Calorimetric Investigation of Adsorption of Organic Compounds by Active Carbons

Enthalpies of wetting of two active carbons and one brown coal coke by several pure liquids (mainly homologous series) were measured at 298.15 K with two quasi-isothermal microcalorimeters. Different measuring cells with cavities of about 0.5 and 15 cm³ were used. The advantage of the larger measuring cell with three independent 15 cm³ cavities is the higher mass of active carbon, leading to a high reproducibility with standard deviations below 1% and a reduced measuring time. Experiments were carried out with n-alkanes, l-alkanols, cycloalkanes and isomers thereof, i.e. 2-propanol, methylcyclohexane, 2,2,4-trimethylpentane (isooctane and 2-ethyl-1-hexanol, and water. Like the polarity, the size and the three-dimensional expansion of the molecules, the energetic and geometric heterogeneity of the adsorbent influences the enthalpy of wetting. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparative Study of the Adsorption from Aqueous Solutions and the Desorption of Phenol and Nonylphenol Substrates on Activated Carbons

Adsorption of phenol and nonylphenol from aqueous solutions on microporous activated carbons has been studied. The phenol isotherm changes from L-shaped for surface oxygen group free carbon (I sample) to a two-stepped isotherm for oxidized carbon (IN sample, HNO(3) treated) Furthermore, the adsorbed amounts diminish in about 25% on IN carbon. It is proposed that a change in the adsorption mechanism take place; i.e., weak interaction forces between the pi electrons in phenol and the pi electron in carbon are present on the original I carbon, while a donor-acceptor complex on the oxidized IN carbon is operating between basic surface oxygen groups and phenol aromatic rings. The shape of nonylphenol isotherms is two-stepped for both carbons. The introduction of acidic oxygen surface groups on the carbon enhances the specific nonylphenol adsorption by about 40%. This may be interpreted as being due to the fact that nonylphenol is hydrogen-bonded to the oxidized carbon surface by means of acidic groups. Thermal desorption experiments indicate that phenol is mainly physisorbed. Thermal desorption further confirms that nonylphenol is possibly bonded to oxygen surface groups by hydrogen bonds. Copyright 2001 Academic Press.     

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.     

Effect of Microwave Irradiation on Reaction of Arylaldehyde Derivatives with Some Active Methylene Compounds in Aqueous Media

Abstract

The effect of microwave irradiation on the condensation reactions of arylaldehydes 1 and active methylene compounds 2 in aqueous media was studied and compared with “classical” conditions. The results show that the condensation was carried out only under microwave irradiation in the presence of ammonium chloride as a catalyst, followed by dehydration, to afford (E)‐olefins 3. The protocol was used to synthesize coumarins by a condensation reaction of salicylaldehyde or its derivatives with various derivatives of ethylacetate 5 (e.g., R³CH₂CO₂Et; R³: CO₂Et, CO₂Me, COMe, CN) in high yields. These investigations will contribute to the development of environmentally friendly and inexpensive processes in organic synthesis.     

Energies of Intermolecular Interaction and Hydration of Benzene Derivatives Molecules Adsorbed on Active Carbon from an Aqueous Solution

Energy heterogeneity of an adsorbent surface does not affect the isotherm of adsorption from aqueous solutions. Therefore, the balance of the changes in the Gibbs energy resulted from the adsorption of sparingly water-soluble substances shows that, in the whole range of filling of the adsorption phase, the pattern of the adsorption isotherm depends on the difference between the energy of the interaction of adsorbed molecules with each other and the energy of their hydration needed to displace water molecules from the adsorption phase. The standard adsorption energy of molecules of benzene and its derivatives from aqueous solutions and the difference between the energy of their interaction in the adsorption phase and the energy of their hydration are determined by the extrapolation of adsorption isotherms of these substances to the standard conditions ( 0, C 0) and to the conditions of maximal approach of the adsorbed molecules to each other ( 1). The hydration energy of the molecules of benzene and its derivatives is calculated based on the proportionality of this energy to the sum of the concentration potentials of the components in a saturated solution, where the proportionality coefficient is equal to the number of water molecules interacting with one organic molecule. Calculated energies of phenol and aniline hydration are equal to the energies of H-bonds of phenol (OH···OH₂) and amino (NH···OH₂) groups. Hydration energies of phenol and aniline derivatives vary according to the effect of a substituent in the benzene ring on the H-bond energy. Negative values of hydration energy of polar hydrophobic molecules result from their hydrophobic effect on water structure. The interaction energy of hydrated and dehydrated adsorbed molecules, whose benzene ring planes are oriented in parallel to the carbon surface, is found from the calculated hydration energies. For H-bond-forming molecules, this energy is equal to the energy of one H-bond formed upon the surface dimerization. The energy of repulsion between polar hydrophobic molecules of benzene derivatives depends on the vertical component of the dipole moment, and is the higher the larger the polar group volume.     

