared with previous determinations using the techniques of mass spectrometry, absorption spectroscopy, laser absorption spectroscopy, and laser induced fluorescence. The implications of the results are discussed with regard to combustion, post combustion, and atmospheric chemistry. The results are also discussed theoretically.

Adsorption of BTEX, MTBE and TAME on natural and modified diatomite.

PubMed

Aivalioti, Maria; Papoulias, Panagiotis; Kousaiti, Athanasia; Gidarakos, Evangelos

2012-03-15

The removal of BTEX (benzene, toluene, ethyl-benzene and m-,p-,o-xylenes), MTBE (methyl tertiary butyl ether) and TAME (tertiary amyl methyl ether) from aqueous solutions by raw, thermally, chemically and both chemically and thermally treated diatomite was studied, through batch adsorption experiments. In total, 14 different diatomite samples were created and tested. Selected physical characteristics of the adsorbents, such as specific surface area and pore volume distribution, were determined. Matrix and competitive adsorption effects were also explored. It was proved that the diatomite samples were effective in removing BTEX, MTBE and TAME from aqueous solutions, with the sample treated with HCl being the most effective, as far as its adsorption capacity and equilibrium time are concerned. Among the contaminants, BTEX appeared to have the strongest affinity, based on mass uptake by the diatomite samples. Matrix effects were proved to be strong, significantly decreasing the adsorption of the contaminants onto diatomite. The kinetics data proved a closer fit to the pseudo second order model, while the isotherm experimental data were a better fit to the Freundlich model. However, the latter produced values of the isotherm constant 1/n greater than one, indicating unfavorable adsorption. Copyright © 2011 Elsevier B.V. All rights reserved.

Irrigation model of bleached Kraft mill wastewater through volcanic soil as a pollutants attenuation process.

PubMed

Navia, R; Inostroza, X; Diez, M C; Lorber, K E

2006-05-01

An irrigation process through volcanic soil columns was evaluated for bleached Kraft mill effluent pollutants retention. The system was designed to remove color and phenolic compounds and a simple kinetic model for determining the global mass transfer coefficient and the adsorption rate constant was used. The results clearly indicate that the global mass transfer coefficient values (K(c)a) and the adsorption rate constants are higher for the irrigation processes onto acidified soil. This means that the pretreatment of washing the volcanic soil with an acid solution has a positive effect on the adsorption rate for both pollutant groups. The enhanced adsorption capacity is partially explained by the activation of the metal oxides present in the soil matrix during the acid washing process. Increasing the flow rate from 1.5 to 2.5 ml/min yielded higher (K(c)a) values and adsorption rate constants for both pollutant groups. For instance, regarding color adsorption onto acidified soil, there is an increment of 43% in the (K(c)a) value for the experiment with a flow rate of 2.5 ml/min. Increasing the porosity of the column from 0.55 to 0.59, yielded a decrease in the (K(c)a) values for color and phenolic compounds adsorption processes. Onto natural soil for example, these decreases reached 21% and 24%, respectively. Therefore, the (K(c)a) value is dependent on both the liquid-phase velocity (external resistance) and the soil fraction in the column (internal resistance); making forced convection and diffusion to be the main transport mechanisms involved in the adsorption process. Analyzing the adsorption rate constants (K(c)a)/m, phenolic compounds and color adsorption rates onto acidified soil of 2.25 x 10(-6) and 2.62 x 10(-6) l/mg min were achieved for experiment 1. These adsorption rates are comparable with other adsorption systems and adsorbent materials.

[Application of classical isothermal adsorption models in heavy metal ions/ diatomite system and related problems].

PubMed

Zhu, Jian; Wu, Qing-Ding; Wang, Ping; Li, Ke-Lin; Lei, Ming-Jing; Zhang, Wei-Li

2013-11-01

In order to fully understand adsorption nature of Cu2+, Zn2+, Pb2+, Cd2+, Mn2+, Fe3+ onto natural diatomite, and to find problems of classical isothermal adsorption models' application in liquid/solid system, a series of isothermal adsorption tests were conducted. As results indicate, the most suitable isotherm models for describing adsorption of Pb2+, Cd2+, Cu2+, Zn2+, Mn2+, Fe3+ onto natural diatomite are Tenkin, Tenkin, Langmuir, Tenkin, Freundlich and Freundlich, respectively, the adsorption of each ion onto natural diatomite is mainly a physical process, and the adsorption reaction is favorable. It also can be found that, when using classical isothermal adsorption models to fit the experimental data in liquid/solid system, the equilibrium adsorption amount q(e) is not a single function of ion equilibrium concentration c(e), while is a function of two variables, namely c(e) and the adsorbent concentration W0, q(e) only depends on c(e)/W(0). Results also show that the classical isothermal adsorption models have a significant adsorbent effect, and their parameter values are unstable, the simulation values of parameter differ greatly from the measured values, which is unhelpful for practical use. The tests prove that four-adsorption-components model can be used for describing adsorption behavior of single ion in nature diatomite-liquid system, its parameters k and q(m) have constant values, which is favorable for practical quantitative calculation in a given system.

The influence of adsorbent microstructure upon adsorption equilibria: Investigations of a model system