Counterion chemistry of 5-halo (X: Cl, Br, I)-uracil derived carbon nitride: unlocking enhanced photocatalytic performance

The performance of modified polymeric carbon nitride (PCN) photocatalysts exceeds that of their bulk counterparts, owing to their distinct advantages and enhanced features. In this work, we present the synthesis methodology for halide-molecular doped PCN through a single molecule precursor approach by combining π-aromatic uracil and halide as a dopant and counterions, respectively. We systematically investigated the effect of halide ions (X⁻: Cl⁻, Br⁻, and I⁻) on the photoactivity of 5-halouracil derived PCN (XUCN). Our results demonstrate that halide counterions significantly enhance the photocatalytic activity of XUCN for hydrogen peroxide and hydrogen production (126.6 μmol h⁻¹ and 0.563 mmol h⁻¹ g⁻¹), compared to the undoped bulk PCN (48.3 μmol h⁻¹ and 0.260 mmol h⁻¹ g⁻¹). The charge-carrier analysis and structural analysis of synthesized XUCN catalysts suggest that the improvement in photoactivity is due to the synergistic interactions of uracil and halide ions, which enhance the charge-carrier lifetime (1.51 to 3.08 ns), generate additional catalytic sites (10.6 to 83.3 m² g⁻¹), and extend light absorption (450 to 480 nm). Theoretical investigations reveal high structural stability for XUCN with favourable adsorption energies to bind with reactive oxygen species. The new insights provided in this study can have important implications for future design and synthesis of metal-free PCN with improved photoactivity via single molecule precursor doping.