Determination of adsorption and desorption of DNA molecules on freshwater and marine sediments.

PubMed

Xue, J; Feng, Y

2018-06-01

Free DNA and its adsorption by sediment in the aquatic environment lead to ambiguity in the identification of recent faecal pollution sources. The goal of this study was to understand the mechanisms of DNA adsorption and desorption on aquatic sediment under various conditions using quantitative polymerase chain reaction (qPCR). Both raw sewage (RS) DNA and purified PCR product (PPP) were used in adsorption and desorption experiments; autoclaved freshwater and marine sediments served as sorbents. Thirty-six hours were needed for adsorption to reach equilibrium. More DNA was adsorbed on both sediments in stream water than in 5 mmol l -1 NaCl and DNA adsorption increased in the presence of Ca 2+ and Mg 2+ . Successive desorption experiments showed that between 5% and 22% of adsorbed DNA was desorbed. Organic matter and clay played a significant role in determining the DNA adsorption capacity on sediment. The data suggest the presence of multilayer adsorption. DNA molecules on sediments were mostly adsorbed through ligand binding rather than electrostatic binding. Quantitative polymerase chain reaction assays provide a better way to investigate the DNA adsorption and desorption mechanisms by sediment. DNA desorption can potentially complicate the outcomes of microbial source tracking studies. © 2018 The Society for Applied Microbiology.

Wide-range and accurate modeling of linear alkylbenzene sulfonate (LAS) adsorption/desorption on agricultural soil.

PubMed

Oliver-Rodríguez, B; Zafra-Gómez, A; Reis, M S; Duarte, B P M; Verge, C; de Ferrer, J A; Pérez-Pascual, M; Vílchez, J L

2015-11-01

In this paper, rigorous data and adequate models about linear alkylbenzene sulfonate (LAS) adsorption/desorption on agricultural soil are presented, contributing with a substantial improvement over available adsorption works. The kinetics of the adsorption/desorption phenomenon and the adsorption/desorption equilibrium isotherms were determined through batch studies for total LAS amount and also for each homologue series: C10, C11, C12 and C13. The proposed multiple pseudo-first order kinetic model provides the best fit to the kinetic data, indicating the presence of two adsorption/desorption processes in the general phenomenon. Equilibrium adsorption and desorption data have been properly fitted by a model consisting of a Langmuir plus quadratic term, which provides a good integrated description of the experimental data over a wide range of concentrations. At low concentrations, the Langmuir term explains the adsorption of LAS on soil sites which are highly selective of the n-alkyl groups and cover a very small fraction of the soil surface area, whereas the quadratic term describes adsorption on the much larger part of the soil surface and on LAS retained at moderate to high concentrations. Since adsorption/desorption phenomenon plays a major role in the LAS behavior in soils, relevant conclusions can be drawn from the obtained results. Copyright © 2015 Elsevier Ltd. All rights reserved.

CO2 adsorption-assisted CH4 desorption on carbon models of coal surface: A DFT study

NASA Astrophysics Data System (ADS)

Xu, He; Chu, Wei; Huang, Xia; Sun, Wenjing; Jiang, Chengfa; Liu, Zhongqing

2016-07-01

Injection of CO2 into coal is known to improve the yields of coal-bed methane gas. However, the technology of CO2 injection-enhanced coal-bed methane (CO2-ECBM) recovery is still in its infancy with an unclear mechanism. Density functional theory (DFT) calculations were performed to elucidate the mechanism of CO2 adsorption-assisted CH4 desorption (AAD). To simulate coal surfaces, different six-ring aromatic clusters (2 × 2, 3 × 3, 4 × 4, 5 × 5, 6 × 6, and 7 × 7) were used as simplified graphene (Gr) carbon models. The adsorption and desorption of CH4 and/or CO2 on these carbon models were assessed. The results showed that a six-ring aromatic cluster model (4 × 4) can simulate the coal surface with limited approximation. The adsorption of CO2 onto these carbon models was more stable than that in the case of CH4. Further, the adsorption energies of single CH4 and CO2 in the more stable site were -15.58 and -18.16 kJ/mol, respectively. When two molecules (CO2 and CH4) interact with the surface, CO2 compels CH4 to adsorb onto the less stable site, with a resulting significant decrease in the adsorption energy of CH4 onto the surface of the carbon model with pre-adsorbed CO2. The Mulliken charges and electrostatic potentials of CH4 and CO2 adsorbed onto the surface of the carbon model were compared to determine their respective adsorption activities and changes. At the molecular level, our results showed that the adsorption of the injected CO2 promoted the desorption of CH4, the underlying mechanism of CO2-ECBM.

Competitive adsorption of heavy metal ions on carbon nanotubes and the desorption in simulated biofluids.

PubMed

Ma, Xin; Yang, Sheng-Tao; Tang, Huan; Liu, Yuanfang; Wang, Haifang

2015-06-15

Carbon nanotubes (CNTs) had meaningful adsorption capacities for Pb(2+), Cu(2+), Zn(2+) and Cd(2+), while Pb(2+) showed the highest adsorption in the competitive adsorption evaluations. The desorption behaviors of heavy metal ions were completely different in various biofluids, where the desorption was significantly influenced by pH and the presence of proteins/other cations. The desorption was most effective in simulated stomach juice, and much less effective in other simulated biofluids. More Pb(2+) stuck to CNTs than others, resulting in less desorption. Interestingly, the competitive desorption behaviors of four ions were largely changed comparing to the individual desorption behaviors. The implications to the biosafety evaluations and synergistic effects of CNT are discussed. Copyright © 2015 Elsevier Inc. All rights reserved.

Effects of wind-wave disturbances on adsorption and desorption of tetracycline and sulfadimidine in water-sediment systems.

PubMed

Liao, Qianjiahua; Huang, Zheng; Li, Shu; Wang, Yi; Liu, Yuqing; Luo, Ran; Shang, Jingge

2018-05-28

Wind-wave disturbances frequently disperse sediment particles into overlying water, which facilitates the adsorption and desorption of contaminants in aquatic ecosystems. Tetracycline (TC) and sulfadimidine (SM2) are common antibiotics that are frequently found in aquatic environments. This study utilized microcosms, comprising sediment and water from Lake Taihu, China, to examine the adsorption and desorption of TC and SM2 under different wind-wave disturbances in a shallow lake environment. The adsorption experiments were conducted with three different concentrations (1, 5, 10 mg/L) of TC and SM2 in the overlying water, and two different (background and strong) wind-wave conditions for 72 h. Subsequently, four microcosms were employed in a 12-h desorption study. Analysis of adsorption progress showed that TC concentration in the overlying water decreased quickly, while SM2 remained almost constant. In the desorption experiments, SM2 released to the overlying water was an order of magnitude greater than TC. These results indicate that sediment particles strongly adsorb TC but weakly adsorb SM2. Compared to background conditions, the strong wind-wave conditions resulted in higher concentrations of TC and SM2 in sediment and facilitated their migration to deeper sediment during adsorption, correspondingly promoting greater release of TC and SM2 from sediment particles into the overlying water during desorption.

Adsorption and Desorption Characteristics of Cd2+ and Pb2+ by Micro and Nano-sized Biogenic CaCO3

PubMed Central

Liu, Renlu; Guan, Yong; Chen, Liang; Lian, Bin

2018-01-01

The purpose of this study was to elucidate the characteristics and mechanisms of adsorption and desorption for heavy metals by micro and nano-sized biogenic CaCO3 induced by Bacillus subtilis, and the pH effect on adsorption was investigated. The results showed that the adsorption characteristics of Cd2+ and Pb2+ are well described by the Langmuir adsorption isothermal equation, and the maximum adsorption amounts for Cd2+ and Pb2+ were 94.340 and 416.667 mg/g, respectively. The maximum removal efficiencies were 97% for Cd2+, 100% for Pb2+, and the desorption rate was smaller than 3%. Further experiments revealed that the biogenic CaCO3 could maintain its high adsorption capability for heavy metals within wide pH ranges (3–8). The FTIR and XRD results showed that, after the biogenic CaCO3 adsorbed Cd2+ or Pb2+, it did not produce a new phase, which indicated that biogenic CaCO3 and heavy metal ions were governed by a physical adsorption process, and the high adsorptive capacity of biogenic CaCO3 for Cd2+ and Pb2+ were mainly attributed to its large total specific surface area. The findings could improve the state of knowledge about biogenic CaCO3 formation in the environment and its potential roles in the biogeochemical cycles of heavy metals. PMID:29434577

Kinetics of tetracycline, oxytetracycline, and chlortetracycline adsorption and desorption on two acid soils.

PubMed

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

2015-01-01

The purpose of this work was to quantify retention/release of tetracycline, oxytetracycline, and chlortetracycline on two soils, paying attention to sorption kinetics and to implications of the adsorption/desorption processes on transfer of these pollutants to the various environmental compartments. We used the stirred flow chamber (SFC) procedure to achieve this goal. All three antibiotics showed high affinity for both soils, with greater adsorption intensity for soil 1, the one with the highest organic matter and Al and Fe oxides contents. Desorption was always <15%, exhibiting strong hysteresis in the adsorption/desorption processes. Adsorption was adequately modeled using a pseudo first-order equation with just one type of adsorption sites, whereas desorption was better adjusted considering both fast and slow sorption sites. The adsorption maximum (qmax) followed the sequence tetracycline > oxytetracycline > chlortetracycline in soil 1, with similar values for the three antibiotics and the sequence tetracycline > chlortetracycline > oxytetracycline in soil 2. The desorption sequences were oxytetracycline > tetracycline > chlortetracycline in soil 1 and oxytetracycline > chlortetracycline > tetracycline in soil 2. In conclusion, the SFC technique has yielded new kinetic data regarding tetracycline, oxytetracycline, and chlortetracycline adsorption/desorption on soils, indicating that it can be used to shed further light on the retention and transport processes affecting antibiotics on soils and other media, thus increasing knowledge on the behavior and evolution of these pharmaceutical residues in the environment.

Adsorption and Desorption of Hydrogen by Gas-Phase Palladium Clusters Revealed by In Situ Thermal Desorption Spectroscopy.

PubMed

Takenouchi, Masato; Kudoh, Satoshi; Miyajima, Ken; Mafuné, Fumitaka

2015-07-02

Adsorption and desorption of hydrogen by gas-phase Pd clusters, Pdn(+), were investigated by thermal desorption spectroscopy (TDS) experiments and density functional theory (DFT) calculations. The desorption processes were examined by heating the clusters that had adsorbed hydrogen at room temperature. The clusters remaining after heating were monitored by mass spectrometry as a function of temperature up to 1000 K, and the temperature-programmed desorption (TPD) curve was obtained for each Pdn(+). It was found that hydrogen molecules were released from the clusters into the gas phase with increasing temperature until bare Pdn(+) was formed. The threshold energy for desorption, estimated from the TPD curve, was compared to the desorption energy calculated by using DFT, indicating that smaller Pdn(+) clusters (n ≤ 6) tended to have weakly adsorbed hydrogen molecules, whereas larger Pdn(+) clusters (n ≥ 7) had dissociatively adsorbed hydrogen atoms on the surface. Highly likely, the nonmetallic nature of the small Pd clusters prevents hydrogen molecule from adsorbing dissociatively on the surface.

N2 and CO Desorption Energies from Water Ice

NASA Astrophysics Data System (ADS)

Fayolle, Edith C.; Balfe, Jodi; Loomis, Ryan; Bergner, Jennifer; Graninger, Dawn; Rajappan, Mahesh; Öberg, Karin I.

2016-01-01

The relative desorption energies of CO and N2 are key to interpretations of observed interstellar CO and N2 abundance patterns, including the well-documented CO and N2H+ anti-correlations in disks, protostars, and molecular cloud cores. Based on laboratory experiments on pure CO and N2 ice desorption, the difference between CO and N2 desorption energies is small; the N2-to-CO desorption energy ratio is 0.93 ± 0.03. Interstellar ices are not pure, however, and in this study we explore the effect of water ice on the desorption energy ratio of the two molecules. We present temperature programmed desorption experiments of different coverages of 13CO and 15N2 on porous and compact amorphous water ices and, for reference, of pure ices. In all experiments, 15N2 desorption begins a few degrees before the onset of 13CO desorption. The 15N2 and 13CO energy barriers are 770 and 866 K for the pure ices, 1034-1143 K and 1155-1298 K for different submonolayer coverages on compact water ice, and 1435 and 1575 K for ˜1 ML of ice on top of porous water ice. For all equivalent experiments, the N2-to-CO desorption energy ratio is consistently 0.9. Whenever CO and N2 ice reside in similar ice environments (e.g., experience a similar degree of interaction with water ice) their desorption temperatures should thus be within a few degrees of one another. A smaller N2-to-CO desorption energy ratio may be present in interstellar and circumstellar environments if the average CO ice molecules interacts more with water ice compared to the average N2 molecules.

Pore size distribution calculation from 1H NMR signal and N2 adsorption-desorption techniques

NASA Astrophysics Data System (ADS)

Hassan, Jamal

2012-09-01

The pore size distribution (PSD) of nano-material MCM-41 is determined using two different approaches: N2 adsorption-desorption and 1H NMR signal of water confined in silica nano-pores of MCM-41. The first approach is based on the recently modified Kelvin equation [J.V. Rocha, D. Barrera, K. Sapag, Top. Catal. 54(2011) 121-134] which deals with the known underestimation in pore size distribution for the mesoporous materials such as MCM-41 by introducing a correction factor to the classical Kelvin equation. The second method employs the Gibbs-Thompson equation, using NMR, for melting point depression of liquid in confined geometries. The result shows that both approaches give similar pore size distribution to some extent, and also the NMR technique can be considered as an alternative direct method to obtain quantitative results especially for mesoporous materials. The pore diameter estimated for the nano-material used in this study was about 35 and 38 Å for the modified Kelvin and NMR methods respectively. A comparison between these methods and the classical Kelvin equation is also presented.

Dimethyl Methylphosphonate Adsorption Capacities and Desorption Energies on Ordered Mesoporous Carbons.

PubMed

Huynh, Kim; Holdren, Scott; Hu, Junkai; Wang, Luning; Zachariah, Michael R; Eichhorn, Bryan W

2017-11-22

In this study, we determine effective adsorption capacities and desorption energies for DMMP with highly ordered mesoporous carbons (OMCs), 1D cylindrical FDU-15, 3D hexagonal CMK-3, 3D bicontinuous CMK-8, and as a reference, microporous BPL carbon. After exposure to DMMP vapor at room temperature for approximately 70 and 800 h, the adsorption capacity of DMMP for each OMC was generally proportional to the total surface area and pore volume, respectively. Desorption energies of DMMP were determined using a model-free isoconversional method applied to thermogravimetric analysis (TGA) data. Our experiments determined that DMMP saturated carbon will desorb any weakly bound DMMP from pores >2.4 nm at room temperature, and no DMMP will adsorb into pores smaller than 0.5 nm. The calculated desorption energies for high surface coverages, 25% DMMP desorbed from pores ≤2.4 nm, are 68-74 kJ mol -1 , which is similar to the DMMP heat of vaporization (52 kJ mol -1 ). At lower surface coverages, 80% DMMP desorbed, the DMMP desorption energies from the OMCs are 95-103 kJ mol -1 . This is overall 20-30 kJ mol -1 higher in comparison to that of BPL carbon, due to the pore size and diffusion through different porous networks.

Study of Adsorption and Desorption Performances of Zr-Based Metal–Organic Frameworks Using Paper Spray Mass Spectrometry

PubMed Central

Wang, Xiaoting; Chen, Ying; Zheng, Yajun

2017-01-01

The dynamic pore systems and high surface areas of flexible metal–organic framework materials make them excellent candidates to be used in different kinds of adsorption processes. However, the adsorption and desorption behaviors of therapeutic drugs on metal–organic frameworks in solution are not fully developed. Here, we systematically investigated the adsorption and desorption behaviors of a typical therapeutic drug, verapamil, over several Zr-based metal–organic frameworks [e.g., Zr-FUM, UiO-66(Zr), UiO-66(Zr)-NH2 and UiO-66(Zr)-2COOH] as well as ZrO2 in an acetonitrile solution by using paper spray mass spectrometry. In contrast to other materials, UiO-66(Zr)-2COOH demonstrated a superior adsorption performance to verapamil due to their strong acid-base and/or hydrogen-bond interactions, and the adsorption process fitted well with the pseudo-second-order kinetic model. As verapamil-adsorbed materials were used for desorption experiments, ZrO2 demonstrated the most favorable desorption performance, whereas UiO-66(Zr)-2COOH yielded the poorest desorption capability. These Zr-based materials had also been coated at the surface with filter papers for the analysis of various drugs and proteins in the process of paper spray mass spectrometry. The results demonstrated that among the studied materials, ZrO2-coated paper gave the most favorable desorption performance as a pure drug solution, whereas the paper from UiO-66(Zr) demonstrated the optimal capability in the analyses of therapeutic drugs in a complex matrix (e.g., blood) and a protein (e.g., myoglobin). PMID:28773131

Bile salts at the air-water interface: adsorption and desorption.

PubMed

Maldonado-Valderrama, J; Muros-Cobos, J L; Holgado-Terriza, J A; Cabrerizo-Vílchez, M A

2014-08-01

Bile salts (BS) are bio-surfactants which constitute a vital component in the process of fat digestion. Despite the importance of the interfacial properties in their biological role, these have been scarcely studied in the literature. In this work, we present the adsorption-desorption profiles of two BS (NaTC and NaGDC) including dilatational rheology. Findings from this study reveal very different surface properties of NaTC and NaGDC which originate from different complexation properties relevant to the digestion process. Dynamic adsorption curves show higher adsorption rates for NaTC and suggest the existence of various conformational regimes in contrast to NaGDC which presents only one conformational regime. This is corroborated by analysis of the adsorption isotherms and more in detail by the rheological behaviour. Accordingly, the dilatational response at 1Hz displays two maxima of the dilatational modulus for NaTC as a function of bulk concentration, in contrast to NaGDC which displays only one maximum. The desorption profiles reveal that NaTC adopts an irreversibly adsorbed form at high surface coverage whereas NaGDC fully desorbs from the surface within the whole range of concentrations used. Analysis of the adsorption-desorption profiles provides new insight into the surface properties of BS, suggesting a surface complexation of NaTC. This knowledge can be useful since through interfacial engineering we might control the extent of lipolysis providing the basis for the rational design of food products with tailored digestibility. Copyright © 2014 Elsevier B.V. All rights reserved.

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.

Study of Adsorption and Desorption Performances of Zr-Based Metal-Organic Frameworks Using Paper Spray Mass Spectrometry.

PubMed

Wang, Xiaoting; Chen, Ying; Zheng, Yajun; Zhang, Zhiping

2017-07-08

The dynamic pore systems and high surface areas of flexible metal-organic framework materials make them excellent candidates to be used in different kinds of adsorption processes. However, the adsorption and desorption behaviors of therapeutic drugs on metal-organic frameworks in solution are not fully developed. Here, we systematically investigated the adsorption and desorption behaviors of a typical therapeutic drug, verapamil, over several Zr-based metal-organic frameworks [e.g., Zr-FUM, UiO-66(Zr), UiO-66(Zr)-NH₂ and UiO-66(Zr)-2COOH] as well as ZrO₂ in an acetonitrile solution by using paper spray mass spectrometry. In contrast to other materials, UiO-66(Zr)-2COOH demonstrated a superior adsorption performance to verapamil due to their strong acid-base and/or hydrogen-bond interactions, and the adsorption process fitted well with the pseudo-second-order kinetic model. As verapamil-adsorbed materials were used for desorption experiments, ZrO₂ demonstrated the most favorable desorption performance, whereas UiO-66(Zr)-2COOH yielded the poorest desorption capability. These Zr-based materials had also been coated at the surface with filter papers for the analysis of various drugs and proteins in the process of paper spray mass spectrometry. The results demonstrated that among the studied materials, ZrO₂-coated paper gave the most favorable desorption performance as a pure drug solution, whereas the paper from UiO-66(Zr) demonstrated the optimal capability in the analyses of therapeutic drugs in a complex matrix (e.g., blood) and a protein (e.g., myoglobin).

Adsorption-desorption kinetics of soft particles onto surfaces

NASA Astrophysics Data System (ADS)

Osberg, Brendan; Gerland, Ulrich

A broad range of physical, chemical, and biological systems feature processes in which particles randomly adsorb on a substrate. Theoretical models usually assume ``hard'' (mutually impenetrable) particles, but in soft matter physics the adsorbing particles can be effectively compressible, implying ``soft'' interaction potentials. We recently studied the kinetics of such soft particles adsorbing onto one-dimensional substrates, identifying three novel phenomena: (i) a gradual density increase, or ''cramming'', replaces the usual jamming behavior of hard particles, (ii) a density overshoot, can occur (only for soft particles) on a time scale set by the desorption rate, and (iii) relaxation rates of soft particles increase with particle size (on a lattice), while hard particles show the opposite trend. The latter occurs since unjamming requires desorption and many-bodied reorganization to equilibrate -a process that is generally very slow. Here we extend this analysis to a two-dimensional substrate, focusing on the question of whether the adsorption-desorption kinetics of particles in two dimensions is similarly enriched by the introduction of soft interactions. Application to experiments, for example the adsorption of fibrinogen on two-dimensional surfaces, will be discussed.

Adsorption-desorption behavior of atrazine on agricultural soils in China.

PubMed

Yue, Lin; Ge, ChengJun; Feng, Dan; Yu, Huamei; Deng, Hui; Fu, Bomin

2017-07-01

Adsorption and desorption are important processes that affect atrazine transport, transformation, and bioavailability in soils. In this study, the adsorption-desorption characteristics of atrazine in three soils (laterite, paddy soil and alluvial soil) were evaluated using the batch equilibrium method. The results showed that the kinetics of atrazine in soils was completed in two steps: a "fast" adsorption and a "slow" adsorption and could be well described by pseudo-second-order model. In addition, the adsorption equilibrium isotherms were nonlinear and were well fitted by Freundlich and Langmuir models. It was found that the adsorption data on laterite, and paddy soil were better fitted by the Freundlich model; as for alluvial soil, the Langmuir model described it better. The maximum atrazine sorption capacities ranked as follows: paddy soil>alluvial soil>laterite. Results of thermodynamic calculations indicated that atrazine adsorption on three tested soils was spontaneous and endothermic. The desorption data showed that negative hysteresis occurred. Furthermore, lower solution pH value was conducive to the adsorption of atrazine in soils. The atrazine adsorption in these three tested soils was controlled by physical adsorption, including partition and surface adsorption. At lower equilibrium concentration, the atrazine adsorption process in soils was dominated by surface adsorption; while with the increase of equilibrium concentration, partition was predominant. Copyright © 2016. Published by Elsevier B.V.

Tailoring pore properties of MCM-48 silica for selective adsorption of CO2.

PubMed

Kim, Sangil; Ida, Junichi; Guliants, Vadim V; Lin, Jerry Y S

2005-04-07

Four different types of amine-attached MCM-48 silicas were prepared and investigated for CO(2) separation from N(2). Monomeric and polymeric hindered and unhindered amines were attached to the pore surface of the MCM-48 silica and characterized with respect to their CO(2) sorption properties. The pore structures and amino group content in these modified silicas were investigated by XRD, FT-IR, TGA, N(2) adsorption/desorption at 77 K and CHN/Si analysis, which confirmed that in all cases the amino groups were attached to the pore surface of MCM-48 at 1.5-5.2 mmol/g. The N(2) adsorption/desorption analysis showed a considerable decrease of the pore volume and surface area for the MCM-48 silica containing a polymeric amine (e.g., polyethyleneimine). The CO(2) adsorption rates and capacities of the amine-attached MCM-48 samples were studied employing a sorption microbalance. The results obtained indicated that in addition to the concentration of surface-attached amino groups, specific interactions between CO(2) and the surface amino groups, and the resultant pore structure after amine group attachment have a significant impact on CO(2) adsorption properties of these promising adsorbent materials.

Adsorption and desorption characteristics of arsenic onto ceria nanoparticles

PubMed Central

2012-01-01

The rapid increase in the use of engineered nanoparticles [ENPs] has resulted in an increasing concern over the potential impacts of ENPs on the environmental and human health. ENPs tend to adsorb a large variety of toxic chemicals when they are emitted into the environment, which may enhance the toxicity of ENPs and/or adsorbed chemicals. The study was aimed to investigate the adsorption and desorption behaviors of arsenic on ceria NPs in aqueous solution using batch technique. Results show that the adsorption behavior of arsenic on ceria NPs was strongly dependent on pH and independent of ionic strength, indicating that the electrostatic effect on the adsorption of these elements was relatively not important compared to surface chemical reactions. The adsorption isotherms fitted very well to both the Langmuir and Freundlich models. The thermodynamic parameters (ΔH0, ΔS0, and ΔG0) for the adsorption of arsenic were determined at three different temperatures of 283, 303, and 323 K. The adsorption reaction was endothermic, and the process of adsorption was favored at high temperature. The desorption data showed that desorption hysteresis occurred at the initial concentration studied. High adsorption capacity of arsenic on ceria NPs suggests that the synergistic effects of ceria NPs and arsenic on the environmental systems may exist when they are released into the environment. PMID:22269298

Adsorption/Desorption Transition of Recombinant Human Neurotrophin 4: Physicochemical Characterization.

PubMed

Dąbkowska, Maria; Adamczak, Małgorzata; Barbasz, Jakub; Cieśla, Michał; Machaliński, Bogusław

2017-09-26

Bulk physicochemical properties of neurotrophin 4 (NT-4) in electrolyte solutions and its adsorption/desorption on/from mica surfaces have been studied using dynamic light scattering (DLS), microelectrophoresis, a solution depletion technique (enzyme-linked immunosorbent assay, ELISA), and AFM imaging. Our study presents a determination of the diffusion coefficient, hydrodynamic diameters, electrophoretic mobility, and isoelectric point of the NT-4 under various ionic strength and pH conditions. The size of the NT-4 homodimer for an ionic strength of 0.015 M was substantially independent of pH and equal to 5.1 nm. It has been found that the number of electrokinetic charges per NT-4 molecule was equal to zero for all studied ionic strengths at pH 8.1, which was identified as the isoelectric point (iep). The protein adsorption/desorption on/from mica surfaces was examined as a function of ionic strength and pH. The kinetics of neurotrophin adsorption/desorption were evaluated at pH 3.5, 7.4, and 11 by direct AFM imaging and the ELISA technique. A monotonic increase in the maximum coverage of adsorbed NT-4 molecules with ionic strength (up to 5.5 mg/m 2 ) was observed at pH 3.5. These results were interpreted in terms of the theoretical model postulating an irreversible adsorption of the protein governed by the random sequential adsorption (RSA). Our measurements revealed a significant role of ionic strength, pH, and electrolyte composition in the lateral electrostatic interactions among differently charged NT-4 molecules. The transition between adsorption/desorption processes is found for the region of high pH and low surface concentration of adsorbed neurotrophin molecules at constant ionic strength. Additionally, results presented in this work show that the adsorption behavior of neurotrophin molecules may be governed by intrasolvent electrostatic interactions yielding an aggregation process. Understanding polyvalent neurotrophin interactions may have an impact on

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

Kinetics of Cd(ii) adsorption and desorption on ferrihydrite: experiments and modeling.

PubMed

Liang, Yuzhen; Tian, Lei; Lu, Yang; Peng, Lanfang; Wang, Pei; Lin, Jingyi; Cheng, Tao; Dang, Zhi; Shi, Zhenqing

2018-05-15

The kinetics of Cd(ii) adsorption/desorption on ferrihydrite is an important process affecting the fate, transport, and bioavailability of Cd(ii) in the environment, which was rarely systematically studied and understood at quantitative levels. In this work, a combination of stirred-flow kinetic experiments, batch adsorption equilibrium experiments, high-resolution transmission electron microscopy (HR-TEM), and mechanistic kinetic modeling were used to study the kinetic behaviors of Cd(ii) adsorption/desorption on ferrihydrite. HR-TEM images showed the open, loose, and sponge-like structure of ferrihydrite. The batch adsorption equilibrium experiments revealed that higher pH and initial metal concentration increased Cd(ii) adsorption on ferrihydrite. The stirred-flow kinetic results demonstrated the increased adsorption rate and capacity as a result of the increased pH, influent concentration, and ferrihydrite concentration. The mechanistic kinetic model successfully described the kinetic behaviors of Cd(ii) during the adsorption and desorption stages under various chemistry conditions. The model calculations showed that the adsorption rate coefficients varied as a function of solution chemistry, and the relative contributions of the weak and strong ferrihydrite sites for Cd(ii) binding varied with time at different pH and initial metal concentrations. Our model is able to quantitatively assess the contributions of each individual ferrihydrite binding site to the overall Cd(ii) adsorption/desorption kinetics. This study provided insights into the dynamic behavior of Cd(ii) and a predictive modeling tool for Cd(ii) adsorption/desorption kinetics when ferrihydrite is present, which may be helpful for the risk assessment and management of Cd contaminated sites.

Diamine-Functionalization of a Metal-Organic Framework Adsorbent for Superb Carbon Dioxide Adsorption and Desorption Properties.

PubMed

Lee, Woo Ram; Kim, Jeong Eun; Lee, Sung Jin; Kang, Minjung; Kang, Dong Won; Lee, Hwa Young; Hiremath, Vishwanath; Seo, Jeong Gil; Jin, Hailian; Moon, Dohyun; Cho, Moses; Jung, Yousung; Hong, Chang Seop

2018-05-25

For real-world postcombustion applications in the mitigation of CO 2 emissions using dry sorbents, adsorption and desorption behaviors should be controlled to design and fabricate prospective materials with optimal CO 2 performances. Herein, we prepared diamine-functionalized Mg 2 (dobpdc) (H 4 dobpdc=4,4'-dihydroxy-(1,1'-biphenyl)-3,3'-dicarboxylic acid). (1-diamine) with ethylenediamine (en), primary-secondary (N-ethylethylenediamine-een and N-isopropylethylenediamine-ipen), primary-tertiary, and secondary-secondary diamines. A slight alteration of the number of alkyl substituents on the diamines and their alkyl chain length dictates the desorption temperature (T des ) at 100 % CO 2 , desorption characteristics, and ΔT systematically to result in the tuning of the working capacity. The existence of bulky substituents on the diamines improves the framework stability upon exposure to O 2 , SO 2 , and water vapor, relevant to real flue-gas conditions. Bulky substituents are also responsible for an interesting two-step behavior observed for the ipen case, as revealed by DFT calculations. Among the diamine-appended metal-organic frameworks, 1-een, which has the required adsorption and desorption properties, is a promising material for sorbent-based CO 2 capture processes. Hence, CO 2 performance and framework durability can be tailored by the judicial selection of the diamine structure, which enables property design at will and facilitates the development of desirable CO 2 -capture materials. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Coverage-dependent adsorption and desorption of oxygen on Pd(100)

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

Dunnen, Angela den; Jacobse, Leon; Wiegman, Sandra

2016-06-28

We have studied the adsorption and desorption of O{sub 2} on Pd(100) by supersonic molecular beam techniques and thermal desorption spectroscopy. Adsorption measurements on the bare surface confirm that O{sub 2} initially dissociates for all kinetic energies between 56 and 380 meV and surface temperatures between 100 and 600 K via a direct mechanism. At and below 150 K, continued adsorption leads to a combined O/O{sub 2} overlayer. Dissociation of molecularly bound O{sub 2} during a subsequent temperature ramp leads to unexpected high atomic oxygen coverages, which are also obtained at high incident energy and high surface temperature. At intermediatemore » temperatures and energies, these high final coverages are not obtained. Our results show that kinetic energy of the gas phase reactant and reaction energy dissipated during O{sub 2} dissociation on the cold surface both enable activated nucleation of high-coverage surface structures. We suggest that excitation of local substrate phonons may play a crucial role in oxygen dissociation at any coverage.« less

Kinetic and isothermal adsorption-desorption of PAEs on biochars: effect of biomass feedstock, pyrolysis temperature, and mechanism implication of desorption hysteresis.

PubMed

Jing, Fanqi; Pan, Minjun; Chen, Jiawei

2018-04-01

Biochar has the potential to sequester biomass carbon efficiently into land, simultaneously while improving soil fertility and crop production. Biochar has also attracted attention as a potential sorbent for good performance on adsorption and immobilization of many organic pollutants such as phthalic acid esters (PAEs), a typical plasticizer in plastic and presenting a current environmental issue. Due to lack of investigation on the kinetic and thermodynamic adsorption-desorption of PAEs on biochar, we systematically assessed adsorption-desorption for two typical PAEs, dimethyl phthalate (DMP) and diethyl phthalate (DEP), using biochar derived from peanut hull and wheat straw at different pyrolysis temperatures (450, 550, and 650 °C). The aromaticity and specific surface area of biochars increased with the pyrolysis temperature, whereas the total amount of surface functional groups decreased. The quasi-second-order kinetic model could better describe the adsorption of DMP/DEP, and the adsorption capacity of wheat straw biochars was higher than that of peanut hull biochars, owing to the O-bearing functional groups of organic matter on exposed minerals within the biochars. The thermodynamic analysis showed that DMP/DEP adsorption on biochar is physically spontaneous and endothermic. The isothermal desorption and thermodynamic index of irreversibility indicated that DMP/DEP is stably adsorbed. Sorption of PAEs on biochar and the mechanism of desorption hysteresis provide insights relevant not only to the mitigation of plasticizer mobility but also to inform on the effect of biochar amendment on geochemical behavior of organic pollutants in the water and soil.

Adsorption/desorption characteristics of lead on various types of soil

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

Peters, R.W.; Shem, L.

1994-09-01

Laboratory studies were conducted to address the phenomena of adsorption/desorption of lead onto various types of soils, both in the absence and presence of the chelating agent, ethylenediaminetetraacetic acid (EDTA). The linear and Freundlich isotherm models provided adequate description of the adsorption/desorption behavior. Over the range of EDTA concentrations employed in the study (0.01 to 0.10M), no significant difference in the isotherm parameters was observed as a result of the applied EDTA concentration. The presence of EDTA significantly altered the adsorption/desorption behavior of lead on the soil, resulting in less of the metal being adsorbed. The soil with the highermore » silt/clay content had a greater amount of lead adsorbed onto it (as compared with the sandy soil).« less

Isosteric heat of water adsorption and desorption in homoionic alkaline-earth montmorillonites

NASA Astrophysics Data System (ADS)

Belhocine, M.; Haouzi, A.; Bassou, G.; Phou, T.; Maurin, D.; Bantignies, J. L.; Henn, F.

2018-02-01

The aim of the present work is to study by means of thermodynamic measurements and Infrared spectroscopy, the effect of the interlayer cations on the adsorption-desorption of water in the case of a montmorillonite exchanged with alkaline-earth metals. For the first time, the net isosteric heat of water adsorption and desorption is determined from isotherms recorded at three temperatures. The net isosteric heat is a very useful parameter for getting more insights into the sorption mechanism since it provides information about the sorption energy evolution which can be complementary to that obtained from structural or gravimetric measurements. The homoionic montmorillonite samples are prepared from purification and cationic exchanged in aqueous solution of the raw material, i.e. the reference SWy-2 Wyoming material. XRD at the dry state and elemental chemical analysis confirm that the treatment does not deteriorate the clay structure and yield the expected homoionic composition. The sorption isotherms measured at various temperatures show that the nature of the interlayer, i.e. exchangeable, cation changes the adsorbed/desorbed amount of water molecules for a given water relative pressure. The total amount of water adsorbed at P/P∘ = 0.5 follows the cation sequence Ca ∼ Mg>Ba while the sorption isosteric heats follow a slightly different sequence, i.e. Ca > Mg>Ba. This discrepancy between the adsorption and desorption heat is due to the higher irreversibility of water sorption process in the Ca exchanged montmorillonite. Finally, analysis of the IR spectra recorded at room temperature and under a primary vacuum reveals that the amount of adsorbed water follows the same sequence as that of the isosteric heat of adsorption and shows the coexistence of liquid-like and solid-like water confined in the interlayer space.

Adsorption of small hydrocarbons on rutile TiO 2(110)

DOE PAGES

Chen, Long; Smith, R. Scott; Kay, Bruce D.; ...

2015-11-21

Here, temperature programmed desorption and molecular beam scattering were used to study the adsorption and desorption of small hydrocarbons (n-alkanes, 1-alkenes and 1-alkynes of C 1–C 4) on rutile TiO 2(110). We show that the sticking coefficients for all the hydrocarbons are close to unity (> 0.95) at an adsorption temperature of 60 K. The desorption energies for hydrocarbons of the same chain length increase from n-alkanes to 1-alkenes and to 1-alkynes. This trend is likely a consequence of additional dative bonding of the alkene and alkyne π system to the coordinatively unsaturated Ti 5c sites. Similar to previous studiesmore » on the adsorption of n-alkanes on metal and metal oxide surfaces, we find that the desorption energies within each group (n-alkanes vs. 1-alkenes vs. 1-alkynes) from Ti 5c sites increase linearly with the chain length. The absolute saturation coverages of each hydrocarbon on Ti 5c sites were also determined. The saturation coverage of CH 4, is found to be ~ 2/3 monolayer (ML). The saturation coverages of C 2–C 4 hydrocarbons are found nearly independent of the chain length with values of ~ 1/2 ML for n-alkanes and 1-alkenes and 2/3 ML for 1-alkynes. This result is surprising considering their similar sizes.« less

Adsorption and Desorption of Nickel(II) Ions from Aqueous Solution by a Lignocellulose/Montmorillonite Nanocomposite

PubMed Central

Zhang, Xiaotao; Wang, Ximing

2015-01-01

A new and inexpensive lignocellulose/montmorillonite (LNC/MMT) nanocomposite was prepared by a chemical intercalation of LNC into MMT and was subsequently investigated as an adsorbent in batch systems for the adsorption-desorption of Ni(II) ions in an aqueous solution. The optimum conditions for the Ni(II) ion adsorption capacity of the LNC/MMT nanocomposite were studied in detail by varying parameters such as the initial Ni(II) concentration, the solution pH value, the adsorption temperature and time. The results indicated that the maximum adsorption capacity of Ni(II) reached 94.86 mg/g at an initial Ni(II) concentration of 0.0032 mol/L, a solution pH of 6.8, an adsorption temperature of 70°C, and adsorption time of 40 min. The represented adsorption kinetics model exhibited good agreement between the experimental data and the pseudo-second-order kinetic model. The Langmuir isotherm equation best fit the experimental data. The structure of the LNC/MMT nanocomposite was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), whereas the adsorption mechanism was discussed in combination with the results obtained from scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier-transform infrared spectroscopy analyses (FTIR). The desorption capacity of the LNC/MMT nanocomposite depended on parameters such as HNO3 concentration, desorption temperature, and desorption time. The satisfactory desorption capacity of 81.34 mg/g was obtained at a HNO3 concentration, desorption temperature, and desorption time of 0.2 mol/L, 60 ºC, and 30 min, respectively. The regeneration studies showed that the adsorption capacity of the LNC/MMT nanocomposite was consistent for five cycles without any appreciable loss in the batch process and confirmed that the LNC/MMT nanocomposite was reusable. The overall study revealed that the LNC/MMT nanocomposite functioned as an effective adsorbent in the detoxification of Ni

Counterion adsorption and desorption rate of a charged macromolecule

NASA Astrophysics Data System (ADS)

Shi, Yu; Yang, Jingfa; Zhao, Jiang

The rate constant of counterion adsorption to and desorption from a synthetic polyelectrolyte, polystyrene sulfonate (PSS-), is measured in aqueous solution by single molecule fluorescence spectroscopy. The results show that both adsorption and desorption rate of counterions have strong dependence on polymer concentration, salt concentration as well as the molecular weight of polyelectrolytes. The results clearly demonstrate that the contribution of electrostatic interaction and the translational entropy to the distribution of counterions of a polyelectrolyte molecule. The information is helpful to the understanding of polyelectrolyte physics. National Natural Science Foundation of China.

Overcoming double-step CO2 adsorption and minimizing water co-adsorption in bulky diamine-appended variants of Mg2(dobpdc).

PubMed

Milner, Phillip J; Martell, Jeffrey D; Siegelman, Rebecca L; Gygi, David; Weston, Simon C; Long, Jeffrey R

2018-01-07

Alkyldiamine-functionalized variants of the metal-organic framework Mg 2 (dobpdc) (dobpdc 4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) are promising for CO 2 capture applications owing to their unique step-shaped CO 2 adsorption profiles resulting from the cooperative formation of ammonium carbamate chains. Primary , secondary (1°,2°) alkylethylenediamine-appended variants are of particular interest because of their low CO 2 step pressures (≤1 mbar at 40 °C), minimal adsorption/desorption hysteresis, and high thermal stability. Herein, we demonstrate that further increasing the size of the alkyl group on the secondary amine affords enhanced stability against diamine volatilization, but also leads to surprising two-step CO 2 adsorption/desorption profiles. This two-step behavior likely results from steric interactions between ammonium carbamate chains induced by the asymmetrical hexagonal pores of Mg 2 (dobpdc) and leads to decreased CO 2 working capacities and increased water co-adsorption under humid conditions. To minimize these unfavorable steric interactions, we targeted diamine-appended variants of the isoreticularly expanded framework Mg 2 (dotpdc) (dotpdc 4- = 4,4''-dioxido-[1,1':4',1''-terphenyl]-3,3''-dicarboxylate), reported here for the first time, and the previously reported isomeric framework Mg-IRMOF-74-II or Mg 2 (pc-dobpdc) (pc-dobpdc 4- = 3,3'-dioxidobiphenyl-4,4'-dicarboxylate, pc = para -carboxylate), which, in contrast to Mg 2 (dobpdc), possesses uniformally hexagonal pores. By minimizing the steric interactions between ammonium carbamate chains, these frameworks enable a single CO 2 adsorption/desorption step in all cases, as well as decreased water co-adsorption and increased stability to diamine loss. Functionalization of Mg 2 (pc-dobpdc) with large diamines such as N -( n -heptyl)ethylenediamine results in optimal adsorption behavior, highlighting the advantage of tuning both the pore shape and the diamine size for the development of

Competitive adsorption-desorption reactions of two hazardous heavy metals in contaminated soils.

PubMed

Davari, Masoud; Rahnemaie, Rasoul; Homaee, Mehdi

2015-09-01

Investigating the interactions of heavy metals is imperative for sustaining environment and human health. Among those, Cd is toxic for organisms at any concentration. While Ni acts as a micronutrient at very low concentration but is hazardous toxic above certain threshold value. In this study, the chemical adsorption and desorption reactions of Ni and Cd in contaminated soils were investigated in both single and binary ion systems. Both Ni and Cd experimental data demonstrated Langmuir type adsorption. In the competitive systems, an antagonistic effect was observed, implying that both ions compete for same type of adsorption sites. Adverse effect of Cd on Ni adsorption was slightly stronger than that of opposite system, consistent with adsorption isotherms in single ion systems. Variation in ionic strength indicated that Ca, a much weaker adsorbate, could also compete with Cd and Ni for adsorption on soil particles. Desorption data indicated that Cd and Ni are adsorbed very tightly such that after four successive desorption steps, less than 0.5 % of initially adsorbed ions released into the soil solution. This implies that Ca, at concentration in equilibrium with calcite mineral, cannot adequately compete with and replace adsorbed Ni and Cd ions. This adsorption behavior was led to considerable hysteresis between adsorption and desorption in both single and binary ion systems. In the binary ion systems, desorption of Cd and Ni was increased by increase in both equilibrium concentration of adsorbed ion and concentration of competitor ion. The overall results obtained in this research indicate that Cd and Ni are strongly adsorbed in calcareous soil and Ca, the major dissolved ion, insignificantly influences metal ions adsorption. Consequently, the contaminated soils by Ni and Cd can simultaneously be remediated by environmentally oriented technologies such as phytoremediation.

Adsorption and desorption performance of benzene over hierarchically structured carbon-silica aerogel composites.

PubMed

Dou, Baojuan; Li, Jinjun; Wang, Yufei; Wang, Hailin; Ma, Chunyan; Hao, Zhengping

2011-11-30

Hierarchically structured carbon-silica aerogel (CSA) composites were synthesized from cheap water glass precursors and granulated activated carbon via a post-synthesis surface modification with trimethylchlorosilane (TMCS) and a low-cost ambient pressure drying procedure. The resultant CSA composites possess micro/mesoporous structure and hydrophobic surface. The adsorption and desorption performance of benzene on carbon-silica aerogel composite (CSA-2) under static and dynamic conditions were investigated, comparing with pure silica aerogel (CSA-0) and microporous activated carbon (AC). It was found that CSA-2 has high affinity towards aromatic molecules and fast adsorption kinetics. Excellent performance of dynamic adsorption and desorption observed on CSA-2 is related to its higher adsorption capacity than CSA-0 and less mass transfer resistance than AC, arising from the well-developed microporosity and open foam mesostructure in the CSA composites. Copyright © 2011 Elsevier B.V. All rights reserved.

Adsorption-desorption of oxytetracycline on marine sediments: Kinetics and influencing factors.

PubMed

Li, Jia; Zhang, Hua

2016-12-01

To reveal the kinetics and mechanisms of antibiotic adsorption/desorption processes, batch and stirred flow chamber (SFC) experiments were carried out with oxytetracycline (OTC) on two marine sediments. The OTC adsorption capacities of the marine sediments were relatively weak and related to their organic carbon (OC) and contents of fine particles. Sorption isotherms of OTC on marine sediment can be well described by both the Langmuir and Freundlich models. Langmuir adsorption maxima (q max ) and Freundlich distribution coefficients (K f ) increased with the decrease of salinity and pH, which indicated the importance of variable charged sites on sediment surfaces. A second order kinetic model successfully described adsorption and desorption kinetics of OTC and well reproduced the concentration change during stop-flow. The adsorption kinetic rates (k a ) for OTC under different experimental conditions ranged from 2.00 × 10 -4 to 1.97 × 10 -3  L (mg min) -1 . Results of SFC experiments indicated that diffusive mass transfer was the dominant mechanism of the time-dependent adsorption of OTC and its release from marine sediment was mildly hysteretic. The high desorption percentage (43-75% for LZB and 58-75% for BHB) implied that binding strength of OTC on two marine sediments was weak. In conclusion, marine sediment characteristics and environmental factors such as salinity, pH, and flow rate are critical factors determine extent of OTC sorption on marine sediment and need to be incorporated in modeling fate and transport of OTC in marine environment. Copyright © 2016 Elsevier Ltd. All rights reserved.

Electrothermal adsorption and desorption of volatile organic compounds on activated carbon fiber cloth.

PubMed

Son, H K; Sivakumar, S; Rood, M J; Kim, B J

2016-01-15

Adsorption is an effective means to selectively remove volatile organic compounds (VOCs) from industrial gas streams and is particularly of use for gas streams that exhibit highly variable daily concentrations of VOCs. Adsorption of such gas streams by activated carbon fiber cloths (ACFCs) and subsequent controlled desorption can provide gas streams of well-defined concentration that can then be more efficiently treated by biofiltration than streams exhibiting large variability in concentration. In this study, we passed VOC-containing gas through an ACFC vessel for adsorption and then desorption in a concentration-controlled manner via electrothermal heating. Set-point concentrations (40-900 ppm(v)) and superficial gas velocity (6.3-9.9 m/s) were controlled by a data acquisition and control system. The results of the average VOC desorption, desorption factor and VOC in-and-out ratio were calculated and compared for various gas set-point concentrations and superficial gas velocities. Our results reveal that desorption is strongly dependent on the set-point concentration and that the VOC desorption rate can be successfully equalized and controlled via an electrothermal adsorption system. Copyright © 2015 Elsevier B.V. All rights reserved.

Adsorption of small hydrocarbons on rutile TiO2(110)

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

Chen, Long; Smith, R. Scott; Kay, Bruce D.

