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Adsorption Mechanism (adsorption + mechanism)
Selected AbstractsEvidence for a Size-Selective Adsorption Mechanism on Oxide Surfaces: Pd and Au atoms on SiO2/Mo(112)CHEMPHYSCHEM, Issue 10 2008Stefan Ulrich Sieving single atoms: The binding of single metal atoms to thin SiO2 films grown on Mo(112) depends on the size of the adatom. While Pd atoms are able to pass the nanopores in the silica network (see figure) and strongly bind to the Mo,SiO2 interface, Au atoms are too big for a penetration and interact only with line defects in the oxide surface. [source] Experimental and theoretical study of recovery mechanism of impurity effect by the addition of EDTACRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2007Y. Asakuma Abstract The impurity effect by trivalent metal ion such as Al3+, Fe3+ and Cr3+ during crystal growth of KDP is reasonably well documented. If a metal ion is adsorbed onto the crystal surface, it prevents the step propagation relevant to the crystal growth rate. However, this impurity adsorption mechanism is still not well understood. Recently, in our work on the addition of chelate agents, a recovery effect of the metal ion adsorption was discovered. However, its recovery mechanism is not clearly understood both theoretically and phenomenally. In this research, ethylene-diamine-tetra-acetic acid, EDTA, which is the most common chelate agent, was used as a recovery agent. The recovery mechanism was considered from the correlation of experimental data and the interfacial distribution model that we proposed in our former study. Furthermore, quantum calculation of EDTA metal complex can explain the relaxation of impurity adsorption by the addition of EDTA. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theoretical framework for the distribution of trace metals among the operationally defined speciation phases of a sedimentENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2001René A. Nome Abstract The use of a model based on Langmuir's isotherm to evaluate the metal associated with separate geochemical phases of a sediment is proposed and its validity tested with sediments of certified composition. The model takes into account a standard procedure for a certified reference material (CRM601), which defines, experimentally, a set of sequential extractions that divide the sediment into four operational fractions. The derived equations allow the treatment of data from sediment of Flumendosa Lake, Italy, and certified material CRM601 and also allow the computation of corrected concentrations, i.e., the metal affinities for each fraction. Experimental values for Ni show its low sensitivity and an equal distribution among different phases, which suggests a similar adsorption mechanism in all cases. In the case of Cd, the corrected concentration in the Fe/Mn oxide phase is nine times higher than for the residual fraction. For sediment of the Bèsos River, Spain, results show the percentage distribution of Ni over different fractions. Affinity values for Ni on a Flumendosa Lake sediment have also been calculated. The present model is simple to apply and shows satisfactory agreement with experimental data. [source] First case of immune-mediated haemolytic anaemia associated to imatinib mesylateEUROPEAN JOURNAL OF HAEMATOLOGY, Issue 6 2003Marcia C. Zago Novaretti Abstract: Imatinib mesylate is a specific inhibitor of protein tyrosine kinase activity secondary to bcr-abl, mostly indicated for the treatment of patients with Philadelphia chromosome positive chronic myeloid leukaemia (CML). Generally, the undesirable effects of imatinib administration observed in clinical trials were of mild-to-moderate degree, and no haemolysis has been associated with this drug. We report here a case of immune-mediated haemolytic anaemia associated to imatinib mesylate successfully treated with prednisone in a patient with CML. Laboratory investigation showed anaemia [haemoglobin (Hb) of 59 g/L], reticulocyte of 61 × 109/L and a positive direct antiglobulin test. Anti-drug in vitro studies revealed a positive result with gel microcolumn assay by an adsorption mechanism. Seventy-four days after prednisone therapy, the patient's Hb level was of 110 g/L with negative direct antiglobulin test and drug in vitro studies. This case demonstrated that patients treated with imatinib mesylate can present immune-mediated haemolysis and adequate management of this event can be done maintaining the drug and associating corticosteroids. [source] Formation of 2,4,D complexes on montmorillonites , an ab initio molecular dynamics studyEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2007D. Tunega Summary Sorption of the anionic form of the pesticide 2,4,D (2,4,dichlorophenoxyacetic acid) on the surface of the clay mineral montmorillonite was investigated using a short-time ab initio molecular dynamics (MD) simulation at room temperature. Three different situations were modelled: sorption on a dry surface, on a hydrated surface and an