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Abstract: Zeolitic tuff was used for the adsorption of phenol from aqueous solutions at different temperatures in a batch process. The adsorption characteristics, i.e., kinetics, mechanism, isotherms, and thermodynamics, of phenol from water onto zeolite were studied. Three different kinetic models, viz., pseudo-first-order, pseudo-second-order, and intraparticle diffusion were used to fit the kinetics data. The pseudo-second-order model best described the experimental data. Concerning the mechanism, the results indicated that the intraparticle diffusion is not the rate limiting step in the phenol adsorption process. The adsorption isotherms at different temperatures were determined and modeled using four different models. The best-fitted adsorption isotherm models were found to be in the order: Freundlich>Redlich–Peterson>Langmiur>Temkin for temperature range 25–45°C. The Langmiur model fitted well the experimental data with a maximum adsorption capacity of 34.5, 24.9, 23.8, and 23.3mg/g at 25, 35, 45, and 55°C. Thermodynamically, it was determined that the adsorption of phenol onto zeolite is physical in nature and enthalpy driven with ΔH°=−10.2kJ/mol. [Copyright &y& Elsevier]

Abstract: Benzoic acid removal is important for the water treatment, and adsorption is an efficient treatment process. Three kinds of modified bentonites, hydroxy-aluminum pillared bentonite (Al(OH)-Bent), octadecyl trimethyl ammonium chloride modified bentonite (OTMAC-Bent), and both octadecyl trimethyl ammonium chloride and hydroxy-aluminum modified bentonite (Al(OH)-OTMAC-Bent) were prepared and characterized by XRD, FTIR, and BET analysis. Experiments were conducted on the adsorption of benzoic acid by the prepared modified bentonites at different temperatures in batch experiments. The results show benzoic acid adsorption capabilities of Na-Bent and Al(OH)-Bent are even low, but high for OTMAC-Bent and Al(OH)-OTMAC-Bent. Optimal conditions for the adsorption of benzoic acid on OTMAC-Bent and Al(OH)-OTMAC-Bent were as follows: pH of 3.5, 0.04g/mL adsorbent, and contact time of 90min. Increased adsorption with temperature indicates that the adsorptions of benzoic acid onto Al(OH)-OTMAC-Bent and OTMAC-Bent are spontaneous and endothermic. The adsorption data could be well interpreted by the Langmuir model and Temkin Equation. The adsorption efficiency was higher than 85%, suggesting that OTMAC-Bent and Al(OH)-OTMAC-Bent are excellent adsorbents for effective benzoic acid removal from water. [Copyright &y& Elsevier]

Abstract: The present study explored the adsorptive characteristics of Brilliant Green dye from aqueous solution onto NaOH treated saw dust of Indian Eucalyptus wood, a timber industry waste. Batch studies were performed to evaluate the influence of various experimental parameters like initial pH, contact time, adsorbent dose, initial concentration and temperature on the removal of Brilliant Green. Optimum conditions were found to be initial pH=2.9, contact time=3h and adsorbent dose=4g/l. The pseudo-second-order kinetic model represented the adsorption kinetics of Brilliant Green onto NaOH treated saw dust. Equilibrium isotherms were analyzed by Freundlich, Langmuir, Redlich–Peterson and Temkin isotherm models using non-linear regression technique. NaOH treated saw dust which was used showed surface area=0.3742m2/g, pore volume=0.00836cm3/g and average pore diameter=893.6A0. Adsorption of Brilliant Green onto NaOH treated saw dust is favorably influenced by decrease in the temperature of the operation. Thermodynamics showed that the Brilliant Green adsorption was most favorable onto NaOH treated saw dust. [Copyright &y& Elsevier]

Abstract: The adsorption thermodynamic for the adsorption of trichloroacetic acid (TCA) from aqueous solutions on composite cation exchanger polypyrrole Th(IV) phosphate has been studied. Thermodynamics of adsorption process was studied considering equilibrium time, pH, cation exchanger doses, trichloroacetic concentration and temperature as controlling parameters. Freundlich isotherm is well fitted for the adsorption results of the trichloroacetic acid. As a result some thermodynamic parameters like Freundlich constants, thermodynamic equilibrium constants (K o), standard free energy changes (ΔG°), and standard enthalpy changes (ΔH°) and standard entropy changes (ΔS°) have been evaluated. [Copyright &y& Elsevier]

The reversible adsorption process occurring on patchwise heterogeneous bivariate surfaces is studied by Monte Carlo simulation and mean-field approximation. These surfaces are characterized by a collection of deep and shallow adsorbing patches with a typical length scale l. Patches can be either arranged in a deterministic chessboard structure or in a random way. Previous studies showed that the topography of a given surface can be obtained from the knowledge of the corresponding adsorption isotherm and a reference curve. In the present work, we discuss the advantages and disadvantages of using different reference curves. One of the main consequences of this analysis is to provide an improved method for the determination of the energetic topography of the surface from adsorption measurements. [ABSTRACT FROM AUTHOR]

Abstract: Brazilian pine-fruit shells (Araucaria angustifolia) in natural form and as activated carbon were tested as adsorbents for the removal of remazol black B (RB) textile dye from aqueous effluents. The effects of shaking time, adsorbent dosage and pH on the adsorption capacity were studied. RB uptake was favorable at pH values ranging from 2.0 to 2.5 and from 2.0 to 7.0 for the biosorbent and the activated carbon, respectively. The contact time required to obtain the equilibrium using the biosorbent and the activated carbon was 12 and 4h at 298K, respectively. The fractionary-order kinetic model provided the best fit to experimental data compared with other models. Equilibrium data were better fit to the Sips isotherm model using the biosorbent as well as the activated carbon. The enthalpy and entropy of adsorption of RB were obtained from adsorption experiments ranging from 298 to 323K. Simulated dyehouse effluents were used to check the applicability of the proposed adsorbents for effluent treatment. [Copyright &y& Elsevier]

