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We studied the adsorption of Brilliant Yellow (BY) from aqueous solutions onto sepiolite and determined the adsorption equilibrium isotherms. We applied pseudo-first-order and pseudo-second-order kinetic models; the adsorption of BY onto sepiolite was best described by the pseudo-second-order kinetic model. The experimental data obtained at different temperatures were analyzed using various isotherm models; the Koble-Corrigan isotherm model provided the best fits for the BY adsorption data at all temperatures. The thermodynamic parameters of the BY adsorption onto sepiolite indicated that the adsorption process is spontaneous and exothermic in nature. [ABSTRACT FROM AUTHOR]

The optimal activated carbon produced from Prosopis africana seed hulls (PASH-AC) was obtained using the impregnation ratio of 3.19, activation temperature of 780 ° C and activation time of 63 min with surface area of 1095.56 m2/g and monolayer adsorption capacity of 498.67 mg/g. The adsorption data were also modeled using five various forms of the linearized Langmuir equations as well as Freundlich and Temkin adsorption isotherms. In comparing the legitimacy of each isotherm model, chi square ( x 2 ) was incorporated with the correlation coefficient ( R 2 )to justify the basis for selecting the best adsorption model. Langmuir-2 > Freundlich > Temkin isotherms was the best order that described the equilibrium adsorption data. The results revealed pseudo-second-order to be the most ideal model in describing the kinetics data. [ABSTRACT FROM AUTHOR]

In this study, bentonite originating from Turkey (Eskişehir province) and activated carbon obtained from grapeseed were used as adsorbents for the removal of lead (Pb2+) and copper (Cu2+) ions from aqueous solutions. Experiments were performed in single- and binary-ion systems at constant temperature of 298 K and pH value of 5. In order to describe the adsorption mechanism Langmuir, Freundlich and Temkin isotherms were used. The total adsorption capacity values of adsorbents were compared. It was observed that the total adsorption capacity values were changed depending on the type of adsorbent used, type of metal ion and interaction between metal ions. [ABSTRACT FROM PUBLISHER]

Multi-walled carbon nanotubes (MWCNTs) and powder-activated carbon (PAC) were used as adsorbents for adsorption of nitrofurazone, a veterinary medicine, from aqueous solutions. The adsorbents were characterized using FTIR transform infrared spectroscopy, N2adsorption/desorption isotherms, and scanning electron microscopy. The effects of initial pH, contact time, and temperature on adsorption capacity of the adsorbents were investigated. For MWCNT and PAC, the result showed that when the pH value was ranged from 2.0 to 10.0, the dosage of adsorbent was 0.02 g, and adsorptive time is 4 hours, the removal efficiencies for nitrofurazone were 96.8% and 94.7%, and the corresponding maximum capacities at 283 K were close to 50.8 mgg−1and 59.9 mgg−1, respectively. For nitrofurazone, the pseudo-second-order kinetic model provided the best fit to the experimental data. The Boyd model indicated the mechanism for adsorption processes was mainly external mass transfer, while the effect of particle internal diffusion was relatively weak. Liu model could best fit to the experimental data of isothermal adsorption. The data of adsorption thermodynamics showed that the adsorption process was spontaneous. [ABSTRACT FROM PUBLISHER]

Methane storage was studied on the wet activated carbons by hydrate formation in the mesopore structures. Coconut shell was used as a raw material for preparation of the activated carbon samples. These highly mesoporous samples were prepared by the combination of both physical and chemical activation processes. After wetting the adsorbents with a constant water/carbon weight ratio (R) close to 1, the isotherms were obtained at 2°C up to the pressure of 80 bars. Wetted carbons exhibited stepwise isotherms at the critical pressure in the pressure range of 25–50 bars depending on the activated carbon samples. At this critical pressure, hydrate formation took place slowly. The amounts of methane uptake at 80 bars were obtained ranging from 14.9 to 24.8 mmol.g–1based on the dry adsorbent for different samples. By considering the density of activated carbon samples, the amounts of methane storage varied in the range of 185–237 V/V. [ABSTRACT FROM PUBLISHER]

Cr(VI) adsorption from aqueous solutions on Mg-Al hydrotalcite and Mg-Al hydrotalcite-gibbsite with Al/(Al+Mg) ratios (R) of 0.3 and 0.6 (MgAlHTR = 0.3and MgAlHTGR = 0.6) was investigated as a function of the pH and chromium concentration. The results showed that the maximum Cr(VI) adsorption by Mg-Al compounds do not depend on the value of R at pH 7. In addition, the chromate equilibrium sorption capacity for MgAlHTGR = 0.6is at least 4.8 times higher than that for MgAlHTR = 0.3at pH 5. The Cr(VI) maximum capacities of MgAlHTR = 0.3and MgAlHTGR = 0.6at pH 7 were similar, 6.5 and 6.8 mgCr(VI)/g, respectively. [ABSTRACT FROM PUBLISHER]

The adsorption of FD&C red 2 and FD&C yellow 5 onto chitosan films (CFs) was evaluated by equilibrium isotherms, thermodynamics, and kinetic studies. The effects of temperature (298–328 K), initial dye concentration (50–300 mg L−1), stirring rate (50–350 rpm), and contact time (0–120 min) were investigated at pH of 2.0 and 100 mg L−1of CFs. The dye concentration was determined by spectrophotometry. Freundlich and Langmuir models were used to represent the equilibrium data. The Langmuir model was the more adequate to represent the equilibrium data (R2 > 0.99 and average relative error <2.50%) and the maximum adsorption capacities were 494.13 and 480.00 mg g−1for FD&C red 2 and FD&C yellow 5, respectively, obtained at 298 K. TheRLvalues ranged from 0.044 to 0.145. The adsorption was exothermic, spontaneous, and favorable. For the FD&C red 2, 90% of saturation was attained at 120 min and the Elovich model was the more appropriate. For the FD&C yellow 5, 95% of saturation was attained at 20 min and the pseudo first-order model was the more adequate to fit the kinetic data. CFs were easily separated from the liquid phase after the adsorption process, providing benefits for industrial applications, and its application range can be extended for azo dyes. [ABSTRACT FROM PUBLISHER]