intercalation between montmorillonite layers. In all three cases, the calcium cation compensates the excess negative charge of the montmorillonite layer and the negative charge of the 2,4,D anion. It was found that in all models with direct contact of the Ca2+ cation with the montmorillonite layer, the most stable position of Ca2+ is above the ditrigonal hole of the mineral layer. While in the case of a dry surface very stable bidentate binding is created between the 2,4,D anion and the Ca2+ cation, the formation of the monodentate complexes is preferred in all models that include water molecules. Hydrogen bonds formed between water molecules and the 2,4,D anion make a considerable contribution to the formation of the monodentate complexes. Tetrahedral substitutions in the montmorillonite layer have a significant effect on the formation of the complexes of any type. However, the MD simulations did not support the role of Ca2+ as a cation bridge in the adsorption mechanism. Calculations showed that hydrated 2,4,D···Ca2+ complexes are thermodynamically more stable than complexes in which the Ca2+ cation acts as a bridge to the surface. On the other hand, it is possible that phyllosilicates with a greater concentration of isomorphic substitutions (e.g. mica) will be able to form stable surface complexes with a cation bridge mechanism. [source] Synergistic effect of halide ions and polyethylene glycol on the corrosion inhibition of aluminium in alkaline mediumJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009S.A. Umoren Abstract The corrosion inhibition of aluminium in alkaline medium was studied at 30 and 40°C in the presence of polyethylene glycol (PEG) using gravimetric (weight loss) and thermometric techniques. The effect of halides (KCl, KBr, and KI) on the inhibitory action of PEG was also studied. It was found that PEG acted as inhibitor for aluminium corrosion in the alkaline medium. Inhibition efficiency increased with increasing inhibitor concentration. An increase in temperature led to increase in both the corrosion rate and inhibition efficiency in the absence and presence of inhibitor and halides. Phenomenon of chemical adsorption mechanism is proposed from the values of Ea, Qads, and ,G obtained. The adsorption of PEG on the surface of aluminium was found to obey Flory,Huggins and Temkin adsorption isotherms. The synergism parameter, S1 evaluated was found to be greater than unity indicating that the enhanced inhibition efficiency caused by the addition of halides is synergistic in nature. The inhibition efficiency, surface coverage and synergism parameter increased in the order; I,> Br,> Cl, showing that a joint adsorption of PEG and halide ions on aluminium plays a significant role in the adsorption process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] The removal of reactive azo dyes by natural and modified zeolitesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2003B Arma Abstract The adsorption mechanism of three reactive dyes by zeolite has been examined with the aim of identifying the ability of zeolite to remove textile dyes from aqueous solutions. Towards this aim, a series of batch adsorption experiments was carried out, along with determination of the electrokinetic properties of both natural and modified zeolites. The adsorbent in this study is a clinoptilolite from the Gördes region of Turkey. The reactive dyes CI Reactive Black 5, Red 239 and Yellow 176 are typical azo dyes extensively used in textile dyeing. Adsorption tests were carried out as a function of mixing time, solids concentration, dye concentration and pH. The adsorption results indicate that the natural zeolite has a limited adsorption capacity for reactive dyes but is substantially improved upon modifying its surfaces with quaternary amines. An electrostatic adsorption mechanism involving the formation of a bilayer of amine molecules on the clinoptilolite surface onto which anionic dye molecules adsorb, depending on their polarities, is proposed. The results are also supported by electrokinetic measurements. The adsorption data were fitted to the Langmuir isotherm and it was found that the modified sepiolite yields adsorption capacities (qe) of 111, 89 and 61 mg g,1 for Red, Yellow and Black, respectively. These results are comparable to a popular adsorbent, activated carbon. Copyright © 2003 Society of Chemical Industry [source] Effect of an aliphatic spacer group on the adsorption mechanism on the colloidal silver surface of L -proline phosphonodipeptidesJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2008Edyta Podstawka Abstract A comparative study of molecular structures of five L -proline (L -Pro) phosphonodipeptides: L -Pro-NH-C(Me,Me)-PO3H2 (P1), L -Pro-NH-C(Me,iPr)-PO3H2 (P2), L -Pro- L -NH-CH(iBu)-PO3H2 (P3), L -Pro- L -NH-CH(PA)-PO3H2 (P4) and L -Pro- L -NH-CH(BA)-PO3H2 (P5) has been carried out using Raman and absorption infrared techniques of molecular spectroscopy. The interpretation of the obtained spectra has been supported by density functional