多孔氧化铝/铋系异质结原位构建及其吸附富集/光催化降解VOCs机制研究

Photocatalytic degradation of volatile organic compounds (VOCs) over bismuth-based materials has received attention and research because of the high-efficiency and low-cost. However, the present synthesis processes of bismuth-based materials are complex and the understanding on the relationship of structure and performance is not profound. Based on the facts that holes and superoxide anion radicals generated in bismuth-based materials are the main active species responsible for the degradation of pollutants, this project plans to synthesize heterojunctions composed of porous alumina with high specific surface area and bismuth oxide with surface oxygen vacancies (SOVs) via self-combustion of ionic liquids. The design of porous structure and high specific surface area would improve the physisorption of catalysts towards VOCs. The construction of SOVs aims at decreasing the energy band gap of catalyst, enhancing the chemisorption and activation of molecular oxygen and VOCs on the surface of catalyst. Both physisorption and chemisorption would concentrate the VOCs on the surface of catalyst and then enhance the contact between VOCs and photo-induced holes. The fabrication of heterostructured materials could increase separation efficiency of photo-induced charge carriers of bismuth-based materials on the basis of the characteristic that the defects of Al2O3 can accept photo-generated electrons from other semiconductors. The interaction between oxygen vacancies and VOCs will be revealed via the investigation on the influence of SOVs on surface charges and the quantum chemical calculation. The separation and transfer mechanism of photo-induced carriers will be proposed on the basis of determination of the essential reason for the photocatalytic activity of amorphous Al2O3 and the energy band structures of hybrid components. The degradation route and mechanism of VOCs over bismuth-based photocatalysts with multifunctional SOVs will be proposed. This project would provide references for the development of new chemical industry materials and the treatment of VOCs, as well as broaden the application of inexpensive alumina in chemical industry.

铋系材料光催化降解挥发性有机物(VOCs)以其高效、低成本，近年来受到关注与研究，但存在合成过程复杂及缺乏结构设计等问题。本项目基于空穴和超氧阴离子自由基是铋系材料主要活性物种，拟通过离子液体自燃烧原位构建多孔高比表面氧化铝及具有氧空位的铋系材料异质结，以多孔结构提高氧化铝对VOCs的物理吸附，以氧空位降低铋系材料禁带宽度并增强其对分子氧及VOCs的化学吸附和超氧自由基产生，利用吸附富集VOCs以增强其与催化剂表面空穴的接触，以氧化铝缺陷位转移铋系材料光生电子以提升量子效率。通过自由基探测、中间物种分析及量子化学计算，揭示氧空位电子对分子氧和VOCs的活化作用；探讨无定形氧化铝具有光催化活性原因，确定异质结组分能级结构，明确异质结界面光生载流子分离及迁移机制；阐明基于多功能性氧空位的VOCs光降解途径。本研究可为化工新材料开发及VOCs治理提供借鉴，拓宽地壳丰富的氧化铝在化工行业中的应用。

光催化降解挥发性有机物(VOCs)具有高效、低成本等优点，但传统的TiO2等催化剂仅能吸收紫外光且主要活性物种是羟基自由基，需要吸附水分子，与VOCs之间存在竞争吸附而降低催化活性。本项目基于空穴和超氧阴离子自由基是铋系材料主要活性物种的学术思路出发，开发了系列铋系材料，研究了其主要结构及表面性质对其光催化活性的影响，并研究了其降解VOCs的性能，主要工作如下：. 1. 基于界面缺陷思路构建并调控了铋系材料的能带结构，提出了价带下移比分离效率更能提高污染物降解能力的学术思路。分离效率与价带位哪个更重要，是异质结光催化剂亟待解决的重要科学问题。本项目基于界面缺陷思路构建异质结，通过制备不同比例的Bi3O4Br/α-Bi2O3、β-Bi2O3/Bi2O2CO3等异质结材料，首次发现在铋系材料中下移价带位置比提高电荷分离效率更重要。该研究深化了对异质结作用机理的认识，避免了传统异质结构建中只注重分离效率的问题，为构筑异质结提供了新思路。. 2. 提出了离子吸附反向诱导晶面生长的方法，发现了富铋型卤氧铋主晶面在光催化活性中的重要作用，创建了主副晶面反转生长的合成路线。在离子液体自燃烧合成Bi5O7I中，发现了 {314}晶面具有择优生长现象，揭示其原因是燃料中的I-的吸附作用，提出了“离子吸附反向诱导晶面生长”的方法。同时发现，但适当提高主晶面{314}的择优生长、降低传统高活性{001}晶面的比例，反而有利于其降解污染物光催化活性的提高。该研究开创了晶面调控新方法，并为富铋型卤氧铋的主晶面研究提供了新思路。. 3. 发现了羟基自由基在甲苯光催化降解中对于催化剂活性和稳定性的副作用，提出在VOCs光降解中应构建价带位置和超氧阴离子自由基为活性物种的催化剂。分别利用离子液体自燃烧法（C-BiOCl）和水热法（H-BiOCl）制备了不同的BiOCl光催化剂，由于表面和能带结构的差异，H-BiOCl可以产生羟基自由基，而C-BiOCl不能产生。富产羟基自由基的H-BiOCl会使甲苯生成酚类中间产物并会优先覆盖活性位点，从而使光催化剂的活性和稳定性降低，证实了羟基自由基的不利影响以及氧空位容易被有毒中间体覆盖而失活的缺点。本研究对于VOCs降解途径的认识和气相光催化剂的设计具有一定的指导意义。