Enhancement and Stabilization of Isolated Hydroxyl Groups via the Construction of Coordinatively Unsaturated Sites on Surface and Subsurface of Hydrogenated TiO2 Nanotube Arrays for Photocatalytic Complete Mineralization of Toluene

Abstract Hydroxyl groups on the photocatalyst surface provide adsorption sites and starting species to form hydroxyl radicals, and are thus considered as the most important species for the photocatalytic degradation of toluene. However, the complete mineralization of toluene over TiO2 photocatalysts is still challenging because of insufficient and unstable hydroxyl groups. Here, a hydrogenated TiO2 nanotube array mesh (H-TiO2) was fabricated. H-TiO2 capable of trapping light and serving high surface areas for active sites exhibited a toluene mineralization conversion of 100%. It was found that surface distortion and oxygen vacancies ensured the chemical dissociative adsorption of water to generate sufficient isolated hydroxyls on the surface and subsurface and benefited the regeneration in long-term operations. This study may provide an efficient TiO2-based photocatalyst for the removal of volatile organic compounds for air purification and give comprehensive understandings of the photocatalyst surface modification and theoretical guidance for designing hydroxyl-demanding photocatalysts.