The behaviour of high polar organic solvents on platinum electrodes—I. The study of adsorption and electrode reactions of dimethylsulphoxide

The adsorption of dimethylsulphoxide and reactions of adsorbed molecules at platinized platinum electrode were studied by potentiodynamic and radiometric techniques. The adsorption of dimethylsulphoxide is described by Temkin type isotherm. The adsorbed dimethylsulphoxide is reduced in two steps to dimethylsulphide in the hydrogen range of potentials and oxidized to dimethylsulphone above 0.6 V. The latter product is desorbed from the surface of the electrode.     

The behaviour of high polar organic solvents at platinum electrode—III. the study of adsorption and electrode reactions of N,N-dimethylformamide

The adsorption of N,N-dimethylformamide and oxidation of adsorbed species at platinized platinum electrode in 0.5 M aq H₂SO₄ were studied by potentiodynamic, potentiostatic and radiometric techniques. It was shown, that adsorption occurs with decomposition of DMF molecule. Below 0.15 V the adsorbed species are desorbed from the electrode surface.The kinetics of adsorption and oxidation of DMF are described by Langmuire type relation. The mechanism of adsorption of DMF as well as oxidation of adsorbed products has been considered.     

The influence of electrode structure on the adsorption and electro-oxidation of ethylene on platinum

The adsorption and electro-oxidation of ethylene in acid electrolyte were studied on differently prepared platinum electrodes. A clear dependence of the apparent specific catalytic activity for ethylene electro-oxidation on platinum electrode structure was observed. Platinized platinum electrodes exhibit a low apparent specific catalytic activity which decreases on increasing the roughness factor due to additional overpotential contributions within the pores. The specific adsorptive characteristics and catalytic activity of non-porous platinum electrodes prepared by electroreduction of thick platinum oxide layers are independent of roughness factor and similar to those of smooth platinum electrodes.     

The behaviour of high polar organic solvents at platinum electrode — II. Adsorption and electrode reactions of acetonitrile

The adsorption of acetonitrile and reduction of adsorbed molecules at platinized platinum electrode were studied by potentiodynamic and radiometric techniques. During acetonitrile adsorption the reversibly and irreversibly adsorbed species are formed. One electron reduction process occurs in the potential range 0.45-0.15 V. Below 0.15 V the deeper reduction of adsorbed acetonitrile takes place — the final products are ammonia and ethane. The differences of smooth and platinized platinum electrodes properties are briefly discussed.     

The oxidation of aromatic organic compounds at a lead dioxide electrode

The direct electrochemical oxidation of some aromatic hydrocarbons has been investigated using the methods of electrode kinetics. The results are used to suggest conditions under which the oxidation reaction could be used for larger scale synthesis of the corresponding aromatic alcohol and aldehyde.     

Radiotracer study of the adsorption of pimelic acid at a platinized platinum electrode

The adsorption of pimelic acid has been studied in 1 mol dm⁻³ HClO₄ supporting electrolyte. The potential dependence of the adsorption, the mobility of the adsorbed species and the effect of other saturated aliphatic acids (acetic, malonic, succinic and adipic acids) and Cl⁻ ions on the adsorption were investigated. A reversible adsorption was found in the potential range from 400 to 800 mV. At lower potentials (100-400 mV) a slow chemisorption takes place resulting in strongly chemisorbed species which can be eliminated by reduction and oxidation. The behaviour of loosely adsorbed species involved in the reversible process is similar to that observed for other saturated acids. A sequence for the relative adsorbability of different dicarboxylic acids was established on the basis of the experimental results. Factors influencing the adsorbability were discussed.     

介孔分子筛在挥发性有机化合物吸附中的研究进展

挥发性有机化合物(VOCs)是破坏生态环境质量的重要污染物,近年来发现介孔分子筛对VOCs有较好的吸附效果.综述了近年来介孔分子筛在VOCs吸附中的研究进展,详细讨论了VOCs在介孔分子筛吸附剂上的吸附过程,并对以后介孔分子筛吸附剂的研究提出了建议.     

