【作者】 吕晓萌；

【导师】 谢吉民；

【作者基本信息】 江苏大学 ， 环境工程， 2007， 博士

【摘要】 近年来,随着环境污染的加重,环境污染的治理尤其是环境中有机污染物的治理成为当今世界关注的热点问题。作为新兴的技术—光催化在治理有机污染物方面的应用日益受到人们的重视。人们希望找到电荷分离效率高,光响应范围较宽,能充分吸收利用太阳光且光催化效率较高的光催化剂。本文从影响能带结构和电子-空穴复合率的关键因素入手,利用各种控制方法和新的合成路线制备出一系列新型复合材料,对其形成机理及影响因素、微结构特征、光吸收性质、光催化特性等进行了系统研究,取得了一些有重要意义的结果。1)以d区元素氧化物TiO₂为考察对象,通过溶胶-凝胶和水热合成制备了掺杂氮原子以及x（M）=0.005(M=Fe³⁺,Cu²⁺,V⁵⁺,Pd²⁺)TiO₂复合体系;研究了掺杂不同离子对TiO₂纳米粉体的结构、吸光性能以及晶粒粒度等性质的影响;探讨了单一掺杂和复合掺杂对TiO₂纳米粉体的光催化性能及其光解机制的影响。测试了样品对室内污染物之一的甲醛气体降解的光催化活性,得到不同样品在可见光下的光降解活性依次为:Cu-TiO₂/N＞Fe-TiO₂/N＞V-TiO₂/N＞Pd-TiO₂/N＞TiO₂/N。Cu-TiO₂/N样品较高的荧光强度和较大的比表面积,导致了其较高的可见光光解活性。以p区元素氧化物Bi₂O₃为考察对象,通过化学沉淀法,以十二烷基苯磺酸钠为修饰剂,制备了掺杂不同金属离子(V⁵⁺,Pb²⁺,Ag⁺,Co²⁺)的Bi₂O₃粉体。探讨了不同金属离子的掺杂对Bi₂O₃粉体的表面形貌和吸光性能的影响;以玫瑰红的光催化氧化为探针反应,考察了不同金属离子的掺杂对样品的光催化活性的影响,样品活性次序依次为:Bi₂O₃(V⁵⁺)＞Bi₂O₃(Pb²⁺)＞Bi₂O₃（Ag⁺）＞Bi₂O₃(Co²⁺)。光催化活性的差别可归因于掺杂离子的半径,样品的表面形貌及吸光性能等因素。上述的实验结果表明,半导体氧化物经适量杂化改性后可得到吸收光谱明显红移的新化合物,从而发展成为一种新型的光催化体系。一方面制备了可见光响应的光催化剂;另一方面光催化降解了模拟的室内空气有机污染物和低浓度偶氮染料废水,为治理环境中有机污染物提供理论基础和活性依据。2)基于多酸与TiO₂结构的相似性以及多酸组成与其吸收光谱的可调变性,通过自组装合成方法分别制备了SiW₁₀Fe₂的季胺盐、钴钨酸(Co^ⅡW₁₂)/SiO₂复合催化剂,并与H₂O₂组成类Fenton体系。以偶氮染料（甲基橙、橙黄Ⅱ）为模型反应物,探讨染料降解的起始浓度、过氧化氢浓度、pH不同等因素对光脱色速率的影响。结果表明,上述复合体系皆得到了比Fenton体系较宽的pH值应用范围,同时通过对多酸组成的改变（调换杂原子和配原子）,有效地调节了多酸的光谱性质,得到了具有可见光响应的光催化材料。3)多元复合金属氧化物因其晶体结构和电子结构的多样性,有可能同时具备响应可见光激发的能带结构和高的光生载流子移动性,是一种潜在的高效光催化材料。文中探讨了钙钛矿型化合物BiFeO₃的光催化性能,考察了形貌与吸光性能的关系,以及形貌对其光解活性的影响。结果表明,H₂O₂存在的条件下,不同形貌的BiFeO₃片状催化剂显示出了光降解橙黄Ⅱ的活性,并且其活性与表面形貌相关。通过微波合成这种环境友好的合成路线,以水为反应介质,纳米级碳黑为模板,尿素为沉淀剂,利用聚乙烯醇大分子链的空间位阻效应和高分子网络的隔阻作用,均相沉淀法合成出YFeO₃前驱体。纯相YFeO₃的吸收阈值为580 nm,紫外和可见光辐照下YFeO₃光解橙黄Ⅱ的活性表明,YFeO₃在可见光辐照下得到了优于TiO₂的光催化降解活性。考虑到YFeO₃的半导体性质,通过物理混合制备了p-YFeO₃/n-TiO₂复合材料,以橙黄Ⅱ的光催化降解来评价该纳米复合材料的光催化活性。实验结果表明,复合体系的光催化活性与组分含量和焙烧温度相关,实验中得到的理想的复合材料是为600℃焙烧下,ω（TiO₂）=0.90的YFeO₃-TiO₂。由于在二氧化钛基体中掺入YFeO₃纳米粒子,既可以促进光生载流子的电荷分离,又可以使二氧化钛的光响应波长向可见光区域拓展,提高了太阳能利用率。光催化活性的提高可归因于p-YFeO₃与n-TiO₂间存在的p-n结,同时对p-n结的电子和空穴迁移过程的研究亦有利于探索新型、高效可见光光催化剂。更多还原

