In2O3表面活性氢物种调控及其实现PBDEs光催化深度脱溴的反应机制研究

Common metal oxides photocatalysts such as TiO2 could not degrade the PBDEs completely. The reason is that the hydrogen species coupled with photo-induced electrons on the surface of photocatalysts could not reach the activation energy for the debromination of low-bromine substrates and the complete debromination of PBDEs needs the participation of H• or H-. In2O3 is a kind of nonstoichiometric metal oxides and can effectively bond with active hydrogen species (H• or H-) on the sites of oxygen vacancies. Hence, this project would regulate the active hydrogen species on the surface of In2O3 as well as optimize the concentrations and ratios of three hydrogen species (H+, H• and H-) to realize the deep photocatalytic debromination of PBDEs by following aspects: 1) In the preparation steps of catalysts, regulate and control the characteristic defects on the surface of the catalysts and study the generation feasibility of three hydrogen species (H+ H• and H-) under regulation of defects; 2) In the photocatalytic reaction system, regulate and control the synergistic effects between defect regulation and common hydrogen donors such as small molecule alcohols and alcohol amines in the reaction and find out the best activation transition-state as well as hydrogen species on the surface of catalysts for different brominated intermediates; 3) utilize various in-situ characterization measurements and density functional theory calculations to quantitatively characterize the regulation of active hydrogen species and study its pathway of generation and transfer as well as the characteristics of dynamic and thermodynamic parameters in the reaction with PBDEs. This project is expected to provide theoretical basis and experimental foundation for the design and development of photocatalysts which can degrade PBDEs efficiently and completely.

TiO2等常见金属氧化物光催化剂对多溴联苯醚脱溴不彻底。原因在于，这类光催化剂表面与光生电子耦合的氢物种（H+/e-）无法达到低溴底物脱溴所需的活化能，完全脱溴需要有活性氢物种H•或H-。In2O3是一种非化学计量比的金属氧化物，其表面氧缺陷可有效结合活性氢物种（H•或H-）。因此，本项目拟从以下方面调控In2O3表面活性氢物种，优化三类氢物种H+、H•和H-的浓度和比例，实现多溴联苯醚的完全脱溴：1)催化剂制备方面，调控催化剂表面特征性缺陷，探索三类氢物种H+、H•和H-在调控下产生的规律；2)光催化反应体系中，调控氢供体如小分子醇、醇胺等与催化剂表面缺陷调控的协同效应，找到不同溴代中间物在催化剂表面最佳的活化过渡态和氢物种；3)利用多种原位手段结合理论计算，定量表征活性氢物种的调控和其产生、转化规律以及与PBDEs反应的动力学/热力学特性，为开发高效全脱溴的光催化剂提供理论和实验基础。

已有研究表明，TiO2等常见金属氧化物光催化剂对多溴联苯醚（PBDEs）等难降解的芳香基溴化物脱溴不彻底。原因在于，这类光催化剂表面与光生电子耦合的氢物种（H+/e-）通常无法达到低溴底物脱溴（<4Br）所需的活化能，深度脱溴需要有更强的活性氢物种H•或H-。In2O3是一种非化学计量比的金属氧化物，其表面氧缺陷可有效结合活性氢物种（H•或H-）。因此，本项目从In2O3表面特征性缺陷以及氢供体调控着手、研究不同氢供体与催化剂表面缺陷调控的协同效应，探究活性氢物种的产生、转化规律以及与PBDEs反应的动力学/热力学特性，优化氢物种的浓度和比例，实现PBDEs等芳香溴化物的完全脱溴。主要研究工作如下：. 首先，利用水热法、沉淀/焙烧法等多种方法，通过调控反应条件及前驱体制备出了具有不同氧缺陷浓度的In2O3光催化材料。研究结果表明，以小分子醇作为氢供体时，催化剂表面氢物种浓度与氧缺陷浓度呈正相关性，且PBDEs等芳香溴化物的降解率随氢物种浓度的增大而逐渐增加。因此，对In2O3表面缺陷位点调控可提高其氢物种浓度，进而增强其脱溴性能。. 其次，筛选出具有最高氧缺陷浓度的In2O3纳米片作为目标光催化剂，通过调控氢供体的方式，优化了催化剂表面氢物种的浓度和比例。研究结果表明，以氢气作为氢供体时，催化剂表面氢物种为H+和H-，与In2O3以受阻路易斯酸碱对的形式结合。与小分子醇作为氢供体时的质子耦合电子转移反应机制不同的是，H-物种优先亲核进攻C-Br键，实现了低溴芳基溴化物的高效深度脱溴。Arrhenius公式计算得出，氢气条件下的活化能（11.751 KJ/mol）远小于小分子醇条件下的活化能（37.736 KJ/mol）。. 最后，进一步研究了以氢气作为氢供体时，溶剂对于In2O3光催化还原PBDEs反应的影响。结果表明，溶剂的极性变化可改变催化剂表面酸碱位点，影响催化剂活化氢气，产生氢物种的速率，进而决定In2O3深度还原PBDEs等芳香溴化物的性能。本项目的研究，为开发可高效深度脱溴的金属氧化物光催化剂提供了理论和实验基础。