基于表面氧空位活化分子氧功能的纳米MgO光催化降解VOCs机制研究

Surface oxygen vacancies (SOVs) not only can capture electrons and improve the separation efficiency of photo-induced carriers, but also can promote the adsorption and activation ability to flexible gas. On basis of these multifunctional roles, the solution combustion method would be used to fabricate nano magnesium oxide (MgO) photocatalyst with SOVs under a reducing atmosphere to promote lattice oxygen atoms to escape from the surface, which can make MgO to be a semiconductor. The effects of synthetic factors such as fuel types and their quantities, calcination temperature and atmosphere, dopant of elements on their types and concentrations of SOVs would be investigated in order to determine the main factors for the formation of SOVs by this method. The interaction between SOVs (and/or their captured electrons ) and the adsorbed molecular oxygen would be explored in this project. The correlation between the abovementioned interaction and the formation of singlet oxygen, superoxide oxygen and hydroxyl radicals on the surface of MgO would be revealed to further illuminate the photocatalytic activation approach and mechanism of these reactive oxygen species on the SOVs of MgO. The adsorption-activation state and product form of VOCs under different atmospheres would be determined to clarify the influences of SOVs and their captured electrons on the degradation approach and mechanism of VOCs over the obtained MgO. Finally, the reuse experiments of adsorption/degradation reactions would be carried out to obtain the stable conditions for SOVs. This project can develop a further application into environment fields for MgO, deepen the function mechanism of SOVs and provide a reference for an insulator to be a semiconductor.

基于表面氧空位可俘获电子、提高光生载流子的分离效率及吸附活化等多功能作用，本项目拟构建溶液燃烧过程中的还原气氛促使晶格氧的逸出以合成含表面氧空位的纳米氧化镁，使传统氧化镁半导体化；考察该方法中燃料种类及用量、焙烧温度及气氛、元素掺杂等合成因素对表面氧空位的类型及浓度的影响；研究表面氧空位及所俘获的多余电子与吸附态分子氧之间的相互作用以揭示其对合成氧化镁表面上单线态氧、超氧阴离子和羟基自由基等活性氧物种的生成之间的相关性，进而阐明表面氧空位光催化产生活性氧物种的途径及机制；确定不同气氛下VOCs分子在氧化镁表面上的吸附活化态及产物形式，探究表面氧空位及其所俘获电子对VOCs分子的光催化降解机制及途径的影响；考察催化剂使用前后表面氧空位的变化情况以摸索缺陷态材料的稳定存在条件。本项目可拓宽地表丰富的氧化镁在环境领域中的应用，深化表面氧空位作用机理，为绝缘体材料的半导体化提供借鉴。

基于表面氧空位可俘获电子、提高光生载流子的分离效率及吸附活化等多功能作用，本项目通过调控燃料的种类及用量构建缺陷态纳米MgO，使其半导体化；揭示了尿素、柠檬酸和葡萄糖等对缺陷态镁基材料活性晶面暴露、吸光能力、磁性、电荷密度、氧空位浓度及其活化分子氧能力的影响机制，为缺陷态材料的快速合成提供重要的参考。具体的主要工作如下：.1. 调控柠檬酸合成了含镁氧双空位结构的缺陷态纳米MgO，研究了空位结构和电荷密度对超氧阴离子和过氧阴离子自由基的影响机制，借助550度下100小时的热催化氧化甲烷考察了合成材料的稳定使用情况，发现了合成MgO具有超越过渡金属氧化的低温催化氧化甲烷的能力，拓宽其在环境领域中的作用；.2. 以葡萄糖为燃料合成了缺陷态纳米CeO2并考察其光热催化氧化VOCs的性能，发现了与高浓度氧空位相比，电荷密度增强更加有利于提高低温光热催化氧化活性。理论计算表明电荷密度增强的来源可能是与{200}/{111}晶面比值有关，而不是氧空位的浓度；.3. 采用燃烧法合成了缺陷态镁铈复合氧化物。CeO2的加入增强了MgO的光吸收能力和电荷密度。但是，复合氧化物表面氧空位的含量随着CeO2含量的增多逐渐减小。光激发和温度利于均利于表面超氧阴离子和羟基自由基在复合氧化物表面上形成。当镁铈摩尔比为1：0.75时，复合氧化物在350度对1500 ppm甲苯的转化率达到90%。当切断反应气空气后，复合氧化物的光热催化瞬时活性大幅度下降，重新通入空气后光热催化活性可以再次回复，表明分子氧吸附活化对反应起着至关重要的作用。当引入水蒸汽后复合氧化物的光热催化活性下降了约30%，但是活性随着水蒸气的消失逐渐恢复;.4. 采用固相法制备了磷酸盐修饰型纳米MgO，并对其进行了物相组成、形貌、比表面积、光学性能及能带结构等进行了分析；首次实现以水为反应介质可见光照射下光催化还原CO2为CO的能力并揭示了CO2分压对其活性的影响机制，六次循环实验证实了该合成材料具有较好的稳定性。