theory calculations (DFT) at the B3LYP; 6,31 + + G** level using Gaussian 2003 software. The surface-enhanced Raman scattering (SERS) on Ag-sol in aqueous solutions of these phosphonopeptides has also been investigated. The surface geometry of these molecules on a silver colloidal surface has been determined by observing the position and relative intensity changes of the Pro ring, amide, phosphonate and so-called spacer (,R) groups vibrations of the enhanced bands in their SERS spectra. Results show that P4 and P5 adsorb onto the silver as anionic molecules mainly via the amide bond (,1630, ,1533, ,1248, ,800 and ,565 cm,1), Pro ring (,956, ,907 and ,876 cm,1) and carboxylate group (,1395 and ,909 cm,1). Coadsorption of the imine nitrogen atom and PO group with the silver surface, possibly by formation of a weaker interaction with the metal, is also suggested by the enhancement of the bands at 1158 and 1248 cm,1. P1, P2 and P3 show two orientations of their main chain on the silver surface resulting from different interactions of the CCH3, NH and CONH fragments with this surface. Bonding to the Ag surface occurs mainly through the imino atom (1166 cm,1) for P2, while for P1 and P3 it occurs via the methyl group(s) (1194,1208 cm,1). The amide group functionality (CONH) is practically not involved in the adsorption process for P1 and P2, whereas the CsP bonds do assist in the adsorption. Copyright © 2008 John Wiley & Sons, Ltd. [source] Surface-enhanced Raman scattering study of the adsorption of the anthraquinone pigment alizarin on Ag nanoparticlesJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2004M. V. Cañamares Abstract FT-Raman and surface-enhanced Raman scattering (SERS) spectroscopy were applied in the vibrational characterization and study of the adsorption and acidity behavior of the highly fluorescent anthraquinone dye alizarin on Ag colloids prepared by chemical reduction with hydroxylamine hydrochloride. The SERS spectra were obtained at different conditions of pH, excitation wavelength and pigment concentration in order to deduce the adsorption mechanism of this molecule. On the basis of the results found we propose an adsorption model for alizarin, which has a different acidic behavior on the metal surface to that in solution. On the metal the deprotonation order of the OH groups changes with respect to the aqueous solution, the OH in position 1 being the first to be ionized instead of that in position 2 as occurs in solution. The two main alizarin forms identified on the metal surface correspond to the mono- and dianionic alizarin species. Copyright © 2004 John Wiley & Sons, Ltd. [source] Adsorption interaction parameter of polyethers in ternary mobile phases: The critical adsorption lineJOURNAL OF SEPARATION SCIENCE, JSS, Issue 8 2010Nguyen V. Cuong Abstract It is shown that in LC of polymers, the interaction parameter in ternary mobile phases can be described by a plane, which is determined by the dependencies in binary mobile phases. Instead of a critical adsorption point, critical conditions are observed along a straight line of composition between the two critical points in binary mobile phases. Consequently, a separation of block copolymers under critical conditions for one block by an adsorption mechanism for the other block can be achieved in ternary mobile phases of different compositions, which allows an adjustment of the retention of the adsorbing block. [source] Brief analysis of the retention process in RP-HPLC systems with a C30 bonded stationary phaseJOURNAL OF SEPARATION SCIENCE, JSS, Issue 13 2008Wojciech Zapa Abstract The influence of the mobile-phase composition on the retention of eight model substances in different RP-HPLC systems with a C30 alkyl bonded stationary phase has been studied. The aim of this study was to compare the performance of four valuable retention models assuming the partition and adsorption mechanism of retention. All the models were verified for different experimental data by four criteria: the sum of squared differences between the experimental and theoretical data; the approximation of the standard deviation; the Fisher test; and the F-test ratio. [source] An experimental model for cold water generation based on eco-friendly refrigeration systemTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009G. N. Halder Abstract A laboratory model refrigeration system based on indigenously developed activated carbon,carbon dioxide pair using pressure swing adsorption mechanism is developed for substituting chlorofluorocarbons from conventional refrigeration systems. The model has successfully produced chilled water at 4°C (277,K) from ambient water available at 26°C (299,K). The paper describes the design and description of the above refrigeration system model and details of the experimental result. Un système de réfrigération de modèle de laboratoire, fondé sur le couple charbon actif/dioxyde de carbone produit sur place, créé au moyen d'un mécanisme d'adsorption modulée en pression a été conçu afin de