Adsorption of benzene on the fresh steel surface formed by cutting under high vacuum

The adsorption of benzene on a fresh steel surface was carried out in high vacuum at room temperature. The fresh surface was formed by cutting in a high vacuum chamber, and benzene was allowed to adsorb on the surface during cutting. The adsorption and the surface reaction of benzene was monitored with a quadrupole mass spectrometer. It was found that the cut surface was so active that the catalytic decomposition of benzene occured even at room temperature. The adsorption rate and the sticking probability of benzene were estimated. The adsorption rate linearly increased with cutting speed, that is, the formation rate of the fresh steel surface. It was found that the adsorbed amount was under the monolayer level, and that the adsorption activity of toluene on the fresh surface was about two times larger than that of benzene.     

Adsorption of aromatic compounds from the biodegradation of azo dyes on activated carbon

The adsorption of three selected aromatic compounds (aniline, sulfanilic acid and benzenesulfonic acid) on activated carbons with different surface chemical properties was investigated at different solution pH. A fairly basic commercial activated carbon was modified by means of chemical treatment with HNO₃, yielding an acid activated carbon. The textural properties of this sample were not significantly changed after the oxidation treatment. Equilibrium isotherms of the selected compounds on the mentioned samples were obtained and the results were discussed in relation to their surface chemistry. The influence of electrostatic and dispersive interactions involved in the uptake of the compounds studied was evaluated. The Freundlich model was used to fit the experimental data. Higher uptakes are attained when the compounds are present in their molecular form. In general, adsorption was disfavoured by the introduction of oxygen-containing groups on the surface of the activated carbon.     

The influence of nonpolar organics adsorption on the electrochemical behaviour of powdered activated carbon electrodes in aqueous electrolytes

Adsorption and electrochemical studies were carried out on three activated carbon samples first oxidized, then heat-treated under vacuum (at 180, 500 and 900 °C). The investigations were performed with aqueous electrolyte (Na₂HPO₄ and H₃PO₄) solutions containing selected nonpolar organics (benzene and n-hexane). Adsorption measurements were carried out on solution with a wide range of organics concentration (up to saturation point). Cyclovoltammetric curves of powdered electrodes prepared from the activated carbon samples were recorded for the organics in saturated solutions. The electric double layer capacities of the anodic and cathodic parts were estimated, and the surface anodic and cathodic charge was calculated both in absence and presence of organics in the electrochemical systems. The relative surface charge (in relation to systems without organics) was found to decrease with a reduction in the concentration of surface oxygen-containing groups. Other physicochemical parameters characterizing the degree of surface oxidation (total oxygen concentration, primary water adsorption centres) were also taken into consideration. The correlation between adsorption capacity towards the nonpolar organic compounds (obtained from adsorption isotherms) and change of surface charge was analyzed.     

Low energy electron diffraction and work function change studies of the adsorption of substituted aromatic molecules on the (111) and (100) crystal faces of platinum

The chemisorption of toluene, m-xylene, mesitylene, n-butylbenzene, t-butylbenzene, aniline, nitrobenzene and cyanobenzene were studied on the (111) and (100) crystal faces of platinum at low pressures (10^?9 to 10^?7 torr) and at temperatures of 20 to 300 °C by low energy electron diffraction and work function change measurements. After adsorption, reorientation of the molecules in the adsorbed layer is necessary to form the ordered structures. Molecules that have either higher rotational symmetry (mesitylene) or have only small size substituents on the benzene rings exhibit better ordering if the adsorption is carried out at low incident flux. The adsorbed layers are more ordered on the (111) crystal face than on the (100) crystal face of platinum. The work function changes upon adsorption rangs from ?1.4 eV for nitrobenzene to ?1.8 eV for aniline. Both the diffraction and work function change data indicate that, under the conditions of these experiments, all of the molecules chemisorb with their benzene ring parallel to the surface and interact with the metal surface primarily via the π-electrons in the benzene ring. The substituent groups play an important role in determining the ordering characteristics of the overlayers but do not markedly effect the strength of the chemical bond between the substrate and the adsorbate.     

