Catalytic oxidation of organic compounds in aqueous media

Ru, Pt and Rh catalysts supported on titania, ceria or active carbon and a Mn/Ce composite oxide catalysts were prepared and their catalytic behavior in Wet Air Oxidation ( 20 bar O₂) of phenol and acetic acid were investigated. Phenol was found to be an easily oxidizable compound as 170°C, while acetic acid was a very refractory molecule, even at 200°C. Ru(5 wt.-%)/C is a very efficient catalyst for the WAO of acetic acid without any leaching of noble metal.     

Ozonation of vinasse in acid and alkaline media

The production of ethanol by fermentation and subsequent distillation generates wastewater known as ‘vinasse’. This waste is highly polluting on account of its high organic load and antibacterial activity—which arises from the presence of phenolic compounds that reduce the efficiency of the detoxification treatments best suited to this type of waste (eg anaerobic digestion). This can be avoided by using a pre‐treatment based on a chemical oxidant (ozone) at an acid or alkaline pH. Ozonation in acid media provides more selective elimination of phenolic compounds and a more readily biodegradable waste (ie an increased BOD₅/COD ratio). Copyright © 2003 Society of Chemical Industry     

Aluminum pigments encapsulated by inorganic–organic hybrid coatings and their stability in alkaline aqueous media

Encapsulated aluminum pigments were prepared by sol–gel derived inorganic–organic hybrid coatings. Aluminum pigments were first coated with sol–gel film by using tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) as the precursor, followed by free radical copolymerization of styrene (St), divinylbenzene (DVB) and maleic acid anhydride (MAA) with the vinyl group of the VTES. The as-prepared encapsulated aluminum pigment was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Subsequently the stability of the aluminum pigments in alkaline aqueous media was examined. It was found that both the TEOS-and-VTES-coated (TV-coated) and the TEOS–VTES–St–DVB–MAA-coated (TVSDM-coated) aluminum pigments were superior in the stability test over the uncoated aluminum pigments. Furthermore, the corrosion protection efficiency of the TVSDM-coated aluminum pigments reaches 99.8%, indicating that the inorganic–organic hybrid composite layer on the surface of the aluminum pigments can protect them well.     

Determination of total carbonyl compounds in aqueous media

A method for the quantitative determination of total carbonyl compounds in aqueous media has been developed. The analysis is based on the reaction of 2,4-dinitrophenylhydrazine with aldehydes and the subsequent formation of the quinoidal ion under basic conditions. The aldehydes react with 2,4-dinitrophenylhydrazine in both ethanol and aqueous-ethanol media. The optimal wavelength to determine the total carbonyl compounds is 425 nm where the molar absorption coefficient of saturated aldehydes equals that of unsaturated aldehydes. The method can be used to determine all aldehydes in aqueous food media.     

Corrosion inhibition of copper and brass pigments in aqueous alkaline media by copolymers

Copper and brass pigments corrode in aqueous alkaline media with absorption of oxygen which can be measured gasvolumetrically. These corrosion reactions can be inhibited by certain copolymers, the metallic sparkle and the colour of the pigments being preserved. The brass pigment (rich gold) is inhibited more effectively by copolymers than the copper pigment. The corrosion inhibiting effect of styrene–maleic acid–acrylic ester copolymers on copper pigment decreases with increasing the chain length of the ester alcohol of the acrylate monomer. The most effective copolymer examined in this study is the styrene–maleic acid–ethyl acrylate copolymer which inhibited the corrosion reactions of copper and brass pigment both at pH 8.5 and 10.     