remplacer les chlorurofluorurocarbones dans les systèmes de réfrigération classiques. Le modèle a permis d'obtenir de l'eau refroidie à 4°C (277,K) à partir d'eau à une température ambiante de 26°C (299,K). Le document décrit la conception et la description du modèle de système de réfrigération ci-dessus ainsi que les détails du résultat expérimental. [source] Liquid-Phase Hydrogenation of Unsaturated Aldehydes: Enhancing Selectivity of Multiwalled Carbon Nanotube-Supported Catalysts by Thermal ActivationCHEMCATCHEM, Issue 2 2010Bruno Abstract Platinum and iridium organometallic precursors are used to prepare nanosized, thermally stable multiwalled carbon nanotube-supported catalysts. The materials are characterized by N2 adsorption at 77,K, temperature-programmed desorption coupled with mass spectrometry, H2 chemisorption, transmission electron microscopy and thermogravimetric analysis; they are tested in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol under mild conditions (363,K and 1,MPa). A thermal activation at 973,K is found to have a very positive effect over both activity and selectivity, leading to selectivities of approximately 70,%, at 50,% conversion, regardless of the active metal phase (Pt or Ir). Since no noticeable differences in the metal particle sizes are detected, the results are interpreted in light of an enhanced metal/support interaction. This effect, induced by the removal of oxygenated surface groups, is thought to change the adsorption mechanism of the cinnamaldehyde molecule. [source] Rapid and Effective Adsorption of Lead Ions on Fine Poly(phenylenediamine) MicroparticlesCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2006Mei-Rong Huang Prof. Abstract Fine microparticles of poly(p -phenylenediamine) (PpPD) and poly(m -phenylenediamine) (PmPD) were directly synthesized by a facile oxidative precipitation polymerization and their strong ability to adsorb lead ions from aqueous solution was examined. It was found that the degree of adsorption of the lead ions depends on the pH, concentration, and temperature of the lead ion solution, as well as the contact time and microparticle dose. The adsorption data fit the Langmuir isotherm and the process obeyed pseudo-second-order kinetics. According to the Langmuir equation, the maximum adsorption capacities of lead ions onto PpPD and PmPD microparticles at 30,°C are 253.2 and 242.7 mg,g,1, respectively. The highest adsorptivity of lead ions is up to 99.8,%. The adsorption is very rapid with a loading half-time of only 2 min as well as initial adsorption rates of 95.24 and 83.06 mg,g,1 min,1 on PpPD and PmPD particles, respectively. A series of batch experiment results showed that the PpPD microparticles possess an even stronger capability to adsorb lead ions than the PmPD microparticles, but the PmPD microparticles, with a more-quinoid-like structure, show a stronger dependence of lead-ion adsorption on the pH and temperature of the lead-ion solution. A possible adsorption mechanism through complexation between Pb2+ ions and N groups on the macromolecular chains has been proposed. The powerful lead-ion adsorption on the microparticles makes them promising adsorbents for wastewater cleanup. [source] Dynamic Surface Tensions of Fluorous Surfactant SolutionsCHINESE JOURNAL OF CHEMISTRY, Issue 4 2005Gao Yan-An Abstract Dynamic surface properties of aqueous solutions of cationic fluorous surfactant CF3CF2CF2O(CF(CF3)CF2O)2CF(CF3)CONH(CH2)3N+(C2H5)2CH3I - (abbrev. FC-4 ) were reported. The critical micelle concentration (cmc) (3.6×10 -5 mol/L) and equilibrium surface tensions ,eq were measured by Krüss K12 tension apparatus. Dynamic surface tension ,(t) was measured in the range of 15 ms to 200 s using the MBP tensiometer. The surface excess ,, as a function of concentration, was obtained from equilibrium tensiometry using the Gibbs equation. Data from these experiments were combined to analyze the ,(t) decays according to the asymptotic Ward and Tordai equation. The results show that at the initial adsorption stage, the dynamic surface tension data were all consistent with this diffusion-controlled mechanism, and at the end of the adsorption process, there were some evidences for an adsorption barrier, suggesting a mixed diffusion-controlled adsorption mechanism. Using measured quantities, the barrier strength was estimated as between 25 and 35 kJ/mol at 25 °C. The surface pressure plays an important role in contributing to the barrier. [source] Surface-enhanced resonance Raman spectroscopy of rifamycins on silver nanoparticles: insight into their adsorption mechanismsJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2006Barry D. Howes Abstract Three widely used antibiotics from the rifamycin family, rifamycin SV sodium salt, rifampicin and rifaximin, have been characterized by resonance Raman (RR) and surface-enhanced resonance Raman spectroscopy (SERRS). SERRS spectra were recorded using aqueous silver colloidal dispersions prepared with two reducing agents, sodium borohydride and hydroxylamine