Structural properties and photocatalytic activity of amorphous-crystalline TiO2 thin films

Abstract

TiO2-coated glass plates were prepared by dip coating using TiO2 coating sol with a mixed amorphous and crystalline structure. These samples were dried at 100°C or calcined at 500°C, which were referred to as MT and CT, respectively. The TiO2 thin films on glass plates were characterized by X-ray diffraction, thermogravimetry-differential thermal analysis, X-ray photoelectron spectroscopy, Fourier transformed infrared spectroscopy, Brunauer-Emmett-Teller surface area measurement, scanning electron microscopy, and ultraviolet–visible diffuse reflectance spectra. The TiO2 thin films of MT samples had mixed amorphous and crystalline structures, while those of CT samples had only crystalline structures. The photocatalytic activity of the samples was investigated on the basis of methylene blue (MB) decomposition under ultraviolet and visible light irradiation. In the dark stabilization, MT samples had a higher MB adsorption capacity than CT samples. MT samples had a smaller amount of anatase TiO2 than CT samples, but both glass plate samples showed the same MB photocatalytic activity under ultraviolet light irradiation. We presumed that these results were because the amorphous-crystalline TiO2 thin films had a high specific surface area, so they had more adsorption and active sites. Under visible light irradiation, only the MT samples had photocatalytic activity, which can be attributed to their high visible light absorbance, which may be due to their peroxo groups, disordered structure, and larger specific surface area.