几种植物基活性炭材料的表面结构与吸附性能比较——(II)表面化学结构与吸附性能研究

用X-射线光电子能谱对3种植物基活性炭材料:椰壳活性炭 (CAC4)、剑麻茎基活性炭(SSAC)和剑麻基活性碳纤维 (SACF) 的表面化学结构进行了表征,并研究和对比了它们的吸附性能,包括对碘、苯酚和亚甲基蓝的液相吸附性能,对有机蒸汽的吸附性能以及对Au3+的还原吸附性能等。结果表明,3个样品表面均含有多种含氧官能团,吸附能力SACF>SSAC> CAC4。样品的吸附性能主要取决于自身孔结构,与其表面化学结构也有密切的关系。     

A Study of the Influence of Hydrophobicity of Activated Carbon on the Adsorption Equilibrium of Aromatics in Non-Aqueous Media

The effect of hydrophobicity on the adsorption of aromatics on metal-free activated carbons was studied. Adsorption isotherms for phenol, aniline, benzene, and xylene were generated in cyclohexane and heptane media, using seven carbons with different surface heterogeneity. The hydrophobicity of these carbons was probed using flow microcalorimetry (FMC). Surface polarity and solvent and adsorbate hydrophobicity were found to influence the adsorption capacity. For adsorbates that do not form hydrogen bonds with oxygen on the carbon surface, higher surface acidity lowers adsorption capacity due to increased polarity. In contrast, for adsorbates that can form hydrogen bonds with surface oxygen, the capacity is enhanced at higher surface acidities. A higher solvent hydrophobicity was found to decrease capacity for all the aromatic adsorbates studied, except at high surface polarity, where the effect of the solvent was found to be minimal.     

Effects of Cetylpyridinium Chloride on Phase and Rheological Behavior of the Diluted C(12)E(4)/Benzyl Alcohol/Water System

The influence of the pore size distribution of activated carbon on the adsorption of phenol from aqueous solutions was explored. Activated carbons with different porous structures were prepared by gasifying a bituminous coal char to different extents of burn-off. The results of adsorption experiments show that the phenol capacity of these carbons does not proportionally increase with their BET surface area. This reflects the heterogeneity of the carbon surface for adsorption. The pore size distributions of these carbons, determined according to the Dubinin-Stoeckli equation, were found to vary with the burn-off level. By incorporating the distribution with the Dubinin-Radushkevich equation using an inverse proportionality between the micropore size and the adsorption energy, the isotherms for the adsorption of phenol onto these carbons can be well predicted. The present study has demonstrated that the heterogeneity of carbon surface for the phenol adsorption can be attributed to the different energies required for adsorption in different-size micropores. Copyright 2000 Academic Press.     

The roles of template complexation and ligand binding conditions on recognition in bupivacaine molecularly imprinted polymers

A model for the molecular basis for ligand recognition in bupivacaine imprinted methacrylic acid-ethylene glycol dimethacrylate co-polymers has been developed based upon a series of (1)H-NMR studies in conjunction with HPLC and radioligand binding analyses. (1)H-NMR studies indicated that functional monomer-template complexes survive the polymerisation process, at least up until the stage of gelation. Polymers were synthesised and characterised by surface area analysis (BET), FT-IR and SEM. A combination of zonal and frontal chromatographic studies in aqueous and non-polar media indicate that selectivity arises from a combination of hydrophobic and electrostatic interactions. However, in the concentration regime employed for LC-based studies, ligand recognition in aqueous media was shown to be predominantly non-specific and hydrophobic in character. Radioligand binding studies, in lower ligand binding concentration regimes, permitted closer examination of the higher affinity binding sites. It was shown that the presence of a polar modifier in a non-polar solvent, or an organic modifier in water, produced enhanced selectivity. Variable temperature studies showed that the temperature of binding influences selectivity as well as the apparent number of sites available and that this effect is different in organic and aqueous environments. This indicates that the system studied is more complex in character than is generally appreciated. A comparison of the techniques employed here indicates that although chromatographic studies provide a valuable first-round screen for polymer-ligand selectivities, the level of detail obtainable using radioligand binding studies (lower concentrations and true equilibrium binding) makes them superior for detailed evaluations of molecularly imprinted polymers.     