In the present study, expanded graphite (EG) was prepared with 50 mesh crude graphite through chemical oxidation and its adsorption kinetics and thermodynamic characteristics for polyethylene glycol (PEG) with different molecular weight (MW) in aqueous solution was investigated. We studied the influence of initial PEG concentration, temperature, pH and ionic strength on adsorption capacity. Langmuir constants and Gibbs free energy change (DG°) were calculated according to experimental data, respectively. Thermodynamic study indicates that all the equilibrium adsorbance increase with the rise in ionic strength. However, solution acidity does not have an obvious effect. Adsorption of EG for PEG with different MW is all types and PEG molecule lies flat on EG surface. Adsorption processes are all spontaneous. Kinetic studies show that the kinetic data can be delineated by pseudo second-order kinetic model. Second-order rate constants and the initial adsorption rate rise with the increasing of temperature and half-adsorption time decreases with the increasing of temperature. The adsorption activation energy of each PEG is less than 30 kJ mol-1, physical adsorption is the major mode of the overall adsorption process. [ABSTRACT FROM AUTHOR]

Abstract: Equilibrium adsorption isotherms for CO2 and N2 were measured on a fully exchanged potassium chabazite (KCHA) zeolite, and partially exchanged sodium-chabazite (NaCHA) and lithium-chabazite (LiCHA) zeolites. This work presents integral thermodynamic functions and isosteric heats of N2 and CO2 adsorption equilibria on a fully exchanged potassium chabazite (KCHA) zeolite, and compares these to those functions measured on sodium exchanged chabazite (NaCHA) and lithium exchanged chabazite (LiCHA) zeolites. The thermodynamic quantities were calculated from equilibrium isotherms as function of loading. Adsorption of N2 on KCHA was considered with distinct layers in inter-crystal spaces and mesopores volume, while CO2 adsorption in KCHA cavities was more readily interpreted as fluid-like volume filling mechanism. The molecules comprising this fluid (CO2) are in the dispersion energy field of the crystals and of each other, bounded also by considerable field-gradient quadrupole energy. In all cationic forms the adsorption equilibrium loading and differential enthalpies for CO2 were considerably higher than those for N2. The CO2 integral entropy showed a rapid decreasing trend close to the saturation capacity of the cavities, demonstrating an appreciable loss of molecule degrees of freedom. The results of this work provide useful thermodynamic information that help in understanding the adsorption of N2 and CO2 on a fully exchanged KCHA zeolite. [Copyright &y& Elsevier]

Abstract: Arsenic and its compounds are toxic pollutants for the environment and all living organisms. At present, there is considerable interest in studying new sorbent materials for the removal of arsenic from aqueous solutions. This work discusses the feasibility of arsenic uptake onto dolomite which is considered to be a potential inexpensive adsorbent. Thermodynamic and kinetic experiments were undertaken to assess the capacity and rate of As uptake onto dolomite. Experimental data were mathematically described using adsorption kinetic models, namely pseudo-first-order and pseudo-second-order models. The arsenic removal was found to be dependent on the dosage of dolomite, adsorbent particle size and the presence of various anions. Thermodynamic results indicate that the adsorption follows an exothermic chemisorption process. The experimental data indicate successful removal of As(V) ion from aqueous solution indicating that dolomite be used as an inexpensive treatment process. [Copyright &y& Elsevier]

Abstract: It was found that Rh, Pd and Pt contained in the spent ceramic automotive catalysts could be effectively extracted by dry chlorination with chlorine. In order to concentrate Pd(II) contained in the chloride solution obtained from the dry chlorination process, thermodynamic and kinetics studies for adsorption of Pd(II) complexes from the chloride solutions on anionic exchange resin Diaion WA21J were carried out. It was found that Pd, Pt, Rh, Al, Fe, Si, Zn and Pb from the chloride solution could be adsorbed on the resin. The isothermal adsorption of Pd(II) was found to fit Freundlich, Langmuir and Dubinin–Kaganer–Radushkevich models under the adsorption conditions. The adsorption of Pd(II) on the resin was favorable according to the values of 1/n and RL from Freundlich and Langmuir adsorption isotherms, respectively. The maximum monolayer adsorption capacities Q max based on Langmuir adsorption isotherms were 5.70, 4.84 and 4.05mg/g and the corresponding value Xm based on Dubinin–Kaganer–Radushkevich were 5.55, 4.69 and 4.01mg/g at temperatures 18°C, 28°C and 40°C, respectively. The apparent adsorption energies (Ead ) based on Dubinin–Kaganer–Radushkevich isotherm were −15.43, −16.22 and −23.57kJ/mol for the temperatures 18°C, 28°C and 40°C, respectively. Chemical adsorption was a main mechanism involved in the adsorption process. Pd(II) adsorption on the resin could be accelerated by increasing the adsorption temperature. The adsorption of Pd(II) from the chloride solution on the resin underwent pseudo-first order kinetic process and the apparent adsorption activation energy Ea was 15.0kJ/mol. The intra-particle diffusion was a main rate controlling step in the Pd(II) adsorption process under the adsorption conditions. [Copyright &y& Elsevier]

To improve the adsorption capacity of chitosan, a novel technique for preparation of β-cyclodextrin-grafted chitosan (CD-CTS) was carried out by the reaction of β-cyclodextrin with epoxy-activated chitosan under alkaline conditions. Adsorption of Acid Red R (ARR) in aqueous solution onto CD-CTS was investigated in a batch system. Adsorption isotherm, adsorption kinetics and adsorption thermodynamics of ARR onto CD-CTS were examined. The influence factors on ARR adsorption were also investigated and described in details, such as contact time, pH value and initial ARR concentration. Equilibrium data agreed very well with the Langmuir model. Kinetic studies showed that the adsorption followed a pseudo second-order kinetic model. Thermodynamic parameters showed the endothermic heat of adsorption and the feasibility of the process. Compared with chitosan (CTS), the adsorption capacity of CD-CTS for ARR was increased by 20.2 mg/g after adsorption equilibrium. Results showed that CD-CTS is a favorable adsorbent. [ABSTRACT FROM AUTHOR]