Wettability modification of pitch-based spherical activated carbon by air oxidation and its effects on phenol adsorption

The surface chemistry of pitch-based spherical activated carbon (PSAC) was modified by air oxidation to enhance its wettability as well as adsorption properties. Changes of PSAC after modification in texture, surface chemistry and wettability were studied by different techniques including N₂ adsorption, X-ray photoelectron spectroscopy (XPS) and dynamic contact angle analyzer (DCA). Phenol adsorption characteristics in different solvents on PSAC were also investigated. When PSAC was modified under an atmosphere with 20 vol.% oxygen at 400 and 450 °C for 5 h, surface acidic groups increased from 0.11 to 1.22 and 1.60 meq/g, while basic groups decreased from 0.52 to 0.03 and 0.02 meq/g, respectively. After PSAC was modified, the increase of the oxygen-containing groups, especially carboxylic and phenolic ones, is responsible for the increasing of the surface acidity and the significant improvement of the wettability of PSAC. PSAC with a relatively high oxygen content provided a low adsorption capacity to phenol in aqueous solution, and the adsorption isotherms change from Langmuir class (L) to the S-shaped curve; while the solvent is changed into cyclohexane, all adsorption isotherms are type L, and the adsorption capacity to phenol increases with increasing oxygen-containing groups. Possible reasons, including the solvent effect, π-π dispersion and donor-acceptor interactions are discussed.     

两种不同极性有机小分子在方解石(104)面吸附的密度泛函研究

利用密度泛函理论研究苯甲酸和甲苯两种不同极性的有机小分子在方解石（104）面的吸附特征，分析极性对有机小分子吸附的影响.结果表明：苯甲酸趋向于以分子态、单齿吸附模式倾斜吸附于方解石（104）面，吸附能为-1.394 eV；甲苯平行吸附于方解石（104）面，吸附能为-0.362 eV.有机小分子吸附于方解石（104）面过程中体系的几何结构和电子结构发生明显变化.苯甲酸分子几何结构变化幅度远大于甲苯.苯甲酸与方解石（104）面之间形成Ca-O离子键和H-O共价键，甲苯与方解石（104）面之间仅存在微弱的氢键相互作用.苯甲酸和甲苯等两种不同极性有机小分子在方解石（104）面的吸附特征和吸附机理存在较大的差异，苯甲酸分子的吸附强度远高于甲苯.本文揭示了不同极性有机小分子在方解石（104）面的吸附机理，为提高油藏采收率和矿物浮选等工程问题提供理论依据.     

An In Situ Testing Method for Analyzing the Changes of Active Groups in Coal Oxidation at Low Temperatures

This study details an in situ Fourier transform infrared spectroscopy analytical system that was employed to follow chemical variations in the functional groups on coal surface during the oxidation process at low temperatures. In the reported in situ Fourier transform infrared spectroscopy system, a special chamber was used to contain the coal powders, and a gas inlet tube and a programmable heater were used to simulate different reaction atmospheres and temperatures. The comparisons between in situ and ex situ Fourier transform infrared spectroscopy spectra indicate that the in situ Fourier transform infrared spectroscopy data offer a more accurate reflection of changes in the functional groups. The real-time changes of aliphatic hydrocarbon groups and oxygen-containing groups in a lignite coal sample were analyzed from 30°C to 220°C using in situ Fourier transform infrared spectroscopy. The experimental results indicate that the chemical variations in the functional groups are affected by their relative chemical activities. The results show that the presence of aliphatic groups on the coal surface varies with temperature. Over the range of 30–70°C the presence of these groups decreases, but then their abundance increases over the range of 70–180°C and finally decreases again when the temperature is increased to between 180°C and 220°C. With respect to oxygen-containing functional groups, three various trends were observed as the test temperature was varied. Our conclusion was that these variations are a function of the reaction activities of the various oxygen-containing functional groups.     

