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.     

Kinetic evaluation of phenol/aniline mixtures adsorption from aqueous solutions onto activated carbon and hypercrosslinked polymeric resin (MN200)

Kinetic adsorption of phenol and aniline from aqueous solution onto activated carbon and hypercrosslinked polymeric resin MN200 were evaluated in single and binary system. Larger phenol and aniline uptakes were observed for activated carbon in single as well as binary system, which can be attributed to the better physical properties of activated carbon, for instance larger surface area and micropore area. The kinetic experimental data was properly fitted by the pseudo-first and pseudo-second-order rate equations. A synergetic effect between solutes was observed since phenol and aniline sorption kinetic in binary system was faster than the individual sorption of each solute in single system, as well as a slight increase in the kinetic parameters obtained in binary system. The particle diffusion rate was defined as the rate limiting mechanism in the singles and binary system for phenol and aniline kinetic adsorption on both adsorbents. Two steps were markedly defined by the Weber and Morris intraparticle diffusion analysis for phenol and aniline onto both adsorbents. In binary systems, the intraparticle diffusion was influenced by the physical properties of adsorbents.     

Adsorption of dyes and humic acid from water using chitosan‐encapsulated activated carbon

The adsorption isotherms and rates of two dyes and humic acid from aqueous solutions onto chitosan‐encapsulated activated carbon (CEAC) beads were measured at 30 °C. Such beads were prepared by mixing different weight percents of cuttlefish‐based chitosan (100%, 80%, 67%, and 55%) and rice‐based activated carbons. It was shown that the isotherms of dyes and humic acid were well fitted by the Freundlich equation. The adsorption capacity and rate could be enhanced when activated carbon was encapsulated with chitosan. Four simplified kinetic models including the pseudo‐first‐order equation, pseudo‐second‐order equation, intraparticle diffusion model, and the Elovich equation were tested to follow the adsorption processes. The adsorption of dyes was best described by the Elovich equation, but that of humic acid was best described by the intraparticle diffusion model. The kinetic parameters of each best‐fit model were calculated and are discussed in this paper. © 2002 Society of Chemical Industry     

Adsorption Characteristics of Sulfamethoxazole and Metronidazole on Activated Carbon

In this work, the removal of two pharmaceuticals i.e., an antibiotic drug, sulfamethoxazole and an antiparasitary drug, metronidazole onto activated carbon from aqueous solutions were studied. Batch adsorption studies were carried out at different pH, adsorbent concentrations, and temperatures. Adsorption isotherms have been modeled by Freundlich, Langmuir, and Dubinin-Raduskevitch (D-R) equations. The adsorption of these drugs was better represented by the Langmuir equation. The effect of the solution pH on the adsorbed amount of SM and MN was studied by varying the initial pH under constant process parameters at equilibrium conditions. The increase in pH of the solutions caused to decrease adsorption of SM and MN on AC. The kinetics of adsorption in view of three kinetic models, i.e., the first-order Lagergren model, the pseudo-second-order model, and the intraparticle diffusion model was discussed. The pseudo-second-order kinetic model describes the adsorption of both sulfamethoxazole and metronidazole on activated carbon. Rate constants for adsorption and desorption, and surface coverage have been evaluated with the help of another approach of the kinetic scheme. The effect of temperature was also studied at the range between 293 and 313 K. Thermodynamic parameters were calculated. The negative value of enthalpy change (ΔH°) indicated the exothermic nature of the adsorption process, and the negative values of free energy change (ΔG°) were indicative of spontaneity of the adsorption process. In this work adsorption behaviour of SM and MN on activated carbon was also evaluated by the data obtained from column experiments.     

Kinetic analysis of phenol adsorption from aqueous systems

The kinetic adsorption of mixtures of phenolic compounds onto a polymeric adsorbent from aqueous solutions was studied. Experimental data for single‐component solutions were obtained and fitted to a parallel diffusion model. Effective diffusion coefficients were related to liquid‐phase diffusion and surface diffusion. The effect of solute concentration and salinity on these parameters was also analysed. Van Laar's equation is proposed to evaluate the influence of concentration on diffusion. The adsorption kinetics for phenol and pcresol mixtures at different initial concentration ratios were determined and correctly adjusted to the mentioned kinetic model. Results confirm that adsorption from multicomponent aqueous solutions is a surface diffusion‐controlled process.     