2016-08-01

Temperature programmed desorption and molecular beam scattering were used to study the adsorption and desorption of small hydrocarbons (n-alkanes, 1-alkenes and 1-alkynes with 1 - 4 carbon atoms of C1-C4) on rutile TiO2(110). We show that the sticking coefficients for all the hydrocarbons are close to unity (> 0.95) at an adsorption temperature of 60 K. The desorption energies for hydrocarbons of the same chain length increase from n-alkanes to 1-alkenes and to 1-alkynes. This trend is likely a consequence of an additional dative bonding of the alkene and alkyne π system to the coordinatively unsaturated Ti5c sites. Similar tomore » previous studies on the adsorption of n-alkanes on metal and metal oxide surfaces, we find the desorption energies within each group (n-alkanes vs. 1-alkenes vs. 1-alkynes) from Ti5c sites increase linearly with the chain length. The absolute saturation coverages of each hydrocarbon on Ti5c sites were also determined. The saturation coverage of CH4, is found to be ~ 2/3 monolayer (ML). The saturation coverages of C2-C4 hydrocarbons are found nearly independent of the chain length with values of ~1/2 ML for n-alkanes and 1-alkenes and 2/3 ML for 1-alkynes. This result is surprising considering their similar sizes.« less

Impact of styrenic polymer one-step hyper-cross-linking on volatile organic compound adsorption and desorption performance.

PubMed

Ghafari, Mohsen; Atkinson, John D

2018-06-05

A novel one-step hyper-cross-linking method, using 1,2-dichloroethane (DCE) and 1,6-dichlorohexane (DCH) cross-linkers, expands the micropore volume of commercial styrenic polymers. Performance of virgin and modified polymers was evaluated by measuring hexane, toluene, and methyl-ethyl-ketone (MEK) adsorption capacity, adsorption/desorption kinetics, and desorption efficiency. Hyper-cross-linked polymers have up to 128% higher adsorption capacity than virgin polymers at P/P 0  = 0.05 due to micropore volume increases up to 330%. Improvements are most pronounced with the DCE cross-linker. Hyper-cross-linking has minimal impact on hexane adsorption kinetics, but adsorption rates for toluene and MEK decrease by 6-41%. Desorption rates decreased (3-36%) for all materials after hyper-cross-linking, with larger decreases for DCE hyper-cross-linked polymers due to smaller average pore widths. For room temperature desorption, 20-220% more adsorbate remains in hyper-cross-linked polymers after regeneration compared to virgin materials. DCE hyper-cross-linked polymers have 13-92% more residual adsorbate than DCH counterparts. Higher temperatures were required for DCE hyper-cross-linked polymers to completely desorb VOCs compared to the DCH hyper-cross-linked and virgin counterparts. Results show that the one-step hyper-cross-linking method for modifying styrenic polymers improves adsorption capacity because of added micropores, but decreases adsorption/desorption kinetics and desorption efficiency for large VOCs due to a decrease in average pore width. Copyright © 2018 Elsevier B.V. All rights reserved.

Adsorption and desorption of oxytetracycline and carbamazepine by multiwalled carbon nanotubes.

PubMed

Oleszczuk, Patryk; Pan, Bo; Xing, Baoshan

2009-12-15

We investigated the adsorption-desorption by multiwalled carbon nanotubes (MWCNTs) of two pharmaceuticals, oxytetracycline (OTC) and carbamazepine (CBZ). The pharmaceuticals demonstrated relatively fast sorption kinetics on MWCNTs. All adsorption isotherms were nonlinear and fit the Polanyi-Manes model (PMM). The single point adsorption coefficient (K) values for OTC were more than 1 order of magnitude higher than those for CBZ on corresponding MWCNTs. The adsorbed volume capacity (Q(0)) and K values of PMM showed a significant relationship with surface areas and the meso- and micropore volume of MWCNTs for both chemicals. Depending on the MWCNT outer diameter, 13.8-25.2% and 62.7-90.6% of initially adsorbed OTC and CBZ, respectively, were desorbed after 200 h. The rate of desorption of both OTC and CBZ depended upon pH and the quantity of initially adsorbed pharmaceuticals, as well as aggregation in the case of OTC.

Hydrogen Desorption and Adsorption Measurements on Graphite Nanofibers

NASA Technical Reports Server (NTRS)

Ahn, C. C.; Ye, Y.; Ratnakumar, B. V.; Witham, C. K.; Bowman, R. C., Jr.; Fultz, B.

1998-01-01

Graphite nanofibers were synthesized and their hydrogen desorption and adsorption properties are reported for 77 and 300 K. Catalysts were made by several different methods including chemical routes, mechanical alloying and gas condensation.

Overcoming double-step CO 2 adsorption and minimizing water co-adsorption in bulky diamine-appended variants of Mg 2(dobpdc)

DOE PAGES

Milner, Phillip J.; Martell, Jeffrey D.; Siegelman, Rebecca L.; ...

2017-10-26

Alkyldiamine-functionalized variants of the metal–organic framework Mg 2(dobpdc) (dobpdc 4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) are promising for CO 2 capture applications owing to their unique step-shaped CO 2 adsorption profiles resulting from the cooperative formation of ammonium carbamate chains. Primary,secondary (1°,2°) alkylethylenediamine-appended variants are of particular interest because of their low CO 2 step pressures (≤1 mbar at 40 °C), minimal adsorption/desorption hysteresis, and high thermal stability. Herein, we demonstrate that further increasing the size of the alkyl group on the secondary amine affords enhanced stability against diamine volatilization, but also leads to surprising two-step CO 2 adsorption/desorption profiles. This two-step behaviormore » likely results from steric interactions between ammonium carbamate chains induced by the asymmetrical hexagonal pores of Mg 2(dobpdc) and leads to decreased CO 2 working capacities and increased water co-adsorption under humid conditions. To minimize these unfavorable steric interactions, we targeted diamine-appended variants of the isoreticularly expanded framework Mg 2(dotpdc) (dotpdc 4- = 4,4''-dioxido-[1,1':4',1''-terphenyl]-3,3''-dicarboxylate), reported here for the first time, and the previously reported isomeric framework Mg-IRMOF-74-II or Mg 2(pc-dobpdc) (pc-dobpdc 4- = 3,3'-dioxidobiphenyl-4,4'-dicarboxylate, pc = para-carboxylate), which, in contrast to Mg 2(dobpdc), possesses uniformally hexagonal pores. By minimizing the steric interactions between ammonium carbamate chains, these frameworks enable a single CO 2 adsorption/desorption step in all cases, as well as decreased water co-adsorption and increased stability to diamine loss. Functionalization of Mg 2(pc-dobpdc) with large diamines such as N-(n-heptyl)ethylenediamine results in optimal adsorption behavior, highlighting the advantage of tuning both the pore shape and the diamine size for the development of new

Adsorption/Desorption Measurements of Nitroglycerin and Dinitrotoluene in Camp Edwards, Massachusetts Soil

DTIC Science & Technology

2010-02-01

87 8 References...without biocide to K7 soil. ................................................ 31 Figure 8 . The 2,4-DNT concentration in the measured aqueous phase (C...28 Table 8 . Adsorption and desorption partitioning

Adsorption-desorption and hysteresis phenomenon of tebuconazole in Colombian agricultural soils: Experimental assays and mathematical approaches.

PubMed

Mosquera-Vivas, Carmen S; Martinez, María J; García-Santos, Glenda; Guerrero-Dallos, Jairo A

2018-01-01

The adsorption-desorption, hysteresis phenomenon, and leachability of tebuconazole were studied for Inceptisol and Histosol soils at the surface (0-10 cm) and in the subsurface (40-50 cm) of an agricultural region from Colombia by the batch-equilibrium method and mathematical approaches. The experimental K fa and K d (L kg -1 ) values (7.9-289.2) decreased with depth for the two Inceptisols and increased with depth for the Histosol due to the organic carbon content, aryl and carbonyl carbon types. Single-point and desorption isotherms depended on adsorption reversibility and suggested that tebuconazole showed hysteresis; which can be adequately evaluated with the single-point desorption isotherm and the linear model using the hysteresis index HI. The most suitable mathematical approach to estimate the adsorption isotherms of tebuconazole at the surface and in the subsurface was that considering the combination of the n-octanol-water partition coefficient, pesticide solubility, and the mass-balance concept. Tebuconazole had similar moderate mobility potential as compared with the values of other studies conducted in temperate amended and unamended soils, but the risk of the fungicide to pollute groundwater sources increased when the pesticide reached subsurface soil layers, particularly in the Inceptisols. Copyright © 2017 Elsevier Ltd. All rights reserved.

The phosphorus fractions and adsorption-desorption characteristics in the Wuliangsuhai Lake, China.

PubMed

Wang, Xinglei; Wei, Jinxing; Bai, Na; Cha, Hancaicike; Cao, Can; Zheng, Kexuan; Liu, Ying

2018-05-11

The phosphorus (P) fractions and adsorption-desorption characteristics in the Wuliangsuhai Lake were investigated through molybdenum blue/ascorbic acid method and indoor simulation experiments, respectively. The results showed that the highest total phosphorus concentration in overlying water (W-TP) was found in S1 which was in the hypereutrophic type. The mean concentration of particulate organic phosphorus (POP) was the most abundant P fraction (31.35% of the W-TP). The results of TP contents in sediments (S-TP) indicated that the most sampling sites were in the mild level of pollution. The contents of calcium-bound P (HCl-P) and residual P (Res-P) fractions together comprised 83.03-98.10% of the S-TP. Pseudo-second-order models fitted well with the adsorption-desorption kinetic of P fractions. The Langmuir and Freundlich models well described the adsorption isotherm of P fractions. The results of adsorption-desorption of P fractions indicated that the adsorption capacity was strong, the chemical adsorption was dominant, and the sediments was a source of P. Accordingly, we concluded that the Wuliangsuhai Lake was in the moderate pollution level, and the sediments as a source could desorb P in natural aquatic environment.

Strontium-90 adsorption-desorption properties and sediment characterization at the 100 N-Area

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

Serne, R.J.; LeGore, V.L.

1996-01-01

Strontium-90 ({sup 90}Sr) has been seeping into the Columbia River since the early 1980s. The likely source is subsurface migration of {sup 90}Sr from once-through cooling water from the Hanford N Reactor disposed into the two disposal crib/trench facilities. Background information has been provided on the operational history of the two liquid waste disposal facilities and some of the regulatory drivers that have lead to the various characterization activities and remediation demonstrations being performed to help choose future full-scale remediation alternatives. The work presented in this topical report had two main objectives. First, we obtained numerous borehole samples from newlymore » installed wells/borings and performed physical and chemical characterization that,included particle size analysis, moisture content, and Strontium-90, Tritium and gamma activity analyses to help improve the conceptual model of where the contaminants currently reside in the sediments. The second objective was to perform laboratory adsorption-desorption tests using both batch and flow- through column techniques to gather data for use in contaminant transport conceptual models and to aid in specific pump-and-treat calculations needed to interpret a field demonstration.« less

Adsorption-desorption and degradation of insecticides clothianidin and thiamethoxam in agricultural soils.

PubMed

Li, Yang; Su, Peidong; Li, Yadong; Wen, Kejun; Bi, Guihong; Cox, Michael

2018-09-01

Studied were the adsorption-desorption and degradation of two widely used neonicotinoid insecticides clothianidin and thiamethoxam in three different agricultural soils in the state of Mississippi. The adsorptions of both the neonicotinoids fit a linear isotherm model. In different soils at different depths with different moisture contents, the adsorption distribution coefficients of clothianidin and thiamethoxam were found to be 0.62 to 1.94 and 0.59-2.03 L kg -1 , respectively. These distribution coefficients showed strong positive correlations with organic carbon content and pH of the soils. The desorptions of clothianidin and thiamethoxam also followed a linear isotherm, but were irreversible in respect to their adsorption isotherms. The desorption distribution coefficients ranged from 0.14 to 0.62 L kg -1 , increased with the decrease of organic carbon content. The degradations of clothianidin and thiamethoxam in the soils were found to be slow with half-lives ranged from 90 to 280 and 65 to 170 d for clothianidin and thiamethoxam respectively. The degradation rates increased with the increase of the organic carbon content in the soils. The moisture content in the soils had a positive effect on the degradation rates. The Groundwater Ubiquity Scores calculated from the adsorption distribution coefficient, organic content, and half-life suggest that clothianidin and thiamethoxam have moderate to high potential to leach to groundwater. Copyright © 2018 Elsevier Ltd. All rights reserved.

Adsorption and desorption of carbaryl on hexadecyl trimethyl ammonium bromide modified zeolite NaY using RGB portable photometer

NASA Astrophysics Data System (ADS)

Patdhanagul, Nopbhasinthu; Chanpaka, Saiphon; Intharaksa, Orapan; Sirival, Rujikarn; Thanomsith, Kannikar; Wongkwanklom, Sarayuth

2018-04-01

The carbaryl adsorption-desorption isotherms of zeolite NaY and hexadecyl trimethyl ammonium bromide (HTAB) modified zeolite NaY were investigated. Zeolite NaY was synthesized and modified by HTAB in the concentration range 0.1 - 10.0 mM. The adsorption isotherms indicated that zeolite modified with HTAB could significantly enhance the carbaryl adsorption capacity. Zeolite NaY modified with 5.0 mM HTAB gave great carbaryl adsorption because of hydrophilic surface. The 5.0 mM HTAB could adsorb up to 145.75 ppm g-1 of carbaryl which was equivalent to a 36.7% increase. The Surface area characterization showed the remaining of pore volume and pore size diameter and external surface area whereas the BET surface area and micropore surface area of modified zeolite slightly decreased. The XRD results indicate that modification of zeolite NaY with HTAB does not change the crystallinity of the starting zeolite. The elemental analysis indicated that the Si/Al ratio of synthesized zeolite NaY was close to 2.43. Desorption of carbaryl was tested by organic solvents such as methanol, ethanol, tetrahydrofuran, hexane and Deionized water. The results demonstrated that the percentage desorption of methanol is the highest. Carbaryl was quantitatively desorbed with percentage desorption of 82-100 %. It indicated sorption mechanism of carbaryl on the modified sorbent which was principally driven by hydrophobic forces.

Film growth, adsorption and desorption kinetics of indigo on SiO2.

PubMed

Scherwitzl, Boris; Resel, Roland; Winkler, Adolf

2014-05-14

Organic dyes have recently been discovered as promising semiconducting materials, attributable to the formation of hydrogen bonds. In this work, the adsorption and desorption behavior, as well as thin film growth was studied in detail for indigo molecules on silicon dioxide with different substrate treatments. The material was evaporated onto the substrate by means of physical vapor deposition under ultra-high vacuum conditions and was subsequently studied by Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy, X-Ray Diffraction, and Atomic Force Microscopy. TDS revealed initially adsorbed molecules to be strongly bonded on a sputter cleaned surface. After further deposition a formation of dimers is suggested, which de-stabilizes the bonding mechanism to the substrate and leads to a weakly bonded adsorbate. The dimers are highly mobile on the surface until they get incorporated into energetically favourable three-dimensional islands in a dewetting process. The stronger bonding of molecules within those islands could be shown by a higher desorption temperature. On a carbon contaminated surface no strongly bonded molecules appeared initially, weakly bonded monomers rather rearrange into islands at a surface coverage that is equivalent to one third of a monolayer of flat-lying molecules. The sticking coefficient was found to be unity on both substrates. The desorption energies from carbon covered silicon dioxide calculated to 1.67 ± 0.05 eV for multilayer desorption from the islands and 0.84 ± 0.05 eV for monolayer desorption. Corresponding values for desorption from a sputter cleaned surface are 1.53 ± 0.05 eV for multilayer and 0.83 ± 0.05 eV for monolayer desorption.

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.

Ab initio molecular dynamics determination of competitive O 2 vs. N 2 adsorption at open metal sites of M 2 (dobdc)

DOE PAGES

Parkes, Marie V.; Greathouse, Jeffery A.; Hart, David B.; ...

2016-04-04

The separation of oxygen from nitrogen using metal–organic frameworks (MOFs) is of great interest for potential pressure-swing adsorption processes for the generation of purified O 2 on industrial scales. This study uses ab initio molecular dynamics (AIMD) simulations to examine for the first time the pure-gas and competitive gas adsorption of O 2 and N 2 in the M 2(dobdc) (M = Cr, Mn, Fe) MOF series with coordinatively unsaturated metal centers. Effects of metal, temperature, and gas composition are explored. Lastly, this unique application of AIMD allows us to study in detail the adsorption/desorption processes and to visualize themore » process of multiple guests competitively binding to coordinatively unsaturated metal sites of a MOF.« less

Modeling Adsorption-Desorption Processes at the Intermolecular Interactions Level

NASA Astrophysics Data System (ADS)

Varfolomeeva, Vera V.; Terentev, Alexey V.

2018-01-01

Modeling of the surface adsorption and desorption processes, as well as the diffusion, are of considerable interest for the physical phenomenon under study in ground tests conditions. When imitating physical processes and phenomena, it is important to choose the correct parameters to describe the adsorption of gases and the formation of films on the structural materials surface. In the present research the adsorption-desorption processes on the gas-solid interface are modeled with allowance for diffusion. Approaches are proposed to describe the adsorbate distribution on the solid body surface at the intermolecular interactions level. The potentials of the intermolecular interaction of water-water, water-methane and methane-methane were used to adequately modeling the real physical and chemical processes. The energies calculated by the B3LYP/aug-cc-pVDZ method. Computational algorithms for determining the average molecule area in a dense monolayer, are considered here. Differences in modeling approaches are also given: that of the proposed in this work and the previously approved probabilistic cellular automaton (PCA) method. It has been shown that the main difference is due to certain limitations of the PCA method. The importance of accounting the intermolecular interactions via hydrogen bonding has been indicated. Further development of the adsorption-desorption processes modeling will allow to find the conditions for of surface processes regulation by means of quantity adsorbed molecules control. The proposed approach to representing the molecular system significantly shortens the calculation time in comparison with the use of atom-atom potentials. In the future, this will allow to modeling the multilayer adsorption at a reasonable computational cost.

Adsorption-desorption mechanism of phosphate by immobilized nano-sized magnetite layer: interface and bulk interactions.

PubMed

Zach-Maor, Adva; Semiat, Raphael; Shemer, Hilla

2011-11-15

Phosphate adsorption mechanism by a homogenous porous layer of nano-sized magnetite particles immobilized onto granular activated carbon (nFe-GAC) was studied for both interface and bulk structures. X-ray Photoelectron Spectroscopy (XPS) analysis revealed phosphate bonding to the nFe-GAC predominantly through bidentate surface complexes. It was established that phosphate was adsorbed to the magnetite surface mainly via ligand exchange mechanism. Initially, phosphate was adsorbed by the active sites on the magnetite surface, after which it diffused into the interior of the nano-magnetite layer, as indicated by intraparticle diffusion model. This diffusion process continues regardless of interface interactions, revealing some of the outer magnetite binding sites for further phosphate uptake. Desorption, using NaOH solution, was found to be predominantly a surface reaction, at which hydroxyl ions replace the adsorbed phosphate ions only at the surface outer biding sites. Five successive fix-bed adsorption/regeneration cycles were successfully applied, without significant reduction in the nFe-GAC adsorption capacity and at high regeneration efficiency. Copyright © 2011 Elsevier Inc. All rights reserved.

Pentaethylenehexamine-Loaded Hierarchically Porous Silica for CO2 Adsorption

PubMed Central

Ji, Changchun; Huang, Xin; Li, Lei; Xiao, Fukui; Zhao, Ning; Wei, Wei

2016-01-01

Recently, amine-functionalized materials as a prospective chemical sorbent for post combustion CO2 capture have gained great interest. However, the amine grafting for the traditional MCM-41, SBA-15, pore-expanded MCM-41 or SBA-15 supports can cause the pore volume and specific surface area of sorbents to decrease, significantly affecting the CO2 adsorption-desorption dynamics. To overcome this issue, hierarchical porous silica with interparticle macropores and long-range ordering mesopores was prepared and impregnated with pentaethylenehexamine. The pore structure and amino functional group content of the modified silicas were analyzed by scanning electron microscope, transmission electron microscope, N2 adsorption, X-ray powder diffraction, and Fourier transform infrared spectra. Moreover, the effects of the pore structure as well as the amount of PEHA loading of the samples on the CO2 adsorption capacity were investigated in a fixed-bed adsorption system. The CO2 adsorption capacity reached 4.5 mmol CO2/(g of adsorbent) for HPS−PEHA-70 at 75 °C. Further, the adsorption capacity for HPS-PEHA-70 was steady after a total of 15 adsorption-desorption cycles. PMID:28773956

Adsorption and desorption characteristics of methamphetamine, 3,4-methylenedioxymethamphetamine, and pseudoephedrine in soils.

PubMed

Pal, Raktim; Megharaj, Mallavarapu; Kirkbride, K Paul; Naidu, Ravi

2015-06-01

This work presents, for the first time, information on the adsorption-desorption characteristics of illicit drugs and precursors in soils and an estimation of their potential bioavailability. The experiment was conducted using a batch equilibrium technique for the parent drugs methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) and the precursor pseudoephedrine in three South Australian soils varying in physiochemical properties. The individual compounds exhibited different adsorption mechanisms in the test soils, and the results fitted better with the Freundlich isotherm model (r (2) ≥ 0.99). The maximum adsorption capacity was recorded for pseudoephedrine (2,000 μg g(-1)). However, pseudoephedrine recorded lower organic carbon normalized adsorption coefficient values (<250 mL g(-1)), lower magnitudes of Gibb's free energy change, and higher percent desorption (73-92 %) compared to methamphetamine and MDMA. The results thus showed pseudoephedrine to be the most mobile compound in the soils under study, to have the highest availability for degradation of the three compounds, and to have the highest susceptibility to biotic degradation in test soils.

Film growth, adsorption and desorption kinetics of indigo on SiO2

PubMed Central

Scherwitzl, Boris; Resel, Roland; Winkler, Adolf

2015-01-01

Organic dyes have recently been discovered as promising semiconducting materials, attributable to the formation of hydrogen bonds. In this work, the adsorption and desorption behavior, as well as thin film growth was studied in detail for indigo molecules on silicon dioxide with different substrate treatments. The material was evaporated onto the substrate by means of physical vapor deposition under ultra-high vacuum conditions and was subsequently studied by Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy, X-Ray Diffraction, and Atomic Force Microscopy. TDS revealed initially adsorbed molecules to be strongly bonded on a sputter cleaned surface. After further deposition a formation of dimers is suggested, which de-stabilizes the bonding mechanism to the substrate and leads to a weakly bonded adsorbate. The dimers are highly mobile on the surface until they get incorporated into energetically favourable three-dimensional islands in a dewetting process. The stronger bonding of molecules within those islands could be shown by a higher desorption temperature. On a carbon contaminated surface no strongly bonded molecules appeared initially, weakly bonded monomers rather rearrange into islands at a surface coverage that is equivalent to one third of a monolayer of flat-lying molecules. The sticking coefficient was found to be unity on both substrates. The desorption energies from carbon covered silicon dioxide calculated to 1.67 ± 0.05 eV for multilayer desorption from the islands and 0.84 ± 0.05 eV for monolayer des orption. Corresponding values for desorption from a sputter cleaned surface are 1.53 ± 0.05 eV for multilayer and 0.83 ± 0.05 eV for monolayer desorption. PMID:24832297

Study on Desorption Process of n-Heptane and Methyl Cyclohexane Using UiO-66 with Hierarchical Pores.

PubMed

Chen, Sijia; Zhang, Lin; Zhang, Zhao; Qian, Gang; Liu, Zongjian; Cui, Qun; Wang, Haiyan

2018-06-06

UiO-66 (UiO for University of Oslo), is a zirconium-based MOF with reverse shape selectivity, gives an alternative way to produce high purity n-heptane used for the manufacture of high-purity pharmaceuticals. Couple of studies have shown that UiO-66 gives a high selectivity on the separation of n-/iso-alkanes. However, the microporous structure of UiO-66 causes poor mass transport during the desorption process. In this work, hierarchical-pore UiO-66 (H-UiO-66) was synthesized and utilized as an adsorbent of n-heptane (nHEP) and methyl cyclohexane (MCH) for systematically studying the desorption process of n/iso-alkanes. A suite of physical methods, including XRD patterns verified the UiO-66 structures and HRTEM showed the existence of hierarchical pores. N2 adsorption-desorption isotherms further confirmed the size distribution of hierarchical pores in H-UiO-66. Of particular note, the MCH/nHEP selectivity of H-UiO-66 is similar with UiO-66 in the same adsorption conditions, the desorption process of nHEP/MCH from H-UiO-66 is dramatically enhanced, viz, the desorption rates for nHEP/MCH from H-UiO-66 is enhanced by 30%/23% as comparing to UiO-66 at most. Moreover, desorption activation energy (Ed) derived from temperature-programmed desorption (TPD) experiments indicate that the Ed for nHEP/MCH is lower on H-UiO-66, i.e., the Ed of MCH on H-UiO-66 is ~37% lower than that on UiO-66 at most, leading to a milder condition for the desorption process. The introduction of hierarchical structures will be applicable for the optimization of desorption process during separation on porous materials.

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.

Film growth, adsorption and desorption kinetics of indigo on SiO{sub 2}

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

Scherwitzl, Boris, E-mail: b.scherwitzl@tugraz.at; Resel, Roland; Winkler, Adolf

2014-05-14

Organic dyes have recently been discovered as promising semiconducting materials, attributable to the formation of hydrogen bonds. In this work, the adsorption and desorption behavior, as well as thin film growth was studied in detail for indigo molecules on silicon dioxide with different substrate treatments. The material was evaporated onto the substrate by means of physical vapor deposition under ultra-high vacuum conditions and was subsequently studied by Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy, X-Ray Diffraction, and Atomic Force Microscopy. TDS revealed initially adsorbed molecules to be strongly bonded on a sputter cleaned surface. After further deposition a formation ofmore » dimers is suggested, which de-stabilizes the bonding mechanism to the substrate and leads to a weakly bonded adsorbate. The dimers are highly mobile on the surface until they get incorporated into energetically favourable three-dimensional islands in a dewetting process. The stronger bonding of molecules within those islands could be shown by a higher desorption temperature. On a carbon contaminated surface no strongly bonded molecules appeared initially, weakly bonded monomers rather rearrange into islands at a surface coverage that is equivalent to one third of a monolayer of flat-lying molecules. The sticking coefficient was found to be unity on both substrates. The desorption energies from carbon covered silicon dioxide calculated to 1.67 ± 0.05 eV for multilayer desorption from the islands and 0.84 ± 0.05 eV for monolayer desorption. Corresponding values for desorption from a sputter cleaned surface are 1.53 ± 0.05 eV for multilayer and 0.83 ± 0.05 eV for monolayer desorption.« less

Study of CeO2 Modified AlNi Mixed Pillared Clays Supported Palladium Catalysts for Benzene Adsorption/Desorption-Catalytic Combustion

PubMed Central

Li, Jingrong; Yang, Peng; Qi, Chenze

2017-01-01

A new functional AlNi-pillared clays (AlNi-PILC) with a large surface area and pore volume was synthesized. The performance of adsorption/desorption-catalytic combustion over CeO2-modified Pd/AlNi-PILC catalysts was also studied. The results showed that the d001-value and specific surface area (SBET) of AlNi-PILC reached 2.11 nm and 374.8 m2/g, respectively. The large SBET and the d001-value improved the high capacity for benzene adsorption. Also, the strong interaction between PdCe mixed oxides and AlNi-PILC led to the high dispersion of PdO and CeO2 on the support, which was responsible for the high catalytic performance. Especially, 0.2% Pd/12.5% Ce/AlNi-PILC presented high performance for benzene combustion at 240 °C and high CO2 selectivity. Also, the combustion temperatures were lower compared to the desorption temperatures, which demonstrated that it could accomplish benzene combustion during the desorption process. Furthermore, its activity did not decrease after continuous reaction for 1000 h in dry air, and it also displayed good resistance to water and the chlorinated compound, making it a promising catalytic material for the elimination of volatile organic compounds. PMID:28809809

Temperature-programmed desorption study of NO reactions on rutile TiO2(110)-1×1

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

Kim, Boseong; Dohnálek, Zdenek; Szanyi, János

2016-10-01

Systematic temperature-programmed desorption (TPD) studies of NO adsorption and reactions on rutile TiO2(110)-1×1 surface reveal several distinct reaction channels in a temperature range of 50 – 500 K. NO readily reacts on TiO2(110) to form N2O which desorbs between 50 and 200 K (LT N2O channels), which leaves the TiO2 surface populated with adsorbed oxygen atoms (Oa) as a byproduct of N2O formation. In addition, we observe simultaneous desorption peaks of NO and N2O at 270 K (HT1 N2O) and 400 K (HT2 N2O), respectively, both of which are attributed to reaction-limited processes. No N-derived reaction product desorbs from TiO2(110)more » surface above 500 K or higher, while the surface may be populated with Oa’s and oxidized products such as NO2 and NO3. The adsorbate-free TiO2 surface with oxygen vacancies can be regenerated by prolonged annealing at 850 K or higher. Detailed analysis of the three N2O desorption yields reveals that the surface species for the HT channels are likely to be various forms of NO dimers.« less

Temperature-programmed desorption study of NO reactions on rutile TiO 2(110)-1×1

DOE PAGES

Kim, Boseong; Dohnalek, Zdenek; Szanyi, Janos; ...

2016-02-24

In this study, systematic temperature-programmed desorption (TPD) studies of NO adsorption and reactions on rutile TiO 2(110)-1 × 1 surface reveal several distinct reaction channels in a temperature range of 50–500 K. NO readily reacts on TiO 2(110) to form N 2O, which desorbs between 50 and 200 K (LT N 2O channels), which leaves the TiO 2 surface populated with adsorbed oxygen atoms (O a) as a by-product of N 2O formation. In addition, we observe simultaneous desorption peaks of NO and N 2O at 270 K (HT1 N 2O) and 400 K (HT2 N 2O), respectively, both ofmore » which are attributed to reaction-limited processes. No N-derived reaction product desorbs from TiO 2(110) surface above 500 K or higher, while the surface may be populated with Oa's and oxidized products such as NO 2 and NO 3. The adsorbate-free TiO 2 surface with oxygen vacancies can be regenerated by prolonged annealing at 850 K or higher. Detailed analysis of the three N 2O desorption yields reveals that the surface species for the HT channels are likely to be various forms of NO dimers.« less

Concurrent separation of CO2 and H2O from air by a temperature-vacuum swing adsorption/desorption cycle.

PubMed

Wurzbacher, Jan Andre; Gebald, Christoph; Piatkowski, Nicolas; Steinfeld, Aldo

2012-08-21

A temperature-vacuum swing (TVS) cyclic process is applied to an amine-functionalized nanofibrilated cellulose sorbent to concurrently extract CO(2) and water vapor from ambient air. The promoting effect of the relative humidity on the CO(2) capture capacity and on the amount of coadsorbed water is quantified. The measured specific CO(2) capacities range from 0.32 to 0.65 mmol/g, and the corresponding specific H(2)O capacities range from 0.87 to 4.76 mmol/g for adsorption temperatures varying between 10 and 30 °C and relative humidities varying between 20 and 80%. Desorption of CO(2) is achieved at 95 °C and 50 mbar(abs) without dilution by a purge gas, yielding a purity exceeding 94.4%. Sorbent stability and a closed mass balance for both H(2)O and CO(2) are demonstrated for ten consecutive adsorption-desorption cycles. The specific energy requirements of the TVS process based on the measured H(2)O and CO(2) capacities are estimated to be 12.5 kJ/mol(CO2) of mechanical (pumping) work and between 493 and 640 kJ/mol(CO2) of heat at below 100 °C, depending on the air relative humidity. For a targeted CO(2) capacity of 2 mmol/g, the heat requirement would be reduced to between 272 and 530 kJ/mol(CO2), depending strongly on the amount of coadsorbed water.

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.

Adsorption-desorption reactions of selenium (VI) in tropical cultivated and uncultivated soils under Cerrado biome.

PubMed

Lessa, J H L; Araujo, A M; Silva, G N T; Guilherme, L R G; Lopes, G

2016-12-01

Soil management may affect selenium (Se) adsorption capacity. This study investigated adsorption and desorption of Se (VI) in selected Brazilian soils from the Cerrado biome, an area of ever increasing importance for agriculture expansion in Brazil. Soil samples were collected from cultivated and uncultivated soils, comprising clayed and sandy soils. Following chemical and mineralogical characterization, soil samples were subjected to Se adsorption and desorption tests. Adsorption was evaluated after a 72-h reaction with increasing concentrations of Se (0-2000 μg L -1 ) added as Na 2 SeO 4 in a NaCl electrolyte solution (pH 5.5; ionic strength 15 mmol L -1 ). Desorption, as well as distribution coefficients (K d ) for selenate were also assessed. Soil management affected Se adsorption capacity, i.e., Se adsorbed amounts were higher for uncultivated soils, when compared to cultivated ones. Such results were also supported by data of K d and maximum adsorption capacity of Se. This fact was attributed mainly to the presence of greater amounts of competing anions, especially phosphate, in cultivated soils, due to fertilizer application. Phosphate may compete with selenate for adsorption sites, decreasing Se retention. For the same group of soils (cultivated and uncultivated), Se adsorption was greater in the clayed soils compared to sandy ones. Our results support the idea that adding Se (VI) to the soil is a good strategy to increase Se levels in food crops (agronomic biofortification), especially when crops are grown in soils that have been cultivated over the time due to their low Se adsorption capacity (high Se availability). Copyright © 2016 Elsevier Ltd. All rights reserved.

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.

Role of organic matter on boron adsorption-desorption hysteresis of soils

USDA-ARS?s Scientific Manuscript database

In this study we evaluated the boron (B) adsorption/desorption reaction in six soils and examined the extent to which organic matter content, as well as incubation time affected B release. Six soils varying in initial pH, clay content, and were selected for the study. Adsorption experiments were c...

The effect of chars and their water extractable organic carbon (WEOC) fractions on atrazine adsorption-desorption processes

NASA Astrophysics Data System (ADS)

Cavoski, I.; Jablonowski, N.; Burauel, P.; Miano, T.

2012-04-01

Chars are carbonaceous material produced from different type of biomass by pyrolysis. They are known as highly effective adsorbents for atrazine therefore limiting its degradation and its diffusion into the aqueous phase. The aim of the present work is to study the effects of different chars and char's derived WEOC on atrazine sorption-desorption processes. The five chars been used in this study derived from: 1) fast pyrolysis from hard wood (FP1); 2) flash pyrolysis from soft wood (FP2); 3) slow pyrolysis from deciduous wood (CC); 4) gasification from deciduous wood (GC) and 5) the market, purchased as activated charcoal standard (AC). Short-term batch equilibration tests were conducted to assess the sorption-desorption behavior of 14C-labeled atrazine on the chars, with a special focus on the desorption behavior using successive dilution method with six consecutive desorption step. Chars and their WEOC were physically and chemically characterized. Results demonstrate that biomass and pyrolysis process used to produce chars affect their physical and chemical properties, and atrazine adsorption-desorption behavior. Atrazine desorption resulted from the positive and competitive interactions between WEOC and chars surfaces. WEOC pool play important role in atrazine adsorption-desorption behavior. FP1 and FP2 with higher concentration of WEOC showed higher desorption rates, whereas GC, CC and AC with insignificant WEOC concentration strongly adsorb atrazine with low desorption rates. According to our results, when high WEOC pools chars are concerned, an increase in atrazine desorption can be observed but further studies would help in confirming the present results.

Comparison between different adsorption-desorption kinetics schemes in two dimensional lattice gas

NASA Astrophysics Data System (ADS)

Huespe, V. J.; Belardinelli, R. E.; Pereyra, V. D.; Manzi, S. J.

2017-12-01

Monte Carlo simulation is used to study the adsorption-desorption kinetics in the framework of the kinetic lattice-gas model. Three schemes of the so-called hard dynamics and five schemes of the so called soft dynamics were used for this purpose. It is observed that for the hard dynamic schemes, the equilibrium and non-equilibrium observable, such as adsorption isotherms, sticking coefficients, and thermal desorption spectra, have a normal or physical sustainable behavior. While for the soft dynamics schemes, with the exception of the transition state theory, the equilibrium and non-equilibrium observables have several problems.

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.

Physisorption and desorption of H2, HD and D2 on amorphous solid water ice. Effect on mixing isotopologue on statistical population of adsorption sites.

PubMed

Amiaud, Lionel; Fillion, Jean-Hugues; Dulieu, François; Momeni, Anouchah; Lemaire, Jean-Louis

2015-11-28

We study the adsorption and desorption of three isotopologues of molecular hydrogen mixed on 10 ML of porous amorphous water ice (ASW) deposited at 10 K. Thermally programmed desorption (TPD) of H2, D2 and HD adsorbed at 10 K have been performed with different mixings. Various coverages of H2, HD and D2 have been explored and a model taking into account all species adsorbed on the surface is presented in detail. The model we propose allows to extract the parameters required to fully reproduce the desorption of H2, HD and D2 for various coverages and mixtures in the sub-monolayer regime. The model is based on a statistical description of the process in a grand-canonical ensemble where adsorbed molecules are described following a Fermi-Dirac distribution.

Theoretical and experimental studies of hydrogen adsorption and desorption on Ir surfaces

DOE PAGES

Kaghazchi, Payam; Jacob, Timo; Chen, Wenhua; ...

2013-06-03

Here, we report adsorption and desorption of hydrogen on planar Ir(210) and faceted Ir(210), consisting of nanoscale {311} and (110) facets, by means of temperature programmed desorption (TPD) and density functional theory (DFT) in combination with the ab initio atomistic thermodynamics approach. TPD spectra show that only one H 2 peak is seen from planar Ir(210) at all coverages whereas a single H 2 peak is observed at around 440 K (F1) at fractional monolayer (ML) coverage and an additional H 2 peak appears at around 360 K (F2) at 1 ML coverage on faceted Ir(210), implying structure sensitivity inmore » recombination and desorption of hydrogen on faceted Ir(210) versus planar Ir(210), but no evidence is found for size effects in recombination and desorption of hydrogen on faceted Ir(210) for average facet sizes of 5-14 nm. Calculations indicate that H prefers to bind at the two-fold short-bridge sites of the Ir surfaces. In addition, we studied the stability of the Ir surfaces in the presence of hydrogen at different H coverages through surface free energy plots as a function of the chemical potential, which is also converted to a temperature scale. Moreover, the calculations revealed the origin of the two TPD peaks of H 2 from faceted Ir(210): F1 from desorption of H 2 on {311} facets while F2 from desorption of H 2 on (110) facets.« less

Desorption Kinetics of Ar, Kr, Xe, N2, O2, CO, Methane, Ethane, and Propane from Graphene and Amorphous Solid Water Surfaces.

PubMed

Smith, R Scott; May, R Alan; Kay, Bruce D

2016-03-03

The desorption kinetics for Ar, Kr, Xe, N2, O2, CO, methane, ethane, and propane from graphene-covered Pt(111) and amorphous solid water (ASW) surfaces are investigated using temperature-programmed desorption (TPD). The TPD spectra for all of the adsorbates from graphene have well-resolved first, second, third, and multilayer desorption peaks. The alignment of the leading edges is consistent the zero-order desorption for all of the adsorbates. An Arrhenius analysis is used to obtain desorption energies and prefactors for desorption from graphene for all of the adsorbates. In contrast, the leading desorption edges for the adsorbates from ASW do not align (for coverages < 2 ML). The nonalignment of TPD leading edges suggests that there are multiple desorption binding sites on the ASW surface. Inversion analysis is used to obtain the coverage dependent desorption energies and prefactors for desorption from ASW for all of the adsorbates.

Investigation of molecule-adsorption kinetics by a pulsed laser desorption technique

NASA Astrophysics Data System (ADS)

Varakin, V. N.; Lozovskii, A. D.; Panesh, A. M.; Simonov, A. P.

1987-02-01

The laser thermal desorption technique is used to measure the adsorption kinetics of SO2 and CO molecules on stainless steel with the aim of investigating the initial stage of oxidation of the steel by adsorbed CO molecules. Attention is given to the dependence of the rate of establishment of the equilibrium concentration of adsorbed molecules on SO2-gas pressure; CO adsorption kinetics on stainless steel at a gas pressure of 9 x 10 to the -8th torr; and the dependence of the concentration of adsorbed CO molecules on exposure in the gas at a pressure of 9 x 10 to the -8th torr under irradiation by laser pulses with repetition periods of 1-2, 2-4, 3-6, and 4-8 min.

Biodegradation of persistent organics can overcome adsorption-desorption hysteresis in biological activated carbon systems.

PubMed

Abromaitis, V; Racys, V; van der Marel, P; Meulepas, R J W

2016-04-01

In Biological Activated Carbon (BAC) systems, persistent organic pollutants can be removed through a combination of adsorption, desorption and biodegradation. These processes might be affected by the presence of other organics, especially by the more abundant easily-biodegradable organics, like acetate. In this research these relations are quantified for the removal of the persistent pharmaceutical metoprolol. Acetate did not affect the adsorption and desorption of metoprolol, but it did greatly enhance the metoprolol biodegradation. At least part of the BAC biomass growing on acetate was also able to metabolise metoprolol, although metoprolol was only converted after the acetate was depleted. The presence of easily-degradable organics like acetate in the feeding water is therefore beneficial for the removal of metoprolol in BAC systems. The isotherms obtained from metoprolol adsorption and desorption experiments showed that BAC systems are subject to hysteresis; for AC bioregeneration to take place the microbial biomass has to reduce the concentration at the AC-biomass interface 2.7 times compared to the concentration at which the carbon was being loaded. However, given the threshold concentration of the MET degrading microorganisms (<0.08 μg/L) versus the average influent concentration (1.3 μg/L), bioregeneration is feasible. Copyright © 2016 Elsevier Ltd. All rights reserved.

Desorption Kinetics of Ar, Kr, Xe, N2, O2, CO, Methane, Ethane, and Propane from Graphene and Amorphous Solid Water Surfaces

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

Smith, R. Scott; May, Robert A.; Kay, Bruce D.

2016-03-03

The desorption kinetics for Ar, Kr, Xe, N2, O2, CO, methane, ethane, and propane from grapheme covered Pt(111) and amorphous solid water (ASW) surfaces are investigated using temperature programmed desorption (TPD). The TPD spectra for all of the adsorbates from graphene have well-resolved first, second, third, and multi- layer desorption peaks. The alignment of the leading edges is consistent the zero-order desorption for all of the adsorbates. An Arrhenius analysis is used to obtain desorption energies and prefactors for desorption from graphene for all of the adsorbates. In contrast, the leading desorption edges for the adsorbates from ASW do notmore » align (for coverages < 2 ML). The non-alignment of TPD leading edges suggests that there are multiple desorption binding sites on the ASW surface. Inversion analysis is used to obtain the coverage dependent desorption energies and prefactors for desorption from ASW for all of the adsorbates.« less

Characterization of adsorption and desorption of lawn herbicide siduron in heavy metal contaminated soils.

PubMed

Jiang, Rong; Wang, Meie; Chen, Weiping

2018-08-01

Siduron is a widely used herbicide in urban lawn and has been frequently detected in urban and suburban surface water. However, characteristics of its environmental behavior in soil are seldom reported. The combined pollution of heavy metals, especially for Cu, Pb, Cd, Zn and siduron would be common because of the widely existence of heavy metal pollution in urban soils. In this study, four soils with similar physicochemical properties but different levels of preexisting heavy metals were selected to investigate the adsorption and successive desorption of siduron using batch experiments. The results revealed a low sorption of siduron to all the tested soils. The organic carbon normalized distribution coefficient (K oc ) of siduron in the studied soils ranged from 117 to 137 L kg -1 and was not significantly correlated to heavy metal levels. No apparent desorption hysteresis was observed with the hysteresis index (HI) ranging from 0.921 to 1.11. More than 50% of the sorbed siduron was readily released into soil solution. Results suggested that siduron was highly mobile and bioavailable in the studied soils. Significant correlation was found between adsorption/desorption parameters and soil organic carbon (SOC) in four soils. soil organic matter was thus considered as the dominant factor determining the adsorption and desorption of siduron in soils. Different from most of reported studies conducted by laboratory-amended soils, the influence of preexisting heavy metals on the adsorption-desorption of siduron was not significant in this work. Copyright © 2018 Elsevier Ltd. All rights reserved.

pH profile of the adsorption of nucleotides onto montmorillonite. II - Adsorption and desorption of 5-prime-AMP in iron-calcium montmorillonite systems

NASA Technical Reports Server (NTRS)

Banin, A.; Lawless, J. G.; Mazzurco, J.; Church, F. M.; Margulies, L.; Orenberg, J. B.

1985-01-01

The interaction of 5-prime-AMP with montmorillonite saturated with various ratios of two metals found ubiquitously on the surface of earth, that is, iron and calcium, is investigated. Adsorption and desorption of the nucleotide were studied in the pH range of 2-12 at three levels of addition: 0.080, 0.268 and 0.803 mmole 5-prime-AMP per gram of clay. Two desorption stages were employed - H2O wash and NaOH extraction (pH = 12.0). 5-prime-AMP was preferentially adsorbed on the Fe-containing clays relative to the Ca clay. The nucleotide was fully recovered by the two desorption stages, mostly by the NaOH extraction. The evidence at hand indicates that 5-prime-AMP reaction with clay is affected by electrostatic interactions involving both attraction and repulsion forces. Some specific adsorption, possibly the result of covalent bonding and complex formation with the adsorbed ion, cannot be ruled out for iron but does not appear to operate for calcium. Changes in pH cause varying degrees of attaction and repulsion of 5-prime-AMP and may have been operating on the primitive earth, leading to sequences of adsorption and release of this biomolecule.

ADSORPTION, DESORPTION AND OXIDATION OF ARSENIC AFFECTED BY CLAY MINERALS AND AGING PROCESS

EPA Science Inventory

Adsorption/desorption and oxidation/reduction of arsenic at clay surfaces are very important to the natural attenuation of arsenic in the subsurface environment. Although numerous studies have concluded that iron oxides have high affinities for the adsorption of As(V), very litt...

Experimental study on removals of SO2 and NO(x) using adsorption of activated carbon/microwave desorption.

PubMed

Ma, Shuang-Chen; Yao, Juan-Juan; Gao, Li; Ma, Xiao-Ying; Zhao, Yi

2012-09-01

Experimental studies on desulfurization and denitrification were carried out using activated carbon irradiated by microwave. The influences of the concentrations of nitric oxide (NO) and sulfur dioxide (SO2), the flue gas coexisting compositions, on adsorption properties of activated carbon and efficiencies of desulfurization and denitrification were investigated. The results show that adsorption capacity and removal efficiency of NO decrease with the increasing of SO2 concentrations in flue gas; adsorption capacity of NO increases slightly first and drops to 12.79 mg/g, and desulfurization efficiency descends with the increasing SO2 concentrations. Adsorption capacity of SO2 declines with the increasing of O2 content in flue gas, but adsorption capacity of NO increases, and removal efficiencies of NO and SO2 could be larger than 99%. Adsorption capacity of NO declines with the increase of moisture in the flue gas, but adsorption capacity of SO2 increases and removal efficiencies of NO and SO2 would be relatively stable. Adsorption capacities of both NO and SO2 decrease with the increasing of CO2 content; efficiencies of desulfurization and denitrification augment at the beginning stage, then start to fall when CO2 content exceeds 12.4%. The mechanisms of this process are also discussed. The prominent SO2 and NOx treatment techniques in power plants are wet flue gas desulfurization (FGD) and the catalytic decomposition method like selective catalytic reduction (SCR) or nonselective catalytic reduction (NSCR). However, these processes would have some difficulties in commercial application due to their high investment, requirement of expensive catalysts and large-scale equipment, and so on. A simple SO2 and NOx reduction utilizing decomposition by microwave energy method can be used. The pollutants control of flue gas in the power plants by the method of microwave-induced decomposition using adsorption of activated carbon/microwave desorption can meet the

Adsorption, desorption and fractionation of As(V) on untreated and mussel shell-treated granitic material

NASA Astrophysics Data System (ADS)

Seco-Reigosa, N.; Cutillas-Barreiro, L.; Nóvoa-Muñoz, J. C.; Arias-Estévez, M.; Álvarez-Rodríguez, E.; Fernández-Sanjurjo, M. J.; Núñez-Delgado, A.

