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Adsorption Isotherms (adsorption + isotherm)
Kinds of Adsorption Isotherms Selected AbstractsMolecular Mechanism of the Hydration of Candida antarctica Lipase B in the Gas Phase: Water Adsorption Isotherms and Molecular Dynamics SimulationsCHEMBIOCHEM, Issue 18 2009Ricardo J. F. Branco Dr. Abstract Hydration is a major determinant of activity and selectivity of enzymes in organic solvents or in gas phase. The molecular mechanism of the hydration of Candida antarctica lipase B (CALB) and its dependence on the thermodynamic activity of water (aw) was studied by molecular dynamics simulations and compared to experimentally determined water sorption isotherms. Hydration occurred in two phases. At low water activity, single water molecules bound to specific water binding sites at the protein surface. As the water activity increased, water networks gradually developed. The number of protein-bound water molecules increased linearly with aw, until at aw=0.5 a spanning water network was formed consisting of 311 water molecules, which covered the hydrophilic surface of CALB, with the exception of the hydrophobic substrate-binding site. At higher water activity, the thickness of the hydration shell increased up to 10 Å close to aw=1. Above a limit of 1600 protein-bound water molecules the hydration shell becomes unstable and the formation of pure water droplets occurs in these oversaturated simulation conditions. While the structure and the overall flexibility of CALB was independent of the hydration state, the flexibility of individual loops was sensitive to hydration: some loops, such as those part of the substrate-binding site, became more flexible, while other parts of the protein became more rigid upon hydration. However, the molecular mechanism of how flexibility is related to activity and selectivity is still elusive. [source] Ni2+ removal from aqueous solutions using conditioned clinoptilolites: Kinetic and isotherm studiesENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 1 2009Semra Çoruh Abstract The aim of this study is to investigate the effects of conditioning with NaCl and HCl solutions on removal of Ni2+ ions from aqueous solutions using natural clinoptilolite. Batch studies were performed to evaluate the effects of various parameters such as chemically conditioning, adsorbent amount, contact time, initial pH of the solution, mixing temperature, and initial metal ions. The results clearly showed that the conditioning improved both the exchange capacity and the removal efficiency. Langmuir, Freundlich, Temkin, and Dubinin-Kaganer-Radushkevich (DKR) isotherm models were adopted to describe the adsorption isotherms. Adsorption isotherms of Ni2+ ions could be best modeled by Langmuir equation. Three simplified models including pseudo-second-order, intraparticle diffusion and Elovich were used to test the adsorption kinetics. These results indicate a significant potential for the natural and conditioned clinoptilolites as an adsorbent/ion-exchange material for heavy metal removal. © 2008 American Institute of Chemical Engineers Environ Prog, 2009 [source] Capacity of activated carbon derived from pistachio shells by H3PO4 in the removal of dyes and phenolicsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2003Amina A Attia Abstract Two activated carbons were obtained from pistachio shells by impregnation with H3PO4 under standard conditions of acid concentration (50 wt%) and heat treatment at 773 K for 2 h. The soaking time was 24 and 72 h for the two samples before thermal pyrolysis. Analysis of the N2/77 K adsorption isotherms proved that both were highly adsorbing carbons with considerable microporosity, and that the prolonged contact with activant enhanced total porosity (surface area and pore volume) and increased the amount of mesoporosity. Adsorption isotherms of probe molecules, viz methylene blue (MB), rhodamine B (RB), phenol (P) and p -nitrophenol (PNP), were determined at room temperature, from aqueous solutions. Both the Langmuir and Freundlich model adsorption equations show satisfactory fit to experimental data. Both carbons exhibit similar adsorption parameters irrespective of their porosity characteristics. The sequence of uptake per unit weight was: PNP > MB > RB > P. Low affinity towards phenol may be associated with its competition with water molecules which are more favourably attracted to the acid surface which has a high oxygen functionality. Preferred adsorption in the order PNP > MB > RB is proposed to be a function of carbon porosity, related to the increased molecular dimensions of the solutes. Adsorption from a binary mixture of equal concentrations of MB and RB showed reduced uptake for both sorbates in comparison to the single component experiments. RB removal surpasses that of MB in the binary test and may be attributed to lower water solubility and higher molecular dimensions. Copyright © 2003 Society of Chemical Industry [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] Adsorption of Cadmium Ion and Gallium Ion to Immobilized Metallothionein Fusion ProteinBIOTECHNOLOGY PROGRESS, Issue 6 2002Masaaki Terashima A fusion protein made from maltose binding protein (pmal) and human metallothionein (MT) was expressed using E. coli. The purified recombinant protein (pmal-MT) was immobilized on Chitopearl resin, and characteristics of pmal-MT for metal binding were evaluated. As expected from the tertiary structure of metallothionein, the pmal-MT ligand adsorbed 12.1 cadmium molecules per one molecule of the ligand at pH 5.2. The pmal-MT ligand also bound 26.6 gallium molecules per one molecule of the ligand at pH 6.5. Neither cadmium ion nor gallium ion bound to a control protein bovine serum albumin (BSA). Adsorption isotherms for both ions were correlated by Langmuir-type equations. Two types of binding sites have been elucidated on the basis of HSAB (hard and soft acid and base) theory. It was suggested that gallium ion specifically binds to amino acid residues containing oxygen and nitrogen atoms, while cadmium ion binds to specific binding sites formed by multiple cysteine residues. The pmal-MT ligand bound these metals in the concentration range of 0.2,1.0 mM, and the bound metal ions could be eluted under relatively mild conditions (pH 2.0). The pmal-MT Chitopearl resin was stable and could be used repeatedly without loss of binding activity. Thus, this new ligand would be useful for recovery of toxic heavy metals and/or valuable metal ions from various aqueous solutions. [source] ChemInform Abstract: Prussian Blue Analogues for CO2 and SO2 Capture and Separation Applications.CHEMINFORM, Issue 33 2010Praveen K. Thallapally Abstract Adsorption isotherms of pure gases present in flue gas including CO2, N2, SO2, NO, H2S, and H2O are measured for M3[Co(CN)6]2·nH2O (M: Co, Zn). [source] Hydrogen Adsorption and Diffusion in p - tert -Butylcalix[4]arene: An Experimental and Molecular Simulation StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 38 2010Dr. Saman Alavi Abstract Experimental adsorption isotherms were measured and computer simulations were performed to determine the nature of the H2 gas uptake in the low-density p - tert -butylcalix[4]arene (tBC) phase. 1H,NMR peak intensity measurements for pressures up to 175,bar were used to determine the H2 adsorption isotherm. Weak surface adsorption (up to ,2,mass,% H2) and stronger adsorption (not exceeding 0.25,mass,% or one H2 per calixarene bowl) inside the calixarene phase were detected. The latter type of adsorbed H2 molecule has restricted motion and shows a reversible gas adsorption/desorption cycle. Pulsed field gradient (PFG) NMR pressurization/depressurization measurements were performed to study the diffusion of H2 in the calixarene phases. Direct adsorption isotherms by exposure of the calixarene phase to pressures of H2 gas to ,60,bar are also presented, and show a maximum H2 adsorption of 0.4,H2 per calixarene bowl. Adsorption isotherms of H2 in bulk tBC have been simulated using grand canonical Monte Carlo calculations in a rigid tBC framework, and yield adsorptions of ,1,H2 per calixarene bowl at saturation. Classical molecular dynamics simulations with a fully flexible calixarene molecular force field are used to determine the guest distribution and inclusion energy of the H2 in the solid with different loadings. [source] Adsorption behaviour of azo disperse dyes on polyurethane fibreCOLORATION TECHNOLOGY, Issue 3 2009Hong-Fei Qian Adsorption isotherms of disperse dyes were measured and the surfaces of dyed polyurethane, cellulose diacetate and polylactic acid fibres were observed using a scanning electron microscope and compared. Obvious crystal growth of the dyes occurred on the surface of the polyurethane fibres. The maximum dye uptake on polyurethane fibres and the degree of crystal growth varied greatly with the dye type. Factors such as the dye affinity for the fibre, crystallisation properties and dye solubility in the dyebath affect the sorbed state of the dye on the fibre surface. A mechanism is proposed for crystal formation on the fibre surface during dyeing of polyurethane fibre with disperse dyes. [source] Improved methods for carbon adsorption studies for water and wastewater treatmentENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 2 2006Wei-chi Ying Abstract An improved method was developed to rank activated carbon in removing organic water pollutants. The simple and standardized evaluation method uses a set of four adsorptive capacity indicators: phenol, iodine, methylene blue, and tannic acid numbers; those four indicator compounds were selected because they cover the molecular size range of most organic water pollutants. An improved microcolumn rapid breakthrough (MCRB) test method was developed from the existing HPMC (high-pressure minicolumn) and RSSCT (rapid small-scale column test) methods by simplifying the experimental procedure and using readily available