Oxygen-Linked Polymeric Heptazine for Selective C–C Cleavage in Synergism with Solar Fuel Generation: Unlocking the Full Potential

Unleashing the power of light, the current study demonstrates the complete harvesting of a biomass-derived lignin model substrate into the simultaneous generation of value-added chemicals and a carbon-free solar fuel in a more sustainable way. Here, the C–C bond cleavage selectivity of 91% with a 67% conversion rate was achieved for the first time along with hydrogen peroxide (H2O2) generation using oxygen-linked polymeric heptazine (CNO) as the catalyst compared to melamine-derived carbon nitride (CNM). The porous CNO exhibits a low emission intensity and a decreased lifetime in time-resolved photoluminescence, deducing the high mobility and reduced recombination of charge carriers. The lower work function, decreased surface potential difference, increased population of unpaired electrons in the conduction band of CNO, and in situ electrochemical experiments demonstrate higher electron density, effective charge-carrier separation, and their migration in CNO. Further, the experimental results were supported by the atomistic computations exhibiting stronger adsorption of the lignin model compound over CNO, suggesting that CNO displays greater activity in facilitating C–C cleavage than CNM. All of the above factors infer the crucial role of C–O–C bridging and C–OH dangling groups of CNO in enhancing its photocatalytic activity. The mechanistic insights reveal the importance of singlet oxygen and superoxide radicals in the cleavage of the Cα–Cβ bond and H2O2 generation, respectively.