Photocatalytic performance of mesoporous composites of TiO2–ZrO2 and phosphotungstic acid

Herein, the mesoporous composite materials, mTiO2–ZrO2/PTAy-x (PTA = phosphotungstic acid, x represents the molar ratio of Ti to Zr, y represents the weight percent of PTA in mTiO2–ZrO2/PTA samples), have been prepared by the surfactant-assisted sol–gel method combined with a subsequent hydrothermal treatment. The as-prepared catalysts were fully characterized by FT-IR, XRD, SEM, TEM, XPS, DRS, PLs and nitrogen adsorption–desorption techniques. The results indicated that mTiO2–ZrO2 sample with the TiO2 and ZrO2 molar ratio of 3 exhibits good crystallinity, large internal surface areas and narrow-sized pores. The PTA clusters incorporated in mTiO2–ZrO2 frameworks preserve intact Keggin structure according to EDX, FT-IR and diffuse reflectance UV/vis/NIR spectroscopy. The band gap energy of as-prepared composites is reduced compared with single components. The PL experiments revealed that the obtained mTiO2–ZrO2 can strongly retard the recombination of photogenerated electrons and holes compared with a single oxide, and the introduction of PTA species can further improve the light adsorption and the photochemical stability, therefore efficiently promoting photocatalytic activity of the ternary composite materials. Photocatalytic experiments confirmed that mTiO2–ZrO2/PTA10-3 displayed highly efficient and durable activity for the photodegradation of methyl orange under simulated sunlight and photoreduction of Cr(VI) under visible light. The study of the photocatalytic mechanism revealed that superoxide radicals (∙O2−) and holes (h+) are the main active species. These materials are very stable in the photocatalytic reactions, and therefore, they are promising and efficient catalysts for practical applications.