Polymeric triazine/heptazine imide heterostructures enable photocatalytic O2reduction to H2O2

Abstract

Heptazine-based carbon nitrides are a class of transition metal free semiconductors, which are extensively studied in various photocatalytic processes. The localized nature of the excitons, incomplete exciton conversion into the charge-separated state and the recombination of the charge carriers are the factors that limit performance of the pristine heptazine-based carbon nitrides. Herein, we design heterojunctions composed of poly(triazine imide) intercalated by LiCl and poly(heptazine imide) phases. The donor-acceptor character of the heterojunctions improves the charge separation yield. The heterojunction with the optimal composition of the phases shows an apparent quantum yield of H2O2 formation of 14 % at 365 nm and 7 % at 465 nm, while the H2O2 production rate reaches 7.8 mol L−1 gphotocatalyst−1 h−1 (39 mmol L−1 h−1 produced by 5 mg of photocatalyst) in batch and 15.9 mol kgphotocatalyst−1 h−1 in flow using a packed-bed photoreactor. The heterojunction undergoes photocharging under anaerobic conditions. The charges stored in the material after irradiation enable O2 reduction to H2O2 in the dark with the rate 367 µmol gphotocatalyst−1 h−1 (1.8 µmol h−1 stored in 5 mg of photocatalyst).