Influence of solvent type on dibenzothiophene adsorption onto activated carbon fiber and granular coconut-shell activated carbon

The adsorption behavior of dibenzothiophene (DBT) on an activated carbon fiber (ACF) and a granular coconut-shell activated carbon (GCSAC) in the solvents n-hexane, n-decane, toluene, and mixture of n-decane and toluene was investigated. The DBT adsorption onto both samples was more active in n-hexane than in n-decane. The lowest DBT adsorption was observed in toluene. Regardless of the type of activated carbons and solvents, all the isotherms fit the Freundlich equation better than the Langmuir equation. At low equilibrium concentrations of <2 mass ppm-S, GCSAC displayed greater capacity for DBT adsorption than did ACF in all the tested solvents. The adsorption kinetics of ACF and GCSAC in all the tested solvents were governed by a pseudo-second-order model.     

Nonionic surfactants adsorption onto activated carbon. Influence of the polar chain length

The adsorption of a nonionic surfactants series characterized by a different length of the hydrophilic tail on an activated carbon has been studied over a wide concentration range. Adsorption isotherms show two steps limited by the critical micelle concentration (c.m.c.) of the surfactants. The adsorption extension depends on the oxyethylenic chain length, in such way that the amount adsorbed decreases with increasing the chain length, although the effect is much lower for the longest polar chains. In the concentration range below the c.m.c. of the surfactants, the molecules are adsorbed by direct interactions with the activated carbon surface, but with different configuration of the polyoxyethylene chain (POE) directed to the aqueous phase. For concentrations above the c.m.c., the adsorption takes place by the interactions between the adsorbed surfactants molecules and differences related to the length of the hydrophilic chain are also found.     

Comparative study of methylene blue dye adsorption onto activated carbon,graphene oxide,and carbon nanotubes

Three different carbonaceous materials, activated carbon, graphene oxide, and multi-walled carbon nanotubes, were modified by nitric acid and used as adsorbents for the removal of methylene blue dye from aqueous solution. The adsorbents were characterized by N₂ adsorption/desorption isotherms, infrared spectroscopy, particle size, and zeta potential measurements. Batch adsorption experiments were carried out to study the effect of solution pH and contact time on dye adsorption properties. The kinetic studies showed that the adsorption data followed a pseudo second-order kinetic model. The isotherm analysis indicated that the adsorption data can be represented by Langmuir isotherm model. The remarkably strong adsorption capacity normalized by the BET surface area of graphene oxide and carbon nanotubes can be attributed to π–π electron donor acceptor interaction and electrostatic attraction.     

Simultaneous adsorption of MIB and NOM onto activated carbon. I. Characterisation of the system and NOM adsorption

The objective of this work was to increase the understanding of the adsorption competition between an odour compound, 2-methylisoborneol, and natural organic material (NOM). Part I describes the characterisation of six commercially available activated carbons, undertaken using nitrogen gas adsorption, surface titrations, and Fourier transform infrared spectroscopy. The natural organic material (NOM) from one raw water and four fractions obtained from an isolation and fractionation procedure undertaken on the same raw water, were characterised using ¹³C NMR, high-performance size exclusion chromatography, UV-visible absorbance and elemental analysis. Simultaneous adsorption of NOM and MIB indicated that the adsorption of the NOM was largely dependent on the pore volume distribution of the activated carbons, and less influenced by the variation in surface chemistry. Larger NOM molecules showed greater relative rates of adsorption where the access to the internal structure of the carbon was restricted by size exclusion, due to the shorter diffusion distances to adsorption sites travelled by the larger molecules. As the concentration of MIB was extremely low compared with that of the NOM in these experiments, no effect of MIB on NOM adsorption was seen. Part II reports the significant effect of the NOM solutions on the adsorption of MIB.     

Effect of chemical activation of an activated carbon using zinc chloride on elemental mercury adsorption

Hg⁰ adsorption experiments with different kinds of activated carbons (ACs) were conducted in nitrogen environment to study the effects of ACs with different surface characteristics on adsorption. Three kinds of ACs prepared by steam activation did not adsorb elemental mercury (Hg⁰) in nitrogen environment, while another kind of AC prepared by chemical activation using zinc chloride (ZnCl₂) showed significant Hg⁰ adsorption capability in the same experimental conditions because Hg⁰ was oxidized by the oxidative elements on the surface of AC. ACs without oxidative elements did not adsorb Hg⁰ through physical adsorption in nitrogen environment. It was therefore concluded that Hg⁰ adsorption by AC was a chemical adsorption process.     