Inhibition of cobalt active dissolution by benzotriazole in slightly alkaline bicarbonate aqueous media

The efficiency of benzotriazole as inhibiting agent for the corrosion of cobalt was probed at pH ranging from 8.3 to 10.2 in a sodium bicarbonate solution, chosen to simulate mild natural environments. From electrochemical, Raman spectroscopy, atomic force microscopy and ellipsometry experiments, we have demonstrated that benzotriazole markedly affects the electrodissolution reactions, which become modeled by the formation of a [Co(II)(BTA)₂·H₂O]_n film according to two different mechanisms. Surface-enhanced Raman spectroscopy has shown that the polarization of a cobalt electrode at cathodic potentials with respect to its potential of zero charge allows a mechanism of specific adsorption of the neutral form of benzotriazole to take place through a suspected metal-to-molecule electron transfer and which follows Frumkin's adsorption isotherms. At the onset of the anodic dissolution, some experimental evidence suggests that these adsorbed neutral benzotriazole molecules deprotonate to yield a very thin [Co(II)(BTA)₂·H₂O]_n polymer-like and water-insoluble protective film, responsible for the inhibition of active dissolution processes occurring at slightly more anodic potentials. In the anodic dissolution region, deprotonated benzotriazole species present in the bulk solution favors the formation of a multilayered [Co(II)(BTA)₂·H₂O]_n film, which also contributes to the inhibition of any further cobalt dissolution usually observed at higher electrode potentials.     

Electrocatalytic oxidation of organic compounds on noble metals in aqueous solution

The oxidatioin of organic compounds on noble metal electrodes in aqueous solution is a complex reaction due to the occurrence of several adsorbed intermediates and reaction products or by-products. This leads to a lot of electrocatalytic problems, such as the elucidation of the nature of reaction products and the structure of adsorbed species, the role of the electrode material, the effect of the structure of the organic compound, and the role of the composition of the electrolytic solution. These topics are illustrated with the help of various organic compounds (formic acid, methanol, ethanol, ethylene-glycol, C—2 compounds derived from ethylene—glycol, butanol isomers) using principally two experimental approaches: cyclic voltammetry at the macroscopic level and infrared spectroscopy (either FTIRS or EMIRS) at the microscopic level.     

Ozonation of a mixture of dialkylphthalates in aqueous solution

Ozonation of dimethyl phthalate, diethyl phthalate and dipropyl phthalate was carried out to evaluate the potential of ozonation for phthalate removal from water. Phthalates with longer alkyl chains, which are often more resistant to biodegradation were found to be more degradable than those with shorter alkyl chains. The degradation of phthalates by ozonation follows the pseudo‐first‐order kinetic model. The rate of phthalates degradation increased exponentially with increasing temperature in the range studied (20 to 50 °C) and in proportion with applied ozone dosages. The rate of phthalates degradation was found to increase with increasing pH of the solution from 2.6 to 11.0, and decreased exponentially with increasing initial concentrations of the phthalates. Degradation of phthalates via ozonation was found to develop dominantly through direct reaction with hydroxyl radicals. Copyright © 2010 Society of Chemical Industry     

Ozonation kinetics of iron and manganese in aqueous solution

Ozonation kinetics of iron and manganese in aqueous solution is experimentally investigated. The effects of pH, initial ion concentration and the ozone dosage on the kinetic rate parameters are examined. It has been found that ozonation of those ions in general follows zero order kinetics.     

Development of novel Lewis acid catalysts for selective organic reactions in aqueous media

New types of Lewis acids as water-compatible catalysts have been developed. Various metal salts were found to work as Lewis acid catalysts in aqueous media, and catalytic asymmetric aldol reactions in such media have been attained. Furthermore, Lewis acid-surfactant combined catalysts, which can be used for reactions in water without using any organic cosolvents, have been also developed. These investigations will contribute to reducing the use of harmful organic solvents and to develop efficient catalytic systems which cannot be realized in conventional organic solvents.     

Leaching of sulphur and calcium from sulphur-infiltrated concrete by alkaline and neutral aqueous media

It has been found that calcium and sulphur are leached by alkaline or neutral aqueous media from sulphur-infiltrated concrete. From chemical examinations and Raman spectroscopy it has been shown that sulphur in the leachate is present as polysulphide anions. It is postulated that homonuclear polymeric anions of sulphur are formed in the presence of moisture when molten sulphur infiltrates concrete. The soluble calcium polysulphides so formed can then be leached by water.     

