Liquid-phase adsorption of dyes and phenols using pinewood-based activated carbons

Physical properties of activated carbons prepared from pinewood at different activation times (0.5, 1.5, 2.7, and 4.0 h) in steam at 900 °C were studied. The adsorption equilibria and kinetics of three dyes and three phenols (phenol, 3-chlorophenol, and o-cresol) from aqueous solutions on such carbons were then examined at 30 °C. The adsorption isotherms of phenols could be well fitted by the Freundlich equation, and those of dyes were adequately described by the Langmuir-Freundlich equation. The effect of microporosity of the carbons on adsorption capacity was explored. Four simplified kinetic models including pseudo-first-order equation, pseudo-second-order equation, intraparticle diffusion model, and the Elovich equation were selected to follow the adsorption processes. The adsorption of all six adsorbates could be best described by the Elovich equation. The kinetic parameters of this best-fit model were calculated and discussed.     

Preparation and characterization of porous chitosan–tripolyphosphate beads for copper(II) ion adsorption

Porous chitosan–tripolyphosphate beads, prepared by the ionotropic crosslinking and freeze‐drying, were used for the adsorption of Cu(II) ion from aqueous solution. Batch studies, investigating bead adsorption capacity and adsorption isotherm for the Cu(II) ion, indicated that the Cu(II) ion adsorption equilibrium correlated well with Langmuir isotherm model. The maximum capacity for the adsorption of Cu(II) ion onto porous chitosan–tripolyphosphate beads, deduced from the use of the Langmuir isotherm equation, was 208.3 mg/g. The kinetics data were analyzed by pseudo‐first, pseudo‐second order kinetic, and intraparticle diffusion models. The experimental data fitted the pseudo‐second order kinetic model well, indicating that chemical sorption is the rate‐limiting step. The negative Gibbs free energy of adsorption indicated a spontaneous adsorption, while the positive enthalpy change indicated an endothermic adsorption process. This study explored the adsorption of Cu(II) ion onto porous chitosan–tripolyphosphate beads, and used SEM/EDS, TGA, and XRD to examine the properties of adsorbent. The use of porous chitosan–tripolyphosphate beads to adsorb Cu(II) ion produced better and faster results than were obtained for nonporous chitosan–tripolyphosphate beads. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis of chitosan beads as boron sorbents

Parameters, such as pH, temperature, initial boron concentration, adsorbent dosage, and ionic strength, affecting boron adsorption onto chitosan beads were examined in this study. The following values were obtained as the optimum conditions in our studied ranges: pH 8.0, temperature = 308 K, amount of chitosan beads = 0.15 g, initial boron concentration = 4 mg L⁻¹, and ionic strength = 0.1 M NaCl]. The adsorption kinetics were also examined in terms of three kinetic models: the pseudo‐first‐order, pseudo‐second‐order, and intraparticle diffusion models. The pseudo‐second‐order kinetic model showed very good agreement with the experimental data. Intraparticle plots seemed to have two steps and indicated multilinearity. Equilibrium data were evaluated with nonlinear and linear forms of the Langmuir and Freundlich equations. The experimental data conformed to the Freundlich equation on the basis of the formation of multilayer adsorption. To characterize the synthesized chitosan beads, we used Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) analyses. As shown by FTIR analysis, the boron species may have interacted with the NH₂ groups on chitosan. Microparticles of about 5 μm appeared in the SEM micrographs of the chitosan beads. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The effect of dye chemical structure on adsorption on activated carbon: a comparative study

The effect of the molecular structure of dyes Eriochrome Black T and Bromophenol Blue on their adsorption on the surface of activated carbon manufactured from locally available biosorbent has been studied. Batch experiments were performed to investigate factors that may affect the adsorption process. The effect of stirring rate was investigated in the range 0–240 rpm, with an initial concentration of 4–100 mg/l and a stirring time of 0–400 min. The mechanism and rate of adsorption were investigated for both dyes using pseudo‐first‐order, pseudo‐second‐order, intraparticle diffusion, and liquid film diffusion models. The monolayer adsorption capacities for Eriochrome Black T and Bromophenol Blue were found to be 36.5 and 39.68 mg/g respectively. The difference in dye uptake was attributed to the presence of the electron‐withdrawing bromine group in Bromophenol Blue. Results showed that the Langmuir isotherm best fitted the adsorption of the two dyes on the prepared activated carbon. The pseudo‐second‐order model best fitted the experimental data, and liquid film diffusion and intraparticle diffusion were the controlling adsorption mechanisms.     