Surface modification of a granular activated carbon by dielectric barrier discharge plasma and its effects on pentachlorophenol adsorption

The surface properties of a granular activated carbon (GAC) were modified by dielectric barrier discharge (DBD) plasma to enhance its adsorption capacity to pentachlorophenol (PCP). Surface characteristics and adsorption capacity of GAC before and after DBD plasma modification were investigated. Results showed that the surface of GAC after plasma modification, especially N₂ plasma, became smoother and the particulates on virgin GAC's surface were eliminated due to deposit effect of plasma. The N₂ plasma modification reduced the specific surface area and surface oxygen-containing functional groups of GAC. In contrast, O₂ plasma modification increased the specific surface area and introduced oxygen-containing groups.     

Controllable synthesis and modification of carbon micro-spheres from deoiled asphalt

A series of size-controllable carbon micro-spheres (CMSs) were synthesized from deoiled asphalt by chemical vapour deposition, with the emphasis on the effect of reaction temperature, Ar flow rate and collection zone. Graphitized carbon micro-spheres (GCMSs) were obtained from as-prepared CMSs by vacuum heat treatment at 2000 °C for 1 h. Air oxidation was performed to realize functionalization of CMSs. Morphologies and structures of CMSs and GCMSs were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and Raman spectroscopy, and the functional groups on the surface of GCMSs and CMSs were characterized by Fourier transformation infra-red spectrometry. Results show that effective mass production of size-controllable CMSs, with diameters ranging from 100 nm to 1 μm, was achieved. As-obtained high purity CMSs were spherical with uniform size and low graphitization degree, but the graphitization degree of GCMSs was enhanced obviously. By air oxidation, some oxygen-containing functional groups were introduced onto the surface of CMSs, while no functional groups were introduced onto the surface of GCMSs.     

乙烯渣油沥青基活性炭纤维和粘胶基活性炭纤维的表面性质与脱硫活性

研究了在Ｏ２和Ｈ２Ｏ存在下,乙烯渣油肝基活性炭纤维（ＥＴＰ ＡＣＦ）和粘胶基活性炭纤维（Ｃｅｌｌｕｌｏｓｅ ＡＣＦ）的脱硫活性,结果表明,在比表面积相近的情况下,ＥＴＰ ＡＣＦ的脱硫活性明显低于Ｃｅｌｌｕｌｏｓｅ ＡＣＦ,官可归因于后者具有较强的吸附和催化氧化ＳＯ２能力及较大的吸水量,尤其是具有较强的催化氧化Ｓ２的能力,这些能力又珉春表面含有含氮官能团以及某些含氧官能团有关,因此ＡＣＦ的表面官能团     

Simple approach to carboxyl-rich materials through low-temperature heat treatment of hydrothermal carbon in air

It was found that a large number of oxygen-containing functional groups (OFGs) could be created on the surface of hydrothermal carbon (HTC) by simply heating at lower temperature in air during the course of our preliminary experiments which focused on oxidation pre-treatment of pristine HTC for the purpose of grafting functionalization. Especially carboxyl groups on HTC would increase significantly, from 0.53 to 3.70 mmol/g after heat treatment at 300 °C. So, effects of heat-treatment on the OFGs on the carbon microsphere were deeply studied to confirm and explain the findings. Experiments involving different materials (HTC, activated carbon and glucose) were performed under varying conditions (heating temperature and time, in air or in Ar atmosphere). A reaction mechanism for newly generating carboxyl groups on HTC surface during heat-treatment process was supposed based on the results from the sample characterization using Boehm titrations, infrared spectra, X-ray photoelectron spectroscopy, energy dispersive spectrometry and elemental analysis. In addition, the as heat-treated product has excellent sorption capability for Pb²⁺ and Cd²⁺ ions.     