Ozonation of chloronitrobenzenes in aqueous solution: kinetics and mechanism

BACKGROUND: Chloronitrobenzenes (ClNBs) are a family of toxic and bio‐resistant organic compounds. Ozone treatment is specifically suitable for partial or complete oxidation of non‐biodegradable components. However, few studies on the decomposition of ClNBs by ozone are available, and kinetics and mechanisms of ClNBs ozonation have not been thoroughly investigated. The kinetics and mechanism of ozonation degradation of ClNBs in aqueous solution were investigated, and the contribution of both molecular ozone and hydroxyl radicals was also evaluated. RESULTS: The results demonstrated that the decomposition of ClNBs was a pseudo‐first‐order reaction with respect to the pollutant concentration and the overall rate constant increased with an increase in pH. It declined, however, with an increase in pollutant and radical scavenger concentration. Furthermore, TOC removal rate was significantly lower than that of ClNBs, but the same order o‐ClNB < m‐ClNB < p‐ClNB was followed. Ozonation could not reduce TOC significantly, p‐chlorophenol, p‐nitrophenol, 2‐chloro‐5‐nitrophenol and 5‐chloro‐2‐nitrophenol were detected as primary degradation intermediates in ozonation of p‐ClNB. Rate constants of the direct reaction between ozone and ClNBs at 25 °C had been found to be lower than 1 M^?1S^?1. More than 95% of ClNBs removal was due to hydroxyl radical oxidation at pH ≥ 7. CONCLUSION: Advanced oxidation processes may be the preferred choice for the elimination of ClNBs from the environment. Copyright © 2008 Society of Chemical Industry     

Styrene copolymers with carboxyl groups as corrosion inhibitors for zinc pigments in aqueous alkaline media

Zinc pigments react in aqueous alkaline media (e.g., water-borne paints) by the evolution of hydrogen. Low molecular weight styrene-maleic acid and styrene-acrylic acid/styrene-acrylate copolymers can inhibit this corrosion reaction of zinc pigments in a mixture of water and butyl glycol in the ratio 9 : 1 at a pH value of 10 (ammonia). High molecular weight styrene-maleic acid copolymers are only very poor corrosion inhibitors. This was proved by volumetric measurement of the evolved hydrogen. There seems to be a correlation between the content of carboxyl groups of the low molecular weight styrene-maleic acid and styrene-acrylic acid/styrene-acrylate copolymers and the evolved hydrogen volume in ammoniacal aqueous medium: The lower the acid number of the styrene copolymers, the lower is the evolved hydrogen volume. Low molecular weight styrene copolymers neutralized with dimethylethanolamine inhibit the corrosion reaction much better than with ammonia. © 1996 John Wiley & Sons, Inc.     

部分有机物对ZHL-02碱性无氰镀银工艺的影响

使用光泽度仪、显微维氏硬度计、X射线粉末衍射仪以及扫描电子显微镜考察了电镀过程中常见的6种有机物(包括乙醇、苯酚、丙酮、4-羟基苯甲醛、冰乙酸和甲基磺酸)在0.5、1.5和2.5 g/L的用量下对ZHL-02无氰镀银工艺所得银镀层性能的影响。结果表明,不同有机物在不同用量和不同电流密度下对镀层晶体形貌有不同影响,导致镀层光泽度和显微硬度有不同的变化。在工作电流密度为1.0~2.0 A/dm2范围内,不同用量的有机物对银镀层的光泽度影响不大;在低电流密度(0.2 A/dm2)下,2.5 g/L的苯酚或丙酮会明显改善银镀层的光泽度;但在高电流密度(3.0 A/dm2)下,乙醇和丙酮对银镀层的光泽度有负面影响。在生产中应尽量避免引起负面效果的有机物进入镀液,而产生正面影响的有机物可以根据实际需要适量添加。     

Studies on electrosynthesis of organic compounds. I. Electrolytic esterification in aqueous solutions

The anodic oxidation of methyl alcohol in the presence of different carboxylic acids was found to give the methyl ester of these acids as the main product. Neither Kolbe products nor formaldehyde were formed. These results are interpreted in terms of a free radical mechanism which involves attack of the carboxylic acids by methoxyl radicals to give the ester.     