low-cost pump, sampler, piping, and fittings. This method can be practiced in an ordinary environmental laboratory to select the best carbon, to verify the treatment effectiveness, and to estimate the adsorption treatment cost based on the observed capacity utilization rate for carbon in the adsorber without the problems often encountered with using small and mini traditional columns. The benefits of the four-parameter carbon selection method and the MCRB method were demonstrated by adsorption isotherm and breakthrough data for several indicator compounds and organic water pollutants. These improved methods will enable efficient carbon adsorption studies necessary for more applications of carbon adsorption technology in water and wastewater treatment. © 2006 American Institute of Chemical Engineers Environ Prog, 2006 [source] Parametric study on the silica gel,calcium chloride composite desiccant rotary wheel employing fractal BET adsorption isothermINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2005X. J. Zhang Abstract In this paper a family of new silica gel,calcium chloride composite adsorbents is presented for desiccant rotary wheel in dehumidification system. For these desiccants the water sorption equilibrium has been measured in a wide relative vapour pressure range. This experimental study shows that the vapour adsorption properties of the composites using calcium chloride as impregnated salt can be controllably modified by varying the amount of the salt inside the pores. The thermodynamic performance of such desiccant rotary wheel is analysed based on the adsorption equilibrium equations obtained through nonlinear regressions using fractal BET theory. The simulation results show that the new composite desiccants can be effectively used in a rotary wheel dehumidifier and to improve its performance, various optimum operational/system parameters have been identified. Copyright © 2005 John Wiley & Sons, Ltd. [source] Theoretical studies of some sulphonamides as corrosion inhibitors for mild steel in acidic mediumINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 14 2010Eno E. Ebenso Abstract Density functional theory (DFT) at the B3LYP/6-31G (d,p) and BP86/CEP-31G* basis set levels and ab initio calculations using the RHF/6-31G (d,p) methods were performed on four sulfonamides (namely sulfaacetamide (SAM), sulfapyridine (SPY), sulfamerazine (SMR), and sulfathiazole (STI)) used as corrosion inhibitors for mild steel in acidic medium to determine the relationship between molecular structure and their inhibition efficiencies (%IE). The order of inhibition efficiency obtained was SMR > SPY > STI > SAM which corresponded with the order of most of the calculated quantum chemical parameters namely EHOMO (highest occupied molecular orbital energy), ELUMO (lowest unoccupied molecular orbital energy), the energy gap (,E), the Mulliken charges on the C, O, N, S atoms, hardness (,), softness (S), polarizability (,), dipole moment (,), total energy change (,ET), electrophilicity (,), electron affinity (A), ionization potential (I), the absolute electronegativity (,), and the fraction of electrons transferred (,N). Quantitative structure activity relationship (QSAR) approach has been used and a correlation of the composite index of some of the quantum chemical parameters was performed to characterize the inhibition performance of the sulfonamides studied. The results showed that the %IE of the sulfonamides was closely related to some of the quantum chemical parameters but with varying degrees/order. The calculated %IE of the sulfonamides studied was found to be close to their experimental corrosion inhibition efficiencies. The experimental data obtained fits the Langmuir adsorption isotherm. The negative sign of the EHOMO values and other thermodynamic parameters obtained indicates that the data obtained supports physical adsorption mechanism. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Polyethylene glycol and polyvinyl alcohol as corrosion inhibitors for aluminium in acidic mediumJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007S. A. Umoren Abstract The corrosion inhibition of aluminum in H2SO4 in the presence of polyethylene glycol (PEG) and polyvinyl alcohol (PVA) as inhibitors at 30,60 °C was studied using gravimetric, gasometric, and thermometric techniques. The inhibition efficiency (%I) increased with increase in concentration of the inhibitors. Increase in temperature increased the corrosion rate in the absence and presence of inhibitors but decreased the inhibition efficiency. Both PEG and PVA were found to obey Temkin adsorption isotherm at all concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameters obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. PEG was found to be a better inhibitor than PVA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Sorption of copper by a highly mineralized peat in batch and packed-bed systemsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2010Marta