紫外和可见光光催化耦合体系的构建及其降解有机污染物

Semiconductor photocatalysis can be used to degrade a variety of organic pollutants. However, the reaction process has a low quantum yield, and hardly utilizes visible light as well. In this project, a coupling system is proposed for the first time between semiconductor photocatalysis under UV light and metal complex sensitization under visible light. This system can extend light absorption, and sufficiently utilize various reactive species generated from two different processes of chemical reactions. As a result, both the efficiencies of organic degradation and mineralization will be greatly improved. The films containing different types of photocatalysts and photosensitizers will be prepared and characterized. The combined system of UV light photocatalysis and visible light sensitization will be constructed. A systematic investigation will be made, including the effects of film composition, the distance between films, and operation conditions on the generation of reactive species, and on the efficiency and reaction mechanism of organic degradation, and on the quantum yield and stability of the combined system. This project is based on a well-done primary work, and is expected to achieve important progress, and to change the turndown situation observed nowadays with semiconductor photocatalysis for environmental protection.

半导体光催化能被用于降解众多的有机污染物,但量子效率较低,且难以利用可见光. 本项目首次提出：将紫外光半导体光催化和可见光金属配合物光敏化耦合起来，拓宽体系吸光波长范围，充分利用这二个不同过程产生的各种活性物种，以期提高有机污染物的降解效率和矿化率。将研究制备和表征不同类型的光催化剂和光敏剂薄膜，构建紫外光光催化和可见光敏化的组合体系，系统考察薄膜组成、膜间距、运行条件等对活性物种的产生、有机物的降解效率和反应机制、组合体系的量子效率和稳定性等的影响。该项目已有较好的前期工作基础，有望获得重要的研究成果，改变目前光催化环保应用出现的低迷局面。

本项目针对水中苯酚等有机物降解，设计紫外光UV和可见光vis光催化的耦合体系。以机械方法，将UV/TiO2膜置于vis/铝酞菁膜之前，该复合膜的UV-vis活性高于两者之和，并与膜参数、膜间距等有关，但1 + 1 > 2效果不显著。系统研究发现，H2O2等活性物种的浓度低、寿命短、扩散慢。以化学法，将 4nm CuO沉积于40 nm CuWO4. 该复合物的UV-vis活性比两者之和提高9倍。光电化学表明，CuO能吸收波长大于570 nm的光，将它的电子转移到CuWO4； CuWO4能吸收吸收波长小于570 nm 的光，将它的空穴电子转移到CuWO4。补充板钛矿数据，证实和完善了我们的重要结论。TiO2的光催化固有活性仅随它的煅烧温度指数性增加，而与它的晶体结构无关。这主要是生成表面缺陷，次要是粒子生长。TiO2的光催化表观活性则与它的固有光催化活性和各项表面物化性能有关。该结论揭示了半导体光催化的本质，符合基本原理。与锐钛矿和板钛矿相比，金红石的表观活性最低，归结于对水中O2吸附最差。但是，它的热稳定性最高，有望成为主流光催化剂。以Cu2+捕获电子，提高金红石量子产率4.5倍；以CeO2-x储存O2、CuWO4催化还原O2，经600oC煅烧的金红石表观活性提升最大，分别是1.6和11倍。以含铁杂钨酸催化O2还原，提升锐钛矿表观活性1.8倍；以CoPi催化空穴转移，能显著提高锐钛矿的表观活性，但CoPi、有机物和O2必须同时处于TiO2表面；以Bi2O3促进空穴转移，Bi2WO6的UV-vis活性提高4倍。以几种无机阴离子表面吸附，都能提高锐钛矿、板钛矿和Bi2WO6的表观活性，但都取决于光催化剂活性、阴离子、有机物和O2吸附量。据此，我们提出半导体空穴转移的阴离子自由基机理，否定了长期假设的OH-/H2O能半导体空穴氧化的OH自由基机理。以上成果对于半导体光催化的发展和应用，具有十分重要的意义。本项目发表论文19篇，培养博士、硕士毕业研究生各4名。