Adsorption of Molybdenum on Titania from Aqueous Solutions

The adsorption of Mo from dilute aqueous solutions (10(-3) to 3x10(-2) M) is effected on three samples of titania, two are anatase and the third is P25, which is composed of rutile and anatase. The adsorption isotherms at 298, 318, and 338 K are analyzed using a Langmuir linear equation. The isotherms on P25 showed a distinct inflection point that is reproduced by two linear portions, indicating different adsorption regimes. This adsorption behavior is explained as follows: with low amount adsorbed the adsorption is initiated by protonation of the basic hydroxyls on which the negatively charged MoO(4)(2-')s are adsorbed, and this is accompanied by an increase in the pH of the impregnating solution. At higher adsorption the coordinatively unsaturated Ti(4+) sites participate in the process, leading to a decline in the initial increase in pH. In the case of the two anatase samples the low surface area resulted in poor distribution of adsorption sites; consequently, the distinction between the two modes of adsorption was not entirely clear. The higher adsorption site density in the case of anatase is accompanied by a lower surface coverage, θ, than that for P25. The heat of adsorption, Q, on the three titania samples showed a linear increase with θ, which is represented by the regression equation: -Q=95.77θ-4.25 (R(2)=0.993). Copyright 2001 Academic Press.     

Adsorption of Zn(OAc)2 from Aqueous Solutions on the Surface of Activated Carbons Modified with Acetic Acid

Adsorption of zinc acetate on the surface of activated carbons modified with acetic acid was studied as a function of the process temperature, initial concentration of the salt, and pH of the initial solution.     

甲烷在特制活性炭上吸附性能

用不同的原料制得了多种高比表面的活性炭吸附剂．用标准容积法测得高压下（０～５０ＭＰａ）不同活性炭对甲烷的吸脱附等温线,得到了吸附容量和有效吸附容量．研究了温度对吸附等温线的影响．利用ＣｌａｕｓｉｕｓＣｌａｐｅｙｒｏｎ方程解析了甲烷在活性炭上的等量吸附热．结果表明,活性炭对甲烷的吸脱附存在着滞后现象,活性炭的比表面和堆密度是活性炭吸附性能的主要指标,找到了最佳甲烷吸附剂．     

活性小分子DHMBA含氮衍生物的合成及其抑菌活性

以没食子酸甲酯为原料,通过甲基化、还原反应制得牡蛎中的活性小分子DHMBA,并进一步通过PCC氧化、缩合反应合成其含氮衍生物(4a～4d);为进行构效分析,分别选用与DHMBA分子结构相近的丁香醛和2,3,4-三羟基苯甲醛作为原料,通过缩合反应制得一系列含氮衍生物(5a～5d)和(6a～6d),其结构经¹H NMR, ¹³C NMR和HR-MS(ESI)表征。采用滤纸片法测试了化合物2～6对大肠杆菌和金黄色葡萄球菌的抑制活性。结果表明:在10～40 mg·mL^-1内,化合物4～6对受试菌种均表现出一定的抑制活性,其中4b、 6b和6d的抑菌活性最为显著。      

