【作者】 田丽红；

【导师】 昝菱；

【作者基本信息】 武汉大学 ， 无机化学， 2012， 博士

【摘要】 近年来，随着科技的飞速发展，环境污染问题日益突出，已严重的威胁着人类的健康和生活，因此保护环境、控制污染以实现可持续发展是目前人们的共同责任和目标。半导体光催化是在应对环境污染的过程中发展起来的一种新型技术。它利用半导体能带结构的不连续性，借助光能将溶液或空气中的污染物催化氧化降解为无毒的无机小分子，从而达到环境修复和太阳能利用的目的。本论文针对一些金属氧化物半导体催化剂量子产率较低的问题，从抑制金属氧化物半导体在光催化过程中产生的电子和空穴复合的角度出发，利用碳材料比表面积大、导电性能优良等优点，将无机金属氧化物半导体与碳纳米材料如碳纳米管、石墨烯等复合以提高金属氧化物半导体的光催化活性，并对碳基/金属氧化物杂化材料的光催化机理进行了详细的研究。论文主要内容如下：（1）采用溶剂热和苯甲醇辅助溶胶-凝胶法合成了MWCNT/TiO₂杂化材料，用X-射线粉末衍射、透射电镜、紫外-可见漫反射吸收光谱和X-射线光电子能谱对材料进行表征，结果表明溶剂热法合成的MWCNT/TiO₂杂化材料中，锐钛矿TiO₂纳米晶均匀地分布在多壁碳纳米管上，而采用溶胶-凝胶法得到的MWCNT/TiO₂材料，碳纳米管被包埋在TiO₂颗粒中。其可见光催化降解亚甲基蓝的实验结果则显示，当MWCNTs与TiO₂的质量比为20%左右时，溶剂热法合成MWCNT/TiO₂杂化材料的光催化活性明显高于溶胶-凝胶法得到的材料。对于MWCNT/TiO₂杂化材料而言，400℃热处理导致了MWCNT/TiO₂之间Ti-C键的形成，由此提高了杂化材料对可见光的吸收和光催化活性的提高。（2）以乙醇和WCl6为原料合成了CNTs-WO₃杂化材料，可见光下此材料显示了很高的光催化活性。TEM和XRD结果显示单斜晶系的WO₃纳米片整齐排列在CNTs的表面，X-射线光电子能谱结果表明WO₃和CNTs之间存在着强烈的相互作用。在CNTs-WO₃杂化材料的形成过程中，CNTs的含量控制WO₃在CNTs表面的分布起着重要的作用，当CNTs的含量逐渐增大时，WO₃纳米片变得越来越小，在CNTs表面均匀的分布着，但CNTs的含量超过15%时，由于大量CNTs在溶液中相互缠绕，导致了WO₃颗粒的团聚。荧光光谱分析法的结果表明CNTs-WO₃加强的光催化活性主要归因于其电子和空穴对能够得到有效的分离，另外，通过自由基捕获实验我们发现·OH自由基是CNTs-WO₃光催化过程中的主要活性基团。（3）采用水热法使WO₃纳米带原位生长在氧化石墨烯的表面，制备了还原石墨烯（RGO）-WO₃杂化材料。SEM和HRTEM观察杂化材料的形貌发现，氧化石墨烯对WO₃有很好的分散作用，但限制了单斜晶系WO₃沿着（002）晶面方向的成长，导致杂化材料中WO₃纳米带变短。RGO-WO₃杂化材料的可见光催化降解染料亚甲基蓝的实验结果表明，RGO-WO₃的光催化活性高于纯的WO₃纳米带，当氧化石墨烯的含量为1.0%时，亚甲基蓝在石墨烯-WO₃表面降解的动力学速率常数是纯WO₃的两倍，这主要归因于RGO与WO₃的协同作用使得电子和空穴有效地分离，因为石墨烯的功函数小于WO₃，所以WO₃被光照激发后，跃迁到WO₃导带的电子会迁移到石墨烯表面，然后与催化剂表面吸附的O₂分子作用生成了H2O₂，H2O₂被继续还原得到·OH自由基，是光催化反应中的主要活性基团。（4）采用苯甲醇作溶剂，溶剂热法合成了RGO-BiOCl杂化材料，此过程中BiOCl的形成经历了缩合脱苄醚和苄基氯的过程得到[Bi₂O₂]n结构单元，即BiOCl的（001）面，因而导致了大的BiOCl微米片，紫外-可见漫反射结果表明其禁带宽度在3.25eV。而在合成中加入氧化石墨烯的DMF溶液后，因为GO与[Bi₂O₂]单元的相互作用，导致BiOCl（001）及（110）晶面的选择性生长，因而得到小的BiOCl纳米片,且RGO-BiOCl杂化材料的禁带相对BiOCl变得更窄，在可见光下显示了高于参考BiOCl的光催化活性，而且随着RGO含量的增加，活性增大，RGO-BiOCl-0.8可见光降解RhB的表观速率常数约为BiOCl微米片和参考BiOCl的3倍左右，RGO-BiOCl的禁带变窄，RGO抑制电子和空穴的传递是导致杂化材料光催化活性增强的根本原因。（5）采用溶剂热法合成表面乙氧基改性的TiO₂纳米晶（S-Et），并对其进行了XRD、TEM、TG-DTA和XPS表征，发现TiO₂纳米晶呈单分散状态，粒径在5-15nm之间，乙氧基改性的TiO₂表现出比“naked”TiO₂更强的可见光光催化活性。zeta电势结果表明S-Et表面带有很高的负电荷，导致染料分子RhB的正电基团-N（Et）2选择吸附在乙氧基改性的TiO₂表面，使RhB经历了优先脱-N（Et）2的降解路线。更多还原