海藻酸纤维对水溶液中Fe~(3+)的吸附动力学研究

以海藻酸纤维作为吸附材料研究了纤维对水溶液中Fe3+的吸附性能,用准一级动力学方程、准二级动力学方程、Elovich方程、粒子扩散方程、双常数方程和指数函数方程数学模型对不同Fe3+浓度、吸附时间的吸附曲线进行分析,研究了其吸附的动力学机理。结果表明:在研究的浓度和条件范围内,准二级动力学模型、Elovich方程和双常数方程的拟合度较好,模拟值与实验值吻合较好,说明海藻酸纤维吸附Fe3+是复杂的非均相扩散的化学吸附过程。粒子扩散方程表明颗粒内扩散不是控制海藻酸纤维吸附Fe3+过程的唯一步骤,而是由膜扩散和颗粒内扩散联合控制。     

Pseudo‐first‐order kinetic studies of the sorption of acid dyes onto chitosan

The adsorption of five acid dyes onto chitosan, derived through the deacetylation of crab‐shell chitin, from aqueous solutions was studied. The equilibrium isotherms were measured and analyzed with the Langmuir, Freundlich, and Redlich–Peterson equations; the results correlated well with the Langmuir equation. Kinetic studies were also performed in an agitated batch adsorber to study the effect of the initial dye concentration and the mass of chitosan. The kinetics were analyzed with the pseudo‐first‐order rate equation, and the rate constants were determined. The first‐order kinetic model correlated the experimental concentration and time data at short times and even up to 60% of the total adsorption period in a number of systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1633–1645, 2004     

Preparation of electrodes for hybrid capacitive deionization and its influence on the adsorption behaviour

ABSTRACT

The influence of the ratio of poly(vinyl chloride) in electrode composition into their surface energetics, hybrid capacitive deionization performance as well as adsorption kinetics and isotherms was evaluated. The electrodes were comprised of lithium manganese titanium oxide or activated carbon. Electrodes were tested by used hybrid capacitive deionization. To testing surface energetic the goniometer measurements were applied. It was possible to calculate free surface energy with its components. For investigated the adsorption kinetics the pseudo first order, pseudo second order, Weber–Morris intraparticle diffusion, Elovich models were chosen. While for the detection of adsorption isotherms Temkin and Harkins–Jura models were examined.     

Adsorption Behavior of Organic Dyes in Biopolymers Impregnated with H3PO4: Thermodynamic and Equilibrium Studies

A lignocellulose‐based waste biopolymer was impregnated with phosphoric acid and used for the removal of two organic dyes, Direct Blue (DB) and Reactive Blue (RB), from aqueous solution. Batch adsorption kinetic studies were carried out at different initial concentrations of the dyes, at different temperatures and various initial pH values (2–10). The equilibrium data obeyed the Langmuir isotherm model with high regression coefficient. The kinetic data were also used to test three different kinetic models. The validity of the kinetic models was analyzed and the pseudo‐second‐order model may be the best fit to explain the rate‐determining step. Adsorption of both dyes follows chemisorption. The effective diffusion coefficient and the activation energy were also calculated at different temperatures to establish the mechanism. Thermodynamic studies suggest that the adsorption of DB and RB is highly endothermic in nature. Mass transfer analysis reveals that the adsorption of DB and RB occurs through a film diffusion mechanism. Based on the Langmuir isotherm equation, the single‐stage batch absorber design of the adsorption of DB and RB onto activated carbon was studied.     

Preparation and adsorption properties of diethylenetriamine‐modified chitosan beads for acid dyes

This work has demonstrated that the novel chitosan derivative, synthesized by phase transition and grafting diethylenetriamine, has a great potential for the adsorption of acid dyes from aqueous solutions. Four acid dyes with different molecular sizes and structures were used to investigate the adsorption performance of diethylenetriamine‐modified chitosan beads (CTSN‐beads). Results indicated that the adsorption of dyes on CTSN‐beads was largely dependent on the pH value and controlled by the electrostatic attraction. In addition, the adsorption rate (AO10 > AO7 > AR18 > AG25) and adsorption capacities (AO7 > AR18 > AO10 > AG25) were directly related to the molecular size of the dye and the amount of the sulfonate groups on the dye molecules. The equilibrium and kinetic data fitted well with the Langmuir–Freundlich and pseudo‐second‐order model. Furthermore, thermodynamic parameters indicated that the adsorption processes occurred spontaneously and higher temperature made the adsorption easier. The reuse tests indicated that the CTSN‐beads can be recovered for multiple uses. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4090–4098, 2013     

Competitive adsorption of acid dyes from aqueous solution on diethylenetriamine‐modified chitosan beads

The interaction between two dyes (AO7 and AG25) during adsorption was studied in detail with diethylenetriamine‐modified chitosan beads (CTSN‐beads) as the adsorbent. Results indicate that the adsorption capacities and rates were directly related to the molecular size of the dye. The adsorption capacity and rate of AO7 could be greatly weakened by interaction with AG 25 during adsorption, which has a larger molecular size. The adsorption followed the pseudo‐second‐order kinetic equation and Freundlich model gave a satisfying correlation with the equilibrium data both in the single and binary component system. Adsorption could be divided into three stages, each controlled by different mechanisms. Temperature experiments showed high temperature was beneficial to the mass transfer of dyes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41168.     

