Comparative Studies of the Micropore Size Distributions of an Alumina Pillared Montmorillonite and a Molecular Sieve Carbon

The aim of this work is to applicate and to compare various analysis methods for the characterization of the microporous structure from nitrogen adsorption at 77 K of an alumina pillared montmorillonite and a molecular sieve carbon. The adsorption potential distribution (X(A)), the Horvath-Kawazoe (HK) method, the Jaroniec-Gadkare-Choma (JGC) one and a numerical algorithm for the reconstruction of the micropore size distribution (MPSD) from the adsorption equilibrium isotherm have been applied. Comparison of all distributions revealed that the molecular sieve carbon shows smaller micropores and smaller structural hetereogeneity than the alumina pillared montmorillonite.     

On the Adsorption of Some Catechol Derivatives from Aqueous Solutions onto Activated Carbon Cloth: Equilibrium and Kinetic Studies

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.     

Competitive Adsorption of Chloroform and Iron Ion onto Activated Carbon Fiber

Chloroform in tap water has been a significant problem because it may be a carcinogenic substituent. Iron ion exists in tap water because of dissolution from iron water pipes. Iron ions in tap water cause discoloration and a bad odor. The isotherms of chloroform and iron ion adsorption onto activated carbon fibers in a single solution (chloroform or iron ion) and in a binary mixture solution (chloroform and iron ion) were investigated to estimate the competitiveness between chloroform and iron ions. The amount of adsorbed iron ions increased with increasing pore volume of the activated carbon fibers, while that of chloroform decreased. The amount of chloroform adsorbed onto the activated carbon fibers in the binary mixture solution was greater than that in the single solution. These results indicate that the adsorption of chloroform and iron ion onto activated carbon fibers could be competitive.     

Single and Mixed Gas Adsorption Equilibria of Carbon Dioxide/Methane on Activated Carbon

Single gas adsorption isotherms of methane and carbon dioxide on micro-porous Norit RB1 activated carbon were determined in a gravimetric analyser in the temperature range of 292 to 349 K and pressures to 0.8 Mpa. Furthermore binary isotherms of carbon dioxide and methane mixtures were determined at 292 K and pressures up to 0.65 MPa. Adsorbed phase compositions were determined from the gravimetric data by the rigorous thermodynamic method of Van Ness.These experimental binary equilibrium data were compared with equilibrium data calculated by the Ideal Adsorbed Solution (IAS) model. Only moderate agreement could be obtained.Finally, activity coefficients, accounting for the non-ideality of the adsorbate mixture, were calculated from the experimental data. The Wilson equation, derived for bulk solutions, was fitted on these activity data and the Wilson interaction parameters were determined. The Wilson equation proved to correlate the experimental data reasonably. However, the Wilson interaction parameters are not only completely different from those found for bulk solutions, but also the physical interpretation of these parameter values is completely lacking.It is concluded that new solution models should be developed encompassing both non-ideal solution behaviour and surface heterogeneity.     

Adsorption of Carbon Dioxide on Activated Carbon

The adsorption of CO2 on a raw activated carbon A and three modified activated carbon samples B, C, and D at temperatures ranging from 303 to 333 K and the thermodynamics of adsorption have been investigated using a vacuum adsorption apparatus in order to obtain more information about the effect of CO2 on removal of organic sulfur-containing compounds in industrial gases. The active ingredients impregnated in the carbon samples show significant influence on the adsorption for CO2 and its volumes adsorbed on modified carbon samples B, C, and D are all larger than that on the raw carbon sample A. On the other hand, the physical parameters such as surface area, pore volume, and micropore volume of carbon samples show no influence on the adsorbed amount of CO2. The Dubinin-Radushkevich (D-R) equation was the best model for fitting the adsorption data on carbon samples A and B, while the Preundlich equation was the best fit for the adsorption on carbon samples C and D. The isosteric heats of adsorption on carbon samples A, B, C, and D derived from the adsorption isotherms using the Clapeyron equation decreased slightly increasing surface loading. The heat of adsorption lay between 10.5 and 28.4 kJ/mol, with the carbon sample D having the highest value at all surface coverages that were studied. The observed entropy change associated with the adsorption for the carbon samples A, B, and C (above the surface coverage of 7 ml/g) was lower than the theoretical value for mobile adsorption. However, it was higher than the theoretical value for mobile adsorption but lower than the theoretical value for localized adsorption for carbon sample D.     