2014-12-01

As(V) adsorption and desorption were studied on granitic material, coarse and fine mussel shell, and granitic material amended with 12 and 24 t ha-1 fine shell, investigating the effect of different As(V) concentrations and different pH, as well as the fractions where the adsorbed As(V) was retained. As(V) adsorption was higher on fine than on coarse shell. Mussel shell amendment increased As(V) adsorption on granitic material. Adsorption data corresponding to the un-amended and shell-amended granitic material were satisfactory fitted to the Langmuir and Freundlich models. Desorption was always < 19% when the highest As(V) concentration (100 mg L-1) was added. Regarding the effect of pH, the granitic material showed its highest adsorption (66%) at pH < 6, and it was lower as pH increased. Fine shell presented notable adsorption in the whole pH range between 6 and 12, with a maximum of 83%. The shell-amended granitic material showed high As(V) adsorption, with a maximum (99%) at pH near 8, but decreasing as pH increased. Desorption varying pH was always < 26%. In the granitic material, desorption increased progressively when pH increased from 4 to 6, contrary to what happened to mussel shell. Regarding the fractionation of the adsorbed As(V), most of it was in the soluble fraction (weakly bound). Globally, the granitic material did not show high As(V) retention capacity, which implies risks of water pollution and transfer to the food chain; however, the mussel shell amendment increased As(V) retention, making this practice recommendable.

Phosphorus Adsorption and Desorption Properties of Minnesota Basalt Lunar Simulant and Lunar Glass Simulant

NASA Technical Reports Server (NTRS)

Sutter, Brad; Hossner, Lloyd R.; Ming, Douglas W.

1996-01-01

Phosphorus (P) adsorption and desorption characteristics of Minnesota Basalt Lunar Simulant (MBLS) and Lunar Glass Simulant (LGS) were evaluated. Results of P interactions with lunar simulants indicated that mineral and glass components adsorbed between 50 and 70% of the applied P and that between 85 and 100% of the applied P was desorbed. The Extended Freundlich equation best described the adsorption data (r(sup 2) = 0.92), whereas the Raven/Hossner equation best described the desorption data ((r(sup 2) = 0.97). Kinetic desorption results indicated that MBLS and LGS released most of their P within 15 h. The expanded Elovich equation fit the data best at shorter times while t/Q(sub DT) equation had a better fit at longer times. These results indicate that P does not strongly adsorb to the two simulants and that any P that was adsorbed was readily desorbed in the presence of anion exchange resin. This work suggests that multiple small applications of P (10-20 mg P/kg) should be added to the simulants to ensure adequate solution P for plant uptake and efficient use of P fertilizer.

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.

Electrostatic Interactions Influence Protein Adsorption (but Not Desorption) at the Silica-Aqueous Interface.

PubMed

McUmber, Aaron C; Randolph, Theodore W; Schwartz, Daniel K

2015-07-02

High-throughput single-molecule total internal reflection fluorescence microscopy was used to investigate the effects of pH and ionic strength on bovine serum albumin (BSA) adsorption, desorption, and interfacial diffusion at the aqueous-fused silica interface. At high pH and low ionic strength, negatively charged BSA adsorbed slowly to the negatively charged fused silica surface. At low pH and low ionic strength, where BSA was positively charged, or in solutions at higher ionic strength, adsorption was approximately 1000 times faster. Interestingly, neither surface residence times nor the interfacial diffusion coefficients of BSA were influenced by pH or ionic strength. These findings suggested that adsorption kinetics were dominated by energy barriers associated with electrostatic interactions, but once adsorbed, protein-surface interactions were dominated by short-range nonelectrostatic interactions. These results highlight the ability of single-molecule techniques to isolate elementary processes (e.g., adsorption and desorption) under steady-state conditions, which would be impossible to measure using ensemble-averaging methods.

Kinetics of Cation and Oxyanion Adsorption and Desorption on Ferrihydrite: Roles of Ferrihydrite Binding Sites and a Unified Model

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

Tian, Lei; Shi, Zhenqing; Lu, Yang

Understanding the kinetics of toxic ion reactions with ferrihydrite is crucial for predicting the dynamic behavior of contaminants in soil environments. In this study, the kinetics of As(V), Cr(VI), Cu, and Pb adsorption and desorption on ferrihydrite were investigated with a combination of laboratory macroscopic experiments, microscopic investigation and mechanistic modeling. The rates of As(V), Cr(VI), Cu, and Pb adsorption and desorption on ferrihydrite, as systematically studied using a stirred-flow method, was highly dependent on the reaction pH and metal concentrations and varied significantly among four metals. Spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) showed, at sub-nano scales, all fourmore » metals were distributed within the ferrihydrite particle aggregates homogeneously after adsorption reactions, with no evidence of surface diffusion-controlled processes. Based on experimental results, we developed a unifying kinetics model for both cation and oxyanion adsorption/desorption on ferrihydrite based on the mechanistic-based equilibrium model CD-MUSIC. Overall, the model described the kinetic results well, and we quantitatively demonstrated how the equilibrium properties of the cation and oxyanion binding to various ferrihydrite sites affected the adsorption and desorption rates. Our results provided a unifying quantitative modeling method for the kinetics of both cation and oxyanion adsorption/desorption on iron minerals.« less

Kinetics of Cation and Oxyanion Adsorption and Desorption on Ferrihydrite: Roles of Ferrihydrite Binding Sites and a Unified Model.

PubMed

Tian, Lei; Shi, Zhenqing; Lu, Yang; Dohnalkova, Alice C; Lin, Zhang; Dang, Zhi

2017-09-19

Quantitative understanding the kinetics of toxic ion reactions with various heterogeneous ferrihydrite binding sites is crucial for accurately predicting the dynamic behavior of contaminants in environment. In this study, kinetics of As(V), Cr(VI), Cu(II), and Pb(II) adsorption and desorption on ferrihydrite was studied using a stirred-flow method, which showed that metal adsorption/desorption kinetics was highly dependent on the reaction conditions and varied significantly among four metals. High resolution scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy showed that all four metals were distributed within the ferrihydrite aggregates homogeneously after adsorption reactions. Based on the equilibrium model CD-MUSIC, we developed a novel unified kinetics model applicable for both cation and oxyanion adsorption and desorption on ferrihydrite, which is able to account for the heterogeneity of ferrihydrite binding sites, different binding properties of cations and oxyanions, and variations of solution chemistry. The model described the kinetic results well. We quantitatively elucidated how the equilibrium properties of the cation and oxyanion binding to various ferrihydrite sites and the formation of various surface complexes controlled the adsorption and desorption kinetics at different reaction conditions and time scales. Our study provided a unified modeling method for the kinetics of ion adsorption/desorption on ferrihydrite.

Titanium-incorporated organic–inorganic hybrid adsorbent for improved CO{sub 2} adsorption performance

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

Zhang, Xiaoyun; Qin, Hongyan; Zhang, Sisi

2015-02-15

Highlights: • Titanium-incorporated organic–inorganic hybrid adsorbent was prepared. • The incorporation of Ti to the adsorbent showed significant effect. • The sorbent shows high CO{sub 2} capture capacity both in pure and diluted CO{sub 2} at RT. • The sorbent exhibits a high recycling stability after 15 cycling runs. - Abstract: The CO{sub 2} adsorption performance of acrylonitrile (AN)–tetraethylenepentamine (TEPA) adduct (hereafter referred to as TN) impregnated adsorbent was greatly enhanced by introduction of Titanium atom into the silica matrix. The adsorbents were characterized by X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), transmission electron microscopy (TEM), N{sub 2} adsorption/desorption, UV–vismore » spectroscopy, Fourier transform infrared (FTIR) spectroscopy. The adsorption experiments together with the physicochemical characterization demonstrated that these adsorbents containing an optimal amount of Titanium (Ti/Si ≈ 0.1) remarkably reinforced the CO{sub 2} adsorption capacity and recycling stability. The highest CO{sub 2} uptakes reached 4.65 and 1.80 mmol CO{sub 2}/g adsorbent at 25 °C under 90% CO{sub 2} (CO{sub 2}/N{sub 2}, 90:10 V/V) and 1% CO{sub 2} (CO{sub 2}/N{sub 2}, 1:99 V/V) conditions for sample Ti(0.1)-DMS-TN, respectively. Repeated adsorption/desorption cycles revealed that the Ti-incorporated adsorbent showed only a tiny decrease in adsorption capacity (1.778 mmol CO{sub 2}/g adsorbent after 15 cycles, decreased by 0.95%), significantly enhanced the adsorbent recycling stability.« less

Biosorption and desorption of Cd2+ from wastewater by dehydrated shreds of Cladophora fascicularis

NASA Astrophysics Data System (ADS)

Deng, Liping; Zhu, Xiaobin; Su, Yingying; Su, Hua; Wang, Xinting

2008-02-01

The adsorption and desorption of algae Cladophora fascicularis and their relation with initial Cd2+ concentration, initial pH, and co-existing ions were studied. Adsorption equilibrium and biosorption kinetics were established from batch experiments. The adsorption equilibrium was adequately described by the Langmuir isotherm, and biosorption kinetics was in pseudo-second order model. The experiment on co-existing ions showed that the biosorption capacity of biomass decreased with an increasing concentration of competing ions. Desorption experiments indicated that EDTA was efficient desorbent for recovery from Cd2+. With high capacities of metal biosorption and desorption, the biomass of Cladophora fascicularis is promising as a cost-effective biosorbent for the removal of Cd2+ from wastewater.

Adsorption and desorption of glyphosate in Mollisols and Ultisols soils of Argentina

NASA Astrophysics Data System (ADS)

Gomez Ortiz, Ana Maria; Okada, Elena; Costa, Jose Luis; Bedmar, Francisco

2017-04-01

Glyphosate is the most used pesticide in Argentina. About 200 million liters of its commercial product are annually applied, representing nearly 60% of the total amount of the commercialized pesticides. This massive use is attributed to the widespread adoption of no-till management combined with genetically modified crops that are glyphosate resistant (e.g. soybean, maize, cotton). In this way, the use of glyphosate has created great concern regarding the potential negative impacts it may have in the environment. The adsorption-desorption process of glyphosate was studied in three Argentinean soils (two Mollisols and one Ultisol) with contrasting properties: organic carbon (1.3-3.4%), clay (14.7-78.5%), pH (5.4-6.3), P Bray (7.6-29.6 mg/kg), total Fe (0.81-8.4%), and Al3+ (0.11-0.69 meq/100 g). Glyphosate adsorption isotherms were modeled using the Freundlich equation to estimate the adsorption coefficient (Kf). In general, glyphosate adsorption was high and the Kf values varied from 115.6 to 1612 (R2 = 0.94-0.99). The main factors controlling adsorption were clay content, total Fe, Al3+, P Bray and soil pH. Decreased hysteresis desorption was found in one of the Mollisols soils with the lowest contents of Al3+, Fe, and clay, as well as high pH and P Bray. In that soil, 12.2% of glyphosate was desorbed after three washing steps indicating a higher potential environmental risk. Results of this study contribute to the knowledge about glyphosate retention in soils and allows the identification of behavior patterns of this extensively applied herbicide in different edaphic scenarios. This is of major importance for the development of decision making tools and criteria to reduce the potential negative impacts on soil and groundwater resources.

Effect of land use pattern change from paddy soil to vegetable soil on the adsorption-desorption of cadmium by soil aggregates.

PubMed

Zhang, Qiu; Li, Zhongwu; Huang, Bin; Luo, Ninglin; Long, Lingzhi; Huang, Mei; Zhai, Xiuqing; Zeng, Guangming

2017-01-01

The influence of land use change from paddy soil to vegetable soil on the adsorption-desorption behavior of Cd in soil aggregates and the variation in soil properties were investigated. The vegetable soil was characterized by lower pH, organic matter content, cation exchange capacity (CEC), free iron oxides, manganese oxides, and catalase activity and higher urease activity compared with the paddy soil. In the isothermal adsorption and desorption experiments, the adsorption characteristics of Cd of the two soils could be well described by Langmuir and Freundlich equations. The adsorption capacity of vegetable soil decreased 22.72 %, and the desorption rate increased 35 % with respect to paddy soil. Therefore, conversion from paddy to vegetable field can reduce the adsorption ability to Cd of the soil to a certain extent. Both the two soils reached the maximum adsorption capacity and the minimum desorption rate in the <0.002-mm faction. The adsorption capacity of Cd in paddy and vegetable soils exhibited great reliance on the content of CEC. Desorption rate was negatively correlated with the four indicators: organic matter, CEC, free iron oxides, and manganese oxides, and specific adsorption was primarily controlled by soil organic matter and manganese oxides.

In-situ regeneration of activated carbon with electric potential swing desorption (EPSD) for the H2S removal from biogas.

PubMed

Farooq, M; Almustapha, M N; Imran, M; Saeed, M A; Andresen, John M

2018-02-01

In-situ regeneration of a granular activated carbon was conducted for the first time using electric potential swing desorption (EPSD) with potentials up to 30 V. The EPSD system was compared against a standard non-potential system using a fixed-bed reactor with a bed of 10 g of activated carbon treating a gas mixture with 10,000 ppm H 2 S. Breakthrough times, adsorption desorption volume, capacities, effect of regeneration and desorption kinetics were investigated. The analysis showed that desorption of H 2 S using the new EPSD system was 3 times quicker compared with the no potential system. Hence, physical adsorption using EPSD over activated carbon is efficient, safe and environmental friendly and could be used for the in-situ regeneration of granular activated carbon without using a PSA and/or TSA system. Additionally, adsorption and desorption cycles can be obtained with a classical two column system, which could lead towards a more efficient and economic biogas to biomethane process. Copyright © 2017 Elsevier Ltd. All rights reserved.

Kinetics of protein adsorption/desorption mediated by pH-responsive polymer layer

NASA Astrophysics Data System (ADS)

Su, Xiao-Hang; Lei, Qun-Li; Ren, Chun-Lai

2015-11-01

We propose a new way of regulating protein adsorption by using a pH-responsive polymer. According to the theoretical results obtained from the molecular theory and kinetic approaches, both thermodynamics and kinetics of protein adsorption are verified to be well controlled by the solution pH. The kinetics and the amount of adsorbed proteins at equilibrium are greatly increased when the solution environment changes from acid to neutral. The reason is that the increased pH promotes the dissociation of the weak polyelectrolyte, resulting in more charged monomers and more stretched chains. Thus the steric repulsion within the polymer layer is weakened, which effectively lowers the barrier felt by the protein during the process of adsorption. Interestingly, we also find that the kinetics of protein desorption is almost unchanged with the variation of pH. It is because although the barrier formed by the polymer layer changes along with the change of pH, the potential at contact with the surface varies equally. Our results may provide useful insights into controllable protein adsorption/desorption in practical applications. Project supported by the National Natural Science Foundation of China (Grant Nos. 21274062, 11474155, and 91027040).

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.

Overcoming double-step CO2 adsorption and minimizing water co-adsorption in bulky diamine-appended variants of Mg2(dobpdc)† †Electronic supplementary information (ESI) available: Additional experimental details, and full characterization (powder X-ray diffraction, infrared spectra, diamine loadings, dry N2 decomposition profiles, and CO2 adsorption data) for all new adsorbents. CCDC 1577354. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc04266c

PubMed Central

Milner, Phillip J.; Martell, Jeffrey D.; Siegelman, Rebecca L.; Gygi, David; Weston, Simon C.

2017-01-01

Alkyldiamine-functionalized variants of the metal–organic framework Mg2(dobpdc) (dobpdc4– = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate) are promising for CO2 capture applications owing to their unique step-shaped CO2 adsorption profiles resulting from the cooperative formation of ammonium carbamate chains. Primary,secondary (1°,2°) alkylethylenediamine-appended variants are of particular interest because of their low CO2 step pressures (≤1 mbar at 40 °C), minimal adsorption/desorption hysteresis, and high thermal stability. Herein, we demonstrate that further increasing the size of the alkyl group on the secondary amine affords enhanced stability against diamine volatilization, but also leads to surprising two-step CO2 adsorption/desorption profiles. This two-step behavior likely results from steric interactions between ammonium carbamate chains induced by the asymmetrical hexagonal pores of Mg2(dobpdc) and leads to decreased CO2 working capacities and increased water co-adsorption under humid conditions. To minimize these unfavorable steric interactions, we targeted diamine-appended variants of the isoreticularly expanded framework Mg2(dotpdc) (dotpdc4– = 4,4′′-dioxido-[1,1′:4′,1′′-terphenyl]-3,3′′-dicarboxylate), reported here for the first time, and the previously reported isomeric framework Mg-IRMOF-74-II or Mg2(pc-dobpdc) (pc-dobpdc4– = 3,3′-dioxidobiphenyl-4,4′-dicarboxylate, pc = para-carboxylate), which, in contrast to Mg2(dobpdc), possesses uniformally hexagonal pores. By minimizing the steric interactions between ammonium carbamate chains, these frameworks enable a single CO2 adsorption/desorption step in all cases, as well as decreased water co-adsorption and increased stability to diamine loss. Functionalization of Mg2(pc-dobpdc) with large diamines such as N-(n-heptyl)ethylenediamine results in optimal adsorption behavior, highlighting the advantage of tuning both the pore shape and the diamine size for the development

Adsorption and desorption characteristics of gradient distributed Bragg reflector porous silicon layers.

PubMed

Um, Sungyong; Lee, Sung Gi; Woo, Hee-Gweon; Cho, Sungdong; Sohn, Honglae

2013-01-01

Adsorption and desorption characteristics of gradient distributed Bragg reflector (DBR) porous silicon (PSi) were investigated under the exposure of organic vapors. Gradient DBR PSi whose average pore size decreased as the lateral distance from the Pt electrode increased was generated by using an asymmetric etching configuration. The reflection resonances were measured as a function of lateral distance from a point closest to the plate Pt electrode to a position on the silicon surface. Two types of gradient DBR PSi (H- and HO-terminated gradient DBR PSi) were used in this study. The detection of volatile organic compounds (VOCs) using the gradient DBR PSi had been achieved. When the vapor of VOCs condensed in the nanopores, the gradient DBR PSi modified with hydrophobic and hydrophilic functionality exhibited different pore adsorption and desorption characteristics.

Extension lifetime for dye-sensitized solar cells through multiple dye adsorption/desorption process

NASA Astrophysics Data System (ADS)

Chiang, Yi-Fang; Chen, Ruei-Tang; Shen, Po-Shen; Chen, Peter; Guo, Tzung-Fang

2013-03-01

In this study, we propose a novel concept of extending the lifetime of dye-sensitized solar cells (DSCs) and reducing the costs of re-conditioning DSCs by recycling the FTO/TiO2 substrates. The photovoltaic performances of DSCs using substrates with various cycles of dye uptake and rinse off history are tested. The results show that dye adsorption and Voc are significantly increased under multiple dye adsorption/desorption process and resulted in the improvement of power conversion efficiency. Moreover, the dyeing kinetics is faster after multiple recycling processes, which is favorable for the industrial application. With surface analysis and charge transport characteristics, we also demonstrate the optimal functionality of TiO2/dye interface for the improved Voc and efficiency. The results confirm that the improved performances are due to increased dye loading and dense packing of dye molecules. Our results are beneficial for the understanding on the extension of DSCs lifetime after long-term operation in the application of DSC modules. This approach may also be applied in the replacement of newly synthesized photosensitizes to the active cells.

Phosphate removal from aqueous solution using iron oxides: Adsorption, desorption and regeneration characteristics.

PubMed

Ajmal, Zeeshan; Muhmood, Atif; Usman, Muhammad; Kizito, Simon; Lu, Jiaxin; Dong, Renjie; Wu, Shubiao

2018-05-24

Dynamics of phosphate (PO 4 3- ) adsorption, desorption and regeneration characteristics of three lab-synthesized iron oxides, ferrihydrite (F), goethite (G), and magnetite (M) were evaluated in this study. Batch experiments were conducted to evaluate the impact of several adsorption parameters including adsorbent dosage, reaction time, temperature, pH, and ionic strength. The results showed that PO 4 3- adsorption increased with reaction time and temperature while it decreased with an increase in solution pH. Adsorption isotherm data exhibited good agreement with the Freundlich and Langmuir model with maximum monolayer adsorption capacities of 66.6 mg·g -1 (F), 57.8 mg·g -1 (M), and 50.5 mg·g -1 (G). A thermodynamics evaluation produced ΔG < 0, ΔH > 0, and ΔS > 0, demonstrating that PO 4 3- adsorption onto tested minerals is endothermic, spontaneous, and disordered. The PO 4 3- removal mostly occurred via electrostatic attraction between the sorbate and sorbent surfaces. Moreover, the PO 4 3- sorption was reversible and could be desorbed at varying rates in both neutral and alkaline environments. The good desorption capacity has practical benefits for potential regeneration and re-use of the saturated particles in wastewater treatment systems. Copyright © 2018 Elsevier Inc. All rights reserved.

Effect of soil pH and organic matter on the adsorption and desorption of pentachlorophenol.

PubMed

Chien, Shui-Wen Chang; Chen, Shou-Hung; Li, Chi-Jui

2018-02-01

Various properties of soil affect the partition of organic contaminants within, and conversely, the properties of the organic contaminants also directly affect their partition behavior in soil. Therefore, understanding the effects of various properties of soil on the partition of organic contaminants favors subsequent assessment and provides soil remediation methods for policymakers. This study selected pentachlorophenol (PCP), a common hydrophobic ionizable organic compound in contaminated sites worldwide, as the target contaminant. The effects of pH, organic matter, and the combination of both, on PCP adsorption/desorption behavior in soil were investigated. Phosphoric acid and potassium hydroxide were used as buffer solutions to modify the soil pH by the batch and column extraction methods. A common retail organic fertilizer and fulvic acid were selected as additives to manipulate the soil organic content. Modifying the pH of the soil samples revealed that acidic soil exhibited a greater PCP adsorption rate than alkaline soil. The amount of PCP desorption increased regardless of pH of the in situ contaminated soil. The adsorption of PCP increased with increasing amount of organic additive. However, addition of fulvic acid yielded different results compared to the addition of organic fertilizer. Specifically, the organic fertilizer could not compete with the in situ contaminated soil in PCP adsorption, whereas fulvic acids increased the PCP dissolution to facilitate adsorbing contaminant adsorption. The combined effect of pH modification and organic matter addition provides additional PCP adsorption sites; therefore, adding the organic fertilizer to decrease the soil pH elevated the PCP adsorption rates of the laterite, alluvial, and in situ contaminated soil samples. The study results revealed that both pH and organic matter content are crucial to PCP adsorption/desorption in soil. Therefore, the effects of soil pH and organic matter should be considered in

Hydrogen adsorption and desorption with 3D silicon nanotube-network and film-network structures: Monte Carlo simulations

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

Li, Ming; Kang, Zhan, E-mail: zhankang@dlut.edu.cn; Huang, Xiaobo

2015-08-28

Hydrogen is clean, sustainable, and renewable, thus is viewed as promising energy carrier. However, its industrial utilization is greatly hampered by the lack of effective hydrogen storage and release method. Carbon nanotubes (CNTs) were viewed as one of the potential hydrogen containers, but it has been proved that pure CNTs cannot attain the desired target capacity of hydrogen storage. In this paper, we present a numerical study on the material-driven and structure-driven hydrogen adsorption of 3D silicon networks and propose a deformation-driven hydrogen desorption approach based on molecular simulations. Two types of 3D nanostructures, silicon nanotube-network (Si-NN) and silicon film-networkmore » (Si-FN), are first investigated in terms of hydrogen adsorption and desorption capacity with grand canonical Monte Carlo simulations. It is revealed that the hydrogen storage capacity is determined by the lithium doping ratio and geometrical parameters, and the maximum hydrogen uptake can be achieved by a 3D nanostructure with optimal configuration and doping ratio obtained through design optimization technique. For hydrogen desorption, a mechanical-deformation-driven-hydrogen-release approach is proposed. Compared with temperature/pressure change-induced hydrogen desorption method, the proposed approach is so effective that nearly complete hydrogen desorption can be achieved by Si-FN nanostructures under sufficient compression but without structural failure observed. The approach is also reversible since the mechanical deformation in Si-FN nanostructures can be elastically recovered, which suggests a good reusability. This study may shed light on the mechanism of hydrogen adsorption and desorption and thus provide useful guidance toward engineering design of microstructural hydrogen (or other gas) adsorption materials.« less

Hydrogen adsorption and desorption with 3D silicon nanotube-network and film-network structures: Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Li, Ming; Huang, Xiaobo; Kang, Zhan

2015-08-01

Hydrogen is clean, sustainable, and renewable, thus is viewed as promising energy carrier. However, its industrial utilization is greatly hampered by the lack of effective hydrogen storage and release method. Carbon nanotubes (CNTs) were viewed as one of the potential hydrogen containers, but it has been proved that pure CNTs cannot attain the desired target capacity of hydrogen storage. In this paper, we present a numerical study on the material-driven and structure-driven hydrogen adsorption of 3D silicon networks and propose a deformation-driven hydrogen desorption approach based on molecular simulations. Two types of 3D nanostructures, silicon nanotube-network (Si-NN) and silicon film-network (Si-FN), are first investigated in terms of hydrogen adsorption and desorption capacity with grand canonical Monte Carlo simulations. It is revealed that the hydrogen storage capacity is determined by the lithium doping ratio and geometrical parameters, and the maximum hydrogen uptake can be achieved by a 3D nanostructure with optimal configuration and doping ratio obtained through design optimization technique. For hydrogen desorption, a mechanical-deformation-driven-hydrogen-release approach is proposed. Compared with temperature/pressure change-induced hydrogen desorption method, the proposed approach is so effective that nearly complete hydrogen desorption can be achieved by Si-FN nanostructures under sufficient compression but without structural failure observed. The approach is also reversible since the mechanical deformation in Si-FN nanostructures can be elastically recovered, which suggests a good reusability. This study may shed light on the mechanism of hydrogen adsorption and desorption and thus provide useful guidance toward engineering design of microstructural hydrogen (or other gas) adsorption materials.

Adsorption/desorption of linear alkylbenzenesulfonate (LAS) and azoproteins by/from activated sludge flocs.

PubMed

Conrad, A; Cadoret, A; Corteel, P; Leroy, P; Block, J-C

2006-01-01

Our study investigated the adsorption/desorption by/from activated sludge flocs, dispersed in river water or in diluted wastewater, of organic compounds (C(11)-LAS, azoalbumin and azocasein) at concentrations relevant to environmental conditions. Activated sludge flocs, used as a model of biological aggregates, are characterized by a very heterogeneous matrix able to sorb the three organic compounds tested at 4 degrees C. The adsorbed amount of C(11)-LAS by activated sludge flocs was higher than that of azocasein or azoalbumin, as shown by the Freundlich parameters (K(ads)=8.6+/-1.7, 1.6+/-0.3 and 0.3+/-0.1 micromol(1-1/n)g(-1)l(1/n) for C(11)-LAS, azocasein and azoalbumin, respectively; n=3 sludges). C(11)-LAS sorption from activated sludge appeared to be partially reversible in river water, while a marked hysteresis phenomenon was observed for azocasein and azoalbumin, implying a low degree of reversibility in their exchange between activated sludge and river water. It has also been displayed that the conductivity variation of bulk water (comprised between 214 and 838 microS cm(-1)) exerted no dramatic effect on the C(11)-LAS desorption from activated sludge flocs, while a little effect of it on azocasein desorption was observed. Thus, biological aggregates as activated sludge flocs can serve as an intermediate carrier for C(11)-LAS, while it represents a sink for proteins.

Perchlorate adsorption and desorption on activated carbon and anion exchange resin.

PubMed

Yoon, In-Ho; Meng, Xiaoguang; Wang, Chao; Kim, Kyoung-Woong; Bang, Sunbaek; Choe, Eunyoung; Lippincott, Lee

2009-05-15

The mechanisms of perchlorate adsorption on activated carbon (AC) and anion exchange resin (SR-7 resin) were investigated using Raman, FTIR, and zeta potential analyses. Batch adsorption and desorption results demonstrated that the adsorption of perchlorate by AC and SR-7 resin was reversible. The reversibility of perchlorate adsorption by the resin was also proved by column regeneration test. Solution pH significantly affected perchlorate adsorption and the zeta potential of AC, while it did not influence perchlorate adsorption and the zeta potential of resin. Zeta potential measurements showed that perchlorate was adsorbed on the negatively charged AC surface. Raman spectra indicated the adsorption resulted in an obvious position shift of the perchlorate peak, suggesting that perchlorate was associated with functional groups on AC at neutral pH through interactions stronger than electrostatic interaction. The adsorbed perchlorate on the resin exhibited a Raman peak at similar position as the aqueous perchlorate, indicating that perchlorate was adsorbed on the resin through electrostatic attraction between the anion and positively charged surface sites.

Ti, Al and N adatom adsorption and diffusion on rocksalt cubic AlN (001) and (011) surfaces: Ab initio calculations

NASA Astrophysics Data System (ADS)

Mastail, C.; David, M.; Nita, F.; Michel, A.; Abadias, G.

2017-11-01

We use ab initio calculations to determine the preferred nucleation sites and migration pathways of Ti, Al and N adatoms on cubic NaCl-structure (B1) AlN surfaces, primary inputs towards a further thin film growth modelling of the TiAlN alloy system. The potential energy landscape is mapped out for both metallic species and nitrogen adatoms for two different AlN surface orientations, (001) and (110), using density functional theory. For all species, the adsorption energies on AlN(011) surface are larger than on AlN(001) surface. Ti and Al adatom adsorption energy landscapes determined at 0 K by ab initio show similar features, with stable binding sites being located in, or near, epitaxial surface positions, with Ti showing a stronger binding compared to Al. In direct contrast, N adatoms (Nad) adsorb preferentially close to N surface atoms (Nsurf), thus forming strong N2-molecule-like bonds on both AlN(001) and (011). Similar to N2 desorption mechanisms reported for other cubic transition metal nitride surfaces, in the present work we investigate Nad/Nsurf desorption on AlN(011) using a drag calculation method. We show that this process leaves a Nsurf vacancy accompanied with a spontaneous surface reconstruction, highlighting faceting formation during growth.

Experimental and Numerical Investigation of Two Dimensional CO2 Adsorption/Desorption in Packed Sorption Beds under Non-Ideal Flows

NASA Technical Reports Server (NTRS)

Mohamadinejad, H.; Knox, J. C.; Smith, J. E.; Croomes, Scott (Technical Monitor)

2001-01-01

The experimental results of CO2 adsorption and desorption in a packed column indicated that the concentration wave front at the center of the packed column differs from those which are close to the wall of column filled with adsorbent material even though the ratio of column diameter to the particle size is greater than 20. The comparison of the experimental results with one dimensional model of packed column shows that in order to simulate the average breakthrough in a packed column a two dimensional (radial and axial) model of packed column is needed. In this paper the mathematical model of a non-slip flow through a packed column with 2 inches in diameter and 18 inches in length filled with 5A zeolite pellets is presented. The comparison of experimental results of CO2 absorption and desorption for the mixed and central breakthrough of the packed column with numerical results is also presented.

Adsorption and desorption for dynamics transport of hexavalent chromium Cr(Ⅵ) in soil column

NASA Astrophysics Data System (ADS)

Tong, J.

2017-12-01

Batch experiments have been carried out to study the adsorption of heavy metals in soils, and the migration and transformation of hexavalent chromium Cr(Ⅵ) in the soil of a vegetable base were studied by dynamic adsorption and desorption soil column experiments. The aim of this study was to investigate the effect of initial concentration and pH value on the adsorption process of Cr(Ⅵ). Breakthrough curve were used to evaluate the capacity of Cr(Ⅵ) adsorption in soil columns. The results show that the higher the initial concentration, the worse the adsorption capacity of Cr(Ⅵ). The adsorption of Cr(Ⅵ) was strongly sensitive to pH value. The capacity of Cr(Ⅵ) adsorption is maximized at very low pH value. This may be due to changes in pH that cause a series of complex reactions in Cr(Ⅵ). In a strongly acidic environment, the reaction of Cr(Ⅵ) with hydrogen ions is accompanied by the formation of Cr3+, which reacts with the soil free iron-aluminum oxide to produce hydroxide in the soil. The results of the desorption experiments indicate that Cr(Ⅵ) is more likely to leach from this soil, but if the eluent is strong acid solution, the leaching process will be slow and persistent. The program CXTFIT was used to fit the breakthrough curve to estimate parameters. The results of the calculation of the dispersion coefficient (D) can be obtained by this program. The two-site model fit the breakthrough curve data of Cr(Ⅵ) well, and the parameters calculated by CXTFIT can be used to explain the behavior of Cr(Ⅵ) migration and transformation in soil columns. When pH=2, the retardation factor (R) reach at 79.71 while the value of the R is generally around 10 in other experiments. The partitioning coefficient β shows that more than half of the adsorption sites are rate-limited in this adsorption process and non-equilibrium effects the Cr(Ⅵ) transport process in this soil.

Oxygen isotopic fractionation of O₂ during adsorption and desorption processes using molecular sieve at low temperatures.

PubMed

Ahn, Insu; Kusakabe, Minoru; Lee, Jong Ik

2014-06-15

Cryogenic trapping using molecular sieves is commonly used to collect O2 extracted from silicates for (17)O/(16)O and (18)O/(16)O analyses. However, gases which interfere with (17)O/(16)O analysis, notably NF3, are also trapped and their removal is essential for accurate direct measurement of the (17)O/(16)O ratio. It is also necessary to identify and quantify any isotopic fractionation associated with the use of cryogenic trapping using molecular sieves. The oxygen isotopic compositions of O2 before and after desorption from, and adsorption onto, 13X and 5A molecular sieves (MS13X and MS5A) at 0°C, -78°C, -114°C, and -130°C were measured in order to determine the oxygen isotopic fractionation at these temperatures. We also investigated whether isotopic fractionation occurred when O2 gas was transferred sequentially into a second cold finger, also containing molecular sieve. It was confirmed that significant oxygen isotopic fractionation occurs between the gaseous O2 and that adsorbed onto molecular sieve, if desorption and adsorption are incomplete. As the fraction of released or untrapped O2 becomes smaller with decreasing trapping temperature (from 0 to -130°C), the isotopic fractionation becomes larger. Approximately half of the total adsorbed O2 is released from the molecular sieve during desorption at -114°C, which is the temperature recommended for separation from NF3 (retained on the molecular sieve), and this will interfere with (17)O/(16)O measurements. The use of a single cold finger should be avoided, because partial desorption is accompanied by oxygen isotopic fractionation, thereby resulting in inaccurate isotopic data. The use of a dual cold finger arrangement is recommended because, as we have confirmed, the transfer of O2 from the first trap to the second is almost 100%. However, even under these conditions, a small isotopic fractionation (0.18 ± 0.05‰ in δ(17)O values and 0.26 ± 0.06‰ in δ(18)O values) occurred, with O2 in

Effect of biochar amendment on tylosin adsorption-desorption and transport in two different soils

Treesearch

Chang Yoon Jeong; Jim J. Wang; Syam K. Dodla; Thomas L. Eberhardt; Les Groom

2012-01-01

The role of biochar as a soil amendment on the adsorption¨C desorption and transport of tylosin, a macrolide class of veterinary antibiotic, is little known. In this study, batch and column experiments were conducted to investigate the adsorption kinetics and transport of tylosin in forest and agricultural corn field soils amended with hardwood and softwood biochars....

Desorption kinetics of {H}/{Mo(211) }

NASA Astrophysics Data System (ADS)

Lopinski, G. P.; Prybyla, J. A.; Estrup, P. J.

1994-08-01

The desorption kinetics of the {H}/{Mo(211) } chemisorption system were studied by thermal desorption and measurement of adsorption isobars. Analysis of the steady-state measurements permits the independent determination of the desorption energy ( Ed) and prefactor ( v). These quantities are found to depend strongly on coverage, with ( Ed) varying continuously from 145 {kJ}/{mol} at low coverage to 65 {kJ}/{mol} near saturation. Three regions of hydrogen adsorption are clearly indicated by the isobars as well as the thermal desorption traces. These regions can be correlated with structural changes observed previously with HREELS and LEED. The coverage dependence of the kinetic parameters is attributed to hydrogen-induced local distortions of the substrate structure. By relating the desorption energy to the isosteric heat the partial molar entropy is also extracted from the data and indicates localized adsorption as well as significant adsorbate-induced changes in the substrate degrees of freedom.

Adsorption properties and photocatalytic activity of TiO2/activated carbon fiber composite

NASA Astrophysics Data System (ADS)

Yao, Shuhua; Song, Shuangping; Shi, Zhongliang

2014-06-01

Photocatalysts of titanium dioxide (TiO2) and TiO2/activated carbon fiber (TiO2/ACF) composite were prepared by sol-gel method, followed by calcining the pure TiO2 sols and the TiO2/ACF sols at 500°C for 2 h in a N2 atmosphere, respectively. These photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N2 adsorption-desorption isotherms measurement. Batch experiments were conducted to study the adsorption property of TiO2/ACF composite using methylene blue as adsorbate. The adsorption data obtained from different batch experiments were analyzed using pseudo-second-order kinetic model, the experimental data can be adequately described by the pseudo-second-order equation. The photodecomposition behavior of TiO2/ACF was investigated in aqueous solution using methylene blue as target pollutant. It was found that methylene blue could be removed rapidly from water by TiO2/ACF, the photocatalytic decomposition was obviously improved when the photocatalyst was used. Kinetics analysis revealed that the photocatalytic decomposition reaction can be described well by a first-order rate equation.

Desorption of isopropyl alcohol from adsorbent with non-thermal plasma.

PubMed

Shiau, Chen Han; Pan, Kuan Lun; Yu, Sheng Jen; Yan, Shaw Yi; Chang, Moo Been

2017-09-01

Effective desorption of isopropyl alcohol (IPA) from adsorbents with non-thermal plasma is developed. In this system, IPA is effectively adsorbed with activated carbon while dielectric barrier discharge is applied to replace the conventional thermal desorption process to achieve good desorption efficiency, making the treatment equipment smaller in size. Various adsorbents including molecular sieves and activated carbon are evaluated for IPA adsorption capacity. The results indicate that BAC has the highest IPA adsorption capacity (280.31 mg IPA/g) under the operating conditions of room temperature, IPA of 400 ppm, and residence time of 0.283 s among 5 adsorbents tested. For the plasma desorption process, the IPA selectivity of 89% is achieved with BAC as N 2 is used as desorbing gas. In addition, as air or O 2 is used as desorbing gas, the IPA desorption concentration is reduced, because air and O 2 plasmas generate active species to oxidize IPA to form acetone, CO 2 , and even CO. Furthermore, the results of the durability test indicate that the amount of IPA desorbed increases with increasing desorption times and plasma desorption process has a higher energy efficiency if compared with thermal desorption. Overall, this study indicates that non-thermal plasma is a viable process for removing VOCs to regenerate adsorbent.

The Effect of Pluronic 123 Surfactant concentration on The N2 Adsorption Capacity of Mesoporous Silica SBA-15: Dubinin-Astakhov Adsorption Isotherm Analysis

NASA Astrophysics Data System (ADS)

Dhaneswara, Donanta; Siti Agustina, A. A. A.; Dewantoro Adhy, P.; Delayori, Farhan; Fajar Fatriansyah, Jaka

2018-04-01

Mesoporous SBA-15 has been successfully synthesized at various concentration of Pluronic 123 surfactant (7mM, 50 mM, 54 mM, 60 mM and 66 mM) and the effect of these various concentrations on the N2 adsorption capacity has been investigated. The adsorption analysis was conducted using Dubinin-Astakhov isotherm model for multilayer adsorption phenomenon. It was found that etryat low concentration of Pluronic 123, the system exhibits type I adsorption isotherm while at high concentration, the system exhibits type IV adsorption with H1 hysteresis curve which indicates the existence of pores with cylindrical geometry, relatively uniform pore size and possibility of pore network effects. It also was found that, by using D-A isotherm model fitting, at 60 mM concentration of Pluronic 123, SBA-15 has the highest adsorption capacity which stands at 421 cm3/gram.

Characterization of polysulfone and polysulfone/vanillin microcapsules by 1H NMR spectroscopy, solid-state 13C CP/MAS-NMR spectroscopy, and N2 adsorption-desorption analyses.

PubMed

Peña, Brisa; de Ménorval, Louis-Charles; Garcia-Valls, Ricard; Gumí, Tània

2011-11-01

Textile detergent and softener industries have incorporated perfume microencapsulation technology to improve their products. Perfume encapsulation allows perfume protection until use and provides a long-lasting fragrance release. But, certain industrial microcapsules show low encapsulation capacity and low material stability. Polysulfone capsules have been already proposed to solve these drawbacks. Among them, PSf/Vanillin capsules were considered as a desirable system. They present both good material stability and high encapsulation capacity. However, several factors such as the final location of the perfume in the polymeric matrix, the aggregation state that it has in the capsule and its interaction with the capsule components have not been studied yet. These factors can provide vast information about the capsule performance and its improvement. With the aim to characterize these parameters, the physical and chemical properties of PSf/Vanillin capsules have been investigated by nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and N(2) adsorption-desorption measurements. AFM micrograph and N(2) isotherms confirm that the presence of vanillin modify the physical structure of PSf/Vanillin microcapsules as it is trapped in the capsule porosity. NMR results show that vanillin is present in solid state in PSf/Vanillin microcapsules.

Adsorption of CO2 on amine-functionalised MCM-41: experimental and theoretical studies.

PubMed

dos Santos, Thiago Custódio; Bourrelly, Sandrine; Llewellyn, Philip L; Carneiro, José Walkimar de M; Ronconi, Célia Machado

2015-04-28

Adsorption of CO2 on MCM-41 functionalised with [3-(2-aminoethylamino)propyl]trimethoxysilane (MCM-41-N2), N(1)-(3-trimethoxysilylpropyl)diethylenetriamine (MCM-41-N3), 4-aminopyridine (MCM-41-aminopyridine), 4-(methylamino)pyridine (MCM-41-methylaminopyridine) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (MCM-41-guanidine) was investigated. The amine-functionalised materials were characterised by (29)Si and (13)C solid-state nuclear magnetic resonance, N2 adsorption/desorption isotherms, X-ray diffraction and transmission electron microscopy. CO2 adsorption at 1.0 bar and 30 °C showed that the amount of CO2 (nads/mmol g(-1)) adsorbed on MCM-41-N2 and MCM-41-N3 is approximately twice the amount adsorbed on MCM-41. For MCM-41-aminopyridine, MCM-41-methylaminopyridine and MCM-41-guanidine, the CO2 adsorption capacity was smaller than that of MCM-41 at the same conditions. The proton affinity (computed with wB97x-D/6-311++G(d,p)) of the secondary amino groups is higher than that of the primary amino groups; however, the relative stabilities of the primary and secondary carbamates are similar. The differential heat of adsorption decreases as the number of secondary amino groups increases.

Ultrafast adsorption and selective desorption of aqueous aromatic dyes by graphene sheets modified by graphene quantum dots

NASA Astrophysics Data System (ADS)

Ying, Yulong; He, Peng; Ding, Guqiao; Peng, Xinsheng

2016-06-01

Graphene modified by graphene quantum dots (GQDs) has been employed to remove toxic organic dyes. An excellent removal capacity (497 mg g-1) and record-breaking adsorption rate (475 mg g-1 min-1 at 20 °C) were demonstrated for Rhodamine B. The enhancement in performance by nearly a factor of three compared to that of graphene was ascribed to the greatly increased accessible surface area of graphene in aqueous solution as well as the increase in surface charges with the modification with GQDs. Besides, this unique adsorption behavior of the modified graphene was expanded to other typical toxic aqueous aromatic dyes such as Evans Blue, Methyl Orange, Malachite Green and Rose Bengal. What is more, a unique desorption behavior of dyes was first observed when employing different solvents, which enabled the GQD-modified graphene to be exploited for selective extraction of dyes and recycling of the adsorbent. The adsorption and desorption mechanism were further investigated. Combining high removal capacity, rapid adsorption kinetics, good recyclability and unique selective desorption, GQD-modified graphene has potential applications in both water purification and separation of aromatic dyes.

[Effects of selective cutting disturbance on soil phosphorus adsorption and desorption in a Korean pine and broad-leaved mixed forest in the Xiaoxing'an Mountains, China.

PubMed

Zhang, Xin; Gu, Hui Yan; Chen, Xiang Wei

2018-01-01

This study examined the characteristics of phosphorus (P) adsorption and desorption in surface soil (0-10 cm) of a secondary forest after selective cutting disturbance at three levels of intensity (low, medium, high) in order to reveal the effects of different disturbance intensities on soil P adsorption and desorption. Maximum adsorption amount (Q m ), adsorption intensity factor, maximum buffer capacity, maximum desorption amount, average desorption rate and readily desorptable phosphorus were measured. Q m in the focal forests was 1383.93-1833.34 mg·kg -1 , and Q m in forests with middle and high disturbance intensities was significantly higher than that in forests with low disturbance intensity and in primary forests. P adsorption intensity was 0.024-0.059 L·mg -1 , and forests with high and low disturbance intensities increased the P adsorption intensity significantly. The maximum buffer capacity varied from 35.68 to 97.97 L·kg -1 , with the highest value found in the forest with the highest disturbance intensity. Selective cutting significantly reduced the potential for phosphorus supply in the forest soils. The maximum desorption amount, average desorption rate and readily desorptable phosphorus content in the focal forests were 526.32-797.54 mg·kg -1 , 14.7%-25.5% and 1.79-5.41 mg·kg -1 , respectively, indicating that the ability of soil to release phosphorus significantly decreased with increasing disturbance intensity. Selective cutting changed the phosphorus adsorption and desorption characteristics by reducing the supply and release of soil phosphorus.

Low-Temperature Desorption of N2O from NO on Rutile TiO2(110)-1x1

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

Kim, Boseong; Li, Zhenjun; Kay, Bruce D.

2014-05-08

We find that NO dosed on rutile TiO2(110)-1×1 at substrate temperatures as low as 50 K readily reacts to produce N2O which desorbs promptly from the surface leaving an oxygen adatom behind. The desorption rate of N2O reaches a maximum value after 1 – 2 sec at an NO flux of 1.2 ×1014 NO/cm2∙sec and then decreases rapidly as the initially clean, reduced TiO2(110) surface with ~5% oxygen vacancies (VO’s) becomes covered with oxygen adatoms and unreacted NO. The maximum desorption rate is also found to increase as the substrate temperature is raised up to about 100 K. Interestingly, themore » N2O desorption during the low-temperature (LT) NO dose is strongly suppressed when molecular oxygen is predosed, whereas it persists on the surface with VO’s passivated by surface hydroxyls. Our results show that the surface charge, not the VO sites, plays a dominant role in the LT N2O desorption induced by a facile NO reduction at such low temperatures.« less

Adsorption, desorption and mobility of metsulfuron-methyl in soils of the oil palm agroecosystem in Malaysia.

