中空Ta_2O_5/TiO_2复合光催化剂的可控氧化制备及性能

以钛粉、钽粉为原料,炭黑作为反应性模板,通过熔盐法在炭黑表面原位生长了TaTiC_2纳米碳化物涂层,并以所得TaTiC_2/C复合物为碳化物前驱体,再经可控氧化制备出中空Ta_2O_5/TiO_2复合光催化剂。采用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、紫外-可见(UV-Vis)漫反射(DRS)及N2物理吸附等手段对所制备的光催化剂进行形貌、显微结构及孔结构表征。以高压汞灯为紫外光源,以亚甲基蓝为目标降解物,通过光催化降解实验评价中空Ta_2O_5/TiO_2复合光催化剂的光催化活性。结果表明,熔盐法生长碳化物涂层厚度均匀(20~30 nm),碳化物主要以TaTiC_2晶相存在且具有纳米级的颗粒尺寸。中空Ta_2O_5/TiO_2复合光催化剂同时具有200 nm左右的中空大孔结构及壳层10 nm左右的介孔结构。中空大孔和介孔的存在提高了所制备催化剂对亚甲基蓝的吸附能力。此外,TiO_2与Ta2O5通过电子能带结构的耦合,有效提高了光生电子和空穴的分离效率,从而显著提高了光催化活性。nTi∶nTa=2.5∶1.5时,相应的中空Ta_2O_5/TiO_2复合光催化剂表现出最佳的光催化活性,对亚甲基蓝的紫外光催化降解率高达97%。

Controllable Oxidation Preparation and Performances of Hollow Ta2O5/TiO2 Composite Photocatalysts

Using Ti and Ta powders as raw materials, carbon black as the reactive template, the nanosized carbide coating of TaTiC₂ were grown in situ on the surface of carbon black by molten salt reaction. And using the as-prepared TaTiC₂/C composites as the carbide precursors, the hollow Ta₂O₅/TiO₂ composite photocatalysts were prepared by the controllable oxidation. The morphology, microstructure and pore structure of as-synthesized photocatalyst were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, UV-Vis diffuse reflectance spectroscopy (DRS) and N₂ physical adsorption measurements. With methylene blue as the aimed degradation pollutant and mercury lamp as light source, The photocatalytic activities of hollow Ta₂O₅/TiO₂ composite photocatalysts were evaluated by the photocatalytic degradation of methylene blue solution. Results indicated that the carbide coatings synthesized by molten salt reaction have uniform thickness (20~30 nm). TaTiC₂ was the main crystalline phase of carbide and had nanosized particle size. The hollow Ta₂O₅/TiO₂ composite photocatalysts have hollow macroporous structure of about 200 nm and mesoporous structure of about 10 nm in the shell. The existence of hollow macropores and mesopores can improve the adsorption of as-prepared photocatalysts for methylene blue. In addition, the coupling of electronic energy band structures of TiO₂ and Ta₂O₅ can enhance the separation efficiency of photogenerated electrons and holes remarkably. Furthermore, the photocatalytic activity was improved observably. When the n_Ti:n_Ta is 2.5:1.5, the corresponding hollow Ta₂O₅/TiO₂ composite photocatalyst exhibits the highest photocatalytic activity, and the ultraviolet light photocatalytic degradation rate for methylene blue is up to 97%.