Preparation, Characterization And Heterogeneous Photocatalytic Activity Of Mesoporous H₃PW₁₂O₄₀/ZrO₂ Composites

Heterogeneous photocatalysis by solid polyoxometalate (POM) is a new branch in the field of photocatalytic chemistry, and some attractive researching progresses have developed in recent years. Although POMs exhibit UV-light photocatalytic activity in homogeneous system, the main disadvantages of them as photocatalysts lie in their low surface area and difficulty of separation from reaction mixture. Therefore, development of novel solid catalysts with advanced characteristics such as surface area and porosity has been a challenge for a long time.In this paper, a series of mesoporous H₃PW₁₂O₄₀/ZrO₂ composites with different H₃PW₁₂O₄₀ loading levels (5 to 20 wt %) and phase structures (amorphous, tetragonal, and the mixed phases of tetragonal and monoclinic) were prepared by a modified wet impregnation method. The phase structures, chemical structures, optical absorption properties, surface physicochemical properties, and morphologies of the composites were well-characterized via X-ray diffraction patterns, FT-IR spectroscopy, Raman scattering spectroscopy, UV-vis diffuse reflectance spectroscopy, nitrogen adsorption/desorption determination, and field emission scanning electron microscopy, indicating that the primary Keggin structure remained intact after formation of the composites, and impregnation of the Keggin unit into the ZrO₂ framework had an influence on the electronic properties of the ZrO₂, and the composites exhibited mesoporous structures. In addition, compared with starting POM, BET surface areas of the solid photocatalytic materials have been improved in the different extents.As-prepared mesoporous H₃PW₁₂O₄₀/ZrO₂ composites were used to photodegrade an aqueous 4-nitrophenol and dye methyl ene blue under UV-light irradiation. The result indicate that the conversions of 4-nitrophenol and dye methylene blue remarkably increased on UV-irradiating these catalysts compared with the starting POM and solid ZrO₂. The photocatalytic activity of the composites were influenced by the factors such as phase structures, optical absorption properties, and surface physicochemical properties. The leakage of the active component from composites was hardly observed during the degradation process by UV-vis spectrophotometer and ICP-AES determination, indicating that as-prepared composites were stable. Moreover, this kind of catalysts was readily be separated from the reaction system and could be reused.