Showing papers on "Langmuir published in 2013"

Methane Adsorption on Shale under Simulated Geological Temperature and Pressure Conditions

Abstract: Shale gas is becoming an increasingly important energy resource. In this study, the adsorption of methane on a dry, organic-rich Alum shale sample was studied at pressures up to ∼14 MPa and temperatures in the range 300–473 K, which are relevant to gas storage under geological conditions. Maximum methane excess uptake was 0.176–0.042 mmol g–1 (125–30 scf t–1) for the temperature range of 300–473 K. The decrease in maximum methane surface excess with increasing temperature can be described with a linear model. An isosteric enthalpy of adsorption 19.2 ± 0.1 kJ mol–1 was determined at 0.025 mmol g–1 using the van’t Hoff equation. Supercritical adsorption was modeled using the modified Dubinin–Radushkevich and the Langmuir equations. The results are compared with absolute isotherms calculated from surface excess and the pore volumes obtained from subcritical gas adsorption (nitrogen (78 K), carbon dioxide (273 and 195 K), and CH4 (112 K)). The subcritical adsorption and the surface excess results allow an upp...

Batch Sorption Experiments: Langmuir and Freundlich Isotherm Studies for the Adsorption of Textile Metal Ions onto Teff Straw (Eragrostis tef) Agricultural Waste

Abstract: �� �� value in the present investigation was less than one, indicating that the adsorption of the metal ion onto ATS is favorable. After treatment with ATS the levels of heavy metals were observed to decrease by 88% (Ni), 82.9% (Cd), 81.5% (Cu), 74.5% (Cr), and 68.9% (Pb). Results indicate that the freely abundant, locally available, low-cost adsorbent , Teff straw can be treated as economically viable for the removal of metal ions from textile effluents.

Functionalization of graphite oxide with magnetic chitosan for the preparation of a nanocomposite dye adsorbent.

Abstract: In the current study, the functionalization of graphite oxide (GO) with magnetic chitosan (Chm) was investigated to prepare a nanocomposite material (GO-Chm) for the adsorption of a reactive dye (Reactive Black 5). The synthesis mechanism was investigated by various techniques (SEM/EDAX, FTIR spectroscopy, XRD, XPS, DTA, DTG, VSM). Characterization results indicated that a significant fraction of the amines of the chitosan (i) were inserted between the GO layers and (ii) reacted with carboxyl and epoxy groups of GO, leading to its reduction and hence the destruction of the layered structure. The concentrations of iron were found to be ∼25% for Chm and ∼12% for GO-Chm. A VSM plot presents the value of 9 emu/g for the saturation magnetization of GO-Chm. The adsorption behavior of the prepared composite was elucidated with a series of experiments. The tests of the effects of pH revealed that the adsorption mechanism dominated (between dye molecules and the GO-Chm matrix) and showed that acidic conditions were the optimum for the adsorption process (pH 3). Kinetic experiments presented the relatively "fast" adsorption phenomenon using pseudo-first-order, pseudo-second-order, and modified pseudo-second-order equations. The equilibrium data were fitted to the Langmuir, Freundlich, and Langmuir-Freundlich (L-F) models, calculating the maximum adsorption capacities at 25, 45, and 65 °C (391, 401, and 425 mg/g, respectively). Thermodynamic analysis was also performed to calculate the changes in free energy (ΔG(0)), enthalpy (ΔH(0)), and entropy (ΔS(0)).

Adsorption isotherms, kinetics and mechanism for the adsorption of cationic and anionic dyes onto carbonaceous particles prepared from Juglans regia shell biomass

Abstract: In the present study, Juglans regia shells were used to prepare activated carbon by acid treatment method. J. regia shell-based activated carbon was used for the adsorption of two synthetic dyes namely, a basic dye malachite green and an acid dye amido black 10B. The prepared adsorbent was crushed and sieved to three different mesh sizes 100, 600 and 1,000 μm. The adsorbent was characterized by scanning electron microscopy, surface acidity and zero-point charge. Batch experiments were carried out by varying the parameters like initial aqueous phase pH, adsorbent dosage and initial dye concentration. The equilibrium data were tested with Langmuir, Freundlich, Redlich–Peterson and Sips isotherm at three different temperatures 293, 300 and 313 K and it was found that the Freundlich isotherm best fitted the adsorption of both the dyes. Kinetic data were tested with pseudo first-order model and pseudo second-order model. The mechanism for the adsorption of both the dyes onto the adsorbent was studied by fitting the kinetic data with intraparticle diffusion model and Boyd plot. External mass transfer was found to be the rate-determining step. Based on the ionic nature of the adsorbates, the extent of film diffusion and intraparticle diffusion varied; both being system specific. Thermodynamic parameters were also calculated. Finally, the process parameters of each adsorption system were compared to develop the understanding of the best suitable system.

