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

Abstract

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.