Type II heterojunction promotes photoinduced effects of TiO2 for enhancing photocatalytic performance

Abstract

Obtaining hydrogen energy from photocatalytic water splitting driven by solar energy is a promising strategy to solve the global energy crisis. Herein, by taking the photoinduced activation effects of TiO₂, we obtained a Ti³⁺ self-doped TiO₂ (Ti³⁺–TiO₂). In situ characterization revealed that the presence of Ti³⁺ is attributed to the reduction reaction of Ti⁴⁺ on the TiO₂ surface under UV light irradiation. The research results prove that the optical properties of TiO₂ are modified by the active species Ti³⁺; the recombination rate of the photogenerated carriers is significantly decreased, and Ti³⁺–TiO₂ exhibits a hydrogen production rate which is 1.7 times superior than that of pristine TiO₂. To further enhance the self-activation effect of TiO₂, we constructed a type II heterojunction TiO₂/UiO-66-NH₂ structure to transfer photoexcited electrons to TiO₂, which gives a higher concentration and duration of the active species Ti³⁺. Ti³⁺–TiO₂/UiO-66-NH₂ shows improved photocatalytic hydrogen evolution activity with a rate 3.2 times better than that of pristine TiO₂ due to the synergistic function of oxygen vacancies and Ti³⁺. A novel perspective was adopted in this work to observe the dynamic variation of active species and electron transfer pathways during TiO₂ photocatalytic reactions. Since Ti³⁺ is generated on the TiO₂in situ, this work could be extended to TiO₂-based photocatalysts.