Enhancing photocatalytic hydrogen peroxide production by doping a trace amount of azo-linked C3N5 into a g-C3N4 matrix

Abstract

We have fabricated a composite system by incorporating a trace amount of azo-linked C₃N₅ inside the 2D matrix of a g-C₃N₄ system through an in situ polymerization process. Detailed structural and elemental characterizations are correlated with the underlying photophysical processes. The results suggest that the trace amount of C₃N₅ inside the 2D backbone of C₃N₄ enhances the amount of visible light absorption along with highly efficient charge separation between the two different counterparts of the composite. The excited-state free carrier dynamics have been further clarified by femtosecond transient absorption spectroscopy. Finally, the composite system has been utilized for photocatalytic H₂O₂ production. The optimized composite system shows 8.2 mmol g⁻¹ h⁻¹ H₂O₂ production with an apparent quantum yield of ∼28% without using any metal sites. This is one of the highest amounts of photocatalytic H₂O₂ production reported to date for this type of all-carbon-based composite system. The photoinduced charge separation process has been further confirmed by electrochemical impedance spectroscopy and transient photocurrent studies. The photocatalytic mechanism has been confirmed by chemical scavenging experiments involving the photoinduced free radicals.