【作者】 何剑；

【导师】 蔡启舟；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2010， 博士

【摘要】 由于WO3与TiO2能级之间良好的匹配性,将WO3与TiO2复合不仅可以促进光生载流子的分离,还能拓展其光响应范围,从而提高光催化活性,在环境污染治理领域具有广阔的应用前景。但是,当前研究的WO3/TiO2复合半导体多是粉末形式,回收再利用困难。将WO3/TiO2复合半导体固定为膜层形式能解决回收难题,而现有的WO3/TiO2复合膜层制备技术,如磁控溅射和溶胶-凝胶等,存在着设备复杂、工艺苛刻,或膜层与基体结合力差等不足。因此,制备负载牢固、高催化活性的WO3/TiO2复合膜层成为光催化技术领域的研究重点之一。本文基于开发半导体复合TiO2光催化剂的新型负载化和改性技术,采用微弧氧化工艺,首次在钨酸钠电解液中制备了WO3/TiO2复合膜层,系统地研究了电解液成分和电源参数对膜层结构与光催化性能的影响；考察了污染物溶液pH值、无机阴离子、污染物初始浓度和阳极偏压等对膜层光催化性能的影响；通过改变电解液成分,制备了可见光响应的WO3/TiO2复合膜层,研究了该膜层的结构与可见光催化性能,探讨了其可见光响应机理,取得了如下结果：以工业纯钛为基体,分别在碱性的磷酸钠和钨酸钠电解液中制备了微弧氧化膜,利用XRD、SEM和EDX表征膜层的结构。结果表明,磷酸钠电解液中制备的膜层(TiO2膜)由锐钛矿和金红石混合晶相组成；而钨酸钠电解液中制备的膜层(WO3/TiO2膜)由锐钛矿、金红石和WO3组成,形成了WO3与TiO2的复合膜。两种膜层表面均为粗糙多孔结构,但WO3/TiO2膜的孔洞数量更多,分布更均匀,具有更大的比表面积。荧光光谱分析发现,WO3/TiO2膜的发光强度比TiO2膜的小,光生电子-空穴之间的分离效果更好。与TiO2膜相比,WO3/TiO2膜的表面酸度更高,吸附有机物和羟基的能力更强。紫外光照射120 min, WO3/TiO2膜能降解85%的罗丹明,而TiO2膜只降解23%的罗丹明。研究了TiO2膜和WO3/TiO2膜光催化降解罗丹明的动力学规律。TiO2膜和WO3/TiO2膜对罗丹明的降解过程符合拟一级反应动力学,动力学方程分别为ln(C0/Ct)=0.0023 t+0.029和ln(C0/Ct)=0.016t+0.1,其表观速率常数分别为0.0023和0.016。研究了电解液组成和电源参数对WO3/TiO2膜结构与光催化性能的影响。结果表明,随着Na2WO4浓度的增加,膜层中W含量增加,W03的结晶度提高,膜层表面酸度增加,但过量Na2WO4引起剧烈的微弧放电会破坏膜层的表面结构,降低光催化活性。优化后的电解液组成为14.7 g/L Na2WO4+2 g/L NaF+2 g/L NaOH.当电源参数为正压400 V、负压-30 V、频率700 Hz、占空比0.3、处理时间5 min时,制备的WO3/TiO2膜的光催化活性最高。以甲基橙为模型污染物,研究了溶液pH值、无机阴离子、甲基橙初始浓度对WO3/TiO2膜光催化性能的影响。中性溶液中甲基橙降解率最低,酸性或碱性溶液中其降解率增加。NO3-、PO43-、HCO3-均促进甲基橙的降解,NO3-的促进效果最显著,这是由于NO3-在大于290 nm的紫外光照射下能产生OH·,使甲基橙的降解主要发生在溶液中而不是催化剂表面。SO42-、Cl-则通过竞争吸附和俘获OH-,抑制甲基橙的降解。随着甲基橙初始浓度的增加,其降解率减小。研究了阳极偏压对WO3/TiO2膜降解甲基橙的影响。甲基橙降解率随阳极偏压增加而增大,当阳极偏压为4V时,甲基橙降解率比未加偏压时提高了78.5%。在酸性钨酸钠电解液中制备了非晶态氧化物膜层,并对其进行高温煅烧,获得微弧氧化-煅烧WO3/TiO2膜,研究了该膜层的结构与光催化性能。结果表明,煅烧后的膜层表面出现裂纹,有白色W03小颗粒分布其上；膜层的孔洞增大、增多,膜层的比表面积增大。微弧氧化-煅烧WO3/TiO2膜的光吸收截止波长约为471nm,较锐钛矿有了大幅度红移。可见光照射720 min,该膜层对罗丹明的降解率达55%。在实验和理论分析的基础上,探索性地提出了微弧氧化-煅烧WO3/TiO2膜的可见光响应机理。更多还原