杉木活性炭吸附处理水溶液中的尼古丁

用不同孔径及化学性质的活性炭对尼古丁水溶液进行吸附研究. 以杉木屑为原料, 分别用氯化锌化学活化法和水蒸气物理活化法制备活性炭, 并分别命名为AC-Z和AC-H. 同时选用椰壳基商品活性炭作为对比吸附剂, 命名为AC-C. 采用比表面积孔径测定分析仪及Boehm滴定法对活性炭进行表征, 分别测定其比表面积、孔径分布和表面官能团含量. 吸附实验主要考虑吸附时间、温度和尼古丁溶液的初始浓度三个因素, 实验数据分析结果表明微孔有利于物理吸附的进行, 而表面酸性官能团及金属原子作为吸附活性位的作用更加重要. 由改变温度对各样品的吸附量影响也能说明活性位在吸附中的作用. AC-Z拥有较多的活性位, 温度变化时尼古丁的吸附量先升高后减小, 这主要是由于适合的温度能加快尼古丁分子的离解并促使其与活性位相结合, 而过高的温度会造成尼古丁分子动能增加, 导致分子间碰撞的机率和强度增大, 使吸附在活性炭表面的尼古丁分子脱落. AC-H和AC-C由较多的微孔和不同程度的活性位组成, 优先发生物理吸附, 并且伴随发生吸附剂表面分子团簇现象, 其吸附趋势与AC-Z相反. 动力学研究表明活性炭对尼古丁的吸附反应非常迅速, 并且符合准二阶动力学程模型. 各热力学参数ΔG⁰, ΔH⁰和ΔS⁰的计算结果表明吸附剂对尼古丁的吸附为吸热和自发性过程.AC-Z和AC-H的ΔH⁰值远低于AC-C, 说明吸附剂表面的活性位对尼古丁分子有强烈的吸引作用, 所以吸附相同数量吸附质分子所需的吸附热更小, 这也说明了活性位在吸附过程中发生作用.     

Adsorption of Organic Bases from Aqueous Solutions on Magnesium Oxide

The adsorption of a series of aromatic and heterocyclic nitrogen-containing compounds on the surface of MgO is investigated under static conditions. It was established that the energy of adsorption of organic bases depends linearly on the effective charge of their nitrogen atoms. It was shown that such a correlation can be explained based on the concepts of the predominant electrostatic interactions in an adsorption complex with a hydrogen bond.     

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.     

Separation of Dyes from Aqueous Solutions by Paper Adsorption

Separation of the dyes methyl violet, methylene blue, and congo red from aqueous solutions by paper capillary permeation adsorption method was studied using paper. Nearly 100% of the investigated dyes could be separated under the optimum conditions. The effect of pH on the separation efficiency was studied in particular. At pH 5–9, 1.3–11, and 7–11, the maximum separation was achieved for methyl violet, methylene blue and congo red, respectively. The effects of dye concentration and some foreign ions on the separatability were examined. Moreover, the selective separation of some dyes was attempted by elution with chemical reagents.     

炭材料对铀的吸附

铀既是核燃料的主要成分又是乏燃料后处理的关键核素。将铀从乏燃料后处理流程中的高放射性料液或者其他含铀废水中分离出来既可以将此宝贵的核燃料回收使用,又有利于降低乏燃料处理后期的处置费用,以及减少铀对环境的污染。而从海水、盐湖水、尾矿废水等贫铀水体中提取铀则可能是解决将来铀资源匮乏的主要方法。炭质材料具有较大的比表面积、较高的孔隙率,耐高温,抗辐射,对各种酸碱环境有很高稳定性,而且本身无毒,环境友好,有望作为吸附剂或固相萃取材料用于从水体中吸附分离铀。本文介绍了活性炭、介孔炭、碳纳米管等材料对铀的吸附研究进展。表面功能化可以提高炭材料对铀酰离子的吸附容量与选择性,对炭材料功能化的方法主要有表面氧化、浸渍、负载和接枝等手段。由于化学稳定性高,采用化学方法在炭材料表面接枝功能分子是具有应用前景的研究方向。采用碳纤维作电极,电吸附铀的方法可以大量地从水溶液中将铀吸附到电极表面,再通过电脱附回收铀,具有工业化应用前景。     