The adsorption behavior of crystal violet (CV+) from aqueous solution onto raw Fatsa (RFB) and thermal-activated Fatsa (TAFB) bentonite samples was investigated as a function of parameters, such as pH, temperature, initial CV+ concentration and contact time. X-ray diffraction (XRD) and differential thermal analysis (DTA) were used for structural and thermal characterization. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. The pseudo-first-order, pseudo-second-order kinetic and intra-particle diffusion models were used to describe the kinetic data. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an investigation of the thermal effects during high pressure filling of a cryo-adsorptive hydrogen storage tank. The adsorbent is powdered activated carbon. A two-dimensional model is formulated, which describes hydrodynamics, heat transfer and adsorption phenomena in cylindrical tanks. Experiments with a tank containing about 10 kg of adsorbent were carried out to parameterize and validate the model. Good agreement between experiments and simulations could be obtained. Numerical results are then presented concerning filling processes. Two cooling concepts are investigated: a LN2 cooling jacket and a recirculation system which uses the hydrogen itself as the cooling fluid. The results show that short filling times can only be achieved with the recirculation system. [Copyright &y& Elsevier]

Abstract: This paper presents a thermodynamic analysis of cryo-adsorption vessels for hydrogen storage. The analysis is carried out with an unsteady lumped model and gives a global assessment of the behavior of the storage system during operation (discharge), dormancy and filling. The adsorbent used is superactivated carbon AX-21™. Cryogenic hydrogen storage, either by compression or adsorption, takes advantage of the effect of temperature on the storage density. In order to store 4.1 kg H2 in 100 L, a pressure of 750 bar at 298 K is necessary, but only 150 bar at 77 K. The pressure is further reduced to 60 bar if the container is filled with pellets of activated carbon . However, adsorption vessels are submitted to intrinsic thermal effects which considerably influence their dynamic behavior and due to which thermal management is required for smooth operation. In this analysis, among energy balances for filling and discharge processes, the influence of the intrinsic thermal effects during vessel operation is presented. Hydrogen losses during normal operation as well as during long periods of inactivity are also considered. The results are compared to those obtained in low-pressure and high-pressure insulated LH2 and CH2 tanks. [Copyright &y& Elsevier]

The binderless 5A zeolite has higher economy when used in adsorption process to improve utilization efficiency of naphtha. Adsorption isotherms of n-pentane, n-hexane, n-heptane and n-octane on binderless 5A zeolite pellets were determined gravimetrically and analyzed in the temperature ranging from 423 to 573 K. Adsorption thermodynamic parameters were extracted from multisite Langmuir (MSL) model. Heats of adsorption for n-paraffins on 5A zeolite show an increasing trend with carbon number. At small degree of sites filling, the heats of adsorption of n-paraffins on binderless pellets increase from 53.19 kJ mol-1 for n-pentane to 72.34 kJ mol-1 for n-octane. [ABSTRACT FROM AUTHOR]

Materials capable of cost-effective on-board hydrogen storage and delivery are currently being sought worldwide as a means to facilitate a hydrogen-based energy transition in the transportation sector. Among the solutions proposed, hydrogen storage by physisorption on porous solids constitutes a main avenue of research, and for intelligent design of such materials a detailed knowledge of gas adsorption thermodynamics is of the utmost importance. Analysis of the available data for hydrogen adsorption on alkali and alkalineearth cation exchanged zeolites clearly shows that standard adsorption enthalpy (ΔH0) and entropy (ΔS0) are correlated, in the sense that larger ΔS0 values correspond to larger ΔH0 values. It was also shown that, referring to absolute values, the relative rate at which adsorption entropy changes decreases gradually as adsorption enthalpy increases thus resulting in a non-linear correlation between ΔH0 and ΔS0. These results are discussed and corresponding implications for hydrogen storage via physisorption are highlighted. [ABSTRACT FROM AUTHOR]

Abstract: Present study explored the adsorptive characteristics of Indigo Carmine (IC) dye from aqueous solution onto rice husk ash (RHA). Batch experiments were carried out to determine the influence of parameters like initial pH (pH0), contact time (t), adsorbent dose (m) and initial concentration (C 0) on the removal of IC. The optimum conditions were found to be: pH0 =5.4, t =8h and m =10.0g/l. The pseudo-second-order kinetic model represented the adsorption kinetics of IC on to RHA. Equilibrium isotherms were analyzed by Freundlich, Langmuir, Temkin and Redlich–Peterson models using a non-linear regression technique. Adsorption of IC on RHA was favorably influenced by an increase in the temperature of the operation. The positive values of the change in entropy (ΔS 0) and heat of adsorption (ΔH 0); and the negative value of change in Gibbs free energy (ΔG 0) indicate feasible and spontaneous adsorption of IC on to RHA. [Copyright &y& Elsevier]

• The relationship between the diameter and thermodynamics of nanowires is deduced. • CeO 2 nanowires with different diameters were prepared by hydrothermal method. • CeO 2 nanowires have good selectivity for different dyes. • The effect of diameter on the thermodynamic properties of nanowires was discussed. Because the influencing mechanism and regularity of diameter on the adsorption thermodynamics of nanowires are still unclear, the relations of adsorption thermodynamic properties of different diameters of nanowires is derived. Experimentally, we prepared CeO 2 nanowires with different diameters, and then the adsorption selectivity of CeO 2 nanowires to different dyes was researched. The adsorption thermodynamic properties of dyes with the best adsorption selectivity were determined, and the influences of the diameter on the adsorption thermodynamic properties were discussed. The experimental results show that the adsorption capacity for congo red is the strongest and that for methylene blue is the weakest. In addition, with the decreases of diameter of CeO 2 nanowires, the adsorption capacity and the adsorption Equilibrium constant increase, while Δ ads G m o , Δ ads H m o and Δ ads S m o decrease, and this thermodynamic properties are linearly related to the reciprocal of diameter, respectively. The experimental results agree with the thermodynamic theory of nanowire adsorption. [ABSTRACT FROM AUTHOR]

This study prepared an LB energy-saving high temperature shift catalyst by optimizing its prepare parameters with artificial neural network, and measured its catalytic activities at various steam-gas ratios. It shows that the LB catalyst performs well at a lower steam-gas ratio. The chromatographic retention parameters of CO, CO2, and H2O on LB catalyst were experimentally determined by means of inverse gas chromatography (IGC). Adsorption enthalpies, Gibbs adsorption free energies and adsorption entropies of different gases were estimated by their retention volumes in infinite dilution region. The interaction parameters ( χ) between absorbate gases and LB catalyst were calculated according to Flory-Huggins theory, and were inversely linear with temperature. The thermodynamics mechanism of the adsorption process was discussed from the view of the microcosmic factors of molecular structure and thermodynamic properties. [ABSTRACT FROM AUTHOR]

