Synergistic Effect in Photocatalysis As Observed for Mixed-Phase Nanocrystalline Titania Processed via Sol−Gel Solvent Mixing and Calcination

Mixed-phase nanocrystalline titania (TiO 2 ) with varying rutile content has been synthesized via solvent mixing and calcination (SMC) treatment of sol−gel-derived nanocrystalline anatase-TiO 2 and rutile-TiO 2 precursors. The mixed-phase nanocrystalline TiO 2 processed via sol−gel SMC has been characterized using X-ray diffraction, the scanning electron microscope, high-resolution transmission electron microscope, and ultraviolet−visible (UV−vis) diffuse reflectance spectroscope for analyzing its morphology, phase contents, nanocrystallite size distribution, and band gap. The photocatalytic activity of mixed-phase nanocrystalline TiO 2 processed via sol−gel SMC is measured by monitoring the degradation of the methylene blue dye in an aqueous solution, under the UV-radiation exposure, using the UV−vis absorption spectroscope. It is demonstrated that the photocatalytic activity of mixed-phase nanocrystalline TiO 2 processed via sol−gel SMC is a function of rutile content with the maximum photocatalytic activity observed for 40 wt% rutile. Thus, the synergistic effect has been observed between anatase-TiO 2 and rutile-TiO 2, which has been satisfactorily explained using a new model based on the band-gap variation in the connected nanocrystallites as a function of the size distribution and the phases involved, which overcomes the limitations of the existing models proposed earlier in the literature.