纳米Ag/ZnO异质结的合成及其紫外-可见光双波段光催化性质研究

Photocatalysis is the green technology for the degradation of organic pollution in wastewater. At present, the mainly problems of photocatalysis are the low absorption of visible light and the easily recombination of photogenerated electron-hole pairs which may decrease the photocatalytic activity. In order to solve these two problems, we try to synthesis the nanosized Ag/ZnO heterostructure with different content Ag by sol-gel method on the basis of nanosized ZnO. The morphology, structure and optical properties of the samples will be studied by the techniques such as the modern high resolution electron microscopy, molecular spectroscopy, and so on. The microstructure and relationship between Ag particles and nanosized ZnO at the interface of the heterostructure will also be studied. In order to restrain the aggregation and improve the repeatable utilization of the nanosized Ag/ZnO heterostructure, the impact of reactant temperature, stirring speed and reaction time will be studied. Moreover, except the acknowledged UV-light-driven photocatalytic activity, the photocatalytic performance of nanosized Ag/ZnO heterostructure under visible light will be detected by using methyl orange as the replaced effluent. Also, the relationship between the content Ag, energy band gap, intensity of light response and photocatalytic activity of nanosized Ag/ZnO heterostructure will be studied. At last, the photocatalytic mechanism of nanosized Ag/ZnO both irradiated under UV and visible light will be explored in order to supply the experimental basis and theoretical foundation for the photocatalysis of nanosized heterostructure.

光催化是一种能够将废水中有机污染物完全降解的绿色技术。目前光催化剂存在对可见光利用率低和光生电子—空穴对容易复合从而降低光催化效率的两大问题。本项目围绕以上关键科学问题，在合成纳米ZnO的基础上，拟采用溶胶—凝胶法设计合成系列不同Ag含量的纳米Ag/ZnO异质结材料。借助现代高分辨电子显微学、分子光谱学等相结合的测试技术探讨材料的形貌、结构和光学性质；研究异质结界面微观结构以及Ag粒子与纳米ZnO的结合方式。探讨反应温度、搅拌速率、生长时间等因素对样品团聚现象的影响，提高可重复利用率。以甲基橙为替代废液，在测试纳米Ag/ZnO异质结传统的紫外光催化性质的同时，研究其可见光条件下的光催化能力；探索Ag的含量与纳米Ag/ZnO异质结禁带宽度、光响应强度和光催化能力的内在联系；推测其在紫外—可见双波段的光催化机理，为纳米异质结光催化处理废水中的有机污染物提供一定的实验基础和理论依据。

为了解决目前光催化剂对可见光利用率低和光生电子—空穴对容易复合而降低光催化效率的问题，本项目通过溶胶-凝胶法在低温开放体系下合成了不同载银量的纳米Ag/ZnO异质结，采用X-射线衍射仪、扫描电镜、透射电镜、紫外-可见分光光度计等对样品的结构、形貌和光学性质进行研究。以甲基橙为替代废液，对比测试Ag含量不同的纳米Ag/ZnO异质结的光催化能力。结果表明，Ag/ZnO异质结样品不但存在纤锌矿结构ZnO相，还出现了单质Ag的特征衍射峰，即Ag粒子并没有进入ZnO晶格，而是复合到ZnO表面上形成异质结。而扫描电镜照片显示不同形状的纳米ZnO和Ag粒子共存。透射电镜显示Ag粒子沿ZnO界面生长形成异质结构。样品的紫外可见吸收光谱显示纯ZnO和载银量不同的纳米Ag/ZnO异质结样品禁带宽度一致，且Ag/ZnO样品中出现了两个吸收带，其中可见光波段的吸收带是由于胞质因子Ag而引起的。以甲基橙为替代废液、市售光催化剂P25为参照物、对不同Ag含量的纳米Ag/ZnO异质结进行光催化能力测试，结果发现纳米Ag/ZnO异质结在紫外光和可见光条件下都具有优良的光催化性质，并且载银量为5%的样品具有最佳的光催化能力。本项目的研究成果可为纳米异质结光催化处理废水中的有机污染物提供一定的实验基础和理论依据。