【作者】 朱馨乐；

【导师】 袁春伟；

【作者基本信息】 东南大学 ， 生物医学工程， 2005， 博士

【摘要】 多相光催化是TiO₂粒子在高于其带隙能级（3.2 eV）紫外光照射下产生价带电子与导带空穴,接着生成多种氧化物种使污染物得到较为完全的降解。本论文探讨了乙腈/水悬浮液中TiO₂光催化降解杀虫剂哒螨酮的反应机理。为将此项技术应用于实际污水处理,研究了表面活性剂悬浮液中光催化降解哒螨酮。最后在模型反应器中进行了小试实验。具体内容如下:对λ≥300nm紫外光照射有机溶剂/水悬浮液中TiO₂光降解哒螨酮中间产物进行鉴定和反应路线推导。利用GC/MS分析共鉴别出8种降解产物,并结合与标准品、合成化合物的对比,使其得到进一步确认。反应路线推导表明降解哒螨酮首先是在苯环与杂环之间C-S键处断裂为两个部分,接着发生取代、氧化,去烷基等系列反应。此外,根据Langmuir - Hinshelwood方程,计算出速率常数k 4.3×10^-5mol.L^-1.min^-1和平衡吸附常数K 3.1×10³ L.mol^-1。通过对比λ≥300nm与λ≥360nm紫外光照射不同反应体系哒螨酮的光降解行为,得出λ≥300nm照射条件下反应以直接光解为主,而λ≥360nm光照时光催化反应占据主要地位。着重以λ≥360nm为照射波长进行光催化降解哒螨酮机理研究。借助于GC-MS对光催化哒螨酮产生的降解产物进行定性分析,共检测出15种中间产物。通过降解产物GC峰面积与时间关系,半定量分析了中间产物的变化。此外,进行了光催化降解动力学研究,诸如:溶剂效应、pH、催化剂用量、照射通量,结果表明降解速率受以上参数的影响较大。为将此项技术更好地应用在工业领域,研究了表面活性剂十六烷基三甲基溴化铵（CTAB）悬浮液中哒螨酮的降解行为。采用1HNMR技术确定CTAB胶束微结构的定量信息。结果表明哒螨酮分子主要增溶在CTAB分子的长链区域,此结构为预胶束在TiO₂粒子表面的吸附模型,以及pH值效应提供了合理解释。加入H₂O₂能显著提高光催化降解速率,其值高于单纯的光催化和H₂O₂降解速率之和,称之为协同效应。此外,借助于GC/MS鉴别的中间产物推测出CTAB悬浮液中光催化哒螨酮的降解路线。利用顺磁共振（ESR）技术捕获光催化反应中产生的活性氧自由基。光催化降解哒螨酮反应在纯乙腈悬浮液中进行时,自旋俘获剂DMPO加成的信号为DMPO-O2·-,随着水含量的增加DMPO-·OH信号逐渐增强。但增加到一定程度后信号强度会降低。此结果证实了不同水含量的乙腈悬浮液中,光催化降解反应速率遵循以下次序:乙腈/H2O: （80/20）> （60/40） > （95/5） > （100/0）。此外,通过ESR观察到DMPO-·OH特征信号在哒螨酮/ CTAB/ TiO₂/ H₂O₂体系中明显增强,解释了H₂O₂的协同效应可产生较多的羟基自由基。为了更好地理解光催化降解哒螨酮反应机理进行了量子化学计算。以UHF/PM3优化的哒螨酮分子稳定几何构型为基准,计算出最高占有轨道（HOMO）最大FEDHOMO2值主要分布在哒螨酮分子的S原子处,推断TiO₂光催化氧化过程中该部位易释放出一个电子形成哒螨酮正电荷自由基进而发生C-S键的断裂。键长计算结果表明: C11- S12键比其他键都长,断定此处不稳定,在氧化自由基进攻下较易断裂。原子电荷计算结果表明哒螨酮分子最大强度的负电荷位于O23上,因此在中性（pH6.0）反应介质中,静电作用使哒螨酮通过带有较强负电荷的羰基吸附在TiO₂粒子表面。采用模型反应器进行降解哒螨酮CTAB悬浮液实验,结果表明:该装置运转良好,能够使哒螨酮完全降解。此外,研究了溶液pH值、氧化剂H₂O₂的添加量以及废水处理量等因素对光催化效率的影响,为工业化光催化降解哒螨酮打下基础。更多还原