Abstract: A factorial design was employed to evaluate the quantitative removal of an anionic red dye from aqueous solutions on epichlorohydrin-cross-linked chitosan. The experimental factors and their respective levels studied were the initial dye concentration in solution (25 or 600mgL−1), the absence or the presence of the anionic surfactant sodium dodecylbenzenesulfonate (DBS) and the adsorption temperature (25 or 55°C). The adsorption parameters were analyzed statistically using modeling polynomial equations. The results indicated that increasing the dye concentration from 25 to 600mgL−1 increases the dye adsorption whereas the presence of DBS increases it. The principal effect of temperature did not show a high statistical significance. The factorial results also demonstrate the existence of statistically significant binary interactions of the experimental factors. The adsorption thermodynamic parameters, namely Δads H, Δads G and Δads S, were determined for all the factorial design results. Exothermic and endothermic values were found in relation to the Δads H. The positive Δads S values indicate that entropy is a driving force for adsorption. The Δads G values are significantly affected by an important synergistic effect of the factors and not by the temperature changes alone. [Copyright &y& Elsevier]

• Steric and energetic parameters were calculated for phenolic compounds on activated carbon. • Adsorption was endothermic and implied a parallel orientation on activated carbon. • Thermodynamic functions were calculated and interpreted. Statistical physics calculations were performed to analyze and interpret the steric and energetic parameters of the adsorption of 3-aminophenol and resorcinol on activated carbon obtained from the carbonization of avocado seed via microwave-heating and ZnCl 2 activation. Experimental isotherms at 25–50 °C and pH 7 were analyzed and interpreted via a monolayer adsorption model with one energy. Results showed that the adsorption of these two pollutants was endothermic and implied a parallel adsorption orientation on activated carbon surface where molecular aggregation was absent in the aqueous solution. Saturation adsorption capacities were maximum at 50 °C (i.e., 406 and 455 mg/g for resorcinol and 3-aminophenol, respectively). Calculated adsorption energies ranged from 22.3 to 31.2 kJ/mol and were associated to a physical adsorption. Thermodynamic functions, namely Gibbs free energy, internal energy and entropy, were calculated and discussed for both adsorption systems showing that the removal of this pollutant was spontaneous. These findings contribute to understand the adsorption mechanism involved in the removal of organic pollutants such as phenolic compounds. [ABSTRACT FROM AUTHOR]

Abstract: Two macroporous crosslinked poly(styrene-co-divinylbenzene) resins functionalized with methoxy and phenoxy groups, PVBME and PVBPE were prepared and their adsorption characteristics for phenol were studied in hexane as well as in aqueous solution. It was shown that the equilibrium adsorption capacity of phenol onto PVBPE was a little larger than that onto PVBME at the same temperature and equilibrium concentration. The adsorption onto PVBME in hexane can be correlated to Langmuir isotherm model, whereas the semi-empirical Freundlich isotherm model characterized the adsorption onto PVBPE better. The adsorption thermodynamic parameters were calculated and it was found that the adsorption enthalpy, adsorption free energy, and adsorption entropy were all negative, and the adsorption thermodynamic parameters onto PVBPE were more negative than the corresponding ones onto PVBME. The relationship of the adsorption capacity with the equilibrium concentration was linear in aqueous solution. The adsorption was hypersensitive to the solution pH in aqueous solution, and the optimum pH was determined to be 6.0. The adsorption dynamics of phenol onto PVBPE in aqueous solution was investigated and it was seen that the adsorption can be well fitted by the pseudo-first-order rate equation. [Copyright &y& Elsevier]

Abstract: Adsorption (at a low temperature) of nitrogen on the protonic zeolite H-Y results in hydrogen bonding of the adsorbed N2 molecules with the zeolite Si(OH)Al Brønsted-acid groups. This hydrogen-bonding interaction leads to activation, in the infrared, of the fundamental N–N stretching mode, which appears at 2334cm−1. From infrared spectra taken over a temperature range, the standard enthalpy of formation of the OH···N2 complex was found to be ΔH 0 =−15.7(±1)kJmol−1. Similarly, variable-temperature infrared spectroscopy was used to determine the standard enthalpy change involved in formation of H-bonded CO complexes for CO adsorbed on the zeolites H-ZSM-5 and H-FER; the corresponding values of ΔH 0 were found to be −29.4(±1) and −28.4(±1)kJmol−1, respectively. The whole set of results was analysed in the context of other relevant data available in the literature. [Copyright &y& Elsevier]

Abstract: A critical review of the adsorption and catalysis of n- and methylalkanes demonstrates that the interior surface of TON- and MTT-type zeolites dominates both adsorption and catalysis, and that the contribution from the exterior surface is negligible. For both n- and methylalkane isomers, the experimental Henry constants at the interior TON-type zeolite surface are more than an order of magnitude greater than those at the exterior surface. Molecular simulations on exclusively interior TON-type silica surface reproduce the adsorption isotherms of n- and methylalkane isomers remarkably well and suggest that even an isomer as bulky as 2,3-dimethylpentane could have access to the interior TON-type zeolite surface. Only the reference state used in solution thermodynamics affords an equitable comparison between internal and external surface thermodynamics. It indicates that methylalkanes adsorb in a structured fashion at the exterior TON-type zeolite surface when the interior surface is inaccessible. But the entropic penalty for this organized exterior surface “pore mouth” or “key-lock” adsorption is high, so that methylalkanes prefer adsorption at the interior surface when it is accessible. We speculate that CHA- and ERI-type sieves exhibit exterior surface catalysis in long n-alkane conversion, but the database remains too small to allow investigation of the full potential of shape selectivity in exterior zeolite surface catalysis. [Copyright &y& Elsevier]