Random forest model for removal of bromophenol blue using activated carbon obtained from Astragalus bisulcatus tree

In this research, activated carbon (AC) simply was prepared from a local, abundant tree in south of Iran. The AC with low cost and toxicity is a good candidate for bromophenol blue (BPB) removal from aqueous media. The AC with nano scale pore diameter is applicable for this dye removal following optimization of the influence of various parameters including contact time, pH, initial dye concentration and amount of adsorbent. Subsequently, experimental data was analyzed by four kinetic models including pseudo first and second-order, Elovich and the intraparticle diffusion equations and subsequently their respective parameters such as rate constants, equilibrium adsorption capacities and correlation coefficients was investigated and based on well known criterion their applicability was judged. The result shows that adsorption of BPB onto proposed adsorbent at all conditions such as versatile adsorbent dosages and initial BPB concentrations sufficiently described by the combination of the pseudo second-order equation and interparticle diffusion model. It was found that equilibrium rate of the BPB adsorption at various adsorbent dosage well fitted by Langmuir. Investigation of experimental result by two approaches (multiple linear regressions (MLR) and random forest (RF)) models show that RF is a powerful tool for prediction of BPB adsorption by activated carbon obtained from Astragalus bisulcatus tree. The optimal tuning parameters for RF model are obtained based on the n_tree = 100, m_try = 2. For the training data set, the MSE values of 0.0006 and the coefficient of determination (R²) values of 0.9895 for RF model and the MSE value of 0.0104 and the R² value of 0.823 for MLR model are obtained.     

Adsorption and desorption of phenylalanine and tryptophane on a nonionic polymeric sorbent

Adsorption equilibrium of two amino acids — Phenylalanine (Phe) and Tryptophane (Trp) — onto nonionic polymeric sorbent, SP850 was studied under various pH values and temperatures. Adsorption equilibrium data of two amino acids on SP850 were fitted well with the Langmuir and Freundlich equations. Thermodynamic parameters such as Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) were evaluated by applying the Van’t Hoff equation. Besides, adsorption kinetic of Phe was also investigated. Adsorption kinetic data were analyzed using the models of pseudo-first-order, pseudo-second-order and intraparticle diffusion. The results indicated that the pseudo-second-order model was more successful in simulating the adsorption kinetic data and the adsorption rate was mainly controlled by the diffusion rate in adsorption process. On the other hand, desorption studies were conducted by employing different organic solvents such as isopropyl alcohol (IPA), ethanol, and methanol. It was found that IPA was the best material for desorbing amino acid on the polymeric sorbent.     

Investigation of adsorption of lead,mercury and nickel from aqueous solutions onto carbon aerogel

Recently a new form of activated carbon has appeared: carbon aerogel (CA). Its use for the removal of inorganic (and especially metal ions) has not been studied. In the present study, the adsorption of three metal ions, Hg(II), Pb(II) and Ni(II), onto carbon aerogel has been investigated. Batch experiments were carried out to assess adsorption equilibria and kinetic behaviour of heavy metal ions by varying parameters such as agitation time, metal ions' concentration, adsorbent dose and pH. They facilitated the computation of kinetic parameters and maximum metal ion adsorption capacities. Increasing the initial solution pH (2–10) and carbon concentration (50–500 mg per 50 cm³) increases the removal of all three metal ions. A decrease of equilibrium pH with an increase of metal ion concentration led us to propose an adsorption mechanism by ion exchange between metal cations and H⁺ at the carbon aerogel surface. Carboxylic groups are especially involved in this adsorption mechanism. Langmuir and Freundlich isotherm models were used to analyse the experimental data of carbon aerogel. The thermodynamics of the metal adsorption was also investigated for the practical implementation of the adsorbent. The sorption showed significant increase with increase of temperature. Kinetics models describing the adsorption of Hg(II), Pb(II) and Ni(II) ions onto carbon aerogel have been compared. Kinetics models evaluated include the pseudo‐first order and second order model. The parameters of the adsorption rate constants have been determined and the effectiveness of each model assessed. The result obtained showed that the pseudo‐second order kinetic model correlated well with the experimental data and better than the pseudo‐first order model examined in the study. Mass transfer coefficients obtained can be useful in designing wastewater treatment systems or in the development of environmental technologies. Copyright © 2005 Society of Chemical Industry     

Adsorption Characteristics and pH‐dependence of Metsulfuron‐Methyl onto Activated Carbons

Abstract

The adsorption characteristics of metsulfuron‐methyl (MM) onto powdered activated carbon (PAC) and granular activated carbon (GAC) were studied at varying solution pHs (4–9) and temperatures (20–40°C). The dependence of pH was observed in aqueous solution with MM. The film mass transfer and intraparticle diffusion coefficients were estimated from concentration decay curves obtained in the batch adsorber. The maximum adsorption capacity decreased with increasing pH and temperature. Among the PAC used, the coconut based PAC had the best adsorption capacity. The adsorption isotherms could be plotted using the Freundlich and Toth models with a reasonable degree of accuracy. The overall adsorption isotherm such as the modified‐Toth model should be applied. The performances of the fixed‐bed GAC system was also simulated by a model developed. The objective of the present study was to investigate the adsorption and pH dependence behavior of MM onto PAC and GAC in order to diminish the environmental risk of MM pollution.     

