Unravelling the redox behaviour of a carbon nitride polymer-based ternary heterostructure for CO2 photoreduction promoted by amine coupling

Imine compounds are essential commodity chemicals used in synthetic organic chemistry and pharmaceuticals. To date, the oxidative coupling of amines produces imines in a pure oxygen atmosphere. Here, we have presented a sustainable and more economical route for producing imines by replacing O2 with inexpensive and likely inert CO2. A noble metal-free ZnV2O6@WO3–g–C3N4 heterojunction has dual photocatalysis ability, converting CO2 into CO and CH4 in 1674 and 683 μmol g−1 yields, respectively, within six hours with the simultaneous oxidative coupling of amines into imines with a maximum of 55% yield for N-benzylidene benzylamine. Also, CO and CH4 yields were 5.3 and 2.9 times higher than those of pristine g-C3N4. The reusability demonstrated the reliability of the present heterojunction, which showed four consecutive uses of the recovered photocatalyst with relatively similar yields. Besides these, extensive corroboration of mechanistic understanding was made through thorough characterization of the intermediates formed during this simultaneous photocatalytic transformation. Thus, replacing molecular oxygen with CO2 to oxidize amines has vast opportunities, as CO2 can be used as an oxidant for sustainable organic transformations into fine chemicals and fuels.