A 23 factorial design was employed to evaluate the quantitative removal of the indigo carmine (IC) dye from aqueous solutions on glutaraldehyde cross-linked chitosan. The variables were chitosan masses of 100 and 300mg, IC concentrations of 2.0 and 5.0×10−5 molL−1 and temperatures of 25 and 35°C. The quantitative and energetic adsorption parameters were analyzed statistically using modeling with bilinear equations. The results indicated that increasing the chitosan mass from 100 to 300mg decreases the IC adsorption/mass ratio (molg−1) whereas a temperature increase of 25–35°C increases it. The principal effect of the IC concentration did not show statistical significance. The factorial experiments demonstrate the existence of a significant antagonistic interaction effect between the chitosan mass and temperature. The adsorption thermodynamic parameters, namely Δads H, Δads G, and Δads S, were determined for all the factorial design results. Endothermic values were found in relation to the Δads H. The positive Δads S values indicate that entropy is a driving force for adsorption. The Δads G values are also significantly affected by important antagonistic and synergistic effects involving all principal and interactive factors. It is concluded that the thermodynamical spontaneity of the IC adsorption parameters are greatly influenced by the interactive factors and not by the temperature changes alone. [Copyright &y& Elsevier]

The present study aims to evaluate the influence of various experimental parameters viz. initial pH (pH0), adsorbent dose, contact time, initial concentration and temperature on the adsorptive removal of furfural from aqueous solution by commercial grade activated carbon (ACC). Optimum conditions for furfural removal were found to be pH0 ≈ 5.9, adsorbent dose ≈ 10 g/l of solution and equilibrium time ≈ 6.0 h. The adsorption followed pseudo-second-order kinetics. The effective diffusion coefficient of furfural was of the order of 10-13 m2/s. Furfural adsorption onto ACC was found to be best represented by the Redlich-Peterson isotherm. A decrease in the temperature of the operation favorably influenced the adsorption of furfural onto ACC. The positive values of the change in entropy (ΔS0); and the negatived value of heat of adsorption (ΔH0) and change in Gibbs free energy (ΔG0) indicated feasible, exothermic, and spontaneous nature of furfural adsorption onto ACC. [ABSTRACT FROM AUTHOR]

The present study deals with the sorptive removal of furfural from aqueous solution by carbon-rich bagasse fly ash (BFA). Batch studies were performed to evaluate the influence of various experimental parameters, namely, initial pH (pH0), adsorbent dose, contact time, initial concentration, and temperature on the removal of furfural. Optimum conditions for furfural removal were found to be pH0 ≈ 5.5, adsorbent dose ≈4 g/L of solution, and equilibrium time ≈4 h. The adsorption followed pseudo-second-order kinetics. The effective diffusion coefficient of furfural is of the order of 10-13 m2/s. Equilibrium adsorption data on BFA was analyzed by Freundlich, Langmuir, Dubnin-Radushkevich, Redlich-Peterson, and Temkin isotherm equations using regression and error analysis. The Redlich-Peterson isotherm was found to best represent the data for furfural adsorption onto BFA. Adsorption of furfural on BFA is favorably influenced by a decrease in the temperature of the operation. Values of the change in entropy (ΔS0) and heat of adsorption (ΔH0) for furfural adsorption on BFA were negative. The high negative value of change in Gibbs free energy (ΔG0) indicates the feasible and spontaneous adsorption of furfural on BFA. [ABSTRACT FROM AUTHOR]

The effects of temperature, pH and ionic strength on the adsorption of crystal violet (CV+) by raw, Ni-saturated (Ni-), Co-saturated (Co-) and Zn-saturated (Zn-) bentonite samples were investigated. The amounts of CV+ adsorbed in equilibrium at 298.15K were 0.27, 0.37, 0.49 and 0.54mmolg−1 bentonite, which correspond to 108%, 148%, 196% and 216% of the cation exchange capacity (CEC) of the raw, Ni-, Zn-and Co-saturated bentonite samples, respectively. The adsorption of the dye on these samples is pH-independent within the range (2.5–8.5), and it increases with ionic strength from 0 to 0.6moll−1. Thermodynamic and Langmuir parameters showed that cation-saturated bentonite samples have relatively stronger ability than the raw bentonite towards the crystal violet (CV+) cation. [Copyright &y& Elsevier]

Activated carbon was prepared from the sewage sludge of municipal wastewater treatment plant by chemical activation (activation reagent is ZnCl2) and was used for the adsorption of dye (reactive brilliant red K-2BP). The impact of adsorbent amount, adsorption time and pH value on adsorption effect, the adsorption kinetics, and the adsorption thermodynamics were discussed according to batch adsorption tests. The results indicated that the activated carbon developed from sewage sludge (ACSS), which was mesoporous, possessed opened porous structures. The iodine number of the ACSS was 326 mg·g−1. The rate of achievement was 51.31%. The BET surface area was 298 m2·g−1 and the contents of heavy metals in the leachate didn’t exceed the contents limit. The adsorption kinetics of reactive brilliant red K-2BP on the ACSS was accorded with the two-step kinetics rate equation and pseudo-second-order kinetics equation. Compared to the Freundlich isotherm equation, the Langmuir isotherm equation showed better applicability for the adsorption. The adsorption which was favorable was an endothermic (enthalpy Δ H > 0) and spontaneous (free energy Δ G < 0) process and was accompanied by an increase in entropy (Δ S > 0). [ABSTRACT FROM AUTHOR]

Abstract: The present study deals with the adsorption of brilliant green (BG) on carbon rich bagasse fly ash (BFA). BFA is a solid waste obtained from the particulate collection equipment attached to the flue gas line of the bagasse-fired boilers of cane sugar mills. Batch studies were performed to evaluate the influences of various experimental parameters like initial pH (pH0), contact time, adsorbent dose and initial concentration (C 0) on the removal of BG. Optimum conditions for BG removal were found to be pH0 ≈3.0, adsorbent dose≈3g/l of solution and equilibrium time≈5h. Adsorption of BG followed pseudo-second-order kinetics. Intra-particle diffusion does not seem to control the BG removal process. Equilibrium isotherms for the adsorption of BG on BFA were analyzed by Freundlich, Langmuir, Redlich–Peterson, Dubnin–Radushkevich, and Temkin isotherm models using non-linear regression technique. Redlich–Peterson and Langmuir isotherms were found to best represent the data for BG adsorption onto BFA. Adsorption of BG on BFA is favourably influenced by an increase in the temperature of the operation. Values of the change in entropy () and heat of adsorption () for BG adsorption on BFA were positive. The high negative value of change in Gibbs free energy () indicates the feasible and spontaneous adsorption of BG on BFA. [Copyright &y& Elsevier]

