Fabrication of a direct Z-scheme heterojunction of UiO-66-NH2 and tubular g-C3N4 for the stable photocatalytic reduction of CO2 to CO and CH4

The conversion of CO₂ into high-value fuels and industrial chemicals using solar energy has always been a popular research topic, and the development of highly active and stable photocatalysts is the key. In the present work, a direct Z-scheme heterojunction composite of tubular g-C₃N₄(TCN) and amino-functionalized UiO-66(UNH) were synthesized by solvothermal method. XRD, SEM and XPS showed that UNH grew in situ on the surface of the tubular structure of TCN and there was a close interaction via “–CO–NH–” covalent bonding between them. Photocatalytic CO₂ reduction experiments exhibited that the composite T/U-0.65 possessed the optimal catalytic performance, with CH₄ yields 14.85 times and 3 times higher than those of pure TCN and pure UNH, respectively. In addition, T/U-0.65 had excellent cycle stability, maintaining a CH₄ yield of 89.25% through the 8th cycle. Photoelectrochemical characterization and ESR radical trapping experiments further demonstrated that the heterojunction composition was conducive to the photocatalytic reduction of CO₂ activity.