PubMed

Ismail, B S; Ooi, K E

2012-05-01

Laboratory experiments were conducted to evaluate adsorption, desorption and mobility of metsulfuron-methyl in soils of the oil palm agroecosystem consisting of the Bernam, Selangor, Rengam and Bongor soil series. The lowest adsorption of metsulfuron-methyl occurred in the Bongor soil (0.366 ml g(-1)), and the highest in the Bemam soil (2.837 ml g(-1). The K(fads) (Freundlich) values of metsulfuron-methyl were 0.366, 0.560, 1.570 and 2.837 ml g(-1) in Bongor, Rengam, Selangor and Bemam soil, respectively. The highest K(fdes) value of metsulfuron-methyl, observed in the Bemam soil, was 2.563 indicating low desorption 0.280 (relatively strong retention). In contrast, the lowest K(fdes) value of 0.564 was observed for the Bongor soil, which had the lowest organic matter (1.43%) and clay content (13.2%). Soil organic matter and clay content were the main factors affecting the adsorption of metsulfuron-methyl. The results of the soil column leaching studies suggested that metsulfuron-methyl has a moderate potential for mobility in the Bernam and Bongor soil series with 19.3% and 39%, respectively for rainfall at 200 mm. However, since metsulfuron-methyl is applied at a very low rate (the maximum field application rate used was 30 g ha(-1)) and is susceptible to biodegradation, the potential forground water contamination is low.

ε-Polylysine-based thermo-responsive adsorbents for immunoglobulin adsorption-desorption under mild conditions.

PubMed

Maruyama, Masashi; Shibuya, Keisuke

2017-08-22

Thermo-responsive adsorbents for immunoglobulin G (IgG) employing ε-polylysine (EPL) as a polymer backbone were developed. The introduction of mercaptoethylpyridine (MEP) as an IgG-binding ligand and hydrophobization of side chains afforded thermo-responsive IgG adsorbents, whose thermo-responsive IgG desorption ratio was up to 88% (EPL/MEP derivative 3m). The changes in surface densities of active MEP groups, which are caused by thermal conformational changes of the adsorbents, play key roles for IgG desorption. Although a trade-off of IgG adsorption capacity and IgG desorption ratio was observed, the present study offers a novel molecular design for thermo-responsive adsorbents with high synthetic accessibility and potentially low toxicity.

Comparison of Adsorption/Desorption of Volatile Organic Compounds (VOCs) on Electrospun Nanofibers with Tenax TA for Potential Application in Sampling

PubMed Central

Chu, Lanling; Deng, Siwei; Zhao, Renshan; Deng, Jianjun; Kang, Xuejun

2016-01-01

The objective of this study was to compare the adsorption/desorption of target compounds on homemade electrospun nanofibers, polystyrene (PS) nanofibers, acrylic resin (AR) nanofibers and PS-AR composite nanofibers with Tenax TA. Ten volatile organic compounds (VOCs) were analyzed by preconcentration onto different sorbents followed by desorption (thermal and solvent orderly) and analysis by capillary gas chromatography. In comparison to Tenax TA, the electrospun nanofibers displayed a significant advantage in desorption efficiency and adsorption selectivity. Stability studies were conducted as a comparative experiment between PS-AR nanofibers and Tenax TA using toluene as the model compound. No stability problems were observed upon storage of toluene on both PS-AR nanofibers and Tenax TA over 60 hours period when maintained in an ultra-freezer (−80°C). The nanofibers provided slightly better stability for the adsorbed analytes than Tenax TA under other storage conditions. In addition, the nanofibers also provided slightly better precision than Tenax TA. The quantitative adsorption of PS-AR nanofibers exhibited a good linearity, as evidenced by the 0.988–0.999 range of regression coefficients (R). These results suggest that for VOCs sampling the electrospun nanofibers can be a potential ideal adsorbent. PMID:27776140

Characterizing particle-scale equilibrium adsorption and kinetics of uranium(VI) desorption from U-contaminated sediments

USGS Publications Warehouse

Stoliker, Deborah L.; Liu, Chongxuan; Kent, Douglas B.; Zachara, John M.

2013-01-01

Rates of U(VI) release from individual dry-sieved size fractions of a field-aggregated, field-contaminated composite sediment from the seasonally saturated lower vadose zone of the Hanford 300-Area were examined in flow-through reactors to maintain quasi-constant chemical conditions. The principal source of variability in equilibrium U(VI) adsorption properties of the various size fractions was the impact of variable chemistry on adsorption. This source of variability was represented using surface complexation models (SCMs) with different stoichiometric coefficients with respect to hydrogen ion and carbonate concentrations for the different size fractions. A reactive transport model incorporating equilibrium expressions for cation exchange and calcite dissolution, along with rate expressions for aerobic respiration and silica dissolution, described the temporal evolution of solute concentrations observed during the flow-through reactor experiments. Kinetic U(VI) desorption was well described using a multirate SCM with an assumed lognormal distribution for the mass-transfer rate coefficients. The estimated mean and standard deviation of the rate coefficients were the same for all <2 mm size fractions but differed for the 2–8 mm size fraction. Micropore volumes, assessed using t-plots to analyze N2 desorption data, were also the same for all dry-sieved <2 mm size fractions, indicating a link between micropore volumes and mass-transfer rate properties. Pore volumes for dry-sieved size fractions exceeded values for the corresponding wet-sieved fractions. We hypothesize that repeated field wetting and drying cycles lead to the formation of aggregates and/or coatings containing (micro)pore networks which provided an additional mass-transfer resistance over that associated with individual particles. The 2–8 mm fraction exhibited a larger average and standard deviation in the distribution of mass-transfer rate coefficients, possibly caused by the abundance of

CO adsorption on W(100) during temperature-programmed desorption: A combined density functional theory and kinetic Monte Carlo study

NASA Astrophysics Data System (ADS)

Albao, Marvin A.; Padama, Allan Abraham B.

2017-02-01

Using a combined density functional theory (DFT) and kinetic Monte Carlo (KMC) simulations, we study the adsorption at 800 K and subsequent desorption of CO on W(100) at higher temperatures. The resulting TPD profiles are known experimentally to exhibit three desorption peaks β1, β2, and β3 at 930 K, 1070 K, and 1375 K, respectively. Unlike more recent theoretical studies that propose that all three aforementioned peaks are molecularly rather than associatively desorbed, our KMC analyses are in support of the latter, since at 800 K dissociation is facile and that CO exists as dissociation fragments C and O. We show that these peaks arise from desorption from the same adsorption site but whose binding energy varies depending on local environment, that is, the presence of CO as well as dissociation fragments C and O nearby. Furthermore we show that several key parameters, such as desorption, dissociation and recombination barriers all play a key role in the TPD spectra-these parameter effectively controls not only the location of the TPD peaks but the shape and width of the desorption peaks as well. Moreover, our KMC simulations reveal that varying the heating rate shifts the peaks but leaves their shape intact.

Adsorption and Desorption of Cesium in Clay Minerals: Effects of Natural Organic Matter and pH

NASA Astrophysics Data System (ADS)

Yoon, Hongkyu; Ilgen, Anastasia; Mills, Melissa; Lee, Moo; Seol, Jeung Gun; Cho, Nam Chan; Kang, Hyungyu

2017-04-01

Cesium (Cs) released into the environment (e.g., Fukushima accident) poses significant environmental concerns and remediation challenges. A majority of Cs in the environment have remained within the surface soils due to the strong adsorption affinity of Cs towards clay minerals. Different clay minerals have different bonding sites, resulting in various adsorption mechanisms at nanometer scale. For example, the illite commonly has a basal spacing of 1.0 nm, but becomes wider to 1.4 nm once other cations exchange with K in the interlayer site. Cs adsorbs into these expanded wedged zone strongly, which can control its mobility in the environment. In addition, natural organic matter (NOM) in the surface soils can interact with clay minerals, which can modify the mechanisms of Cs adsorption on the clay minerals by blocking specific adsorption sites and/or providing Cs adsorption sites on NOM surface. In this work, three representative clay minerals (illite, vermiculite, montmorillonite) and humic acid (HA) are used to systematically investigate the adsorption and desorption behavior of Cs. We performed batch adsorption experiments over a range of Cs concentrations on three clay minerals with and without HA, followed by sequential desorption batch testing. We tested desorption efficiency as a function of initial adsorbed Cs concentration, HA content, sodium concentration, and pH. The sequential extraction results are compared to the structural changes in clay minerals, measured using extended X-ray absorption fine structure spectroscopy (EXAFS) and aberration-corrected (scanning) transmission electron microscopy (TEM) - energy dispersive X-ray spectroscopy (EDX). Hence, this work aims to identify the mechanisms of Cs fixation at the nanometer (or atomic-) scale as a function of the clay mineral properties (e.g. expandability, permanent surface charge) and varying organic matter content at different pH values and to enhance our atomic-scale mechanistic understanding of

Adsorption mechanism of different organic chemicals on fluorinated carbon nanotubes.

PubMed

Li, Hao; Zheng, Nan; Liang, Ni; Zhang, Di; Wu, Min; Pan, Bo

2016-07-01

Multi-walled carbon nanotubes (MC) were fluorinated by a solid-phase reaction method using polytetrafluoroethylene (PTFE). The surface alteration of carbon nanotubes after fluorination (MC-F) was confirmed based on surface elemental analysis, TEM and SEM. The incorporation of F on MC surface was discussed as F incorporation on carbon defects, replacement of carboxyl groups, as well as surface coating of PTFE. The adsorption performance and mechanisms of MC-F for five kinds of representative organic compounds: sulfamethoxazole (SMX), ofloxacin (OFL), norfloxacin (NOR), bisphenol a (BPA) and phenanthrene (PHE) were investigated. Although BET-N2 surface area of the investigated CNTs decreased after fluorination, the adsorption of all five chemicals increased. Because of the glassification of MC-F surface coating during BET-N2 surface area measurement, the accessible surface area of MC-F was underestimated. Desorption hysteresis was generally observed in all the sorption systems in this study, and the desorption hysteresis of MC-F were stronger than the pristine CNTs. The enhanced adsorption of MC-F may be attributed the pores generated on the coated PTFE and the dispersed CNT aggregates due to the increased electrostatic repulsion after fluorination. The rearrangement of the bundles or diffusion of the adsorbates in MC-F inner pores were the likely reason for the strong desorption hysteresis of MC-F. The butterfly structure of BPA resulted in its high sorption and strong desorption hysteresis. The exothermic sorption character of OFL on CNTs resulted in its strong desorption hysteresis. Copyright © 2016 Elsevier Ltd. All rights reserved.

Various causes behind the desorption hysteresis of carboxylic acids on mudstones.

PubMed

Rasamimanana, S; Lefèvre, G; Dagnelie, R V H

2017-02-01

Adsorption desorption is a key factor for leaching, migration and (bio)degradation of organic pollutants in soils and sediments. Desorption hysteresis of apolar organic compounds is known to be correlated with adsorption/diffusion into soil organic matter. This work focuses on the desorption hysteresis of polar organic compounds on a natural mudstone sample. Acetic, citric and ortho-phthalic acids displayed adsorption-desorption hysteresis on Callovo-Oxfordian mudstone. The non-reversible behaviours resulted from three different mechanisms. Adsorption and desorption kinetics were evaluated using 14C- and 3H-labelled tracers and an isotopic exchange method. The solid-liquid distribution ratio of acetate decreased using a NaN 3 bactericide, indicating a rapid bacterial consumption compared with negligible adsorption. The desorption hysteresis of phthalate was apparent and suppressed by the equilibration of renewal pore water with mudstone. This confirms the significant and reversible adsorption of phthalate. Finally, persistent desorption hysteresis was evidenced for citrate. In this case, a third mechanism should be considered, such as the incorporation of citrate in the solid or a chemical perturbation, leading to strong desorption resilience. The results highlighted the different pathways that polar organic pollutants might encounter in a similar environment. Data on phthalic acid is useful to predict the retarded transport of phthalate esters and amines degradation products in sediments. The behaviour of citric acid is representative of polydentate chelating agents used in ore and remediation industries. The impact of irreversible adsorption on solid/solution partitioning and transport deserves further investigation. Copyright © 2016 Elsevier Ltd. All rights reserved.

Angle-Dependent Atomic Force Microscopy Single-Chain Pulling of Adsorbed Macromolecules from Planar Surfaces Unveils the Signature of an Adsorption-Desorption Transition.

PubMed

Grebíková, Lucie; Whittington, Stuart G; Vancso, Julius G

2018-05-23

The adsorption-desorption behavior of polymer chains is at the heart of macromolecular surface science and technology. With the current developments in atomic force microscopy (AFM), it has now become possible to address the desorption problem from the perspective of a single macromolecule. Here, we report on desorption of single polymer chains on planar surfaces by AFM-based single molecule force spectroscopy (SMFS) as a function of the pulling angle with respect to the surface-normal direction. SMFS experiments were performed in water with various substrates using different polymers covalently attached to the AFM probe tip. End-grafting at the AFM tip was achieved by surface-initiated polymerization using initiator functionalized tips. We found that the desorption force increases with a decreasing pulling angle, i.e., an enhanced adhesion of the polymer chain was observed. The magnitude of the desorption force shows a weak angular dependence at pulling angles close to the surface normal. A significant increase of the force is observed at shallower pulling from a certain pulling angle. This behavior carries the signature of an adsorption-desorption transition. The angular dependence of the normalized desorption force exhibits a universal behavior. We compared and interpreted our results using theoretical predictions for single-chain adsorption-desorption transitions.

The effects of intra-particle concentration gradient on consecutive adsorption-desorption of oryzanol from rice bran oil in packed-column

NASA Astrophysics Data System (ADS)

Susanti, Ari Diana; Sediawan, Wahyudi Budi; Wirawan, Sang Kompiang; Budhijanto

2017-05-01

Utilization of valuable trace components in agriculture by product such as rice bran oil is interesting to be explored. Among the valuables, oryzanol, a healthy nutrition for cardiovascular prevention, is the most promising one. Literature studies suggest that adsorption-desorption is a prospective method for oryzanol isolation. Design of commercial scale adsorption-desorption system for oryzanol needs a quantitative description of the phenomena involved. In this study, quantitative modeling of the consecutive adsorption-desorption in packed column has been proposed and verified through experimental data. The offered model takes into account the intra-particle concentration gradient in the adsorbent particle. In this model, the rate of mass transfer from the bulk of the liquid to the surface of the adsorbent particle or vice versa is expressed by film theory. The mass transfer of oryzanol from the liquid in the pore of the particle to the adjacent pore surface is assumed to be instantaneous, so solid-liquid equilibrium on the surface of the pores is always attained. For simplicity, the adsorption equilibrium model applied was coefficient distribution approach. The values of the parameters implicated in the model were obtained by curve fitting to the experimental data. It verified that the model proposed works well to quantitatively describe the consecutive adsorption-desorption of oryzanol from rice bran oil in packed column.

[Preparation of Pb2+ imprinted acrylic acid-co-styrene and analysis of its adsorption properties by FAAS].

PubMed

Shawket, Abliz; Abdiryim, Supahun; Wang, Ji-De; Ismayil, Nurulla

2011-06-01

With lead ion template, acrylic acid as functional monomer, potassium persulfate as initiator, strytrene as framework monomer, lead ion imprinted polymers (Pb(II)-IIPs) were prepared using free emulsion polymerization method. The structure and morphology of the polymers were analyzed by UV-spectra, FTIR and scanning electron microscopy. The adsorption/ desorption and selectivity for Pb2+ were investigated by flame atomic absorption spectrometry (FAAS) as the detection means. The results show that compared with non-imprinted polymers(NIPs), the Pb(II)-IIPs had higher specific adsorption properties and selective recognition ability for Pb(II). The relative selectivity coefficient of Pb(II)-IIPs for Pb(II) was 6.25, 6.18, 6.25 and 6.38 in the presence of Cd(II), Cu(II), Mn(II) and Zn(II) interferences, respectively. The absorption rate was the best at the pH of adsorbent solution of 6, Adsorption rate reached 96% during the 2.5 h static adsorption time. Using 3.0 mol x L(-1) HCI as the best desorption solvent to desorb the adsorbents, the desorbtion rate reached 98%. Under the best adsorption conditions, the adsorption capacity of Pb(II)-IIPs for Pb(II) was found to be 40. mg x g(-1).

Insights into the Hydrothermal Stability of Triamine-Functionalized SBA-15 Silica for CO2 Adsorption.

PubMed

Jahandar Lashaki, Masoud; Ziaei-Azad, Hessam; Sayari, Abdelhamid

2017-10-23

The hydrothermal stability of triamine-grafted, large-pore SBA-15 CO 2 adsorbents was studied by using steam stripping. Following two 3 h cycles of steam regeneration, lower CO 2 uptakes, lower CO 2 /N ratios, and slower adsorption kinetics were observed relative to fresh samples, particularly at the lowest adsorption temperature (25 °C). CO 2 adsorption measurements for a selected sample exposed to 48 h of steam stripping depicted that after the initial loss during the first exposure to steam (3-6 h), the adsorptive properties stabilized. For higher adsorption temperatures (i.e., 50 and 75 °C), however, all adsorptive properties remained almost unchanged after steaming, indicating the significance of diffusional limitations. Thermogravimetric analysis and FTIR spectroscopy on grafted samples before and after steam stripping showed no amine leaching and no change in the chemical nature of the amine groups, respectively. Also, a six-cycle CO 2 adsorption/desorption experiment under dry conditions showed no thermal degradation. However, N 2 adsorption measurement at 77 K showed significant reductions in the BET surface area of the grafted samples following steaming. Based on the pore size distribution of calcined, grafted samples before and after steaming, it is proposed that exposure to steam restructured the grafted materials, causing mass transfer resistance. It is inferred that triamine-grafted, large-pore SBA-15 adsorbents are potential candidates for CO 2 capture at relatively high temperatures (50-75 °C; for example, flue gas) combined with steam regeneration. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Single-component and binary CO2 and H2O adsorption of amine-functionalized cellulose.

PubMed

Gebald, Christoph; Wurzbacher, Jan A; Borgschulte, Andreas; Zimmermann, Tanja; Steinfeld, Aldo

2014-02-18

A fundamental analysis of single-component and binary CO2 and H2O adsorption of amine-functionalized nanofibrillated cellulose is carried out in the temperature range of 283-353 K and at CO2 partial pressures in the range of 0.02-105 kPa, where the ultralow partial pressure range is relevant for the direct capture of CO2 from atmospheric air. Single-component CO2 and H2O adsorption experimental data are fitted to the Toth and Guggenheim-Anderson-de Boer models, respectively. Corresponding heats of adsorption, derived from explicit solutions of the van't Hoff equation, are -50 kJ/mol CO2 and -48.8 kJ/mol H2O. Binary CO2/H2O adsorption measurements for humid air reveal that the presence of H2O at 2.55 kPa enhances CO2 adsorption, while the presence of CO2 at 0.045 kPa does not influence H2O adsorption. The energy demand of the temperature-vacuum-swing adsorption/desorption cycle for delivering pure CO2 from air increases significantly with H2O adsorption and indicates the need to reduce the hygroscopicity of the adsorbent.

Segregation of O2 and CO on the surface of dust grains determines the desorption energy of O2

NASA Astrophysics Data System (ADS)

Noble, J. A.; Diana, S.; Dulieu, F.

2015-12-01

Selective depletion towards pre-stellar cores is still not understood. The exchange between the solid and gas phases is central to this mystery. The aim of this paper is to show that the thermal desorption of O2 and CO from a submonolayer mixture is greatly affected by the composition of the initial surface population. We have performed thermally programmed desorption (TPD) experiments on various submonolayer mixtures of O2 and CO. Pure O2 and CO exhibit almost the same desorption behaviour, but their desorption differs strongly when mixed. Pure O2 is slightly less volatile than CO, while in mixtures, O2 desorbs earlier than CO. We analyse our data using a desorption law linking competition for binding sites with desorption, based on the assumption that the binding energy distribution of both molecules is the same. We apply Fermi-Dirac statistics in order to calculate the adsorption site population distribution, and derive the desorbing fluxes. Despite its simplicity, the model reproduces the observed desorption profiles, indicating that competition for adsorption sites is the reason for lower temperature O2 desorption. CO molecules push-out or `dislodge' O2 molecules from the most favourable binding sites, ultimately forcing their early desorption. It is crucial to consider the surface coverage of dust grains in any description of desorption. Competition for access to binding sites results in some important discrepancies between similar kinds of molecules, such as CO and O2. This is an important phenomenon to be investigated in order to develop a better understanding of the apparently selective depletion observed in dark molecular clouds.

NH3 adsorption on anatase-TiO2(101)

NASA Astrophysics Data System (ADS)

Koust, Stig; Adamsen, Kræn C.; Kolsbjerg, Esben Leonhard; Li, Zheshen; Hammer, Bjørk; Wendt, Stefan; Lauritsen, Jeppe V.

2018-03-01

The adsorption of ammonia on anatase TiO2 is of fundamental importance for several catalytic applications of TiO2 and for probing acid-base interactions. Utilizing high-resolution scanning tunneling microscopy (STM), synchrotron X-ray photoelectron spectroscopy, temperature-programmed desorption (TPD), and density functional theory (DFT), we identify the adsorption mode and quantify the adsorption strength on the anatase TiO2(101) surface. It was found that ammonia adsorbs non-dissociatively as NH3 on regular five-fold coordinated titanium surface sites (5f-Ti) with an estimated exothermic adsorption energy of 1.2 eV for an isolated ammonia molecule. For higher adsorbate coverages, the adsorption energy progressively shifts to smaller values, due to repulsive intermolecular interactions. The repulsive adsorbate-adsorbate interactions are quantified using DFT and autocorrelation analysis of STM images, which both showed a repulsive energy of ˜50 meV for nearest neighbor sites and a lowering in binding energy for an ammonia molecule in a full monolayer of 0.28 eV, which is in agreement with TPD spectra.

Adsorption-desorption of dimethenamid and fenarimol onto three agricultural soils as affected by treated wastewater and fresh sewage sludge-derived dissolved organic carbon.

PubMed

Rodríguez-Liébana, José Antonio; Peña, Aránzazu

2018-07-01

The use of treated wastewaters (TWW) in agriculture is widening in areas suffering drought, such as southern Europe, to preserve freshwater supply for human consumption. The composition of TWW, especially concerning their organic carbon (OC) content, has been demonstrated to influence the processes governing the behavior of non-ionic pesticides in soils. Three OC-poor agricultural soils (SV, RM1 and RM3) from the province of Granada (Spain) were chosen for the assessment of the adsorption and desorption of the herbicide dimethenamid (DIM) and the fungicide fenarimol (FEN). TWW and sewage sludge extracts at different dissolved OC (DOC) concentrations (30, 90 and 300 mg L -1 ) were considered to evaluate their effect on pesticide adsorption-desorption. As expected by their properties, DIM and FEN were weakly and moderately adsorbed to the soils, respectively. Soil OC seemed to be the major factor controlling FEN adsorption, whereas the mineral fraction played a key role in DIM adsorption, especially in RM1 with high clay:OC ratio. Although TWW did not significantly modify the adsorption of pesticides, it enhanced DIM desorption from the three soils. Adsorption of FEN to SV and RM3 was directly related to the concentration of DOC, possibly due to co-sorption phenomena. Hysteretic desorption was found in all cases, indicating partially reversible adsorption. While FEN desorption was not altered by the solutions, the use of sludge extracts at the highest DOC concentration (300 mg L -1 ) enhanced DIM desorption as occurred with TWW. Interactions with DOC in solution seemed to predominate for this less hydrophobic compound, thus increasing the risk of natural waters contamination if TWW will be used. Copyright © 2018 Elsevier Ltd. All rights reserved.

Adsorptive removal of 2-chlorophenol by low-cost coir pith carbon.

PubMed

Namasivayam, C; Kavitha, D

2003-03-17

Adsorption of 2-chlorophenol (2-CP) by coir pith carbon was carried out by varying the parameters such as agitation time, 2-CP concentration, adsorbent dose, pH and temperature. Adsorption equilibrium reached at 40, 60, 80 and 100 min for 2-CP concentration of 10, 20, 30 and 40 mg/l, respectively. Adsorption followed second-order kinetics. The adsorption equilibrium data obeyed Freundlich isotherm. Acidic pH was favorable for the adsorption of 2-CP. Desorption studies showed that chemisorption plays a major role in the adsorption process. Copyright 2003 Elsevier Science B.V.

Finite-Temperature Hydrogen Adsorption/Desorption Thermodynamics Driven by Soft Vibration Modes

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

Woo, Sung-Jae; Lee, Eui-Sup; Yoon, Mina

2013-01-01

It is widely accepted that room-temperature hydrogen storage on nanostructured or porous materials requires enhanced dihydrogen adsorption. In this work we reveal that room-temperature hydrogen storage is possible not only by the enhanced adsorption, but also by making use of the vibrational free energy from soft vibration modes. These modes exist for example in the case of metallo-porphyrin-incorporated graphenes (M-PIGs) with out-of-plane ( buckled ) metal centers. There, the in-plane potential surfaces are flat because of multiple-orbital-coupling between hydrogen molecules and the buckled-metal centers. This study investigates the finite-temperature adsorption/desorption thermodynamics of hydrogen molecules adsorbed on M-PIGs by employing first-principlesmore » total energy and vibrational spectrum calculations. Our results suggest that the current design strategy for room-temperature hydrogen storage materials should be modified by explicitly taking finite-temperature vibration thermodynamics into account.« less

Chitosan/nanohydroxyapatite composite based scallop shells as an efficient adsorbent for mercuric ions: Static and dynamic adsorption studies.

PubMed

Hassan, Asaad F; Hrdina, Radim

2018-04-01

Chitosan/nanohydroxyapatite composites based on scallop shells (CP12, CP14 and CP21) were prepared with different chitosan: nanohydroxyapatite ratios (1:2, 1:4 and 2:1, respectively). Nanohydroxyapatite (P), chitosan(C) and their composites were characterized by means of TGA, XRD, N 2 adsorption/desorption analysis, SEM, Zeta potential and FTIR. The BET surface area ranged between 189 and 512 m 2 /g. Static adsorption of Hg +2 was tested for the effect of adsorbent dosage, pH, time and initial Hg +2 concentrations indicating that maximum static adsorption capacity was confirmed by CP12 (111.6 mg/g). Static adsorption well fitted with Langmuir adsorption isotherm and Pseudo-second order kinetic models. CP12 was selected for dynamic adsorption of Hg +2 considering the effect of bed height, flow rate and the effect of Hg +2 concentrations. Maximum dynamic adsorption capacity was confirmed at bed height of 3 cm, 2.0 mL/min flow rate and 300 mg/L as Hg +2 concentration with breakthrough time (t b ) and exhaustion time (t e ) of 9 and 21 h. Yoon-Nelson and Thomas models best described the experimental Hg +2 breakthrough curve model. After static adsorption, EDTA solution confirmed the maximum desorption efficiency. The validity of CP12 was tested through three cycles of column dynamic adsorption-desorption. Copyright © 2017 Elsevier B.V. All rights reserved.

Fabrication of ultrathin MIL-96(Al) films and study of CO2 adsorption/desorption processes using quartz crystal microbalance.

PubMed

Andrés, Miguel A; Benzaqui, M; Serre, C; Steunou, N; Gascón, I

2018-06-01

This contribution reports the fabrication and characterization of ultrathin films of nanoparticles of the water stable microporous Al tricarboxylate metal organic framework MIL-96(Al). The preparation of MOF dispersions in chloroform has been optimized to obtain dense monolayer films of good quality, without nanoparticle agglomeration, at the air-water interface that can be deposited onto solid substrates of different nature without any previous substrate functionalization. The MOF studied shows great interest for CO 2 capture because it presents Al 3+ Lewis centers and hydroxyl groups that strongly interact with CO 2 molecules. A comparative CO 2 adsorption study on drop-cast, Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) films using a Quartz Crystal Microbalance-based setup (QCM) has revealed that the CO 2 uptake depends strongly on the film fabrication procedure and the storage conditions. Noteworthy the CO 2 adsorption capacity of LB films is increased by 30% using a simple and green treatment (immersion of the film into water during 12 h just after film preparation). Finally, the stability of LB MOF monolayers upon several CO 2 adsorption/desorption cycles has been demonstrated, showing that CO 2 can be easily desorbed from the films at 303 K by flowing an inert gas (He). These results show that MOF LB monolayers can be of great interest for the development of MOF-based devices that require the use of very small MOF quantities, especially gas sensors. Copyright © 2018 Elsevier Inc. All rights reserved.

Adsorption, aggregation, and desorption of proteins on smectite particles.

PubMed

Kolman, Krzysztof; Makowski, Marcin M; Golriz, Ali A; Kappl, Michael; Pigłowski, Jacek; Butt, Hans-Jürgen; Kiersnowski, Adam

2014-10-07

We report on adsorption of lysozyme (LYS), ovalbumin (OVA), or ovotransferrin (OVT) on particles of a synthetic smectite (synthetic layered aluminosilicate). In our approach we used atomic force microscopy (AFM) and quartz crystal microbalance (QCM) to study the protein-smectite systems in water solutions at pH ranging from 4 to 9. The AFM provided insights into the adhesion forces of protein molecules to the smectite particles, while the QCM measurements yielded information about the amounts of the adsorbed proteins, changes in their structure, and conditions of desorption. The binding of the proteins to the smectite surface was driven mainly by electrostatic interactions, and hence properties of the adsorbed layers were controlled by pH. At high pH values a change in orientation of the adsorbed LYS molecules and a collapse or desorption of OVA layer were observed. Lowering pH to the value ≤ 4 caused LYS to desorb and swelling the adsorbed OVA. The stability of OVT-smectite complexes was found the lowest. OVT revealed a tendency to desorb from the smectite surface at all investigated pH. The minimum desorption rate was observed at pH close to the isoelectric point of the protein, which suggests that nonspecific interactions between OVT and smectite particles significantly contribute to the stability of these complexes.

Distribution law of temperature changes during methane adsorption and desorption in coal using infrared thermography technology

NASA Astrophysics Data System (ADS)

Zhao, Dong; Chen, Hao; An, Jiangfei; Zhou, Dong; Feng, Zengchao

2018-05-01

Gas adsorption and desorption is a thermodynamic process that takes place within coal as temperature changes and that is related to methane (CH4) storage. As infrared thermographic technology has been applied in this context to measure surface temperature changes, the aim of this research was to further elucidate the distribution law underlying this process as well as the thermal effects induced by heat adsorption and desorption in coal. Specimens of two different coal ranks were used in this study, and the surface temperature changes seen in the latter were detected. A contour line map was then drawn on the basis of initial results enabling a distribution law of temperature changes for samples. The results show that different regions of coal sample surfaces exhibit different heating rates during the adsorption process, but they all depends on gas storage capacity to a certain extent. It proposes a correlation coefficient that expresses the relationship between temperature change and gas adsorption capacity that could also be used to evaluate the feasibility of coalbed CH4 extraction in the field. And finally, this study is deduced a method to reveal the actual adsorption capacity of coal or CH4 reservoirs in in situ coal seams.

Study of CeO₂ Modified AlNi Mixed Pillared Clays Supported Palladium Catalysts for Benzene Adsorption/Desorption-Catalytic Combustion.

PubMed

Li, Jingrong; Zuo, Shufeng; Yang, Peng; Qi, Chenze

2017-08-15

A new functional AlNi-pillared clays (AlNi-PILC) with a large surface area and pore volume was synthesized. The performance of adsorption/desorption-catalytic combustion over CeO 2- modified Pd/AlNi-PILC catalysts was also studied. The results showed that the d 001 -value and specific surface area ( S BET ) of AlNi-PILC reached 2.11 nm and 374.8 m²/g, respectively. The large S BET and the d 001 -value improved the high capacity for benzene adsorption. Also, the strong interaction between PdCe mixed oxides and AlNi-PILC led to the high dispersion of PdO and CeO₂ on the support, which was responsible for the high catalytic performance. Especially, 0.2% Pd/12.5% Ce/AlNi-PILC presented high performance for benzene combustion at 240 °C and high CO₂ selectivity. Also, the combustion temperatures were lower compared to the desorption temperatures, which demonstrated that it could accomplish benzene combustion during the desorption process. Furthermore, its activity did not decrease after continuous reaction for 1000 h in dry air, and it also displayed good resistance to water and the chlorinated compound, making it a promising catalytic material for the elimination of volatile organic compounds.

Molecular and Dissociative Adsorption of Water on (TiO 2 ) n Clusters, n = 1–4

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

Chen, Mingyang; Straatsma, Tjerk P.; Dixon, David A.

In the low energy structures of the (TiO 2) n(H 2O) m (n ≤ 4, m ≤ 2n) and (TiO 2) 8(H 2O) m (m = 3, 7, 8) clusters were predicted using a global geometry optimization approach, with a number of new lowest energy isomers being found. Water can molecularly or dissociatively adsorb on pure and hydrated TiO 2 clusters. Dissociative adsorption is the dominant reaction for the first two H 2O adsorption reactions for n = 1, 2, and 4, for the first three H 2O adsorption reactions for n = 3, and for the first four Hmore » 2O adsorption reactions for n = 8. As more H 2O’s are added to the hydrated (TiO 2)n cluster, dissociative adsorption becomes less exothermic as all the Ti centers become 4-coordinate. Furthermore two types of bonds can be formed between the molecularly adsorbed water and TiO 2 clusters: a Lewis acid–base Ti–O(H 2) bond or an O···H hydrogen bond. The coupled cluster CCSD(T) results show that at 0 K the H 2O adsorption energy at a 4-coordinate Ti center is ~15 kcal/mol for the Lewis acid–base molecular adsorption and ~7 kcal/mol for the H-bond molecular adsorption, in comparison to that of 8–10 kcal/mol for the dissociative adsorption. The cluster size and geometry independent dehydration reaction energy, ED, for the general reaction 2(-TiOH) → -TiOTi– + H 2O at 4-coordinate Ti centers was estimated from the aggregation reaction of nTi(OH) 4 to form the monocyclic ring cluster (TiO 3H 2) n + nH 2O. E D is estimated to be -8 kcal/mol, showing that intramolecular and intermolecular dehydration reactions are intrinsically thermodynamically allowed for the hydrated (TiO 2) n clusters with all of the Ti centers 4-coordinate, which can be hindered by cluster geometry changes caused by such processes. Finally by bending force constants for the TiOTi and OTiO bonds are determined to be 7.4 and 56.0 kcal/(mol·rad 2). Infrared vibrational spectra were calculated using density functional theory, and the new bands appearing upon water adsorption

Molecular and Dissociative Adsorption of Water on (TiO 2 ) n Clusters, n = 1–4

DOE PAGES

Chen, Mingyang; Straatsma, Tjerk P.; Dixon, David A.

2015-10-20

In the low energy structures of the (TiO 2) n(H 2O) m (n ≤ 4, m ≤ 2n) and (TiO 2) 8(H 2O) m (m = 3, 7, 8) clusters were predicted using a global geometry optimization approach, with a number of new lowest energy isomers being found. Water can molecularly or dissociatively adsorb on pure and hydrated TiO 2 clusters. Dissociative adsorption is the dominant reaction for the first two H 2O adsorption reactions for n = 1, 2, and 4, for the first three H 2O adsorption reactions for n = 3, and for the first four Hmore » 2O adsorption reactions for n = 8. As more H 2O’s are added to the hydrated (TiO 2)n cluster, dissociative adsorption becomes less exothermic as all the Ti centers become 4-coordinate. Furthermore two types of bonds can be formed between the molecularly adsorbed water and TiO 2 clusters: a Lewis acid–base Ti–O(H 2) bond or an O···H hydrogen bond. The coupled cluster CCSD(T) results show that at 0 K the H 2O adsorption energy at a 4-coordinate Ti center is ~15 kcal/mol for the Lewis acid–base molecular adsorption and ~7 kcal/mol for the H-bond molecular adsorption, in comparison to that of 8–10 kcal/mol for the dissociative adsorption. The cluster size and geometry independent dehydration reaction energy, ED, for the general reaction 2(-TiOH) → -TiOTi– + H 2O at 4-coordinate Ti centers was estimated from the aggregation reaction of nTi(OH) 4 to form the monocyclic ring cluster (TiO 3H 2) n + nH 2O. E D is estimated to be -8 kcal/mol, showing that intramolecular and intermolecular dehydration reactions are intrinsically thermodynamically allowed for the hydrated (TiO 2) n clusters with all of the Ti centers 4-coordinate, which can be hindered by cluster geometry changes caused by such processes. Finally by bending force constants for the TiOTi and OTiO bonds are determined to be 7.4 and 56.0 kcal/(mol·rad 2). Infrared vibrational spectra were calculated using density functional theory, and the new bands appearing upon water adsorption

Synthesis, characterization, and application of Zn(NH 3)(CO3) for selective adsorptive separation of CO2

NASA Astrophysics Data System (ADS)

Khazeni, Naasser

This study explores the potential of Zn(NH3)(CO3) for selective CO2 separation. It develops a novel, highly controllable, single-pot synthesis approach based on urea hydrolysis and solvothermal aging to increase the feasibility of synthesizing Zn(NH3)(CO3), determines the structure of Zn(NH3)(CO3) in detail through single crystal X-ray diffraction and powder X-ray diffraction analyses, and performs adsorption analyses for the compound using CO2, N 2, H2, O2, and CH4 as adsorptives. Through adsorptive characterization, a systematic adsorbent selection screening is performed to assess the potential application of Zn(NH3)(CO 3) for adsorptive separation of CO2 from an upstream gas mixture of power generation, hydrogen production, and natural gas industries. Structural analysis shows Zn(NH3)(CO3) to have an inorganic helical framework that consists of a small helix of (ZnOCO) 2 and a large helix of (ZnOCO)4 with two ammines (NH 3) pendant from every other zinc. In terms of adsorption capacity and CO2 selectivity, Zn(NH3)(CO3) adsorbed 0.550 mmole/g CO2 at 293 K and 4500 mmHg, but only 0.047 mmole/g N 2, 0.084 mmole/g H2, 0.207 mmole/g 02, and 0.060 mmole/g CH4 at the same temperature and pressure. This behavior demonstrates considerable equilibrium selectivities - 36, 31, 63, and 11 - for separating CO2 from CH4, CO2 from H 2, CO2 from N2, and CO2 from 02, respectively. During adsorption, the pendant ammines act as the gates of check-valves: applied pressure opens the gates for adsorption; and during desorption, the gates are closed, trapping the adsorbates, until a reduction of pressure to near-atmospheric levels. Therefore, Zn(NH3)(CO3) exhibits low-pressure H3 or H4 hysteresis, indicating that the Zn(NH3)(CO3) framework can achieve gas storage at near-atmospheric pressures. Additionally, the compound proves structurally stable, with an adsorption decrease of 0.8% after 20 adsorption/desorption cycles - a factor that, considered with the other characteristics of Zn

Comparative adsorption of Pb2+ and Cd2+ by cow manure and its vermicompost.

PubMed

Zhu, Weiqin; Du, Wenhui; Shen, Xuyang; Zhang, Hangjun; Ding, Ying

2017-08-01

Organic waste has great potential for use as an amendment to immobilize heavy metals in the environment. Therefore, this study investigates various properties of cow manure (CM) and its derived vermicompost (CV), including the pH, cationic exchangeable capacity (CEC), elemental composition and surface structure, to determine the potential of these waste products to remove Pb 2+ and Cd 2+ from solution. The results demonstrate that CV has a much higher pH, CEC and more irregular pores than CM and is enriched with minerals and ash content but has a lower C, H, O and N content. Adsorption isotherms studies shows that the adsorption of Pb 2+ and Cd 2+ onto either CM or CV follows a Langmuir model and presents maximum Pb 2+ and Cd 2+ adsorption capacities of 102.77 mg g -1 and 38.11 mg g -1 onto CM and 170.65 and 43.01 mg g -1 onto CV, respectively. Kinetic studies show that the adsorption of Pb 2+ onto CM and CV fits an Elovich model, whereas the adsorption of Cd 2+ onto CM and CV fits a pseudo-second-order model. Desorption studies indicate that CV is more effective than CM in removing Pb 2+ and Cd 2+ . FTIR analysis demonstrates that the adsorption of Pb 2+ and Cd 2+ onto CM mainly depends on existed aliphatic alcohol, aromatic acid as well as new produced carbonates, whereas that onto CV may be contributed by the existed aliphatic alcohol, aromatic acids as well as some carbonates and phosphates. Thus, vermicomposting disposal of cow manure with destination mineral addition may broaden the way of its recycle and environmental usage. Copyright © 2017 Elsevier Ltd. All rights reserved.

Adsorption and desorption variability of four herbicides used in paddy rice production.

PubMed

Alister, Claudio A; Araya, Manuel A; Kogan, Marcelo

2011-01-01

This investigation was performed to determine the effect of physicochemical soil properties on penoxsulam, molinate, bentazon, and MCPA adsorption-desorption processes. Four soils from Melozal (35° 43' S; 71° 41' W), Parral (36° 08' S; 71° 52' W), San Carlos (36° 24' S; 71° 57' W), and Panimavida (35° 44' S; 71° 24' W) were utilized. Herbicide adsorption reached equilibrium after 4 h in all soils. The Freundlich L-type isotherm described the adsorption process, which showed a high affinity between herbicides and sorption sites mainly because of hydrophobic and H-bonds interaction. Penoxsulam showed the highest adsorption coefficients (4.23 ± 0.72 to 10.69 ± 1.58 mL g⁻¹) and were related to soil pH. Molinate showed K(d) values between 1.72 ± 0.01 and 2.3 ± 0.01 mL g⁻¹ and were related to soil pH and organic matter, specifically to the amount of humic substances. Bentazon had a high relationship with pH and humic substances and its K(d) values were the lowest, ranging from 0.11 ± 0.01 to 0.42 ± 0.01 mL g⁻¹. MCPA K(d) ranged from 0.14 ± 0.02 to 2.72 ± 0.01 mL g⁻¹, however its adsorption was related to humic acids and clay content. According to these results, the soil factors that could explain the sorption process of the studied herbicides under paddy rice soil conditions, were principally humic substances and soil pH. Considering the sorption variability observed in this study and the potential risk for groundwater contamination, it is necessary to develop weed rice management strategies that limit use of herbicides that exhibit low soil adsorption in areas with predisposing conditions to soil leaching.

Mathematical modelling of cyclic pressure swing adsorption processes

NASA Astrophysics Data System (ADS)

Skvortsov, S. A.; Akulinin, E. I.; Golubyatnikov, O. O.; Dvoretsky, D. S.; Dvoretsky, S. I.

2018-05-01

The paper discusses the results of a numerical analysis of the properties and regimes of the adsorption air separation and oxygen concentration process with a purity of ∼ 40-60%, carried out in a 2-adsorption vacuum-pressure plant with a granular zeolite adsorbent 13X with a productivity of 1.6 · 10-5 m3/s. Computational experiments were carried out using the developed mathematical model and the influence of temperature, pressure, reflux ratio, the duration of the adsorption and desorption stages, the harmonic fluctuations of the inlet pressure during the adsorption stage and the outlet pressure during the desorption stage on the kinetics, and the efficiency of the air separation process by the PSA method were investigated. It is established that the specially organized harmonic fluctuations of the inlet pressure at the stage of adsorption and outlet pressure during the desorption stage lead to an increase in the purity of product oxygen by 4% (vol.).

Waste Isolation Safety Assessment Program. Task 4. Third Contractor Information Meeting. [Adsorption-desorption on geological media

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

Not Available

1980-06-01

The study subject of this meeting was the adsorption and desorption of radionuclides on geologic media under repository conditions. This volume contans eight papers. Separate abstracts were prepared for all eight papers. (DLC)

Interaction of D2 with H2O amorphous ice studied by temperature-programmed desorption experiments.

PubMed

Amiaud, L; Fillion, J H; Baouche, S; Dulieu, F; Momeni, A; Lemaire, J L

2006-03-07

The gas-surface interaction of molecular hydrogen D2 with a thin film of porous amorphous solid water (ASW) grown at 10 K by slow vapor deposition has been studied by temperature-programmed-desorption (TPD) experiments. Molecular hydrogen diffuses rapidly into the porous network of the ice. The D2 desorption occurring between 10 and 30 K is considered here as a good probe of the effective surface of ASW interacting with the gas. The desorption kinetics have been systematically measured at various coverages. A careful analysis based on the Arrhenius plot method has provided the D2 binding energies as a function of the coverage. Asymmetric and broad distributions of binding energies were found, with a maximum population peaking at low energy. We propose a model for the desorption kinetics that assumes a complete thermal equilibrium of the molecules with the ice film. The sample is characterized by a distribution of adsorption sites that are filled according to a Fermi-Dirac statistic law. The TPD curves can be simulated and fitted to provide the parameters describing the distribution of the molecules as a function of their binding energy. This approach contributes to a correct description of the interaction of molecular hydrogen with the surface of possibly porous grain mantles in the interstellar medium.

MgO-based adsorbents for CO2 adsorption: Influence of structural and textural properties on the CO2 adsorption performance.

PubMed

Elvira, Gutiérrez-Bonilla; Francisco, Granados-Correa; Víctor, Sánchez-Mendieta; Alberto, Morales-Luckie Raúl

2017-07-01

A series of MgO-based adsorbents were prepared through solution-combustion synthesis and ball-milling process. The prepared MgO-based powders were characterized using X-ray diffraction, scanning electron microscopy, N 2 physisorption measurements, and employed as potential adsorbents for CO 2 adsorption. The influence of structural and textural properties of these adsorbents over the CO 2 adsorption behaviour was also investigated. The results showed that MgO-based products prepared by solution-combustion and ball-milling processes, were highly porous, fluffy, nanocrystalline structures in nature, which are unique physico-chemical properties that significantly contribute to enhance their CO 2 adsorption. It was found that the MgO synthesized by solution combustion process, using a molar ratio of urea to magnesium nitrate (2:1), and treated by ball-milling during 2.5hr (MgO-BM2.5h), exhibited the maximum CO 2 adsorption capacity of 1.611mmol/g at 25°C and 1atm, mainly via chemisorption. The CO 2 adsorption behaviour on the MgO-based adsorbents was correlated to their improved specific surface area, total pore volume, pore size distribution and crystallinity. The reusability of synthesized MgO-BM2.5h was confirmed by five consecutive CO 2 adsorption-desorption times, without any significant loss of performance, that supports the potential of MgO-based adsorbent. The results confirmed that the special features of MgO prepared by solution-combustion and treated by ball-milling during 2.5hr are favorable to be used as effective MgO-based adsorbent in post-combustion CO 2 capture technologies. Copyright © 2016. Published by Elsevier B.V.

H 2 Desorption from MgH 2 Surfaces with Steps and Catalyst-Dopants

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

Reich, Jason M.; Wang, Lin-Lin; Johnson, Duane D.

2014-03-10

Light-metal hydrides, like MgH 2, remain under scrutiny as prototypes for reversible H-storage materials. For MgH 2, we assess hydrogen desorption/adsorption properties (enthalpy and kinetic barriers) for stepped, catalyst-doped surfaces occurring, e.g., from ball-milling in real samples. Employing density functional theory and simulated annealing in a slab model, we studied initial H 2 desorption from stepped surfaces with(out) titanium (Ti) catalytic dopant. Extensive simulated annealing studies were performed to find the dopant’s site preferences. For the most stable initial and final (possibly magnetic) states, nudged elastic band (NEB) calculations were performed to determine the H 2-desorption activation energy. We usedmore » a moment-transition NEB method to account for the dopant’s transition to the lowest-energy magnetic state at each image along the band. We identify a dopant-related surface-desorption mechanism that reloads via bulk H diffusion. While reproducing the observed bulk enthalpy of desorption, we find a decrease of 0.24 eV (a 14% reduction) in the activation energy on doped stepped surface; together with a 22% reduction on a doped flat surface, this brackets the assessed 18% reduction in kinetic barrier for ball-milled MgH 2 samples with low concentration of Ti from experiment.« less

Two-step adsorption on jungle-gym-type porous coordination polymers: dependence on hydrogen-bonding capability of adsorbates, ligand-substituent effect, and temperature.