Abstract: A surface tension technique was used to determine the critical aggregation concentration (cac) of a yellow and a red dye in relation to the presence of the anionic surfactant sodium dodecylbenzene sulfonate (DBS) and to temperature changes in buffered aqueous solutions. The cac values of the yellow dye increase from 25 to 45 °C (from 41.37 to 50.32 mg L−1) and decrease from 45 to 55 °C (from 50.32 to 38.72 mg L−1). The cac values for the red dye/DBS aggregates decrease (from 124.52 to 88.50 mg L−1) from 25 to 55 °C. Adsorption of the two dyes onto a mesoporous aminopropyl silica (Sil–NH2) was also studied. The adsorption of the yellow dye increases with an increase in temperature from 25 to 55 °C. In the presence of DBS the adsorption on Sil–NH2 for the yellow dye decreases, and for the red dye increases from 25 to 55 °C. Adsorptions occurred below and above the cac of the anionic dyes/DBS aggregates. Adsorption of the dyes onto Sil–NH2 fitted well to the Langmuir, Freundlich, and Redlich–Peterson adsorption models. However, in the presence of DBS, only the Freundlich model fit the experimental adsorption data at low dye concentrations (less than 400 mg L−1). In this case, the Redlich–Peterson model was only fitted to the red dye adsorption data. The magnitude of the Dubinin–Radushkevich energetic parameters (E, from 7.00 to 15.00 kJ mol−1) indicates that the adsorption of the dyes onto Sil–NH2, in the absence and in the presence of DBS, is controlled by water adsorbed/dye in solution ion-exchange interactions. It is observed that the values of are positive for both dyes and the values are quite similar to each other. The exception is the adsorption of the yellow dye in the presence of DBS, which is slightly exothermic. The values are all negative. However, the interactions of the dyes with Sil–NH2 silica are more spontaneous in the presence of the surfactant. The positive adsorption entropy values () for the interaction of the dyes suggest that entropy is a driving force of the dye adsorptions. However, the entropic contribution is higher for the adsorptions in the presence of DBS. It was suggested that the chemical structures of the dyes play an important role in the formation of the dye/DBS aggregates and in dye adsorption onto the aminopropyl silica. [Copyright &y& Elsevier]

A 23 factorial design was employed to evaluate the quantitative removal of Cu(II) and Co(II) on glutaraldehyde-cross-linked chitosan from kinetic isotherms, using chitosan masses of 100 and 300mg and temperatures of 25 and 35°C. The adsorption parameters were analyzed statistically using modeling polynomial equations and a cumulative normal probability plot. The results indicated the higher quantitative preference of the chitosan for Cu(II) in relation to Co(II). Increasing the chitosan mass decreases the adsorption/mass ratio (molg−1) for both metals. The principal effect of the temperature did not show statistical importance. The adsorption thermodynamic parameters, namely Δads H, Δads G and Δads S, were determined. Exothermic and endothermic results were found in relation to a specific factorial design experiment. A comparison of Δads H values was made in relation to some metal–adsorbent interactions in literature. It is suggested that the adsorption thermodynamic parameters are determined by the influence of the principal and interactive experimental parameters and not by the temperature changes alone. [Copyright &y& Elsevier]

Abstract: Adsorption (at a low temperature) of nitrogen on the protonic zeolite H-FER results in hydrogen bonding of the adsorbed N2 molecules with the zeolite Si(OH)Al Brønsted acid groups. This hydrogen bonding interaction leads to activation, in the IR, of the fundamental Ning mode, which appears at 2331cm−1. From the infrared spectra taken over a temperature range, while simultaneously recording integrated IR absorbance, temperature and nitrogen equilibrium pressure, the thermodynamics of the adsorption process was studied. The standard adsorption enthalpy and entropy resulted to be ΔH°=−20(±1)kJmol−1 and ΔS°=−131(±10)Jmol−1 K−1, respectively. [Copyright &y& Elsevier]

Abstract: A mesoporous hybrid gel is prepared with tetraethoxysilane (TEOS) and bis(trimethoxysilyl)hexane (TSH) as precursors without using any templating agent. Nitrogen sorption, TG-DTA, FTIR, and point of zero charge (PZC) measurement are used to characterize the gel. The gel has a specific surface area of 695 m2 g−1 with a pore size of 3.5 nm, a pore volume of 0.564 cm3 g−1, and a point of zero charge (PZC) of 6.2. The kinetics and thermodynamics of bromophenol blue (BPB) adsorption by the gel in aqueous solution are investigated comprehensively. The effects of initial BPB concentration, pH, ionic strength, and temperature on the adsorption are investigated. Kinetic studies show that the kinetic data are well described by the pseudo-second-order kinetic model. Initial adsorption rate increases with the increase in initial BPB concentration and temperature. Adsorption activation energy is found to be 62.5–67.5 kJ mol−1 depending on the initial BPB concentration. Internal diffusion appears to be the rate-limiting step for the adsorption process. The equilibrium adsorption amount increases with the increase in the initial BPB concentration, solution acidity, and ionic strength, but decreases with the increase in temperature. The thermodynamic analysis indicates that the adsorption is spontaneous and exothermic. The adsorption isotherms can be well described with Freundlich equation indicating the heterogeneity of the hybrid gel surface. Electrostatic and hydrophobic interactions are suggested to be the dominant mechanism for adsorption. [Copyright &y& Elsevier]

Abstract: The equilibrium moisture curves of the two-phase solid olive oil extraction by-product (SOB) are used in order to get a complete understanding of the relationship between water and the solid components within the solid. For that purpose, fundamental thermodynamics of an idealised system, in which the solid acts as an inert adsorbent and the water vapour behaviour corresponds to an ideal gas that adsorbs over the solid surface, were employed to find out an estimation of the most important thermodynamic parameters related to the water adsorption process. The net isosteric heat and entropy of water adsorption were calculated and revealed that only the water molecules in the monolayer, which are very close to the solid surface, are intensively attracted by the adsorbent agent. The interaction energy in the monolayer reached a maximum at 19kJmol−1, in accordance with the typical energy amount involved in physisorption phenomena. The behaviour of the water spreading pressure versus water activity was also studied, yielding in the equilibrium moisture curves in terms of spreading pressure from which it is possible to compute the net integral values of the enthalpy and entropy involved in water adsorption. These integral quantities represent in fact a real quantification of the equilibrium enthalpy and entropy of the adsorbed water molecules. The analysis of these data provides all the information concerning the degree of association between water and the two-phase SOB, the different energetical binding levels of the water and the quantity of energy required to remove this water in a drying treatment of this product. [Copyright &y& Elsevier]

