量子点敏化磁载TiO2花状微球的制备及可见光催化性能研究

Nanostructural TiO2 has received much attention in the field of environmental photocatalysis due to its low cost, non-toxicity, high stability and unique photochemical property. However, it has no response under visible-light irradiation and possesses low photo quantum yield. Moreover, the recycle of TiO2 is usually difficult. These drawbacks greatly restrict its practical application. This project intends to fabricate the composite of magnetic TiO2 flower-like microsphere sensitized by quantum dots. Thus the photocatalyst can be recycled due to the superparamagnetism of magnetic nuclei, and the quantum yields and utilization of visible-light can be increased effectively because heterostructure interface can be well used to facilitate the separation of photoinduced carriers, by using the advantages of large specific surface area and aspect ratio of the flower-like microsphere unit and the small size of quantum dots. The study will mainly focus on the following questions: exploring the correlation between magnetic property and the Fe/Si molar ratio of the magnetic nuclei protected by isolated layer; studying the formation mechanism of flower-like structure and property of the microstructure on, and revealing the effect of these microstructures on the migration of photoinduced carriers and photocatalytic property of the composites; studying the energy band structure and absorption spectrum of quantum dots with different crystal sizes, the transmission mechanism of photoinduced carriers, and the dynamics process of photocatalytic reaction. The study of this project will provide experimental basis and theoretical guidance for exploring the synthesis of magnetic composite photocatalyst with special morphology and structure.

纳米TiO2由于具有廉价、无毒无害、结构稳定和光化学性能优良等特点而在环境光催化领域备受研究者们青睐。然而，回收困难、光量子产率较低以及无可见光响应这些因素严重限制了其在生活中的实际应用。本项目拟合成量子点敏化的磁载TiO2花状微球，通过磁核的超顺磁性实现对催化剂快速便捷的回收，同时利用花状结构开放型的表面结构和窄带隙量子点小尺寸的特点，充分发挥异质界面对载流子的分离作用并提高复合材料对可见光的利用率。探索受隔离层保护的磁核的磁性与其成分比例之间的关联规律；重点研究磁核外TiO2花状结构的形成机理与微结构特征，并揭示这些微结构对催化剂光生载流子输运特性和光催化活性的影响；研究量子点在不同尺寸下的能带结构和光谱响应特征，并进一步研究所制备复合结构中光生载流子的传输机理、反应物的降解行为及其动力学过程。本项目的研究将为探索制备具有特殊形貌结构的磁载复合光催化材料提供理论依据和奠定实验基础。

TiO2纳米材料具有廉洁、无毒无害、耐酸碱腐蚀且光化学性能优良等特点，在有机污染物降解和重金属离子去除等方面备受研究者青睐。然而，回收困难、光生载流子分离效率低及无可见光响应这些因素严重限制了其在生活中的实际应用。本项目围绕催化剂的磁性回收、TiO2花状结构在磁核外的生长及CdS量子点的修饰，系统研究了CdS量子点敏化磁载TiO2花状微球的制备、微结构特征、形成机理及光催化特性。在磁核的设计与尺寸调控方面，研究发现，通过调控溶剂热体系中水含量、聚乙二醇与铁离子的浓度能实现对Fe3O4超顺磁性粒子在较大范围内的有效调控。Fe3O4的饱和磁化强度随着颗粒的增大而增大，当其颗粒尺寸为260 nm左右时既能保证磁载催化剂的便捷磁性回收，又便于充分发挥壳层催化剂的光催化作用。在此基础上，通过溶胶-凝胶与溶剂热相结合的方法，实现了TiO2花状结构在磁核外的生长。高分辨透射显微镜测试发现，所形成的磁载TiO2花状微球颗粒尺寸约为500 nm，壳层TiO2由片状单元构成，片层的厚度约为3 nm。这种超薄结构大大减小了光生电子-空穴迁移到催化剂表面的距离，有利于光生载流子分离效率的提高。另外，样品的BET比表面积高达328 m2/g，大的比表面不仅有利于量子点在其表面的负载，还为光催化反应提供了大量的反应活性位。为拓宽TiO2的光谱响应范围，我们采用溶胶-凝胶法实现了3-8 nm CdS量子点在磁载TiO2花状微球表面的负载，CdS量子点颗粒尺寸随着反应体系中CdS溶胶浓度的减小而减小。紫外漫反射及光电流测试结果表明，CdS量子点的负载不仅有效拓宽了催化剂的光谱响应范围，还显著促进了光生载流子的有效分离。