低成本木质素吸附剂对废水中Pb2+吸附性能的研究

首次尝试以马尾松为原料的木质素制备低成本重金属吸附剂,采用N2物理吸附和红外漫反射技术对其结构和表面化学进行了表征,研究了pH值,温度对其吸附水溶液中Pb2 的影响,并与麦草木质素和商业活性炭进行了对比,探讨了它吸附重金属离子的吸附机理以及结构和表面化学对重金属离子吸附的影响。结果表明,马尾松木质素吸附剂对水溶液中Pb2 的吸附机理主要是化学吸附,其表面的功能基有利于吸附水溶液中Pb2 ,尽管商业活性炭的比表面积是马尾松碱木素的200多倍,在相同的实验条件下,所制备的马尾松碱木素对Pb2 的单位比表面积平衡吸附量却是商业活性炭的1000多倍。     

The oxidation of aqueous thiols on a graphite intercalation compound adsorbent

Aqueous phase adsorption of thiols onto a graphite intercalation compound (GIC) adsorbent was shown to be accompanied by surface assisted oxidation of the thiols to their disulfide dimer. This effect was studied for three thiols; ethanethiol, propanethiol and sec-butanethiol. Unlike the case of thiol oxidation on activated carbons in aqueous conditions, the generation of dimer did not affect the adsorbent’s ability to oxidise the thiols in solution in the concentration range studied (0–100 ppm). This was attributed to the non-porous, crystalline nature of the adsorbent. This meant that once formed the dimers migrated from the active sites for thiol oxidation, believed to be mainly at the edges of the graphite planes, onto the hydrophobic basal plane where they could be adsorbed. Oxidation of the GIC adsorbent in the anodic compartment of an electrochemical cell was shown to attenuate the adsorbent’s ability to oxidise thiols. It was inferred that this was a result of a decrease in the amount of CO groups at the plane edges caused by this oxidation process.     

Adsorption of fatty acids from solutions in organic solvents on the surface of finely dispersed magnetite: 2. Heats of oleic,linoleic, and linolenic acid adsorption from carbon tetrachloride and hexane

Differential and integral heats of oleic, linoleic, and linolenic acid adsorption on the surface of finely dispersed magnetite from solutions in carbon tetrachloride and hexane are measured by the calorimetric method. The thermodynamic parameters of the adsorption for the systems under examination are calculated from the obtained experimental data. It is discovered that, at low concentrations, the volume filling of micropores in the particle aggregates of the adsorbent occurs with the formation of ordered adsorbate structures in the pores. At high concentrations, the fatty acids are adsorbed in mesopores and on the outer surface of the adsorbent. It is shown that, at high concentrations, the key contributions to the integral heat of adsorption are made by the endothermic processes of desolvation of adsorbates and the adsorbent surface, as well as by the competitive adsorption of solvent and fatty acid molecules on the active sites of the adsorbent surface.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 784–787.Original Russian Text Copyright © 2004 by Korolev, Blinov, Ramazanova.     

Liquid-phase adsorption of multi-ring thiophenic sulfur compounds on carbon materials with different surface properties

This work examines the effects of structural and surface properties of carbon materials on the adsorption of benzothiophene (BT), dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyl-dibenzothiophene (4,6-DMDBT) in the presence of 10 wt % of aromatics in liquid alkanes that simulate sulfur compounds in diesel fuels. The equilibrium-adsorption capacity varies significantly, from 1.7 to 7.0 mg-S/g-A. The results show that different carbon materials have significantly different sulfur-adsorption capacities and selectivities that depend not only on textural structure but also on surface functional groups. The adsorption of multi-ring sulfur compounds on carbon materials was found to obey the Langmuir isotherm. On the basis of adsorption tests and the characterization of carbon materials by BET and XPS, the oxygen-containing functional groups on the surface appear to play an important role in increasing sulfur-adsorption capacity. The adsorption-selectivity trend of the carbon materials for various compounds increases in the order of BT < naphthalene < 2-methylnaphthalene < DBT < 4-MDBT < 4,6-DMDBT, regardless of carbon material types. This selectivity trend for sulfur compounds is dramatically different and almost opposite from that previously observed for adsorption over nickel-based adsorbents. The regeneration of spent activated carbons was also conducted by solvent washing. The high-adsorption capacity and selectivity for methyl DBTs indicate that certain activated carbons are promising adsorbents for selective adsorption for removing sulfur (SARS) as a new approach to ultra deep desulfurization of diesel fuels.     