Analysis of differential pore-volume distribution (PVD) patterns of commercial clinoptilolite fractions [(<125 µ (Z8; fine), 125–250 µ (Z9; medium), and >250 µ (Z10; coarse)] has been conducted experimentally using an analyzer to measure the nitrogen (N2) adsorption isotherms. The differential PVDs of the clinoptilolite fractions were calculated from the hysteresis loop according to the adsorption and desorption curves of the Barret, Joyner, and Halenda (BJH) model. The adsorption and desorption cycles of BJH produced heterogeneous as well as dissimilar differential PVD patterns with assorted peaks. While the adsorption curve has prolonged up to 300 nm, the desorption cycle was confined up to 190-nm pore diameter only. In the adsorption cycle, all the clinoptilolite fractions displayed U-shaped curves and had a differential pore volume in the range of 3 × 10–3to 8 × 10–3 cm3/g A° in the micropore region with a sole peak at 1.75 nm for the fine fraction (Z8). In contrast, the curves were linear in the mesoporous region for all the fractions, with the fine fraction (Z8) having the greatest differential pore volume, whereas the other two fractions were almost parallel to each other. The desorption cycle has revealed an inverted V-shape curve with no definite patterns for the microporous region. Although the adsorption cycle could ascertain the micropore region, the desorption cycle was unable to do so. It was apparent from the differential PVD of the BJH model that fraction size has a major role in determining the textural properties of clinoptilolite fractions. [ABSTRACT FROM AUTHOR]

The purpose of this work is to evaluate the valorization of agricultural waste, wheat straw (WS) and corn cob leaves (CCLs) as textile dye adsorbents. Physico-chemical and superficial characteristics of the agricultural wastes, together with the interactions with the CI Basic Violet 4 (BV4) dye, were investigated by means of the determination of the isotherm adsorption at different temperatures. The morphological characterization showed that the solid surface is coarse with a low pore level. However, through Fourier transformed infrared analysis, the presence of carboxylic and hydroxylic acid groups and hydrophobic methyl groups was detected. The concentration of acid groups is determined by the Boehm method and was found to be 1.00 and 0.89 meq/g for WS and CCLs, respectively. The point zero charge for each adsorbent was 5.76 and 4.08. Adsorption experimental data presented a better-fit Langmuir model, indicating that adsorption occurred in a monolayer with preferential interaction. The maximum adsorption capacity was determined to be 70.0–89.0 and 47.0–68.0 mg/g for CCLs and WS, respectively. The thermodynamic analysis of the Langmuir parameter b showed that the adsorption of the BV4 dye is spontaneous and exothermic with adsorption energies of 14.43 and 5.58 KJ/mol for CCLs and WS, respectively. [ABSTRACT FROM PUBLISHER]

We have studied the adsorption of argon at 87 K in slit pores of finite length with a smooth graphitic potential, open at both ends or closed at one end. Simulations were carried out using conventional GCMC (grand canonical Monte Carlo) or kMC (kinetic Monte Carlo) in the canonical ensemble with extremely long Markov chain, of at least 2 × 108configurations; selected simulations with much longer Markov chains do not show any change in the results. When the pore width is in the micropore range (0.65 nm), type I isotherms are obtained for both pore models and for both simulation methods. However, wider pores (1, 2 and 3 nm in width) all exhibit hysteresis loops in the GCMC simulations, while in the canonical ensemble simulations, the isotherms pass through a sigmoid van der Waals type loop in the transition region. This loop locates the true equilibrium transition. For the pores with one closed end, this transition is close to, or coincides with, the adsorption branch of the GCMC hysteresis loop, but for the open-ended pores, it is more closely associated with the desorption branch. In a separate study of adsorption hysteresis in an infinitely long slit pore, using both simulation techniques, the van der Waals loop follows the adsorption branch of the GCMC isotherm to the transition, then reverts to a long vertical section that falls midway between the two hysteresis branches and finally moves to the desorption transition close to the evaporation pressure. An examination of molecular distributions inside the pores reveals two coexisting phases in the canonical simulations, whereas in the grand canonical simulations, the molecules are uniformly distributed along the length of the pores. [ABSTRACT FROM AUTHOR]

Waste sugar beet pulp has been used as adsorbent for the removal of a hazardous cationic dye, Basic violet 16, from its aqueous solution. Adsorption of the dye was studied as function of time, pH of the solution, dosage of the adsorbent, sieve size of the particles, concentration of the dye, and temperature. The initial pH of the dye solution did not affect the chemistry of the dye molecule and the surface of beet pulp. Langmuir and Freundlich adsorption isotherms were successfully employed, and on the basis of these models, the thermodynamic parameters were evaluated. Adsorption of Basic violet 16 on beet pulp was found to be an exothermic reaction. Time contact studies showed that more than 80% adsorption of the dye is achieved in less than 1 h. Kinetics investigations confirmed both pseudo-first-order and pseudo-second-order behaviors; on the other hand, it shows that the intraparticle diffusion step is not the only rate-controlling step in all concentrations. [ABSTRACT FROM AUTHOR]

The biosorption of cyanide ions from aqueous solution by bagasse was studied in a batch adsorption system with pH, contact time, cyanide ion concentration, metal ion concentration, and adsorbent dosage as variables. XRD, FT-IR spectroscopy, CHN, proximate, ultimate, and TG/DTG thermal analyses were used for the characterization of bagasse. The biosorption capacities and rates of biosorption of cyanide ions onto bagasse were evaluated. The Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Biosorption isothermal data were interpreted by the Langmuir model followed by the Freundlich model with maximum adsorption capacity of 98% of cyanide ion on bagasse. The kinetic experimental data were properly correlated with the first- and second-order kinetic model. [ABSTRACT FROM AUTHOR]