Removal of metal ions from aqueous solution by adsorption onto activated carbon cloths: adsorption competition with organic matter

Activated carbon cloths are recent adsorbents whose adsorption properties are well known for monocomponent solutions of organics or metal ions. However, to treat wastewaters with these materials, their performance has to be determined in multicomponent solution. This work studies adsorption competition between metal ions (Cu²⁺, Pb²⁺) and organic matter (benzoic acid). The first part investigates adsorption equilibrium of monocomponent metal ions solutions and shows the dependence of adsorption capacities on adsorbent porosity and metal ions chemical properties (molecular weight, ionic radius and electronegativity). The influence of pH is also demonstrated. The second part focuses on adsorption competition: (1) between both metal ions (a decrease of adsorption capacities is observed, whose value is related to adsorption kinetics of metal ions); (2) between metal ions and organic matter, in solution or adsorbed onto the activated carbon cloth (a strong influence of pH is shown: when benzoic acid is under benzoate form, in both cases adsorption is increased due to the formation of ligands between adsorbed benzoate ions and metals).     

Effects of chemical and physical properties of influent on copper sorption onto activated carbon fixed-bed columns

Experimental studies were carried out to determine the effects of influent pH, ionic strength, metal concentration, and empty-bed contact time (EBCT) on copper sorption in the activated carbon fixed-bed columns. As the influent pH was increased, the column performance significantly improved. An overshoot of the effluent concentration was observed at pH 3.0 due to desorption of copper from the surface-metal complexes. The uptake enhanced as the ionic strength was increased; however, this role was much weaker than that of pH. An increase in metal concentration resulted in a decrease in the bed volumes at the breakthrough. In the beginning of all the experiments, the effluent pH increased dramatically and then dropped and approached lower values. Less sorption was observed when prewashed columns were used, in which the pH in the columns was kept constant. Modelling of the metal sorption in the prewashed columns was performed using a metal ion transport model hydrogeochem and a fixed-bed model.     

Effect of pH on adsorption of 2,4-dinitrophenol onto an activated carbon

The adsorption characteristics of 2,4-dinitrophenol from water onto a granular activated carbon, F-400, were studied at pH 4.3, 7 and 10. Adsorption equilibria of 2,4-dinitrophenol on GAC could be represented by Sips equation. Equilibrium capacity increased with decreasing pH. The differences in the rates of adsorption are primarily attributable to the differences in the equilibrium at the various pHs. Intraparticle diffusion was explained by surface diffusion mechanism. An adsorption model based on the linear driving force approximation (LDFA) was used for simulating the adsorption behavior of 2,4-dinitrophenol in a fixed bed adsorber. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8-10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University.     

The importance of finite adsorption kinetics in the sorption of hydrocarbon gases onto a nutshell-derived activated carbon

An activated carbon sample was synthesized from nutshells using a sequential step of carbonization and CO₂ physical activation. Sorption equilibria and kinetics of hydrocarbon gases were measured on this sample at various temperatures and concentrations. The structural heterogeneity of the carbon is characterized by its micropore distribution, which is derived from the analysis of isotherms. The finite kinetics (FK) model [Do, D.D., Wang, K., 1998b. Predictions of adsorption equilibria of non-polar hydrocarbons onto activated carbon. Langmuir 14, 7271-7277; Do, D.D., Wang, K., 1998a. Dual diffusion and finite mass exchange model for adsorption kinetics in activated carbon. A.I.Ch.E. Journal 44, 68.] was employed to describe the sorption kinetics of pure gases and to predict those of binary gas mixtures. The performance of the FK model is compared to that of the HMSD model which assumes the same surface heterogeneity but infinite rates of interchange between the bulk and adsorbed phases. It is demonstrated that the finite kinetics play an important role in the simulation/prediction of desorption kinetics and sorption kinetics of binary gas mixtures.     