Influence of Initial pH Value on the Adsorption of Reactive Black 5 Dye on Powdered Activated Carbon: Kinetics,Mechanisms, and Thermodynamics

The aim of this work was to investigate the influence of initial pH value (pH₀) on the isothermal adsorption of Reactive Black 5 (RB5) dye on commercial powdered activated carbon. Four initial pH values were chosen for this experiment: pH₀ = 2.00, 4.00, 8.00, and 10.00. In order to investigate the mechanism of adsorption kinetic, studies have been performed using pseudo-first-order and pseudo-second-order kinetic models as well as an intraparticle diffusion model. In addition, thermodynamic parameters of adsorption were determined for pH₀ = 4.00. Results of this research showed that the initial pH value significantly influences the adsorption of RB5 dye onto activated carbon. The highest adsorption capacities (q_e) and efficiencies of decolouration were observed for initial pH values of pH₀ = 2.00 (q_e = 246.0 mg g⁻¹) and 10.00 (q_e = 239.1 mg g⁻¹) due to strong electrostatic interactions and attractive π···π interactions, respectively. It was also shown that the adsorption of RB5 dye on activated carbon at all initial pH values is kinetically controlled, assuming a pseudo-second-order model, and that intraparticle diffusion is not the only process that influences on the adsorption rate.     

Multicomponent Adsorption of Pesticides onto Activated Carbon Fibers

The adsorption equilibria of pesticides and metabolites (atrazine, deethylatrazine, deisopropylatrazine and simazine) are studied onto activated carbon fibers –ACF– with a broad pore size distribution (32% mesopore volume, 68% micropore volume). Mono-and multi-component isotherms have been determined for low concentrations, from 0.23×10⁻⁶ to 9.52×10⁻⁶ mol L⁻¹. Single solute isotherms, modeled by Freundlich and Langmuir models, tend to prove the influence of the adsorbate's solubility in the adsorption capacity of activated carbon fibers. Binary solute isotherms confirm the strong influence of pesticide solubility on the competitive adsorption mechanism: the competition is higher in the case of adsorbates of different solubilities (atrazine and DEA or DIA for example). Multicomponent experimental data were modeled by extended Langmuir-based equations and the Ideal Adsorbed Solution theory. Whereas the first ones failed to model accurately binary adsorption due to restrictive hypothesis, the IAS model showed a good agreement between experimental and predicted data. It emphasised also the difficulty in satisfying the hypothesis of the model in the case of highly adsorbed compounds. Finally, the simultaneous adsorption of atrazine and NOM (in a natural water, DOC = 18.2 mg L⁻¹) shows no adsorption competition effects between natural organic matter and atrazine. This is due to the presence of secondary micropores (0.8–2 nm) and mesopores in the ACF, which limit a pore blockage phenomenon by NOM.     

A Branched Pore Model Analysis for the Adsorption of Acid Dyes on Activated Carbon

A new branched-pore adsorption model has been developed using an external mass transfer coefficient, K _f, an effective diffusivity, D _eff, a lumped micropore diffusion rate parameter, K _b, and the fraction of macropores, f, to describe sorption kinetic data from initial adsorbent-adsorbate contact to the long-term adsorption phase. This model has been applied to an environmental pollution problem—the removal of two dyes, Acid Blue 80 (AB80) and Acid Red 114 (AR114), by sorption on activated carbon. A computer program has been used to generate theoretical concentration-time curves and the four mass transfer kinetic parameters adjusted so that the model achieves a close fit to the experimental data. The best fit values of the parameters have been determined for different initial dye concentrations and carbon masses. Since the model is specifically applicable to fixed constant values of these four parameters, a further and key application of this project is to see if single constant values of these parameters can be used to describe all the experimental concentration-time decay curves for one dye-carbon system.The error analysis and best fit approach to modeling the decay curves for both dye systems show that the correlation between experimental and theoretical data is good for the fixed values of the four fitted parameters. A significantly better fit of the model predictions is obtained when K _f, K _b and f are maintained constant but D _eff is varied. This indicates that the surface diffusivity may vary as a function of surface coverage.     