【Abstract】 In recent years, as the increasing of industry and agricultural, environmentalpollution especially water contamination is paid more attention. Somenon-biodegradable substrates such as dyes and dye intermediates are harmful to notoly human but also animals and plants. Photocatalytic decomposition of organicpollutants with metal oxide semiconductor is fascinating due to involving theconversion of solar energy. However, some inorganic semiconductors have lowquantum efficiency. For example TiO₂, it has wide binding energy and only absorbsultraviolet light. WO₃has high conductive energy and electrons on conduct band cannot react with O₂, so there are a few reports on the degradation of organic pollutantson WO₃catalysts. In this paper, we take note of the excellent properties of carbonmaterials such as carbon nanotubes and graphene and synthesize the carbonmaterials/semiconductors hybrids to enhance the photocataytic activity ofsemiconductors. The main investigations are as follows:（1） MWCNT/TiO₂hybrid nanostructures were prepared via solvothermal synthesisand sol–gel method with benzyl alcohol as a surfactant. As-prepared hybrid materialswere characterized by X-ray diffraction, transmission electron microscopy, UV–visdiffuse reflectance spectra and X-ray photoelec-tron spectroscopy.The resultsshowed that MWCNTs were uniformly decorated with anatase nanocrystals insolvothermal condition, but MWCNTs were embedded in a majority of TiO₂nanoparticles by sol–gel method.When the weight ratio of MWCNTs to TiO₂was20%, MWCNT/TiO₂hybrid nanostructures prepared by solvothermal synthesisexhibited higher visible-light-driven photocatalytic activity than that prepared bysol–gel method. Post-annealing of MWCNT/TiO₂nanostructures at400℃resulted inthe formation of the carbonaceous Ti–C bonds on the interface between TiO₂andMWCNTs, which enhanced the photoabsorbance of the hybrid materials in the visiblelight region and improved the visible-light degradation efficiency of methylene blue.（2） The CNTs-WO₃hybrid nanostructures were fabricated by a facile solvothermalsynthesis and found to existing high photocatalytic activity for degradation of methylblue under visible light irradiation. The materials were investigated by TEM, XRD,UV-vis and XPS respectively. The results demonstrated that monoclinic WO₃nanosheets aligned on CNTs and a strong interaction existed between CNTs and WO₃.It is interesting that the content of CNTs played the important role on controlling the dispersion of WO₃on CNTs surface. When the content of CNTs was15%, small andthin WO₃nanosheets laid on CNTs uniformly. PL results of CNTs-WO₃indicated thatthe enhanced photocatalytic activity was attributed to the effective separation ofelectrons and holes on hybrid materials under visible light irradiation. In addition, thepresence of radical scavengers such as KI、Fe3+and methanol demonstrated thathydroxyl radicals were responsible for the photocatalytic degradation of organic dyeon CNTs-WO₃, which were mainly originated from the photoreduction of oxygen.（3） A series of reduced graphene oxide-WO₃nanobelt hybrids were fabricated via insitu hydrothermal method. The morphology and structure of hybrids werecharacterized by scanning electron micrograph and high-resolution transmissionelectron micrograph. It is found that graphene oxide restrains the growth oforthorhombic WO₃along （002） orientation and results in the shorter WO₃nanobeltscompared with pure WO₃. WO₃nanobelts well-decorate on graphene oxide surface.RGO-WO₃nanobelt hybrids show an enhanced visible light photocatalytic activity ondegradation of methylene blue. The optimum hybrid is that one with1.0wt%graphene oxide and its pseudo-first-order rate constant （k） is up to2-foldimprovement compared to the pure WO₃nanobelts. The enhancement ofphotocatalytic activity is ascribed to the synergistic effects between WO₃and reducedgraphene oxide, which efficiently separate the photogenerated electrons and holes.Accordingly, the photocatalytic mechanism of RGO-WO₃nanobelt hybrids is alsoproposed and confirmed by transient photocurrent response.（4） Reduced graphene oxide-BiOCl hydrid materials were fabricated bysolvothermal method with benzyl alcohol as solvent. Condensation steps led to theformation of [Bi₂O₂]nbonds in nonaqueous solvothermal processes such as alkylhalide elimination and ester elimination. Therefore,（001） planes dominated BiOClmicrosheets were obtained. UV-vis diffuse reflection results showed the band gap ofBiOCl microsheets was about3.25eV. However, for RGO-BiOCl hybrid materials, theaddition of GO resulted in the formation of BiOCl nanoplates on the edge of reducedgraphene oxide, which was ascribed to selective growth of （001） and （110） planefamily of BiOCl. RGO-BiOCl hybrid materials showed enhanced photocatalyticactivity under visible light irradiation compared with BiOCl-ref. The band gap ofRGO-BiOCl narrowed and RGO prohibited the combination of electrons and holes,which ehanced the photocatalytic activity of RGO-BiOCl.（5） TiO₂nanocrystals modified by ethoxy groups were prepared by a facilenonhydrolytic solvothermal method and characterized by XRD, TEM, TG-DTA and XPS, which showed an enhanced visible-light photocatalytic activity on thedegradation of Rhodamine B compared with TiO₂modified by benzyloxy groups andthe“naked”TiO₂. The adsorption and degradation pathway of Rhodamine B on TiO₂modified by ethoxy groups were also investigated. The zeta-potential （ζ） resultsshowed that the TiO₂modified by ethoxy groups had high negative surface charge,which incited the positive-N（Et）2group of RhB absorbing on the TiO₂surface andpreferably led the N-dealkylation pathway under visible light irradiation.更多还原