PubMed

Uemura, Kazuhiro; Yamasaki, Yukari; Onishi, Fumiaki; Kita, Hidetoshi; Ebihara, Masahiro

2010-11-01

A preliminary study of isopropanol (IPA) adsorption/desorption isotherms on a jungle-gym-type porous coordination polymer, [Zn(2)(bdc)(2)(dabco)](n) (1, H(2)bdc = 1,4-benzenedicarboxylic acid, dabco =1,4-diazabicyclo[2.2.2]octane), showed unambiguous two-step profiles via a highly shrunk intermediate framework. The results of adsorption measurements on 1, using probing gas molecules of alcohol (MeOH and EtOH) for the size effect and Me(2)CO for the influence of hydrogen bonding, show that alcohol adsorption isotherms are gradual two-step profiles, whereas the Me(2)CO isotherm is a typical type-I isotherm, indicating that a two-step adsorption/desorption is involved with hydrogen bonds. To further clarify these characteristic adsorption/desorption behaviors, selecting nitroterephthalate (bdc-NO(2)), bromoterephthalate (bdc-Br), and 2,5-dichloroterephthalate (bdc-Cl(2)) as substituted dicarboxylate ligands, isomorphous jungle-gym-type porous coordination polymers, {[Zn(2)(bdc-NO(2))(2)(dabco)]·solvents}(n) (2 ⊃ solvents), {[Zn(2)(bdc-Br)(2)(dabco)]·solvents}(n) (3 ⊃ solvents), and {[Zn(2)(bdc-Cl(2))(2)(dabco)]·solvents}(n) (4 ⊃ solvents), were synthesized and characterized by single-crystal X-ray analyses. Thermal gravimetry, X-ray powder diffraction, and N(2) adsorption at 77 K measurements reveal that [Zn(2)(bdc-NO(2))(2)(dabco)](n) (2), [Zn(2)(bdc-Br)(2)(dabco)](n) (3), and [Zn(2)(bdc-Cl(2))(2)(dabco)](n) (4) maintain their frameworks without guest molecules with Brunauer-Emmett-Teller (BET) surface areas of 1568 (2), 1292 (3), and 1216 (4) m(2) g(-1). As found in results of MeOH, EtOH, IPA, and Me(2)CO adsorption/desorption on 2-4, only MeOH adsorption on 2 shows an obvious two-step profile. Considering the substituent effects and adsorbate sizes, the hydrogen bonds, which are triggers for two-step adsorption, are formed between adsorbates and carboxylate groups at the corners in the pores, inducing wide pores to become narrow pores. Interestingly, such

Synthesis, Structural, and Adsorption Properties and Thermal Stability of Nanohydroxyapatite/Polysaccharide Composites.

PubMed

Skwarek, Ewa; Goncharuk, Olena; Sternik, Dariusz; Janusz, Wladyslaw; Gdula, Karolina; Gun'ko, Vladimir M

2017-12-01

A series of composites based on nanohydroxyapatite (nHAp) and natural polysaccharides (PS) (nHAp/agar, nHAp/chitosan, nHAp/pectin FB300, nHAp/pectin APA103, nHAp/sodium alginate) was synthesized by liquid-phase two-step method and characterized using nitrogen adsorption-desorption, DSC, TG, FTIR spectroscopy, and SEM. The analysis of nitrogen adsorption-desorption data shows that composites with a nHAp: PS ratio of 4:1 exhibit a sufficiently high specific surface area from 49 to 82 m 2 /g. The incremental pore size distributions indicate mainly mesoporosity. The composites with the component ratio 1:1 preferably form a film-like structure, and the value of S BET varies from 0.3 to 43 m 2 /g depending on the nature of a polysaccharide. Adsorption of Sr(II) on the composites from the aqueous solutions has been studied. The thermal properties of polysaccharides alone and in nHAp/PS show the influence of nHAp, since there is a shift of characteristic DSC and DTG peaks. FTIR spectroscopy data confirm the presence of functional groups typical for nHAp as well as polysaccharides in composites. Structure and morphological characteristics of the composites are strongly dependent on the ratio of components, since nHAp/PS at 4:1 have relatively large S BET values and a good ability to adsorb metal ions. The comparison of the adsorption capacity with respect to Sr(II) of nHAp, polysaccharides, and composites shows that it of the latter is higher than that of nHAp (per 1 m 2 of surface).

Adsorption of octylamine on titanium dioxide

NASA Astrophysics Data System (ADS)

Siwińska, Daria; Kołodziejczak-Radzimska, Agnieszka; Krysztafkiewicz, Andrzej; Jesionowski, Teofil

2009-05-01

Processes of adsorption and desorption of a model active substance (octylamine) on the surface of unmodified titanium dioxide (E 171) have been performed. The effects of concentration of octylamine and time of the process on the character of adsorption have been studied and the efficiency of the adsorption/desorption has been determined. The samples obtained have been studied by X-ray diffraction. The nitrogen adsorption/desorption isotherms, particle size distribution and absorption capacities of water, dibutyl phthalate and paraffin oil have been determined. The efficiency of octylamine adsorption on the surface of the titanium dioxide has been found positively correlated with the concentration of octylamine in the initial solution. The desorption of octylamine has decreased with increasing concentration of this compound adsorbed. For octylamine in low concentrations the physical adsorption has been found to dominate, which is desirable when using TiO 2 in the production of pharmaceuticals.

Gas adsorption capacity of wood pellets

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

Yazdanpanah, F.; Sokhansanj, Shahabaddine; Lim, C. Jim

In this paper, temperature-programmed desorption (TPD) analysis was used to measure and analyze the adsorption of off-gases and oxygen by wood pellets during storage. Such information on how these gases interact with the material helps in the understanding of the purging/stripping behavior of off-gases to develop effective ventilation strategies for wood pellets. Steam-exploded pellets showed the lowest carbon dioxide (CO 2) uptake compared to the regular and torrefied pellets. The high CO 2 adsorption capacity of the torrefied pellets could be attributed to their porous structure and therefore greater available surface area. Quantifying the uptake of carbon monoxide by pelletsmore » was challenging due to chemical adsorption, which formed a strong bond between the material and carbon monoxide. The estimated energy of desorption for CO (97.8 kJ/mol) was very high relative to that for CO 2 (7.24 kJ/mol), demonstrating the mechanism of chemical adsorption and physical adsorption for CO and CO 2, respectively. As for oxygen, the strong bonds that formed between the material and oxygen verified the existence of chemical adsorption and formation of an intermediate material.« less

Gas adsorption capacity of wood pellets

DOE PAGES

Yazdanpanah, F.; Sokhansanj, Shahabaddine; Lim, C. Jim; ...

2016-02-03

In this paper, temperature-programmed desorption (TPD) analysis was used to measure and analyze the adsorption of off-gases and oxygen by wood pellets during storage. Such information on how these gases interact with the material helps in the understanding of the purging/stripping behavior of off-gases to develop effective ventilation strategies for wood pellets. Steam-exploded pellets showed the lowest carbon dioxide (CO 2) uptake compared to the regular and torrefied pellets. The high CO 2 adsorption capacity of the torrefied pellets could be attributed to their porous structure and therefore greater available surface area. Quantifying the uptake of carbon monoxide by pelletsmore » was challenging due to chemical adsorption, which formed a strong bond between the material and carbon monoxide. The estimated energy of desorption for CO (97.8 kJ/mol) was very high relative to that for CO 2 (7.24 kJ/mol), demonstrating the mechanism of chemical adsorption and physical adsorption for CO and CO 2, respectively. As for oxygen, the strong bonds that formed between the material and oxygen verified the existence of chemical adsorption and formation of an intermediate material.« less

Leaching potential of chlorpyrifos in an Andisol and Entisol: adsorption-desorption and degradation studies

NASA Astrophysics Data System (ADS)

Mosquera-Vivas, Carmen; Walther Hansen, Eddy; Garcia-Santos, Glenda; Obregón-Neira, Nelson; Celis-Ossa, Raul Ernesto; González-Murillo, Carlos Alberto; Juraske, Ronnie; Hellweg, Stefanie; Guerrero-Dallos, Jairo Arturo

2017-04-01

Ecological status of tropical soils like high OC content and microbial activity plays a key role to reduce the leaching of insecticide chlorpyrifos through the soil profile and therefore into groundwater. We found that chlorpyrifos has "transitional" leaching potential (GUS values varied between 1.8 and 2.5) throughout the soil depth, which differs from the "nonleacher" classification for temperate soils as based on surface level t1/2 and Koc values from international databases. These findings provide strong evidence of the importance of estimating the transport parameters and insecticide concentrations in different soil layers, especially when the amount and type of OC content vary throughout the soil profile. We got to such conclusions after studying the soil profile structural composition of soil organic matter and the adsorption/desorption characteristics of the insecticide in two different soil profiles (Andisol and Entisol) under agriculture production using Fourier transform infrared spectroscopy, nuclear magnetic resonance, and batch analysis methods.

Adsorption and desorption of phthalic acid esters on graphene oxide and reduced graphene oxide as affected by humic acid.

PubMed

Lu, Lun; Wang, Jun; Chen, Baoliang

2018-01-01

The implications of humic acid (HA) regarding surface properties of graphene materials and their interactions with phthalic acid esters (PAEs) are not vivid. We report the role of HA on graphene oxide (GO) and reduced graphene oxide (RGO) for sorption-desorption behavior of PAEs. Besides higher surface area and pore volume, the hydrophobic π-conjugated carbon atoms on RGO ensured prominent adsorption capacity towards PAEs in comparison to hydrophilic GO, highlighting the hydrophobic effect. After adjusting for the hydrophobic effect by calculating the hexadecane-water partition coefficient (K HW ) normalized adsorption coefficient (K d /K HW ), the dimethyl phthalate (DMP) molecule portrayed a higher adsorption affinity towards RGO by π-π electron donor-acceptor (EDA) interaction for active sites on graphene interface via sieving effect. In contrast to RGO, the weak π-π EDA interactions and H-bonding was observed between the carbonyl groups of PAEs and oxygen containing functional groups on GO. There was no obvious change in morphologies of GO and RGO before and desorption as revealed by SEM and TEM images, as desorption hysteresis did not occur in all conditions. The presence of HA also resulted in shielding effect thereby decreasing the adsorption rate and capacity of diethyl phthalate (DEP) on GO and RGO, while it had little effect on DMP, probably due to the adsorbed HA as new active sites. The desorption of DMP and DEP on RGO in presence of HA was quick and enhanced. These results should be important for evaluating the fate and health risk of graphene materials and PAEs in the environment. Copyright © 2017 Elsevier Ltd. All rights reserved.

Oxygen sorption and desorption properties of selected lanthanum manganites and lanthanum ferrite manganites.

PubMed

Nielsen, Jimmi; Skou, Eivind M; Jacobsen, Torben

2015-06-08

Temperature-programmed desorption (TPD) with a carrier gas was used to study the oxygen sorption and desorption properties of oxidation catalysts and solid-oxide fuel cell (SOFC) cathode materials (La(0.85) Sr(0.15)0.95 MnO(3+δ) (LSM) and La(0.60) Sr(0.40) Fe(0.80) Mn(0.20) O(3-δ) (LSFM). The powders were characterized by X-ray diffractometry, atomic force microscopy (AFM), and BET surface adsorption. Sorbed oxygen could be distinguished from oxygen originating from stoichiometry changes. The results indicated that there is one main site for oxygen sorption/desorption. The amount of sorbed oxygen was monitored over time at different temperatures. Furthermore, through data analysis it was shown that the desorption peak associated with oxygen sorption is described well by second-order desorption kinetics. This indicates that oxygen molecules dissociate upon adsorption and that the rate-determining step for the desorption reaction is a recombination of monatomic oxygen. Typical problems with re-adsorption in this kind of TPD setup were revealed to be insignificant by using simulations. Finally, different key parameters of sorption and desorption were determined, such as desorption activation energies, density of sorption sites, and adsorption and desorption reaction order. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hard versus soft dynamics for adsorption-desorption kinetics: Exact results in one-dimension.

PubMed

Manzi, S J; Huespe, V J; Belardinelli, R E; Pereyra, V D

2009-11-01

The adsorption-desorption kinetics is discussed in the framework of the kinetic lattice-gas model. The master equation formalism has been introduced to describe the evolution of the system, where the transition probabilities are written as an expansion of the occupation configurations of all neighboring sites. Since the detailed balance principle determines half of the coefficients that arise from the expansion, it is necessary to introduce ad hoc, a dynamic scheme to get the rest of them. Three schemes of the so-called hard dynamics, in which the probability of transition from single site cannot be factored into a part which depends only on the interaction energy and one that only depends on the field energy, and five schemes of the so-called soft dynamics, in which this factorization is possible, were introduced for this purpose. It is observed that for the hard dynamic schemes, the equilibrium and nonequilibrium observables, such as adsorption isotherms, sticking coefficients, and thermal desorption spectra, have a normal or physical sustainable behavior. While for the soft dynamics schemes, with the exception of the transition state theory, the equilibrium and nonequilibrium observables have several problems. Some of them can be regarded as abnormal behavior.

Measurement of toxic volatile organic compounds in indoor air of semiconductor foundries using multisorbent adsorption/thermal desorption coupled with gas chromatography-mass spectrometry.

PubMed

Wu, Chien-Hou; Lin, Ming-Nan; Feng, Chien-Tai; Yang, Kuang-Ling; Lo, Yu-Shiu; Lo, Jiunn-Guang

2003-05-09

A method for the qualitative and quantitative analysis of volatile organic compounds (VOCs) in the air of class-100 clean rooms at semiconductor fabrication facilities was developed. Air samples from two semiconductor factories were collected each hour on multisorbent tubes (including Carbopack B, Carbopack C, and Carbosieve SIII) with a 24-h automatic active sampling system and analyzed using adsorption/thermal desorption coupled with gas chromatography-mass spectrometry. Experimental parameters, including thermal desorption temperature, desorption time, and cryofocusing temperature, were optimized. The average recoveries and the method detection limits for the target compounds were in the range 94-101% and 0.31-0.89 ppb, respectively, under the conditions of a 1 L sampling volume and 80% relative humidity. VOCs such as acetone, isopropyl alcohol, 2-heptanone, and toluene, which are commonly used in the semiconductor and electronics industries, were detected and accurately quantified with the established method. Temporal variations of the analyte concentrations observed were attributed to the improper use of organic solvents during operation.

Surface modification of a low cost bentonite for post-combustion CO2 capture

NASA Astrophysics Data System (ADS)

Chen, Chao; Park, Dong-Wha; Ahn, Wha-Seung

2013-10-01

A low cost bentonite was modified with PEI (polyethylenimine) through a physical impregnation method. Bentonite in its natural state and after amine modification were characterized by scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, N2 adsorption-desorption isotherms, and investigated for CO2 capture using a thermogravimetric analysis unit connected to a flow panel. The effect of adsorption temperature, PEI loading and CO2 partial pressure on the CO2 capture performance of the PEI-modified bentonite was examined. A cyclic CO2 adsorption-desorption test was also carried out to assess the stability of PEI-modified bentonite as a CO2 adsorbent. Bentonite in its natural state showed negligible CO2 uptake. After amine modification, the CO2 uptake increased significantly due to CO2 capture by amine species introduced via chemisorption. The PEI-modified bentonites showed high CO2 capture selectivity over N2, and exhibited excellent stability in cyclic CO2 adsorption-desorption runs.

Technological applications of organo-montmorillonites in the removal of pyrimethanil from water: adsorption/desorption and flocculation studies.

PubMed

Flores, Federico M; Undabeytia, Tomas; Morillo, Esmeralda; Torres Sánchez, Rosa M

2017-06-01

Pyrimethanil (2-aniline-4, 6-dimethylpyrimidine, PRM) is used in fruit packing plants to control fungal infections and diseases. The effluents greatly polluted with this fungicide, as a point source contamination, need to be technologically treated for their regeneration before they reach water bodies. This work evaluates the use of organo-montmorillonites, synthetized in our laboratory, for their application in adsorption and coagulation/flocculation processes for the removal of PRM from water. The adsorption-desorption performance of PRM in a raw montmorillonite (Mt) and several organo-montmorillonites (organo-Mt) obtained by different amounts and types of exchanged surfactants (octadecyltrimethylammonium (ODTMA) and didodecyldimethylammonium (DDAB) bromides and benzyltrimethylammonium chloride (BTMA)) was studied. The PRM adsorption on raw Mt was assigned mainly to an interlayer occupancy, while hydrophobic interactions between PRM and the surfactants in the exchanged samples increased PRM adsorption, which was correlated with the surfactant loading. PRM desorption showed irreversible behavior in raw Mt, which changed to reversible for organo-Mt samples, and was also correlated with the increase of surfactant loading.Two of the organo-Mt with high surfactant loading (twice the CEC) were assayed for the removal of commercial PRM in coagulation/flocculation tests, and their performance was compared to that of the native clay (Mt). The use of the organo-Mt produced flocculation at a very low ratio (0.5 g L -1 ), whereas no flocculation was observed with Mt. These results proved the feasibility of the use of organo-Mt for the treatment of wastewater contaminated with PRM using a low organo-Mt/liquid ratio.

Adsorption of n-butane on graphene/Ru(0001)—A molecular beam scattering study

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

Sivapragasam, Nilushni; Nayakasinghe, Mindika T.; Burghaus, Uwe, E-mail: uwe.burghaus@ndsu.edu

2016-07-15

Adsorption kinetics/dynamics of n-butane on graphene, physical vapor deposited on Ru(0001) (hereafter G/Ru), and bare Ru(0001) (hereafter Ru) are discussed. The chemical activity of the supported-graphene as well as the support was probed by thermal desorption spectroscopy (adsorption kinetics). In addition and to the best of our knowledge, for the first time, molecular beam scattering data of larger molecules were collected for graphene (probing the adsorption dynamics). Furthermore, samples were inspected by x-ray photoelectron spectroscopy and Auger electron spectroscopy. At the measuring conditions used here, n-butane adsorption kinetics/dynamics are molecular and nonactivated. Binding energies of butane on Ru and G/Rumore » are indistinguishable within experimental uncertainty. Thus, G/Ru is “kinetically transparent.” Initial adsorption probabilities, S{sub 0}, of n-butane decrease with increasing impact energy (0.76–1.72 eV) and are adsorption temperature independent for both Ru and G/Ru, again consistent with molecular adsorption. Also, S{sub 0} of Ru and G/Ru are indistinguishable within experimental uncertainty. Thus, G/Ru is “dynamically transparent.” Coverage dependent adsorption probabilities indicate precursor effects for graphene/Ru.« less

CO{sub 2} adsorption-based separation by metal organic framework (Cu-BTC) versus zeolite (13X)

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

Zhijian Liang; Marc Marshall; Alan L. Chaffee

2009-05-15

The potential for the metal organic framework (MOF) Cu-BTC to selectively adsorb and separate CO{sub 2} is considered. Isotherms for CO{sub 2}, CH{sub 4}, and N{sub 2} were measured from 0 to 15 bar and at temperatures between 25 and 105{sup o}C. The isotherms suggest a much higher working capacity (x4) for CO{sub 2} adsorption on Cu-BTC relative to the benchmark zeolite 13X over the same pressure range. Higher CO{sub 2}/N{sub 2} and CO{sub 2}/CH{sub 4} selectivities in the higher pressure range (1-15 bar) and with lower heats of adsorption were also demonstrated. Cu-BTC was observed to be stable inmore » O{sub 2} at 25{sup o}C, but its crystallinity was reduced in humid environments. The CO{sub 2} adsorption capacity was progressively reduced upon cyclic exposure to water vapor at low relative humidity (<30%), but leveled out at 75% of its original value after several water adsorption/desorption cycles. 27 refs., 1 fig.« less

Effect of additives on adsorption and desorption behavior of xylanase on acid-insoluble lignin from corn stover and wheat straw.

PubMed

Li, Yanfei; Ge, Xiaoyan; Sun, Zongping; Zhang, Junhua

2015-06-01

The competitive adsorption between cellulases and additives on lignin in the hydrolysis of lignocelluloses has been confirmed, whereas the effect of additives on the interaction between xylanase and lignin is not clear. In this work, the effects of additives, poly(ethylene glycol) 2000, poly(ethylene glycol) 6000, Tween 20, and Tween 80, on the xylanase adsorption/desorption onto/from acid-insoluble lignin from corn stover (CS-lignin) and wheat straw (WS-lignin) were investigated. The results indicated that the additives could adsorb onto isolated lignin and reduce the xylanase adsorption onto lignin. Compared to CS-lignin, more additives could adsorb onto WS-lignin, making less xylanase adsorbed onto WS-lignin. In addition, the additives could enhance desorption of xylanase from lignin, which might be due to the competitive adsorption between xylanase and additives on lignin. The released xylanase from lignin still exhibited hydrolytic capacity in the hydrolysis of isolated xylan and xylan in corn stover. Copyright © 2015 Elsevier Ltd. All rights reserved.

CO adsorption on small Au{sub n} (n = 1–4) structures supported on hematite. I. Adsorption on iron terminated α-Fe{sub 2}O{sub 3} (0001) surface

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

Pabisiak, Tomasz; Kiejna, Adam, E-mail: kiejna@ifd.uni.wroc.pl; Winiarski, Maciej J.

2016-01-28

This is the first of two papers dealing with the adsorption of Au and formation of Au{sub n} nanostructures (n = 1–4) on hematite (0001) surface and adsorption of CO thereon. The stoichiometric Fe-terminated (0001) surface of hematite was investigated using density functional theory in the generalized gradient approximation of Perdew-Burke-Ernzerhof (PBE) form with Hubbard correction U, accounting for strong electron correlations (PBE+U). The structural, energetic, and electronic properties of the systems studied were examined for vertical and flattened configurations of Au{sub n} nanostructures adsorbed on the hematite surfaces. The flattened ones, which can be viewed as bilayer-like structures, weremore » found energetically more favored than vertical ones. For both classes of structures the adsorption binding energy increases with the number of Au atoms in a structure. The adsorption of Au{sub n} induces charge rearrangement at the Au{sub n}/oxide contact which is reflected in work function changes. In most considered cases Au{sub n} adsorption increases the work function. A detailed analysis of the bonding electron charge is presented and the corresponding electron charge rearrangements at the contacts were quantified by a Bader charge analyses. The interaction of a CO molecule with the Au{sub n} nanostructures supported on α-Fe{sub 2}O{sub 3} (0001) and the oxide support was studied. It is found that the CO adsorption binding to the hematite supported Au{sub n} structures is more than twice as strong as to the bare hematite surface. Analysis of the Bader charges on the atoms showed that in each case CO binds to the most positively charged (cationic) atom of the Au{sub n} structure. Changes in the electronic structure of the Au{sub n} species and of the oxide support, and their consequences for the interactions with CO, are discussed.« less

Adsorption and leaching behaviour of bispyribac-sodium in soils.

PubMed

Singh, Neera; Singh, S B

2015-01-01

Adsorption-desorption of the herbicide bispyribac-sodium was studied in four Indian soil types. Bispyribac-sodium was poorly adsorbed in the four soils and adsorption decreased with an increase in the herbicide concentration in solution. Freundlich adsorption coefficient (Kf) values for bispyribac-sodium ranged between 0.37 and 0.87. Slope (1/n) values varied from 0.2 to 0.31 suggesting that bispyribac-sodium adsorption was highly dependent on its initial concentration in solution. Bispyribac-sodium adsorption showed a positive correlation with soil pH (r = 0.809) and clay content (r = 0.699) while no correlation was observed with the organic carbon (r = 0.063) content. Sorbed herbicide was completely desorbed during a single desorption step suggesting that the herbicide was bound by weak adsorptive forces. Leaching studies of herbicide in soil 1 packed column indicated complete loss of soil applied herbicide under a simulated rainfall equivalent to 162 mm.

New Insights into CO2 Adsorption on Layered Double Hydroxide (LDH)-Based Nanomaterials

NASA Astrophysics Data System (ADS)

Tang, Nian; He, Tingyu; Liu, Jie; Li, Li; Shi, Han; Cen, Wanglai; Ye, Zhixiang

2018-02-01

The interlamellar spacing of layered double hydroxides (LDHs) was enlarged by dodecyl sulfonate ions firstly, and then, (3-aminopropyl)triethoxysilane (APS) was chemically grafted (APS/LDHs). The structural characteristics and thermal stability of these prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), reflectance Fourier transform infrared spectrometer (FTIR), thermogravimetric analysis (TG), and elemental analysis (EA) respectively. The CO2 adsorption performance was investigated adopting TG and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results presented that the CO2 adsorption capacity on APS/LDHs was as high as 90 mg/g and showed no obvious reduction during a five cyclic adsorption-desorption test, indicating its superior performance stability. The DRIFTS results showed that both carbamates and weakly bounded CO2 species were generated on APS/LDHs. The weakly adsorbed species was due to the different local chemical environment for CO2 capture provided by the surface moieties of LDHs like free silanol and hydrogen bonds.

Poly(hydroxyethyl methacrylate-co-methacryloylglutamic acid) nanospheres for adsorption of Cd2+ ions from aqueous solutions

NASA Astrophysics Data System (ADS)

Esen, Cem; Şenay, Raziye Hilal; Feyzioğlu, Esra; Akgöl, Sinan

2014-02-01

Poly(2-hydroxyethyl methacrylate-co- N-methacryloyl-( l)-glutamic acid) p(HEMA-MAGA) nanospheres have been synthesized, characterized, and used for the adsorption of Cd2+ ions from aqueous solutions. Nanospheres were prepared by surfactant free emulsion polymerization. The p(HEMA-MAGA) nanospheres were characterized by SEM, FTIR, zeta size, and elemental analysis. The specific surface area of nanospheres was found to be 1,779 m2/g. According to zeta size analysis results, average size of nanospheres is 147.3 nm with poly-dispersity index of 0.200. The goal of this study was to evaluate the adsorption performance of p(HEMA-MAGA) nanospheres for Cd2+ ions from aqueous solutions by a series of batch experiments. The Cd2+ concentration was determined by inductively coupled plasma-optical emission spectrometer. Equilibrium sorption experiments indicated a Cd2+ uptake capacity of 44.2 mg g-1 at pH 4.0 at 25 °C. The adsorption of Cd2+ ions increased with increasing pH and reached a plateau value at around pH 4.0. The data were successfully modeled with a Langmuir equation. A series of kinetics experiments was then carried out and a pseudo-second order equation was used to fit the experimental data. Desorption experiments which were carried out with nitric acid showed that the p(HEMA-MAGA) nanospheres could be reused without significant losses of their initial properties in consecutive adsorption and elution operations.

Adsorption characteristics of UO(2)(2+) and Th(4+) ions from simulated radioactive solutions onto chitosan/clinoptilolite sorbents.

PubMed

Humelnicu, Doina; Dinu, Maria Valentina; Drăgan, Ecaterina Stela

2011-01-15

Adsorption features of UO(2)(2+) and Th(4+) ions from simulated radioactive solutions onto a novel chitosan/clinoptilolite (CS/CPL) composite as beads have been investigated compared with chitosan cross-linked with epichlorohydrin. The effects of contact time, the initial metal ion concentration, sorbent mass and temperature on the adsorption capacity of the CS-based sorbents were investigated. The adsorption kinetics was well described by the pseudo-second order equation, and the adsorption isotherms were better fitted by the Sips model. The maximum experimental adsorption capacities were 328.32 mg Th(4+)/g composite, and 408.62 mg UO(2)(2+)/g composite. The overall adsorption tendency of CS/CPL composite toward UO(2)(2+) and Th(4+) radiocations in the presence of Cu(2+), Fe(2+) and Al(3+), under competitive conditions, followed the order: Cu(2+)>UO(2)(2+)>Fe(2+)>Al(3+), and Cu(2+)>Th(4+)>Fe(2+)>Al(3+), respectively. The negative values of Gibbs free energy of adsorption indicated the spontaneity of the adsorption of radioactive ions on both the CS/CPL composite and the cross-linked CS. The desorption level of UO(2)(2+) from the composite CS/CPL, by using 0.1M Na(2)CO(3), was around 92%, and that of Th(4+) ions, performed by 0.1M HCl, was around 85%, both values being higher than the desorption level of radiocations from the cross-linked CS, which were 89% and 83%, respectively. Copyright © 2010 Elsevier B.V. All rights reserved.

Analysis of volatiles in fire debris by combination of activated charcoal strips (ACS) and automated thermal desorption-gas chromatography-mass spectrometry (ATD/GC-MS).

PubMed

Martin Fabritius, Marie; Broillet, Alain; König, Stefan; Weinmann, Wolfgang

2018-06-04

Adsorption of volatiles in gaseous phase to activated charcoal strip (ACS) is one possibility for the extraction and concentration of ignitable liquid residues (ILRs) from fire debris in arson investigations. Besides liquid extraction using carbon dioxide or hexane, automated thermo-desorption can be used to transfer adsorbed residues to direct analysis by gas chromatography-mass spectrometry (GC-MS). We present a fire debris analysis work-flow with headspace adsorption of volatiles onto ACS and subsequent automated thermo-desorption (ATD) GC-MS analysis. Only a small portion of the ACS is inserted in the ATD tube for thermal desorption coupled to GC-MS, allowing for subsequent confirmation analysis with another portion of the same ACS. This approach is a promising alternative to the routinely used ACS method with solvent extraction of retained volatiles, and the application to fire debris analysis is demonstrated. Copyright © 2018 Elsevier B.V. All rights reserved.

A soil-column gas chromatography (SCGC) approach to explore the thermal desorption behavior of hydrocarbons from soils.

PubMed

Yu, Ying; Liu, Liang; Shao, Ziying; Ju, Tianyu; Sun, Bing; Benadda, Belkacem

2016-01-01

A soil-column gas chromatography approach was developed to simulate the mass transfer process of hydrocarbons between gas and soil during thermally enhanced soil vapor extraction (T-SVE). Four kinds of hydrocarbons-methylbenzene, n-hexane, n-decane, and n-tetradecane-were flowed by nitrogen gas. The retention factor k' and the tailing factor T f were calculated to reflect the desorption velocities of fast and slow desorption fractions, respectively. The results clearly indicated two different mechanisms on the thermal desorption behaviors of fast and slow desorption fractions. The desorption velocity of fast desorption fraction was an exponential function of the reciprocal of soil absolute temperature and inversely correlated with hydrocarbon's boiling point, whereas the desorption velocity of slow desorption fraction was an inverse proportional function of soil absolute temperature, and inversely proportional to the log K OW value of the hydrocarbons. The higher activation energy of adsorption was found on loamy soil with higher organic content. The increase of carrier gas flow rate led to a reduction in the apparent activation energy of adsorption of slow desorption fraction, and thus desorption efficiency was significantly enhanced. The obtained results are of practical interest for the design of high-efficiency T-SVE system and may be used to predict the remediation time.

Factors Influencing NO2 Adsorption/Reduction on Microporous Activated Carbon: Porosity vs. Surface Chemistry

PubMed Central

Ghouma, Imen; Limousy, Lionel; Bennici, Simona

2018-01-01

The textural properties and surface chemistry of different activated carbons, prepared by the chemical activation of olive stones, have been investigated in order to gain insight on the NO2 adsorption mechanism. The parent chemical activated carbon was prepared by the impregnation of olive stones in phosphoric acid followed by thermal carbonization. Then, the textural properties and surface chemistry were modified by chemical treatments including nitric acid, sodium hydroxide and/or a thermal treatment at 900 °C. The main properties of the parent and modified activated carbons were analyzed by N2-adsorption, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) techniques, in order to enlighten the modifications issued from the chemical and thermal treatments. The NO2 adsorption capacities of the different activated carbons were measured in fixed bed experiments under 500 ppmv NO2 concentrations at room temperature. Temperature programmed desorption (TPD) was applied after adsorption tests in order to quantify the amount of the physisorbed and chemisorbed NO2. The obtained results showed that the development of microporosity, the presence of oxygen-free sites, and the presence of basic surface groups are key factors for the efficient adsorption of NO2. PMID:29670008

Microporous metal organic framework [M2(hfipbb)2(ted)] (M=Zn, Co; H2hfipbb=4,4-(hexafluoroisopropylidene)-bis(benzoic acid); ted=triethylenediamine): Synthesis, structure analysis, pore characterization, small gas adsorption and CO2/N2 separation properties

NASA Astrophysics Data System (ADS)

Xu, William W.; Pramanik, Sanhita; Zhang, Zhijuan; Emge, Thomas J.; Li, Jing

2013-04-01

Carbon dioxide is a greenhouse gas that is a major contributor to global warming. Developing methods that can effectively capture CO2 is the key to reduce its emission to the atmosphere. Recent research shows that microporous metal organic frameworks (MOFs) are emerging as a promising family of adsorbents that may be promising for use in adsorption based capture and separation of CO2 from power plant waste gases. In this work we report the synthesis, crystal structure analysis and pore characterization of two microporous MOF structures, [M2(hfipbb)2(ted)] (M=Zn (1), Co (2); H2hfipbb=4,4-(hexafluoroisopropylidene)-bis(benzoic acid); ted=triethylenediamine). The CO2 and N2 adsorption experiments and IAST calculations are carried out on [Zn2(hfipbb)2(ted)] under conditions that mimic post-combustion flue gas mixtures emitted from power plants. The results show that the framework interacts with CO2 strongly, giving rise to relatively high isosteric heats of adsorption (up to 28 kJ/mol), and high adsorption selectivity for CO2 over N2, making it promising for capturing and separating CO2 from CO2/N2 mixtures.

In situ surface transfer process of Cry1Ac protein on SiO2： The effect of biosurfactants for desorption.

PubMed

Miao, Shuzhou; Yuan, Xingzhong; Liang, Yunshan; Wang, Hou; Leng, Lijian; Wu, Zhibin; Jiang, Longbo; Li, Yifu; Mo, Dan; Zeng, Guangming

2018-01-05

Genetically modified Bacillus thuringiensis (Bt) crops, which have been widely used in agricultural transgenic plants, express insecticidal Cry proteins and release the toxin into soils. Taking into consideration the environmental risk of Cry proteins, biosurfactant-rhamnolipids were applied to desorb Cry proteins from soil environment, which has not been elucidated before. Quartz crystal microbalance with dissipation (QCM-D) was used in this article to investigate the adsorption and desorption behaviors of Cry1Ac on SiO 2 surface (model soil). Results showed that patch-controlled electrostatic attraction (PCEA) governed Cry1Ac adsorption to SiO 2, and the solution pH or ionic strength can affect PCEA. The adsorption kinetics could be fitted by the pseudo-second-order model, and the adsorption isotherm was fitted to Langmuir model with correlation coefficients higher than 0.999. The desorption characteristics of Cry1Ac from SiO 2 were assessed in the presence of mono-rhamnolipid, di-rhamnolipid or complex-rhamnolipid. Mono-rhamnolipid exhibited the most significant positive effect on desorption performance. With a complete removal of Cry1Ac reached when mono-rhamnolipid concentration was up to 50mgL -1 . Additionally, the desorption was enhanced at alkaline pH range, and Cry1Ac can be completely and rapidly desorbed by rhamnolipids from SiO 2 at ionic strength of 5×10 -2 M. Copyright © 2017 Elsevier B.V. All rights reserved.

Desorption of oxygen from alloyed Ag/Pt(111)

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

Jankowski, Maciej; Wormeester, Herbert, E-mail: h.wormeester@utwente.nl; Zandvliet, Harold J. W.

2014-06-21

We have investigated the interaction of oxygen with the Ag/Pt(111) surface alloy by thermal desorption spectroscopy (TDS). The surface alloy was formed during the deposition of sub-monolayer amounts of silver on Pt(111) at 800 K and subsequent cooling to 300 K. The low-temperature phase of the surface alloy is composed of nanometer-sized silver rich stripes, embedded within platinum-rich domains, which were characterized with spot profile analysis low energy electron diffraction. The TDS measurements show that oxygen adsorption is blocked on Ag sites: the saturation coverage of oxygen decreases with increasing Ag coverage. Also, the activation energy for desorption (E{sub des})more » decreases with Ag coverage. The analysis of the desorption spectra from clean Pt(111) shows a linear decay of E{sub des} with oxygen coverage, which indicates repulsive interactions between the adsorbed oxygen atoms. In contrast, adsorption on alloyed Ag/Pt(111) leads to an attractive interaction between adsorbed oxygen atoms.« less

Drastic reduction of adsorption of CO and H2 on (111)-type Pd layers

NASA Technical Reports Server (NTRS)

Poppa, H.; Soria, F.

1983-01-01

Clean surfaces of (111)-type Pd layers, grown from the vapor phase on Mo(110) at room temperature, were used to study the adsorption of CO and H2 by temperature-programmed desorption, Auger electron spectroscopy, and low-energy electron diffraction. Mild annealing of the as-grown layers during a single desorption cycle (to about 600 K) drastically reduces the adsorption for both adsorbates. Low-dose argon-ion bombardment introduces surface imperfections which restore a high adsorption probability. The results are interpreted in terms of particular (111)-type surface structures that persist tp layer thicknesses of about four monolayers; the results raise questions with respect to the surface structure of supported thin epitaxial islands and particles of Pd and possibly also with respect to conventional methods of preparing bulk surfaces of Pd for adsorption studies.

The effect of H2O on the adsorption of NO2 on γ-Al2O3: an in situ FTIR/MS study

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

Szanyi, Janos; Kwak, Ja Hun; Chimentao, Ricardo J.

2007-02-15

The effect of water on the adsorption of NO2 onto a γ-Al2O3 catalyst support surface was investigated using Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS). Upon room temperature exposure of the alumina surface to small amounts of NO2, nitrites and nitrates are formed, and at higher NO2 doses only nitrates are observed. The surface nitrates formed were of bridging monodentate, bridging bidentate, and monodentate configuration. At elevated NO2 pressures, the surface hydroxyls were consumed in their reaction with NO2 giving primarily bridge-bound nitrates. A significant amount of weakly adsorbed N2O3 was seen as well. Exposure of the NO2-saturatedmore » γ-Al2O3 surface to H2O resulted in the desorption of some NO2 + NO as H2O interacted with the weakly-held N2O3, while the bridging monodentate surface nitrates converted into monodentate nitrates. The conversion of these oxide-bound nitrates to water-solvated nitrates was observed at high water doses when the presence of liquid-like water is expected on the surface. The addition of H2O to the NO2-saturated γ-Al2O3 did not affect the amount of NOx strongly adsorbed on the support surface. In particular, no NOx desorption was observed when the NO2-saturated sample was heated to 573K prior to room temperature H2O exposure. The effect of water is completely reversible; i.e., during TPD experiments following NO2 and H2O coadsorption, the same IR spectra were observed at temperatures above that required for H2O desorption as seen for NO2 adsorption only experiments.« less

Adsorption of toxic metal ion Cr(VI) from aqueous state by TiO2-MCM-41: equilibrium and kinetic studies.

PubMed

Parida, Kulamani; Mishra, Krushna Gopal; Dash, Suresh Kumar

2012-11-30

This paper deals with the immobilization of various weight percentage of TiO(2) on mesoporous MCM-41, characterization of the materials by X-ray diffraction (XRD), nitrogen adsorption-desorption, Fourier Transform Infrared (FTIR) analysis, UV-vis diffuse reflectance spectroscopy (DRS) and evaluation of the adsorption capacity toward Cr(VI) removal. It is found that the MCM-41 structure retained after loading of TiO(2) but the surface area and pore diameter decreased due to pore blockage. Adsorption of Cr(VI) from aqueous state was investigated on TiO(2)-MCM-41 by changing various parameters such as pH, metal ion concentration, and the temperature. When TiO(2) loading was more than 20 wt.%, the adsorption activity (25)TiO(2)-MCM-41 reduced significantly due to considerable decrease in the surface area. It is also observed that TiO(2) and neat MCM-41 exhibits very less Cr(VI) adsorption compared to TiO(2)-MCM-41. The adsorption of Cr(VI) onto (20)TiO(2)-MCM-41 at pH~5.5 and temperature 323 K was 91% at 100mg/L Cr(VI) metal ion concentration in 80 min. The experimental data fitted well to Langmuir and Freundlich isotherms. The adsorption of Cr(VI) on TiO(2)-MCM-41 followed a second order kinetics with higher values of intra-particle diffusion rate. Thermodynamic parameters suggested that the adsorption process is endothermic in nature and desorption studies indicated a chemisorption mode. Copyright © 2012 Elsevier B.V. All rights reserved.

Effect of equilibration time on Pu desorption from goethite

DOE PAGES

Wong, Jennifer C.; Zavarin, Mavrik; Begg, James D.; ...

2015-01-28

Strongly sorbing ions such as plutonium may become irreversibly bound to mineral surfaces over time implicates near- and far-field transport of Pu. Batch adsorption–desorption data were collected as a function of time and pH to study the surface stability of Pu on goethite. Pu(IV) was adsorbed to goethite over the pH range 4.2 to 6.6 for different periods of time (1, 6, 15, 34 and 116 d). Moreover, following adsorption, Pu was leached from the mineral surface with desferrioxamine B (DFOB), a complexant capable of effectively competing with the goethite surface for Pu. The amount of Pu desorbed from the goethitemore » was found to vary as a function of the adsorption equilibration time, with less Pu removed from the goethite following longer adsorption periods. This effect was most pronounced at low pH. Logarithmic desorption distribution ratios for each adsorption equilibration time were fit to a pH-dependent model. Model slopes decreased between 1 and 116 d adsorption time, indicating that overall Pu(IV) surface stability on goethite surfaces becomes less dependent on pH with greater adsorption equilibration time. The combination of adsorption and desorption kinetic data suggest that non-redox aging processes affect Pu sorption behavior on goethite.« less

Desorption Product Yields Following Cl2 Adsorption on Si(111)7x7: Coverage and Temperature Dependence

DTIC Science & Technology

1991-04-12

only desorption product at approximately 950 K. At higher chloride coverages of 8/6s5 )0.t, a small’ SICl4 TrD signal -’as als:; monitored at 950 K...SiCI2 desorption along with SiCl4 descrption (20). SiCI4 desorbed from a low temperature desorption state at 400 K, whereas SiCI4 and SiCI2 both desorbed...The ratio of the S "l3 an,’ SiC]4 TPD areas suggests that the SiC]3 and SiC]4 TPD signals are both derived froin the desorption of SiCl4 . The growth

Application of activated carbon modified by acetic acid in adsorption and separation of CO2 and CH4

NASA Astrophysics Data System (ADS)

Song, Xue; Wang, Li'ao; Zeng, Yunmin; Zhan, Xinyuan; Gong, Jian; Li, Tong

2018-03-01

Compared with the methods to modify the activated carbons by alkalis for gas adsorption, fewer studies of that by organic acids have been reported. The acid modified activated carbons are usually utilized to treat wastewater, whereas the application in the separation of CO2/CH4 has less been studied. In this study, acetic acid was used to modify activated carbon. N2 adsorption/desorption isotherms and FT-IR were adopted to describe the properties of the samples. According to the adsorption data of pure gas component at 298 K, the gas adsorbed amount and the selectivity on the modified samples were larger than that on the raw sample. Besides, the adsorbed amount of CO2 and the selectivity on 15H-AC in the adsorption breakthrough experiments showed better performance. The results confirm that the method to modify the activated carbons with acetic acid is feasible to improve the adsorption capacity and the separation effect of CO2/CH4.

Effects of aging process on adsorption-desorption and bioavailability of fomesafen in an agricultural soil amended with rice hull biochar.

PubMed

Khorram, Mahdi Safaei; Lin, Dunli; Zhang, Qian; Zheng, Yuan; Fang, Hua; Yu, Yunlong

2017-06-01

Biochar has been introduced as an acceptable soil amendment due to its environmental benefits such as sequestering soil contaminants. However, the aging process in biochar amended soil probably decreases the adsorption capacity of biochar through changing its physico-chemical properties. Adsorption, leaching and bioavailability of fomesafen to corn in a Chinese soil amended by rice hull biochar after 0, 30, 90 and 180days were investigated. Results showed that the addition of 0.5%-2% fresh biochar significantly increases the adsorption of fomesafen 4-26 times compare to unamended soil due to higher SSA of biochar. Biochar amendment also decreases fomesafen concentration in soil pore water by 5%-23% resulting lower risk of the herbicide for cultivated plants. However, the aging process decreased the adsorption capacity of biochar since the adsorption coefficient values which was 1.9-12.4 in 0.5%-2% fresh biochar amended soil, declined to 1.36-4.16, 1.13-2.78 and 0.95-2.31 in 1, 3 and 6-month aged treatments, respectively. Consequently, higher desorption, leaching and bioavailable fraction of fomesafen belonged to 6-month aged treatment. Nevertheless, rice hull biochar was effective for sequestering fomesafen as the adsorption capacity of biochar amended soil after 6months of aging was still 2.5-5 times higher compared to that of unamended soil. Copyright © 2016. Published by Elsevier B.V.

Green preparation of a novel red mud@carbon composite and its application for adsorption of 2,4-dichlorophenoxyacetic acid from aqueous solution.

PubMed

Kazak, Omer; Eker, Yasin Ramazan; Akin, Ilker; Bingol, Haluk; Tor, Ali

2017-10-01

This study reports the eco-friendly preparation of a novel composite material consisting of red mud and carbon spheres, denoted as red mud@C composite, and its application for the removal of 2,4-dichlorophenoxyacetic acid herbicide (2,4-D) from aqueous solution. The preparation route has a green approach because it follows the low-energy consuming one-step hydrothermal process by using starch as a renewable carbon precursor and red mud as a waste from aluminum production industry. Characterization of the red mud@C composite was performed by FT-IR, TGA, SEM, TEM, BET, XRD, and Raman microscopy analyses. The batch adsorption studies revealed that the red mud@C composite has higher 2,4-D adsorption efficiency than those of the red mud and the naked carbon spheres. The maximum removal at initial pH of 3.0 is explained by considering the pKa of 2,4-D and pH of point of zero charge (pH pzc ) of the composite material. The adsorption equilibrium time was 60 min, which followed the pseudo-second-order kinetic model together with intra-particle diffusion model. The isotherm analysis indicated that Freundlich isotherm model better represented the adsorption data, with isotherm parameters of k [15.849 (mg/g) (mg/L) -1/n ] and n (2.985). The prepared composite is reusable at least 5 cycles of adsorption-desorption with no significant decrease in the adsorption capacity.

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

NASA Technical Reports Server (NTRS)

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

1994-01-01

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

Desorption and sublimation kinetics for fluorinated aluminum nitride surfaces

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

King, Sean W., E-mail: sean.king@intel.com; Davis, Robert F.; Nemanich, Robert J.

2014-09-01

The adsorption and desorption of halogen and other gaseous species from surfaces is a key fundamental process for both wet chemical and dry plasma etch and clean processes utilized in nanoelectronic fabrication processes. Therefore, to increase the fundamental understanding of these processes with regard to aluminum nitride (AlN) surfaces, temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) have been utilized to investigate the desorption kinetics of water (H{sub 2}O), fluorine (F{sub 2}), hydrogen (H{sub 2}), hydrogen fluoride (HF), and other related species from aluminum nitride thin film surfaces treated with an aqueous solution of buffered hydrogen fluoride (BHF) dilutedmore » in methanol (CH{sub 3}OH). Pre-TPD XPS measurements of the CH{sub 3}OH:BHF treated AlN surfaces showed the presence of a variety of Al-F, N-F, Al-O, Al-OH, C-H, and C-O surfaces species in addition to Al-N bonding from the AlN thin film. The primary species observed desorbing from these same surfaces during TPD measurements included H{sub 2}, H{sub 2}O, HF, F{sub 2}, and CH{sub 3}OH with some evidence for nitrogen (N{sub 2}) and ammonia (NH{sub 3}) desorption as well. For H{sub 2}O, two desorption peaks with second order kinetics were observed at 195 and 460 °C with activation energies (E{sub d}) of 51 ± 3 and 87 ± 5 kJ/mol, respectively. Desorption of HF similarly exhibited second order kinetics with a peak temperature of 475 °C and E{sub d} of 110 ± 5 kJ/mol. The TPD spectra for F{sub 2} exhibited two peaks at 485 and 585 °C with second order kinetics and E{sub d} of 62 ± 3 and 270 ± 10 kJ/mol, respectively. These values are in excellent agreement with previous E{sub d} measurements for desorption of H{sub 2}O from SiO{sub 2} and AlF{sub x} from AlN surfaces, respectively. The F{sub 2} desorption is therefore attributed to fragmentation of AlF{sub x} species in the mass spectrometer ionizer. H{sub 2} desorption

Comparison of two common adsorption materials for thermal desorption gas chromatography - mass spectrometry of biogenic volatile organic compounds.

