Well-designed ZnV2O6/g-C3N4 2D/2D nanosheets heterojunction with faster charges separation via pCN as mediator towards enhanced photocatalytic reduction of CO2 to fuels

Fabrication of well-designed 2D/2D heterojunction composite with effective interfacial contact by incorporating zinc vanadium oxide (ZnV2O6) and protonated g-C3N4 (pCN) for enhanced photocatalytic CO2 reduction has been investigated. The 2D/2D ZnV2O6/pCN samples, synthesized by a one-pot solvothermal method, were analysed using XRD, SEM, EDX-mapping, TEM, N-2 sorption, XPS, UV-vis, RAMAN and PL characterization techniques. It was observed that surface charge modification through protonation of graphitic carbon nitride serves as a mediator and trapped photo-excited electrons. The performance of composite catalysts was investigated in a liquid and gas phase photocatalytic systems under UV and visible light irradiations. Using slurry system, CH3OH production rate enhanced up to 3742 mu mol g-cat(-1) over ZnV2O6/pCN, 1.15 and 5 times higher than the pure ZnV2O6 (3254 mu mol g-cat(-1)) and pCN (753 mu mol g-cat(-1)) samples, respectively. Instead, the CO evolution rate as a main product over ZnV2O6/pCN nanosheets of 3237 mu mol g-cat(-1) was obtained using gas phase system. This enhanced activity can be mainly ascribed to the addition of pCN with ZnV2O6 in a controlled ratio as well as synergistic effect of ZnV2O6/pCN nanosheet heterojunctions. Besides, hierarchical structure, higher interfacial interaction, abundant 2D coupling interfaces and efficient separation of charges could efficiently promote both the photo-activity and products selectivity. The obtained ZnV2O6/pCN 2D/2D nanosheets heterojunction with a mediator exhibited excellent photocatalytic stability, which prevailed even after 32 h of operation time for continuous CH3OH production. The possible reaction mechanism anticipated to understand the movement of electrons and holes for CO2 reduction over the ZnV2O6/pCN photocatalyst.