Kinetic analysis of the sorption of copper(II) ions on chitosan

The removal of copper ions from aqueous effluents by chitosan was studied in equilibrium and agitated batch contacting systems. The sorption capacities of chitosan for copper ions are 1.26 and 1.12 mmol g^?1 at pH 3.5 and 4.5, respectively. The equilibrium experimental data were best correlated by the Langmuir equation. The kinetics of sorption were studied at an initial solution pH of 4.5 and a chitosan particle size of 355–500 µm. The kinetics were analyzed using four models: the pseudo‐first‐order, pseudo‐second‐order, modified second‐order and Elovich equations. The rate parameters for the four models were determined and the Elovich equation provided the best correlation of the experimental kinetic data. Copyright © 2003 Society of Chemical Industry     

Characterization and use of acid‐activated montmorillonite‐illite type of clay for lead(II) removal

The natural local deposits of montmorillonite‐illite type of clay (MIC) were susceptible for acid activation. Raw clay was taken for experimentation, disintegrated on acid activation with sulfuric acid, which showed a particle size distribution. The montmorillonite and illite phases in the raw clay disappeared on acid activation and the activated clay, MIC(AA), showed with sodium‐aluminum‐silicate and beidellite phases apart from quartz (low) phase. The raw and acid‐activated clays were characterized using X‐ray powder diffractometry, X‐ray fluorescence, Fourier transform infrared spectrometry, and energy dispersive X‐ray, and their adsorption capacities were compared. When tested for adsorption of Pb(II) in aqueous solutions, the acid‐activated clay showed about 50% increased adsorption than raw clay. Sips adsorption isotherm and pseudo‐second‐order kinetic models were found to be best for the batch adsorption data. Kinetic studies showed the existence of film diffusion and intraparticle diffusion. A two‐stage batch adsorber was designed for the removal of Pb(II) from aqueous solutions. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

In-Situ UV-Visible Spectroscopic Study on the Adsorption of some Dyes onto Activated Carbon Cloth

Abstract

Adsorptive removal of the dyes C.I. Basic Blue 9, C.I. Basic Red 2, and C.I. Acid Blue 74 from aqueous solution onto the activated carbon cloth (ACC) has been investigated. The removal of each dye has been followed by in-situ UV-visible spectroscopic method using the so-called scanning kinetics technique. Kinetic data obtained in this way were tested according to pseudo-first order, pseudo-second order, Elovich, and intraparticle diffusion models. Pseudo-second order model was found to be the best in representing the experimental kinetic data. Adsorption isotherms at 30°C were derived for each dye. Isotherm data were found to fit best to Freundlich isotherm model among the three isotherm models tested; Langmuir, Freundlich, and Redlich-Peterson. High specific surface area of the ACC allowed almost complete removal of each dye under the experimental conditions applied. Adsorption capacity of the ACC for the three dyes was correlated with the dimensions of dye molecules and pore sizes of the ACC.     

Characteristics of Elovich equation used for the analysis of adsorption kinetics in dye-chitosan systems

The Elovich equation has been widely used in adsorption kinetics, which describes chemical adsorption (chemical reaction) mechanism in nature. The approaching equilibrium parameter of Elovich equation (R_E) was used here to describe the characteristic curves of adsorption kinetics. Of 64 adsorption systems surveyed in this work, 80% of the R_E values were between 0.1 and 0.3 with an adsorption curve belonging to “mild rising”. The results of three examples revealed that the characteristic curve of Elovich equation was between those of Lagergren's first-order equation and intraparticle diffusion model. Chitosans prepared from prawn, lobster, and crab shells were used for the adsorption of a reactive dye. The mean deviation obtained from the three kinetic models revealed that Elovich equation was the most suitable one. All the adsorption systems were in the “mild rising” zone. The R_E value was related to the type of raw material but not to the particle size of chitosan, which agreed with chemical adsorption nature of the Elovich equation. According to an optimal adsorbent consumption of 85% coupled with its corresponding operating time (t_0.85) proposed, these two parameters could be used for engineering design.     