Selective removal of chlorine from chloroaromatic pollutants by electrocatalytic reduction over palladium-loaded carbon felt

This brief review outlines work on effective hydrodechlorination of environmentally persistent chlorine-containing aromatic pollutants by electrocatalytic reduction at Pd-loaded carbon felt. The selective removal of chlorine from phenoxy herbicides 2,4-D and 2,4,5-T, chlorinated biphenyls and naphthalene was readily achieved (i) at room temperature and (ii) directly in aqueous media. No highly active reducing chemicals were required for such a treatment. The use of carbon felt of high surface area as a solution-permeable cathode offered high adsorption capacity for chloroaromatics, while supported palladium provided the system with a highly reactive reducing species supposed to be a surface-bound hydride, which was generated upon electrochemical reductive decomposition of water. A facilitating effect of bulky tetraalkylammonium cations of a supporting electrolyte on substrate conversion and product recovery is considered. The reaction mechanism for selective hydrodechlorination of chloroaromatics in aqueous media and scheme for activation of Pd-loaded carbon felt by electrolytic pre-treatment are proposed and discussed.     

NiY分子筛表面酸性影响其选择性吸附脱硫性能的机理研究

采用原位红外光谱技术,以噻吩、环己烯和苯为模型探针分子,分别考察单一烃分子在NiY分子筛上的吸附与反应行为以及噻吩与烯烃、芳烃间的竞争吸附和催化反应行为。单一探针分子吸附研究发现,NiY分子筛中与Ni物种相关的Lewis(L)酸位是噻吩的选择性吸附活性位;噻吩和环己烯在NiY分子筛中Brnsted(B)酸位上发生的质子化和低聚反应明显弱于HY分子筛。双探针分子竞争吸附研究发现,环己烯二聚体在NiY中强B酸位上的强化学吸附与噻吩存在显著的竞争吸附行为。另外,苯和噻吩在NiY上的竞争吸附现象在373K时明显减弱。由此,在选择性吸附脱硫过程中,减少吸附剂表面B酸中心可降低烯烃对噻吩的竞争吸附,另外适当提高吸附体系的温度可以有效避免芳烃对噻吩的竞争吸附。     

The Use of High Surface Area Mesoporous-Activated Carbon from Longan Seed Biomass for Increasing Capacity and Kinetics of Methylene Blue Adsorption from Aqueous Solution

Microporous- and mesoporous-activated carbons were produced from longan seed biomass through physical activation with CO₂ under the same activation conditions of time and temperature. The specially prepared mesoporous carbon showed the maximum porous properties with the specific surface area of 1773 m²/g and mesopore volume of 0.474 cm³/g which accounts for 44.1% of the total pore volume. These activated carbons were utilized as porous adsorbents for the removal of methylene blue (MB) from an aqueous solution and their effectiveness was evaluated for both the adsorption kinetics and capacity. The adsorption kinetic data of MB were analyzed by the pseudo-first-order model, the pseudo-second-order model, and the pore-diffusion model equations. It was found that the adsorption kinetic behavior for all carbons tested was best described by the pseudo-second-order model. The effective pore diffusivity (D_e) derived from the pore-diffusion model had the values of 4.657 × 10⁻⁷–6.014 × 10⁻⁷ cm²/s and 4.668 × 10⁻⁷–19.920 × 10⁻⁷ cm²/s for the microporous- and mesoporous-activated carbons, respectively. Three well-known adsorption models, namely the Langmuir, Freundlich and Redlich–Peterson equations were tested with the experimental MB adsorption isotherms, and the results showed that the Redlich–Peterson model provided the overall best fitting of the isotherm data. In addition, the maximum capacity for MB adsorption of 1000 mg/g was achieved with the mesoporous carbon having the largest surface area and pore volume. The initial pH of MB solution had virtually no effect on the adsorption capacity and removal efficiency of the methylene blue dye. Increasing temperature over the range from 35 to 55 °C increased the adsorption of methylene blue, presumably caused by the increase in the diffusion rate of methylene blue to the adsorption sites that could promote the interaction frequency between the adsorbent surface and the adsorbate molecules. Overall, the high surface area mesoporous carbon was superior to the microporous carbon in view of the adsorption kinetics and capacity, when both carbons were used for the removal of MB from an aqueous solution.     

Use of Adsorbents for Recovery of Acetic Acid from Aqueous Solutions Part II—Factors Governing Selectivity

Measurements have been made of uptake of acetic acid and water from low-pH aqueous solution onto polymeric adsorbents and activated carbons. In additon to composite isotherms, isotherms were obtained for acetic acid and water individually by use of gas-chromatographic and Karl Fisher techniques for analyses of both bulk solution and the material taken up by the adsorbent. While capacities for acetic acid are determined by the surface area and the chemical nature of the adsorbent, selectivity is governed by the pore volume and the wetting and swelling tendencies of the sorbent, with the latter being particularly important for polymers. Activated carbons and pyrolyzed polymers give better selectivity than do common polymeric adsorbents.