VOCs在分子筛上吸附性能的研究进展

简单介绍了一些常见分子筛的构型及特点,讨论了不同构型分子筛对各种VOCs废气吸附效果的研究进展。总结了各类分子筛对VOCs的吸附特性,发现立方构型的分子筛对VOCs废气的吸附效果最佳。小结了影响分子筛吸附性能的因素,发现分子筛的比表面积、孔容、硅铝比、表面官能团等自身性质都会对吸附VOCs废气的性能产生一定的影响。另外,分子筛的吸附容量还与吸附时的进气流速、入口气体浓度、吸附剂床层高度等工况有关。最后,对现有研究做了总结与展望,为分子筛吸附VOCs的合理应用提供了理论支持。     

Removal of hydrophilic pollutants from water with organic adsorption polymers: Part I. Adsorption behaviour of selected model compounds

The adsorbability of 2-aminonaphthalene-1-sulfonate, diuron, 1-naphthol and natural organic matter (NOM) onto an organic polymer resin and onto activated carbon was investigated. Isotherms with the substances alone and in the presence of dissolved NOM were measured. There was a good adsorbability of diuron and 1-naphthol on both sorbents. At low initial concentrations of the compounds the activated carbon showed higher adsorptivity, whereas for high initial concentrations the polymer resin showed an equal or better adsorption behaviour. 2-Aminonaphthalene-1-sulfonate and the NOM showed favorable adsorption behaviour to activated carbon but was only poorly adsorbed on the polymer resin. In the presence of NOM, the adsorbability of the single compounds decreased significantly on activated carbon. Nearly no influence was found for the adsorption of the pollutants on the resin. For the polymer resin, additionally, the breakthrough behaviour of the substances was investigated. The results obtained in the batch experiments for the single substances were confirmed. However, in the presence of NOM the breakthrough occurred at shorter times for all three substances. Regeneration of the resin with isopropanol proved to be a good cleaning method. A recovery of 92–96% of the substances was reached.     

The adsorption of chlorobenzene on the gold electrode

The dependence of adsorption of chlorobenzene at the gold/electrolyte (0.5 M H₂SO₄) interface on electrode potential, bulk concentration and temperature has been investigated using a ¹⁴C-radiotracer technique. For higher bulk concentrations of chlorobenzene, multilayer adsorption has been observed. It has been shown that the diffusion is the rate determining step of the adsorption process. The chlorobenzene molecule are probably perpendicularly Orientated to the Au surface and the chlorine atom of the molecule is contacting the gold electrode.     

湿度对油烟中易挥发有机化合物吸附的影响

主要研究了甲醛、乙醛和苯在有机硅烷KH560和1706改性活性炭(AC)表面的脱附活化能,并通过透过曲线实验测定了不同湿度对三者在改性活性炭上吸附的影响,最后用光电子能谱(XPS)分析材料表面的亲水基团和憎水基团比例的变化。结果表明,采用有机硅烷改性活性炭可提高材料的憎水性,在较高湿度下(RH60%),三者在未改性活性炭固定床穿透时间减少得最多,1706/AC固定床次之,KH560/AC固定床最小;程序升温脱附(TPD)实验表明,用有机硅烷改性活性炭可以削弱水和活性炭表面的结合力,增强与甲醛、乙醛和苯的结合力。通过XPS分析,与未改性活性炭相比,经有机硅烷改性的活性炭,其憎水性得到提高。     

Water-induced effects on the adsorption on polycrystalline platinum (II. Interaction of carbon monoxide and water)

The adsorption and desorption of carbon monoxide and water as well as interaction between them on polycrystalline platinum has been studied using the technique of thermal desorption spectroscopy (TDS) under ultrahigh vacuum (UHV) conditions. A small amount of water adsorbs on the surface of the platinum at 310K and desorbs readily and steadily in the temperature range of 350-450 K. When exposure of water by more than 100 L is followed by saturation exposure of carbon monoxide, the height of carbon monoxide desorption peak appeared at 790 K becomes higher. It suggests that preadsorbed water dissociates a small part of carbon monoxide to atomic carbon and oxygen on the surface of the sample. And, interaction of water and carbon monoxide (or atomic carbon) results in the water-gas shift reaction.     

Electrocatalytic oxidation of organic molecules in alkaline solutions—I. Oxidation of 1,3 dioxolane at platinum

The electroadsorption and electrooxidation of 1,3 dioxolane at platinum in 1 M KOH solutions were investigated under a wide range of experimental conditions. The potential of maximum adsorption (E^max_ad) is ca. 0.4 V and the degree of surface coverage depends linearly with the logarithm of organic concentration as predicted by a Temkin type adsorption isotherm. The kinetics of the electroadsorption process follows a Roginskii-Zel'dovich equation. From (eps)_ad, (eps)_ox and analysis of oxidation products a mechanism is postulated which consists of an adsorption with simultaneous dehydrogenation step followed by cycle rupture and electroadsorption and dehydrogenation of further residues.     

