基于BiOX（X=Cl、Br、I）构建光生空穴直接氧化的高效降解体系去除水体中全氟羧酸和全氟磺酸研究

Perfluorinated carboxylic acids and perfluorooctane sulfonic acids, as a kind of new persistent organic pollutants, are resistant to the traditional advance oxidation technologies which focus on the hydroxyl radicals generation. Therefore, it is urgent to establish a new effective method to degrade perfluorinated carboxylic acids and perfluorooctane sulfonic acids in an oxidative way. In this research project, the efficient photogenerated holes direct oxidation system with BiOX(X=Cl、Br、I) will be adopted on the basis of the character of perfluorinated carboxylic acids and perfluorooctane sulfonic acids. Under light irradiation, the layer structure of BiOX(X=Cl、Br、I) can separate the photogenerated hole-electron pair efficiently. Besides, due to the low bond energy and long bond length of the Bi-O bond, the exposed oxygen atoms on the surface of BiOX(X=Cl、Br、I) can escape from lattice to form vacancies which binds the target substrate tightly by inserting the O atom of –COOH or –SO3- into the position of vacancy and thus facilitate the hole direct oxidization degradation of perfluorinated carboxylic acids or perfluorooctane sulfonic acids. Meanwhile, the regulation of the exposed crystal face, morphology and growth dimension can further improve these compounds degradation by increasing the concentration of oxygen vacancy of BiOX(X=Cl、Br、I). The impact of water quality on the degradation efficiency of perfluorinated carboxylic acids and perfluorooctane sulfonic acids is investigated and the related elimination methods for interferences are proposed. Hence, a new method of photogenerated hole direct oxidation degradation of perfluorinated carboxylic acids and perfluorooctane sulfonic acids will be established. The type and concentration of the photo-generated radical species for the perfluorinated carboxylic acids and perfluorooctane sulfonic acids degradation is controlled by the interface chemistry, which realizes the effective oxidative degradation. This is very significant in sciences, and it will bring great benefit to environment and economy.

全氟羧酸和全氟磺酸是一类新兴的持久性有机污染物，传统围绕羟基自由基产生开展的高级氧化技术不能实现其有效降解，急需建立新型高效的氧化降解方法。本项目根据全氟羧酸和全氟磺酸的分子结构特征，采用新型层状材料BiOX（X=Cl、Br、I）为光催化剂，通过光生空穴直接氧化的方法实现其有效降解。在光照条件下，催化剂的层状结构有利于降低光生空穴与光生电子的复合，表面弱的Bi-O键导致产生的氧空位所介导的吸附能够有效抑制光生空穴向羟基自由基的转变；同时，调控催化剂的暴露晶面、形貌以及生长维度能够促进氧空位的产生，进一步提高氧化降解全氟羧酸和全氟磺酸的能力。研究水质对全氟羧酸和全氟磺酸降解效率的影响及干扰消除方法，进而提出一种高效氧化降解去除污染水体中全氟羧酸和全氟磺酸的新方法。本项目通过界面化学手段调控进攻氧化物种种类及其浓度，实现难降解全氟羧酸和全氟磺酸有机污染物的高效降解，具有重要科学意义和经济效益。

全氟辛酸（PFOA）和全氟辛烷磺酸（PFOS）是一类新兴的持久性有机污染物，具有耐氧化、抗常规化学处理的特点，急需建立新型高效的降解方法。鉴于传统围绕羟基自由基（•OH）产生开展的高级氧化技术不能实现PFOA有效降解，本项目采用新型层状材料氯氧化铋（BiOCl）为光催化剂，通过光生空穴（h+）直接氧化的方法实现其有效降解。在光照条件下，催化剂本身特有的层状结构及间接带隙跃迁有利于促进光生载流子的分离，表面弱的Bi-O键导致产生的氧空位所介导的单齿配位能够实现PFOA的紧密吸附，从而有效抑制h+向•OH的转变，达到直接氧化的目的，同时氧空位作为捕获中心能进一步降低光生载流子的复合。水解沉淀法制备BiOCl简单易行，无需外加试剂与能量辅助，所得催化剂具有{001}面暴露的纳米片结构，该晶面上存在高密度的氧空位。通过改变制备时盐酸用量及沉淀剂种类可改变体系pH，实现{001}晶面暴露的调控，进而达到连续调控氧空位的目的，使得BiOCl氧化降解PFOA的能力得以进一步提升。PFOA氧化降解及脱氟分别满足准一级动力学和准零级动力学过程，端基断裂后逐级脱除CF2单元生成系列短链中间产物（C2-C7）。在此过程中，BiOCl表现出良好的循环稳定性。鉴于PFOS难于进行氧化降解的特点，本项目采用亚硫酸盐（SO32-）紫外光解生水合电子（eaq-）实现其有效的还原降解。相比通过激光闪光光解及碘化钾获得eaq-的方法而言，SO32-体系成本低且不易造成二次污染。PFOS还原降解的脱氟动力学满足PEK模型，其快反应与慢反应分别对应于PFOS支链异构体与直链异构体的降解。提高体系SO32-浓度、溶液pH、反应温度及降低辐照波长均能促进eaq-的产生，加快PFOS的还原脱氟。除了端基断裂和氟原子直接脱除的方式外，PFOS亦可通过中间C-C键断裂的方式发生还原降解，从而使得短链全氟丙酸和全氟丁酸的浓度明显高于其它产物。本项目通过界面化学手段调控进攻物种种类及其浓度，实现难降解PFOA和PFOS的高效降解，具有重要的科学意义和经济效益。