Izquierdo Abstract BACKGROUND: The performance of peat for copper sorption was investigated in batch and fixed-bed experiments. The effect of pH was evaluated in batch experiments and the experimental data were fitted to an equilibrium model including pH dependence. Hydrodynamic axial dispersion was estimated by tracing experiments using LiCl as a tracer. Six fixed-bed experiments were carried out at copper concentrations between 1 and 60 mg dm,3 and the adsorption isotherm in dynamic mode was obtained. A mass transport model including convection,dispersion and sorption processes was applied for breakthrough curve modelling. RESULTS: Maximum uptake capacities in batch mode were 22.0, 36.4, and 43.7 mg g,1 for pH values of 4.0, 5.0, and 6.0, respectively. Uptake capacities in continuous flow systems varied from 36.5 to 43.4 mg g,1 for copper concentrations between 1 and 60 mg dm,3. Dynamic and batch isotherms showed different shapes but a similar maximum uptake capacity. Sorbent regeneration was successfully performed with HCl. A potential relationship between dispersion coefficient and velocity was obtained with dispersion coefficients between 5.00 × 10,8 and 2.95 × 10,6 m2 s,1 for water velocities ranging between 0.56 × 10,4 and 5.03 × 10,4 m s,1. The mass transport model predicted both the breakpoints and the shape of the breakthrough curves. CONCLUSIONS: High retention capacities indicate that peat can be used as an effective sorbent for the treatment of wastewater containing copper ions. Copyright © 2009 Society of Chemical Industry [source] Effect of adsorption characteristics of a modified cellulase on indigo backstainingJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2004Diomi Mamma Abstract The effect of limited proteolysis (digestion) of a commercial cellulase preparation (Ecostone® L350) on backstaining with indigo was investigated. The influence of protease (papain) concentration on limited proteolysis of cellulase preparation was studied, applying different ratios of papain/cellulase (w/w). Changes in adsorption on Avicel cellulose of the non-digested compared with the papain-digested Ecostone® L350 were examined using the Langmuir adsorption isotherm. The non-digested Ecostone® L350 exhibited stronger interaction to Avicel cellulose compared with the digested form, while the maximum efficiency of cellulase adsorption to Avicel cellulose decreased after digestion. When papain-digested Ecostone® L350 was applied on cotton fabrics during the dyeing procedure with indigo, a reduction of indigo backstaining was obtained compared with the non-digested Ecostone® L350. Copyright © 2004 Society of Chemical Industry [source] Characterization and use of acid-activated montmorillonite-illite type of clay for lead(II) removalAICHE JOURNAL, Issue 9 2010John U. Kennedy Oubagaranadin Abstract The natural local deposits of montmorillonite-illite type of clay (MIC) were susceptible for acid activation. Raw clay was taken for experimentation, disintegrated on acid activation with sulfuric acid, which showed a particle size distribution. The montmorillonite and illite phases in the raw clay disappeared on acid activation and the activated clay, MIC(AA), showed with sodium-aluminum-silicate and beidellite phases apart from quartz (low) phase. The raw and acid-activated clays were characterized using X-ray powder diffractometry, X-ray fluorescence, Fourier transform infrared spectrometry, and energy dispersive X-ray, and their adsorption capacities were compared. When tested for adsorption of Pb(II) in aqueous solutions, the acid-activated clay showed about 50% increased adsorption than raw clay. Sips adsorption isotherm and pseudo-second-order kinetic models were found to be best for the batch adsorption data. Kinetic studies showed the existence of film diffusion and intraparticle diffusion. A two-stage batch adsorber was designed for the removal of Pb(II) from aqueous solutions. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Sorption dynamics in fixed-beds of inert core spherical adsorbents including axial dispersion and Langmuir isothermAICHE JOURNAL, Issue 7 2009M. Khosravi Koocheksarayi Abstract The effects of axial dispersion and Langmuir isotherm on transient behavior of sorption and intraparticle diffusion in fixed-beds packed with monodisperse shell-type/inert core spherical sorbents are studied. The system of partial differential equations of the mathematical model is solved numerically using finite difference methods. Results are presented in the form of breakthrough curves for adsorption and desorption processes. Results reveal that the shape of the breakthrough curves is influenced by both hydrodynamic and kinetic factors. Hydrodynamic factor is governed by axial dispersion and is controlled by changes of Peclet number. Simulation results reveal that when linear adsorption isotherm is used, the effect of axial dispersion on breakthrough curves of the system is important for Peclet numbers smaller than 50, whereas, for Langmuir isotherm axial dispersion is considerable for Peclet numbers less than 80. In addition, effects of type of adsorption isotherms and size of adsorbents on breakthrough curves are investigated, and results are compared with existing reports in the pertinent literature. