Patchy Amorphous TiO2 on Crystalline TiO2 Microspheres with Regulated Surface Hydroxyl Groups for Highly Efficient Photocatalytic Toluene Mineralization

Abstract Photocatalysis is a promising technology for the removal of volatile organic compounds (VOCs), but achieving complete mineralization of aromatic VOCs remains challenging due to the limited number of active sites and insufficient supply of hydroxyl radicals on the photocatalyst. In this study, we developed a strategy to functionalize crystalline TiO2 microspheres with patchy amorphous TiO2 surface layers, which provided the catalyst with abundant surface hydroxyl groups. Although these groups do not enhance toluene adsorption, they efficiently capture photogenerated charge carriers during the photocatalytic process to produce abundant hydroxyl radicals, which subsequently drive toluene oxidation toward complete mineralization. The optimized photocatalyst demonstrated a toluene degradation efficiency of 100% and a mineralization rate of 94.6%. Combining the results of in situ diffuse reflectance infrared Fourier transform spectroscopy and theoretical calculations revealed that, compared with pure TiO2, water molecules are more likely to form hydroxyl groups when reaching the surface of amorphous TiO2. Furthermore, under illumination, amorphous TiO2 continuously provides more hydroxyl radicals than pure TiO2 to attack toluene and achieve complete mineralization. This study offers a design prototype for the development of high-performance photocatalysts tailored for VOCs abatement.