纳米TiO_2光催化芳香醛的缩醛反应研究

本文以纳米TiO2为催化剂,UV-LED（=365 nm）为紫外光源,在自制的恒温石英玻璃光催化反应器中成功实现了芳香醛的非均相光催化缩醛反应.以乙醇等作为溶剂和反应物,快速高效和高选择性地合成了苯甲醛二乙基缩醛（BDA）.在光强为0.6 mw/cm2,苯甲醛初始浓度为0.05 mol/L,催化剂TiO2（P25）用量为5.0 g/L,反应时间为15 min的条件下,苯甲醛二乙缩醛的产率可达99.86%.研究表明,氧气的存在是顺利发生光催化缩醛反应的重要条件.反应液pH值、醇溶剂种类及苯环对位取代基等因素都会对光催化缩醛反应速率和产率产生影响.pH值及醇溶剂的pKa越小,缩醛反应速率越快.苯环上对位取代基会抑制缩醛反应的进行,其中供电子取代基相对吸电子取代基更有利于缩醛反应进行.结合实验,提出了光催化缩醛反应的机理.     

Aerobic oxidation of cumene photocatalyzed by iron salts

Photooxidation of cumene by air in an aqueous emulsion in the presence of Fe(ClO₄)₃ results in the formation of considerable amounts of acetophenone, the product of the C-C bond cleavage.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1422–1424, June, 1996.     

Titanium dioxide xerogel modified with powder cellulose in oxidation of trimethylhydroquinone

A procedure was developed for modification of titanium dioxide xerogel by addition of powder cellulose in the stage preceding hydrolysis of tetramethoxytitanium. The resulting catalytic systems based on the new material were studied in a model liquid-phase catalytic process of oxidative dehydrogenation of trimethylhydroquinone with atmospheric oxygen.     

Titanium dioxide photocatalysis

Scientific studies on photocatalysis started about two and a half decades ago. Titanium dioxide (TiO₂), which is one of the most basic materials in our daily life, has emerged as an excellent photocatalyst material for environmental purification. In this review, current progress in the area of TiO₂ photocatalysis, mainly photocatalytic air purification, sterilization and cancer therapy are discussed together with some fundamental aspects. A novel photoinduced superhydrophilic phenomenon involving TiO₂ and its applications are presented.     

Modelization of photocatalyzed oxidation of polyolefins. II. ZnO and TiO2 photocatalyzed decomposition of tert-butyl hydroperoxide and atactic polypropylene hydroperoxides

Direct evidence of the TiO₂ and ZnO photocatalytic decomposition of tert-butyl hydroperoxide and atactic polypropylene hydroperoxides in solution is reported. Molecular and macromolecular hydroperoxides behaved similarly. Untreated TiO₂ in the rutile form was a far more efficient photocatalyst than ZnO in solution; the photoactivities of both pigments were limited on preferential absorption sites. In the solid state no preferential reaction sites were observed. When added to preoxidized atactic polypropylene both pigments were photocatalysts of the formation of macromolecular hydroperoxides and of their decomposition. The photoreactivities of untreated TiO₂ and ZnO varied less than in solution.     

Titanium dioxide plasma treatment

After a review of the literature on titanium production under plasma conditions, the main parameters controlling the reactions (residence time, type and relative quantity of reducer, reaction temperature, etc.) are emphasized. The controlled-atmosphere chamber where the rutile or anatase particles are heated and partly reduced in a crucible by a d.c. plasma torch with Ar-H₂ as plasma gas is described. Study of the temperature dependence of the Gibbs free energy allows one to explain, at least qualitatively, the experimental results obtained which correspond at best to 10% (weight) of TiO₂ reduced to TiO by carbon.     

Titanium dioxide photocatalysis of adamantane

TiO₂ photocatalysis of adamantane in oxygen equilibrated MeCN yields 1- and 2-adamantanol and adamantanone with limited degradation and preference for functionalization at the 1 position, particularly in the presence of silver salts. Oxidation in CH₂Cl₂ is less selective. The oxidation of cyclohexane and cyclododecane is slower. In N₂-flushed solutions with Ag⁺ as a sacrificial acceptor, products from the trapping of both 1-adamantyl radical (adamantyl methyl ketone) and cation (N-adamantylacetamide) are obtained. Furthermore, alkylation of an electrophilic alkene (isopropylydenmalononitrile) has been obtained, though in a low yield.     