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Enhanced hydrogenation in a reverse flow chromatographic reactorAICHE JOURNAL, Issue 5 2006Guillermo A. Viecco Abstract An experimental study of the reverse flow chromatographic reactor is carried with the equilibrium limited hydrogenation of 1,3,5-trimethylbenzene (mesitylene, MES) to 1,3,5-trimethylcyclohexane. The reaction is pseudo first-order when carried out in excess hydrogen. A simple experimental setup is used to evaluate the effects of carrier flow, reactant feed concentration, and amount of catalyst on conversion. Conversions exceeding the thermodynamic equilibrium conversion are obtained for a wide variety of switching times, catalyst amounts, carrier flow rates, and reactant concentrations, showing the robustness of the system. While the qualitative features of the process can be predicted for a simple linear adsorption equilibrium model, the experimental results are best fitted by assuming a linear adsorption isotherm combined with an adjusted interfacial mass-transfer resistance. The experimental results are very similar to those reported in previous research of the same reaction in a simulated moving-bed chromatographic reactor. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Inhibition of 304 stainless steel corrosion in acidic solution by Ferula gumosa (galbanum) extractMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 11 2009M. Behpour Abstract The inhibition effect of the extract of galbanum (Ferula gummosa Boiss.) on the corrosion of 304 stainless steel in 2 M HCl solution was studied by weight loss measurements, Tafel polarization, and electrochemical impedance spectroscopy (EIS) methods. It was found that the inhibition efficiency (IE) increases as the extract concentration is increased. Tafel polarization method revealed the mixed mode inhibition of galbanum extract (GE) with predominant control of anodic reaction. The effect of temperature on the corrosion behavior of steel indicates that inhibition efficiency of the natural substance increases with the rise in temperature. At all temperatures, the adsorption of the extract components onto the steel surface was found to follow the Temkin adsorption isotherm. [source] Simulation and validation of ethanol removal from water in an adsorption packed bed: Isotherm and mass transfer parameter determination in batch studiesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2010R. A. Jones Abstract Preferential adsorption of ethanol from ethanol/water mixtures in batch equilibrium and kinetic experiments were carried out on a commercially available activated carbon adsorbent Filtrasorb 600 (F-600). A model based on finite difference method was developed and employed to determine the mass transfer parameters and equilibrium behaviour for the adsorption of ethanol from simple batch systems. The estimates of the adsorption isotherm along with the mass transfer parameters were used to simulate the transient performance that could be expected in a packed bed under various operating conditions (feed flow rate, feed concentration, and particle size). The applicability of the simulation results were found to be a good match with experimental packed bed experiments over the entire range of operating conditions tested. La cinétique et l'isotherme d'adsorption de l'éthanol des mélanges eau/éthanol lors d'expériences en discontinus ont été déterminées pour un adsorbant au charbon activé disponible dans le commerce, le Filtrasorb 600 (F-600). Un modèle basé sur la méthode des différences finies a été développé et utilisé pour déterminer les paramètres de transfert de matière et étudier le comportement à l'équilibre pour l'adsorption préférentielle de l'éthanol en systèmes discontinus. Les estimations de l'isotherme d'adsorption aussi bien que les paramètres de transfert de matière ont été utilisées pour simuler la performance en régime transitoire d'un lit d'adsorbant sous diverses conditions de fonctionnement (taux d'écoulement du mélange, concentration du mélange et la taille des particules). L'applicabilité des résultats de simulation s'est avérée tout à fait concordante avec les données expérimentales sous toutes les conditions de fonctionnement examinées. [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] Parametric study of a 6-column countercurrent solvent gradient purification (MCSGP) unit,BIOTECHNOLOGY & BIOENGINEERING, Issue 5 2007Lars Aumann Abstract The novel "multicolumn countercurrent solvent gradient purification" (MCSGP) process has been modeled for the purification of a polypeptide mixture characterized by a strong non-linear competitive adsorption isotherm. As a model system, the purification of an industrial polypeptide