可见光活化分子氧产生羟基自由基降解有机污染物的新途径

Hydroxyl radical(oOH), a kind of transient species with high reaction activity, is an optimal oxidant to eliminate pernicious organic pollutants in water. But the product of oOH largely depends on the decomposition of reagents (H2O2,O3) and the irradiation of ultraviolet with high energy. Bi-based halogen oxides (BiOX) can efficiently use visible light. It is possible to activate molecular oxygen (O2)to oOH by regulating the hybridization form of O 2p and X np under low energy visible light irradiation. Bi-based oxyhalide BiOX1(n)X2(1-n) (X1,2 = F, Cl, Br, I) with identified composition and crystalline are used as photocatalyst to degrade different pollutants, which have higher or lower oxidation potential than the valence band of catalysts. NMR, LC-MS and GC-MS are employed to analyze the intermediate products in hydroxylation and decarboxylic reaction. Isotope labeling technique is used to determine the fate of oxygen. The band composition and structure of catalysts which can high-efficiently activate O2 to oOH are tested using ESR and In-Situ-IR techniques. The key factors of the oOH yield are investigated by changing the ratio of O 2p and X np in the band structure and composition from single X1 to binary hybrid system X1(n)X2(1-n). This method is hopeful to provide a novel approach for the degradation of organic pollutants in water by means of the accumulation of low energy to high-energy oxidatant species.

OH是高反应活性瞬态物种，是消除水中顽固有机污染物的理想氧化剂，但其产生需要高能紫外光和分解高能试剂(H2O2,O3)。BiOX能有效利用可见光，通过调控带结构中O2p 与X np杂化方式，有可能用低能量可见光将O2活化成 OH。本项目以具有确定组成和晶型的BiOX1(n)X2(1-n)（X1,2=F,Cl,Br,I）为光催化剂，选择高于和低于价带氧化电位的不同污染物为底物，运用NMR、LC-MS和GC-MS等手段分析底物发生羟基化、脱羧反应的中间产物，采用同位素标记技术确定氧归属，结合ESR和In-Situ-IR手段，考察和筛选在可见光激发下能高效率将O2转化成 OH的催化剂带组成和带结构，通过改变O2p与Xnp在带结构中的比率及单一X1到二元混合体系X1(n)X2(1-n) 带组成来确定 OH产率的关键因素，提供一类低能量累积导致高能氧化物种降解水中有机污染物的新途径。

羟基自由基作为消除水中顽固有机污染物的一种理想氧化剂，其产生需要高能紫外光和分解高能试剂。为了充分利用太阳光诱导高能的羟基自由基的产生和转化，本项目首先制备和筛选出多个具有活化分子氧(O2)的可见光催化剂，采用水热法或模版法制备得到以下不同种类的可见光催化剂，包括卤氧化铋(BiOXs, X=F, Cl, Br, I)、金属有机框架结构(MOF)、钒酸盐等催化剂和其他能活化O2的可见光催化剂，运用同位素标记技术深入地研究其活化O2效率以及降解有机污染物的能力，为制备新型可见光催化剂和调控光催化反应提供了科学依据。主要筛选出BiOXs降解有机污染物藻毒素(MC-LR)的运行参数，运用NMR、LC-MS和GC-MS等手段，分析推导出藻毒素光化学氧化反应路径及氧化反应中氧的来源和转化形式，深入揭示了BiOBr催化降解有机污染物的反应机制；并对磷酸盐(Ag3PO4)和疏水性席夫碱配合物等可见光催化剂活化O2选择性光催化降解有机污染物机理进行了深入地研究，一定程度上揭示了可见光催化活化O2对有机污染物降解机理。