Photodegradation of a herbicide derivative, 2,4-dichlorophenoxy acetic acid in aqueous suspensions of titanium dioxide

The photocatalytic degradation of a herbicide derivative, 2,4-dichlorophenoxy acetic acid (2,4-D, 1), has been investigated in aqueous suspensions of titanium dioxide. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic analysis and decrease in Total Organic Carbon (TOC) content as a function of irradiation time in the presence of UV light source. The degradation kinetics was investigated under a variety of conditions, such as different types of TiO₂, pH, catalyst and substrate concentrations. Higher photonic efficiencies were observed with Degussa P25 as compared with other photocatalysts. The degradation products were analysed by GC-MS and probable pathways for the formation of different products were proposed.     

Experimental study of photocatalytic oxidation of formaldehyde and its by-products

Formaldehyde is one of the most harmful pollutants that endanger occupants' health and the way of its effective removal has become a focus in the field of air quality. This paper studies the static photocatalytic removal of formaldehyde experimentally and finds out that carbon monoxide, which is more harmful to occupants' health than the formaldehyde itself, is one of the by-products in the process of photocatalytic oxidation of formaldehyde. The increase of carbon monoxide concentration should be taken into consideration in the photocatalytic application. The photocatalyst surface at room temperature can weakly adsorb CO and CO₂, which can deactivate the photocatalysts.     

液相沉积法制备光催化活性TiO2薄膜和纳米粉体

采用液相沉积法，在35℃通过向六氟钛酸铵水溶液中添加硼酸和结晶诱导剂锐 铁矿型TiO2纳米晶，沉积出具有光催化活性的Ti02薄膜和纳米粉体．用XRD，AFM， 阶梯仪,UV-vis，BET法对Ti02薄膜和粉体的沉积条件、结构、厚度和性能进行了测 定和表征，并用亚甲兰的降解，评价了TiO2薄膜和纳米粉体的光催化活性．结果表 明，当反应物六氟钛酸铵与硼酸的摩尔比为1：2—1：4时，沉积的粉体和薄膜含有 锐钛矿相Ti02；经300℃热处理的Ti02薄膜和纳米粉体具有最高的光催化活性，它 的光催化活性是未经热处理前的5倍．本文还解释了经300℃热处理的薄膜和纳米粉 体具有最高光催化活性的原因．     

Titanium-dioxide-mediated photocatalysis reaction of three selected pesticide derivatives

The photocatalysis reaction of three selected pesticide derivatives, namely methoxychlor (1), chlorothalonil (2) and disulfoton (3), has been investigated in an acetonitrile/water mixture in the presence of titanium dioxide and oxygen. The change as a function of irradiation time has been monitored using the UV spectroscopic analysis technique. An attempt has been made to identify the product formed during the photooxidation process through GC/MS analysis technique. The photolysis of methoxychlor (1) led to the formation of methoxychlor olefin (4) and 4,4-dimethoxybenzophenone (9), whereas chlorothalonil (2) gave rise to 2,3,4,5-tetrachlorophenol (17) as the only product. On the other hand, the photolysis of disulfoton (3) under analogous conditions gave disulfoton sulfoxide (25) and phosphorodithioic acid (21). All the products have been identified by comparing the molecular ion and mass fragmentation peaks of the products with those reported in the library. A probable mechanism for the formation of the products has been proposed.     

Photocatalytic degradation of dimethyl terephthalate in aqueous suspensions of titanium dioxide

The photocatalytic degradation of dimethyl terephthalate (DMT, 1) has been investigated in aqueous suspensions of titanium dioxide (TiO2) by monitoring the depletion of Total Organic Carbon (TOC) content as a function of irradiation time under a variety of conditions. The degradation kinetics were studied using different parameters such as pH, substrate and photocatalyst concentration, a different kind of titanium dioxide and the presence of electron acceptors such as H2O2, KBrO3 and (NH4)2S2O8 in addition to molecular oxygen. The photocatalytic activity was better for Degussa P25 as compared to the other photocatalysts. From the obtained kinetic data a detailed account of the influence of various parameters on the degradation rate for the mineralization of the compound is given. The degradation products were analyzed using the GC/MS technique and probable pathways for the formation of different products have been proposed.     

In situ FT-IR studies on mechanistics of heterogeneous photocatalytic oxidation of ethene over uranyl species anchored on MCM-41

The uranyl species encapsulated within the mesopores of siliceous MCM-41 serves as efficient heterogeneous photo-catalyst for the sunlight-assisted direct oxidation of ethene. The mode of oxidation is through abstraction of H-atom from ethene by the photolytically excited uranyl species and the consequent formation of peroxy species. The in situ IR spectroscopy results indicate that these peroxy species give rise to final products such as carbon dioxide and water on further oxidation via formation of formate-type transient species. Furthermore, the silanol groups of the host matrix help in immobilization of these peroxy species through hydrogen bonding and, at the same time, they participate in the subsequent oxidation reactions also.     

铜配合物催化的环状烯烃的光化学顺、反异构化反应

在大于300nm光波照射下,氯化亚铜或乙酰丙酮基铜(I)等低价铜配合物可以有效地催化中大环环状烯烃的顺、反异构化反应,对在大于250nm光波照射下,顺,顺-1,5-环辛二烯分子内环加成形成三环[3.3.0.0^2^.^6]-辛烷的反应机制,进行了讨论。     

硫化镉光催化氧化二苯甲醇的反应

半导体粉能对烯烃, 芳烃等的光催化氧化, 但效率低, 揭示其机理, 研究提高催化效率是研究半导体光催化的突出问题. 本文研究了硫化镉粉末光催化氧化二苯甲醇的反应, 发现能从硫化镉导带上捕获电子的物质都能促使电荷分离, 引发或加速反应, 而自由基猝灭剂却能完全猝灭反应. 本文进一步揭示了硫化镉光催化特性并探讨了反应机理.     

金属卟啉化合物光谱化反应研究 Ⅱ. 周边取代与轴向配位对金属卟啉光敏化反应的影响

本文研究了中-四(对三甲胺基苯基)金属卟啉(MeTPI, Me=H2, Zn(Ⅱ),Cu(Ⅱ), Ni(Ⅱ), Mn(Ⅲ), Co(Ⅲ))光敏化还原甲基紫精(MVI2)反应, 用动力学方程参数a, 诱导时间ti和初始反应速率v0来衡量光敏剂的优劣。同时讨论了不同的取代基以及不同的轴向配体对光敏剂光敏性的影响。结果表明: Zn(Ⅱ)TPI的光敏性较好; 含氮芳香有机碱对光敏剂起"增敏"作用, 并且通过引入带有正电荷的轴向配体, 使"增敏"效果更加显著, 同时发现, 脂肪胺起"降敏"作用。