mixture containing 46% of the hormone calcitonin has been selected. The many impurities contained in the mixture have been lumped into three key impurities, which are selected as the ones eluting closer to the main component. The simulation model allows for a better understanding of the complex operating behavior of the multicolumn system, which has been experimentally investigated in a previous work. Through a systematic parametric analyses of the model behavior, the main operating parameters controlling the process performance in terms of purity and yield are investigated. The study of internal liquid and adsorbed phase concentration profiles along the unit for the different operating conditions allow elucidating the working principle of the new separation process. It is found that the MCSGP unit achieves much higher yields for a given product purity than the corresponding single-column batch units. Biotechnol. Bioeng. 2007;98: 1029,1042. © 2007 Wiley Periodicals, Inc. [source] Fast enzymatic saccharification of switchgrass after pretreatment with ionic liquidsBIOTECHNOLOGY PROGRESS, Issue 1 2010Hua Zhao Abstract The pretreatment of cellulose using ionic liquids (ILs) has been shown to be an effective method for improving the enzymatic hydrolysis of cellulose; this technique affords a fast and complete saccharification of cellulose into reducing sugars (Dadi et al., Biotechnol Bioeng. 2006; 95:904,910; Liu and Chen, Chinese Sci Bull. 2006; 51:2432,2436; Zhao et al., J Biotechnol. 2009; 139:47,54). Motivated by these advances, this study examines the effect of IL-pretreatment on the enzymatic hydrolysis of purified xylan (as a model system of hemicellulose) and switchgrass (as a real lignocellulose). The IL-pretreatment resulted in no improvement in the hydrolysis of xylan. The likely reason is that pure xylan has a low degree of polymerization (DP), and is readily biodegraded even without any pretreatment. However, in real cellulosic materials (such as switchgrass), xylan is entrapped within the cellulosic matrix, and cannot be conveniently accessed by enzymes. Our data demonstrate that the IL-pretreatment of switchgrass significantly improved the enzymatic saccharification of both cellulose (96% D -glucose yield in 24 h) and xylan (63% D -xylose yield in 24 h). The compositional analysis of switchgrass suggests a lower lignin content after IL-pretreatment. In addition, the infrared spectrum of regenerated switchgrass indicates a lower substrate crystallinity, whereas the enzyme adsorption isotherm further implies that the regenerated substrate is more accessible to enzymes. This study has further confirmed that IL-pretreatment is an effective tool in enhancing the enzymatic hydrolysis of cellulosic biomass, and allowing a more complete saccharification. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Hydrogen Adsorption and Diffusion in p - tert -Butylcalix[4]arene: An Experimental and Molecular Simulation StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 38 2010Dr. Saman Alavi Abstract Experimental adsorption isotherms were measured and computer simulations were performed to determine the nature of the H2 gas uptake in the low-density p - tert -butylcalix[4]arene (tBC) phase. 1H,NMR peak intensity measurements for pressures up to 175,bar were used to determine the H2 adsorption isotherm. Weak surface adsorption (up to ,2,mass,% H2) and stronger adsorption (not exceeding 0.25,mass,% or one H2 per calixarene bowl) inside the calixarene phase were detected. The latter type of adsorbed H2 molecule has restricted motion and shows a reversible gas adsorption/desorption cycle. Pulsed field gradient (PFG) NMR pressurization/depressurization measurements were performed to study the diffusion of H2 in the calixarene phases. Direct adsorption isotherms by exposure of the calixarene phase to pressures of H2 gas to ,60,bar are also presented, and show a maximum H2 adsorption of 0.4,H2 per calixarene bowl. Adsorption isotherms of H2 in bulk tBC have been simulated using grand canonical Monte Carlo calculations in a rigid tBC framework, and yield adsorptions of ,1,H2 per calixarene bowl at saturation. Classical molecular dynamics simulations with a fully flexible calixarene molecular force field are used to determine the guest distribution and inclusion energy of the H2 in the solid with different loadings. [source] Interaction of Flavin Adenine Dinucleotide (FAD) with a Glassy Carbon Electrode SurfaceCHEMISTRY & BIODIVERSITY, Issue 8 2008Haizhen Wei Abstract The interaction of flavin adenine dinucleotide (FAD) with a glassy carbon electrode (GCE) surface was investigated in terms of the FAD adsorption thermodynamics and kinetics, the subsequent electroreduction mechanism, and the corresponding electron-transfer rate. The kinetics of FAD electroreduction at the GCE was found to be an adsorption-controlled process. A set of electroreduction kinetic parameters was calculated: the true number of electrons involved in the FAD