Synergistic potassium intercalation and cyano group modification on crystalline carbon nitride homojunction towards dual-functional photoredox coupling of H₂O₂ and benzaldehyde production

Advancement in photocatalysts is essential for improving their feasibility. This can be achieved by eliminating the need for sacrificial agents in conventional half-reactions. Additionally, co-producing two products via the redox reaction allows for the full utilization of electron-hole pairs in photocatalysis. Herein, a carbon nitride heptazine/triazine homojunction was synthesized via eutectic salt-assisted one-step ionothermal polymerization for the simultaneous photoreduction of O₂ into H₂O₂ and selective photooxidation benzyl alcohol (BA) into benzaldehyde (BAD). The optimal CCN-550 demonstrated robust photocatalytic performances with yields of 5838.91 and 7041.32 µmol L^-1h⁻¹ for H₂O₂ and BAD simultaneously with 100 % selectivity, recording 31.7 and 14.5-fold higher compared to the pristine structure, respectively with an apparent quantum yield of 11.57 % (420 nm). The photoredox reaction mechanism was unveiled as a sequential two-step single electron transfer process, attested by the 1.38 electron transfer from rotating disk electrode (RDE), radical quenching test and electron paramagnetic resonance. The bolstered catalytic performance is attributed to the PHI/PTI homojunction and the synergistic effect from the homojunction owing to intercalated K⁺ for instantaneous charge transmission and the formation of cyano group serving as the electron traps.