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

Polymeric g-C3N4 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-C3N4 with two-phase anatase/brookite TiO2 nanoparticles to form multiple heterojunctions. Results have shown that under visible light illumination, photogenerated electrons transfer from g-C3N4 to TiO. In addition, systematic comparison was carried out among different type of heterojunctions, viz., g-C3N4 coupled with a single phase of TiO2 (anatase or brookite), dual-phase TiO2 (anatase/brookite or anatase/rutile), or a three-phase TiO2 (anatase/brookite/rutile) mixture. g-C3N4 with two-phase anatase/brookite TiO2 produces the largest amount of hydrogen under visible light illumination. The comparison reveals two important factors behind photo catalytic 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. (C) 2016 Elsevier Inc. All rights reserved.