Adsorption of Cr(VI) using thermally activated weed Salvinia cucullata

Cr(VI) removal studies were carried out by using activated carbon obtained from waste weed, Salvinia cucullata. Effects of various parameters, such as pH, contact time, temperature, adsorbate concentration, adsorbent dose and particle size of the adsorbent on percentage of adsorption were studied. The adsorption studies were carried out at an agitation speed of 600 rpm to minimize the film diffusion. The adsorption kinetics followed dual rate; it was fast during a first stage and then it was reduced. The equilibrium was achieved in 12 h. The kinetics increased with decrease in pH. Adsorbate and adsorbent concentration also influenced the kinetics. The adsorption process was endothermic in nature. The reaction kinetics followed pseudo-second-order kinetic equation. Empirical rate equation developed, which explained the effect of various adsorption parameters, was studied. Theoretical numbers of stages were calculated based on the results. Intra-particle diffusion was found to be the rate-controlling step. Optimization studies were also carried out to establish the upper and lower breakthrough points.     

二苯并呋喃在活性炭上的吸附相平衡和动力学

The adsorption of dibenzofuran on three commercial granular activated carbons （ACs） was investigated by dynamic experiment to correlate the adsorption equilibrium and kinetics with the structure of activated carbons. Physical properties including surface area, average pore diameter, micropore area and micropore volume of the activated carbons were characterized by N2 adsorption experiment on ASAP2010. To calculate the adsorption parameters, adsorption isotherm data were fitted to the Langmuir equation, and adsorption kinetic data were fitted to the linear driving force （LDF） diffusion model. From the correlation results, it is concluded that the adsorption equilibrium and diffusion coefficient of dibenzofuran on activated carbon are controlled respectively by the total adsorbent surface area and the adsorbent pore diameter.     

Study of adsorption behavior using activated carbon for removal of colored impurities from 30% caprolactam solution produced by means of SNIA-toluene-technology

We studied the adsorption removal of the colored impurities from caprolactam solution by granular activated carbons. It was observed that removal was favored at lower pH (pH 3.84 or below) and higher temperature. The effects of concentration, dosage of activated carbons, contact time have been also reported. Uptake of colored impurities was very rapid in the first 100 minutes and reached equilibrium after 24 h. The batch adsorption kinetics was found to follow the pseudo-second-order model and the rate constants of adsorption for all these kinetic models have been calculated. Three isotherm expressions Langmuir, Freundlich and Trinomial were shown to fit with the experimental results successfully. The mass transfer coefficientβ and the effective diffusion coefficient in aqueous phase Deff was calculated under a temperature 35–80 °C. The value of the mean free energy of adsorption E signifies that the adsorption of colored impurities onto activated carbon has a physical nature.     

Adsorption of N-Vinylpyrrolidone from Polyvinylpyrrolidone Solution onto Bamboo-Based Activated Carbon

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.     

Adsorption characteristics of antibiotics trimethoprim on powdered and granular activated carbon

The adsorption characteristics of trimethoprim (TMP) onto powdered activated carbon (PAC) and granular activated carbon (GAC) were studied. The adsorption isotherms could be plotted using the Langmuir, Freundlich and Toth models with a reasonable degree of accuracy. Toth isotherm model was better for describing the adsorption equilibrium than Freundlich model, even though the Langmuir model also agreed with the experimental data well. It shows that the Toth model is adequate for fitting equilibrium data for adsorption of TMP on both PAC and GAC in this study. Fixed-bed breakthrough curves were studied under various operating conditions. The performances of the fixed-bed GAC system was also simulated by a model developed with homogeneous surface diffusion model (HSDM).     