【Abstract】 Heterogeneous photocatalysis is that irradiation of TiO₂ particles under UV irradiation that carries energy greater than the band gap （3.2 eV） induces conduction band electrons and valance band holes,which can further generate various oxidizing species and degrade pollutants to a great extent. This dissertation studied the reaction mechanism of TiO₂ photocatalytic degradation of pesticide pyridaben in acetonitrile/water suspension. For applying to really polluted waters, photocatalytic degradation pyridaben in surfactant suspension was investigated. Ultimately, small-scale experiments in the model reactor were carried out. The main works and achievements are presented as follows:Underλ≥300nm UV light irradiation, intermediates identification and reaction route proposition were conducted in TiO₂ photodegradation of pyridaben in organic/water suspension. Eight kinds of degradation products （DPs） were identified by GC/MS analysis, which were further confirmed by matching with authentic or synthesized compounds. The proposition of reaction pathway suggested that the initial degradation of pyridaben proceed via C-S bond cleavage between phenyl ring and heterocyclic group, and then promote a serious of reactions such as substitution, oxidation and dealkylation. Besides, on the basis of Langmuir-Hinshelwood equation, kinetic constant k 4.3×10^-5 mol.L^-1.min^-1and equilibrium adsorption constant K 3.1×10³ L.mol^-1 were derived.By comparing photodegradation behavior of pyridaben byλ≥300nm andλ≥360nm UV irradiation in different systems, we concluded that the photodecay of pyridaben byλ≥300 nm irradiation was dominated by a direct photolysis whereas a photocatalytic nature was confirmed byλ≥360nm irradiation. Mechanistic investigation of photocatalytic degradation pyridaben was mainly conducted byλ≥360nm irradiation. A qualitative study of degradation products generated during the photocatalytic process was performed by GC-MS and up to fifteen compounds were detected. The evolution of intermediates was analyzed semiquantitatively by plotting areas of the corresponding GC peaks as functions of irradiation time. Moreover, photocatalytic degradation kinetics were studied such as solvent effect, pH, catalyst concentration as well as radiant flux, which indicated that the degradation rates were strongly influenced by these parameters.For better application to industry, photocatalytic degradation pyridaben in surfactant cetyltrimethyl ammonium bromide（CTAB）suspension was studied.1HNMR was used to determine the quantitative information about the microstructure of CTAB micelles. The result indicated that pyridaben molecule mainly located in long chain groups of CTAB, which presented reasonable explanations for adsorption model of hemi-micelles on TiO₂ surface and the effect of pH values. The photocatalytic degradation rate could be significantly improved in the presence of hydrogen peroxide,which was higher than that of summation photocatalysis with H2O2 effect and was called synergic effect. In addition, a degradation pathway of photocatalysis pyridaben in CTAB suspension was proposed upon identified intermediates by GC/MS.Electron Spin Resonance （ESR）was used to detect active oxygen radicals formed during photocatalytic reaction. Evidence for the DMPO spin-trapping adducts DMPO-O2?- signals were presented in the pure acetonitrile suspension and the production of DMPO-?OH adducts increased as the water content increased gradually in photocatalytic degradation pyridaben. However, continuously increasing H2O content to a certain extent could decrease the signal intensity. It confirmed that the reaction rates of various water content in acetonitrile suspension followed the sequence: acetonitrile /H2O （80/20）> （60/40） > （95/5） > （100/0）. In addition, strong DMPO-?OH signals were detected in pyridaben/CTAB/TiO₂/H₂O₂ system by ESR, which indicated that more hydroxyl radicals were generated in synergic effect of H₂O₂.Quantum chemical calculations were performed for a better understanding of the reaction mechanism of photocatalytic degradation pyridaben. On the basis of the optimal geometry conformation of pyridaben molecule obtained at UHF/PM3 level, the highest FED HOMO2 value of the highest occupied molecular orbital （HOMO） was calculated at S atom where would be the most readily extracted an electron to form pyridaben cation radical, and then occur C-S bond cleavage in TiO₂ photocatalysis. The bond length results indicated that C11-S12 bond was the longest among all others, where possessed less stability and easier to cleave under the attacking of oxidative radicals. The atom charge values manifested that the most negative point charge of pyridaben molecule was located at oxygen atom O23 so that the adsorption involved the negative carbonyl group of pyridaben on TiO₂ surface by static interaction in nature medium （pH6.0）.Experiments of degradation pyridaben in CTAB suspension were carried out in the model reactor, which was in good performance and could degrade pyridaben entirely. Furthermore, impact factors such as pH value, the additive amount of oxidant H₂O₂ and disposal capacity of wastewater were investigated, which provided basis for industrialization of photocatalytic degradation pyridaben.更多还原