Abstract: Present study deals with the adsorption of phenol on carbon rich bagasse fly ash (BFA) and activated carbon-commercial grade (ACC) and laboratory grade (ACL). BFA is a solid waste obtained from the particulate collection equipment attached to the flue gas line of the bagasse-fired boilers of cane sugar mills. Batch studies were performed to evaluate the influences of various experimental parameters like initial pH (pH0), contact time, adsorbent dose and initial concentration (C 0) on the removal of phenol. C 0 varied from 75 to 300mg/l for the adsorption isotherm studies and the effect of temperature on adsorption. Optimum conditions for phenol removal were found to be pH0 ≈6.5, adsorbent dose ≈10g/l of solution and equilibrium time ≈5h. Adsorption of phenol followed pseudo-second order kinetics with the initial sorption rate for adsorption on ACL being the highest followed by those on BFA and ACC. The effective diffusion coefficient of phenol is of the order of 10−10 m2/s. Equilibrium isotherms for the adsorption of phenol on BFA, ACC and ACL were analysed by Freundlich, Langmuir, Temkin, Redlich–Peterson, Radke–Prausnitz and Toth isotherm models using non-linear regression technique. Redlich–Peterson isotherm was found to best represent the data for phenol adsorption on all the adsorbents. The change in entropy (ΔS°) and heat of adsorption (ΔH°) for phenol adsorption on BFA were estimated as 1.8MJ/kgK and 0.5MJ/kg, respectively. The high negative value of change in Gibbs free energy (ΔG°) indicates the feasible and spontaneous adsorption of phenol on BFA. The values of isosteric heat of adsorption varied with the surface loading of phenol. [Copyright &y& Elsevier]

Abstract: Adsorption thermodynamics of interacting particles adsorbed on nanotube bundles is studied through a lattice-gas model and Monte Carlo simulations. The adsorbent is modeled as one-dimensional channels of equivalent adsorption sites arranged in a triangular cross-sectional structure. Two kinds of lateral interaction energies have been considered: (1) , interaction energy between nearest-neighbor particles adsorbed along a single channel and (2) , interaction energy between particles adsorbed across nearest-neighbor channels. We focus on the case of repulsive transversal interactions , for which a rich variety of ordered phases are observed in the adlayer, depending on the value of the parameters ( being the Boltzmann constant) and . The influence of each ordered structure on adsorption isotherms and differential heat of adsorption has been analyzed and discussed in the context of the lattice-gas theory. [Copyright &y& Elsevier]

Abstract: We investigate the kinetics and thermodynamics of brilliant blue FCF (BBF) adsorption on a mesoporous hybrid xerogel derived from tetraethoxysilane (TEOS) and propyltriethoxysilane (PTES) with cetyltrimethylammonium bromide (CTAB) as a templating agent. We study the effect of initial BBF concentration, temperature, pH, and ionic strength on the adsorption of BBF from aqueous solution. Kinetic studies show that the kinetic data are well described by the pseudo second-order kinetic model. Initial adsorption rate increases with the increase in initial BBF concentration and temperature. The internal diffusion appears to be the rate-limiting step for the adsorption process. The equilibrium adsorption amount increases with the increase in initial BBF concentration, temperature, solution acidity, and ionic strength. The thermodynamic analysis indicates that the adsorption is spontaneous and endothermic. Electrostatic attraction and hydrophobic interaction are suggested to be the dominant interactions between dye and the xerogel surface. [Copyright &y& Elsevier]

The adsorption isotherms for sodium dodecyl sulfate (SDS) adsorption from aqueous solutions (pH 4.69) onto wool/water interfaces at 15, 25 and 35°C, respectively, are satisfactorily expressed in linear plots based on a stoichiometric displacement model of adsorption (SDM-A). The studies on adsorption parameters of SDM-A suggest that assembly of SDS molecules on the wool/solution interface follows the partition regularity and stoichiometric displacement relation between the two phases based on the SDM-A. The fact that the general displacement adsorption heats obtained in the calorimetric measurement and the enthalpies calculated by the thermodynamics of SDM-A in the presentation are well in accordance with each other shows that thermodynamic function fraction study of SDM-A is reliable. The studies on thermodynamic parameters and function fractions suggest that at the start of adsorption, the - SO4- groups occupy the sites from which the water molecules are released and simultaneously driven to the edges of alkyl chains closed to polar heads. The surface hydrophobic interactions increase in the way that the adsorbed SDS molecules on the surface favor to form bilayer micelles while every individual SDS molecule in the surface micelles may attach to surface first. The investigation of fluorescence probe of pyrene indicates that surface micelle formation begins in lower surface coverage while the aggregation numbers of micelles grow at high surface coverage. [Copyright &y& Elsevier]

Abstract: Adsorption of dihydrogen onto the zeolites Na-ZSM-5 and K-ZSM-5 renders the fundamental H–H stretching mode infrared active. The corresponding infrared absorption bands were found at 4101 and 4112cm−1 for H2/Na-ZSM-5 and H2/K-ZSM-5, respectively. Thermodynamic characterization of the adsorbed state was carried out by means of variable-temperature infrared spectroscopy; simultaneously measuring integrated band intensity, temperature and equilibrium pressure of the gas phase. For the H2/Na-ZSM-5 system, the standard adsorption enthalpy and entropy resulted to be ΔH° =−10.3 (±0.5)kJmol−1 and ΔS° =−121 (±10)Jmol−1 K−1. For H2/K-ZSM-5 corresponding values were −9.1 (±0.5)kJmol−1 and −124 (±10)Jmol−1 K−1, respectively. [Copyright &y& Elsevier]

Abstract: While the adsorption dynamics of surfactants is quantitatively understood, the formation of protein adsorption layers is in a premature state yet. The same is true for mixed protein–surfactant layers at liquid interfaces. However, there are first theoretical models which allow a quite good description for mixtures of proteins and nonionic surfactants. For such surface layers, theoretical models (for the equilibrium state as well as for the adsorption kinetics) have to be developed yet. [Copyright &y& Elsevier]