PubMed

Marcillo, Andrea; Jakimovska, Viktorija; Widdig, Anja; Birkemeyer, Claudia

2017-09-08

Volatile organic compounds (VOCs) are commonly collected from gaseous samples by adsorption to materials such as the porous polymer Tenax TA. Adsorbed compounds are subsequently released from these materials by thermal desorption (TD) and separated then by gas chromatography (GC) with flame ionization (FID) or mass spectrometry (MS) detection. Tenax TA is known to be particularly suitable for non-polar to semipolar volatiles, however, many volatiles from environmental and biological samples possess a rather polar character. Therefore, we tested if the polymer XAD-2, which so far is widely used to adsorb organic compounds from aqueous and organic solvents, could provide a broader coverage for (semi)polar VOCs during gas-phase sampling. Mixtures of volatile compounds covering a wide range of volatility (bp. 20-256°C) and different chemical classes were introduced by liquid spiking into sorbent tubes with one of the two porous polymers, Tenax TA or XAD-2, and analyzed by TD/GC-MS. At first, an internal standard mixture composed of 17 authentic standards was used to optimize desorption temperature with respect to sorbent degradation and loading time for calibration. Secondly, we tested the detectability of a complex standard mixture composed of 57 volatiles, most of them common constituents of the body odor of mammals. Moreover, the performance of XAD-2 compared with Tenax TA was assessed as limit of quantitation and linearity for the internal standard mixture and 33 compounds from the complex standard mixture. Volatiles were analyzed in a range between 0.01-∼250ng/tube depending on the compound and material. Lower limits of quantitation were between 0.01 and 3 ng±<25% RSD (R 2 >0.9). Interestingly, we found different kinetics for compound adsorption with XAD-2, and a partially better sensitivity in comparison with Tenax TA. For these analytes, XAD-2 might be recommended as an alternative of Tenax TA for TD/GC-MS analysis. Copyright © 2017 Elsevier B.V. All rights

Functionalized SBA-15 materials for bilirubin adsorption

NASA Astrophysics Data System (ADS)

Tang, Tao; Zhao, Yanling; Xu, Yao; Wu, Dong; Xu, Jun; Deng, Feng

2011-05-01

To investigate the driving force for bilirubin adsorption on mesoporous materials, a comparative study was carried out between pure siliceous SBA-15 and three functionalized SBA-15 mesoporous materials: CH 3-SBA-15 (MS), NH 2-SBA-15 (AS), and CH 3/NH 2-SBA-15 (AMS) that were synthesized by one-pot method. The obtained materials exhibited large surface areas (553-810 m 2/g) and pore size (6.6-7.1 nm) demonstrated by XRD and N 2-ad/desorption analysis. The SEM images showed that the materials had similar fiberlike morphology. The functionalization extent was calculated according to 29Si MAS NMR spectra and it was close to the designed value (10%). The synthesized mesoporous materials were used as bilirubin adsorbents and showed higher bilirubin adsorption capacities than the commercial active carbon. The adsorption capacities of amine functionalized samples AMS and AS were larger than those of pure siliceous SBA-15 and MS, indicating that electrostatic interaction was the dominant driving force for bilirubin adsorption on mesoporous materials. Increasing the ionic strength of bilirubin solution by adding NaCl would decrease the bilirubin adsorption capacity of mesoporous material, which further demonstrated that the electrostatic interaction was the dominant driving force for bilirubin adsorption. In addition, the hydrophobic interaction provided by methyl groups could promote the bilirubin adsorption.

Influence of dissolved organic matter and activated carbon pore characteristics on organic micropollutant desorption.

PubMed

Aschermann, Geert; Zietzschmann, Frederik; Jekel, Martin

2018-04-15

By simulating decreasing inflow concentrations, the extent of desorption of organic micropollutants (OMP) from three activated carbons (AC) was examined in laboratory batch tests. The tested AC showed strong differences in pore size distribution and could therefore be characterized as typical micro-, meso- and macroporous AC, respectively. Adsorption and desorption conditions were varied by using drinking water (containing dissolved organic matter (DOM)) and DOM-free pure water as background solutions to examine the influence of DOM on OMP desorption for the different AC. Under ideal conditions (adsorption and desorption in pure water) adsorption of the tested OMP was found to be highly up to completely reversible for all tested AC. Under real conditions (adsorption and desorption in drinking water) additional DOM adsorption affects desorption in different ways depending on the AC pore structure. For the micro- and mesoporous AC, an increased irreversibility of OMP adsorption was found, which shows that DOM adsorption prevents OMP desorption. This could be referred to pore blockage effects that occur during the parallel adsorption of DOM and OMP. For the macroporous AC, DOM adsorption led to an enhanced OMP desorption which could be attributed to displacement processes. These results show that smaller pores tend to be blocked by DOM which hinders OMP from desorption. The overall larger pores of the macroporous AC do not get blocked which could allow (i) OMP to desorb and (ii) DOM to enter and displace OMP. Copyright © 2018 Elsevier Ltd. All rights reserved.

Efficient adsorption of Hg (II) ions in water by activated carbon modified with melamine

NASA Astrophysics Data System (ADS)

Qin, Hangdao; Meng, Jingling; Chen, Jing

2018-04-01

Removal of Hg (II) ions from industrial wastewater is important for the water treatment, and adsorption is an efficient treatment process. Activated carbon (AC) was modified with melamine, which introduced nitrogen-containing functional groups onto AC surface. Original AC and melamine modified activated carbon (ACM) were characterized by elemental analysis, N2 adsorption-desorption, determination of the pH of the point of zero charge (pHpzc) and X-ray photoelectron spectroscopy (XPS) and their performance in the adsorption of Hg(II) ions was investigated. Langmuir model fitted the experimental data of equilibrium isotherms well. ACM showed the higher Hg (II) ions adsorption capacity, increasing more than more than 1.8 times compared to the original one. Moreover, ACM showed a wider pH range for the maximum adsorption than the parent AC.

Molecular simulation of methane adsorption characteristics on coal macromolecule

NASA Astrophysics Data System (ADS)

Yang, Zhiyuan; He, Xiaoxiao; Meng, Zhuoyue; Xue, Wenying

2018-02-01

In this paper, the molecular model of anthracite named Wender2 was selected to study the adsorption behaviour of single component CH4 and the competitive adsorption of CH4/CO2, CH4/H2O and CH4/N2. The molecular model of anthracite was established by molecular simulation software (Materials Studio 8.0), and Grand Canonical Monte Carlo (GCMC) simulations were carried out to investigate the single and binary component adsorption. The effects of pressure and temperature on the adsorption position, adsorption energy and adsorption capacity were mainly discussed. The results show that for the single component adsorption, the adsorption capacity of CH4 increases rapidly with the pressure ascending, and then tends to be stable after the first step. The low temperature is favourable for the adsorption of CH4, and the high temperature promotes desorption quantity of CH4 from the coal. Adsorbent molecules are preferentially adsorbed on the edge of coal macromolecules. The order of adsorption capacity of CH4/CO2, CH4/H2O and CH4/N2 in the binary component is H2O>CO2>CH4>N2. The change of pressure has little effect on the adsorption capacity of the adsorbent in the competitive adsorption, but it has a great influence on the adsorption capacity of the adsorbent, and there is a positive correlation between them.

Adsorption of selected volatile organic vapors on multiwall carbon nanotubes.

PubMed

Shih, Yang-hsin; Li, Mei-syue

2008-06-15

Carbon nanotubes are expected to play an important role in sensing, pollution treatment and separation techniques. This study examines the adsorption behaviors of volatile organic compounds (VOCs), n-hexane, benzene, trichloroethylene and acetone on two multiwall carbon nanotubes (MWCNTs), CNT1 and CNT2. Among these VOCs, acetone exhibits the highest adsorption capacity. The highest adsorption enthalpies and desorption energies of acetone were also observed. The strong chemical interactions between acetone and both MWCNTs may be the result from chemisorption on the topological defects. The adsorption heats of trichloroethylene, benzene, and n-hexane are indicative of physisorption on the surfaces of both MWCNTs. CNT2 presents a higher adsorption capacity than CNT1 due to the existence of an exterior amorphous carbon layer on CNT2. The amorphous carbon enhances the adsorption capacity of organic chemicals on carbon nanotubes. The morphological and structure order of carbon nanotubes are the primary affects on the adsorption process of organic chemicals.

Adsorption of CO2 on KOH activated, N-enriched carbon derived from urea formaldehyde resin: kinetics, isotherm and thermodynamic studies

NASA Astrophysics Data System (ADS)

Tiwari, Deepak; Bhunia, Haripada; Bajpai, Pramod K.

2018-05-01

High surface area nitrogen enriched carbon adsorbents were prepared from a low cost and widely available urea-formaldehyde resin using a standard chemical activation with KOH and characterized using different characterization techniques for their porous structure and surface functional groups. Maximum surface area and total pore volume of 4547 m2 g-1 and 4.50 cm3 g-1 were found by controlling the activation conditions. Nitrogen content of this sample was found to be 5.62%. Adsorption of CO2 uptake for the prepared carbon adsorbents was studied using a dynamic fixed bed adsorption system at different adsorption temperatures (30-100 °C) and at different CO2 concentrations (5-12.5%), relevant from the flue gas point application. Maximum CO2 uptake of 1.40 mmol g-1 for UFA-3-700 at 30 °C under 12.5% CO2 flow was obtained. Complete regenerability of the adsorbents over multiple adsorption-desorption cycles was obtained. Fractional order kinetic model provided best description over all adsorption temperatures and CO2 concentrations. Heterogeneity of the adsorbent surface was confirmed from Temkin adsorption isotherm model fit and isosteric heat of adsorption values. Negative value of ΔG° and ΔH° confirms spontaneous, feasible nature and exothermic nature of adsorption process. Overall, very high surface area of carbon adsorbent makes this adsorbent a new promising carbon material for CO2 capture from power plant flue gas and for other relevant applications.

Nanoscale zerovalent iron (nZVI) supported by natural and acid-activated sepiolites: the effect of the nZVI/support ratio on the composite properties and Cd2+ adsorption.

PubMed

Habish, Amal Juma; Lazarević, Slavica; Janković-Častvan, Ivona; Jokić, Bojan; Kovač, Janez; Rogan, Jelena; Janaćković, Đorđe; Petrović, Rada

2017-01-01

Natural (SEP) and partially acid-activated (AAS) sepiolites were used to prepare composites with nanoscale zerovalent iron (nZVI) at different (SEP or AAS)/nZVI ratios in order to achieve the best nZVI dispersibility and the highest adsorption capacity for Cd 2+ . Despite the higher surface area and pore volume of AAS, better nZVI dispersibility was achieved by using SEP as the support. On the other hand, a lower oxidation degree was achieved during the synthesis using AAS. X-ray photoelectron spectroscopy (XPS) analysis of the composite with the best nZVI dispersibility, before and after Cd 2+ adsorption, confirmed that the surface of the nZVI was composed of oxidized iron species. Metallic iron was not present on the surface, but it was detected in the subsurface region after sputtering. The content of zerovalent iron decreased after Cd 2+ adsorption as a result of iron oxidation during Cd 2+ adsorption. The XPS depth profile showed that cadmium was present not only at the surface of the composite but also in the subsurface region. The adsorption isotherms for Cd 2+ confirmed that the presence of SEP and AAS decreased the agglomeration of the nZVI particles in comparison to the pure nZVI, which provided a higher adsorption capacity. The results showed that the prevention of both aggregation and oxidation during the synthesis was necessary for obtaining an SEP/AAS-nZVI composite with a high adsorption capacity, but oxidation during adsorption was beneficial for Cd 2+ removal. The formation of strong bonds between Cd 2+ and the adsorbents sites of different energy until monolayer formation was proposed according to modeling of the adsorption isotherms.

H{sub 2} adsorption in Li-decorated porous graphene

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

Seenithurai, S.; Pandyan, R. Kodi; Kumar, S. Vinodh

Porous graphene (PG) has been decorated with Li atoms and subsequently studied the hydrogen (H{sub 2}) adsorption characteristics, by using Density Functional Theory (DFT)-based calculations. A 2×2 PG has been decorated with eight Li atoms. Upto four H{sub 2} molecules get adsorbed on each Li atom. The maximum H{sub 2} storage capacity that could be achieved in 2×2PG-8Li is 8.95 wt% which is higher than the U.S. DOE’s revised target for the on-board vehicles. The average H{sub 2} adsorption binding energy is 0.535 eV/H{sub 2}, which lies between 0.2-0.6 eV/H{sub 2} that is required for achieving adsorption and desorption atmore » near ambient conditions. Thus, Li-decorated PG could be a viable option for on-board automobile applications.« less

SO2 Adsorption on CeO2(100) and CeO2(111)

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

Mullins, David R.

2016-09-13

The adsorption and reaction of sulfur dioxide, SO2, was studied on oxidized and reduced CeOX(100) and compared to previous results on CeOX(111). SO2 adsorbs on oxidized CeO2(100) as sulfite, SO32-, at 200 K and sulfite is the only adsorbate observed on the surface at any temperature. The sulfite desorbs monotonically from 200 to 700 K. The adsorption and desorption of SO2 does not result in any change in the Ce4+ oxidation state. SO2 also adsorbs as sulfite on reduced CeO1.7(100) at 200 K. There is also a small amount of elemental sulfur, S0, formed. As the sample is heated themore » sulfite decomposes into sulfide, S2-. Roughly 25 % of the adsorbed S either desorbs or diffuses into the bulk of the reduced ceria. The decomposition, and resulting formation of S2- and O2-, re-oxidize some of the Ce3+ to Ce4+. Unlike what has been observed following the adsorption and reaction of many other molecules, the adsorption and reaction of SO2 is virtually identical on CeOX(100) and CeOX(111).« less

Fiber optic sensors based on hybrid phenyl-silica xerogel films to detect n-hexane: determination of the isosteric enthalpy of adsorption.

PubMed

Echeverría, Jesús C; Calleja, Ignacio; Moriones, Paula; Garrido, Julián J

2017-01-01

We investigated the response of three fiber optic sensing elements prepared at pH 10 from phenyltriethoxysilane (PhTEOS) and tetraethylsilane (TEOS) mixtures with 30, 40, and 50% PhTEOS in the silicon precursor mixture. The sensing elements are referred to as Ph30, Ph40 and Ph50, respectively. The films were synthesized by the sol-gel method and affixed to the end of optical fibers by the dip-coating technique. Fourier transform infrared spectroscopy, N 2 adsorption-desorption at 77 K and X-ray diffraction analysis were used to characterize the xerogels. At a given pressure of n -hexane, the response of each sensing element decreased with temperature, indicating an exothermic process that confirmed the role of adsorption in the overall performance of the sensing elements. The isosteric adsorption enthalpies were obtained from the calibration curves at different temperatures. The magnitude of the isosteric enthalpy of n -hexane increased with the relative response and reached a plateau that stabilized at approximately -31 kJ mol -1 for Ph40 and Ph50 and at approximately -37 kJ mol -1 for Ph30. This indicates that the adsorbate-adsorbent interaction was dominant at lower relative pressure and condensation of the adsorbate on the mesopores was dominant at higher relative pressure.

Experimental study on removals of SO2 and NOX using adsorption of activated carbon/microwave desorption.

PubMed

Ma, Shuang-Chen; Yao, Juan-Juan; Gao, Li; Ma, Xiao-Ying; Zhao, Yi

2012-09-01

Experimental studies on desulfurization and denitrification were carried out using activated carbon irradiated by microwave. The influences of the concentrations of nitric oxide (NO) and sulfur dioxide (SO 2 ), the flue gas coexisting compositions, on adsorption properties of activated carbon and efficiencies of desulfurization and denitrification were investigated. The results show that adsorption capacity and removal efficiency of NO decrease with the increasing of SO 2 concentrations in flue gas; adsorption capacity of NO increases slightly first and drops to 12.79 mg/g, and desulfurization efficiency descends with the increasing SO 2 concentrations. Adsorption capacity of SO 2 declines with the increasing of O 2 content in flue gas, but adsorption capacity of NO increases, and removal efficiencies of NO and SO 2 could be larger than 99%. Adsorption capacity of NO declines with the increase of moisture in the flue gas, but adsorption capacity of SO 2 increases and removal efficiencies of NO and SO 2 would be relatively stable. Adsorption capacities of both NO and SO 2 decrease with the increasing of CO 2 content; efficiencies of desulfurization and denitrification augment at the beginning stage, then start to fall when CO 2 content exceeds 12.4%. The mechanisms of this process are also discussed. [Box: see text].

Ammonia modification of activated carbon to enhance carbon dioxide adsorption: Effect of pre-oxidation

NASA Astrophysics Data System (ADS)

Shafeeyan, Mohammad Saleh; Daud, Wan Mohd Ashri Wan; Houshmand, Amirhossein; Arami-Niya, Arash

2011-02-01

A commercial granular activated carbon (GAC) was subjected to thermal treatment with ammonia for obtaining an efficient carbon dioxide (CO2) adsorbent. In general, CO2 adsorption capacity of activated carbon can be increased by introduction of basic nitrogen functionalities onto the carbon surface. In this work, the effect of oxygen surface groups before introduction of basic nitrogen functionalities to the carbon surface on CO2 adsorption capacity was investigated. For this purpose two different approaches of ammonia treatment without preliminary oxidation and amination of oxidized samples were studied. Modified carbons were characterized by elemental analysis and Fourier Transform Infrared spectroscopy (FT-IR) to study the impact of changes in surface chemistry and formation of specific surface groups on adsorption properties. The texture of the samples was characterized by conducting N2 adsorption/desorption at -196 °C. CO2 capture performance of the samples was investigated using a thermogravimetric analysis (TGA). It was found that in both modification techniques, the presence of nitrogen functionalities on carbon surface generally increased the CO2 adsorption capacity. The results indicated that oxidation followed by high temperature ammonia treatment (800 °C) considerably enhanced the CO2 uptake at higher temperatures.

Adsorption and Photodesorption of CO from Charged Point Defects on TiO 2 (110)

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

Mu, Rentao; Dahal, Arjun; Wang, Zhi-Tao

Adsorption and photodesorption of weakly-bound carbon monoxide, CO, from reduced and hydroxylated rutile TiO2(110) (r- and h- TiO2(110)) at sub-monolayer coverages is studied with atomically-resolved scanning tunneling microscopy (STM) along with ensemble-averaged temperature-programmed desorption (TPD) and angle-resolved photon-stimulated desorption (PSD) at low temperatures ( 50 K). STM data weighted by the concentration of each kind of adsorption sites on r-TiO2(110) give an adsorption probability which is the highest for the bridging oxygen vacancies (VO) and very low for the Ti5c sites closest to VO. Occupancy of the remaining Ti5c sites with CO is significant, but smaller than for VO. Themore » probability distribution for the different adsorption sites corresponds to a very small difference in CO adsorption energies: < 0.02 eV. We also find that UV irradiation stimulates both diffusion and desorption of CO at low temperature. CO photodesorbs primarily from the vacancies with a bi-modal angular distribution. In addition to a major, normal to the surface component, there is a broader cosine component indicating scattering from the surface which likely also leads to photo-stimulated diffusion. Hydroxylation of VO’s does not significantly change the CO PSD yield and angular distribution, indicating that not atomic but rather electronic surface defects are involved in the site-specific PSD process. We suggest that photodesorption can be initiated by recombination of photo-generated holes with excess unpaired electrons localized near the surface point-defect (either VO or bridging hydroxyl), leading to the surface atoms rearrangement and ejection of the weakly-bound CO molecules.« less

Amination of activated carbon for enhancing phenol adsorption: Effect of nitrogen-containing functional groups

NASA Astrophysics Data System (ADS)

Yang, Guo; Chen, Honglin; Qin, Hangdao; Feng, Yujun

2014-02-01

To study the contribution of different nitrogen-containing functional groups to enhancement of phenol adsorption, the aminated activated carbons (AC) were characterized by N2 adsorption/desorption, XPS, Boehm titration, and pH drift method and tested for adsorption behaviors of phenol. Adsorption isotherm fitting revealed that the Langmuir model was preferred for the aminated ACs. The adsorption capacity per unit surface area (qm/SSABET) was linearly correlated with the amount of pyridinic and pyrrolic N, which suggested that these two functional groups played a critical role in phenol adsorption. The enhancement of adsorption capacity was attributed to the strengthened π-π dispersion between phenol and basal plane of AC by pyridinic, pyrrolic N. The adsorption kinetics was found to follow the pseudo-second-order kinetic model, and intraparticle diffusion was one of the rate-controlling steps in the adsorption process.

Photoluminescence Probing of Complex H2O Adsorption on InGaN/GaN Nanowires.

PubMed

Maier, Konrad; Helwig, Andreas; Müller, Gerhard; Hille, Pascal; Teubert, Jörg; Eickhoff, Martin

2017-02-08

We demonstrate that the complex adsorption behavior of H 2 O on InGaN/GaN nanowire arrays is directly revealed by their ambient-dependent photoluminescence properties. Under low-humidity, ambient-temperature, and low-excitation-light conditions, H 2 O adsorbates cause a quenching of the photoluminescence. In contrast, for high humidity levels, elevated temperature, and high excitation intensity, H 2 O adsorbates act as efficient photoluminescence enhancers. We show that this behavior, which can only be detected due to the low operation temperature of the InGaN/GaN nanowires, can be explained on the basis of single H 2 O adsorbates forming surface recombination centers and multiple H 2 O adsorbates forming surface passivation layers. Reversible creation of such passivation layers is induced by the photoelectrochemical splitting of adsorbed water molecules and by the interaction of reactive H 3 O + and OH - ions with photoactivated InGaN surfaces. Due to electronic coupling of adsorbing molecules with photoactivated surfaces, InGaN/GaN nanowires act as sensitive nanooptical probes for the analysis of photoelectrochemical surface processes.

Electrostatic Repulsion-Induced Desorption of Dendritic Viologen-Arranged Molecules Anchored on a Gold Surface through a Gold-Thiolate Bond Leading to a Tunable Molecular Template.

PubMed

Kawauchi, Takehiro; Kojima, Takahiro; Sakaguchi, Hiroshi; Iyoda, Tomokazu

2018-06-05

We investigated the adsorption and desorption behavior of self-assembled monolayers (SAMs) on gold derived from dendritic viologen-arranged molecules with an ω-mercaptodecyl group (A n, n (dendritic generation) = 0-3) at the apex of the dendritic structure in polar solvents. The adsorption of the dendritic molecules occurred quickly and saturated within a few minutes in an acetonitrile/ethanol (1/1, v/v) mixture at a concentration of 2 mM. Atomic force microscopy images of the SAMs showed flat surfaces regardless of the dendritic generation because the peripheral viologen units were closely packed at the surface of the molecular layer. Individual A3 molecules immobilized on the substrate were observed by scanning tunneling microscopy measurements of a mixed SAM with decanethiol. The desorption behaviors of dendritic molecules from the A n-SAMs in several solvents such as water were also investigated. The spontaneous desorption of the A n-SAM occurred more rapidly than that of a conventional n-alkanethiol SAM. However, the desorption was inhibited by adding electrolytes such as NaNO 3 due to the shielding effect on the electrostatic repulsion between the dendritic molecules. These results indicate that the surface density of the dendritic molecules can be controlled through the desorption.

Response properties in the adsorption-desorption model on a triangular lattice

NASA Astrophysics Data System (ADS)

Šćepanović, J. R.; Stojiljković, D.; Jakšić, Z. M.; Budinski-Petković, Lj.; Vrhovac, S. B.

2016-06-01

The out-of-equilibrium dynamical processes during the reversible random sequential adsorption (RSA) of objects of various shapes on a two-dimensional triangular lattice are studied numerically by means of Monte Carlo simulations. We focused on the influence of the order of symmetry axis of the shape on the response of the reversible RSA model to sudden perturbations of the desorption probability Pd. We provide a detailed discussion of the significance of collective events for governing the time coverage behavior of shapes with different rotational symmetries. We calculate the two-time density-density correlation function C(t ,tw) for various waiting times tw and show that longer memory of the initial state persists for the more symmetrical shapes. Our model displays nonequilibrium dynamical effects such as aging. We find that the correlation function C(t ,tw) for all objects scales as a function of single variable ln(tw) / ln(t) . We also study the short-term memory effects in two-component mixtures of extended objects and give a detailed analysis of the contribution to the densification kinetics coming from each mixture component. We observe the weakening of correlation features for the deposition processes in multicomponent systems.

Ad-/desorption behavior of Sulfadiazine on soil and soil components

NASA Astrophysics Data System (ADS)

Meng, N.; Lewandowski, H.; Kasteel, R.; Narres, H.-D.; Klumpp, E.; Vereecken, H.

2009-04-01

Sulfadiazine [4-amino-N-(2-pyrimidinyl)benzene sulfonamide, SDZ] belongs to the widely used antibacterial veterinary pharmaceuticals which reach the environment by the application of manure. Therefore the adsorption and desorption behavior of 14C labeled sulfadiazine was investigated with different inorganic soil components including Al2O3, goethite, illite and compared with air-dried topsoil. The batch sorption experiments with Al2O3and soil were performed in natural pH-values (8.2 and 7.5, negatively charged SDZ). Experiments with illite and goethite were done with pH-values of 4.2 and 6.8 (natural pH of illite and goethite, neutral and partly negatively charged SDZ) and also done in buffer solution about pH 8 for comparing the adsorption on all adsorbents in same pH range. The adsorption isotherms on all sorbents are strongly nonlinear and can be fitted well by the Freundlich equation. From the initial slope of the isotherm the partition coefficient Kd could be determined. The adsorption of SDZ on illite at pH 4.2 and on goethite at pH 6.8 has higher Kd-values than at pH 8, which demonstrates that the negative charge of SDZ obstructs the adsorption. The desorption isotherms show hysteresis effects for all adsorbents. The strong hysteresis was found for goethite and soil indicates strongly physical or chemical binding. On the other hand, the low hysteresis effect for Al2O3 and illite indicates the weak binding of the adsorbed SDZ. The properties of the inorganic matrix and especially the charges of the inorganic compounds in relation to the charge of SDZ are important parameters for the sorption process. The data could be described by modeling with different sorption rates and sites.

Synthesis of Hierarchically Structured Hybrid Materials by Controlled Self-Assembly of Metal-Organic Framework with Mesoporous Silica for CO2 Adsorption.

PubMed

Chen, Chong; Li, Bingxue; Zhou, Lijin; Xia, Zefeng; Feng, Nengjie; Ding, Jing; Wang, Lei; Wan, Hui; Guan, Guofeng

2017-07-12

The HKUST-1@SBA-15 composites with hierarchical pore structure were constructed by in situ self-assembly of metal-organic framework (MOF) with mesoporous silica. The structure directing role of SBA-15 had an obvious impact on the growth of MOF crystals, which in turn affected the morphologies and structural properties of the composites. The pristine HKUST-1 and the composites with different content of SBA-15 were characterized by XRD, N 2 adsorption-desorption, SEM, TEM, FT-IR, TG, XPS, and CO 2 -TPD techniques. It was found that the composites were assembled by oriented growth of MOF nanocrystals on the surfaces of SBA-15 matrix. The interactions between surface silanol groups and metal centers induced structural changes and resulted in the increases in surface areas as well as micropore volumes of hybrid materials. Besides, the additional constraints from SBA-15 also restrained the expansion of HKUST-1, contributing to their smaller crystal sizes in the composites. The adsorption isotherms of CO 2 on the materials were measured and applied to calculate the isosteric heats of adsorption. The HS-1 composite exhibited an increase of 15.9% in CO 2 uptake capacity compared with that of HKUST-1. Moreover, its higher isosteric heats of CO 2 adsorption indicated the stronger interactions between the surfaces and CO 2 molecules. The adsorption rate of the composite was also improved due to the introduction of mesopores. Ten cycles of CO 2 adsorption-desorption experiments implied that the HS-1 had excellent reversibility of CO 2 adsorption. This study was intended to provide the possibility of assembling new composites with tailored properties based on MOF and mesoporous silica to satisfy the requirements of various applications.

The adsorption-desorption transition of double-stranded DNA interacting with an oppositely charged dendrimer induced by multivalent anions.

PubMed

Jiang, Yangwei; Zhang, Dong; Zhang, Yaoyang; Deng, Zhenyu; Zhang, Linxi

2014-05-28

The adsorption-desorption transition of DNA in DNA-dendrimer solutions is observed when high-valence anions, such as hexavalent anions, are added to the DNA-dendrimer solutions. In the DNA-dendrimer solutions with low-valence anions, dendrimers bind tightly with the V-shaped double-stranded DNA. When high-valence anions, such as pentavalent or hexavalent anions, are added to the DNA-dendrimer solutions, the double-stranded DNA chains can be stretched straightly and the dendrimers are released from the double-stranded DNA chains. In fact, adding high-valence anions to the solutions can change the charge spatial distribution in the DNA-dendrimer solutions, and weaken the electrostatic interactions between the positively charged dendrimers and the oppositely charged DNA chains. Adsorption-desorption transition of DNA is induced by the overcharging of dendrimers. This investigation is capable of helping us understand how to control effectively the release of DNA in gene/drug delivery because an effective gene delivery for dendrimers includes non-covalent DNA-dendrimer binding and the effective release of DNA in gene therapy.

Fate and transport with material response characterization of green sorption media for copper removal via desorption process.

PubMed

Chang, Ni-Bin; Houmann, Cameron; Lin, Kuen-Song; Wanielista, Martin

2016-07-01

Multiple adsorption and desorption cycles are required to achieve the reliable operation of copper removal and recovery. A green sorption media mixture composed of recycled tire chunk, expanded clay aggregate, and coconut coir was evaluated in this study for its desorptive characteristics as a companion study of the corresponding adsorption process in an earlier publication. We conducted a screening of potential desorbing agents, batch desorption equilibrium and kinetic studies, and batch tests through 3 adsorption/desorption cycles. The desorbing agent screening revealed that hydrochloric acid has good potential for copper desorption. Equilibrium data fit the Freundlich isotherm, whereas kinetic data had high correlation with the Lagergren pseudo second-order model and revealed a rapid desorption reaction. Batch equilibrium data over 3 adsorption/desorption cycles showed that the coconut coir and media mixture were the most resilient, demonstrating they could be used through 3 or more adsorption/desorption cycles. FE-SEM imaging, XRD, and EDS analyses supported the batch adsorption and desorption results showing significant surface sorption of CuO species in the media mixture and coconut coir, followed by partial desorption using 0.1 M HCl as a desorbing agent. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effect of inorganic regenerant properties on pharmaceutical adsorption and desorption performance on polymer anion exchange resin.

PubMed

Zheng, Shaokui; Li, Xiaofeng; Zhang, Xueyu; Wang, Wei; Yuan, Shengliu

2017-09-01

This study investigated the potential effect of four frequently used inorganic regenerant properties (i.e., ionic strength, cation type, anion type, and regeneration solution volume) on the desorption and adsorption performance of 14 pharmaceuticals, belonging to 12 therapeutic classes with different predominant chemical forms and hydrophobicities, using polymeric anion exchange resin (AER)-packed fixed-bed column tests. After preconditioning with NaCl, NaOH, or saline-alkaline (SA) solutions, all resulting mobile counterion types of AERs effectively adsorbed all 14 pharmaceuticals, where the preferential magnitude of OH - -type = Cl -  + OH - -type > Cl - -type. During regeneration, ionic strength (1 M versus 3 M NaCl) had no significant influence on desorption performance for any of the 14 pharmaceuticals, while no regenerant cation (HCl versus NaCl) or anion type (NaCl versus NaOH and SA) achieved higher desorption efficiencies for all pharmaceuticals. A volumetric increase in 1 M or 3 M NaCl solutions significantly improved the desorption efficiencies of most pharmaceuticals, irrespective of ionic strength. The results indicate that regeneration protocols, including regenerant cation type, anion type and volume, should be optimized to improve pharmaceutical removal by AERs. Copyright © 2017 Elsevier Ltd. All rights reserved.

Development of TRPN dendrimer-modified disordered mesoporous silica for CO{sub 2} capture

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

Zhang, Xiaoyun; Zhang, Sisi; Qin, Hongyan

2014-08-15

Highlights: • A novel series of TRPN dendrimers are synthesized. • Structurally disordered mesoporous silica was used to develop the CO{sub 2} adsorbent. • The CO{sub 2} adsorption capacity is relatively high. • The sorbent exhibits a high stability after 12 cycling runs. • The sorbent achieves complete desorption at low temperature (60 °C). - Abstract: A novel series of tri(3-aminopropyl) amine (TRPN) dendrimers were synthesized and impregnated on structurally disordered mesoporous silica (DMS) to generate CO{sub 2} adsorbents (TS). The physicochemical and adsorption properties of the adsorbents before and after dendrimer modification were characterized by X-ray diffraction (XRD), thermogravimetricmore » analysis (TGA), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and N{sub 2} adsorption–desorption (N{sub 2}-BET) techniques. CO{sub 2} adsorption–desorption tests indicated that the sorbent demonstrates high CO{sub 2} adsorption capacity (138.1 mg g{sup −1} for G1 sample TS-G1-3CN-50 and 91.7 mg g{sup −1} for G2 sample TS-G2-6CN-50), and can completely desorb CO{sub 2} under vacuum at 60 °C. Its CO{sub 2} adsorption capacity at 25 °C increases with the amine loading, achieving the highest adsorption capacity (140.6 mg g{sup −1} for TS-G1-3CN) at 60%. The developed TS materials exhibited excellent cycling stability. After 12 consecutive adsorption–desorption runs, TS-G1-3CN-50 shows an adsorption capacity of 136.0 mg g{sup −1}, retaining 98.5% of its original value.« less

Time-resolved chromatographic analysis and mechanisms in adsorption and catalysis.

PubMed

Roubani-Kalantzopoulou, Fani

2009-03-06

The main object of this review is the study of fundamentals of adsorption and heterogeneous catalysis, a benefit for the understanding of adsorptive and catalytic properties. This work aims to define and record, with the utmost accuracy, the phenomena and the possible reactions. A new methodology for the study of the adsorption is presented, which is a version of the well-known inverse gas chromatography. This reversed-flow inverse gas chromatography (RF-IGC) is technically very simple, and it is combined with a mathematical analysis that gives the possibility for the estimation of various physicochemical parameters related to adsorbent or catalyst characterization, under conditions compatible with the operation of real adsorbents and catalysts. On this base, this methodology has been successfully applied to the study of the impact of air pollutants, volatile organic and/or inorganic, on many solids such as marbles, ceramics, oxide-pigments of works of art, building materials, authentic statues of the Greek Archaeological Museums. Moreover, this methodology proved to be a powerful tool for studying the topography of active sites of heterogeneous surfaces in the nano-scale domain. Thus, some very important local quantities for the surface chemistry have been determined experimentally for many solids including thin films. These physicochemical local quantities (among which adsorption energy and entropy, surface diffusion coefficient, probability density function) have been determined from the experimental pairs of height of extra chromatographic peaks and time by a nonlinear least-squares method, through personal computer programs written in GW BASIC and lately in FORTRAN. Through the time-resolved analysis the surface characterization of the examined materials took place. In addition, the kinetic constants responsible for adsorption/desorption and surface chemical reactions have also been calculated. Thus, important answers have been provided to the following

Adsorption of Reactive Red M-2BE dye from water solutions by multi-walled carbon nanotubes and activated carbon.

PubMed

Machado, Fernando M; Bergmann, Carlos P; Fernandes, Thais H M; Lima, Eder C; Royer, Betina; Calvete, Tatiana; Fagan, Solange B

2011-09-15

Multi-walled carbon nanotubes and powdered activated carbon were used as adsorbents for the successful removal of Reactive Red M-2BE textile dye from aqueous solutions. The adsorbents were characterised by infrared spectroscopy, N(2) adsorption/desorption isotherms and scanning electron microscopy. The effects of pH, shaking time and temperature on adsorption capacity were studied. In the acidic pH region (pH 2.0), the adsorption of the dye was favourable using both adsorbents. The contact time to obtain equilibrium at 298K was fixed at 1h for both adsorbents. The activation energy of the adsorption process was evaluated from 298 to 323K for both adsorbents. The Avrami fractional-order kinetic model provided the best fit to the experimental data compared with pseudo-first-order or pseudo-second-order kinetic adsorption models. For Reactive Red M-2BE dye, the equilibrium data were best fitted to the Liu isotherm model. Simulated dyehouse effluents were used to check the applicability of the proposed adsorbents for effluent treatment. Copyright © 2011 Elsevier B.V. All rights reserved.

Synthesis and application of a new carboxylated cellulose derivative. Part I: Removal of Co(2+), Cu(2+) and Ni(2+) from monocomponent spiked aqueous solution.

PubMed

Teodoro, Filipe Simões; Ramos, Stela Nhandeyara do Carmo; Elias, Megg Madonyk Cota; Mageste, Aparecida Barbosa; Ferreira, Gabriel Max Dias; da Silva, Luis Henrique Mendes; Gil, Laurent Frédéric; Gurgel, Leandro Vinícius Alves

2016-12-01

A new carboxylated cellulose derivative (CTA) was prepared from the esterification of cellulose with 1,2,4-Benzenetricarboxylic anhydride. CTA was characterized by percent weight gain (pwg), amount of carboxylic acid groups (nCOOH), elemental analysis, FTIR, TGA, solid-state (13)C NMR, X-ray diffraction (DRX), specific surface area, pore size distribution, SEM and EDX. The best CTA synthesis condition yielded a pwg and nCOOH of 94.5% and 6.81mmolg(-1), respectively. CTA was used as an adsorbent material to remove Co(2+), Cu(2+) and Ni(2+) from monocomponent spiked aqueous solution. Adsorption studies were developed as a function of the solution pH, contact time and initial adsorbate concentration. Langmuir model better fitted the experimental adsorption data and the maximum adsorption capacities estimated by this model were 0.749, 1.487 and 1.001mmolg(-1) for Co(2+), Cu(2+) and Ni(2+), respectively. The adsorption mechanism was investigated by using isothermal titration calorimetry. The values of ΔadsH° were in the range from 5.36 to 8.09kJmol(-1), suggesting that the mechanism controlling the phenomenon is physisorption. Desorption and re-adsorption studies were also performed. Desorption and re-adsorption efficiencies were closer to 100%, allowing the recovery of both metal ions and CTA adsorbent. Copyright © 2016 Elsevier Inc. All rights reserved.

Kinetic and equilibrium aspects of adsorption and desorption of class II hydrophobins HFBI and HFBII at silicon oxynitride/water and air/water interfaces.

PubMed

Krivosheeva, Olga; Dėdinaitė, Andra; Linder, Markus B; Tilton, Robert D; Claesson, Per M

2013-02-26

Hydrophobins are relatively small globular proteins produced by filamentous fungi. They display unusual high surface activity and are implied as mediators of attachment to surfaces, which has resulted in high scientific and technological interest. In this work we focus on kinetic and equilibrium aspects of adsorption and desorption properties of two representatives of class II hydrophobins, namely HFBI and HFBII, at a negatively charged hydrophilic solid/water interface and at the air/water interface. The layers formed at the air/liquid interface were examined in a Langmuir trough, whereas layers formed at the solid/liquid interface were studied using dual polarization interferometry (DPI) under different flow conditions. For comparison, another globular protein, lysozyme, was also investigated. It was found that both the adsorbed amount and the adsorption kinetics were different for HFBI and HFBII, and the adsorption behavior of both hydrophobins on the negatively charged surface displayed some unusual features. For instance, even though the adsorption rate for HFBI was slowed down with increasing adsorbed amount as expected from packing constraints at the interface, the adsorption kinetics curves for HFBII displayed a region indicating adsorption cooperativity. Further, it was found that hydrophobin layers formed under flow partly desorbed when the flow was stopped, and the desorption rate for HFBII was enhanced in the presence of hydrophobins in solution.

Adsorption of methyl orange on mesoporous γ-Fe2O3/SiO2 nanocomposites

NASA Astrophysics Data System (ADS)

Deligeer, W.; Gao, Y. W.; Asuha, S.

2011-02-01

Mesoporous γ-Fe2O3/SiO2 nanocomposite containing 30 mol% of γ-Fe2O3 was prepared by a template-free sol-gel method, and its removal ability for methyl orange (MO) was investigated. The nanocomposite was characterized using X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier transform infrared (FTIR) absorption measurements, nitrogen adsorption-desorption measurements, and magnetic measurements. The synthesized γ-Fe2O3/SiO2 nanocomposite has a mesoporous structure with an average pore size of 3.5 nm and a specific surface area of 245 m2/g, and it exhibits ferrimagnetic characteristics with the maximum saturation magnetization of 20.9 emu/g. The adsorption of MO on the nanocomposite reaches the maximum adsorbed percentage of ca. 80% within a few minutes, showing that most of MO can be removed in a short time. The MO adsorption data fit well with both Langmuir and Freundlich adsorption isotherms. The maximum adsorption capacity of MO is estimated to be 476 mg/g.

The adsorption of Run (n = 1-4) on γ-Al2O3 Surface: A DFT study

NASA Astrophysics Data System (ADS)

Liu, Zhe; Guo, Yafei; Chen, Yu; Shen, Rong

2018-05-01

The density functional theory (DFT) was adopted to study the adsorption and growth of Run (n = 1-4) clusters on γ-Al2O3 surface, which is of great significances for the design of many important catalysts, especially for carbon dioxide methanation. It is found that both the Rusbnd Ru bond length and adsorption energy Eads of Ru clusters with the surface increase with the Run clusters increasing. The growth ability of the supported Run cluster is weaker than the gas phase Run clusters through comparing their respective growth process, which ascribes to the stabilization of γ-Al2O3 support. An interesting discovery is that the basin structure was supposed to be the most favorable adsorption geometry for Run clusters. Additionally, the distances between Ru atoms in the adsorbed clusters are longer than that in their isolated counterparts. Bader charge analysis was conducted for the most stable configurations of Run (n = 1-4) clusters on γ-Al2O3 surface as well. And the results suggest that Run (n = 1-4) clusters serve as the electron donators. The result of projected density of states (PDOS) shows that strong adsorption of Ru atom on the γ-Al2O3 surface correlates with strong interaction between d orbital of Ru atom and p orbital of Al or O atom of the Al2O3 support.

Changes induced on the surfaces of small Pd clusters by the thermal desorption of CO

NASA Technical Reports Server (NTRS)

Doering, D. L.; Poppa, H.; Dickinson, J. T.

1980-01-01

The stability and adsorption/desorption properties of supported Pd crystallites less than 5 nm in size were studied by Auger electron spectroscopy and repeated flash thermal desorption of CO. The Pd particles were grown epitaxially on heat-treated, UHV-cleaved mica at a substrate temperature of 300 C and a Pd impingement flux of 10 to the 13th atoms/sq cm s. Auger analysis allowed in situ measurement of relative particle dispersion and contamination, while FTD monitored the CO desorption properties. The results show that significant changes in the adsorption properties can be detected. Changes in the Pd Auger signal and the desorption spectrum during the first few thermal cycles are due to particle coalescence and facetting and the rate of this change is dependent on the temperature and duration of the desorption. Significant reductions in the amplitude of the desorptions peak occur during successive CO desorptions which are attributed to increases of surface carbon, induced by the desorption of CO. The contamination process could be reversed by heat treatment in oxygen or hydrogen

Lead sorption-desorption from organic residues.

PubMed

Duarte Zaragoza, Victor M; Carrillo, Rogelio; Gutierrez Castorena, Carmen M

2011-01-01

Sorption and desorption are mechanisms involved in the reduction of metal mobility and bioavailability in organic materials. Metal release from substrates is controlled by desorption. The capacity of coffee husk and pulp residues, vermicompost and cow manure to adsorb Pb2+ was evaluated. The mechanisms involved in the sorption process were also studied. Organic materials retained high concentrations of lead (up to 36,000 mg L(-1)); however, the mechanisms of sorption varied according to the characteristics of each material: degree of decomposition, pH, cation exchange capacity and percentage of organic matter. Vermicompost and manure removed 98% of the Pb from solution. Lead precipitated in manure and vermicompost, forming lead oxide (PbO) and lead ferrite (PbFe4O7). Adsorption isotherms did not fit to the typical Freundlich and Langmuir equations. Not only specific and non-specific adsorption was observed, but also precipitation and coprecipitation. Lead desorption from vermicompost and cow manure was less than 2%. For remediation of Pb-polluted sites, the application of vermicompost and manure is recommended in places with alkaline soils because Pb precipitation can be induced, whereas coffee pulp residue is recommended for acidic soils where Pb is adsorbed.

Paraquat adsorption on NaX and Al-MCM-41.

PubMed

Rongchapo, Wina; Deekamwong, Krittanun; Loiha, Sirinuch; Prayoonpokarach, Sanchai; Wittayakun, Jatuporn

2015-01-01

The aim of this work is to determine paraquat adsorption capacity of zeolite NaX and Al-MCM-41. All adsorbents were synthesized by hydrothermal method using rice husk silica. For Al-MCM-41, aluminum (Al) was added to the synthesis gel of MCM-41 with Al content of 10, 15, 20 and 25 wt%. The faujasite framework type of NaX and mesoporous characteristic of Al-MCM-41 were confirmed by X-ray diffraction. Surface area of all adsorbents determined by N2 adsorption-desorption analysis was higher than 650 m2/g. Al content and geometry were determined by X-ray fluorescence and 27Al nuclear magnetic resonance, respectively. Morphology of Al-MCM-41 were studied by transmission electron microscopy; macropores and defects were observed. The paraquat adsorption experiments were conducted using a concentration range of 80-720 mg/L for NaX and 80-560 mg/L for Al-MCM-41. The paraquat adsorption isotherms from all adsorbents fit well with the Langmuir model. The adsorption capacity of NaX was 120 mg/g-adsorbent. Regarding Al-MCM-41, the 10% Al-MCM-41 exhibited the lowest capacity of 52 mg/g-adsorbent while the other samples had adsorption capacity of 66 mg/g-adsorbent.

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

A Diaminopropane-Appended Metal–Organic Framework Enabling Efficient CO 2 Capture from Coal Flue Gas via a Mixed Adsorption Mechanism

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

Milner, Phillip J.; Siegelman, Rebecca L.; Forse, Alexander C.

A new diamine-functionalized metal–organic framework comprised of 2,2-dimethyl-1,3-diaminopropane (dmpn) appended to the Mg 2+ sites lining the channels of Mg 2(dobpdc) (dobpdc4– = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) is characterized for the removal of CO 2 from the flue gas emissions of coal-fired power plants. Unique to members of this promising class of adsorbents, dmpn–Mg2(dobpdc) displays facile step-shaped adsorption of CO 2 from coal flue gas at 40 °C and near complete CO 2 desorption upon heating to 100 °C, enabling a high CO 2 working capacity (2.42 mmol/g, 9.1 wt %) with a modest 60 °C temperature swing. Evaluation of the thermodynamic parametersmore » of adsorption for dmpn–Mg 2(dobpdc) suggests that the narrow temperature swing of its CO 2 adsorption steps is due to the high magnitude of its differential enthalpy of adsorption (Δhads = -73 ± 1 kJ/mol), with a larger than expected entropic penalty for CO 2 adsorption (Δsads = -204 ± 4 J/mol·K) positioning the step in the optimal range for carbon capture from coal flue gas. In addition, thermogravimetric analysis and breakthrough experiments indicate that, in contrast to many adsorbents, dmpn–Mg 2(dobpdc) captures CO 2 effectively in the presence of water and can be subjected to 1000 humid adsorption/desorption cycles with minimal degradation. Solid-state 13C NMR spectra and single-crystal X-ray diffraction structures of the Zn analogue reveal that this material adsorbs CO 2 via formation of both ammonium carbamates and carbamic acid pairs, the latter of which are crystallographically verified for the first time in a porous material. Taken together, these properties render dmpn–Mg 2(dobpdc) one of the most promising adsorbents for carbon capture applications.« less

A Diaminopropane-Appended Metal-Organic Framework Enabling Efficient CO2 Capture from Coal Flue Gas via a Mixed Adsorption Mechanism.

