Increased solar absorption and promoted photocarrier separation in atomically thin 2D carbon nitride sheets for enhanced visible-light photocatalysis

Abstract

The preparation of sulfur-doped and nitrogen-vacant CN (S-CN V ) by annealing CN in S vapor is reported. The results show that the formation of C-S-C bonds and the introduction of nitrogen vacancies in S-CN V matrix could contribute to increased solar absorption and promoted photocarrier separation as well as greatly enhanced photocatalytic activity. • The preparation of sulfur-doped and nitrogen-vacant CN (S-CN V ) by annealing CN in S vapor is reported. • This strategy can dramatically increase solar absorption and promote photocarrier separation in atomically thin CN. • The visible-light photocatalytic activity of S-CN V photocatalyst significantly exceeds CN photocatalyst. Atomically thin two-dimensional (2D) carbon nitride (CN) has been widely used in solar energy conversion as a metal-free photocatalyst. However, because of the wide band gap (3.06 eV) and rapid recombination of photogenerated electron-hole pairs, the visible-light photocatalytic efficiency of CN is still low. In this study, successful preparation of sulphur-doped and nitrogen-vacant CN (S-CN V ) by annealing CN in S vapour is reported. The photocatalytic hydrogen production rate of S-CN V under visible-light irradiation (>420 nm) reached 5192.2 μmol h −1 g −1 , which is much higher than that of previously reported CN. The structural characterisations combined with theoretical calculations show that (i) the formation of C-S-C bonds and introduction of nitrogen vacancies in the edges can narrow the band gap of CN from 3.06 to 2.79 eV, which expands the visible-light absorption band; and (ii) the S-CN V charge distribution has local characteristics, which promotes the separation and transmission of photogenerated carriers. This study provides a new approach to narrow the band gap and promote the photoexcited carrier separation in 2D carbon-nitride-based materials.