In the present study, adsorption capacity of mercury(II) on β-zeolite, zeolite Y, and mordenite is investigated. It has been observed that removal rate of Hg(II) is better with zeolite Y than β-zeolite and mordenite, whereas, adsorption capacity of β-zeolite is found to be more than that of zeolite Y and mordenite. Five equilibrium isotherms have been tested to fit the adsorption data. The kinetic data are analyzed using the pseudo-first order, pseudo-second order, and diffusion models. The Freundlich isotherm model shows better fit for β-zeolite and zeolite Y, whereas, in the case of mordenite, Temkin isotherm fits the data well. The kinetic data of adsorption of Hg(II) on β-zeolite, zeolite Y, and mordenite fit well with pseudo-second order. Diffusion studies show that the adsorption of mercury on β-zeolite and zeolite Y are intraparticle diffusion controlled, and mordenite is film-diffusion controlled. [ABSTRACT FROM AUTHOR]

In this study, the adsorption behavior of Basic Red 46 (BR 46) in aqueous solutions by single-walled carbon nanotube (SWCNTs) and functionalized SWCNTs having covalent attachments of carboxylic group (SWCNT-COOH) surface as adsorbents were investigated. The adsorption equilibrium data were analyzed using various adsorption isotherms, and the results have shown that adsorption behavior of BR 46 could be described reasonably well by a generalized isotherm. Kinetic studies indicated adsorption of BR 46 by SWCNTs and SWCNT-COOH surfaces follows a pseudo-order model. The maximum adsorption capacities of BR46 by SWCNTs and SWCNT-COOH surfaces are reported at 298 K, 38.35 and 49.45 mg/g, respectively. The adsorption of BR 46 depends on the initial pH of the solution with maximum uptake occurring at about pH 9. Decrease in the absolute value of ΔG0 with increasing temperature indicates that higher temperatures hardship the adsorption. The negative value of ΔH0 reflects an exothermic adsorption and indicates that the adsorption is favored at low temperature. The negative entropy states that the adsorption of BR 46 by SWCNT-COOH and SWCNTs surfaces are orderly adsorbed by the surfaces. [ABSTRACT FROM AUTHOR]

Amino-functionalized Zr-MOF (amino-Zr-MOF) was synthesized using 2-aminoterephthalic acid as an organic linker. The physicochemical properties of the material were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and N2adsorption to understand its crystalline structure, morphology, thermal stability, and porous structure. CO2adsorption isotherms on amino-Zr-MOF were obtained at 1 atm and at different temperatures. In addition, CO2and CH4adsorption at high pressure (up to 10 atm) was also measured. CO2adsorption capacity on amino-Zr-MOF was 9 mmol/g at 988 kPa, 0°C, while CH4adsorption capacity was 3.7 mmol/g at 900 kPa, 0°C. The heat of CO2adsorption on amino-Zr-MOF was estimated to be 29.4 kJ/mol. Continuous column tests of CO2adsorption were performed at different concentrations of CO2in nitrogen at 20 mL/min and 0.7 g adsorbent and total adsorbed amounts of CO2within the column during the breakthrough time were calculated to be 4.55, 5.26 and 4.37 mmol/g at 10%, 15% and 20%CO2, respectively. [ABSTRACT FROM PUBLISHER]

This study evaluated the adsorption capacity of ethylenthiourea (ETU) and 1H-1,2,4-triazole (1,2,4-T) for two commercial activated carbons: charcoal-powdered activated carbon (CPAC) and bovine bone-powdered activated carbon (BPAC). The tests were conducted at a bench scale, with ETU and 1,2,4-T diluted in water, for isotherm and adsorption kinetic studies. The removal of the compounds was accompanied by a total organic carbon (TOC) analysis and ultraviolet (UV) reduction analysis. The coals were characterized by their surface area using nitrogen adsorption/desorption, by a scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS) and by a zero charge point analysis (pHpcz). The results showed that adsorption kinetics followed a pseudo-second-order model for both coals, and the adsorption isotherms for CPAC and BPAC were adjusted to the Langmuir and Freundlich isotherms, respectively. The CPAC removed approximately 77% of the ETU and 76% of the 1,2,4-T. The BPAC was ineffective at removing the contaminants. [ABSTRACT FROM PUBLISHER]

This paper reports the monolayer characteristics of cationic octadecylamine (ODA) on both distilled water and aqueous Erythrosine B (EB) dye solution at the air-water interface. From the pressure-area isotherms at various pHs, EB anions in the subphase were found to interact with the insoluble monolayer of cationic octadecylamine (ODA). Adsorption kinetics shows that the amount of dye adsorbed depends on the concentration of the dye present in the subphase. It was observed that the adsorption process mainly occurred due to the electrostatic interaction between the cationic amino group of long chain amine and the anionic part of EB. The spectroscopic characteristics of the mixed LB films, solution, have been compared using UV-vis absorption and fluorescence spectroscopic data. These studies indicate the formation of aggregates in the thin films. Scanning electron microscopic study certainly confirms the presence of aggregates of EB dye in the (ODA-EB) mixed LB films. [ABSTRACT FROM PUBLISHER]

This study provides an electrocoagulation process for the removal of metals such as cobalt, copper, and chromium from water using magnesium as anode and galvanized iron as cathode. The various parameters like pH, current density, temperature, and inter electrode distance on the removal efficiency of metals were studied. The results showed that maximum removal efficiency was achieved for cobalt, copper, and chromium with magnesium as anode and galvanized iron as cathode at a current density of 0.025 A dm−2 at pH 7.0. First- and second-order rate equations were applied to study adsorption kinetics. The adsorption process follows second-order kinetics model with good correlation. The Langmuir and Freundlich adsorption isotherm models were studied using the experimental data. The Langmuir adsorption isotherm favors monolayer coverage of adsorbed molecules for the adsorption of cobalt, copper, and chromium. Temperature studies showed that adsorption was endothermic and spontaneous in nature. [ABSTRACT FROM PUBLISHER]

The technical feasibility of utilization of fly ash as a low-cost adsorbent for the removal of metals from water has been studied. For two types of fly ashes, the retention capacities of copper, lead, and zinc metal ions have been studied. Contact time, initial concentration, and pH have been varied and their effect on retention mechanism has been studied. The dominant mechanisms responsible for retention are found to be precipitation due to the presence of calcium hydroxide, and adsorption due to the presence of silica and alumina oxide surfaces in the fly ash. First-order kinetic plots have revealed that the rate constant increases with increase in the initial concentration and pH. Langmuir adsorption isotherms have been plotted to study the maximum adsorption capacities for metal ions considered under different conditions. X-ray diffraction studies revealed the formation of new peaks corresponding to respective metal ions precipitates under alkaline conditions. [ABSTRACT FROM PUBLISHER]