Removal of pyridine derivatives from aqueous solution by activated carbons developed from agricultural waste materials

The paper investigates the ability of activated carbons developed from coconut shell to adsorb α-picoline, β-picoline, and γ-picolin from aqueous solution. The developed carbons are designated as SAC (activated carbon derived from coconut shells with out any treatment) and ATSAC (activated carbon derived from acid treated coconut shells). The carbons were, characterized and utilized for the sorption of α-picoline, β-picoline, and γ-picoline at different temperatures, particle size, pH and solid to liquid ratio. All the studies were performed by batch method to determine various equilibrium and kinetic parameters. The Langmuir and Freundlich isotherm models were applied and the Langmuir model was found to best report the equilibrium isotherm data. The adsorption of α-, β-, and γ-picoline followed the pseudo-second order rate kinetics. On the basis of kinetic studies, various rate and thermodynamic parameters such as effective diffusion coefficients, activation energy and activation entropy were evaluated. It was concluded that in majority of cases, the adsorption is controlled by particle diffusion at temperatures 10° and 25 °C while at 40 °C it is controlled by film diffusion mechanism. Similarly at concentrations 25 and 50 mg/l the adsorption was governed by particle diffusion in most of the cases while at >50 mg/l it was film diffusion controlled. The overall capacity of ATSAC was higher than SAC. The sorption capacity of γ-picoline was found more followed by β-picoline and α-picoline.     

3种芳香磺酸在超高交联吸附树脂上的吸附行为

研究了胺基修饰的超高交联吸附树脂NDA-99对水溶液中对甲苯磺酸、4-氯苯磺酸、4B酸等3种芳香磺酸的静态吸附性能。结果表明,Freundlich方程能够对3种芳香磺酸的吸附等温线进行很好的拟合,相关系数均大于0.99,其平衡吸附量的顺序为4B酸>对甲苯磺酸>4-氯苯磺酸。对吸附热力学与动力学的研究表明,NDA-99树脂对3种芳香磺酸的吸附均为自发进行的放热过程,主要表现为物理吸附;4-氯苯磺酸的吸附速率主要由液膜扩散控制,而对甲苯磺酸和4B酸吸附速率主要由颗粒内扩散控制。     

Fixed bed modelling for acid dye adsorption onto activated carbon

The adsorption of three separate acid dyes onto activated carbon has been studied using fixed bed adsorption. A film‐pore diffusion model was developed and applied to the experimental breakthrough curve data. A sensitivity analysis showed that pore diffusion was the dominant mass transport mechanism. Pore diffusion coefficients were determined by an optimization routine with a minimization of the sum of errors squared. The external mass transfer coefficients were sensitive to the external fluid dynamic parameters, such as liquid flow rate and mean particle size. These fluid dynamic parameters did not affect the effective diffusion coefficient. The effective diffusion coefficient was not affected by changes in the fluid dynamic parameters but did change with differing initial dye concentrations. This may be due to a contribution from surface diffusion to the effective diffusion coefficient. Copyright © 2003 Society of Chemical Industry     

聚酯醇解废液的脱色动力学

为实现聚酯醇解废液的有效再利用,本文研究了物理吸附法及电化学氧化法对实际聚酯醇解废液的脱色纯化,同时提出了脱色后醇解废液再利用的方法。选用γ-Al₂O₃、Fe₃O₄、Fe₃O₄@壳聚糖以及活性炭对醇解废液进行物理吸附脱色,选用Fe₃O₄@壳聚糖为分散电极对醇解废液进行电化学氧化脱色,对比不同脱色方法及反应条件对脱色效果的影响,分析吸附动力学参数及电化学氧化动力学参数。数据表明,采用物理吸附法脱色,活性炭表现出最强脱色能力,活性炭投加量为200mg/L时,吸附平衡需12h,最大单位吸附质量为44.84mg/g,脱色率为84.56%,吸附动力学曲线符合伪二级反应动力学模型;采用电化学氧化脱色法,脱色平衡时间可缩短至5h,最大脱色率为94.62%,动力学曲线符合一级反应动力学模型。     

Removal of methylene blue from aqueous solutions by adsorption onto chemically activated halloysite nanotubes

This study examines the adsorption behavior of methylene blue (MB) from aqueous solutions onto chemically activated halloysite nanotubes. Adsorption of MB depends greatly on the adsorbent dose, pH, initial concentration, temperature and contact time. The Langmuir and Freundlich models were applied to describe the equilibrium isotherms and the Langmuir model agrees very well with experimental data. The maximum adsorption capacities for MB ranged from 91.32 to 103.63 mg·g⁻¹ between 298 and 318 K. A comparison of kinetic models applied to the adsorption data was evaluated for pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion equation. The results showed the adsorption process was well described by the pseudo-second-order and intra-particle diffusion mode. Thermodynamic parameters suggest that the adsorption is spontaneous and endothermic. The obtained results indicated that the product had the potential to be utilized as low-cost and effective alternative for dye removal in wastewater.