【作者】 马健；

【导师】 谭欣；

【作者基本信息】 天津大学 ， 环境科学， 2018， 博士

【摘要】 光催化技术是太阳能开发和利用的一种重要方法。半导体光催化剂是该技术的核心部分,其质量直接决定着反应效率。本研究选取TiO₂光催化剂为研究对象,通过半导体复合的方法将窄带隙有机半导体石墨相氮化碳g-C₃N₄与其结合以提高TiO₂的光催化效率,并在此基础上结合形貌、晶面以及能带调控等方法进一步提高光能利用率和量子效率。研究方法如下:以三聚氰胺为前驱体,采用热解法制备了g-C₃N₄。并将不同质量的g-C₃N₄与高活性{001}晶面暴露的TiO₂结合制备出一系列g-C₃N₄/{001}TiO₂复合材料。该复合材料的微观形貌为{001}TiO₂纳米片组装而成的多级球,g-C₃N₄沉积于多级球的表面。通过与g-C₃N₄的复合,增强了TiO₂的光吸收能力,扩展了其光响应范围。通过可见光下对染料Rh B的降解来评价该系列复合材料的光催化性能。Mott-Schottky关系曲线测试表明复合材料的载流子浓度均高于单纯的g-C₃N₄与TiO₂。稳态荧光光谱、电化学阻抗谱、瞬态光电流测试表明所合成的复合材料具有较高的光生电子-空穴分离能力。为了提高g-C₃N₄的层间电子传输性能合成了一系列K原子插层的g-C₃N₄材料:K-g-C₃N₄,并将其与TiO₂纳米带复合,制备了K-g-C₃N₄/TiO₂纳米带复合材料。通过DFT理论计算确定K离子在g-C₃N₄中的掺杂位置。通过XRD、XPS、SEM与TEM分析所合成样品的结构、微观形貌以及K-g-C₃N₄与TiO₂纳米带之间的相界面。K-g-C₃N₄的引入增强了TiO₂纳米带的可见光吸收以及光生载流子的传输与分离能力。通过可见光下的光解水制氢实验来研究所合成材料的光催化还原性能。板钛矿TiO₂具有较高的导带电势和还原能力,为了提高其光能利用率和可见光下的光催化产氢效率,将二维g-C₃N₄纳米片与板钛矿TiO₂结合,采用水热法制备了一系列g-C₃N₄纳米片/板钛矿TiO₂复合材料。通过XRD、XPS、DRS、SEM与TEM分析所合成样品的结构、光响应范围和形貌。通过可见光下的光解水制氢实验来分析和评价该系列复合材料的光催化性能。通过稳态荧光光谱测试与光电化学性能测试证明g-C₃N₄纳米片与TiO₂之间的有效结合以及光生电子-空穴的分离过程。制备了表面羟基化的g-C₃N₄与含有氧缺陷TiO₂的复合材料:CN-OH/Vo-TiO₂。通过FT-IR及原位ESR测试证明了g-C₃N₄表面羟基化的实现。通过ESR测试证明TiO₂中氧空位的存在。通过XRD,XPS和TEM测试研究CN-OH与Vo-TiO₂之间的有效复合。通过可见光下对苯酚水溶液的氧化反应来评价该系列复合材料的光催化性能,以及活性基团的俘获实验探索苯酚氧化反应过程的机理。更多还原

【Abstract】 Photocatalytic provides a potential strategy to utilize solar energy.Semiconductor photocatalyst is one of the most important parts of the reaction system,and its quality is closely related to the reaction activity.In this research,an organic narrow band gap semiconductor g-C₃N₄ was hybridized with TiO₂ to improve its photocatalytic efficiency.Furthermore,morphology,crystal and band gap adjustion of g-C₃N₄/TiO₂ composite materials were adopted to further enhance the utilization of solar energy and quantum efficiency.The research methods are as follows:Graphitic carbon nitride was synthesized by pyrolysis method using melamine as precursor.A series of g-C₃N₄/{001}TiO₂ composite materials were fabricated by changing the dosage of g-C₃N₄.The morphology of the composite materials was hierarchical spheres with g-C₃N₄ deposited on the surface.The light absorption ability of TiO₂ was effectively enhanced by the combination with g-C₃N₄.Photocatalytic performances of the as-synthesized samples were tested for the photodegradation of Rh B solution under visible light irradiation.Mott-Schottky plotes test indicated that the composite materials have much higher free charge carrier density.The charge separation efficiency of the composite samples was confirmed by steady fluorescence spectroscopy,electrochemical impedance spectroscopy and transient photocurrent density measurements.A series of K intercalated g-C₃N₄ with different dosage of K atoms were fabricated to enhance the charge transform efficiency between the CN layers in g-C₃N₄.TiO₂ nanobelts were combined with the as synthesized K-g-C₃N₄ and formed K-g-C₃N₄/TiO₂ nanobelts composite materials.DFT calculation was carried out to determine the doping sites of K atoms in g-C₃N₄.XRD,XPS,SEM and TEM were used to analyze the structure,morphology and the interface between K-g-C₃N₄ and TiO₂ nanobelts.The light absorption and charge separation ability of TiO₂ was effectively enhanced by the combination with K-g-C₃N₄.Brookite TiO₂ are possessed of higher CB potential and reducibility.In this section,g-C₃N₄ nanosheet was combined with brookite TiO₂ via a hydrothermal method to further enhance its light use efficiency and photocatalytic H₂ production activity under visible light irradiation.XRD,XPS,DRS,SEM,and TEM were used to analyze the structure,light absorption ability and morphology of samples.The photocatalytic efficiency of as synthesized samples was studied by H₂ evolution from water splitting under visible light irradiation.The interfacial connections between brookite TiO₂ and g-C₃N₄ nanosheet as well as the charge separation efficiency of the composite samples were confirmed by steady fluorescence spectroscopy and photoelectrochemical tests.A series of g-C₃N₄-OH/Vo-TiO₂ composite materials have been successfully synthesized.The hydroxylation of g-C₃N₄ was confirmed by FT-IR and in-situ ESR tests.The existence of oxygen vacancies in Vo-TiO₂ was confirmed by ESR test.XRD,XPS and TEM were used to analyze the interface between g-C₃N₄-OH and Vo-TiO₂.Photocatalytic performances of the as-synthesized samples were tested for the photooxidation of phenol solution under visible light irradiation.Trapping experiments were carried out to detect the photocatalytic mechanisms.更多还原