The removal of some of pollutants including catechol, 3-methylcatechol, 3-methoxycatechol, and 2,3-dihydroxybenzoic acid by adsorption onto activated carbon cloth (ACC) at 35.0 ± 0.1°C was investigated. The equilibrium experimental data were fitted to Langmuir, Freundlich, Temkin, Langmuir-Freundlich, and Redlich-Peterson isotherms. Also the kinetic experimental data were fitted to the pseudo-first-order and pseudo-second-order kinetic models. It was found that the pseudo-second-order model describes the kinetic of adsorption better than the other one. By comparing the obtained results with the previously reported data, it can be concluded that ACC is a high efficient adsorbent for removal of phenolic compounds from aqueous solutions. [ABSTRACT FROM AUTHOR]

The present study explores the adsorption potential of Mentha piperita (an agricultural solid waste) to remove Cu2+ from aqueous solution. Different operational parameters such as the effect of pH, surfactant, equilibrium time, temperature, and initial metal ion concentrations were studied. Maximum adsorption of Cu2+ took place at pH range 5.0. Nearly 180 minutes are required to gain sorption equilibrium. The maximum adsorption capacity of mentha was 72.0 mg g−1 for Cu2+. FTIR analysis pointed out the involvement of amine (–NH2) and carboxylic (–COOH) groups in the adsorption process. Simple Langmuir and Freundlich isotherm models were used to explain the sorption phenomenon. The adsorption dependence of Cu2+ on temperature was investigated and the thermodynamic parameters ΔS0, ΔH0, and ΔG0 were calculated. The activation energy of the Cu2+ adsorption was calculated using the Arrhenius equation. The desorption of the adsorbent was found to be more than 90% by 0.1 M NaCl. [ABSTRACT FROM AUTHOR]

In this study, the removal of BTEX (benzene, toluene, ethylbenzene, p-xylene and o-xylene) from aqueous solution using Moringa oleifera seed cake (MOSC) was investigated. The effect of parameters such as contact time, pH and initial BTEX concentration were studied to optimize the conditions for maximum removal. Maximum removal values of 75±1%, 85±2%, 86±2%, 88±2% and 87±1% were obtained for benzene, toluene, ethylbenzene, p-xylene and o-xylene, respectively, at pH 7.0, with a 20 min contact time for an adsorbent dose of 10 g L−1 of 1 mg L−1 BTEX concentration. The adsorption data fitted the Langmuir and Freundlich adsorption isotherms. The capacity of MOSC to adsorb BTEX was compared with that for a commercial activated carbon. The results from the two methods were not significantly different (judged by t-test at 95% confident interval). A low cost, easy purchase and the satisfactory experimental results indicated that MOSC is a promising natural material for the removal of BTEX from aqueous solution. [ABSTRACT FROM PUBLISHER]

In the present study, the processes of adsorption of denim blue by Fe-zeolitic tuff from aqueous solutions at different pH values were determined. The parameters, Kd(n), Kd(i), Φn, pKa were accurately predicted by applying the linear model to sorption isotherms at different pH values of denim blue. Maximum removal of denim blue was observed at pH values between 3 and 5, where neutral species are the main components of the solution. The results indicate that pH has a pronounced effect on denim blue sorption depending on the conditions of the system. [ABSTRACT FROM PUBLISHER]

The competency of a locally available granular activated carbon (GAC) in removing color from textile wastewater was studied in a fluidized bed. The characteristics of the fluidized bed with different GAC particles were obtained. A reactive dye was used to prepare the colored water of different dye concentrations. The effects of the GAC particle size, velocity and initial concentration of the colored water on dye removal were investigated. Equilibrium adsorption isotherm and breakthrough curves were generated to determine adsorption characteristics of activated carbon as well as mass transfer coefficients of the fluidized bed. The results of these experiments showed that an increase in liquid velocity and a decrease in particle size increased the color removal. The experiments were also carried out with industrial effluent and the de-colorization achieved was satisfactory. The mass transfer coefficient calculated for the fluidized bed was very low, which suggests that the GAC used in the local industries, although less expensive, may not be economically viable for de-colorization of industrial effluent. [ABSTRACT FROM PUBLISHER]

The adsorption of N-vinylpyrrolidone from aqueous polyvinylpyrrolidone solution using bamboo-based activated carbon was studied. The adsorption isotherms of N-vinylpyrrolidone on the carbon were determined and modeled with the Langmuir, Freundlich, and Temkin models. The Langmuir model provides the best fitting for the equilibrium data and the maximum monolayer adsorption capacity was estimated to be 833.3 mg/g. The kinetics of the adsorption process of N-vinyulpyrrolidone were modeled using various equations including pseudo first-order, pseudo second-order, and intra-particle diffusion equations. The adsorption process follows the pseudo second-order kinetic model, suggesting that the adsorption mechanism is chemisorption. The activation energy for the adsorption is 86.4 kJ/mol. Thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy were determined. The positive value of enthalpy change indicates that the adsorption process is endothermic. [ABSTRACT FROM PUBLISHER]

Activated carbon has been applied for the adsorption of Alizarin Red S (ARS) from the waste water in a batch method to obtain high removal percentage. The influence of variables such as pH, temperature, ARS concentration, mass and size of adsorbent, and contact time on ARS removal percentage was investigated. Different kinetics, thermodynamics, and isotherm models were applied for fitting the experimental data. The adsorption process follows a pseudo second-order kinetic model with R 2 of 0.98 and Freundlich, Tempkin, and Dubinin-Radushkevich isotherm models with high determination coefficients (R 2) of 0.91, 0.98, and 0.98, respectively. High enthalpy (positive value), Gibbs free energy (negative value), and high entropy values shows the feasibility and the endothermic spontaneous nature of the removal process. [ABSTRACT FROM PUBLISHER]

