Photodegradation mechanism on recalcitrant substrates in the TiO2 photocataritic degradation

即使细菌修复也不能降解的化学物质积聚在河流、湖泊和其他地方。它们对水生环境造成了严重的生态破坏。本文对持久性有机污染物的解毒和净化工艺进行了研究。(1)用二氧化钛光催化分解不可降解的三嗪类农药，最终生成不矿化为二氧化碳的三尿酸。三聚尿酸不能用二氧化钛降解。氧化锌光诱导降解三聚氰尿酸，可使阿特拉津类农药中的三嗪环容易分解二氧化碳和硝酸盐离子。利用二氧化钛和臭氧催化降解三嗪类化合物，收率高。(2)氯/氟苯甲酸同系物在较短的光照时间内容易发生苯环开环，通过甲酸和乙酸释放出二氧化碳。邻位和旁位的脱氯比位的脱氯更容易发生。然而，所有同源物的除氟是困难的。中间氧化产物含C-F基团，经TOF-MS鉴定。(3)全氟表面活性剂如PFCA和PFSA不能用二氧化钛矿化成含氟离子，但可以用多钨酸盐均相催化剂低收率地进行脱氟。详细探讨了光强、波长、催化剂负载、pH值等最佳实验条件，以及降解机理。

Chemical substances which can not be degraded even by bacteria remediation are accumulated in rivers, lakes and other. They cause a seriously ecological damage in aquatic environment. The detoxification and purification procedure for persistent organic pollutants were focused in this study.(1) Non-degradable triazine agrochemicals were photocatalytically decomposed with titanium dioxide, followed by the final production of cyanuric acid not to be mineralized to carbon dioxide. Cyanuric acid can not be degraded with titanium dioxide. The triazine ring in the atrazine agrochemicals can be easily to carbon dioxide and nitrate ion by the photoinduced degradation of cyanuric acid with zinc oxide. The triazine compounds can be photocatalytically degraded by using titanium dioxide together with ozone in a high yield.(2) Concerning the photodecomposition of chloro/fluoro benzoic acid homologs the benzene ring-opening occurred easily in a short illumination time to evolve carbon dioxide via formic acid and acetic acid. The dechlorination for the ortho-position and para-position happened more easily than that for the meta-position. However, the defluorination for all homologs was difficult. The intermediate oxidative products bearing C-F group were identified by TOF-MS spectroscopy.(3) Perfluoro surfactants such as PFCA and PFSA could not be mineralized to florinated ion with titanium dioxide, but the defluorination was possible with homogeneous catalyst of polytungstanate in a low yield.The optimum experimental factors such as light intensity, wavelength, catalyst-loading and pH value, as well as the degradation mechanism were revealed in detail.