PubMed

Milner, Phillip J; Siegelman, Rebecca L; Forse, Alexander C; Gonzalez, Miguel I; Runčevski, Tomče; Martell, Jeffrey D; Reimer, Jeffrey A; Long, Jeffrey R

2017-09-27

A new diamine-functionalized metal-organic framework comprised of 2,2-dimethyl-1,3-diaminopropane (dmpn) appended to the Mg 2+ sites lining the channels of Mg 2 (dobpdc) (dobpdc 4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) is characterized for the removal of CO 2 from the flue gas emissions of coal-fired power plants. Unique to members of this promising class of adsorbents, dmpn-Mg 2 (dobpdc) displays facile step-shaped adsorption of CO 2 from coal flue gas at 40 °C and near complete CO 2 desorption upon heating to 100 °C, enabling a high CO 2 working capacity (2.42 mmol/g, 9.1 wt %) with a modest 60 °C temperature swing. Evaluation of the thermodynamic parameters of adsorption for dmpn-Mg 2 (dobpdc) suggests that the narrow temperature swing of its CO 2 adsorption steps is due to the high magnitude of its differential enthalpy of adsorption (Δh ads = -73 ± 1 kJ/mol), with a larger than expected entropic penalty for CO 2 adsorption (Δs ads = -204 ± 4 J/mol·K) positioning the step in the optimal range for carbon capture from coal flue gas. In addition, thermogravimetric analysis and breakthrough experiments indicate that, in contrast to many adsorbents, dmpn-Mg 2 (dobpdc) captures CO 2 effectively in the presence of water and can be subjected to 1000 humid adsorption/desorption cycles with minimal degradation. Solid-state 13 C NMR spectra and single-crystal X-ray diffraction structures of the Zn analogue reveal that this material adsorbs CO 2 via formation of both ammonium carbamates and carbamic acid pairs, the latter of which are crystallographically verified for the first time in a porous material. Taken together, these properties render dmpn-Mg 2 (dobpdc) one of the most promising adsorbents for carbon capture applications.

Room-temperature isolation of V(benzene)2 sandwich clusters via soft-landing into n-alkanethiol self-assembled monolayers.

PubMed

Nagaoka, Shuhei; Matsumoto, Takeshi; Okada, Eiji; Mitsui, Masaaki; Nakajima, Atsushi

2006-08-17

The adsorption state and thermal stability of V(benzene)2 sandwich clusters soft-landed onto a self-assembled monolayer of different chain-length n-alkanethiols (Cn-SAM, n = 8, 12, 16, 18, and 22) were studied by means of infrared reflection absorption spectroscopy (IRAS) and temperature-programmed desorption (TPD). The IRAS measurement confirmed that V(benzene)2 clusters are molecularly adsorbed and maintain a sandwich structure on all of the SAM substrates. In addition, the clusters supported on the SAM substrates are oriented with their molecular axes tilted 70-80 degrees off the surface normal. An Arrhenius analysis of the TPD spectra reveals that the activation energy for the desorption of the supported clusters increases linearly with the chain length of the SAMs. For the longest chain C22-SAM, the activation energy reaches approximately 150 kJ/mol, and the thermal desorption of the supported clusters can be considerably suppressed near room temperature. The clear chain-length-dependent thermal stability of the supported clusters observed here can be explained well in terms of the cluster penetration into the SAM matrixes.

Adsorption and Dissociation of CO2 on Ru(0001)

PubMed Central

2017-01-01

The adsorption and dissociation of carbon dioxide on a Ru(0001) single crystal surface was investigated by reflection–absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) spectroscopy for CO2 adsorbed at 85 K. RAIRS spectroscopy shows that the adsorption of CO2 on a Ru(0001) single crystal is partially dissociative, resulting in CO2 and CO. The CO vibrational mode was also observed to split into two distinct modes, indicating two general populations of CO present at the surface. Furthermore, a time-dependent blue-shift is observed, which is characteristic of increasing CO surface coverage. TPD showed that coverages of up to 0.3 ML were obtained, and no evidence for chemisorption of oxygen on ruthenium was found. PMID:28413569

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.

Simultaneous laboratory measurements of CO2 and H2O adsorption on palagonite: Implications for the Martian climate and volatile reservoir

NASA Technical Reports Server (NTRS)

Zent, A. P.; Quinn, R.

1993-01-01

We are measuring the simultaneous adsorption of H2O and CO2 on palagonite materials in order to improve the formulation of climate models for Mars. We report on the initial co-adsorption data. Models of the Martian climate and volatile inventory indicate that the regolith serves as one of the primary reservoirs of outgassed volatiles and that it exchanges H2O and CO2 with the atmosphere in response to changes in insolation associated with astronomical cycles. Physical adsorbate must exist on the surfaces of the cold particulates that constitute the regolith, and the size of that reservoir can be assessed through laboratory measurements of adsorption on terrestrial analogs. Many studies of the independent adsorption of H2O and CO2 on Mars analog were made and appear in the literature. Empirical expressions that relate the adsorptive coverage of each gas to the temperature of the soil and partial pressure have been derived based on the laboratory data. Numerical models incorporate these adsorption isotherms into climatic models, which predict how the adsorptive coverage of the regolith and hence, the pressure of each gas in the atmosphere will vary as the planet moves through its orbit. These models suggest that the regolith holds several tens to hundreds of millibars of CO2 and that during periods of high obliquity warming of the high-latitude regolith will result in desorption of the CO2, and a consequent increase in atmospheric pressure. At lower obliquities, the caps cool and the equator warms forcing the desorption of several tens of millibars of CO2, which is trapped into quasipermanent CO2 caps.

Novel hydrophobic PDVB/R-SiO2 for adsorption of volatile organic compounds from highly humid gas stream.

PubMed

Lu, Han-feng; Cao, Jie-jing; Zhou, Ying; Zhan, De-li; Chen, Yin-fei

2013-11-15

A novel organic-inorganic hydrophobic polydivinylbenzene-silica adsorbent (PDVB/R-SiO2) was successfully prepared by introducing a specific amount of divinylbenzene and solvent (i.e., tetrahydrofuran) to SiO2pores and initiating polymerization under solvothermal conditions. New smaller structures and surface areas were formed in the SiO2 pores. The PDVB/R-SiO2-0.5 samples exhibited a bimodal pore size distribution with both SiO2 micropores/mesopores (0.5-2.0 nm) and mesopores (2.0-5.0 nm). The surface areas increased from 116 m(2)/g (SiO2) to 246 m(2)/g. The breakthrough curves of toluene adsorption indicated that the amount adsorbed on PDVB/R-SiO2-0.5 was 12 times higher than that on SiO2. The highly humid environment exhibited no effect on adsorption because the surface of PDVB was functionalized. The adsorbed toluene was easily desorbed in hot N2 stream at 100 °C. After 10 adsorption-desorption cycles, PDVB/R-SiO2-0.5 continued exhibiting excellent adsorption, indicating superior structural and regeneration abilities. Copyright © 2013 Elsevier B.V. All rights reserved.

Development of chemically activated N-enriched carbon adsorbents from urea-formaldehyde resin for CO2 adsorption: Kinetics, isotherm, and thermodynamics.

PubMed

Tiwari, Deepak; Bhunia, Haripada; Bajpai, Pramod K

2018-07-15

Nitrogen enriched carbon adsorbents with high surface areas were successfully prepared by carbonizing the low-cost urea formaldehyde resin, followed by KOH activation. Different characterization techniques were used to determine the structure and surface functional groups. Maximum surface area and total pore volume of 4547 m 2  g -1 and 4.50 cm 3  g -1 were found by controlling activation conditions. The optimized sample denoted as UFA-3-973 possesses a remarkable surface area, which is found to be one of the best surface areas achieved so far. Nitrogen content of this sample was found to be 22.32%. Dynamic CO 2 uptake capacity of the carbon adsorbents were determined thermogravimetrically at different CO 2 concentrations (6-100%) and adsorption temperatures (303-373 K) which have a much more relevance for the flue gas application. Highest adsorption capacity of 2.43 mmol g -1 for this sample was obtained at 303 K under pure CO 2 flow. Complete regenerability of the adsorbent over four adsorption-desorption cycles was obtained. Fractional order kinetic model provided best description of adsorption over all adsorption temperatures and CO 2 concentrations. Heterogeneity of the adsorbent surface was confirmed from the Langmuir and Freundlich isotherms fits and isosteric heat of adsorption values. Exothermic, spontaneous and feasible nature of adsorption process was confirmed from thermodynamic parameter values. The combination of high surface area and large pore volume makes the adsorbent a new promising carbon material for CO 2 capture from power plant flue gas and for other relevant applications. Copyright © 2018 Elsevier Ltd. All rights reserved.

Functionalized mesoporous silica materials for molsidomine adsorption: Thermodynamic study

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

Alyoshina, Nonna A.; Parfenyuk, Elena V., E-mail: evp@iscras.ru

2013-09-15

A series of unmodified and organically modified mesoporous silica materials was prepared. The unmodified mesoporous silica was synthesized via sol–gel synthesis in the presence of D-glucose as pore-forming agent. The functionalized by phenyl, aminopropyl and mercaptopropyl groups silica materials were prepared via grafting. The fabricated adsorbent materials were characterized by Fourier transform infrared spectroscopy (FTIR) analysis, N{sub 2} adsorption/desorption and elemental analysis methods. Then their adsorption properties for mesoionic dug molsidomine were investigated at 290–313 K and physiological pH value. Thermodynamic parameters of molsidomine adsorption on the synthesized materials have been calculated. The obtained results showed that the adsorption processmore » of molsidomine on the phenyl modified silica is the most quantitatively and energetically favorable. The unmodified and mercaptopropyl modified silica materials exhibit significantly higher adsorption capacities and energies for molsidomine than the aminopropyl modified sample. The effects are discussed from the viewpoint of nature of specific interactions responsible for the adsorption. - Graphical abstract: Comparative analysis of the thermodynamic characteristics of molsidomine adsorption showed that the adsorption process on mesoporous silica materials is controlled by chemical nature of surface functional groups. Molsidomine adsorption on the phenyl modified silica is the most quantitatively and energetically favorable. Taking into account ambiguous nature of mesoionic compounds, it was found that molsidomine is rather aromatic than dipolar. Display Omitted - Highlights: • Unmodified and organically modified mesoporous silica materials were prepared. • Molsidomine adsorption on the silica materials was studied. • Phenyl modified silica shows the highest adsorption capacity and favorable energy. • Molsidomine exhibits the lowest affinity to aminopropyl modified silica.« less

Modification of polystyrene-based activated carbon spheres to improve adsorption of dibenzothiophene

NASA Astrophysics Data System (ADS)

Wang, Qin; Liang, Xiaoyi; Qiao, Wenming; Liu, Chaojun; Liu, Xiaojun; Zhang, Rui; Ling, Licheng

2009-01-01

Polystyrene-based activated carbon spheres (PACS) were modified with either air, HNO 3, (NH 4) 2S 2O 8, H 2O 2 or H 2 to improve their adsorption properties of dibenzothiophene (DBT). The texture and surface chemistry of PACS were characterized by N 2 adsorption, scanning electron microscopy (SEM), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), acid-base titration and elemental analysis. The results showed that HNO 3 and (NH 4) 2S 2O 8 treatments introduced large amount of acidic groups such as carboxylic, lactones and anhydride groups, while air and H 2O 2 had relatively mild effects and introduced a small quantity of phenol, carbonyl and ether groups. In the HNO 3 treatment, the acidic groups might be fixed on the internal and external surface of PACS, which may act as active sites of adsorption, resulting in increase of the adsorption amount by 45%. Whereas H 2O 2 and (NH 4) 2S 2O 8 treatments might fix more oxygen-containing groups on the external surface, which may hinder DBT molecule enter into micropores, leading to rather lower adsorption capacity with the extent of oxidation. So, the concentration, distribution and types of the acidic functional groups are responsible for the removal of DBT.

Desorption of radioactive cesium by seawater from the suspended particles in river water.

PubMed

Onodera, Masaki; Kirishima, Akira; Nagao, Seiya; Takamiya, Kouichi; Ohtsuki, Tsutomu; Akiyama, Daisuke; Sato, Nobuaki

2017-10-01

In 2011, the accident at the Fukushima-Daiichi nuclear power plant dispersed radioactive cesium throughout the environment, contaminating the land, rivers, and sea. Suspended particles containing clay minerals are the transportation medium for radioactive cesium from rivers to the ocean because cesium is strongly adsorbed between the layers of clay minerals, forming inner sphere complexes. In this study, the adsorption and desorption behaviors of radioactive cesium from suspended clay particles in river water have been investigated. The radioactive cesium adsorption and desorption experiments were performed with two kinds of suspended particulate using a batch method with 137 Cs tracers. In the cesium adsorption treatment performed before the desorption experiments, simulated river water having a total cesium concentration ([ 133+137 Cs + ] total ) of 1.3 nM (10 -9  mol/L) was used. The desorption experiments were mainly conducted at a solid-to-liquid ratio of 0.17 g/L. The desorption agents were natural seawater collected at 10 km north of the Fukushima-Daiichi nuclear power plant, artificial seawater, solutions of NaCl, KCl, NH 4 Cl, and 133 CsCl, and ultrapure water. The desorption behavior, which depends on the preloaded cesium concentration in the suspended particles, was also investigated. Based on the cesium desorption experiments using suspended particles, which contained about 1000 ng/g loaded cesium, the order of cesium desorption ratios for each desorption agent was determined as 1 M NaCl (80%) > 470 mM NaCl (65%) > 1 M KCl (30%) ≈ seawater (natural seawater and Daigo artificial seawater) > 1 M NH 4 Cl (20%) > 1 M 133 CsCl (15%) ≫ ultrapure water (2%). Moreover, an interesting result was obtained: The desorption ratio in the 470 mM NaCl solution was much higher than that in seawater, even though the Na + concentrations were identical. These results indicate that the cesium desorption mechanism is not a simple ion exchange reaction

Research of CO2 and N2 Adsorption Behavior in K-Illite Slit Pores by GCMC Method

PubMed Central

Chen, Guohui; Lu, Shuangfang; Zhang, Junfang; Xue, Qingzhong; Han, Tongcheng; Xue, Haitao; Tian, Shansi; Li, Jinbu; Xu, Chenxi; Pervukhina, Marina; Clennell, Ben

2016-01-01

Understanding the adsorption mechanisms of CO2 and N2 in illite, one of the main components of clay in shale, is important to improve the precision of the shale gas exploration and development. We investigated the adsorption mechanisms of CO2 and N2 in K-illite with varying pore sizes at the temperature of 333, 363 and 393 K over a broad range of pressures up to 30 MPa using the grand canonical Monte Carlo (GCMC) simulation method. The simulation system is proved to be reasonable and suitable through the discussion of the impact of cation dynamics and pore wall thickness. The simulation results of the excess adsorption amount, expressed per unit surface area of illite, is in general consistency with published experimental results. It is found that the sorption potential overlaps in micropores, leading to a decreasing excess adsorption amount with the increase of pore size at low pressure, and a reverse trend at high pressure. The excess adsorption amount increases with increasing pressure to a maximum and then decreases with further increase in the pressure, and the decreasing amount is found to increase with the increasing pore size. For pores with size greater larger than 2 nm, the overlap effect disappears. PMID:27897232

Energetics of CO2 and H2O adsorption on zinc oxide.

PubMed

Gouvêa, Douglas; Ushakov, Sergey V; Navrotsky, Alexandra

2014-08-05

Adsorption of H2O and CO2 on zinc oxide surfaces was studied by gas adsorption calorimetry on nanocrystalline samples prepared by laser evaporation in oxygen to minimize surface impurities and degassed at 450 °C. Differential enthalpies of H2O and CO2 chemisorption are in the range -150 ±10 kJ/mol and -110 ±10 kJ/mol up to a coverage of 2 molecules per nm(2). Integral enthalpy of chemisorption for H2O is -96.8 ±2.5 kJ/mol at 5.6 H2O/nm(2) when enthalpy of water condensation is reached, and for CO2 is -96.6 ±2.5 kJ/mol at 2.6 CO2/nm(2) when adsorption ceases. These values are consistent with those reported for ZnO prepared by other methods after similar degas conditions. The similar energetics suggests possible competition of CO2 and H2O for binding to ZnO surfaces. Exposure of bulk and nanocrystalline ZnO with preadsorbed CO2 to water vapor results in partial displacement of CO2 by H2O. In contrast, temperature-programmed desorption (TPD) indicates that a small fraction of CO2 is retained on ZnO surfaces up to 800 °C, under conditions where all H2O is desorbed, with adsorption energies near -200 kJ/mol. Although molecular mechanisms of adsorption were not studied, the thermodynamic data are consistent with dissociative adsorption of H2O at low coverage and with several different modes of CO2 binding.

First-principles study of water desorption from montmorillonite surface.

PubMed

Zhang, Yao; Meng, Yingfeng; Liu, Houbin; Yang, Mingli

2016-05-01

Knowledge about water desorption is important to give a full picture of water diffusion in montmorillonites (MMT), which is a driving factor in MMT swelling. The desorption paths and energetics of water molecules from the surface of MMT with trapped Li(+), Na(+) or K(+) counterions were studied using periodic density functional theory calculations. Two paths--surface and vacuum desorption--were designed for water desorption starting from a stationary structure in which water bonds with both the counterion and the MMT surface. Surface desorption is energetically more favorable than vacuum desorption due to water-surface hydrogen bonds that help stabilize the intermediate structure of water released from the counterion. The energy barriers of water desorption are in the order of Li(+) > Na(+) > K(+), which can be attributed to the short ionic radius of Li(+), which favors strong binding with the water molecule. The temperature dependence of water adsorption and desorption rates were compared based on the computed activation energies. Our calculations reveal that the water desorption on the MMT surface has a different mechanism from water adsorption, which results from surface effects favoring stabilization of water conformers during the desorption process.

Enhanced CO2 adsorptive performance of PEI/SBA-15 adsorbent using phosphate ester based surfactants as additives.

PubMed

Cheng, Dandan; Liu, Yue; Wang, Haiqiang; Weng, Xiaole; Wu, Zhongbiao

2015-12-01

In this study, a series of polyetherimide/SBA-15: 2-D hexagonal P6mm, Santa Barbara USA (PEI/SBA-15) adsorbents modified by phosphoric ester based surfactants (including tri(2-ethylhexyl) phosphate (TEP), bis(2-ethylhexyl) phosphate (BEP) and trimethyl phosphonoacetate (TMPA)) were prepared for CO2 adsorption. Experimental results indicated that the addition of TEP and BEP had positive effects on CO2 adsorption capacity over PEI/SBA-15. In particular, the CO2 adsorption amount could be improved by around 20% for 45PEI-5TEP/SBA-15 compared to the additive-free adsorbent. This could be attributed to the decrease of CO2 diffusion resistance in the PEI bulk network due to the interactions between TEP and loaded PEI molecules, which was further confirmed by adsorption kinetics results. In addition, it was also found that the cyclic performance of the TEP-modified adsorbent was better than the surfactant-free one. This could be due to two main reasons, based on the results of in situ DRIFT and TG-DSC tests. First and more importantly, adsorbed CO2 species could be desorbed more rapidly over TEP-modified adsorbent during the thermal desorption process. Furthermore, the enhanced thermal stability after TEP addition ensured lower degradation of amine groups during adsorption/desorption cycles. Copyright © 2015. Published by Elsevier B.V.

Measurement of the adsorption energy difference between ortho- and para-D2 on an amorphous ice surface.

PubMed

Amiaud, L; Momeni, A; Dulieu, F; Fillion, J H; Matar, E; Lemaire, J-L

2008-02-08

Molecular hydrogen interaction on water ice surfaces is a major process taking place in interstellar dense clouds. By coupling laser detection and classical thermal desorption spectroscopy, it is possible to study the effect of rotation of D(2) on adsorption on amorphous solid water ice surfaces. The desorption profiles of ortho- and para-D(2) are different. This difference is due to a shift in the adsorption energy distribution of the two lowest rotational states. Molecules in J''=1 rotational state are on average more strongly bound to the ice surface than those in J''=0 rotational state. This energy difference is estimated to be 1.4+/-0.3 meV. This value is in agreement with previous calculation and interpretation. The nonspherical wave function J'' =1 has an interaction with the asymmetric part of the adsorption potential and contributes positively in the binding energy.

Adsorption characteristics of hexavalent chromium on HCB/TiO2

NASA Astrophysics Data System (ADS)

Zhang, Li; Zhang, Yonggang

2014-10-01

Sol-gel method was adopted to prepare HCB/TiO2 and its adsorption ability of hexavalent chromium, Cr(VI), and removal from aqueous solution were investigated. The samples were characterized by Power X-ray diffraction (XRD) and a transmission electron microscope (TEM) which showed that the TiO2 was deposited on the surface of HCB. FTIR was used to identify the changes of the surface functional groups before and after adsorption. Potentiometric titration method was used to characterize the zero charge (pHpzc) characteristics of the surface of HCB/TiO2 which showed more acidic functional groups containing. Batch experiments showed that initial pH, absorbent dosage, contact time and initial concentration of Cr(VI) were important parameters for the Cr(VI) adsorption studies. The Freundlich isotherm model better reflected the experimental data better. Cr(VI) adsorption process followed the pseudo-second order kinetic model, which illustrated chemical adsorption. The thermodynamic parameters, such as Gibbs free energy (ΔG), changes in enthalpy change (ΔH) and changes in entropy change (ΔS) were also evaluated. Negative value of free energy occurred at temperature range of 25-45 °C, so Cr(VI) adsorption by HCB/TiO2 is spontaneous. Desorption results showed that the adsorption capacity could maintain 80% after five cycles. The maximum adsorption capacity for Cr(VI) was at 27.33 mg g-1 in an acidic medium, of which the value is worth comparable with other low-cost adsorbents.

Adsorption of alcohols on a two-dimensional SiO2 single crystal - Alcohol adsorption on silicatene

NASA Astrophysics Data System (ADS)

Nayakasinghe, M. T.; Sivapragasam, N.; Burghaus, U.

2017-12-01

The adsorption kinetics of alcohols (methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol) was studied on monoatomic, two-dimensional SiO2 single crystals (silicatene) using thermal desorption spectroscopy (TDS). Silicatene was grown on Mo(1 1 2) at ultra-high vacuum. In contrast to Mo, the alcohols physisorb molecularly on the hydrophobic SiO2/Mo surface. Zero coverage binding energies vary from 46.5 to 65.5 kJ/mol and increase with molecular size. Silicatene was characterized by Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and water TDS.

Metal-porphyrin: a potential catalyst for direct decomposition of N(2)O by theoretical reaction mechanism investigation.

PubMed

Maitarad, Phornphimon; Namuangruk, Supawadee; Zhang, Dengsong; Shi, Liyi; Li, Hongrui; Huang, Lei; Boekfa, Bundet; Ehara, Masahiro

2014-06-17

The adsorption of nitrous oxide (N2O) on metal-porphyrins (metal: Ti, Cr, Fe, Co, Ni, Cu, or Zn) has been theoretically investigated using density functional theory with the M06L functional to explore their use as potential catalysts for the direct decomposition of N2O. Among these metal-porphyrins, Ti-porphyrin is the most active for N2O adsorption in the triplet ground state with the strongest adsorption energy (-13.32 kcal/mol). Ti-porphyrin was then assessed for the direct decomposition of N2O. For the overall reaction mechanism of three N2O molecules on Ti-porphyrin, two plausible catalytic cycles are proposed. Cycle 1 involves the consecutive decomposition of the first two N2O molecules, while cycle 2 is the decomposition of the third N2O molecule. For cycle 1, the activation energies of the first and second N2O decompositions are computed to be 3.77 and 49.99 kcal/mol, respectively. The activation energy for the third N2O decomposition in cycle 2 is 47.79 kcal/mol, which is slightly lower than that of the second activation energy of the first cycle. O2 molecules are released in cycles 1 and 2 as the products of the reaction, which requires endothermic energies of 102.96 and 3.63 kcal/mol, respectively. Therefore, the O2 desorption is mainly released in catalytic cycle 2 of a TiO3-porphyrin intermediate catalyst. In conclusion, regarding the O2 desorption step for the direct decomposition of N2O, the findings would be very useful to guide the search for potential N2O decomposition catalysts in new directions.

Selective Adsorption Resonances in the Scattering of n-H2 p-H2 n-D2 and o-D2 from Ag(111)

NASA Astrophysics Data System (ADS)

Yu, Chien-Fan; Whaley, K. Birgitta; Hogg, Charles S.; Sibener, Steven J.

1983-12-01

Diffractive and rotationally mediated selective adsorption scattering resonances are reported for n-H2 p-H2 n-D2 and o-D2 on Ag(111). Small resonance shifts and line-width differences are observed between n-H2 and p-H2 indicating a weak orientation dependence of the laterally averaged H2/Ag(111) potential. The p-H2 and o-D2 levels were used to determine the isotropic component of this potential, yielding a well depth of ~ 32 meV.

DFT study on stability and H2 adsorption activity of bimetallic Au79-nPdn (n = 1-55) clusters

NASA Astrophysics Data System (ADS)

Liu, Xuejing; Tian, Dongxu; Meng, Changgong

2013-03-01

The stability and H2 adsorption activity of bimetallic Au79-nPdn (n = 1-55) clusters were studied by density functional theory with GGA-PW91 functional. The stability order for four Pd substitution types is face > mid-edge > corner > edge, and the stability is improved with increasing Pd content. In contrast with the stability order, H2 adsorption activity is corner ≈ edge > mid-edge > face. The Au36Pd43 (3) with Au:Pd ≈ 1:1 ratio and twenty-four Pd substitutions at (1 1 1) facets and nineteen Pd substitutions at subshell sites shows high stability and H2 non-activated dissociation activity. The partial density of d-states and d band center revealed that the electronic properties are closely associated with the geometric characteristic and adsorption activity. Correlating the d band center ɛd and the adsorption energies, the ɛd order agrees with the adsorption activity that the Pd substitution at edge and corner sites are more active than at face and mid-edge sites.

Some properties of solid helium and helium nanoclusters using the effective HFD-like interaction potential: Adsorption and desorption inside carbon nanotube

NASA Astrophysics Data System (ADS)

Abbaspour, M.; Akbarzadeh, H.; Banihashemi, S. Z.; Sotoudeh, A.

2018-02-01

We have calculated the zero equation of state of solid helium using a two-body Hartree-Fock dispersion (HFD)-like potential from molecular dynamics (MD) simulation. To take many-body forces into account, our simple and accurate empirical expression is used with the HFD-like potential without requiring an expensive three-body calculation. This potential model also includes the quantum effects for helium at low temperatures. The results indicate that our effective HFD-like potential improves the prediction of the classical two-body results to get better agreement with experiment than many other two-body and three-body potentials of helium reported in the literature. We have also simulated the adsorption and desorption processes of the (He)55, (He)147, (He)309, (He)561, and (He)923 icosahedral nanoclusters confined into the different armchair and zigzag CNTs from 0 to 50 K using our effective model. We have observed an interesting phenomenon at 0 K for helium. The nanoclusters adsorb to the inner CNT wall as a melting process. But, the heavier noble gas clusters (such as Ne and Xe) show the different behavior than the He clusters. They form a multilayered solid structure into the CNT at zero temperature and adsorb into the inner wall of the CNT at higher temperatures. Our results for He clusters show that the absolute value of the adsorption energy increases as the size of the nanocluster increases. The desorption process begins at a certain temperature and represents itself by a jump in the configurational energy values. We have also investigated the structural and dynamical properties of the confined helium nanoclusters during the adsorption and desorption processes at different temperatures.

Rare Earth Desorption Test with Citrate and Bicarbonate

DOE Data Explorer

Jiao, Yongqin; Brewer, Aaron; Park, Dan

2017-06-01

LBT (lanthanide binding tag) cells were grown overnight in LB media with 0.05% Amp. 1:100 subculture taken from overnights, grown for 2 hours. LBT was induced with 0.002% arabinose added for 3 hours. REE adsorption was done by combining 350 ul (0.25% 1M MES, 12.5 uM Tb, and 12.5 uM La or Cu in sterile DI water) and 350 ul (LBT cells with OD = 1 in 10 mM MES), reacted for approx. 30 min. Following adsorption, citrate and bicarbonate solutions were used in desorption to recover rare earth from cell surface, and to further separate REE from non-REEs. The samples were then centrifuged and a fraction of the supernatant was collected for ICP-MS analysis.

Adsorption of H2O, H2, O2, CO, NO, and CO2 on graphene/g-C3N4 nanocomposite investigated by density functional theory

NASA Astrophysics Data System (ADS)

Wu, Hong-Zhang; Bandaru, Sateesh; Liu, Jin; Li, Li-Li; Wang, Zhenling

2018-02-01

Motivated by the photocatalytic reactions of small molecules on g-C3N4 by these insights, we sought to explore the adsorption of H2O and CO2 molecules on the graphene side and H2O, H2, O2, CO, NO, and CO2 molecules on the g-C3N4 side of hybrid g-C3N4/graphene nanocomposite using first-principles calculations. The atomic structure and electronic properties of hybrid g-C3N4/graphene nanocomposite is explored. The adsorption of small molecules on graphene/g-C3N4 nanocomposite is thoroughly investigated. The computational studies revels that all small molecules on graphene/g-C3N4 nanocomposite are the physisorption. The adsorption characteristics of H2O and CO2 molecules on the graphene side are similar to that on graphene. The adsorption of H2O, H2, O2, CO, NO, and CO2 molecules on the g-C3N4 side always leads to a buckle structure of graphene/g-C3N4 nanocomposite. Graphene as a substrate can significantly relax the buckle degree of g-C3N4 in g-C3N4/graphene nanocomposite.

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.

Adsorptive separation studies of ethane-methane and methane-nitrogen systems using mesoporous carbon.

PubMed

Yuan, Bin; Wu, Xiaofei; Chen, Yingxi; Huang, Jianhan; Luo, Hongmei; Deng, Shuguang

2013-03-15

Adsorptive separations of C(2)H(6)/CH(4) and CH(4)/N(2) binary mixtures are of paramount importance from the energy and environmental points of view. A mesoporous carbon adsorbent was synthesized using a soft template method and characterized with TEM, TGA, and nitrogen adsorption/desorption. Adsorption equilibrium and kinetics of C(2)H(6), CH(4), and N(2) on the mesoporous carbon adsorbent were determined at 278, 298, and 318 K and pressures up to 100 kPa. The adsorption capacities of C(2)H(6) and CH(4) on the mesoporous carbon adsorbent at 298 K and 100 kPa are 2.20 mmol/g and 1.05 mmol/g, respectively. Both are significantly higher than those of many adsorbents including pillared clays and ETS-10 at a similar condition. The equilibrium selectivities of C(2)H(6)/CH(4) and CH(4)/N(2) at 298 K are 19.6 and 5.8, respectively. It was observed that the adsorption of C(2)H(6), CH(4), and N(2) gases on the carbon adsorbent was reversible with modest isosteric heats of adsorption, which implies that this carbon adsorbent can be easily regenerated in a cyclic adsorption process. These results suggest that the mesoporous carbon studied in this work is a promising alternative adsorbent for the separations of C(2)H(6)/CH(4) and CH(4)/N(2) gas mixtures. Copyright © 2012 Elsevier Inc. All rights reserved.

Metal ion promoted hydrogels for bovine serum albumin adsorption: Cu(II) and Co(II) chelated poly[(N-vinylimidazole)-maleic acid].

PubMed

Pekel, Nursel; Salih, Bekir; Güven, Olgun

2005-05-10

Poly[(N-vinylimidazole)-maleic acid] (poly(VIm-MA)), copolymeric hydrogels were prepared by gamma-irradiating ternary mixtures of N-vinylimidazole-maleic acid-water in a (60)Co-gamma source. Cu(II) and Co(II) ions were chelated within the gels at pH=5.0. The maximum adsorption capacity of the gels were 3.71 mmol/g dry gel for Cu(II) and 1.25 mmol/g dry gel for Co(II) at pH=5.0. The swelling ratios of the gels were 1200% for poly(VIm-MA), 60 and 45% for Cu(II) and Co(II)-chelated poly(VIm-MA) gels at pH=5.0 in acetate buffer solution. These affinity gels with different swelling ratios for plain poly(VIm-MA), Cu(II)-, and Co(II)-chelated poly(VIm-MA), in acetate and phosphate buffers were used in the bovine serum albumin (BSA) adsorption/desorption studies in batch reactor. The maximum BSA adsorption capacities of the gels were 0.38 g/g dry gel for plain, 0.88 g/g dry gel for Cu(II)-chelated poly(VIm-MA) and 1.05 g/g dry gel for Co(II)-chelated poly(VIm-MA) gels. Adsorption capacity of BSA by the gels was reduced dramatically by increasing the ionic strength adjusted with NaCl. More than 95% of BSA were desorbed in 10 h in desorption medium containing 0.1M of EDTA for metal ion-chelated gels at pH=4.7.

Studies on desorption and regeneration of natural pumice for iron removal from aqueous solution.

PubMed

Indah, S; Helard, D; Binuwara, A

2018-05-01

To make the adsorption process more economic and environmental friendly, it is necessary to study desorption and reutilization of the adsorbents. In the present study, the effectiveness of natural pumice in removal of iron from aqueous solution was investigated in several sorption-desorption cycles. The desorption characteristics of previously adsorbed iron ions on natural pumice were tested by various desorbing agents such as HCl, NaOH and aquadest. Among them, HCl showed the highest desorption efficiency (37.89%) with 0.1 M of concentration and 60 min of contact time. The removal efficiency of iron ions in reused natural pumice could be maintained up to 90% in the third cycle of adsorption. The results indicate that although complete desorption was not achieved, natural pumice from Sungai Pasak, West Sumatra, Indonesia, can be sufficiently reused up to three cycles of adsorption-desorption.

Novel heavy-metal adsorption material: ion-recognition P(NIPAM-co-BCAm) hydrogels for removal of lead(II) ions.

PubMed

Ju, Xiao-Jie; Zhang, Shi-Bo; Zhou, Ming-Yu; Xie, Rui; Yang, Lihua; Chu, Liang-Yin

2009-08-15

A novel polymeric lead(II) adsorbent is prepared by incorporating benzo-18-crown-6-acrylamide (BCAm) as metal ion receptor into the thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel. Both stimuli-sensitive properties and the Pb(2+)-adsorption capabilities of the prepared P(NIPAM-co-BCAm) hydrogels are investigated. The prepared P(NIPAM-co-BCAm) hydrogels exhibit good ion-recognition and Pb(2+)-adsorption characteristics. When crown ether units capture Pb(2+) and form BCAm/Pb(2+) host-guest complexes, the lower critical solution temperature (LCST) of the hydrogel shifts to a higher temperature due to both the repulsion among charged BCAm/Pb(2+) groups and the osmotic pressure within the hydrogel. The adsorption results at different temperatures show that P(NIPAM-co-BCAm) hydrogels adsorb Pb(2+) ions at temperature lower than the LCST, but undergo desorption at temperature higher than the LCST due to the "stretch-to-shrink" configuration change of copolymer networks which is triggered by the change in environmental temperature. This kind of ion-recognition hydrogel is promising as a novel adsorption material for adsorption and separation of Pb(2+) ions. The adsorption and desorption of Pb(2+) could be rationally achieved by simply changing the environmental temperature.

Adsorption and desorption of methylene blue on porous carbon monoliths and nanocrystalline cellulose.

PubMed

He, Xiaoyun; Male, Keith B; Nesterenko, Pavel N; Brabazon, Dermot; Paull, Brett; Luong, John H T

2013-09-11

The dynamic batch adsorption of methylene blue (MB), a widely used and toxic dye, onto nanocrystalline cellulose (NCC) and crushed powder of carbon monolith (CM) was investigated using the pseudo-first- and -second-order kinetics. CM outperformed NCC with a maximum capacity of 127 mg/g compared to 101 mg/g for NCC. The Langmuir isotherm model was applicable for describing the binding data for MB on CM and NCC, indicating the homogeneous surface of these two materials. The Gibbs free energy of -15.22 kJ/mol estimated for CM unravelled the spontaneous nature of this adsorbent for MB, appreciably faster than the use of NCC (-4.47 kJ/mol). Both pH and temperature exhibited only a modest effect on the adsorption of MB onto CM. The desorption of MB from CM using acetonitrile was very effective with more than 94 % of MB desorbed from CM within 10 min to allow the reusability of this porous carbon material. In contrast, acetonitrile was less effective than ethanol in desorbing MB from NCC. The two solvents were incapable of completely desorbing MB on commercial granular coal-derived activated carbon.

Adsorption of VOCs on reduced graphene oxide.

PubMed

Yu, Lian; Wang, Long; Xu, Weicheng; Chen, Limin; Fu, Mingli; Wu, Junliang; Ye, Daiqi

2018-05-01

A modified Hummer's method was adopted for the synthesis of graphene oxide (GO) and reduced graphene oxide (rGO). It was revealed that the modified method is effective for the production of GO and rGO from graphite. Transmission electron microscopy (TEM) images of GO and rGO showed a sheet-like morphology. Because of the presence of oxygenated functional groups on the carbon surface, the interlayer spacing of the prepared GO was higher than that of rGO. The presence of OH and CO groups in the Fourier transform infrared spectra (FTIR) spectrum and G-mode and 2D-mode in Raman spectra confirmed the synthesis of GO and rGO. rGO (292.6m 2 /g) showed higher surface area than that of GO (236.4m 2 /g). The prepared rGO was used as an adsorbent for benzene and toluene (model pollutants of volatile organic compounds (VOCs)) under dynamic adsorption/desorption conditions. rGO showed higher adsorption capacity and breakthrough times than GO. The adsorption capacity of rGO for benzene and toluene was 276.4 and 304.4mg/g, respectively. Desorption experiments showed that the spent rGO can be successfully regenerated by heating at 150.0°C. Its excellent adsorption/desorption performance for benzene and toluene makes rGO a potential adsorbent for VOC adsorption. Copyright © 2017. Published by Elsevier B.V.

Re-analysis of experiments to quantify irreversibility of pesticide sorption-desorption in soil

USDA-ARS?s Scientific Manuscript database

Previously published research has used an isotope-exchange technique to measure irreversibility of pesticide adsorption-desorption in soil. Results have indicated significant irreversibility (6-51%) in the sorption in five pesticide-soil systems measured over 72 hours. Here, we propose a three-site ...

Adsorption of NH4+-N on Chinese loess: Non-equilibrium and equilibrium investigations.

PubMed

Xie, Haijian; Wang, Shaoyi; Qiu, Zhanhong; Jiang, Jianqun

2017-11-01

NH 4 + -N is a crucial pollutant in landfill leachate and can be in high concentrations for a long period of time due to anaerobic condition of landfills. The adsorption properties of NH 4 + -N on the Chinese loess were investigated using Batch test. The influences of ammonium concentration, temperature, reaction time, slurry concentration, and pH on the adsorption process are evaluated. Adsorption kinetics and isotherm behaviors were studied by applying different models to the test data to determine the adsorption parameters. The equilibrating duration was shown to be less than 60 min. The data on adsorption kinetics can be well fitted by the pseudo-second-order kinetics model. According to the Langmuir isotherm model, the adsorption capacity of Chinese loess about NH 4 + -N was predicted to be 72.30 mg g -1 . The uptake of NH 4 + -N by Chinese loess was considered to be the type of physical adsorption on the basis of D-R isotherm analysis. The optimal pH and slurry concentration are 4 and 2 g/50 ml, respectively. According to the calculated values of free energy, enthalpy and entropy change, the adsorption process is determined to be exothermic. The disorder of the system appeared lowest at temperature of 308.15 K. The predicted Gibb's free energies also indicate the adsorption process is endothermic and spontaneous. The FTIR spectrum and EDX analysis showed the adsorption process of NH 4 + involves cation exchange and dissolution of calcite. Copyright © 2017 Elsevier Ltd. All rights reserved.

Adsorption separation of carbon dioxide from flue gas by a molecularly imprinted adsorbent.

PubMed

Zhao, Yi; Shen, Yanmei; Ma, Guoyi; Hao, Rongjie

2014-01-01

CO2 separation by molecularly imprinted adsorbent from coal-fired flue gas after desulfurization system has been studied. The adsorbent was synthesized by molecular imprinted technique, using ethanedioic acid, acrylamide, and ethylene glycol dimethacrylate as the template, functional monomer, and cross-linker, respectively. According to the conditions of coal-fired flue gas, the influencing factors, including adsorption temperature, desorption temperature, gas flow rate, and concentrations of CO2, H2O, O2, SO2, and NO, were studied by fixed bed breakthrough experiments. The experimental conditions were optimized to gain the best adsorption performance and reduce unnecessary energy consumption in future practical use. The optimized adsorption temperature, desorption temperature, concentrations of CO2, and gas flow rate are 60 °C, 80 °C, 13%, and 170 mL/min, respectively, which correspond to conditions of practical flue gases to the most extent. The CO2 adsorption performance was nearly unaffected by H2O, O2, and NO in the flue gas, and was promoted by SO2 within the emission limit stipulated in the Chinese emission standards of air pollutants for a thermal power plant. The maximum CO2 adsorption capacity, 0.57 mmol/g, was obtained under the optimized experimental conditions, and the SO2 concentration was 150 mg/m(3). The influence mechanisms of H2O, O2, SO2, and NO on CO2 adsorption capacity were investigated by infrared spectroscopic analysis.

MnFe2O4-graphene oxide magnetic nanoparticles as a high-performance adsorbent for rare earth elements: Synthesis, isotherms, kinetics, thermodynamics and desorption.

PubMed

Ghobadi, Misagh; Gharabaghi, Mahdi; Abdollahi, Hadi; Boroumand, Zohreh; Moradian, Marzieh

2018-06-05

In recent decades, considerable amounts of rare earth elements have been used and then released into industrial wastewater, which caused serious environmental problems. In this work, in order to recycle rare earth cations (La 3+ and Ce 3+ ) from aqueous solutions, MnFe 2 O 4 -Graphene oxide magnetic nanoparticles were synthesized and after characterization studies, their adsorption isotherms, kinetics, thermodynamics and desorption were comprehensively investigated. Characterized was performed using XRD, FE-SEM, FT-IR, Raman spectroscopy, VSM, BET and DLS. REE adsorption on MnFe 2 O 4 -GO was studied for the first time in the present work and the maximum adsorption capacity at the optimum condition (room temperature and pH = 7) for La 3+ and Ce 3+ were 1001 and 982 mg/g respectively, and the reactions were completed within 20 min. In addition, the adsorption data were well matched with the Langmuir model and the adsorption kinetics were fitted with the pseudo-second order model. The thermodynamic parameters were calculated and the reactions were found to be endothermic and spontaneous. Moreover, the Dubinin-Radushkevich model predicted chemical ion-exchange adsorption. Desorption studies also demonstrated that MnFe 2 O 4 -GO can be regenerated for multiple reuses. Overall, high adsorption capacity, chemical stability, reusability, fast kinetics, easy magnetic separation, and simple synthesis method indicated that MnFe 2 O 4 -GO is a high-performance adsorbent for REE. Copyright © 2018. Published by Elsevier B.V.

Adsorptive removal of selected pharmaceuticals by mesoporous silica SBA-15.

PubMed

Bui, Tung Xuan; Choi, Heechul

2009-09-15

The removal of five selected pharmaceuticals, viz., carbamazepine, clofibric acid, diclofenac, ibuprofen, and ketoprofen was examined by batch sorption experiments onto a synthesized mesoporous silica SBA-15. SBA-15 was synthesized and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N(2) adsorption-desorption measurement, and point of zero charge (PZC) measurement. Pharmaceutical adsorption kinetics was rapid and occurred on a scale of minutes, following a pseudo-second-order rate expression. Adsorption isotherms were best fitted by the Freundlich isotherm model. High removal rates of individual pharmaceuticals were achieved in acidic media (pH 3-5) and reached 85.2% for carbamazepine, 88.3% for diclofenac, 93.0% for ibuprofen, 94.3% for ketoprofen, and 49.0% for clofibric acid at pH 3 but decreased with increase in pH. SBA-15 also showed high efficiency for removal of a mixture of 5 pharmaceuticals. Except for clofibric acid (35.6%), the removal of pharmaceuticals in the mixture ranged from 75.2 to 89.3%. Based on adsorption and desorption results, the mechanism of the selected pharmaceuticals was found to be a hydrophilic interaction, providing valuable information for further studies to design materials for the purpose. The results of this study suggest that mesoporous-silica-based materials are promising adsorbents for removing pharmaceuticals from not only surface water but also wastewater of pharmaceutical industrial manufactures.

Adsorption of vitamin E on mesoporous titania nanocrystals

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

Shih, C.J., E-mail: cjshih@kmu.edu.tw; Lin, C.T.; Wu, S.M.

2010-07-15

Tri-block nonionic surfactant and titanium chloride were used as starting materials for the synthesis of mesoporous titania nanocrystallite powders. The main objective of the present study was to examine the synthesis of mesoporous titania nanocrystals and the adsorption of vitamin E on those nanocrystals using X-ray diffraction (XRD), transmission electron microscopy, and nitrogen adsorption and desorption isotherms. When the calcination temperature was increased to 300 {sup o}C, the reflection peaks in the XRD pattern indicated the presence of an anatase phase. The crystallinity of the nanocrystallites increased from 80% to 98.6% with increasing calcination temperature from 465 {sup o}C tomore » 500 {sup o}C. The N{sub 2} adsorption data and XRD data taken after vitamin E adsorption revealed that the vitamin E molecules were adsorbed in the mesopores of the titania nanocrystals.« less

Desorption of plutonium from montmorillonite: An experimental and modeling study

DOE PAGES

Begg, James D.; Zavarin, Mavrik; Kersting, Annie B.

2017-01-15

Desorption of plutonium (Pu) will likely control the extent to which it is transported by mineral colloids. In this article, we evaluated the adsorption/desorption behavior of Pu on SWy-1 montmorillonite colloids at pH 4, pH 6, and pH 8 using batch adsorption and flow cell desorption experiments. After 21 days adsorption, Pu(IV) affinity for montmorillonite displayed a pH dependency, with K d values highest at pH 4 and lowest at pH 8. The pH 8 experiment was further allowed to equilibrate for 6 months and showed an increase in K d, indicating that true sorption equilibrium was not achieved withinmore » the first 21 days. For the desorption experiments, aliquots of the sorption suspensions were placed in a flow cell, and Pu-free solutions were then pumped through the cell for a period of 12 days. Changes in influent solution flow rate were used to investigate the kinetics of Pu desorption and demonstrated that it was rate-limited over the experimental timescales. At the end of the 12-day flow cell experiments, the extent of desorption was again pH dependent, with pH 8 > pH 6 > pH 4. Further, at pH 8, less Pu was desorbed after an adsorption contact time of 6 months than after a contact time of 21 days, consistent with an aging of Pu on the clay surface. In addition, a conceptual model for Pu adsorption/desorption that incorporated known surface-mediated Pu redox reactions was used to fit the experimental data. The resulting rate constants indicated processes occurring on timescales of months and even years which may, in part, explain observations of clay colloid-facilitated Pu transport on decadal timescales. Importantly, however, our results also imply that migration of Pu adsorbed to montmorillonite colloids at long (50–100 year) timescales under oxic conditions may not be possible without considering additional phenomena, such as co-precipitation.« less

Desorption of plutonium from montmorillonite: An experimental and modeling study

NASA Astrophysics Data System (ADS)

Begg, James D.; Zavarin, Mavrik; Kersting, Annie B.