The objective of this study is the preparation of various types of functionalized silica particles for the capture of Cu(II) ions. Amino-functionalized silica and hybrid chitosan/silica particles have been prepared by grafting silica with amino groups and/or adsorption of chitosan on the surface of silica to develop efficient adsorbents for heavy metals ions in water. The adsorption of Cu(II) on these materials was carried out at pH 5 at 298 K. The kinetics were evaluated utilizing pseudo-first-order and pseudo-second-order models. The best interpretation for equilibrium data was given by both Langmuir and Freundlich isotherm models. The adsorption kinetics followed the mechanism of the pseudo-second-order equation for all systems studied. This study demonstrates that the adsorption capacities for Cu(II) ions are more efficient for the bio-hybrid material compared to amino-functionalized silica. [ABSTRACT FROM AUTHOR]

The characteristics and kinetics of phosphate (P) adsorption on dewatered ferric-alum water treatment residuals (Fe-Al-WTRs) have been investigated. The existence of both aluminum (Al) and iron (Fe) in the residuals can result in significantly high P adsorption capacities. The P adsorption kinetics of Fe-Al-WTRs exhibited an initial rapid phase, followed by a slower phase. This could be described by three models, including a pseudo–first-order equation, a pseudo–second-order equation, and a double-constant rate equation. The latter was especially good for those runs with initial P concentrations of 500 and 1000 mg L−1. Both the Langmuir and Freundlich isotherms fit the experimental data well, particularly the Freundlich isotherm, which had a correlation coefficient of 0.9930. The maximum measured P adsorption capacity of Fe-Al-WTRs was 45.42 mg g−1, which is high when compared to those of most WTRs, as well as other reported adsorbents. The results also show that the P adsorption is a spontaneous endothermic process. Highest P adsorption capacities of Fe-Al-WTRs were measured at low pHs and a particle size range of 0.6 to 0.9 mm. [ABSTRACT FROM PUBLISHER]

The studies of kinetics and thermodynamics of adsorption of Pb(II), Cd(II) and Cu(II) ions in aqueous solutions on single-walled carbon nanotube (SWCNTs) and carboxylate group functionalized single-walled carbon nanotube (SWCNT-COOH) surfaces were by atomic absorption spectroscopy. The adsorption kinetics was well described by a pseudo-second-order rate model, while Langmuir, Freundlich, Redlich-Peterson (R-P) and Tempkin isotherms described the adsorption isotherms, and the adsorption thermodynamic parameters of equilibrium constant (K0), standard free energy (ΔG0), standard enthalpy (ΔH0) and standard entropy changes (ΔS0) were measured. The adsorption of Pb(II), Cd(II) and Cu(II) ions from aqueous solutions on SWCNTs and SWCNT-COOH. The values of ΔH0 and ΔG0 suggested that the adsorption of mentioned ions on SWCNT-COOH and SWCNT were endothermic and spontaneous. The adsorption of mentioned ions on SWCNT-COOH is more than SWCNTs surfaces. [ABSTRACT FROM AUTHOR]

The present study explores the ability of surfactant modified bamboo sawdust in removing zinc (II) ions from aqueous solutions. The modified bamboo sawdust is characterized by surface area analysis, Scanning Electron Microscope, and Fourier Transform Infrared and X-ray fluorescence analysis. Adsorption isotherm and kinetic models were used to study the adsorption characteristics of zinc (II) ions onto modified bamboo sawdust. The equilibrium adsorption isotherm data were fitted into the Langmuir and Freundlich adsorption isotherms. It was found that modified bamboo sawdust yielded maximum adsorption capacity of 111.12 mg/g at 50°C for zinc (II) ions. The kinetic data obtained at different initial concentrations were analyzed using first-order-reversible reaction, pseudo-first-order, and pseudo-second-order models. The results provide strong evidence to support the hypothesis of adsorption mechanism. [ABSTRACT FROM PUBLISHER]

Persimmon tannin was chemically modified to prepare a quaternary amine type of adsorption gel, named as quaternary amine modified persimmon tannin (QAPT) gel. The QAPT gel has been used to investigate the adsorption behaviors for Au(III), Pd(II), and Pt(IV) from HCl media. It was found that the gel exhibited good selectivity towards precious metals over a wide concentration range of HCl. However, it exhibited poor affinity towards base metals such as Cu(II), Fe(III), Ni(II), and Zn(II). The adsorption isotherms of the gel for precious metal ions were described by the Langmuir model. The maximum adsorption capacities for Au(III), Pd(II), and Pt(IV) were evaluated as 4.16, 0.84, and 0.52 mmol g−1, respectively. Although the anion exchange is the main mechanism for the adsorption of anionic species of Au(III), Pt(IV), and Pd(II), adsorption of Au(III) is followed by subsequent reduction, which results in the extraordinary high adsorption capacity for Au(III). Adsorption behavior of QATP gel for Au(III) was also compared to that of the persimmon tannin, the feed material. [ABSTRACT FROM PUBLISHER]

Red mud, an industrial by-product generated during the processing of bauxite ore, was investigated as an inexpensive and effective adsorbent for the adsorption of methylene blue from aqueous solution. Chemical and heat treatments were applied to the raw red mud. The effects of contact time, adsorbent amount, pH, temperature and initial dye concentration were investigated. The adsorption isotherm and kinetics of the raw and activated red mud were studied. Freundlich, Temkin and Dubinin-Radushkevich isotherms were obtained using concentrations of methylene blue ranging from 10 to 70 mg/L. The results indicated that the Dubinin-Radushkevich model provides the best correlation of the experimental data. The adsorption rate data were analysed according to the pseudo-first order kinetic, pseudo-second order kinetic, intraparticle diffusion kinetic and Elovich kinetic models. The pseudo-second order kinetic was the best fit kinetic model for the experimental data. [ABSTRACT FROM AUTHOR]