Open circuit potential shifts of activated carbon in aqueous solutions during chemical and adsorption interactions

Interaction of certain inorganic and organic compounds with activated carbon and the effect of such interaction on open circuit potential of activated carbon were studied. Open circuit potential shifts were observed for an overwhelming majority of the substances and brands of activated carbons investigated. Both negative and positive potential shifts were observed. It was shown that open circuit potential shifts for organic substances depend on degree of coverage of the activated carbon surface. Whereas adsorption of investigated organic compound on activated carbon led to positive potential shifts, desorption of adsorbates from the activated carbon surface led to potential shifts in the opposite direction. Furthermore, time dependencies of open circuit potential shifts were similar for different carbon brands. The magnitude of the shifts depended on the adsorbate, adsorption activity of the adsorbent, and the steric configuration of potential-determinative pores and adsorbate molecules.     

In vitro adsorption study of fluoxetine in activated carbons and activated carbon fibres

We study the in vitro adsorption of fluoxetine hydrochloride by different adsorbents in simulated gastric and intestinal fluid, pH 1.2 and 7.5, respectively. The tested materials were two commercial activated carbons, carbomix and maxsorb MSC30, one activated carbon fibre produced in our laboratory and also three MCM-41 samples, also produced by us. Selected samples were modified by liquid phase oxidation and thermal treatment in order to change the surface chemistry without significant modifications to the porous characteristics. The fluoxetine adsorption follows the Langmuir model. The calculated Q₀ values range from 54 to 1112 mg/g. A different adsorption mechanism was found for the adsorption of fluoxetine in activated carbon fibres and activated carbons. In the first case the most relevant factors are the molecular sieving effect and the dispersive interactions whereas in the activated carbons the mechanism seams to be based on the electrostatic interactions between the fluoxetine molecules and the charged carbon surface. Despite the different behaviours most of the materials tested have potential for treating potential fluoxetine intoxications.     

Electrochemically enhanced adsorption of aniline on activated carbon fibers

For adsorptive separation processes, the adsorption rate and capacity are two important factors affecting the costs. This study describes the anodic polarization of activated carbon fibers (ACFs), which can enhance the adsorption rate and capacity of aniline. The electrosorption kinetics and the affecting factors (bias potential, electrolyte, and pH) of isotherms for aniline on ACFs were investigated. The adsorption/electrosorption of aniline on ACFs follow pseudo-first-order adsorption kinetics, and the adsorption rate improves with increasing bias potential. The electrosorption isotherms, which exhibit a variety of responses depending on bias potential, electrolyte and pH, follow the two classical models of Langmuir and Freundlich. With electrosorption of aniline from aqueous solution, a two-fold enhancement of adsorption capacity is achievable. The initial and saturated ACFs were characterized using scanning electron micrograph (SEM) and Fourier transform infrared spectroscopy (FT-IR). The SEM micrographs show that the surface of ACFs is not oxidized, which is also verified by cyclic voltammetry results. The FT-IR spectroscopy suggests that the interaction between aniline and ACFs is main weak physisorption instead of chemisorption. These experimental results suggest that the electrochemical polarization of ACFs can effectively improve the adsorption rate and capacity of aniline, which may be due to the enhanced affinity between aniline and ACFs instead of the oxidation on the surface of ACFs or in the solution.     

活性炭吸附甲烷和甲苯的分子模拟研究

以石墨片微元构建的多孔碳材料作为活性炭的结构模型,采用巨正则蒙特卡罗方法(GCMC)和分子动力学方法(MD),从分子层面研究甲烷和甲苯在活性炭中的吸附和扩散特性. 结果表明,石墨片微元大小对多孔碳材料吸附甲烷和甲苯有一定影响,37个碳环构成的多孔碳材料是最佳的吸附结构;甲烷气体在活性炭材料中扩散较快,甲苯在活性炭中扩散较慢,随碳环碳原子数增加,气体在多孔碳材料中的自扩散系数逐渐增大;引入基团会使最优密度向高密度方向偏移,用不同基团表面改性的吸附量顺序为羟基>氨基>羧基>未改性,基团引入会改善材料的孔结构,有利于吸附量的增加.     