2017-01-01

Desorption of plutonium (Pu) will likely control the extent to which it is transported by mineral colloids. We evaluated the adsorption/desorption behavior of Pu on SWy-1 montmorillonite colloids at pH 4, pH 6, and pH 8 using batch adsorption and flow cell desorption experiments. After 21 days adsorption, Pu(IV) affinity for montmorillonite displayed a pH dependency, with Kd values highest at pH 4 and lowest at pH 8. The pH 8 experiment was further allowed to equilibrate for 6 months and showed an increase in Kd, indicating that true sorption equilibrium was not achieved within the first 21 days. For the desorption experiments, aliquots of the sorption suspensions were placed in a flow cell, and Pu-free solutions were then pumped through the cell for a period of 12 days. Changes in influent solution flow rate were used to investigate the kinetics of Pu desorption and demonstrated that it was rate-limited over the experimental timescales. At the end of the 12-day flow cell experiments, the extent of desorption was again pH dependent, with pH 8 > pH 6 > pH 4. Further, at pH 8, less Pu was desorbed after an adsorption contact time of 6 months than after a contact time of 21 days, consistent with an aging of Pu on the clay surface. A conceptual model for Pu adsorption/desorption that incorporated known surface-mediated Pu redox reactions was used to fit the experimental data. The resulting rate constants indicated processes occurring on timescales of months and even years which may, in part, explain observations of clay colloid-facilitated Pu transport on decadal timescales. Importantly, however, our results also imply that migration of Pu adsorbed to montmorillonite colloids at long (50-100 year) timescales under oxic conditions may not be possible without considering additional phenomena, such as co-precipitation.

Adsorption and desorption properties of macroporous resins for anthocyanins from the calyx extract of roselle (Hibiscus sabdariffa L.).

PubMed

Chang, Xiu-Lian; Wang, Dong; Chen, Bi-Yun; Feng, Yong-Mei; Wen, Shao-Hong; Zhan, Peng-Yuan

2012-03-07

Adsorption of roselle anthocynins, a natural pigment, onto various macroporous resins was optimized to develop a simple and efficient process for industrial separation and purification of roselle anthocyanins. Nine different macroporous resins (AB-8, X-5, HPD-100, SP-207, XAD-4, LS-305A, DM-21, LS-610B, and LS-305) were evaluated for the adsorption properties of the anthocyanins extracted from the calyx extract of Hibiscus sabdariffa L. The influences of phase contact time, solution pH, initial anthocyanin concentration, and ethanol concentration with different citric acid amounts were studied by the static adsorption/desorption method. The adsorption isotherm data were fitted well to the Langmuir isotherm, and according to this model, LS-610B and LS-305 exhibited the highest monolayer sorption capacities of 31.95 and 38.16 mg/g, respectively. The kinetic data were modeled using pseudo-first-order, pseudo-second-order, and intraparticle diffusion equations. The experimental data were well described by the pseudo-second-order kinetic model. Continuous column adsorption-regeneration cycles indicated negligible capacity loss of LS-305 during operation. The overall yield of pigment product was 49.6 mg/g dried calyces. The content of roselle anthocynins in the pigment product was 4.85%.

Influence of surface coverage on the chemical desorption process

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

Minissale, M.; Dulieu, F., E-mail: francois.dulieu@obspm.fr

2014-07-07

In cold astrophysical environments, some molecules are observed in the gas phase whereas they should have been depleted, frozen on dust grains. In order to solve this problem, astrochemists have proposed that a fraction of molecules synthesized on the surface of dust grains could desorb just after their formation. Recently the chemical desorption process has been demonstrated experimentally, but the key parameters at play have not yet been fully understood. In this article, we propose a new procedure to analyze the ratio of di-oxygen and ozone synthesized after O atoms adsorption on oxidized graphite. We demonstrate that the chemical desorptionmore » efficiency of the two reaction paths (O+O and O+O{sub 2}) is different by one order of magnitude. We show the importance of the surface coverage: for the O+O reaction, the chemical desorption efficiency is close to 80% at zero coverage and tends to zero at one monolayer coverage. The coverage dependence of O+O chemical desorption is proved by varying the amount of pre-adsorbed N{sub 2} on the substrate from 0 to 1.5 ML. Finally, we discuss the relevance of the different physical parameters that could play a role in the chemical desorption process: binding energy, enthalpy of formation, and energy transfer from the new molecule to the surface or to other adsorbates.« less

Adsorption of acetanilide herbicides on soil and its components. II. Adsorption and catalytic hydrolysis of diethatyl-ethyl on saturated Na(+)-, K(+)-, Ca(2+)-, and Mg(2+)-montmorillonite.

PubMed

Liu, W P; Fang, Z; Liu, H J; Yang, W C

2001-04-01

Adsorption and catalytic hydrolysis of the herbicide diethatyl-ethyl [N-chloroacetyl-N-(2,6-diethylphenyl)glycine ethyl ester] on homoionic Na(+)-, K(+)-, Ca(2+)-, and Mg(2+)-montmorillonite clays were investigated in water solution. The Freundlich adsorption coefficient, Ki, got from isotherms on clay followed the order of Na+ approximately K+ > Mg2+ approximately Ca2+. Analysis of FT-IR spectra of diethatyl-ethyl adsorbed on clay suggests probable bonding at the carboxyl and amide carbonyl groups of the herbicide. The rate of herbicide hydrolysis in homoionic clay suspensions followed the same order as that for adsorption, indicating that adsorption may have preceded and thus caused hydrolysis. Preliminary product identification showed that hydrolysis occurred via nucleophilic substitution at the carboxyl carbon, causing the cleavage of the ester bond and formation of diethatyl and its dechlorinated derivative, and at the amide carbon, yielding an ethyl ester derivative and its acid. These pathways also suggest that hydrolysis of diethatyl-ethyl was catalyzed by adsorption on the clay surface.

Formation of titanosilicate precursors of an active adsorption phase

NASA Astrophysics Data System (ADS)

Kuznetsova, T. F.; Ivanets, A. I.; Katsoshvili, L. L.

2017-04-01

Micro-mesoporous titanosilicate precursors of the active absorption phase of a composite ceramic membrane are synthesized, and their textural and adsorption properties are investigated by means of low-temperature nitrogen adsorption/desorption. Low-temperature isotherms of nitrogen adsorption/desorption are analyzed using the BET, Langmuir, comparative t-plot, Barrett-Joyner-Halenda, and density functional theory methods. It is found that at high contents of silicon(IV) oxide, the resulting xerogels have surface areas of 656 and 890 m2/g according to the BET and Langmuir approaches, respectively, while the micropores' inner and outer surfaces are 453 and 466 m2/g, respectively, according to the t-plot. According to the DFT distributions, the mesopore diameters of a sample can be adjusted in the range of 3-9 nm. By analyzing the type of capillary condensation hysteresis in the adsorption/desorption isotherms, it is shown that the pores in the samples are very bottle-like, even though their shape may be different in reality. It is found that in samples with high contents of titanium(IV) oxide, the pore throats are blocked during adsorbate desorption, due to the percolation effect. It is assumed that the stabilization of particles of titanium(IV) oxide by amorphous layers of silica protects the texture of titanosilicate xerogels from full contraction and the coalescence of particles during heat treatment ranging from 393 to 923 K.

Rapid Quantification of N-Methyl-2-pyrrolidone in Polymer Matrices by Thermal Desorption-GC/MS.

PubMed

Kim, Young-Min; Kim, Jae Woo; Moon, Hye Mi; Lee, Min-Jin; Hosaka, Akihiko; Watanabe, Atsushi; Teramae, Norio; Park, Young-Kwon; Myung, Seung-Woon

2017-01-01

Analysis of a residual solvent in polymeric materials has become an important issue due to the increased regulations and standards for its use. N-Methyl-2-pyrrolidone (NMP) is a solvent widely used in many industries and restricted as one of the chemicals under EU REACH regulations due to its potential harmful effects. In this study, thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) is applied for the quantitative analysis of NMP with the use of a polymer-coated sample cup. By using the polymer-coated sample cup, the vaporization of NMP was prevented during waiting time before TD-GC/MS analysis. The calibration curve for the TD method showed good linearity (correlation coefficient, r 2 = 0.9998) and precision values (below 5.3% RSD). NMP recovery rates in different polymer matrices (PS, PMMA and PVC) were in the range of 98.8 to 106.6% with RSD values below 5.0%. The quantification result (600 mg NMP/kg PVC) for the blind NMP carrying sample in a PVC matrix by TD-GC/MS was higher than that (532 mg NMP/kg PVC) by solvent extraction-GC/MS method.

Acetaldehyde Adsorption and Reaction onCeO2(100) Thin Films

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

Mullins, David R; Albrecht, Peter M

2013-01-01

This study reports and compares the adsorption and dissociation of acetaldehyde on oxidized and reduced CeOX(100) thin films. Acetaldehyde reacts and decomposes on fully oxidized CeO2(100) whereas it desorbs molecularly at low temperature on CeO2(111). The primary products are CO, CO2 and water along with trace amounts of crotonaldehyde and acetylene. The acetaldehyde adsorbs as the 2-acetaldehyde species, dioxyethylene. Decomposition proceeds by dehydrogenation through acetate and enolate intermediates. The reaction pathway is similar on the reduced CeO2-X(100) surface however the inability to react with surface O on the reduced surface results in H2 rather than H2O desorption and C ismore » left on the surface rather than producing CO and CO2. C-O bond cleavage in the enolate intermediate followed by reaction with surface H results in ethylene desorption.« less

Adsorption behavior of proteins on temperature-responsive resins.

PubMed

Poplewska, Izabela; Muca, Renata; Strachota, Adam; Piątkowski, Wojciech; Antos, Dorota

2014-01-10

The adsorption behavior of proteins on thermo-responsible resins based on poly(N-isopropylacrylamide) and its copolymer containing an anionic co-monomer has been investigated. The influence of the polymer composition, i.e., the content of the co-monomer and crosslinker on the thermo-sensitivity of the protein adsorption has been quantified. The properties of ungrafted polymer as well grafted onto the agarose matrix have been analyzed and compared. Batch and dynamic (column) experiments have been performed to measure the adsorption equilibrium of proteins and to quantify the phase transition process. As model proteins lysozyme, lactoferrin, α-chymotrypsinogen A and ovalbumin have been used. The adsorption process was found to be governed by ionic interactions between the negatively charged surface of resin and the protein, which enabled separation of proteins differing in electrostatic charge. The interactions enhanced with increase of temperature. Decrease of temperature facilitated desorption of proteins and reduced the salt usage in the desorption buffer. Grafted polymers exhibited markedly higher mechanical stability and, however, weaker temperature response compared to the ungrafted ones. Copyright © 2013 Elsevier B.V. All rights reserved.

Enhanced adsorption of Eu(III) on mesoporous Al2O3/expanded graphite composites investigated by macroscopic and microscopic techniques.

PubMed

Sun, Yubing; Chen, Changlun; Tan, Xiaoli; Shao, Dadong; Li, Jiaxing; Zhao, Guixia; Yang, Shubin; Wang, Qi; Wang, Xiangke

2012-11-21

Mesoporous Al(2)O(3) was intercalated into an expanded graphite (EG) interlayer to prepare mesoporous Al(2)O(3)/EG composites. The basal spacing of mesoporous Al(2)O(3)/EG composites was enlarged as compared to raw graphite from the X-ray diffraction analysis. The massive surface functional groups and wedge-shaped pores were observed in terms of potentiometric acid-base titration analysis and scanning electron microscope, respectively. The pH-dependent adsorption of Eu(III) on mesoporous Al(2)O(3)/EG composites was evidently independent of ionic strength. The maximum adsorption capacity of Eu(III) on mesoporous Al(2)O(3)/EG composites at pH 6.0 and T = 293 K was calculated to be 5.14 mg g(-1). Desorption kinetics and cyclic operation results showed that mesoporous Al(2)O(3)/EG composites presented high hydrothermal stability in aqueous solution. The thermodynamic parameters suggested that Eu(III) adsorption on mesoporous Al(2)O(3)/EG composites is an endothermic and a spontaneous process. The decrease of Eu-O bond distance with the increasing pH demonstrated that the adsorption mechanism between Eu(III) and mesoporous Al(2)O(3)/EG composites would shift from outer-sphere surface complexation to inner-sphere surface complexation in terms of extended X-ray absorption fine structure spectroscopy analysis.

Experimental and Numerical Investigation of Adsorption/Desorption in Packed Sorption Beds Under Ideal and Non-Ideal Flows

NASA Technical Reports Server (NTRS)

Mohamadinejad, H.; Knox, J. C.; Smith, James E.

1999-01-01

The importance of the wall effect on packed beds in the adsorption and desorption of carbon dioxide, nitrogen, and water on molecular sieve 5A of 0.127 cm in radius is examined experimentally and with one-dimensional computer simulations. Experimental results are presented for a 22.5-cm long by 4.5-cm diameter cylindrical column with concentration measurements taken at various radial locations. The set of partial differential equations are solved using finite differences and Newman's method. Comparison of test data with the axial-dispersed, non-isothermal, linear driving force model suggests that a two-dimensional model (submitted to Separation Science and Technology) is required for accurate simulation of the average column breakthrough concentration. Additional comparisons of test data with the model provided information on the interactive effects of carrier gas coadsorption with CO2, as well as CO2-H2O interactions.

Multivariate analysis of progressive thermal desorption coupled gas chromatography-mass spectrometry.

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

Van Benthem, Mark Hilary; Mowry, Curtis Dale; Kotula, Paul Gabriel

belief that this multivariate analysis will enable superior differentiation capabilities. In addition, noise and system artifacts challenge the analysis of GC-MS data collected on lower cost equipment, ubiquitous in commercial laboratories. This research has the potential to affect many areas of analytical chemistry including materials analysis, medical testing, and environmental surveillance. It could also provide a method to measure adsorption parameters for chemical interactions on various surfaces by measuring desorption as a function of temperature for mixtures. We have presented results of a novel method for examining offgas products of a common PDMS material. Our method involves utilizing a stepped TD/GC-MS data acquisition scheme that may be almost totally automated, coupled with multivariate analysis schemes. This method of data generation and analysis can be applied to a number of materials aging and thermal degradation studies.« less

Adsorption and desorption of arsenic to aquifer sediment on the Red River floodplain at Nam Du, Vietnam

PubMed Central

Thi Hoa Mai, Nguyen; Postma, Dieke; Thi Kim Trang, Pham; Jessen, Søren; Hung Viet, Pham; Larsen, Flemming

2016-01-01

The adsorption of arsenic onto aquifer sediment from the Red River floodplain, Vietnam, was determined in a series of batch experiments. Due to water supply pumping, river water infiltrates into the aquifer at the field site and has leached the uppermost aquifer sediments. The leached sediments, remain anoxic but contain little reactive arsenic and iron, and are used in our experiments. The adsorption and desorption experiments were carried out by addition or removal of arsenic from the aqueous phase in sediment suspensions under strictly anoxic conditions. Also the effects of HCO3, Fe(II), PO4 and Si on arsenic adsorption were explored. The results show much stronger adsorption of As(V) as compared to As(III), full reversibility for As(III) adsorption and less so for As(V). The presence or absence of HCO3 did not influence arsenic adsorption. Fe(II) enhanced As(V) sorption but did not influence the adsorption of As(III) in any way. During simultaneous adsorption of As(III) and Fe(II), As(III) was found to be fully desorbable while Fe(II) was completely irreversibly adsorbed and clearly the two sorption processes are uncoupled. Phosphate was the only solute that significantly could displace As(III) from the sediment surface. Compiling literature data on arsenic adsorption to aquifer sediment in Vietnam and Bangladesh revealed As(III) isotherms to be almost identical regardless of the nature of the sediment or the site of sampling. In contrast, there was a large variation in As(V) adsorption isotherms between studies. A tentative conclusion is that As(III) and As(V) are not adsorbing onto the same sediment surface sites. The adsorption behavior of arsenic onto aquifer sediments and synthetic Fe-oxides is compared. Particularly, the much stronger adsorption of As(V) than of As(III) onto Red River as well as on most Bangladesh aquifer sediments, indicates that the perception that arsenic, phosphate and other species compete for the same surface sites of iron oxides in

Thermal desorption of dimethyl methylphosphonate from MoO 3

DOE PAGES

Head, Ashley R.; Tang, Xin; Hicks, Zachary; ...

2017-03-03

Organophosphonates are used as chemical warfare agents, pesticides, and corrosion inhibitors. New materials for the sorption, detection, and decomposition of these compounds are urgently needed. To facilitate materials and application innovation, a better understanding of the interactions between organophosphonates and surfaces is required. To this end, we have used diffuse reflectance infrared Fourier transform spectroscopy to investigate the adsorption geometry of dimethyl methylphosphonate (DMMP) on MoO 3, a material used in chemical warfare agent filtration devices. We further applied ambient pressure X-ray photoelectron spectroscopy and temperature programmed desorption to study the adsorption and desorption of DMMP. While DMMP adsorbs intactmore » on MoO 3, desorption depends on coverage and partial pressure. At low coverages under UHV conditions, the intact adsorption is reversible. Decomposition occurs with higher coverages, as evidenced by PCH x and PO x decomposition products on the MoO 3 surface. Heating under mTorr partial pressures of DMMP results in product accumulation.« less

Adsorption Characteristics of LaNi 5Particles

NASA Astrophysics Data System (ADS)

Song, M. Y.; Park, H. R.

1997-11-01

Nitrogen adsorption on an intermetallic compound, LaNi 5, was studied before and after activation and after hydriding-dehydriding cycling. The specific surface area of activated LaNi 5was 0.271±0.004 m 2g -1. Adsorption and desorption isotherms of activated LaNi 5were obtained. The adsorption isotherm was similar to type II among the five types of isotherms classified by S. Brunauer, L. S. Deming, W S. Deming, and E. Teller ( J. Am. Chem. Soc.62, 1723, 1940). Its hysteresis curve had the type B form among de Boer's five types of hysteresis. Desorption pore-size analyses showed that the activated LaNi 5had only a few mesopores, the diameters of which were around 20-110 Å. The average adsorption rate of the activated LaNi 5showed a first-order dependence on nitrogen pressure at 77 K.

Fiber optic sensors based on hybrid phenyl-silica xerogel films to detect n-hexane: determination of the isosteric enthalpy of adsorption

PubMed Central

Calleja, Ignacio; Moriones, Paula; Garrido, Julián J

2017-01-01

We investigated the response of three fiber optic sensing elements prepared at pH 10 from phenyltriethoxysilane (PhTEOS) and tetraethylsilane (TEOS) mixtures with 30, 40, and 50% PhTEOS in the silicon precursor mixture. The sensing elements are referred to as Ph30, Ph40 and Ph50, respectively. The films were synthesized by the sol–gel method and affixed to the end of optical fibers by the dip-coating technique. Fourier transform infrared spectroscopy, N2 adsorption–desorption at 77 K and X-ray diffraction analysis were used to characterize the xerogels. At a given pressure of n-hexane, the response of each sensing element decreased with temperature, indicating an exothermic process that confirmed the role of adsorption in the overall performance of the sensing elements. The isosteric adsorption enthalpies were obtained from the calibration curves at different temperatures. The magnitude of the isosteric enthalpy of n-hexane increased with the relative response and reached a plateau that stabilized at approximately −31 kJ mol−1 for Ph40 and Ph50 and at approximately −37 kJ mol−1 for Ph30. This indicates that the adsorbate–adsorbent interaction was dominant at lower relative pressure and condensation of the adsorbate on the mesopores was dominant at higher relative pressure. PMID:28326238

Sorption and desorption of lead (II) from wastewater by green algae Cladophora fascicularis.

PubMed

Deng, Liping; Su, Yingying; Su, Hua; Wang, Xinting; Zhu, Xiaobin

2007-05-08

Biosorption is an effective method to remove heavy metals from wastewater. In this work, adsorption features of Cladophora fascicularis were investigated as a function of time, initial pH, initial Pb(II) concentrations, temperature and co-existing ions. Kinetics and equilibria were obtained from batch experiments. The biosorption kinetics followed the pseudo-second order model. Adsorption equilibria were well described by the Langmuir and Freundlich isotherm models. The maximum adsorption capacity was 198.5 mg/g at 298K and pH 5.0. The adsorption processes were endothermic and the biosorption heat was 29.6 kJ/mol. Desorption experiments indicated that 0.01 mol/L Na(2)EDTA was an efficient desorbent for the recovery of Pb(II) from biomass. IR spectrum analysis suggested amido or hydroxy, CO and C-O could combine intensively with Pb(II).

Combining the Physical Adsorption Approach and the Covalent Attachment Method to Prepare a Bifunctional Bioreactor

PubMed Central

Dong, Mengxing; Wu, Zhuofu; Lu, Ming; Wang, Zhi; Li, Zhengqiang

2012-01-01

Aminopropyl-functionalized SBA-15 mesoporous silica was used as a support to adsorb myoglobin. Then, in order to avoid the leakage of adsorbed myoglobin, lysozyme was covalently tethered to the internal and external surface of the mesoporous silica with glutaraldehyde as the coupling agent. The property of amino-functionalized mesoporous silica was characterized by N2 adsorption-desorption and thermogravimetric (TG) analysis. The feature of the silica-based matrix before and after myoglobin adsorption was identified by fourier transform infrared (FTIR) and UV/VIS measurement. With o-dianisidine and H2O2 as the substrate, the peroxidase activity of adsorbed myoglobin was determined. With Micrococus lysodeilicus as the substrate, the antibacterial activity of covalently tethered lysozyme was measured. Results demonstrated that the final product not only presented peroxidase activity of the myoglobin but yielded antibacterial activity of the lysozyme. PMID:23109864

Correlating N2 and CH4 adsorption on microporous carbon using a new analytical model

USGS Publications Warehouse

Sun, Jielun; Chen, S.; Rood, M.J.; Rostam-Abadi, M.

1998-01-01

A new pore size distribution (PSD) model is developed to readily describe PSDs of microporous materials with an analytical expression. Results from this model can be used to calculate the corresponding adsorption isotherm to compare the calculated isotherm to the experimental isotherm. This aspect of the model provides another check on the validity of the model's results. The model is developed on the basis of a 3-D adsorption isotherm equation that is derived from statistical mechanical principles. Least-squares error minimization is used to solve the PSD without any preassumed distribution function. In comparison with several well-accepted analytical methods from the literature, this 3-D model offers a relatively realistic PSD description for select reference materials, including activated-carbon fibers. N2 and CH4 adsorption is correlated using the 3-D model for commercial carbons BPL and AX-21. Predicted CH4 adsorption isotherms at 296 K based on N2 adsorption at 77 K are in reasonable agreement with experimental CH4 isotherms. Use of the model is also described for characterizing PSDs of tire-derived activated carbons and coal-derived activated carbons for air-quality control applications.

Adsorption of caffeine on mesoporous activated carbon fibers prepared from pineapple plant leaves.

PubMed

Beltrame, Karla K; Cazetta, André L; de Souza, Patrícia S C; Spessato, Lucas; Silva, Taís L; Almeida, Vitor C

2018-01-01

The present work reports the preparation of activated carbon fibers (ACFs) from pineapple plant leaves, and its application on caffeine (CFN) removal from aqueous solution. The preparation procedure was carried out using the H 3 PO 4 as activating agent and slow pyrolysis under N 2 atmosphere. The characterization of materials was performed from the N 2 adsorption and desorption isotherms, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, Boehm titration and pH pzc method. ACFs showed high BET surface area value (S BET = 1031m 2 g -1 ), well-developed mesoporous structure (mesopore volume of 1.27cm³ g -1 ) and pores with average diameter (D M ) of 5.87nm. Additionally, ACFs showed features of fibrous material with predominance of acid groups on its surface. Adsorption studies indicated that the pseudo-second order kinetic and Langmuir isotherm models were that best fitted to the experimental data. The monolayer adsorption capacity was found to be 155.50mgg -1 . thermodynamic studies revealed that adsorption process is spontaneous, exothermic and occurs preferably via physisorption. The pineapple leaves are an efficient precursor for preparation of ACFs, which were successful applied as adsorbent material for removal of caffeine from the aqueous solutions. Copyright © 2017 Elsevier Inc. All rights reserved.

Retention of Nickel in Soils: Sorption-Desorption and Extended X-ray Absorption Fine Structure Experiments

EPA Science Inventory

Adsorption and desorption of heavy metals in soils are primary factors that influence their bioavailability and mobility in the soil profile. To examine the characteristics of nickel (Ni) adsorption-desorption in soils, kinetic batch experiments were carried out followed by Ni re...

A model for the catalytic reduction of NO with CO and N desorption

NASA Astrophysics Data System (ADS)

Díaz, J. J.; Buendía, G. M.

2018-02-01

In this work we have investigated by Monte Carlo simulations the dynamical behavior of a modified Yaldram-Khan (YK) model for the catalytic reduction of NO on a surface. Our model is simulated on a square lattice and includes the individual desorption of CO molecules and N atoms, processes associated with temperature effects. When CO desorption is added, strong fluctuations appear, which are associated with the spreading of N checkerboard structures on the surface. These structures take a long time to coalesce, allowing the existence of a unsteady but long lasting reactive state. N desorption also favors the reactivity of the system, this time by diminishing the size of the N structures and impeding their coalescence. The combined desorption of CO and N produces a reactive state as well, where reactive zones among N structures can take place on the surface.

Through oven transfer adsorption-desorption interface for the analysis of methyl jasmonate in aromatic samples by on-line RPLC-GC.

PubMed

Flores, Gema; Blanch, Gracia Patricia; Ruiz del Castillo, Maria Luisa

2008-04-01

A fully automated method for the determination of medium volatility compounds in aromatic samples was developed. Specifically, the determination of methyl jasmonate in jasmine fragrances was performed by using the through oven transfer adsorption-desorption (TOTAD) interface for the on-line coupling between RPLC-GC. A study of the most relevant variables involved in the performance of the TOTAD interface for medium volatility compounds was carried out by testing different values of helium flow (100, 300, 400, and 500 mL/min), transfer speed (0.1, 0.3, 0.5, and 2.0 mL/min), and methanol/water percentages (86:14, 85:15, 83:17, 80:20, and 70:30). The method developed provided satisfactory repeatability (RSD for retention times of 0.15% and for peak areas of 9.4%) and recovery (71%) as well as excellent LOD (0.01 mg/L) for methyl jasmonate in commercial jasmine essence under the experimental conditions selected as optimum. Additional advantages of the automated RPLC-TOTAD-GC method proposed in the present work are its rapidness, reliability, and the possibility of directly introducing the sample with no further pretreatment.

Adsorption of Cd2+ ions on plant mediated SnO2 nanoparticles

NASA Astrophysics Data System (ADS)

Haq, Sirajul; Rehman, Wajid; Waseem, Muhammad; Shahid, Muhammad; Mahfooz-ur-Rehman; Hussain Shah, Khizar; Nawaz, Mohsan

2016-10-01

Plant mediated SnO2 nanoparticles were synthesized by using SnCl4.5H2O as a precursor material. The nanoparticles were then characterized for BET surface area measurements, energy dispersive x-rays (EDX), scanning electron microscopy (SEM), UV-vis diffuse reflectance (DRS) spectra and x-rays diffraction (XRD) analysis. The successful synthesis of SnO2 nanoparticles was confirmed by EDX analysis. The particle sizes were in the range 19-27 nm whereas the crystallite size computed from XRD measurement was found to be 19.9 nm. Batch adsorption technique was employed for the removal of Cd2+ ions from aqueous solution. The sorption studies of Cd2+ ions were performed at pHs 4 and 6. The equilibrium concentration of Cd2+ ions was determined by atomic absorption spectrometer (flame mode). The uptake of Cd2+ ions was affected by initial concentration, pH and temperature of the electrolytic solution. It was observed that the adsorption of Cd2+ ions enhanced with increase in the initial concentration of Cd2+ ions whereas a decrease in the percent adsorption was detected. From the thermodynamic parameters, the adsorption process was found spontaneous and endothermic in nature. The n values confirmed 2:1 exchange mechanism between surface protons and Cd2+ ions.

Adsorption of chlorine dioxide gas on activated carbons.

PubMed

Wood, Joseph P; Ryan, Shawn P; Snyder, Emily Gibb; Serre, Shannon D; Touati, Abderrahmane; Clayton, Matthew J

2010-08-01

Research and field experience with chlorine dioxide (ClO2) gas to decontaminate structures contaminated with Bacillus anthracis spores and other microorganisms have demonstrated the effectiveness of this sterilant technology. However, because of its hazardous properties, the unreacted ClO2, gas must be contained and captured during fumigation events. Although activated carbon has been used during some decontamination events to capture the ClO2 gas, no data are available to quantify the performance of the activated carbon in terms of adsorption capacity and other sorbent property operational features. Laboratory experiments were conducted to determine and compare the ClO2 adsorption capacities of five different types of activated carbon as a function of the challenge ClO2 concentration. Tests were also conducted to investigate other sorbent properties, including screening tests to determine gaseous species desorbed from the saturated sorbent upon warming (to provide an indication of how immobile the ClO2 gas and related compounds are once captured on the sorbent). In the adsorption tests, ClO2 gas was measured continuously using a photometric-based instrument, and these measurements were verified with a noncontinuous method utilizing wet chemistry analysis. The results show that the simple activated carbons (not impregnated or containing other activated sorbent materials) were the most effective, with maximum adsorption capacities of approximately 110 mg/g. In the desorption tests, there was minimal release of ClO(2) from all sorbents tested, but desorption levels of chlorine (Cl2) gas (detected as chloride) varied, with a maximum release of nearly 15% of the mass of ClO2 adsorbed.

Cation Movements during Dehydration and NO2 Desorption in a Ba-Y,FAU zeolite: an in situ Time-resolved X-ray Diffraction Study

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

Wang, Xianqin; Hanson, Jonathan C.; Kwak, Ja Hun

2013-02-28

Synchrotron-based in situ time-resolved X-ray diffraction and Rietveld analysis were used to probe the interactions between BaY, FAU zeolite frameworks and H2O or NO2 molecules. These results provided information about the migration of the Ba2+ cations in the zeolite framework during dehydration and during NO2 adsorption/desorption processes in a water free zeolite. In the hydrated structure water molecules form four double rings of hexagonal ice-like clusters [(H2O)6] in the 12-ring openings of the super-cage. These water rings interacted with the cations and the zeolite framework through four cation/water clusters centered over the four 6-membered rings of the super-cage (site II).more » Interpenetrating tetrahedral water clusters [(H2O)4] and tetrahedral Ba+2 cation clusters were observed in the sodalite cage. Consistent with the reported FT-IR results, three different ionic NOx species (NO+, NO+-NO2, and NO3-) were observed following NO2 adsorption by the dehydrated Ba-Y,FAU zeolite. The structure of the water and the NOx species were correlated with the interactions between the adsorbates, the cations, and the framework. The population of Ba2+ ions at different cationic positions strongly depended on the amount of bound water or NOx species. Both dehydration and NO2 adsorption/desorption resulted in facile migration of Ba2+ ions among the different cationic positions. Data obtained in this work have provided direct evidence for the Ba2+ cation migration to accommodate the binding of gas molecules. This important feature may play a pivotal role in the strong binding of NO2 to Ba-Y,FAU zeolite, a prerequisite for high catalytic activity in lean NOx reduction catalysis.« less

Adsorption behavior and mechanism of acidic blue 25 dye onto cucurbit[8]uril: A spectral and DFT study

NASA Astrophysics Data System (ADS)

Luo, Hanhan; Huang, Xiangyu; Luo, Yuhan; Li, Zhuang; Li, Lan; Gao, Chao; Xiong, Jinyan; Li, Wei

2018-03-01

The acidic blue 25 (AB25) dye was efficiently adsorbed by CB [8]; the saturated adsorption capacity (qexp) reached 434.8 mg/g and was far higher than those of previous reported adsorbents. The Langmuir and Freundich isotherms were used to fit the equilibrium data, and the results showed that the Freundlich isotherm seemed to agree better with the AB25 adsorption. The adsorption kinetics followed the pseudo-second-order model. Calculated thermodynamic parameters showed that the adsorption of AB25 onto CB [8] was a spontaneous and enthalpy-driven process. The adsorption mechanism was explored by N2 adsorption-desorption, TG, FT-IR, UV-vis as well as MD simulation and DFT calculations. TG analysis revealed that a new inclusion complex was produced, and FT-IR,UV-vis spectrum and DFT calculations verify its structure. In this inclusion complex, the AB25 dye molecule inserted into cavities of CB [8] from portal, and the sulfonate and phenyl groups stayed in the hydrophobic cavity. TDDFT calculations indicated that all excitation arisen from π → π* transition.

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 of transgenic insecticidal Cry1Ab protein to SiO2. 2. Patch-controlled electrostatic attraction.

PubMed

Madliger, Michael; Sander, Michael; Schwarzenbach, René P

2010-12-01

Adsorption governs the fate of Cry proteins from genetically modified Bt crops in soils. The effect of ionic strength (I) on the adsorption of Cry1Ab (isoelectric point IEP(Cry1Ab) ≈ 6) to negatively charged quartz (SiO(2)) and positively charged poly-L-lysine (PLL) was investigated at pH 5 to 8, using quartz crystal microbalance with dissipation monitoring and optical waveguide lightmode spectroscopy. Cry1Ab adsorbed via positively and negatively charged surface patches to SiO(2) and PLL, respectively. This patch controlled electrostatic attraction (PCEA) explains the observed increase in Cry1Ab adsorption to sorbents that carried the same net charge as the protein (SiO(2) at pH > IEP(Cry1Ab) and PLL at pH < IEP(Cry1Ab)) with decreasing I. In contrast, the adsorption of two reference proteins, BSA and HEWL, with different adsorption mechanism, were little affected by similar changes of I. Consistent with PCEA, Cry1Ab desorption from SiO(2) at pH > IEP(Cry1Ab) increased with increasing I and pH. Weak Cry1Ab-SiO(2) PCEA above pH 7 resulted in reversible, concentration dependent adsorption. Solution depletion experiments showed that PCEA also governed Cry1Ab adsorption to SiO(2) particles at environmentally relevant concentrations (a few ng mL(-1)). These results imply that models describing Cry1Ab adsorption to charged surfaces in soils need to account for the nonuniform surface charge distribution of the protein.

Regeneration of mesoporous silica aerogel for hydrocarbon adsorption and recovery.

PubMed

Zhang, Chengzhao; Dai, Chong; Zhang, Huaqin; Peng, Shitao; Wei, Xin; Hu, Yandi

2017-09-15

Silica aerogel, with mesoporous structure and high hydrophobicity, is a promising adsorbent for oil spill clean-up. To make it economic and environmental-friendly, hydrocarbon desorption and silica aerogel regeneration were investigated. After hydrocarbon desorption at 80°C, silica aerogel maintained its hydrophobicity. After toluene, petrol, and diesel desorption, shrinkage of mesopores (from 19.9 to 16.8, 13.5, and 13.4nm) of silica aerogels occurred, causing decreased adsorption capacities (from 12.4, 11.2, and 13.6 to 12.0, 6.5, and 2.3g/g). Low surface tension of petrol caused high stress on mesopores during its desorption, resulting in significant pore shrinkage. For diesel, its incomplete desorption and oxidation further hindered the regeneration. Therefore, diesel desorption was also conducted at 200°C. Severe diesel oxidation occurred under aerobic condition and destroyed the mesopores. Under anaerobic condition, no diesel oxidation occurred and the decreases in pore size (to 13.2nm) and adsorption efficiency (to 10.0g/g) of regenerated silica aerogels were much less, compared with under aerobic condition. This study provided new insights on silica aerogel regeneration for oil spill clean-up. Copyright © 2017 Elsevier Ltd. All rights reserved.

Thermal Desorption Analysis of Effective Specific Soil Surface Area

NASA Astrophysics Data System (ADS)

Smagin, A. V.; Bashina, A. S.; Klyueva, V. V.; Kubareva, A. V.

2017-12-01

A new method of assessing the effective specific surface area based on the successive thermal desorption of water vapor at different temperature stages of sample drying is analyzed in comparison with the conventional static adsorption method using a representative set of soil samples of different genesis and degree of dispersion. The theory of the method uses the fundamental relationship between the thermodynamic water potential (Ψ) and the absolute temperature of drying ( T): Ψ = Q - aT, where Q is the specific heat of vaporization, and a is the physically based parameter related to the initial temperature and relative humidity of the air in the external thermodynamic reservoir (laboratory). From gravimetric data on the mass fraction of water ( W) and the Ψ value, Polyanyi potential curves ( W(Ψ)) for the studied samples are plotted. Water sorption isotherms are then calculated, from which the capacity of monolayer and the target effective specific surface area are determined using the BET theory. Comparative analysis shows that the new method well agrees with the conventional estimation of the degree of dispersion by the BET and Kutilek methods in a wide range of specific surface area values between 10 and 250 m2/g.

Application of a new bifunctionalized chitosan derivative with zwitterionic characteristics for the adsorption of Cu(2+), Co(2+), Ni(2+), and oxyanions of Cr(6+) from aqueous solutions: Kinetic and equilibrium aspects.

PubMed

de Almeida, Francine Tatiane Rezende; Ferreira, Bruno Christiano Silva; Moreira, Ana Luísa da Silva Lage; de Freitas, Rossimiriam Pereira; Gil, Laurent Frédéric; Gurgel, Leandro Vinícius Alves

2016-03-15

This study describes the synthesis of a new chitosan derivative (C2) with zwitterionic characteristics and its use for the removal of cationic species Cu(2+), Co(2+), and Ni(2+) and anionic species of Cr(6+) in a single aqueous solution. The new adsorbent was synthesized by quaternization of the amine group of chitosan and esterification of hydroxyl groups with EDTA dianhydride. These combined reactions gave both cationic and anionic characteristics to C2 with the release of quaternary ammonium groups and carboxylic groups. The capacity of C2 to adsorb Cu(2+), Co(2+), Ni(2+), and oxyanions of Cr(6+) was evaluated in a batch process with different contact times, pH values, and initial concentrations. Adsorption isotherms were best fitted to the Langmuir and Sips models. The maximum adsorption capacities (Q(max)) of C2 for adsorption of Cu(2+), Co(2+), Ni(2+), and Cr(6+) were 0.698, 1.125, 0.725, and 1.910 mmol/g, respectively. The Δ(ads)G° values were in the range from -20 to -28 kJ/mol. These values suggest a mixed mechanism controlling adsorption. Desorption studies using an aqueous solution consisting of 0.1 mol/L HNO3 were carried out. The reusability of the recovered C2 adsorbent after desorption was also evaluated. Copyright © 2015 Elsevier Inc. All rights reserved.

Characterization of Rhodamine Self-Assembled Films Using Desorption Electrospray Ionization Mass Spectrometry

NASA Astrophysics Data System (ADS)

Shi, Ruixia; Na, Na; Jiang, Fubin; Ouyang, Jin

2013-06-01

Growth process information and molecular structure identification are very important for characterization of self-assembled films. Here, we explore the possible application of desorption electrospray ionization mass spectrometry (DESI-MS) that provides the assembled information of rhodamine B (Rh B) and rhodamine 123 (Rh 123) films. With the help of lab-made DESI source, two characteristic ions [Rh B]+ and [Rh 123]+ are observed directly in the open environment. To evaluate the reliability of this technique, a comparative study of ultraviolet-visible (UV-vis) spectroscopy and our method is carried out, and the result shows good correlation. According to the signal intensity of characteristic ions, the layer-by-layer adsorption process of dyes can be monitored, and the thicknesses of multilayer films can also be comparatively determined. Combining the high sensitivity, selectivity, and speed of mass spectrometry, the selective adsorption of similar structure molecules under different pH is recognized easily from extracted ion chronograms. The variation trend of dyes signalling intensity with concentration of polyelectrolyte is studied as well, which reflects the effect of surface charge on dyes deposition. Additionally, the desorption area, surface morphology, and thicknesses of multilayer films are investigated using fluorescence microscope, scanning electron microscope (SEM), and atomic force microscopy (AFM), respectively. Because the desorption area was approximately as small as 2 mm2, the distribution situation of organic dyes in an arbitrary position could be gained rapidly, which means DESI-MS has advantages on in situ analysis.

Phosphorus recovery using pelletized adsorptive materials ...

EPA Pesticide Factsheets

Phosphorous (P) is one of the essential nutrients for growth and is generally the most limiting nutrient since, it cannot be fixed from the atmosphere. Methods for recovering phosphorous from water systems already exist, but advances are being made to find a more economic, efficient, effective and easy to use method that can allow for reuse of the recovered P. One area of study is in adsorption, which involves finding the best material for adsorption of phosphorous from water and for releasing it back into the environment through desorption or leaching. The goal of this research was to first optimize the capacity for a pelletized adsorptive material that was synthesized with varying amounts of a binder material from 0-20 % and then to study recovering the phosphate for reuse. The pelletized materials were studied through kinetics experiments as well as isotherm experiments to gain insight into the adsorption capacity and mechanism. Following successful adsorption, a simple leaching study was conducted to see how much phosphate would be released back into water without any added desorption aid. Desorption was then studied by changing the pH of solution. Presenting my thesis work with a poster at ACS.

First-principles investigation of CO adsorption on pristine, C-doped and N-vacancy defected hexagonal AlN nanosheets

NASA Astrophysics Data System (ADS)

Ouyang, Tianhong; Qian, Zhao; Ahuja, Rajeev; Liu, Xiangfa

2018-05-01

The optimized atomic structures, energetics and electronic structures of toxic gas CO adsorption systems on pristine, C-doped and N-vacancy defected h-AlN nanosheets respectively have been investigated using Density functional theory (DFT-D2 method) to explore their potential gas detection or sensing capabilities. It is found that both the C-doping and the N-vacancy defect improve the CO adsorption energies of AlN nanosheet (from pure -3.847 eV to -5.192 eV and -4.959 eV). The absolute value of the system band gap change induced by adsorption of CO can be scaled up to 2.558 eV or 1.296 eV after C-doping or N-vacancy design respectively, which is evidently larger than the value of 0.350 eV for pristine material and will benefit the robustness of electronic signals in potential gas detection. Charge transfer mechanisms between CO and the AlN nanosheet have been presented by the Bader charge and differential charge density analysis to explore the deep origin of the underlying electronic structure changes. This theoretical study is proposed to predict and understand the CO adsorption properties of the pristine and defected h-AlN nanosheets and would help to guide experimentalists to develop better AlN-based two-dimensional materials for efficient gas detection or sensing applications in the future.

On the Formation of Nanobubbles in Vycor Porous Glass during the Desorption of Halogenated Hydrocarbons

NASA Astrophysics Data System (ADS)

Mitropoulos, A. C.; Stefanopoulos, K. L.; Favvas, E. P.; Vansant, E.; Hankins, N. P.

2015-06-01

Vycor porous glass has long served as a model mesoporous material. During the physical adsorption of halogenated hydrocarbon vapours, such as dibromomethane, the adsorption isotherm exhibits an hysteresis loop; a gradual ascent is observed at higher pressures during adsorption, and a sharp drop is observed at lower pressures during desorption. For fully wetting fluids, an early hypothesis attributed the hysteresis to mechanistic differences between capillary condensation (adsorption) and evaporation (desorption) processes occurring in the wide bodies and narrow necks, respectively, of ‘ink-bottle’ pores. This was later recognized as oversimplified when the role of network percolation was included. For the first time, we present in-situ small angle x-ray scattering measurements on the hysteresis effect which indicate nanobubble formation during desorption, and support an extended picture of network percolation. The desorption pattern can indeed result from network percolation; but this can sometimes be initiated by a local cavitation process without pore blocking, which is preceded by the temporary, heterogeneous formation of nanobubbles involving a change in wetting states. The capacity of the system to sustain such metastable states is governed by the steepness of the desorption boundary.

On the Formation of Nanobubbles in Vycor Porous Glass during the Desorption of Halogenated Hydrocarbons

PubMed Central

Mitropoulos, A. C.; Stefanopoulos, K. L.; Favvas, E. P.; Vansant, E.; Hankins, N. P.

2015-01-01

Vycor porous glass has long served as a model mesoporous material. During the physical adsorption of halogenated hydrocarbon vapours, such as dibromomethane, the adsorption isotherm exhibits an hysteresis loop; a gradual ascent is observed at higher pressures during adsorption, and a sharp drop is observed at lower pressures during desorption. For fully wetting fluids, an early hypothesis attributed the hysteresis to mechanistic differences between capillary condensation (adsorption) and evaporation (desorption) processes occurring in the wide bodies and narrow necks, respectively, of ‘ink-bottle’ pores. This was later recognized as oversimplified when the role of network percolation was included. For the first time, we present in-situ small angle x-ray scattering measurements on the hysteresis effect which indicate nanobubble formation during desorption, and support an extended picture of network percolation. The desorption pattern can indeed result from network percolation; but this can sometimes be initiated by a local cavitation process without pore blocking, which is preceded by the temporary, heterogeneous formation of nanobubbles involving a change in wetting states. The capacity of the system to sustain such metastable states is governed by the steepness of the desorption boundary. PMID:26047466

On the Formation of Nanobubbles in Vycor Porous Glass during the Desorption of Halogenated Hydrocarbons.

PubMed

Mitropoulos, A C; Stefanopoulos, K L; Favvas, E P; Vansant, E; Hankins, N P

2015-06-05

Vycor porous glass has long served as a model mesoporous material. During the physical adsorption of halogenated hydrocarbon vapours, such as dibromomethane, the adsorption isotherm exhibits an hysteresis loop; a gradual ascent is observed at higher pressures during adsorption, and a sharp drop is observed at lower pressures during desorption. For fully wetting fluids, an early hypothesis attributed the hysteresis to mechanistic differences between capillary condensation (adsorption) and evaporation (desorption) processes occurring in the wide bodies and narrow necks, respectively, of 'ink-bottle' pores. This was later recognized as oversimplified when the role of network percolation was included. For the first time, we present in-situ small angle x-ray scattering measurements on the hysteresis effect which indicate nanobubble formation during desorption, and support an extended picture of network percolation. The desorption pattern can indeed result from network percolation; but this can sometimes be initiated by a local cavitation process without pore blocking, which is preceded by the temporary, heterogeneous formation of nanobubbles involving a change in wetting states. The capacity of the system to sustain such metastable states is governed by the steepness of the desorption boundary.

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.

Adsorption mechanism of 2,4-dichlorophenoxyacetic acid onto nitric-acid-modified activated carbon fiber.

PubMed

Li, Qun; Sun, Jie; Ren, Tianhao; Guo, Lin; Yang, Zhilin; Yang, Qi; Chen, Hai

2018-04-01

Adsorption by carbon materials is one of the relatively fast methods in present research, which is widely used in emergency events. Activated carbon fiber (ACF) modified by nitric acid (N-ACF) was studied in this research to determine the adsorption performance for 2,4-dichlorophenoxyacetic acid (2,4-D). Subsequently, influence factors, adsorption isotherm models, kinetics and thermodynamic were investigated in a batch system to realize this adsorption. Experimental results showed that ACF modified by 0.1M nitric acid had a better removal ability than 2,4-D. Removal rate of 2,4-D by N-ACF was greatly influenced by pH with the optimum pH at 2. The superiority of the Langmuir isotherm model in describing the adsorption equilibrium was revealed by correlation coefficients R2 (R 2  ≥ 0.997). Furthermore, adsorption kinetics was well described by pseudo-second-order model. The results of thermodynamic showed that adsorption was a spontaneous, endothermic process with randomness increasing. Additionally, surface structure properties of adsorbent were characterized by Scanning electron microscopy, Fourier transform infrared spectroscopy, Specific surface area analysis of Brunauer, Emmett and Teller and Boehm's titration. It turned out that the micropore structure and functional groups on N-ACF all can contribute to the removal of 2,4-D.