The adsorption of a synthetic textile dye (Remazol Brilliant Black Reactive) on cocoa pod husk-based activated carbon was investigated in batch process. The adsorbent prepared was characterized by gas adsorption surface analysis (Brunauer Emmett Teller, BET), scanning electron microscopy, and Fourier transform infrared spectroscopy. The effects of initial dye concentration, contact time, solution temperature, and solution pH were evaluated. Equilibrium data were fitted to Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models, the first being the best with maximum monolayer coverage of 111 mg g-1. Kinetic data were fitted into pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models; the pseudo second-order model provided the best correlation. Maximum adsorption was observed at pH 7. Standard free energy, standard enthalpy, and standard entropy were also calculated. The adsorption interaction was found to be endothermic and spontaneous. Both the mean free energy of adsorption and the activation energy show that the mechanism is by physisorption. [ABSTRACT FROM AUTHOR]

The present study explores the ability of a new adsorbent-conch shell powder (CSP) in removing Malachite Green from aqueous solutions. The effect of various process parameters, namely initial solution pH, temperature, initial dye concentration, adsorbent dose, and contact time was investigated. Adsorption equilibrium data were well described by the Langmuir isotherm with maximum adsorption capacity of 92.25 mg g-1 at 303 K. The kinetic data conformed to the pseudo-second-order kinetic model. A thermodynamic study showed the spontaneous nature and feasibility of the adsorption process. The results provide strong evidence to support the hypothesis of adsorption mechanism. [ABSTRACT FROM AUTHOR]

The adsorption behaviors of hydrophobic charge induction chromatography (HCIC) adsorbents with different functional ligands were investigated with immunoglobulin of egg yolk (IgY) as a model antibody. The adsorption isotherm and retention behavior in the column were studied, and the influences of the ligand structure and the pH on the adsorption were discussed. The results indicated that the pI of the target protein and pKa of HCIC ligand are the important parameter to determine the maximum adsorption pH of HCIC adsorbent, and high adsorption of IgY was found at pH 5 for all five adsorbents tested. Some differences could be found for different HCIC adsorbents, and the ligand structure influenced pH effect on the binding/elution of target protein. 2-mercapto-1-methyl-imidazole (MMI) ligand with a sulfone group showed a high adsorption capacity and strong pH-sensitivity, which would be more suitable for antibody purification. Moreover, the retention experiments indicated that IgY could be efficiently eluted from the adsorbents with 4-mercapto-ethyl-pyridine (MEP) or MMI as the ligand at acid conditions, while 2-mercapto-benzimidazole (MBI) ligand showed some difficulties on the elution. The retention study would help in defining not only the effective pH of elution for a given protein but also the elution efficiency of a given adsorbent. [ABSTRACT FROM AUTHOR]

Batch adsorption study was carried out to remove excess fluoride from water using pyrophyllite. Result showed that adsorption of fluoride was rapid in first 20 min and thereafter increased slowly to reach the equilibrium in about 2 hrs. About 85% removal efficiency was obtained within 2 hrs at an adsorbent dose of 4 g/L for initial fluoride concentration of 10 mg/L. Maximum fluoride adsorption takes place at pH 4.9. Thermodynamic parameters such as Gibb's free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes were determined for the adsorption process. Negative ΔH° value signified that the adsorption process was exothermic in nature. From the kinetic study it was found that fluoride adsorption by pyrophyllite followed pseudo-second-order kinetics with an average rate constant of 0.92 g/mg · min. Intraparticle diffusion model was studied to determine the rate limiting step of the adsorption process. The system followed the Langmuir isotherm with maximum adsorption capacity of 2.2 mg/g of fluoride. [ABSTRACT FROM AUTHOR]

We have used grand canonical Monte Carlo simulations to calculate the adsorption isotherms for H2, CH4, Xe and CF4 in Zn(tbip), a metal organic framework material having narrow 1D pores. Simulations show that Xe and CF4 form ordered solid structures when adsorbed in the pores. We have computed the self and transport diffusivities for H2, CH4, Xe and CF4 in Zn(tbip) using equilibrium molecular dynamics simulations. H2 has a diffusivity about one to two order of magnitude higher than CH4, indicating that transport selectivity for H2 over CH4 may be high. Xe and CF4 have very low diffusivities, in the order of 10- 9-10- 8 cm2/s. We have measured experimental adsorption isotherms for H2 at 77 and 298 K for pressures up to 60 bar in Zn(tbip). The H2 isotherms predicted from simulations are in reasonably good agreement with the experiments. [ABSTRACT FROM AUTHOR]

Nanoscale zero-valent iron (NZVI) is increasingly gaining interest as an efficient sorbent for various types of aqueous pollutants. This paper examined the potential for using laboratory synthesized NZVI particles (∼40 nm, 49.2 m2/g) to remove arsenite [As(III)] from drinking water. Batch experiments were conducted to study the removal kinetics, sorption isotherms, and the effect of anions or heavy metal ions on arsenic removal with NZVI. NZVI demonstrated very rapid adsorption and large capacity for the removal of As(III). The maximum As(III) adsorption capacity in batch experiments calculated by Langmuir adsorption isotherm was 76.3 mg/L of As(III)/g of NZVI. The reduction of As(III) followed a pseudo-first-order kinetics that the rate constants (k SA) was 3.42 mL/m2 min. This study suggests that implementation of NZVI for remediation of As(III) from drinking water is sufficient. [ABSTRACT FROM AUTHOR]