Adsorptive Removal of Methyl Orange and Methylene Blue from Aqueous Solution with Finger-Citron-Residue-Based Activated Carbon

Abstract: Activated carbon derived from finger citron residue (FAC) was tested as a new type of adsorbent for the removal of harmful dyes, namely, the anionic dye methyl orange (MO) and the cationic dye methylene blue (MB), from contaminated water. Liquid-phase adsorption experiments were conducted, and the maximum adsorption capacity was determined. Various conditions were evaluated, including initial dye concentration, adsorbent dosage, contact time, solution pH, and temperature. The Langmuir and Freundlich adsorption models were used to describe the equilibrium isotherm and to calculate the isotherm constants. It was found that the adsorption capacity of FAC is much higher than those of other types of activated carbons. Maximum equilibrium adsorption capacities of 934.58 and 581.40 mg/g for MO and MB, respectively, were achieved. Three simplified kinetic models, namely, pseudo-first-order, pseudo-second-order, and intraparticle diffusion equations, were used to investigate the adsorption process. The pseudo-seco...

Adsorption of Eriochrome Black T (EBT) dye using activated carbon prepared from waste rice hulls—Optimization, isotherm and kinetic studies

Abstract: In this study, the adsorptive removal of Eriochrome Black T (EBT) from aqueous solution using rice hull-based activated carbon was investigated. The effects of initial dye concentration, adsorbent dose and pH on the percent removal of EBT were examined. An increase in adsorbent dose, and decrease in initial dye concentration and pH would cause an increase in the removal of EBT. Using the Box–Behnken design, the optimum conditions were obtained to be the following: 95 ppm initial dye concentration, 2.0 g adsorbent dose and pH of 2. The equilibrium data was evaluated using Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm. The Freundlich model best describes the uptake of EBT dye, which implies that the adsorption of EBT dye onto rice hull activated carbon is heterogeneous. The kinetic data were analyzed using pseudo-first order, pseudo-second order and intraparticle diffusion equation. The pseudo-second order exhibited the best fit for the kinetic studies (R2 = 0.9996), which indicates that adsorption of EBT is limited by chemisorption process. The intraparticle diffusion model exhibited a linear relationship (R2 = 0.9921), which shows that pore diffusion is also a limiting step in the overall adsorption process.

Equilibrium and kinetic studies on acid dye Acid Red 88 adsorption by magnetic ZnFe2O4 spinel ferrite nanoparticles

Abstract: A magnetic ZnFe2O4 (MNZnFe) was synthesized by microwave assisted hydrothermal method and was used as an adsorbent for the removal of acid dye Acid Red 88 (AR88) from aqueous solution. The effects of various parameters such as initial AR88 concentration (10-56 mg L(-1)), pH solution (3.2-10.7), and temperature (20-60°C) were investigated. Prepared magnetic ZnFe2O4 was characterized by XRD, SEM, HRTEM, ICP-AES, BET, FTIR, and measurements of the magnetic susceptibility. The experimental data were analyzed by the Langmuir and Freundlich models of adsorption. Equilibrium data fitted well with the Langmuir model. Pseudo-first-order and pseudo-second-order kinetic models and intraparticle diffusion model were used to examine the adsorption kinetic data. The adsorption kinetics was found to follow the pseudo-second-order kinetic model. Thermodynamics parameters, ΔG°, ΔH° and ΔS°, indicate that the adsorption of AR88 onto MNZnFe was spontaneous and exothermic in nature.

Equilibrium, kinetic, and thermodynamic studies for biosorption of cadmium and nickel on grapefruit peel

Abstract: The biosorption of cadmium and nickel onto grapefruit peel from aqueous solution has been investigated using batch technique. Experiments are carried out as a function of solution pH, biosorbent dosage, contact time and temperature. The equilibrium adsorption data are fitted to Langmuir and Freundlich isotherm models and the model parameters are evaluated. The Freundlich model fits the equilibrium data better than the Langmuir model. The maximum uptakes of Cd(II) and Ni(II) by grapefruit peel are found to be 42.09 and 46.13 mg/g, respectively. The kinetics of the biosorption process is found to follow the pseudo-second-order kinetic model. Thermodynamic parameters depict the endothermic nature of biosorption and the process is spontaneous and favorable. Release of cations and protons from the biosorbent during sorption of Cd(II) and Ni(II) reveals that the main sorption mechanism is ion exchange. FTIR analysis demonstrates that carboxyl and hydroxyl groups were involved in the biosorption of the metal ions. The recovery of the Cd(II) and Ni(II) from grapefruit peel is found to be more than 97% using 0.1 M HCl. The results suggest that grapefruit peel can be used effectively for the removal of Cd(II) and Ni(II) ions from wastewaters.