Synthesis and characterization of ZrO2–TiO2 binary oxide semiconductor nanoparticles: Application and interparticle electron transfer process

Abstract

The chemical interaction of Zr–O–Ti in the binary oxide catalysts is found to be a major factor in high performance for the degradation of 4-CP. Photoluminescence provides strong evidence for the existence of the ZrO 2 CB surface trap states which lie below the CB of TiO 2 and facilitate fast electrons injection to the CB of TiO 2 and which prevent the recombination of electrons and holes. A series of nanocrystalline mesoporous ZrO 2 –TiO 2 binary oxide photocatalysts with different wt% of ZrO 2 and TiO 2 were prepared by a sol–gel method. These binary oxide photocatalysts were characterized by XRD, N 2 adsorption–desorption, DRS, FTIR, Raman spectroscopy, photoluminescence and TEM analyses. Detailed investigations revealed that the ZrO 2 –TiO 2 catalysts are highly micro-crystalline in nature with a larger surface area than that of the pure TiO 2 or ZrO 2 catalysts since the added ZrO 2 plays an important role in promoting the formation of nanoparticles with an anatase structure, high surface area and acidity. The photocatalytic reactivity of the catalysts was investigated for the degradation of 4-chlorophenol in an aqueous phase in which the ZrO 2 –TiO 2 photocatalysts were found to exhibit remarkably higher photocatalytic reactivity than that of pure TiO 2 and ZrO 2 . The catalytic activity of the binary oxide photocatalysts for the degradation of 4-chlorophenol was observed to be gradually enhanced with an increase in the ZrO 2 content and reached an optimum at 12 wt% of ZrO 2 while maintaining the same percentage degradation with further loading of ZrO 2 until 50 wt%. Such high reactivity is due to the easy transfer of the photo-formed electrons from the conduction band surface trap states of ZrO 2 to the conduction band of TiO 2 through strong chemical interactions, thereby, preventing the radiative recombination of the photo-formed electrons and holes. The ZrO 2 –TiO 2 catalysts were, thus, found to be highly active for the efficient degradation of 4-chlorophenol and, in fact, exhibited just as efficient activity as the commercial P-25, Degussa TiO 2 catalysts, and a new reaction mechanism has, hereby, been proposed.