New poly[acrylamide/maleic acid/2-methacryloxy ethyl trimethylammonium chloride], poly[AAm/MA/METAC], super absorbent hydrogels (M1-M4) were prepared via microwave irradiated free radical solution polymerization using different compositions. According to swelling experiments, hydrogel M1 with higher METAC content gave relatively higher swelling percentage compared to other hydrogels. The hydrogel M1 was characterized by FT-IR, TGA, and SEM analysis. The influence of the uptake conditions such as pH, time, adsorbent dose and initial feed concentration on the metal ion binding capacity of hydrogel was also tested. Furthermore, the Langmuir and Freundlich adsorption isotherms were applied and they showed a good fit to the experimental data. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of soluble matter removal by a fluidized pellet bed (FPB) reactor, an experimental study was conducted using a laboratory-scale FPB device for treating synthetic wastewater under a condition of no activated sludge seeding and no dissolved oxygen supply so that the physicochemical functions of the FPB reactor could be evaluated. By using polyaluminium chloride and polyacrylamide as coagulants, it was found that most of the substances in the synthetic wastewater could not be effectively removed by conventional coagulation and sedimentation. A similar condition was observed in the start-up period of the FPB operation. However, as a steady FPB was formed usually after about 10 hours' operation, the influent COD, ammonia nitrogen and total phosphorous could be quickly and effectively entrapped by the fluidized grown particle layer. Because these substances were not coagulable under normal conditions, adsorption might have performed an important role in their removal. Through an adsorption experiment using the grown pellets as adsorbent and glucose as adsorbate without dosing coagulants, it was found that the process followed well the Freundlich adsorption isotherm. The adsorption was also confirmed to be reversible by a washing experiment. A scanning electron microscopy coupled with energy dispersive spectroscopy analysis of the pellets before and after washing showed that the elements of carbon and phosphorous in the outer layer of the pellets were easily desorbed. The study results can provide an explanation, other than the coagulation mechanism, for the removal of soluble matter by the FPB. [ABSTRACT FROM AUTHOR]

Chitosan derivatives, such as chitosan alpha-ketoglutaric acid (KCTS) and hydroxamated chitosan alpha-ketoglutaric acid (HKCTS), are prepared and their coordination behavior toward Ca(II) was studied. The adsorption isotherms were correlated by dc/dt = -kcn at 20°C, 30°C, 40°C, 50°C, and 60°C. By linear correlation, the shapes of the isotherm curves were similar to the kinetic function of 1/c = kt and the rate equation was dc/dt = -kc2; the activation energies were 13.31 and 14.76 kJ mol-1 for KCTS and HKCTS, respectively. The overall rate of Ca(II) adsorption is likely to be controlled by the chemical process. The coordination mechanism of chitosan derivatives with Ca(II) was studied by infrared and X-ray photoelectron spectroscopy. The results indicated that -NH- of KCTS was coordinated. Nitrogen of amino, oxygens of hydroxamic acid, and carbonyl in HKCTS coordinated with Ca(II). [ABSTRACT FROM AUTHOR]

The adsorptive performances of alkaline treated peat have been investigated for the removal of Pb(II), Co(II), and Ni(II) ions from aqueous solutions. The influence of initial metal ions concentration and equilibrium contact time was studied in a series of batch experiments, in comparison with natural peat. An increasing of adsorption capacity of alkaline treated peat was obtained for all studied heavy metals (23.07% - Pb(II), 23.53% - Co(II), and 26.19% - Ni(II)). The Langmuir isotherm model was the best model for the mathematical description of studied heavy metals adsorption on alkaline treated peat. A significant decrease of equilibrium contact time in case of alkaline treated peat was also found. The kinetics of Pb(II), Co(II), and Ni(II) uptake by alkaline treated peat followed the pseudo-second order mechanism. The FT-IR spectrometry analysis showed that carboxylic (-COO-) and hydroxyl (-OH) groups play an important role in the heavy metals binding process. The heavy metal could by easily eluted from the loaded adsorbent with 0.1 mol/L HCl and the adsorbent may be reused in several adsorption/desorption cycles. The alkaline treated peat has better adsorption characteristics for the removal of heavy metals from aqueous solutions, and the cost of this treatment is very low. [ABSTRACT FROM AUTHOR]

In this work, a new simple correlation has been derived for the prediction of the bulk porosity decline during nanofiltration of a salty (ionic) solution using the PVD membrane. This model has been developed on the basis of the adsorption of the cations available in the feed onto the membrane. Therefore, three adsorption isotherms were tested and fitted to the equilibrium adsorption data, and the Freundlich isotherm was subsequently realized as the best choice. The porosity model included two adjustable parameters which can be determined theoretically and experimentally. Adsorption isotherms were combined for the determination of the first parameter and a novel method called 'Flux test' was developed for the other parameter estimation. A reasonable agreement was observed between experimental- and model-predicted porosity. The model's ability of estimation indicates a little decrease at higher pressures due to approaching an unfavorable equilibrium adsorption condition and deviation from the isotherm's parameters from the actual equilibrium amounts to this situation. [ABSTRACT FROM AUTHOR]

The structural organization of chitosan hydrogel beads (CSBs) formed by various anionic surfactants, sodium dodecyl sulfate (SDS), sodium decyl sulfate (DS), dodecyl benzenesulfonic acid sodium salt (SDBS), and dioctyl sulfosuccinate sodium salt (DSS), and their applications as adsorbents for environmental purifications were investigated using Congo red (CR) as a model dye. The adsorption capacities of CSB as a function of surfactant concentration revealed that CSBs formed by 5 g/L anionic surfactant were the most effective for CR adsorption. The structure of CSBs and their adsorption capacities for CR depend on the nature of anionic surfactants. The maximum adsorption capacities of CSBSDS, CSBDS, CSBSDBS, and CSBDSS obtained from the Langmuir isotherm model were 186.02, 209.28, 207.25, and 113.83 mg/g, respectively, indicating that CSBDS was the best adsorbent for CR. [ABSTRACT FROM AUTHOR]

In this study, removal of arsenazo(ΙΙΙ) using activated carbon (AC) and multiwalled carbon nanotubes and of methyl red using AC from waste water is reported. The influences of pH, temperature, concentration of the dye, amount of adsorbents, particle size of adsorbent, and contact time on the efficiency of removal from aqueous solution are investigated. Adsorption experiments indicate that the extent of adsorption is strongly dependent on the pH of the solution. Changes in free energy of adsorption ( [image omitted]), enthalpy ( [image omitted]), and entropy ( [image omitted]) are calculated to understand the nature of adsorption. The calculated values of [image omitted] indicate that the adsorption process is spontaneous. The estimated values of [image omitted] and [image omitted] are positive which indicates that the adsorption process is endothermic and that the dye molecules are organized on the adsorbent surface in a more random fashion than in solution. The dye adsorption process follows a pseudo-second-order model under involvement of an intra-particle diffusion mechanism. Standard adsorption isotherms are used to fit the experimental data. [ABSTRACT FROM AUTHOR]