reduction, n=1.76, the apparent transfer coefficient, ,app=0.41, and the apparent heterogeneous electron-transfer rate constant, kapp=1.4,s,1. The deviation of the number of exchanged electrons from the theoretical value for the complete reduction of FAD to FADH2 (n=2) indicates that a small portion of FAD goes to a semiquinone state during the redox process. The FAD adsorption was well described by the Langmuir adsorption isotherm. The large negative apparent Gibbs energy of adsorption (,Gads=,39.7 ±0.4,kJmol,1) indicated a highly spontaneous and strong adsorption of FAD on the GCE. The energetics of the adsorption process was found to be independent of the electrode surface charge in the electrochemical double-layer region. The kinetics of FAD adsorption was modeled using a pseudo -first-order kinetic model. [source] Synergistic genotoxicity caused by low concentration of titanium dioxide nanoparticles and p,p,-DDT in human hepatocytesENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 3 2010Yun Shi Abstract The use of titanium dioxide nanoparticles (nano-TiO2) for the degradation of dichlorodiphenyltrichloroethane (p,p,-DDT) increases the risk of exposure to trace nano-TiO2 and p,p,-DDT mixtures. The interaction of p,p,-DDT and nano-TiO2 at low concentrations may alter toxic response relative to nano-TiO2 or p,p,-DDT alone. In this work, the combined genotoxicity of trace nano-TiO2 and p,p,-DDT on human embryo L-02 hepatocytes without photoactivation was studied. Nano-TiO2 (0.1 g/L) was mixed with 0.01,1 mmol/L p,p,-DDT to determine adsorption isotherms. L-02 cells were exposed to different levels of p,p,-DDT (0, 0.001, 0.01, and 0.1 ,mol/L) and nano-TiO2 (0, 0.01, 0.1, and 1 ,g/mL) respectively. The adsorption of p,p,-DDT by nano-TiO2 was approximately 0.3 mmol/g. Cell viability, apoptosis, and DNA double strand breaks were similar among all test groups. Nano-TiO2 alone (0.01,1 ,g/mL) increased the levels of oxidative stress and oxidative DNA adducts (8-OHdG), but it did not induce DNA breaks or chromosome damage. Addition of trace nano-TiO2 with trace p,p,-DDT synergistically enhanced genotoxicity via increasing oxidative stress, oxidative DNA adducts, DNA breaks, and chromosome damage in L-02 cells. Low concentrations of nano-TiO2 and p,p,-DDT increased oxidativestress by reactive oxygen species (ROS) formation and lipid oxidation. Oxidative stress is a major pathway for DNA and chromosome damage. Dose-dependent synergistic genotoxicity induced by combined exposure of trace p,p,-DDT and nano-TiO2 suggests a potential environmental risk of nano-TiO2 assisted photocatalysis. Environ. Mol. Mutagen., 2010. © 2009 Wiley-Liss, Inc. [source] Ni2+ removal from aqueous solutions using conditioned clinoptilolites: Kinetic and isotherm studiesENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 1 2009Semra Çoruh Abstract The aim of this study is to investigate the effects of conditioning with NaCl and HCl solutions on removal of Ni2+ ions from aqueous solutions using natural clinoptilolite. Batch studies were performed to evaluate the effects of various parameters such as chemically conditioning, adsorbent amount, contact time, initial pH of the solution, mixing temperature, and initial metal ions. The results clearly showed that the conditioning improved both the exchange capacity and the removal efficiency. Langmuir, Freundlich, Temkin, and Dubinin-Kaganer-Radushkevich (DKR) isotherm models were adopted to describe the adsorption isotherms. Adsorption isotherms of Ni2+ ions could be best modeled by Langmuir equation. Three simplified models including pseudo-second-order, intraparticle diffusion and Elovich were used to test the adsorption kinetics. These results indicate a significant potential for the natural and conditioned clinoptilolites as an adsorbent/ion-exchange material for heavy metal removal. © 2008 American Institute of Chemical Engineers Environ Prog, 2009 [source] Effect of earthworm activity (Aporrectodea giardi) on atrazine adsorption and biodegradationEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2006T. Alekseeva Summary We investigated the influence of earthworm (Aporrectodea giardi) activity on soil properties and on atrazine (AT) adsorption and biodegradation by comparing a coarse-textured smectite-free wetland soil (Brittany, France) with the earthworm casts derived from the top horizon of this soil. Casts are characterized by lower pH, are enriched in organic carbon (OC) and clay content, have a larger cation exchange capacity, and a greater exchangeable Ca content. The clay mineralogy of the soil studied and casts is characterized by a muscovite,kaolinite,chlorite association. In addition, the clay fraction of the soil contains lepidocrocite (,-FeOOH), which was not found in the casts. Atrazine adsorption isotherms were reasonably well described by the Freundlich equation and were all non-linear. The mean amounts of adsorbed AT for starting concentrations of 3,30 mg litre,1 ranged from 8 to 34%, being