晶面/缺陷调控羟基自由基生成增强卤氧化铋光催化矿化NOx分子机制

The applicant have recently found the significant enhancement of reactivity and selectivity for the photocatalytic mineralization of NOx over (010) surface of BiOCl experimentally. On the basis of the exploration, the present project aims to solve the two key scientific issues for the extended BiOX (X=Cl, Br or I) class, including light-induced reactivity oxygen species formation and adjustment, and the reaction rate and selectivity of the NOx mineralization. The proposal will optimize the synthesis process systematically and establish the relationship between local structures consisting of preferable terminated surface and defects and the capacity of NOx mineralization. Based on the first principles calculations, altogether with experimental characterizations, the local geometric structure, band structure and effective mass of electrons will be investigated systematically for a range of surfaces exposed and defects contained. The atomistic mechanism for the preferable generation of hydroxyl radicals through light-induced holes and electrons trapping by H2O or O2 will also be investigated. By using the first principles calculation, in-situ DRIFTS and GAS-MASS comprehensively, the active sites, oxidation reaction path, reaction rate and production distribution for NOx mineralization will be illustrated. Combining the results of chemical and geometrical structure, the generation and adjustment of reactive oxygen species and the characteristics of NOx oxidation, the NOx mineralization oriented design of BiOX materials will be established at atomistic level, which could provide theoretical basis for the development of promising photocatalytic technology for NOx removal.

申请者前期发现BiOCl(010）晶面暴露对其光催化NOx矿化活性和选择性有显著增强。在此基础上，本项目将拓展到BiOX(X=Cl、Br、I)，针对光激发活性氧物种生成与调控、NOx矿化反应速率与选择性分子机制两个关键科学问题，系统优化材料制备工艺条件，建立晶面/缺陷微观结构-NOx矿化性能关系。采用第一性原理计算模拟与实验结合，确定不同晶面/缺陷BiOX的微观几何结构、禁带结构及电荷有效质量；揭示材料结构与反应条件调节O2与H2O捕获光生载流子选择性生成羟基自由基的分子机制；综合运用计算模拟、原位红外与气质联用方法，明确NOx氧化活性位、反应路径、控制步骤、反应速率及产物分布特征；综合化学组成、几何结构、活性氧物种形成与调控、NOx氧化反应特点，从分子水平阐明光催化NOx矿化对BiOX材料设计的要求，为开发高活性、高选择性和低毒副产物生成的光催化去除NOx技术提供理论支撑。

目前光催化降解技术仍然存在光吸收波长范围窄、光生载流子分离效率低、光催化反应效率低等问题。本课题采用密度泛函理论计算和原位红外等手段，研究了BiOCl催化剂晶面与掺杂对光催化条件下载流子分离、活性氧物种生成与NO氧化活性改善与毒副产物抑制。通过杂原子掺杂、复合物构建等改性手段开发了具有合适禁带宽度、高效光生载流子分离率的半导体光催化剂。具体而言，将Mn、P掺杂后窄化了氯氧化铋的禁带宽度，拓宽了其光吸收范围；杂化态引起中间能级促进光生电子跃迁，提高了光生载流子分离效率。掺杂还可以增大比表面积，增强光催化材料表面对水分子的吸附能力、弱化了H-O键，提高活性物种的生成数量。碳化钨和氯氧化铋复合成 n-n 型二元光催化剂能够高效降解磺胺甲噁唑。碳化钨和氯氧化铋都呈2D层状结构，碳化钨的引入减少了氯氧化铋薄片的团聚，并提供更多反应位点，吸收更多光能参与光催化反应。氯氧化铋的功函数高于碳化钨，光照后形成一个从碳化钨指向氯氧化铋的内部电场，促进电子的定向迁移。而一步水热合成法制备的Mn3O4/BiOCl 异质结光催化剂，Mn3O4纳米颗粒成功沉积导致表面氧空位的增加，表现出优异的 NO2抑制能力，Mn3O4和BiOCl之间形成的Z型异质结促进了O2·-和OH·自由基的生成，在光照射下可将气相NO氧化为NO3 -，实现了气相NO的高效矿化脱除。本项目研究成果为以BiOCl为基础的稳定廉价催化剂研发和污染物高效降解提供了新思路，对光催化活性氧物种的生成调控与污染物反应分子机制的探索丰富了光催化理论。