hydrochloride, for a range of pH values to identify the SERRS-active substrate surface most suitable for each of the three antibiotics. Rifampicin was found to give intense SERRS signals only for the borohydride-reduced colloid and only at pH < 7.7, whereas the hydroxylamine HCl-reduced colloid was the best substrate for rifaximin, giving considerably more intense SERRS spectra than the borohydride colloid. SERRS spectra of rifaximin were observed only at pH < 7.0. It is proposed that the marked pH dependence of the SERRS enhancement results from a transition from an anionic to a neutral zwitterionic state. SERRS spectra of rifamycin SV were not observed for any experimental conditions. The antibiotics display remarkably contrasting SERRS behaviour, reflecting differences in the nature of the substituent groups on the chromophore ring. A vibrational assignment of the RR spectra and detailed comparison between the RR and SERRS data have given insight into the mechanism of adsorption of the antibiotics onto the Ag surface. Rifampicin and rifaximin adsorb adopting an approximately similar vertical orientation of the chromophore ring with respect to the surface; however, rifampicin adsorbs by direct chemical interaction with the Ag whereas rifaximin does not form a direct bond with the Ag surface. Copyright © 2006 John Wiley & Sons, Ltd. [source] Kinetics and mechanism of Cr(VI) adsorption onto tea-leaves wasteASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2008Md. Salatul Islam Mozumder Abstract Adsorption equilibrium and kinetic experiments have been conducted in batch mode to evaluate Cr(VI)-tea-leaves waste system. The equilibrium data followed the Langmuir adsorption isotherm and the adsorption was viewed as a physicochemical reversible process. A unified approach model was used to describe the adsorption system from both equilibrium and kinetic viewpoints. The model satisfactorily described both kinetic and equilibrium data. The adsorption and desorption rate constants were evaluated from the model fittings and were not dependent on initial concentration and adsorbent doses. pHzpc of the adsorbent was evaluated as 4.2 ± 0.1, and below that pH the adsorbent surface is positively charged. Adsorption of Cr(VI) was found highly pH-dependent, and the removal efficiency dropped sharply from 95 to 10% when pH of the system changed from 2 to 5. The surface functional groups of tea-leaves waste (before and after adsorption) were analyzed by Fourier transform infrared (FTIR) and the amine groups were found to take part in the adsorption of Cr(VI). The experimental result inferred that electrostatic attraction between the surface and the species is one of the major adsorption mechanisms for binding metal ions to the tea-leaves waste. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Studies of lysozyme binding to histamine as a ligand for hydrophobic charge induction chromatographyBIOTECHNOLOGY PROGRESS, Issue 1 2010Qing-Hong Shi Abstract Histamine was immobilized on Sepharose CL-6B (Sepharose) for use as a ligand of hydrophobic charge induction chromatography (HCIC) of proteins. Lysozyme adsorption onto Histamine-Sepharose (HA-S) was studied by adsorption equilibrium and calorimetry to uncover the thermodynamic mechanism of the protein binding. In both the experiments, the influence of salt (ammonium sulfate and sodium sulfate) was examined. Adsorption isotherms showed that HA-S exhibited a high salt tolerance in lysozyme adsorption. This property was well explained by the combined contributions of hydrophobic interaction and aromatic stacking. The isotherms were well fitted to the Langmuir equation, and the equilibrium parameters for lysozyme adsorption were obtained. In addition, thermodynamic parameters (,Hads, ,Sads, and ,Gads) for the adsorption were obtained by isothermal titration calorimetry by titrating lysozyme solutions into the adsorbent suspension. Furthermore, free histamine was titrated into lysozyme solution in the same salt-buffers. Compared with the binding of lysozyme to free histamine, lysozyme adsorption onto HA-S was characterized by a less favorable ,Gads and an unfavorable ,Sads because histamine was covalently attached to Sepharose via a three-carbon-chain spacer. Consequently, the immobilized histamine could only associate with the residues on the protein surface rather than those in the hydrophobic pocket, causing a less favorable orientation between histamine and lysozyme. Further comparison of thermodynamic parameters indicated that the unfavorable ,Sads was offset by a favorable ,Hads, thus exhibiting typical enthalpy-entropy compensation. Moreover, thermodynamic analyses indicated the importance of the dehydration of lysozyme molecule and HA-S during the adsorption and a substantial conformational change of the protein during adsorption. The results have provided clear insights into the adsorption mechanisms of lysozyme onto the new HCIC material. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] | ||||||||||||||||||||||||||||