The adsorption equilibrium isotherms of three aromatic sulfonic acid compounds, 2-naphthalenesulfonic acid, p-toluenesulfonic acid and p-chlorobenzenesulfonic acid, from aqueous solutions by maeroporous weak base anion exchanger within the temperature range of 293 K-313 K were obtained. Several isotherm equations were correlated with the equilibrium data, and the experimental data was found to fit the three-parameter Redlich-Peterson equation best within the entire range of concentrations. The study showed that the hydrophobicity of solute has distinct influence on adsorption capacity of the anion exchanger for the aromatic sulfonic acid. Moreover, estimations of the isosteric enthalpy, free energy, and entropy change of adsorption were also reported. The positive isosteric enthalpy and entropy change for adsorption indicate an endothermic and entropy driven process in the present study. [ABSTRACT FROM AUTHOR]

The adsorption of Congo red from solution was carried out using calcium-rich fly ash with different contact times, concentrations, temperatures, and pHs. While the amount of dye adsorbed per unit weight of fly ash increases with increasing concentration and temperature, it decreases slightly with increasing pH. The adsorption was between 93 and 98% under the conditions studied. Kinetic studies showed that the adsorption process obeyed the pseudo-second-order kinetic model. It was also determined that the adsorption isotherm followed Freundlich and Dubinin–Radushkevich models. From thermodynamic studies, it was seen that the adsorption was spontaneous and endothermic. Desorption studies suggested that desorption was 29.18% in the presence of 0.1 N HCl and was 47.21% in the presence of CH3COOH (50% v/v). This indicated that most of the dye was held by fly ash via chemisorption as well as ion exchange. Furthermore, FTIR study also shows that a chemisorption process occurs between CR and fly ash, probably indicating dye/fly ash complexing. [Copyright &y& Elsevier]

The ability of Japanese cedar (Cryptomeria japonica) bark to remove Cr(VI) from aqueous solutions was investigated. The research parameters included the solution pH, temperature, and initial concentration of Cr(VI) in solution. The removal of Cr(VI) was highly solution pH dependent and adsorbate concentration dependent, and mainly governed by physicochemical adsorption under the weak acidic conditions studied (initial solution pH ≥ 3). However, the reduction of Cr(VI) to Cr(III) occurred extensively at low solution pH (initial solution pH ≤ 2). The equilibrium data at different temperatures fit well in the Langmuir isotherm model. The endothermic nature of the adsorption was confirmed by the positive value of enthalpy change (18.9 kJ mol−1). The positive value of entropy change (65.2 J mol−1 K−1) suggested the increased randomness at the solid–solution interface during the adsorption. The studies showed that Japanese cedar bark can be used as a cost-effective adsorbent for the removal of Cr(VI) from wastewater. [ABSTRACT FROM AUTHOR]

A study on the interactions between silica and elastomers typically used in tire tread production has been carried out by inverse gas chromatography (IGC) and image analysis aided transmission electron microscopy (TEM/AIA). At infinite dilution, IGC has been performed using precipitated silica as the stationary phase to determine its surface properties and to calculate the adsorption free energy and enthalpy of low molecular weight analogues of elastomers, used as the eluates. Vulcanized samples based on different matrices employed in tire formulations, i.e., natural rubber, butadiene rubber, and styrene-butadiene rubber, have been investigated by TEM/AIA to determine the dispersion of the filler within the matrix as well as to achieve quantitative information on aggregate size and shape distribution of silica and, consequently, on the polymer-filler interactions. A comparison between thermodynamic predictions deduced by IGC and the results from morphological analysis concerning filled compounds shows a very satisfactory agreement. [ABSTRACT FROM AUTHOR]

In this paper the effect of additives on adsorption of sodium oleate on kaolinite in aqueous solution is examined. Kaolinite with specific surface area 20.2 m[SUP2] /g and zero point of charge 2.0 is used as adsorbent. Adsorption of sodium oleate on kaolinite has been investigated with or without additives such as NaCI, n-butanol, npenanol, PHPAM (partially hydrolyzed polyacrylamide) and AEO (a nonionic polyoxyethylene surfactant. The adsorption isotherm of sodium oleate, which is different from that of other anionic surfactants on kaolinite, showed two plateaus (i.e. LS type). But it is interesting that an adsorption maximum is found in the isotherms when these additives are added in the liquid/solid adsorption system. Basically, three different adsorption behaviors have been found when the additives are added. The adsorbed amount of sodium oleate decreases considerably when alcohols are added to the solution, while the amount increases when NaCI or PHPAM is added; only a slight alteration is observed when AEO is added to the solution. The adsorption process on kaolinite is found to follow a two-step first-order kinetic rate equation with two different (k[SUB1] and k[SUB2]) rates constants. Values of the energy of activation Ea[SUB1] and Ea[SUB2] are calculated from the slope of the linear plot of - Ink against 1/T for different systems. The enthalpies of activation (ΔH), entropies of activation (ΔS) and free energies of activation (ΔG) are calculated by using thermodynamic equations. It is found that there is an entropy-enthalpy compensation effect in the adsorption process from the values of ΔH and ΔS. These results are usefull in controlling the surfactant's adsorbent loss in tertiary oil recovery. [ABSTRACT FROM AUTHOR]

In order to remove toxic graphene oxide (GO) from aqueous solution, attapulgite (ATP) was used as adsorbent to recycle it by adsorption. In this paper, the effects of different pH, adsorbent mass, GO concentration, time and temperature on the adsorption of GO by attapulgite were studied, and the adsorption performance and mechanism were further explored by XRD, AFM, XPS, FTIR, TEM and SEM tests. The results show that when T = 303 K, pH = 3, and the GO concentration is 100 mg/L in 50 mL of aqueous solution, the removal rate of GO by 40 mg of attapulgite reaches 92.83%, and the partition coefficient K d reaches 16.31. The adsorption kinetics results showed that the adsorption equilibrium was reached at 2160 min, and the adsorption process could be described by the pseudo-second-order adsorption equation, indicating that the adsorption process was accompanied by chemical adsorption and physical adsorption. The isotherm and thermodynamic parameters show that the adsorption of GO by attapulgite is more consistent with the Langmuir isotherm model, and the reaction is a spontaneous endothermic process. The analysis shows that attapulgite is a good material for removing GO, which can provide a reference for the removal of GO in an aqueous environment.