Home OALib Journal OALib PrePrints Submit Ranking News My Lib FAQ About Us Follow Us+
 Title Keywords Abstract Author All
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
 Page 1 /100 Display every page 5 10 20 Item
 Physics , 2008, Abstract: In this work we have analyzed the adsorption-desorption kinetics in the framework of the lattice gas model. We have shown that the coefficients representing the transition probabilities must be carefully chosen even when they fulfill the principle of detailed balance, otherwise the observables arising from the kinetics present anomalous behavior. We have demonstrated that when the adsorption $A_i$ and desorption $D_i$ coefficients are linearly related through a parameter $\gamma$, there are values of lateral interaction, $V$, that lead to bad behavior in the kinetics. We have shown a phase diagram for the allowed values of $V$ and $\gamma$, concluding that detailed balance does not guarantee a correct physical behavior of the observables obtained from the rate equations like adsorption isotherms, sticking coefficients and thermal desorption spectra. Alternatively, we have introduced a description of the adsorption-desorption processes based in a simple but consistent energetic argument that leads to a correct behavior of the observables without physical inconsistencies.
 环境科学学报 , 2012, Abstract: In order to investigate the effect of freezing-thawing on the adsorption-desorption of cadmium,kinetics adsorption isotherms of soil contained with cadmium and the quantity, ratio and speed of adsorption-desorption under freezing-thawing conditions were carried out. The results showed that freezing-thawing promoted cadmium adsorption of the soil. The quantity, ratio and speed of cadmium adsorption increased with the increase of freezing-thawing frequency. Freezing-thawing retarded soil cadmium desorption. With the increasing freezing-thawing cycles, the speed and ratio of soil cadmium desorption decreased and the decrement of the soil cadmium desorption speed increased.
 Physics , 2004, Abstract: A lattice gas model is used to study the equilibrium properties and desorption kinetics of CO on Ru(0001). With interactions obtained from density functional theory (DFT) the phase diagram and temperature programmed desorption (TPD) spectra are calculated up to a coverage of 1/3 ML using top sites only. For coverages beyond 1/3 ML hollow sites are included. Good agreement is obtained between experiment and theory for coverages below 1/3 ML using top sites only. When including hollow sites, DFT calculations fail in predicting the correct binding energy differences between top and hollow sites giving disagreement with TPD, low energy electron diffraction (LEED) and heat of adsorption experiments.
 Journal of Applied Sciences , 2010, Abstract: The adsorption characteristics of basic dye (methylene blue, MB) on activated carbon prepared from oil palm Empty Fruit Bunch (EFB) were evaluated. The effects of dye initial concentration, agitation time, solution pH and temperature on MB adsorption were investigated. The adsorption uptake was found to increase with increase in initial concentration, agitation time and solution temperature. The adsorption equilibrium data were best represented by the Langmuir isotherm. The adsorption kinetics was found to follow the pseudo-second-order kinetic model. The mechanism of the adsorption process was determined from the intraparticle diffusion model. Boyd plot revealed that the adsorption of MB on the activated carbon was mainly governed by external mass transport where particle diffusion was the rate limiting step Thermodynamic parameters such as standard enthalpy (ΔH°), standard entropy (ΔS°), standard free energy (ΔG°) and activation energy were determined. The regeneration efficiency of the spent activated carbon was acceptably high, with MB desorption of 71%.
 Physics , 2015, DOI: 10.1021/ma501454t Abstract: A method is formulated, based on combining self-consistent field theory with dynamically corrected transition state theory, for estimating the rates of adsorption and desorption of end-constrained chains (e.g. by crosslinks or entanglements) from a polymer melt onto a solid substrate. This approach is tested on a polyethylene/graphite system, where the whole methodology is parametrized by atomistically detailed molecular simulations. For short-chain melts, which can still be addressed by molecular dynamics simulations with reasonable computational resources, the self-consistent field approach gives predictions of the adsorption and desorption rate constants which are gratifyingly close to molecular dynamics estimates.