The Adsorption Kinetics of Cethyltrimethylammonium Bromide (CTAB) onto Powdered Active Carbon

This study investigates the adsorption kinetics of CTAB (cethyltrimethylammonium bromide), a cationic surfactant, onto PAC from aqueous solution with respect to the initial CTAB concentration at 20C. The pseudo-first-order, second-order kinetic models and intraparticle diffusion model were used to describe the kinetic data and the rate constants were calculated. The rate parameter, k_i, of intraparticle diffusion, the rate parameter, k₂, of the pseudo-second-order and k₁, the rate parameter for the pseudo-first-order mechanism were compared. It was found that the pseudo-second-order adsorption mechanism is predominant and the overall rate of the CTAB adsorption process appears to be controlled by more than one step, namely both the external mass transfer and intraparticle diffusion mechanisms.     

On the Application of Various Methods to Evaluate the Microporous Properties of Activated Carbons

Three methods, the Horvath-Kawazoe (HK) method, the Jaroniec-Gadkare-Choma (JGC) one and the Density Functional Theory (DFT), have been applied in the characterization of the microporous structure of several activated carbons. The samples were all based on the same parent material, that was subjected to various oxidative treatments, using solutions of concentrated HNO₃ at various temperatures (298, 333, 363 and reflux at 383 K during 3 hours) or solutions of H₂O₂ of various concentrations (1, 5 and 10 M). The nitrogen adsorption isotherms of the solids, were studied at 77 K and in the relative pressure range of 10^–6 < p/p ⁰ < 0.99. Only the isotherm parts up to a relative pressure of 0.2 were taken into consideration for obtaining the micropore size distributions. The evaluation of the method suitability was based on how well each one describes the experimentally obtained data. The three methods describe satisfactorily the experimental results, including the transitions of the isotherms related to the stages of micropore filling. The effects of the oxidative treatment on the structure of the solids, as judged from their micropore size distributions, are also discussed.     

Adsorption of NOM onto Activated Carbon: Effect of Surface Charge, Ionic Strength, and Pore Volume Distribution

Adsorption of natural organic matter (NOM) onto seven activated carbons with a wide range of surface properties was studied at high and low ionic strength over a range of pH values. From adsorption isotherm studies it was found that, for six of seven carbons, at low surface concentrations, increased ionic strength decreased NOM adsorption. As the surface concentration increased, the adsorption isotherms converged and intersected, after which the addition of salt resulted in increased adsorption. This “crossover point” marked a change in the adsorption mechanism from the “screening reduced” to the “screening enhanced” adsorption regimes. The adsorption mechanisms are extremely complicated and appear attributable to various factors, including electrostatic forces, pore volume distribution, and chemical interactions between the NOM and the surface functionalities on the carbon surfaces.     

Sorption and Textural Properties of Activated Carbon Derived from Charred Beech Wood

The aim of this study was to prepare activated carbon materials with different porous structures. For this purpose, the biomass precursor, beech wood, was carbonized in an inert atmosphere, and the obtained charcoal was physically activated using carbon dioxide at 1273 K. Different porous structures were obtained by controlling the time of the activation process. Prepared materials were characterized in terms of textural (N₂ sorption at 77 K), structural (XRD), and sorption properties (CO₂, C₂H₄, C₄H₁₀). The shortest activation time resulted in a mostly microporous structure, which provided a high sorption of CO₂. Increasing the activation time led to an increasing of the pores’ diameters. Therefore, the highest ethene uptake was obtained for the material with an intermediate activation time, while the highest butane uptake was obtained for the material with the highest activation time.     