臭氧修饰(001)晶面TiO2纳米片及其光催化降解甲苯研究

本文系统研究了臭氧修饰对(001)主导晶面锐钛矿型TiO₂光催化剂降解甲苯性能的影响. 利用自行搭建的光催化VOCs降解装置对催化剂光降解甲苯的性能进行了测试. 通过多种表征手段,结合原位DRIFTS和DFT计算研究了臭氧表面修饰及甲苯吸附和降解机理. 结果表明,用臭氧进行表面修饰可以显著提高(001)主导晶面TiO₂光催化降解甲苯的性能. (001)晶面上丰富的5c-Ti不饱和配位是臭氧分子的吸附位点,其解离后形成的Ti-O键与H₂O分子结合,在表面生成大量孤立的Ti_5c-OH. Ti_5c-OH 是甲苯分子的吸附位,它的形成显著提高了对甲苯分子的吸附能力. 在光照下Ti_5c-OH与光生空穴结合能形成·OH自由基. 通过臭氧解离产生的O₂也可以与光生电子结合形成超氧自由基. 这些具有强氧化性活性自由基的形成促进了对气相甲苯的光催化降解速率.     

Effect of oxygen surface groups on adsorption of benzene derivatives from aqueous solutions onto active carbon samples

The process of adsorption of selected benzene derivatives from aqueous solution is investigated on two carbonaceous materials of differentiated surface properties - quantity of oxygen functional groups. Carbon samples were prepared by removal of external layers from granules of unmodified and oxidized active carbon. The surface and structure characteristics of carbon samples were estimated by various methods. The experimental isotherms of organics adsorption from liquid phase were measured and interpreted in terms of the theory of adsorption on heterogeneous solid surfaces. The influence of differences in adsorbate and adsorbent properties on adsorption uptake was analyzed. The adsorption effectiveness was regarded as a result of the differences in adsorbate hydrophobicities and the effect of specific interactions of its functional groups with active sites on carbon surface.     

pH‐dependent surface‐enhanced Raman scattering observation of sulfanilamide on the silver surface

Monolayers of sulfanilamide on metallic surface can serve as an ideal model for understanding the interaction mechanism between the metal and the sulfanilamide molecule. In the present paper, the surface‐enhanced Raman scattering (SERS) technique was employed to obtain the SERS spectra of sulfanilamide monolayers formed on the silver surface under different pH values. Assignments of the spectra were carried out with the aid of density functional theory (DFT) calculations (BLYP/6‐311G). It can be found that the adsorption function of sulfanilamide on the silver surface was influenced by the pH value. The fully protonated sulfanilamide molecule adsorbed on the silver surface through N¹³H₂ group and the benzene ring anchored in a relatively perpendicular manner leading to N⁷H₂ and S¹⁰O₂ groups near the surface, while the completely deprotonated sulfanilamide molecule attached on the silver surface via N⁷H₂ and the benzene ring was perpendicular to, and the N¹³H₂ and S¹⁰O₂ groups were far from the silver surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Regeneration of AG–AC beads for adsorption of monoaromatic compounds

This study investigates the possibility of monoaromatic compounds benzene and toluene adsorption onto alginate gel (AG–AC) beads with impregnated activated carbon and their regeneration possibility using ultrasound method. Kinetic adsorption tests showed that the AG–AC beads were capable of removing the organic compounds from either individual or mixed compound solutions. Removal ratio of the AG–AC beads was as high as that of free PAC powder for benzene and toluene. The removal was more efficient for toluene (97%) than for benzene (75%), and slightly decreased by 7% and 5% for toluene and benzene respectively even after 5 times regeneration. This indicates that the regeneration method utilizing ultrasound is very efficient for desorption of benzene and toluene from the AG–AC beads developed in this study.     

