One-pot synthesis of heterostructures based on S-doped polymeric carbon nitride and carbon dots for enhancing photocatalytic H2 production

Polymeric carbon nitride (PCN) is a promising metal-free visible-light-driven material for solar hydrogen production because of its photocatalytic response to visible light and easy fabrication. However, its photocatalytic activity is limited due to low absorption in a wide solar spectrum, poor charge separation efficiency, and low charge carrier mobility. Herein, we present a strategy to address these issues by combining sulfur-doped PCN (SPCN) with carbon dots (CDs). To this end, we developed a straightforward synthetic procedure based on the calcination of thiourea and small amounts of citric acid. The presence of citric acid in the reaction medium led to the formation of carbon dots (CD) on the surface of the semiconductor material, enhancing light absorption and improving the photocatalytic production of H₂. Different amounts of citric acid were used to explore the influence of the CDs on the hydrogen production of SPCN. The obtained materials were thermally exfoliated to increase the surface area and then characterized using XRD, FT-IR, DRS, SEM, and BET. The optimal SPCNCD heterostructure, obtained with 60 mg of citric acid, exhibited improved H₂ production activity of 1756 μmol g⁻¹ h⁻¹ of H₂ over six hours when irradiated with a solar simulator due to a narrower band gap. Our study provides valuable insights for designing metal-free heterostructures for photocatalysis applications.