Titanium dioxide nanomaterials in electrocatalysis for energy

Over the last two decades, researchers have found many strategies to obtain high surface area nanostructured titanium dioxide. These nanostructures have recently found application as supports for the fabrication of electrodes for electrochemical energy conversion and storage devices. The properties that make titanium dioxide appealing for these applications are as follows: (i) stability in a variety of conditions relevant to electrocatalysis, (ii) electronic conductivity, (iii) synergistic effects with metal catalysts. The work splits TiO₂ nanomaterials into the following two classes: (i) powders and (ii) embedded nanoarchitectures (e.g. titania nanotubes on titanium support). We give an overview of the latest applications, with a special emphasis on fuel cells, electrolysis, and carbon dioxide electroreduction. We conclude with a list of the research needs that, in the opinion of the authors, will support the exploration and consolidation of the use of titania in electrocatalysis for energy.     

Manganese dioxide oxidation of hydroxyamino-sym-triazines

The hydroxyamino group in sym-triazines is readily oxidized by the action of manganese dioxide. The stability of the nitrosotriazines formed in this oxidation depends on the electron donor properties of the other substituents in the molecule.For Previous Communication, see [1]Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 694–699, May, 1993.     

Inorganic by-products in waters disinfected with chlorine dioxide

The continuing diminishing sources of fresh waters has stimulated the search for unconventional water resources, such as effluents from municipal sewage treatment plants, which can be reused for purposes of irrigation in agriculture, cooling water in industry, groundwater aquifer recharge and in the long term even for drinking water. The main problem of using effluents is the presence of pathogenic bacteria and viruses that can affect human and animal health. Therefore, disinfection has been used for many years to control and reduce waterborne diseases.At the moment, most water treatment plants use sodium hypochlorite as their primary biocide. However, the toxicity of chlorinated organic compounds produced during the treatment has led to increased interest in the use of alternative agents. One possible candidate as viable substitute of free chlorine is chlorine dioxide. Before this disinfectant can be recommended for routine use, it is imperative that its safety be assessed.In this research we have investigated the presence of chlorite and chlorate in sewage disinfected with chlorine dioxide. The effect of initial concentration of biocide and contact time was evaluated using a pilot plant fed with the effluent of a municipal treatment plant. Moreover, the influence of ClO₂ generator performance was analyzed and discussed.     

Catalytic air oxidation of manganese in synthetic waters

An attempt was made to study the oxidation of manganese by air in synthetic waters. A series of batch experments were performed at differnet values of concentration, temperature and pH. Unoxidized manganese in the solution was determined by formaldoxime spectrometric method. Results of these studies indicated that the air oxidation of manganese soluble in water can be effectively performed in basic media and that oxidation yield increasedwith an increase in pH and concentration. The yield was very high in the presence of manganese dioxide, sepiolite or clinoptilolite in solution and, the oxidation was almost completed especially at high values of pH and concentration. The reaction was found to be first order with respect to Mn²⁺ with a very low activation energy. A yield of 62% was obtained for the air oxidation of wastewater taken from the treatment plant of Corum Municipality.     

Titanium in natural surface waters: The content and coexisting forms

Results obtained in studying the content and coexisting forms of titanium in surface waters are given. It was established that the titanium concentration lies within 0.0–1180 μg/L in the world’s surface water and within 0.0–573 μg/L in the studied water bodies of Ukraine. The concentration of dissolved and suspended titanium in the water bodies studied also varies within the wide range, 0.0–86.0 and 0.0–534.6 μg/L, respectively. The concentration of its dissolved form in world’s surface water is 0.0–68.7 μg/L. The ratio of dissolved to suspended titanium in water bodies depends on the content of suspended matter and its nature. In river waters, the suspended titanium mostly dominates over the dissolved form. We found that in rivers with the high concentration of suspended matter (6.0–140.6 mg/L), mostly of mineral nature, a fraction of the suspended titanium reaches 62.3–88.6% on the average. A strong correlation between the mass of suspended matter and the concentration of suspended titanium in these surface waters shows that the nature of suspended matter affects the concentration of suspended titanium. The correlation coefficient is between 0.81–0.99 at a significance level of 0.01. The titanium content in the suspended matter and bottom sediments of world’s water bodies makes 0.2–19.8 and 0.1–24.6 mg/g of dry weight of the suspended matter, respectively. In the surface waters studied, its content ranges within 0.0–16.5 mg/g of dry weight of the suspended matter. Taking into account the average values, the titanium content in the suspended matter of the studied rivers, water reservoirs, lakes, and ponds is (mg/g in terms of dry mass): 1.0–7.5, 1.0–4.9, 1.3–3.9, and 1.2–1.3, respectively. The percentage of the adsorbed titanium in the suspended matter of the Kilia Danube delta, Kanev Reservoir, and the Lybid’ River is 91.6–97.3, 67.6–74.4, and 57.1–99.4%, respectively. The acidic (anionic), basic (cationic), and neutral fractions of the dissolved organic substances in the surface waters contained 15.7–89.4, 0.0–33.8, and 0.0–80.7% of dissolved titanium (Ti_diss) (i.e., 44.4, 13.2, and 42.4% of Ti_diss on the average). The presence of dissolved titanium in the anionic fraction shows that titanium forms complexes with humic substances or exists in the form of TiO₂ colloidal particles (nanoparticles) coated with humic substances. In the neutral fraction, a hydrated titanium oxide TiO(OH)₂ may exist as a form of its migration in natural surface waters.     