Measurements of pore volume by immersion in various liquids were compared with pore volumes computed from nitrogen adsorption-desorption measurements and from mercury-intrusion porosimetry. The nitrogen adsorption-desorption results were interpreted to obtain micropore and mesopore volumes. The results from the different methods agree well, if allowance is made for lack of full wetting and for swelling tendencies. Higher selectivity for acetic acid over water is obtained for adsorbents having a large percentage of the pore volume as micropores.

Measurements of competitive adsorption of acetic acid and methyl ethyl ketone from aqueous solution onto different carbons and pyrolyzed polymers showed that a higher surface density of active hydrogen sites, as measured by reaction with LiAlH₄, leads to an improved selectivity for the carboxylic acid.     

The physical and surface chemical characteristics of activated carbons and the adsorption of methylene blue from wastewater

Adsorption of a basic dye, methylene blue, from aqueous solutions onto as-received activated carbons and acid-treated carbons was investigated. The physical and surface chemical properties of the activated carbons were characterized using BET-N(2) adsorption, X-ray photoelectron spectroscopy (XPS), and mass titration. It was found that acid treatment had little effect on carbon textural characteristics but significantly changed the surface chemical properties, resulting in an adverse effect on dye adsorption. The physical properties of activated carbon, such as surface area and pore volume, have little effect on dye adsorption, while the pore size distribution and the surface chemical characteristics play important roles in dye adsorption. The pH value of the solution also influences the adsorption capacity significantly. For methylene blue, a higher pH of solution favors the adsorption capacity. The kinetic adsorption of methylene blue on all carbons follows a pseudo-second-order equation.     

Inhibition of nitrobenzene adsorption by water cluster formation at acidic oxygen functional groups on activated carbon

The inhibition effect of nitrobenzene adsorption by water clusters formed at the acidic groups on activated carbon was examined in aqueous and n-hexane solution. The activated carbon was oxidized with nitric acid to introduce CO complexes and then outgassed in helium flow at 1273 K to remove them completely without changing the structural properties of the carbon as a reference adsorbent. The amounts of acidic functional groups were determined by applying Boehm titration. A relative humidity of 95% was used to adsorb water onto the carbon surface. Strong adsorption of water onto the oxidized carbon can be observed by thermogravimetric analysis. The adsorption kinetic rate was estimated to be controlled by diffusion from the kinetic analysis. Significant decline in both capacity and kinetic rate for nitrobenzene adsorption onto the oxidized carbon was also observed in n-hexane solution by preadsorption of water to the carbon surface, whereas it was not detected for the outgassed carbons. These results might reveal that water molecules forming clusters at the CO complexes inhibited the entrance of nitrobenzene into the interparticles of the carbon.     

Selective removal of chlorine from chloroaromatic pollutants by electrocatalytic reduction over palladium-loaded carbon felt

This brief review outlines work on effective hydrodechlorination of environmentally persistent chlorine-containing aromatic pollutants by electrocatalytic reduction at Pd-loaded carbon felt. The selective removal of chlorine from phenoxy herbicides 2,4-D and 2,4,5-T, chlorinated biphenyls and naphthalene was readily achieved (i) at room temperature and (ii) directly in aqueous media. No highly active reducing chemicals were required for such a treatment. The use of carbon felt of high surface area as a solution-permeable cathode offered high adsorption capacity for chloroaromatics, while supported palladium provided the system with a highly reactive reducing species supposed to be a surface-bound hydride, which was generated upon electrochemical reductive decomposition of water. A facilitating effect of bulky tetraalky lammonium cations of a supporting electrolyte on substrate conversion and product recovery is considered. The reaction mechanism for selective hydrodechlorination of chloroaromatics in aqueous media and scheme for activation of Pd-loaded carbon felt by electrolytic pre-treatment are proposed and discussed.     

The selectivity of active carbons modified by fullerenes with respect to mixtures of metal cations in aqueous solutions

The separating ability of active carbons and active carbons modified with fullerenes with respect to mixtures of nonferrous metal cations was studied. The selectivity series for the extraction of cations from aqueous solutions was Ag⁺ > Cu²⁺ > Pb²⁺. The selectivity of adsorption by active carbon modified with fullerenes was higher than that characteristic of the initial adsorbent, especially for the extraction of silver ions from a mixture of silver and copper cations.     

