Bi-O-X基纳米材料的能带结构调控及其可见光催化降解尼泊金酯的机理研究

Parabens, alkyl esters of 4-hydroxybenzoic acid, are extensively employed as preservatives in a wide range of cosmetics, canned foods, beverages and pharmaceuticals. These chemicals are continuously released in urban wastewater at relatively high levels and have been detected in variety of water samples. The main concern once they reach the environment is that they have proved to show oestrogenic activity. What's more, they can easily react with free chlorine when mixed with chlorinated tap water, yielding mono and dichlorinated derivatives. The resulting disinfection by-products have shown higher acute toxicity. Therefore, a good knowledge of the fate of parabens and their disinfection by-products from water is crucial for environmental protection. So far, researchers have tried to remove parabens from water by various techniques. Among them, the heterogeneous photocatalytic technologies have several advantages such as using solar light as energy source, high degradation efficiency, low cost, and ability to function under ambient conditions. However, to the best of our knowledge, the degradation of parabens and their chlorinated by-products under visible light irradiation has not been reported. By the band structure tuning of Bi-O-X (X = F, Cl, Br, and I) ternary system, a series of nano photocatalysts with different composition, energy band and surface structure can be synthesized. The structure-activity relationship between catalysts, contaminants, and photocatalytic activities are investigated systemically. Then the optimizing catalysts for the photocatalytic degradation of these pollutants under visible light irradiation can be obtained. In addition, the photoreaction mechanisms are studied using both experimental technologies and quantum chemical calculations. Then we can understand the intrinsic link between structure of photocatalysts, photogenerated oxygen species, and degradation intermediates. Thus the degradation pathways of these pollutants can be controlled to avoid the second pollution. This work is expected not only to synthesize highly efficient visible light photocatalysts for the degradation of parabens and their chlorinated by-products, but also to promote the understanding of the photogenerated holes-based photocatalytic mechanisms, as well as to provide support for the highly efficient removal of other emerging contaminants from water.

尼泊金酯被广泛用作防腐剂，但其残留在环境中表现出内分泌干扰活性，且易于生成毒害更大的氯化消毒副产物，已被认定为一类环境新兴污染物，必须尽快开发去除该类污染物的技术并考察其作用机制。光催化技术是解决该问题的有效途径之一，本申请在我们前期研究的基础上，提出通过调控Bi-O-X (X=F,Cl,Br,I)三元体系的能带结构，系统地研究催化剂结构、污染物结构与光催化活性之间的构效关系，合成出高效降解该类污染物的纳米可见光催化剂；并对反应过程中的活性氧化物种和降解中间产物进行识别，揭示催化剂结构与光生氧化物种、污染物降解中间物之间的内在联系，实现对降解路径的预测和调控，避免二次污染的发生。研究结果可望获得可见光条件下应用光催化技术处理该类污染物的解决方案，明确可见光催化活性与催化剂能带结构和污染物结构的关系，丰富光催化技术治理新兴污染物的基础理论和实验方法。

防腐剂在日常生活中大量使用且很难被自然降解，其残留在水体中对水生动植物及人类皆存在潜在危害，必须尽快开发去除该类污染物的技术并考察其作用机制。本课题选取了系列尼泊金酯作为处理目标，通过合成具有不同能带结构的Bi-O-X (X=Cl, Br, I)三元半导体光催化剂，在可见光条件下降解该类污染物，以寻找高效的光催化剂和去除该类污染物的技术方案。采用多种光谱学手段对所合成光催化剂的结构进行表征、对反应体系中的主要活性氧化物种进行分析，利用色谱/质谱技术对降解中间产物进行识别，利用电化学方法对污染物在水环境中的氧化还原行为进行研究，利用量子化学计算方法对催化剂能带构成和污染物前线分子轨道电荷密度进行理论计算，寻找在可见光条件下光催化降解尼泊金酯类残留物的一般规律和反应机理。特别的，通过采用新的实验设计思路，包括采用具有不同微结构的同一种光催化剂降解单一尼泊金酯、多种不同能带结构的光催化剂降解同种尼泊金酯和多种不同能带结构的光催化剂降解多种尼泊金酯，从而揭示了催化剂结构、污染物结构与光催化活性三者之间的关系。实验结果表明，Bi-O-X 基光催化剂是可见条件下利用光催化技术去除尼泊金酯类污染物的高效催化剂，其能够有效去除该类污染物主要原因是该类光催化剂具有高的价带氧化电势和优良的光生载流子分离能力。研究结果不但获得了可见光条件下应用光催化技术高效处理水体中尼泊金酯类污染物的技术方案，而且明确了可见光催化活性与催化剂能带结构和污染物电子结构之间的相互关系，丰富了光催化技术治理新兴污染物的基础理论和实验方法。