Liquid-phase oxidation of thiols with chlorine dioxide

The products and kinetics of the liquid-phase oxidation of 11 aliphatic and aromatic thiols with chlorine dioxide were studied at –10—+70 °C in organic media. The rate constants and activation parameters of the reaction were determined. The influence of the thiol structure on its reactivity was studied. A strong solvent effect on the reaction rate constant was found, and the reaction mechanism was proposed.     

The oxidation of diethylhydroxylamine by nitrogen dioxide

Diethylhydroxylamine, (C₂H₅)₂NOH, was oxidized by NO₂ at 25°C in a long-path-length infrared gas cell. The measured products of the reaction were HONO and CH₃CHO. The reaction scheme which explains the reaction is was oxidized by NO₂, and the reaction was found to be very rapid with k₁ > 10^?16 cm³/s. The products of the reaction were verified by both infrared absorption (CH₃CHO, C₂H₅NO) and gas chromatography (CH₃CHO, NO).     

Chlorine dioxide in chemo- and stereoselective oxidation of sulfides

Data on oxidation of alkyl-, phenyl-, benzyl-, oxo-, and terpenyl-substituted and nitrogen-containing heterocyclic sulfides with chlorine dioxide are reviewed. The oxidation is highly chemoselective and moderately stereo- and enantioselective.     

Activity in CO oxidation of manganese dioxide for batteries

The low temperature oxidation of CO over MnO₂ containing samples for batteries has been investigated. It is found that the samples contain compositional and hydrate water and Mn⁴⁺, Mn³⁺, Mn²⁺ ions. The high efficiency is due to Mn⁴⁺ content.

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CO MnO₂, . , Mn⁴⁺, Mn³⁺, Mn²⁺. Mn⁴⁺.

     

Kinetics of oxidation of phenol with manganese dioxide

The kinetics of oxidation of phenol with manganese dioxide at pH 5.5±0.5 were studied. In the temperature range from 393 to 323 K the reaction is of second order, and it occurs in the kinetic mode with an energy of activation of 42.0 kJ/mol. In the temperature range from 333 to 353 K the reaction follows first-order equation and is controlled by external diffusion; the energy of activation is equal to 6.65 kJ/mol. The oxidation products are hydroquinone and 1,4-benzoquinone, the fraction of the latter being less than 10 mol %.     

光催化Suzuki偶联反应的非均相催化剂研究进展

Suzuki偶联反应作为构建C-C键的最有效的手段之一,在医药、染料和电子工业等领域扮演着重要的角色。传统的Suzuki偶联反应催化体系需要依赖化石能源产生的热能来驱动,不仅造成了不可再生资源的消耗,还会导致相应的环境问题。近年来,光催化技术和绿色有机合成化学蓬勃发展,利用可再生的太阳能光催化Suzuki偶联反应不但可以解决在催化反应过程中的能源与环境问题,还可以在温和条件下获得高产率的联苯化合物产物,正在受到人们的广泛关注。与均相光催化剂相比,非均相光催化剂具有良好的化学稳定性、便捷的可回收性与优异的循环利用性能等优点,因此成为光催化Suzuki偶联反应的研究重点。本文总结了非均相催化剂光催化Suzuki偶联反应的基本原理,介绍了近年来科研工作者对光催化Suzuki偶联反应中非均相催化剂的制备方法、催化性能以及可循环利用性等方面做的一系列研究。     

Kinetics of oxidation of methanol by chlorine dioxide

The kinetics of oxidation of methanol by chlorine dioxide has been investigated at 35 °C. The reaction is first order with respect to both substrate and chlorine dioxide. Molecular chlorine dioxide is the principal oxidant. The influence of various factors, e.g. ionic strength, inorganic salts, D₂O and temperature on the initial rate has been studied. The activation parameters have been calculated and a mechanism involving hydride abstraction has been suggested.

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35 °C. , . . , . , , D₂O , . , .