Construction of polymeric carbon nitride and dibenzothiophene dioxide-based intramolecular donor–acceptor conjugated copolymers for photocatalytic H2 evolution

Abstract

Polymeric carbon nitride (g-C₃N₄) has succeeded as a striking visible-light photocatalyst for solar-to-hydrogen energy conversion, owing to its economical attribute and high stability. However, due to the lack of sufficient solar-light absorption and rapid photo-generated carrier recombination, the photocatalytic activity of raw g-C₃N₄ is still unsatisfactory. Herein, new intramolecular g-C₃N₄-based donor–acceptor (D–A) conjugated copolymers have been readily synthesized by a nucleophilic substitution/condensation reaction between urea and 3,7-dihydroxydibenzo[b,d]thiophene 5,5-dioxide (SO), which is strategically used to improve the photocatalytic hydrogen evolution performance. The experimental results demonstrate that CNSO-X not only improves light utilization, but also accelerates the spatial separation efficiency of the photogenerated electron–hole pairs and increases the wettability with the introduction of SO. In addition, the adsorption energy barrier of CNSO-X to H* has a significant reduction via theoretical calculation. As expected, the CNSO-20 realizes the best photocatalytic H₂ evolution activity of 251 μmol h⁻¹ (50 mg photocatalyst, almost 8.5 times higher than that of pure CN) with an apparent quantum yield of 10.16% at 420 nm, which surpasses most strategies for the organic molecular copolymerization of carbon nitride. Therefore, this strategy opens up a novel avenue to develop highly efficient g-C₃N₄ based photocatalysts for hydrogen production.