有氧条件下可见光催化还原氯代烃体系的构建及电子转移机制

It is an eager issue to develop a metal catalytic reduction dechlorination system to avoid continuous adding of reductive agent and anaerobic reaction atmosphere. Based on the Z-scheme system in hydrogen evolution from water splitting under visible light, the application focus on combining photocatalysts with metal catalysts to match the band gap of photocatalysts well to trap photogenerated holes by water with oxygen produced simultaneously. .The Schottky barrier formed when metal catalysts are deposited on the surface of semiconductor catalysts can facilitate the production of hydrogen atom by donating electron to hydrogen ion. On the basis of the ability to dissolve hydrogen easily, the metal catalysts will be screened and applied to reduce water to hydrogen atom which can be used as an active agent for hydrodechlorination. Accordingly, a new reductive material for photocatalytic reduction dechlorination of chlorinated hydrocarbon can be achieved which will not be affected in the presence of dissolved oxygen in solution. .Advanced approaches of catalyst characterization will be employed to investigate the particle size, specific surface area, composition, surface structure, band structure, density of states (DOS), the lifetime and density of the photogenerated charge carriers, and hydrogen surface coverage of metal. The hydrodechlorination efficiency, according to which the system is modified and improved, is measured for different systems. Consequently, the electron transfer mechanism of the system can be revealed according to the results of isotopic tracing with the aid of HRNMR (high-resolution nuclear magnetic resonance) analysis, as well as with the help of DFT calculations based on the package of Gaussian and Material Studio. .This research will reveal the mechanism of the electron transfer in hydrogen atom generation and hydrodechlorination of chlorinated hydrocarbon. Thus, it will pave the way for the development of innovative remediation methods of chlorohydrocarbon pollution; and elucidate the technology details for an in-situ, efficient, and safe application of photocatalytic reduction of chlorinated hydrocarbon.

金属化学还原法脱除水中有毒氯代烃一直是研究的热点。针对该体系需外加电子供体及厌氧环境条件的限制，本申请类比Z-scheme可见光催化分解水产氢体系，将光催化和金属化学还原有机结合在一起，筛选和匹配具有可见光分解水产氢、产氧性能催化剂的能带结构、电子传递介质，实现水作为抑制剂捕集光生空穴；选择对氢溶解性好的金属，利用金属与半导体间的肖特基势垒，可见光还原水产生原子氢，再由金属的活性位点利用原子氢实现还原加氢脱氯反应，最终构建出一种原位供电子并不受氧影响的光催化加氢脱氯新材料和新还原体系。采用现代材料物理和化学表征手段，研究体系的结构形貌、比表面积、粒径、能带宽度、金属元素形态、光生电子寿命和密度、金属表面氢覆盖率等，探究反应体系的元素平衡并探究体系电子流向。运用同位素示踪，辅以DFT模拟计算揭示原子氢产生、体系加氢脱氯的电子转移机理，为原位、高效、安全的可见光催化净化水体氯代烃提供理论基础。

含氯有机物在工业中应用广泛，其性质稳定，易在环境中积累；有致畸、致癌、致突变等毒害作用，可致生态系统失衡。采用化学还原法脱氯是国内外的研究热点，但必须在厌氧条件下进行，限制了其在自然水体中的应用。为此，构建原位供电子不受氧竞争的还原脱氯体系意义重大。.该项目将光催化技术和金属化学还原有机结合，匹配和筛选具有可见光分解水产氢（还原半反应）性能催化剂的能带结构、电子传递介质，构建一种原位供电子并不受氧影响的光催化还原脱氯新还原体系。制备了Pd/g-C3N4、(AgNbO3)1-x(SrTiO3)x、g-C3N4/Au/Bi2MoO6等多种可见光还原催化剂，探讨了催化剂能带调变机制，形成了能带调控的方法。本研究在光催化产氢半反应和有氧条件下还原含氯有机物方面取得了良好进展。.课题利用光还原法制备了Au/g-C3N4（负载），通过Au与g-C3N4形成肖特基势垒加速光生电子和空穴的分离，以及Au的SPR效应增强了可见光的吸收，提高了光催化活性。Au/g-C3N4 (1%)产氢速率达到222 μmol/h/g，是g-C3N4的125倍。采用煅烧法制备了(AgNbO3)1-x(SrTiO3)x（固溶体），改变x的值可实现对催化剂能带的调变。当x=0.75时，(AgNbO3)0.25(SrTiO3)0.75固溶体的禁带宽度为2.94eV，导带电势为-0.60 eV，此时催化剂具有最高的可见光催化产氢活性。.课题利用上述方法制备了Pd/g-C3N4（负载）。通过Pd与g-C3N4形成肖特基势垒促进光生电子空穴对的分离，以及Pd作为助催化剂提供活性位点，提高了光催化活性。有氧条件下，Pd/g-C3N4 (0.5%) 在8 h内对TCE的降解率为30%，是g-C3N4的6倍。采用光还原法、煅烧法制备了g-C3N4/Au/Bi2MoO6（属Z-scheme体系），该体系具有高效的电子传递路径，促进光生电子和空穴的分离，提高了光催化效率。有氧条件下，8 h内对TCE的降解效率为40%，是g-C3N4的8倍。.本项目采用多种材料表征手段分析材料的形貌结构、比表面积、表面活性基团及光生电子和空穴迁移规律。研究证明：光生电子空穴的有效分离可以增强光催化还原脱氯的效果；匹配催化剂的能带结构，避免O2被电子消耗，体系在有氧条件下可实现光催化还原脱氯。本研究为有氧条件下地表水中氯代烃的还原修复提供理论