Adsorption of salicylic acid in aqueous solution by a water‐compatible hyper‐cross‐linked resin functionalized with amino‐group

On account of the high toxicity of nitrobenzene, 1,2‐dichloroethane was used as solvent. A novel water‐compatible hyper‐cross‐linked resin functionalized with amino‐group (denoted as GQ‐04) was synthesized to remove salicylic acid (SA) in aqueous solution. The maximum adsorption capacity of SA onto GQ‐04 was observed at pH of 1.88. The adsorption capacity increased with the increasing salt concentration. The adsorption kinetic data obeyed the pseudo‐second‐order rate equation and the adsorption isotherms can be characterized by Freundlich model. The intraparticle diffusion was the main rate‐controlling step. The saturated adsorption quantity of SA was up to 119.9 mg·mL‐1 according to the dynamic adsorption at 293 K. The resin could be regenerated by the 6 BV mixed solution of 80% ethanol and 0.5 mol/L NaOH. The size matching and hydrogen bonding between GQ‐04 and SA and the micropore structure resulted in the larger adsorption capacity in comparison with XAD‐4 and H103 resin. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Uptake of Fluoride by Al3+ Pretreated Low‐Silica Synthetic Zeolites: Adsorption Equilibrium and Rate Studies

Abstract

The removal of fluoride from single component aqueous solution using Al³⁺‐ pretreated low‐silica synthetic zeolites (Al‐Na‐HUD, Al‐HUD, Al‐F9, and Al‐A4) was studied. The effects of adsorbent mass, initial solution pH, and initial concentration on fluoride removal in a batch system were evaluated. Equilibrium data were simulated using simple isotherms such as the Freundlich (F), Langmuir‐Freundlich (LF), Redlich‐Peterson (RP) and Dubinin‐Radushkevitch (DR) isotherms. From the DR model, initial pH effects and desorption studies, it was considered that the fluoride adsorption onto the zeolites proceeded by ion‐exchange or chemisorption mechanism. In interpreting the kinetic results, reaction kinetics (using Elovich equation) and mass transfer processes (both external mass transfer and intraparticle diffusion) were considered. Equilibrium and kinetic results of fluoride adsorption onto the adsorbents demonstrated the following order of performance: Al‐Na‐HUD>Al‐F9> Al‐HUD>Al‐A4.     

Removal of reactive dyes from wastewater by acrylate polymer beads bearing amino groups: isotherm and kinetic studies

The aim of this study was to prepare a novel resin for the removal of reactive dyes from aqueous media. To prepare the resin, poly(2‐hydroxyethyl methacrylate/ethylene glycol dimethacrylate) beads were grafted with poly(glycidyl methacrylate) by surface‐initiated atom transfer radical polymerisation. Epoxy groups of the grafted polymer were modified with tris(2‐aminoethyl)amine ligand. The modified resin was characterised by swelling studies, FT‐IR and SEM. Three different reactive dyes were selected (CI Reactive Brown 10, CI Reactive Red 120 and CI Reactive Green 5) and used in the removal studies. The effects of pH, temperature, ionic strength and initial dye concentration on the adsorption capacity of the resin were investigated. The adsorption capacity of the resin for Reactive Brown 10, Reactive Red 120 and Reactive Green 5 was 0.029 ± 0.010, 0.032 ± 0.0019 and 0.042 ± 0.0013 mmol/g resin (34.1 ± 1.2, 47.6 ± 2.3 and 69.3 ± 1.7 mg/g resin) respectively. The equilibrium adsorption data were analysed by Langmuir, Dubinin–Radushkevich, Freundlich and Temkin isotherm models. A good fit was found between the Langmuir isotherm and data for the three dyes on resin. The adsorption kinetic data were modelled using pseudo‐first‐order, pseudo‐second‐order and intraparticle diffusion kinetic equations. It was found that the pseudo‐second‐order equation could describe the adsorption kinetics. The results indicated that the modified resin is an attractive alternative for removing reactive dyes from wastewater.     

Study of adsorption isotherms and kinetic models for Methylene Blue adsorption on activated carbon developed from Egyptian rice hull (Part II)

Adsorption of Methylene Blue (MB) from aqueous solutions on activated carbon prepared from Egyptian rice hulls (ERHA) is studied experimentally. Results obtained indicate that the removal efficiency of Methylene Blue at 25 °C exceeds 99% and that the adsorption process is highly pH-dependent. Results showed that the optimum pH lies between 5 and 9. The amount of Methylene Blue adsorbed form aqueous solution increases with the increase of the initial Methylene Blue concentration and temperature. Smaller adsorbent particle adds to increase the percentage removal of Methylene Blue.The results fit the BET model for adsorption of MB on ERHA, corroborating the assumption of that the adsorbate molecules could be adsorbed in more than one layer thick on the surface of the adsorbent.A comparison of kinetic models at different conditions (pH, Temperature, adsorbent particle size, adsorbent dose and adsorbate concentration) applied to the adsorption of Methylene Blue on the adsorbent was evaluated for the pseudo first-order, the pseudo second-order, Elovich and intraparticle diffusion kinetic models, respectively. Results showed that the pseudo second-order kinetic model correlate the experimental data well.