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, N₂ 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 μmol g-cat⁻¹ over ZnV₂O₆/pCN, 1.15 and 5 times higher than the pure ZnV₂O₆ (3254 μmol g-cat⁻¹) and pCN (753 μmol g-cat⁻¹) samples, respectively. Instead, the CO evolution rate as a main product over ZnV₂O₆/pCN nanosheets of 3237 μmol 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.