Theoretical and experimental SO2 adsorption onto pistachio-nut-shell activated carbon for a fixed-bed column

The adsorption and desorption behaviours of SO₂ onto activated carbons, which were prepared from pistachio-nut shells, were studied theoretically and experimentally in a fixed-bed column. A mathematical model considering non-equilibrium, non-isothermal and non-adiabatic effects for a single gas adsorbate on a fixed-bed system was derived and the model was solved by a finite-difference method. A linear driving force (LDF) approximation is used for heat and mass transfer rates. The temperature-dependent Langmuir equilibrium isotherm is used to represent gas–solid equilibrium isotherm. The theoretical study was conducted to compare the present model with the isothermal and adiabatic model. The effects of inlet concentration, flow rate and temperature were studied experimentally. These experimental data showed that the breakthrough time decreased with increasing feed concentration, increasing flow rate and increasing temperature and the trends were correctly predicted by the model calculations.     

Effects of high relative humidity on the dynamic adsorption of dimethyl methylphosphonate (DMMP) on activated carbon

The effects of high relative humidity (RH) on the breakthrough of the nerve agent simulant dimethyl methylphosphonate (DMMP) vapor in beds of ASC-impregnated, activated carbon were investigated. Maximum concentrations of DMMP at room temperature and RH > 60% were found to be lower by more than an order of magnitude than in dry air. The breakthrough time (t_B) of 1.2 × 10⁻⁴ g l⁻¹ DMMP in pre-humidified beds and humid air of RH = 90% was shortened by a factor of 1.6 relative to adsorption in dry beds and dry air. Analysis of the breakthrough curves according to the Wheeler–Jonas model indicated that the high RH lowered the dynamic adsorption capacity (W_E) but had nearly no effect on the critical bed weight (W_C). The reduction of W_E by humidity correlates with the observed displacement of adsorbed water by DMMP. The use of DMMP for testing filter performance is limited to low and intermediate relative humidities. On the other hand, DMMP in dry air can be used to advantage for testing the capacity of new or used respirator filters and for the detection of filter channeling.     

A model for the adsorption of single metal ion solutes in aqueous solution onto activated carbon produced from pecan shells

Adsorption isotherms for activated carbon made from pecan shells have been obtained at 25 °C and an approximate pH of 3 for a number of metal ion solutes. It was found that the Slips and Freundlich equations were satisfactory for explaining the experimental data. The correlation of metal ion adsorption with the solute parameters of metal ion electronegativity and first stability constant of the metal hydroxide was investigated. In the case of most of the metal ions studied, higher electronegativities and stability constants corresponded to the higher adsorption levels of metal ions onto the activated carbon. A correlation was developed that predicts the constants of the Freundlich equation from the selected parameters of the metal ions, and thus can predict the adsorption isotherms at constant pH. The developed correlation gives results with acceptable deviations from experimental data. A procedure is proposed for obtaining similar correlations for different conditions (temperature, pH, carbon type and dosage). The ratio of equivalent metal ions adsorbed to protons released is calculated for the studied metal ions over a range of concentrations. In most cases, particularly at low concentrations, this ratio is close to one, confirming that ion exchange of one proton with one equivalent metal ion is the dominant reaction mechanism.     

Role of activated carbon structural properties and surface chemistry in mercury adsorption

In this work the performance of activated carbons prepared from raw and demineralised lignite for gas-phase Hg° removal was evaluated. A two-stage activation procedure was used for the production of the activated samples. In order to study the effect of mineral matter on pore structure development and surface functionality of the activated carbons, a demineralisation procedure involving a three-stage acid treatment of coals, was used, prior to activation. Hg° adsorption tests were realized in laboratory-scale unit consisted of a fixed-bed reactor charged with the tested activated samples. The examined adsorbent properties that may affect removal capacity were the pore structure, the surface chemistry and the presence of sulphur on the surface of activated carbons. The obtained results revealed that activated carbons produced from demineralised lignite posses a high-developed micropore structure with increased total pore volume and BET surface area. These samples exhibit enhanced Hg° adsorptive capacity. In all cases, mercury removal efficiency increased by sulphur addition. Finally, the starting material properties and activation conditions affect the concentration and the type of the oxygen groups on activated carbon surface, that have been determined with TPD-MS experiments.