Influence of organic vapours on exo-electron emission from sandblasted mild steel

The influence of various organic vapours on the exo-electron glow curves for sandblasted mild steel was examined. The emission intensity of the peak which was observed at 51–66 °C in the glow curve was ranked as follows: n-butyl chloride? acetonitrile < benzene < methanol?toluene?acetone?ethanol?isopropyl alcohol< ethyl acetate? propylamines. This listing closely resembles to that of the proton attracting power of the functional groups of the organics. From this, it is supposed that the peak emission may be promoted through the formation of hydrogen bond between the functional groups and the deformed solid surface.     

Heterogeneous adsorption and catalytic oxidation of benzene, toluene and xylene over spent and chemically regenerated platinum catalyst supported on activated carbon

The heterogeneous adsorption and catalytic oxidation of benzene, toluene and o-xylene (BTX) over the spent platinum catalyst supported on activated carbon (Pt/AC) as well as the chemically treated spent catalysts were studied to understand their catalytic and adsorption activities. Sulfuric aqueous acid solution (0.1N, H₂SO₄) was used to regenerate the spent Pt/AC catalyst. The physico-chemical properties of the catalysts in the spent and chemically treated states were analyzed by using nitrogen adsorption-desorption isotherm and elemental analysis (EDX). The gravimetric adsorption and the light-off curve analysis were employed to study the BTX adsorption and oxidation on the spent catalyst and its modified Pt/AC catalysts. The experimental results indicate that the spent Pt/AC catalyst treated with the H₂SO₄ aqueous solution has a higher toluene adsorption and conversion ability than that of the spent Pt/AC catalyst. A further studies of H₂SO₄ treated Pt/AC catalyst on their catalytic and heterogeneous adsorption behaviours for BTX revealed that the activity of the H₂SO₄ treated Pt/AC catalyst follows the sequence of benzene > toluene > o-xylene. The adsorption equilibrium isotherms of BTX on the H₂SO₄ treated Pt/AC were measured at different temperatures ranging from 120 to 180 °C. To correlate the equilibrium data and evaluate their adsorption affinity for BTX, the two sites localized Langmuir (L2m) isotherm model was employed. The heterogeneous surface feature of the H₂SO₄ treated Pt/AC was described in detail with the information obtained from the results of isosteric enthalpy of adsorption and adsorption energy distributions. Furthermore, the activity of H₂SO₄ treated Pt/AC about BTX was found to be directly related to the Henry's constant, isosteric enthalpy of adsorption and adsorption energy distribution functions.     

Ethylene and phenylene bridged polysilsesquioxanes functionalized by amine and thiol groups as adsorbents of volatile organic compounds

Ethylene and phenylene bridged polysilsesquioxane xerogels having amine and thiol groups attached to the surface have been obtained by the sol-gel method from 1,2-bis(triethoxysilyl)ethane or 1,4-bis(triethoxysilyl)benzene and functionalized silanes in the presence of an ammonium fluoride catalyst in an ethanol solution. The synthesized samples have a porous structure (700-850 m²/g) and a high content of functional groups (1.4-1.9 mmol/g). The obtained porous bridged polysilsesquioxanes exhibit a considerable affinity for adsorbing several organic compounds (n-hexane, n-heptane, benzene, cyclohexane, acetonitrile and triethylamine) from the gas phase. The sample with an ethylene bridge and amino groups in the surface layer has the highest uptake of all compounds. Data from adsorption measurements show that functionalized organosilicon materials can be used as effective adsorbents of organic contaminants from the gas phase.     

Quantum chemical and NMR investigations on structure of surface complexes

The semiempirical quantum chemical CNDO/2 method is used to calculate models of specific interaction between benzene, toluene, and butene molecules, respectively, and ions or hydroxyls representing active sites of adsorption on zeolitic surfaces. From energy minima of full potential curves the stabilization energies of the surface complexes have been obtained. On the basis of proposed complexes theoretical carbon-13 NMR chemical shifts of adsorbed molecules are calculated. The theoretical results are in rather good agreement with the experimental ones, confirming the conception of surface complexes. Moreover, experimental paramagnetic shifts of surface complexes containing Co²⁺ ions are tried to interprete in a quite similar way.