【Abstract】 With the grave pollution of environment,the treatment of mankind living environment especially the treatment of organic pollution has become hot topic.As one of the novel technology,photocatalysis gains more and more attention in the field of environmental treatment field.It is important to develop new photocatalysts to extend the absorbed wavelength range into the visible region,where less expensive light sources exist.In recent years,many research groups devoted to the exploration of more effective photocatalysts by increasing the efficency of charge separation and extending the photo-harvesting range.In the present dissertation,we prepared several novel photocatalysts by new synthesis method.Their physical property and chemical property have been systemic investigated as well as their photocatalytic activity and photocatalytic mechanism.Some significant results are as follows:1) Take d zone oxide-TiO₂ as an example,titania particles doped with nitrogen and Fe³⁺,Cu²⁺,V⁵⁺,Pd²⁺（x（M）=0.005） as dopants were synthesized by sol-gel and hydrothermal method.Influence of dopants to the structure,light absorption,crystal size of TiO₂ has been discussed.Also, influence of single dopant and composite dopants to photocatalytic property and photocatalytic mechanism has been studied.The result indicated that dopant had not only widened the light absorption but improved the photocatalytic efficiency.The photocatalytic activity was investigated and formaldehyde was taken as test gas.The photodegradation rate is in the following order:Cu-TiO₂/N＞Fe-TiO₂/N＞V-TiO₂/N＞Pd-TiO₂/N＞TiO₂/N.Good dispersion of Cu²⁺ dopant onto the surface of titania,adequate surface area and decrease of recombination center on the surface of Cu-TiO₂/N photocatalyst may contribute to its comparatively higher photocatalytic activity.Take p zone oxide-Bi₂O₃ as example,Bi₂O₃ samples doped with transition metal ions,M-Bi₂O₃（M=V^Ⅴ,Pb^Ⅱ,Ag^Ⅰand Co^Ⅱ） were synthesized by wet chemical precipitation method in the presence of sodium dodecyl benzene sulphonate（SDBS）.The obtained monoclinic microcrystal samples not only have different morphology but also visible light harvesting.The photo-catalytic activity of M-Bi₂O₃ was evaluated by decolorization of Rhodamine B under visible light illumination.The photodecolorization efficiency varied with the type of the transition metal ions and followed the order:Bi₂O₃(V⁵⁺)＞Bi₂O₃(Pb²⁺)＞Bi₂O₃（Ag⁺）＞Bi₂O₃(Co²⁺)＞Bi₂O₃.The ionic radii,surface morphology and photo absorption property may attribute to the difference of photodegradation activity.The above results indicated that semiconductor could develop into another novel photocatalyst afer being appropriately doped.On the one hand,visible-light-driven photocatalysts have been synthesized and on the other hand,photodegradation of room pollution gas and low concentration ozodye have been achieved,which have provided demonstrating study for the treatment of environmental pollution.2) Since the structure of polyoxometallate is similar with TiO₂ and its changeable absorption spectra,tetrabutylammonium salt of SiW₁₀Fe₂ and Co^ⅡW₁₂/SiO₂ composite catalyst were synthesized and oze dye（methyl orange and orangeⅡ） were taken as test pollutant.The result indicated that the above composites got wider pH application range and via the change of polyoxometallate composite,the spectra property of polyoxometallate has changed and visible-light driven photocatalyst has been obtained.3) Composite oxides may possess visible-light excited band structure and high mobility of carrier,which had been widely studied as effectively potential photocatalyst.Photocatalytic performance of BiFeO₃ has been studied.The morphology,photo absorption and its influence to the photocatalytic activity have also been discussed.The result indicated that BiFeO₃ nanoplates have a potential application for photodegradation of orangeⅡunder the condition of H₂O₂.A novel microwave-assisted progress for the preparation of nanocrystalline pure YFeO₃ phase has been developed.Synthesis of perovskite YFeO₃ has been achieved with carbon to enhance microwave absorption,polyvinyl alcohol as inhibitor and urea as homogeneous precipitator.Photocatalytic activity for the degradation of orangeⅡin water under visible light irradiation shows that perovskite YFeO₃ is superior to TiO₂（P-25）.Oxygen vacancies of the perovskite sample may explain its high activity.Effects of microwave irradiation time and calcination temperature on the phase structure of the product were also studied.Considersing the band structure of YFeO₃,YFeO₃-TiO₂ composite photocatalysts with p-n heterojunction have been prepared by physical amalgamation.Effects of calcination temperature and constitute content on structure and surface characterizations have also been investigated.Results show that the presence of p-n junction not only has visible light harvesting but potential force for hole-electron pair separation.A preliminary investigation of photocatalytic activity on orangeⅡshowed that YFeO₃-TiO₂ heterojunctions can be activated under visible light irradiation. The optimum junction is sample ofω（TiO₂）=0.90 after calcining at 600℃.The improved photocatalytic activity,comparing with that of pure TiO₂ and pure YFeO₃,might attribute to the p-n heterojunction composed of p-type YFeO₃ and n-type TiO₂.Study of the process of electron and hole migratation will facilitate the exploitation of novel,highly efficient, visible-light-driven photocatalyst.更多还原