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Alternative TitleDegradation of refractory organic pollutants in water by photocatalytic ozonation
Thesis Advisor曹宏斌 ; 谢勇冰
Degree Grantor中国科学院研究生院
Degree Discipline环境工程
Keyword难降解有机物 光-臭氧催化氧化 双层水热 掺氮
Abstract随着我国经济的快速发展,人类向环境中排放的废水日益增多。工业废水因其含有大量难降解有机物而成为环境科学领域关注重点,这些难降解有机物由于高毒性而严重威胁人类健康。高级氧化法是一类能够将低浓度难降解有机物完全矿化的处理方法。光催化氧化是一种具有广阔应用前景的高级氧化技术,但其处理效率较低;臭氧催化氧化法虽然已经应用在饮用水消毒处理中,但存在臭氧无效分解及选择性氧化有机物的缺点。因此研究两者协同处理难降解有机废水,不仅具有提高处理效果缩短反应时间的实际意义,而且通过耦合机理的研究能够加深对作用过程的理解。 论文选取商业用P25,通过添加均相催化剂和以不同的反应底物为模拟污染物,对光-臭氧催化氧化过程进行了系统研究。光-臭氧催化氧化能够显著改善TOC去除效果而缩短反应时间。不同类型的有机物其耦合作用机理不同,光催化臭氧氧化降解苯酚主要依赖臭氧分子直接氧化和臭氧分子作为强的电子捕捉剂进而促进光生电子和空穴的分离并产生更多的?OH,而降解草酸主要依赖臭氧分子在紫外光条件下被激发和臭氧分子作为强的电子捕捉剂两种方式而通过链式反应产生?OH。均相催化剂可以通过自身相态的转变参与反应并影响反应过程,Fe3+可以通过吸收光生电子而被还原为Fe2+然后被臭氧重新氧化为Fe3+,Ag+同样可以通过光还原而沉积在TiO2表面而后通过臭氧的氧化作用而重新转变为Ag+。前者可以在转变过程中参与产生?OH的反应,而后者则能够消耗臭氧而对有机物的降解和TOC去除起到阻碍作用,同时,它们都可以和草酸络合而加速光催化臭氧氧化过程。 本研究采用一种简单的双层水热法合成了过渡金属离子掺杂的TiO2,物理化学表征表明该种方法合成的改性光催化剂具有比表面积大、较为规则的孔径分布,其掺杂方式为间歇掺杂,金属离子在水热过程中的价态并未发生转变。其紫外光和可见光降解草酸的活性根据掺杂的金属离子的不同而不同。在此基础上通过高温掺氮,制备出一种具有良好可见光响应度和较好紫外光活性的Co/N-TiO2,并研究了初始pH、温度、光辐射量和臭氧浓度对光-臭氧催化氧化降解硝基苯的影响。得出pH对污染物去除和TOC影响较小,常温最有利于反应,而光照强度主要影响TOC去除,入口臭氧浓度主要影响硝基苯的去除。
Other AbstractWith the rapid development of economy in China, larger amout of wastewater is discharged into the environment. Moreover, industrial wastewater draws much attention due to the tremendous refractory organic pollutants contained, which are of high toxicity and thus threaten the human health and safety. Advanced oxidation processes are a kind of effective ways to mineralize the refractory organics of low concentration. Photocatalysis is one of promising advanced oxidation technologies in the application of organic compound degradation but the removal efficiency is relatively low; although ozonation and catalytic ozonation has been applied to the disinfection of drinking water, the molecule ozone is easy to decompose and owes reaction selectivity based on different kinds of organic pollutants. Therefore the research on combined processes of these two technologies to degrade refractory organic pollutants is not only practical in terms of prompting degradation efficiency and shortening the reaction time, but also can intensify the understanding about the synergetic effect of the two processes. By using commercial P25 and adding homogenous catalysts, the systematic research on photocatalytic ozonation to degrade different kinds of organics was conducted. The combined process could enhance TOC removal ratio and therefore shorten the reaction time compared with single process. The reaction pathways largely depended on the inner properties of the pollutants. For the pollutants easily oxidized with ozone, the active hydroxyl radicals produced in photocatalysis and catalytic ozonation in the simultaneous system played an important role in organics removal and mineralization. For the pollutants hardly oxidized with ozone, hydrogen peroxide was firstly produced in the simultaneous process and evolved to hydroxyl radicals later. The transformation of metal ions was highly related with their roles in the photocatalytic ozonation. Fe3+ was almost totally reduced to be Fe2+ in a short time during photocatalysis of phenol and OA, while then quickly reduced Fe2+ was gradually oxidized after 45 min when phenol was completely degraded in photocatalytic ozonation. Fe3+ was hardly reduced in the photocatalytic ozonation of OA because of the complex reaction between Fe3+ and oxalate. Ag+ was easily reduced under photo illumination and deposited on the surface of TiO2, but dissolved into the solution again in the presence of ozone. Fe3+ could induce the generation of hydroxyl radicals while Ag impair the degradation and mineralization by decompose ozone. A two layered, one-pot hydrothermal method was developed to prepare metal ions doped TiO2. The synthesized particles were sphere and uniform, with an average particle size of 10.4 nm. Their high surface area and strong adsorption to light with different wavelengths benefited their application in environmental photocatalysis. The results revealed Cu2+–TiO2 showed the highest activity under UV and Co2+–TiO2 had the best response to visible light. This method can be widely applied to synthesize metal ions doped TiO2 and lead to a new approach for modified photocatalysts. Co and N co-doped TiO2 prepared by combining the former method with calcinations under high temperature was used as catalyst for the degradation of nitrobenzene by photocatalytic ozonation. The removal efficiency of nitrobenzene was largely enhanced in the present of Co/N–TiO2 than the bare TiO2 and Co–TiO2. The mechanism and synergetic effect of photocatalysis and ozonation were discussed through a different view by examining the experimental conditions such as initial pH, temperature, radiant flux and ozone dosage. Due to the synergetic effect, pH showed little impact on the nitrobenzene and TOC removal. The effect of temperature by the combined process is in accordance with that of ozonation. Photocatalysis played an active role in the mineralization in the combined process and ozonation significantly influenced the decomposition of tar
Document Type学位论文
Recommended Citation
GB/T 7714
陈莹莹. 光-臭氧催化氧化耦合处理难降解有机废水[D]. 中国科学院研究生院,2013.
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