Activated carbon sorbents were synthesized from bamboo precursors by carbonization in an inert atmosphere followed by physiochemical activation with carbon dioxide and finally acidulation in hydrochloric acid. Bamboo strips with and without the epidermal tissue (bark) were used. The morphology and specific surface area changes due to the treatment were analysed. The adsorption characteristics of these sorbents after each stage of treatment were also analysed and the data were correlated to the changes in the physical characteristics of the sorbents. Kinetic studies were conducted on these samples. The adsorption equilibrium and kinetics of elemental mercury adsorption on these carbons were evaluated at room temperature. Elemental mercury uptake at different sorbent loading and initial elemental mercury concentrations were examined. The adsorption rate constants and the mass transfer constants were estimated for the sorbents prepared under different conditions. Adsorption isotherms of the elemental mercury on these activated carbons were determined and correlated with Langmuir and Freundlich adsorption isotherm equations. It was found that the overall process was mass transfer controlled and that the adsorption equilibrium could be described by a linear isotherm for the concentrations used in this study. [ABSTRACT FROM AUTHOR]

The adsorption characteristics of Pb2+ on pre-boiled treated onion skins (PTOS) and formaldehyde-treated onion skins (FTOS) were evaluated. The effects of Pb2+ initial concentration, agitation rate, solution pH, and temperature on Pb2+ adsorption were investigated in batch systems. Pb2+ adsorption was found to increase with increase in initial concentration. The point of zero net charge (PZC) was 6.53. The optimum pH for the maximum removal of Pb2+ was 6.0. The adsorption equilibrium data was best represented by the Langmuir isotherm model for FTOS and the Freundlich isotherm model for PTOS. The maximum amounts of Pb2+ adsorbed (qm), as evaluated by the Langmuir isotherm, was 200 mgg-1 for FTOS. The efficiencies of PTOS and FTOS for Pb2+ removal were 84,8.0% and 93.5% at 0.15 g/200 mL-1 adsorbent dose, respectively. (C0 = 50 mg L-1). Study concluded that onion skins, a waste material, have good potential as an adsorbent to remove toxic metals like Pb2+ from water. Boehm titration analysis was conducted to determine the surface groups. It was found that the adsorption kinetics of Pb2+ obeyed pseudo-first-order kinetic model as based on Δq (%) values. FTIR and SEM images before and after adsorption was recorded to explore changes in adsorbent-surface morphology. Activation energy (Ea) was obtained as 25.596 kJ/mol. [ABSTRACT FROM AUTHOR]

Bentonite clay is tailored in three different ways to produce porous materials viz. PCH1, PCH2, and PILC, where PCH1 and PCH2 are two different clay heterostructures and PILC is a Zr-oxide pillared clay. Surface characterization materials shows that both of PCHs have a higher surface area than PILC, and have micro and mesoporosity, where PILC is basically a microporous. DRIFT and X-ray techniques were used to investigate the surface-groups and height of micropores in PCHs and PILC, respectively. Adsorption isotherms of ethane and ethylene were measured on these materials up to high pressure (1000 kPa) under different temperatures, and by processing the obtained data these materials were evaluated for their aptness for ethane ethylene separation. Isosteric heats of adsorption were observed higher for ethylene than ethane during initial surface coverage for each material-gas system. Interaction in each material-gas system with gradual increase in pressure was elucidated with the help of isosteric heat curves. Adsorption performances of these materials were compared with already studied materials (reported by other workers for ethane/ethane separation). Comparison was based on selectivity and working capacity, which are the two decisive parameters for screening suitability of any adsorbent material (for PSA application). [ABSTRACT FROM AUTHOR]

Carica papaya, a novel sorbent, was evaluated for sorption of Hg(II) from synthetic aqueous solutions using various pseudo-second order kinetic models as well as equilibrium sorption models. Batch kinetic and equilibrium experiments were carried out for the sorption of Hg(II) onto C. papaya at pH 6.5 and solid to liquid ratio (s/l) 1.0 g L-1. The kinetic data were fitted to second order models of Sobkowsk and Czerwinski, Ritchie, Blanchard, Ho and McKay, whereas Langmuir, Freundlich, and Redlich-Peterson models were used for the equilibrium data. A comparative study on both linear and nonlinear regression showed that the Sobkowsk and Czerwinski and Ritchie's second order model were the same. Ho and McKay's pseudo-second order model fitted well to the experimental data when compared with the other second order kinetic expressions. Langmuir isotherm parameters obtained from the four Langmuir linear equations by using linear method were dissimilar, but were the same when nonlinear method was used. Additionally, various thermodynamic parameters, such as ΔG0, ΔH0, and ΔS0, were calculated. The negative values of Gibbs free energy (ΔG0) and ΔH0 confirmed the intrinsic nature of biosorption process and exothermic, respectively. The negative value of ΔS0 showed the decreased randomness at the solid-solution interface during biosorption. [ABSTRACT FROM AUTHOR]

The adsorption behavior of 17β-estradiol (E2) on marine sediments treated by different methods was investigated in the presence of bisphenol A (BPA), dibutyl phthalate (DBP), cationic surfactant cetyltrimethylammonium bromide (CTAB), nonionic surfactant polyoxyethylene (80) sorbitan esters (Tween 80) and anionic surfactant sodium dodecylbenzene sulfonate (SDBS). Four sets of experiments were conducted to determine the adsorption isotherms of E2 with coexisting contaminants, to explore the effects of concentrations and types of coexisting contaminants on the E2 adsorption capacity, and to examine the influence of pH on E2 adsorption on the sediments. The adsorption behavior of E2 to marine sediments without the addition of surfactant mainly related to organic carbon content of sediments and fitted well with the Freundlich model. The presence of CTAB or Tween 80 enhanced the adsorption capacity of E2 of marine sediments. In contrast, the presence of BPA, DBP and SDBS inhibited the adsorption capacity of E2. The pH value of the solution could influence the adsorption behavior of E2 of the marine sediments. A decline in pH values was beneficial to the adsorption of E2 with the addition of surfactants. [ABSTRACT FROM AUTHOR]