largest in earthworm casts. Soil AT adsorption capacity was well correlated with OC content. Non-decomposed organic matter present in the coarse size fractions and specific compounds present in earthworm casts (proteins, mono- and polysaccharides, polyphenols, sugars, lignin) and microbial and fungal biomass contribute to AT adsorption. Weak electrostatic (physical) sorption of AT on organic compounds and on mineral surfaces prevails. For casts, the formation of additional hydrophobic interactions between AT and SOM is proposed. We also studied AT biodegradation by the model bacterium Pseudomonas sp. strain ADP in the presence of soils or earthworm casts. An enhancement of the AT disappearance rate was observed in the presence of all the solid matrices tested compared with that obtained in an aqueous medium. The biodegradation rate was shown to be dependent not only on the OC content of the solid matrix, but mainly on its composition and structure. [source] Synthesis,Structure,Property Relationships for Hyperbranched Aminosilica CO2 AdsorbentsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Jeffrey H. Drese Abstract Hyperbranched aminosilica (HAS) adsorbents are prepared via the ring-opening polymerization of aziridine in the presence of mesoporous silica SBA-15 support. The aminopolymers are covalently bound to the silica support and capture CO2 reversibly in a temperature swing process. Here, a range of HAS materials are prepared with different organic loadings. The effects of organic loading on the structural properties and CO2 adsorption properties of the resultant hybrid materials are examined. The residual porosity in the HAS adsorbents after organic loading, as well as the molecular weights and degrees of branching for the separated aminopolymers, are determined to draw a relationship between adsorbent structure and performance. Humid adsorption working capacities and apparent adsorption kinetics are determined from experiments in a packed-bed flow system monitored by mass spectrometry. Dry adsorption isotherms are presented for one HAS adsorbent with a high amine loading at 35 and 75,°C. These combined results establish the relationships between adsorbent synthesis, structure, and CO2 adsorption properties of the family of HAS materials. [source] Modeling and CFD prediction for diffusion and adsorption within room with various adsorption isothermsINDOOR AIR, Issue 2003S. Murakami Abstract This paper presents physical models that are used for analyzing numerically the transportation of volatile organic compounds (VOCs) from building materials in a room. The models are based on fundamental physicochemical principles of their diffusion and adsorption/desorption (hereafter simply sorption) both in building materials and in room air. The performance of the proposed physical models is examined numerically in a test room with a technique supported by computational fluid dynamics (CFD). Two building materials are used in this study. One is a VOC emitting material for which the emission rate is mainly controlled by the internal diffusion of the material. The other is an adsorptive material that has no VOC source. It affects the room air concentration of VOCs with its sorption process. The floor is covered with an emission material made of polypropylene styrene,butadiene rubber (SBR). An adsorbent material made of coal-based activated carbon is spread over the sidewalls. The results of numerical prediction show that the physical models and their numerical simulations explain well the mechanism of the transportation of VOCs in a room. [source] The influence of pH and digestion with commercial enzymes on calcium adsorption in casabeINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 9 2006Petra Beatriz Navas Summary The Ca2+ binding capacity of a sample of casabe made from cassava (Manihot esculenta) was evaluated by using adsorption isotherms after a digestion process with commercial enzymes. It was found that enzymatic treatment increased the ability of vegetable material to retain calcium and to release endogenous mineral ions as a consequence of possible modifications to the carbohydrate matrix. Untreated casabe did not release mineral ions. pH also influenced the retention of Ca2+: at pH 4.5 release was the main process but adsorption increases with alkalinity up to pH 8.5. The Ca concentrations at which neither adsorption nor release occurred [Ca2+]e were as follows: 5.2 mm (pH 4.5), 3.5 mm (pH 7.1), and 0.63 mm (pH 8.5). The pH effect was explained by an increase in the density of negatively charged functional groups produced by ionization reactions at pH below the point of zero net charge (pHo) which was evaluated by using the Gouy,Chapman double layer model. Values of pHo were 6.4 for raw material and 4.1 after digestion with enzymes. In both cases, the density of positively charged sites below pHo was much higher that the density of negatively charged sites above pHo. [source] | |||||||||||||||||||||||||||||||||||||