挥发性有机物治理工艺及催化剂研究进展

介绍近几年挥发性有机物治理工艺的研究进展,并对所用到的吸附剂及催化剂进行综述。综合考虑处理挥发性有机物的效率、原料成本和能耗等因素,以分子筛作为吸附载体和催化剂载体的吸附与催化氧化联用法是目前处理挥发性有机物的最佳工艺选择。     

Electrosorption of benzoic acid on platinum electrode

The electrosorption of benzoic acid on platinized electrode was studied by voltammetric and radiometric techniques. The free energy of adsorption, the heterogeneity factor of electrode surface and the surface concentration of adsorbate were determined. The adsorption of benzoic acid may be described by logarithmic isotherms. The kinetics of benzoic acid adsorption was also studied.     

Breakthrough data analysis of adsorption of volatile organic compounds on granular activated carbon

Volatile Organic Compounds (VOCs) such as methanol, ethanol, methyl ethyl keton, benzene, n-propanol, toluene, and o-xylene were adsorbed in a laboratory-scale packed-bed adsorber using granular activated carbon (GAC) at 101.3 kPa. The adsorber was operated batchwise to obtain the breakthrough curves of VOCs under the adsorption conditions such as adsorption temperatures (298–323 K), flow rates of nitrogen (60×10⁻⁶-150×10⁻⁶m³/min), GAC amount of 0.002 kg, and concentration of VOCs (3,000–6,000 ppmv). The adsorption kinetics was obtained by fitting the experimental breakthrough data to the deactivation model, combining the adsorption of VOCs and the deactivation of GAC. The adsorption isotherm, and adsorbed amount and adsorption heat of VOCs were obtained using the breakthrough curve: the former for comparison with the conventional isotherm models, the latter for correlation with the physical properties of VOCs.     

Gas-solid adsorption of selected volatile organic compounds on titanium dioxide Degussa P25

This paper focuses on the adsorption of gaseous trichloroethylene, toluene and chlorobenzene on the photocatalyst TiO₂ Degussa P25. An optimized EPICS (Equilibrium Partitioning In Closed Systems) methodology was used to study equilibrium partitioning. For the three compounds investigated, equilibrium adsorption was reached within of incubation. Adsorption isotherms, determined at a temperature (T) of and relative humidities (RH) of 0.0% and 57.8% were found to be linear (R²>0.993,n=5), indicating that no monolayer surface coverage was reached in the concentration interval studied ). Within the linear part of the isotherm, the influence of both relative humidity and temperature was investigated in a systematic way and discussed from a thermodynamic point of view. Data analysis resulted in a double linear regression for 22% ?RH?90% and . The equilibrium adsorption coefficient represents the equilibrium concentration ratio and ΔU_ads is the internal energy of adsorption . At RH=0.0%, experimental K values were a factor 5-10 higher than those expected from the regression equation, indicating that another adsorption mechanism becomes important below monolayer surface coverage of TiO₂ by water vapour molecules. Since surface interactions are of primary importance in photocatalytic reactions, this paper contributes to a better understanding of the basic mechanisms of TiO₂ mediated heterogeneous photocatalysis and is an interesting tool for developing optimized mathematical models.     

The role of charge transfer in the adsorption of aromatic molecules at metal electrodes

Thermodynamic data for the electrosorption of aromatic molecules at metal electrodes (the electrosorption valency γ, surface concentration Γ, the double layer capacity C_D, and the free adsorption enthalpy ΔG_ad) are analysed for phenol at mercury as an example. At small Γ the phenol molecule is adsorbed in a flat position, but at Γ > Γ^″_max this changes to perpendicular. γ is negative and λ ≈ 0.2 for flat orientation, but negligible for the perpendicular one. C_D decreases with increasing coverage for both orientations, indicating a dominating thickening of the double layer. From ΔG_ad values a small π-bond contribution ΔG_π ≈ 50 kJ mol⁻¹ is estimated. The energetic analysis shows that an anodic charge transfer takes place if the electrode potential approaches the oxidation potential ε_ox and a cathodic charge transfer in the vicinity of ε_red. Charge transfer data for other aromatic and heterocyclic compounds were obtained using the same thermodynamic analysis. In general, the charge transfer is positive, 0 < λ < 0.3. These data can be successfully correlated with the oxidation potential, the ionization potential and the electron density in the ring respectively.