Adsorption of Toxic Tetracycline,Thiamphenicol and Sulfamethoxazole by a Granular Activated Carbon (GAC) under Different Conditions

Activated carbon can be applied to the treatment of wastewater loading with different types of pollutants. In this paper, a kind of activated carbon in granular form (GAC) was utilized to eliminate antibiotics from an aqueous solution, in which Tetracycline (TC), Thiamphenicol (THI), and Sulfamethoxazole (SMZ) were selected as the testing pollutants. The specific surface area, total pore volume, and micropore volume of GAC were 1059.011 m²/g, 0.625 cm³/g, and 0.488 cm³/g, respectively. The sorption capacity of GAC towards TC, THI, and SMZ was evaluated based on the adsorption kinetics and isotherm. It was found that the pseudo-second-order kinetic model described the sorption of TC, THI, and SMZ on GAC better than the pseudo-first-order kinetic model. According to the Langmuir isotherm model, the maximum adsorption capacity of GAC towards TC, THI, and SMZ was calculated to be 17.02, 30.40, and 26.77 mg/g, respectively. Thermodynamic parameters of ΔG⁰, ΔS⁰, and ΔH⁰ were obtained, indicating that all the sorptions were spontaneous and exothermic in nature. These results provided a knowledge base on using activated carbon to remove TC, THI, and SMZ from water.     

Mesoporous Carbons of Well-Organized Structure in the Removal of Dyes from Aqueous Solutions

Mesoporous carbons with differentiated properties were synthesized by using the method of impregnation of mesoporous well-organized silicas. The obtained carbonaceous materials and microporous activated carbon were investigated by applying different methods in order to determine their structural, surface and adsorption properties towards selected dyes from aqueous solutions. In order to verify applicability of adsorbents for removing dyes the equilibrium and kinetic experimental data were measured and analyzed by applying various equations and models. The structural and acid-base properties of the investigated carbons were evaluated by Small-Angle X-ray Scattering (SAXS) technique, adsorption/desorption of nitrogen, potentiometric titration, and Transmission Electron Microscopy (TEM). The results of these techniques are complementary, indicating the type of porosity and structural ordering, e.g., the pore sizes determined from the SAXS data are in good agreement with those obtained from nitrogen sorption data. The SAXS and TEM data confirm the regularity of mesoporous carbon structure. The adsorption experiment, especially kinetic measurements, reveals the utility of mesoporous carbons in dye removing, taking into account not only the adsorption uptake but also the adsorption rate.     

Adsorption of Pentafluorophenol onto Powdered,Granular, and Cloth Activated Carbons

In the present study, the adsorption of pentafluorophenol from aqueous solution onto granular activated carbon, powdered activated carbon, and activated carbon cloth has been investigated from the equilibrium and kinetic points of view. To the best of our knowledge, the removal of pentafluorophenol from aqueous solution onto activated carbon have not been reported in the literature. The experimental equilibrium data, suitably fitted by the Toth, Langmuir-Freundlich, and Redlich-Peterson isotherms, have shown that the cloth and powdered carbons exhibit the highest adsorption capacity. For all the investigated samples, the experimental kinetic data have been satisfactorily interpreted by a pseudo-second-order model. From the fitting results it has been observed that the highest rate constant and initial rate of adsorption is shown by powdered activated carbon.     

Structural Characterization and Property Study on the Activated Alumina-activated Carbon Composite Material

AlCl3,NH3·H2O,HNO3 and activated carbon were used as raw materials to prepare one new type of activated alumina-activated carbon composite material.The influence of heat treatment conditions on the structure and property of this material was discussed;The microstructures of the composite material were characterized by XRD,SEM,BET techniques;and its formaldehyde adsorption characteristic was also tested.The results showed that the optimal heat treatment temperature of the activated alumina-activated carbon composite material was 450 ℃,iodine adsorption value was 441.40 mg/g,compressive strength was 44 N,specific surface area was 360.07 m2/g,average pore size was 2.91 nm,and pore volume was 0.26 m3/g.According to the BET pore size distribution diagram,the composite material has dual-pore size distribution structure,the micro-pore distributes in the range of 0.6-1.7 nm,and the meso-pore in the range of 3.0-8.0 nm.The formaldehyde adsorption effect of the activated alumina-activated carbon composite material was excellent,much better than that of the pure activated carbon or activated alumina,and its saturated adsorption capacity was 284.19 mg/g.     