【Abstract】 Coupling TiO2 with WO3 could not only promote the separation of photo-generated carriers, but also extend the photoresponse range of TiO2, resulting in the improvement of photocatalytic activity, due to that the energy levels of TiO2 and WO3 are a great match for each other. Thus, WO3/TiO2 composite semiconductors have a great potential in environmental treatment. However, most of current studies on WO3/TiO2 composite photocatalyst focus on the use of crystalline powder, which is easy to agglomerate and yet difficult to recycle. To promote practical application of WO3/TiO2 photocatalysis, it must be immobilized in film. Present preparation techniques of WO3/TiO2 composite film, such as magnetron sputtering and sol-gel, still face some difficulties, for instance, complicated equipment, hard process or poor adhesion between the film and the substrate, and so forth. Therefore, preparation of WO3/TiO2 composite film with good adhesion and high catalytic activity becomes one of the most important focuses in photocatalysis field.In this paper, Micro-arc Oxidation (MAO) technique was firstly chosen to prepare WO3/TiO2 composite film in alkaline sodium tungstate electrolyte in order to develop new immobilization and modification technique of TiO2 photocatalyst. The effects of electrolyte composition and power parameters on the microstructure and photocatalytic property of WO3/TiO2 composite film were investigated systematically. The effects of external factors, including pH of pollutant solution, inorganic anions, initial pollutant concentration and anodic bias, on the photocatalytic property of WO3/TiO2 composite film were studied. Visible-light-responsive WO3/TiO2 composite film was gained by changing electrolyte composition. The microstructure and visible-light catalytic property were studied and the visible-light-responsive mechanism is discussed. The overall results were as follows.MAO films were prepared on titanium in phosphate and tungstate electrolytes, respectively. The microstructure of two films was characterized by XRD, SEM and EDX. The film formed in phosphate electrolyte (TiO2 film) consisted of a mixture phase of anatase and rutile; while the film formed in tungstate electrolyte (WO3/TiO2 film) consisted of anatase, rutile and WO3. Both of these two films had a kind of rough and porous surface. But, more pores with larger specific surface area distributed uniformly on the surface of WO3/TiO2 film. According to spectrofluorimetry, the photo luminescene intensity of WO3/TiO2 film was lower than that of TiO2 film, implying that its separation between photo-generated electrons and holes was more effective. Compared with TiO2 film, WO3/TiO2 film had higher surface acidity, demonstrating stronger capacity of absorbing organic substance and hydroxyl group. More than 85% of rhodanmine was degraded by the WO3/TiO2 film while only 23% of rhodamine by the TiO2 film in UV light for 120 min.The degradation kinetics of rhodamine by TiO2 film and WO3/TiO2 film were studied, which were coherent with pseudo first order reaction. The kinetic equations caused by TiO2 film and WO3/TiO2 film were In (C0/Ct)=0.0023 t+0.029 and In (C0/Ct)=0.0161+ 0.1 and the corresponding apparent rate constant were 0.0023 and 0.016, respectively.The effects of electrolyte composition and power parameters on the microstructure and photocatalytic property of WO3/TiO2 film were investigated systematically. The content of tungsten, the crystallinity of WO3 and the surface acidity increased with the increase of tungstate concentration, but violent microarc discharge caused by excess Na2WO4 could destroy the surface structure of the film. The optimized electrolyte consisted of 14.7 g/L Na2WO4,2 g/L NaOH,2 g/L NaF. When the positive voltage, negative voltage, frequency, duty cycle and processing time were 400 V,-30 V,700 Hz,0.3 and 5 min, respectively, the prepared WO3/TiO2 film had best photocatalytic activity.Methyl orange was chosen as model pollutant, the effect of solution pH, inorganic anions, initial concentration and anodic bias on the photocatalytic property of WO3/TiO2 film was systematically studied. The degradation efficiency of methyl orange was the lowest in neutral solution, while that would be increased either in acidic or alkaline solution. Methyl orange was degraded faster with addition of NO3-, PO43- and HCO3-, and the best facilitation was caused by NO3- for OH·could be produced when NO3-was irradiated in the UV (λ＞290 nm). Thus, methyl orange was mainly degraded in solution rather than at the surface of WO3/TiO2 film. SO42- and Cl- inhibited the degradation of methyl orange through competitive adsorbing and capturing OH-. The degradation efficiency of methyl orange decreased as its concentration decreased.The influence of anodic bias on the photocatalytic activity of WO3/TiO2 film was investigated. The degradation efficiency of methyl orange increased with the increase of anodic bias. When the applied anodic bias is 4 V, the degradation efficiency of methyl orange exceeded that without bias by 78.5% approximately.Amorphous oxide film was prepared in the acidic sodium tungstate electrolyte by MAO technique, and sequentially subjected to high temperature calcination to get crystal WO3/TiO2 film. The microstructure and photocatalytic property of WO3/TiO2 film were investigated. The results showed that both cracks and white small particles of WO3 appeared at the surface of film after calcination. The total number and average size of pores in the inner of film increased. All of these increased the specific surface area of the film. The absorption edge of MAO-calcined WO3/TiO2 film was about 471 nm. Compared with anntase, a significant red-shift was obtained.55% Rhodamine can be effectively degraded by WO3/TiO2 film under visible light irradiation for 720 min. The visible-light-responsive mechanism of MAO-calcined WO3/TiO2 film was tentatively put forward on the basis of experiment and theoretical analysis.更多还原