Enhanced visible light hydrogen production via a multiple heterojunction structure with defect-engineered g-C3N4 and two-phase anatase/brookite TiO2

Abstract Polymeric g-C 3 N 4 is a promising candidate for solar hydrogen production. However, its hydrogen production rate is low when used alone due to fast recombination of photogenerated electron–hole pairs. In this paper, we report much improved hydrogen production by coupling g-C 3 N 4 with two-phase anatase/brookite TiO 2 nanoparticles to form multiple heterojunctions. Results have shown that under visible light illumination, photogenerated electrons transfer from g-C 3 N 4 to TiO 2 . In addition, systematic comparison was carried out among different type of heterojunctions, viz., g-C 3 N 4 coupled with a single phase of TiO 2 (anatase or brookite), dual-phase TiO 2 (anatase/brookite or anatase/rutile), or a three-phase TiO 2 (anatase/brookite/rutile) mixture. g-C 3 N 4 with two-phase anatase/brookite TiO 2 produces the largest amount of hydrogen under visible light illumination. The comparison reveals two important factors behind photocatalytic hydrogen generation: effective charge transfer and the conduction band potential position. The band edge positions of all the constituent phases of the heterojunction have to be more cathodic than the hydrogen reduction potential in order to realize the full benefit of effective charge separation.