Titanium silicalite-1 macrostructures for photocatalytic removal of organic pollutants from aqueous media

Titanium silicalite-1 (TS-1) structures in the form of macroscopic beads with hierarchical porosity were prepared by the resin templating method. The Ti content within the samples was varied between 1 and 7 wt%, with corresponding surface areas ranging from 725 to 350 m² g^?1, respectively. The samples contained a large amount of amorphous material, which was necessary to achieve high mechanical stability of the beads. The TS-1 macrostructures were used as catalysts for the photocatalytic degradation of methylene blue (MB), and results were compared to the results for a commercial anatase nanopowder (CristalACTiV? PC500). All TS-1 beads showed similar MB degradation rates independently of their Ti content, which was linked to variations in the surface areas and structure. The macroscopic shape of the TS-1 beads allowed easy recovery from the mother liquor upon decolouration of the MB solutions, which was highly beneficial compared to the reference anatase nanopowder. The TS-1 beads could be reused in subsequent photocatalytic cycles after decanting exhausted solutions and replacing with fresh MB solutions without any energy-consuming regeneration steps involved. The samples were tested in five consecutive cycles and MB degradation rates remained broadly unchanged during all tests.     

臭氧化去除水中对硝基氯苯动力学及机理

引言 对硝基氯苯(pCNB)广泛应用于农药、染料、医药、防腐剂等工业领域.随着工业废水的排放,我国一些主要水体中均有pCNB的检出[1-2].     

Spectroscopic characterization of the electrochemical functionalization of single-walled carbon nanotubes in aqueous and organic media

An electrochemical method of functionalizing of single-walled carbon nanotubes (SWCNTs) in aqueous and organic electrolytes by the electrolysis of bromide solutions at anodic potentials is proposed. Cyclic voltammeter studies point to a substantial increase in the SWCNTs electrode capacitance after its electrochemical treatment, which is associated with an increase in the electrode working surface accessible to solution. This effect is attributed to the formation of functional groups on the SWCNTs surface. This conclusion is confirmed by analyzing the electrochemically processed SWCNTs by the methods Raman, UV–Vis–Nir and X-ray photoelectron spectroscopies. The electrolysis of potassium bromide solutions in both aqueous and nonaqueous media is shown to produce functional groups containing oxygen and, to a smaller extent, bromine. The dependence of the degree of SWCNT functionalization (the number of chemically bound foreign atoms per the number of carbon atoms) on the electrolyte nature is observed experimentally. The degree of functionalization reached in dimethyl sulfoxide is comparable with that of the original SWCNTs, whereas in aqueous solutions, the high density of functional groups (one O atom per 3–4 C atoms) is observed.     

Determination of organic substances with different boiling points in aqueous media by capillary gas-liquid chromatography

Studies were conducted on separation of organic substances with different boiling points and polarity when simultaneously present in water by capillary gas-liquid chromatography on a Kristall 2000 m chromatograph. The effect of the column phase and temperature conditions on the separation factor and component exit time was investigated. Column temperature programming was used to reduce the component, especially heavy component, retention time. The chromatography regime was selected and a fast method was developed for determining components with different volatility in water during one analysis with sufficiently high reproducibility and reliability of the results. It was shown that the time of the analysis decreased by more than two times with the same accuracy as with the standard methods. The method can be recommended for fast analysis of wastewaters for making a decision on the treatment method.     

Zn/Fe双金属催化羰基化合物的水相Reformatsky反应研究

以低浓度盐酸水溶液作为反应介质,研究了Zn/Fe双金属催化羰基化合物的水相Reformatsky反应.考察了金属配比、金属用量、温度、溶剂水用量等反应因素对反应产率的影响.实验获得的最佳条件为:20 mmol Zn/Fe(1:1)、5mmol羰基化合物、15 mmol溴乙酸乙酯、10 mL HCl(1 mol/L)、1...