 Chinese Science Bulletin , 2008, DOI: 10.1007/s11434-007-0489-1 Abstract: Acetone plays an important role in photooxidation processes in the atmosphere. Up to date, little is known regarding the heterogeneous fate of acetone. In this study, the adsorption and desorption processes of acetone on SiO2 particles, which are the major constituent of mineral dust in the atmosphere, have been investigated for the first time under the simulated atmospheric conditions, using in situ transmission Fourier transform infrared spectroscopy. It is found that acetone molecules are adsorbed on the surfaces of SiO2 particles by van der Waals forces and hydrogen bonding forces in a nonreactive and reversible state. The rates of initial adsorption and initial desorption, initial uptake coefficients and adsorption concentrations at equilibrium have been determined at different relative humidity. The presence of water vapor cannot result in the formation of new substances, but can decrease the adsorption ability by consuming or overlapping the isolated OH groups on the surfaces of SiO2 particles. In the desorption process, a considerable amount of acetone molecules will remain on SiO2 particles in dry air, whereas acetone molecules are almost completely desorbed at a high relative humidity. In order to evaluate the role of heterogeneous reactions of acetone and other carbonyl compounds in the atmosphere, a new model fitting the atmospheric conditions is needed.
 科学通报(英文版) , 2008, Abstract: Acetone plays an important role in photooxidation processes in the atmosphere. Up to date, little is known regarding the heterogeneous fate of acetone. In this study, the adsorption and desorption processes of acetone on SiO2 particles, which are the major constituent of mineral dust in the atmosphere, have been investigated for the first time under the simulated atmospheric conditions, using in situ transmission Fourier transform infrared spectroscopy. It is found that acetone molecules are adsorbed on the surfaces of SiO2 particles by van der Waals forces and hydrogen bonding forces in a nonreactive and reversible state. The rates of initial adsorption and initial desorption, initial uptake coefficients and adsorption concentrations at equilibrium have been determined at different relative humidity. The presence of water vapor cannot result in the formation of new substances, but can decrease the adsorption ability by consuming or overlapping the isolated OH groups on the surfaces of SiO2 particles. In the desorption process, a considerable amount of acetone molecules will remain on SiO2 particles in dry air, whereas acetone molecules are almost completely desorbed at a high relative humidity. In order to evaluate the role of heterogeneous reactions of acetone and other carbonyl compounds in the atmosphere, a new model fitting the atmospheric conditions is needed. Supported by the National Natural Science Foundation of China (Grant Nos. 20677002 and 20107001) and the Project of Development Plan of the State Key Fundamental Research (Grant No. 2002CB410802)
 Journal of Engineering and Applied Sciences , 2011, Abstract: The study describes the results of batch experiments on removal of reactive orange16 from aqueous solution onto activated carbon prepared from Ananas Comosus leaves. The adsorbent has been studied as a function of contact time, temperature, pH and initial dye concentration by batch experiments. pH 2-3 was found suitable for maximum removal of RO16. A dye adsorption capacity of activated carbon for the RO16 is 147.05 mg/g adsorbent. Langmuir, Freundlich, Tempkin, Dubinin-Raduskevich isotherm models were applied for the analysis of isotherm data. Thermodynamic treatment of adsorption data showed an exothermic nature of adsorption. The dye uptake process was found to follow second order kinetics.
 Physics , 2012, DOI: 10.1103/PhysRevE.86.036316 Abstract: We use a stochastic approach to show how Taylor dispersion is affected by kinetic processes of adsorption and desorption onto surfaces. A general theory is developed, from which we derive explicitly the dispersion coefficients of canonical examples like Poiseuille flows in planar and cylindrical geometries, both in constant and sinusoidal velocity fields. These results open the way for the measurement of adsorption and desorption rate constants using stationary flows and molecular sorting using the stochastic resonance of the adsorption and desorption processes with the oscillatory velocity field.
 Physics , 1999, DOI: 10.1063/1.480715 Abstract: Many experimental studies of protein deposition on solid surfaces involve alternating adsorption/desorption steps. In this paper, we investigate the effect of a desorption step (separating two adsorption steps) on the kinetics, the adsorbed-layer structure, and the saturation density. Our theoretical approach involves a density expansion of the pair distribution function and an application of an interpolation formula to estimate the saturation density as a function of the density at which the desorption process commences, $\rho_1$, and the density of the depleted configuration, $\rho_2$. The theory predicts an enhancement of the saturation density compared with that of a simple, uninterrupted RSA process and a maximum in the saturation density when $\rho_2={2/3}\rho_1$. The theoretical results are in qualitative and in semi-quantitative agreement with the results of numerical simulations.
 Page 1 /100 Display every page 5 10 20 Item

 Home Copyright © 2008-2017 Open Access Library. All rights reserved.