Distribution of Platinum Particles in the Bimodal Micropore System of Activated Carbon

Platinum (Pt)/activated‐carbon catalysts were prepared and characterized by pore‐size distribution (PSD), propane‐sorption dynamics, and activity of cyclohexane dehydrogenation to benzene. The batch‐type frequency‐response (FR) spectroscopic technique was applied to determine the mass‐transport rate of propane sorption. Two parallel sorption processes of different time constants were distinguished, suggesting that adsorption proceeds in smaller and larger micropores that are not interconnected. Increasing Pt loading affected the propane mobility, but increased the dehydrogenation activity only up to ca. 1 wt‐% of Pt content. It was concluded that clusters of metallic Pt‐atoms are located preferentially at the narrowest pores. Blocking these micropores, the Pt reduces the carbon surface available for sorption; also, a significant fraction of the metal becomes inaccessible for the reactant.     

Estimation of Adsorption Capacity for Dissociating and Non Dissociating Aromatic Compounds on Activated Carbon with Different Models

The process of adsorption of two dissociating and two non-dissociating aromatic compounds from dilute aqueous solutions on an untreated commercially available activated carbon (B.D.H.) was investigated systematically. All adsorption experiments were carried out in pH controlled aqueous solutions. The experimental isotherms were fitted into four different models (Langmuir homogenous Models, Langmuir binary Model, Langmuir-Freundlich single model and Langmuir-Freundlich double model). Variation of the model parameters with the solution pH was studied and used to gain further insight into the adsorption process. The relationship between the model parameters and the solution pH and pK_a was used to predict the adsorption capacity in molecular and ionic form of solutes in other solution.A relationship was sought to predict the effect of pH on the adsorption systems and for estimating the maximum adsorption capacity of carbon at any pH where the solute is ionized reasonably well.N₂ and CO₂ adsorption were used to characterize the carbon. X-ray Photoelectron Spectroscopy (XPS) measurement was used for surface elemental analysis of the activated carbon.     

粉末活性炭基复合材料制备及净化含油污水的性能和机制

针对粉末活性炭对亲水小分子有机物吸附效率低和固液分离速度慢的问题, 本研究以粉末活性炭(PAC)、腐植酸盐(HS)、聚合氯化铝(PACl)为原料, 通过融合法成功制备了粉末活性炭基复合材料PACMC (powdered activated carbon matrix composites), 将其作为含油污水的净化吸附剂. 扫描电子显微镜-X射线能量色散谱仪(SEM-EDS)和傅里叶红外光谱(FT-IR)等表征分析确认了PACMC的微观形貌和化学组成, 证实了PAC、HS和PACl是通过化学反应生成了PACMC. PACMC具有层状多孔结构和活性官能团, 有利于含油污水分子的传输扩散和化学吸附. 通过静态吸附实验研究了PACl、PAC和PACMC对含油污水中有机物的吸附性能, 结果表明: PACMC对含油污水中有机污染物的吸附能力是PAC和PACl的2~3倍(q_e=23.04 mg•g^‒1, C₀=300 mg•L^‒1); 当吸附时间达到120 min 时, PACMC上的活性位点与含油污水中有机污染物的结合已基本达到饱和(q_e=23.04 mg•g^‒1, C₀=300 mg•L^‒1). 溶液pH值对PACMC吸附去除含油污水中有机物的影响显著, pH=3时, 吸附效果最好(q_e=27.6 mg•g^‒1, C₀=300 mg•L^‒1); 伪二级动力学方程能很好地描述含油污水中有机物在PACMC上的吸附行为, 动力学拟合结果表明其吸附过程分多步进行, 化学吸附和内扩散均具有重要作用. 等温吸附数据符合Dubinin-Radushkevich模型, 证明其吸附机理为化学吸附. 因此, PACMC吸附含油污水的机理包括化学结合/螯合作用、疏水力作用和静电吸附作用.