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

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-CNV) by annealing CN in S vapour is reported. The photocatalytic hydrogen production rate of S-CNV 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-CNV 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.