Liquid-Plasma Hydrogenated Synthesis of Gray Titania with Engineered Surface Defects and Superior Photocatalytic...

Defect engineering in photocatalysts recently exhibits promising performances in solar-energy-driven reactions. However, defect engineering techniques developed so far rely on complicated synthesis processes and harsh experimental conditions, which seriously hinder its practical applications. In this work, we demonstrated a facile mass-production approach to synthesize gray titania with engineered surface defects. This technique just requires a simple liquid-plasma treatment under low temperature and atmospheric pressure. The in situ generation of hydrogen atoms caused by liquid plasma is responsible for hydrogenation of TiO₂. Electron paramagnetic resonance (EPR) measurements confirm the existence of surface oxygen vacancies and Ti³⁺ species in gray TiO_2-x. Both kinds of defects concentrations are well controllable and increase with the output plasma power. UV-Vis diffused reflectance spectra show that the bandgap of gray TiO_2-x is 2.9 eV. Due to its extended visible-light absorption and engineered surface defects, gray TiO_2-x exhibits superior visible-light photoactivity. Rhodamine B was used to evaluate the visible-light photodegradation performance, which shows that the removal rate constant of gray TiO_2-x reaches 0.126 min^-1 and is 6.5 times of P25 TiO₂. The surface defects produced by liquid-plasma hydrogenation are proved stable in air and water and could be a candidate hydrogenation strategy for other photocatalysts.