Isotherms of poly(ethylene glycol) adsorption from aqueous solutions by carbon adsorbents

Isotherms of adsorption of poly(ethylene glycols) PEG300, PEG6000, and PEG15 000 from aqueous solutions on graphitized carbon black and active carbon were measured at 25°C. Isotherms of excess adsorption of PEG6000 and PEG15 000 from aqueous solutions on both adsorbents were characterized by a distinct maximum. Comparison of adsorption isotherms for PEG6000 and PEG15 000 on a mesoporous AU-87 carbon testified to the existence of a sieve effect upon the adsorption of large PEG15 000 macromolecules in the accessible pores of this adsorbent. The analysis of the dependence of maximal adsorption values on the PEG molecular mass indicated a possible unfolding of macromolecular coils in the field of adsorption forces. As a result, all oxygen and carbon atoms of PEG macromolecules in a monolayer tend to approach active sites on the surface of a carbon adsorbent. The calculated values of thickness of dense adsorption monolayers of PEG300, PEG6000, and PEG15 000 lie within 0.36–0.63 nm for both adsorbents. PEG300 adsorption monolayers also contain, in addition to macromolecules, molecules of a solvent (water).Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 856–859.Original Russian Text Copyright © 2004 by Eltekov, Eltekova, Roldughin.     

Monolith Passive Adsorbers Prepared with Hydrophobic Porous Silica Rods Coated with Hydrogel

This work focuses on the synthesis and characterization of porous silica monolith-based adsorbent materials. Materials with bimodal porosity (macro and meso) were prepared through a sol–gel process. The capacity of adsorption of organic molecules was ensured by grafting of hydrophobic organic coating on the silica surface. Alkylsilane chains or lauryl acrylate polymer were used for this purpose. The adsorption kinetic behavior of the produced materials was assessed through benzophenone adsorption studies in aqueous media. The results have shown that the macropore size of the monoliths had no effect on the adsorption capacity. The thicker organic layer prepared by polymerization of lauryl acrylate has decreased the adsorption kinetics without affecting the total adsorption capacity. The over-coating with additional external layer of hydrogel further slowed the diffusion of benzophenone thus better matches the passive-sampler requirements.     

Cationic dyes adsorption onto high surface area ‘almond shell’ activated carbon: Kinetics,equilibrium isotherms and surface statistical modeling

Almond shell agricultural biomass was used to prepare high surface area activated carbon using potassium hydroxide as activating agent. The activated carbon (AC) was characterized using X-Ray photoelectron spectroscopy, X-Ray diffraction, Thermogravimetric and differential thermal analyses, Scanning electron microscopy, Fourier transform infrared, Brunauer–Emmett–Teller surface area and Raman spectroscopy. The AC was found to have a high surface area of 2054 m² g^?1. The influence of various key parameters was evaluated on the adsorption process including contact time, adsorbent dose and solution pH. Isotherm data were modeled using Langmuir and Freundlich models. Langmuir isotherm model presented the best fit to experimental data suggesting homogeneous distribution of adsorption sites. The adsorbent demonstrated high monolayer adsorption capacity of 833.33 and 625.0 mg/g for Methylene Blue and Crystal Violet, respectively. The efficiency of the adsorption process was linked to the micro-mesoporous structure and to the availability of the surface adsorption sites. Response surface methodology was used to optimize the removal efficiency from aqueous solution.     

Cadmium ion adsorption on different carbon adsorbents from aqueous solutions. Effect of surface chemistry, pore texture, ionic strength, and dissolved natural organic matter

Adsorption of Cd(II) species at pH = 5 was studied on three carbon adsorbents: granular activated carbon, activated carbon fiber, and activated carbon cloth. As-received and oxidized adsorbents were used. Cd(II) adsorption greatly increased after oxidation due to the introduction of carboxyl groups. The use of a buffer solution to control the pH introduced some changes in the surface chemistry of carbons through the adsorption of one of the compounds used, biphthalate anions. The increase in ionic strength reduced Cd(II) uptake on both as-received and oxidized carbons due to a screening of the electrostatic attractions between the Cd(II) positive species and the negative surface charge, which in the case of as-received carbons derived from the biphthalate anions adsorbed and in the oxidized ones from the carboxyl groups. Tannic acid was used as a model compound for natural organic matter. Its adsorption was greatly reduced after oxidation, and most of the carbon adsorbents preadsorbed with tannic acid showed an increase in Cd(II) uptake. In the case of competitive adsorption between Cd(II) species and tannic acid molecules, there was a decrease in Cd(II) uptake on the as-received carbon whereas the contrary occurred with the oxidized carbons. These results illustrate the great importance of carbon surface chemistry in this competitive adsorption process. Finally, under all experimental conditions used, when the adsorption capacity of carbons was compared under the same conditions it increased in the following order: granular activated carbon < activated carbon fiber < activated carbon cloth.