Fractal Approach to Adsorption Isotherms of Water Vapor on Active Carbons

Adsorption isotherms of water vapor on active carbons are interpreted in terms of the fractal approach. The linear range of plots in the steep rise of the adsorption branch is the process of the cluster formation of water on the seed water molecules adsorbed on the primary adsorption centers, mainly the oxygen-surface complexes, with the fractal dimension D = 1.64-1.67 which is equivalent to that for the diffusion-limited aggregation (DLA) model with D approximately 1.66. Also, it is shown that the two-dimensional characteristics of micropore structures are reflected in the adsorption branch and the three-dimensional ones are in the desorption branch, respectively, by the analyses of the D and the average micropore width L based on the characteristic adsorption amounts at the beginning and the ending points of the steeply rising and falling linear ranges on both branches. Copyright 1999 Academic Press.     

Tailoring Properties of Resol Resin-Derived Spherical Carbons for Adsorption of Phenol from Aqueous Solution

The polycondensation of resorcinol and formaldehyde in a water–ethanol mixture using the adapted Stöber method was used to obtain resol resins. An optimization of synthesis conditions and the use of an appropriate stabilizer (e.g., poly(vinyl alcohol)) resulted in spherical grains. The resins were carbonized in the temperature range of 600–1050 °C and then chemically activated in an aqueous HNO₃ solution, gaseous ammonia, or by an oxidation–reduction cycle (soaking in a HNO₃ solution followed by treatment with NH₃). The obtained carbons were characterized by XRD, the low-temperature adsorption of nitrogen, SEM, TGA, and XPS in order to determine degree of graphitization, porosity, shape and size of particles, and surface composition, respectively. Finally, the materials were tested in phenol adsorption. The pseudo-second order model perfectly described the adsorption kinetics. A clear correlation between the micropore volume and the adsorption capacity was found. The content of graphite domains also had a positive effect on the adsorption properties. On the other hand, the presence of heteroatoms, especially oxygen groups, resulted in the clogging of the pores and a decrease in the amount of adsorbed phenol.     

4A沸石从水溶液中吸附氯化十四烷基吡啶

4A沸石可部分或全部代替三聚磷酸钠,以减少合成洗涤剂对水质富营养化的影响,在硬水中使用也不致降低洗涤效力.本文研究了4A沸石在不同pH水溶液中和无机盐存在下对氯化十四烷基吡啶(TPC)的吸附作用,初步探讨了吸附机制.     

Partial Molar Volumes of Aqueous Solutions of Some Halo and Amino Derivatives of Uracil

Apparent molar volumes were experimentally determined at 25, 35, and 45°Cfor aqueous solutions of uracil, 5-fluorouracil, 5-chlorouracil, 6-chlorouracil,5-bromouracil, 5-iodouracil, 5-aminouracil, 6-aminouracil,6-amino-1,3-dimethyluracil, and 5-nitrouracil. The solubility of each compound in water was measuredat 25°C. Partial molar volumes and structural parameters of the moleculesinvestigated were determined. The relations between these data and solubility andpolarity were found and discussed. The partial molar volumes for halo derivativesand 6-amino-1,3-dimethyluracil increase, with increasing temperature whereasthose for 5-aminouracil, 6-aminouracil, and 5-nitrouracil remain constant withinthe limit of experimental error.     

Solubilization of Benzene and Several Benzene Derivatives in Dilute Aqueous Solution of 18-Crown-6

Solubilities of benzene, toluene, nitrobenzene, p-and o-nitrotoluene in dilute aqueous solutions of 18-crown-6 have been determined by UV-spectrometry at 15, 25, and 35°C. The saturation concentration of each aromatic solute depends linearly on the l8-crown-6 concentration. Experimental results show that 18-crown-6 molecules form host-guest complexes (with 1:1 stoichiometry) with the aromatic molecules, which supports the assumption that the force of combination between the crown ether and the aromatic molecules is a weak hydrophobic interaction.