Z-Scheme heterojunction ZnO-Au-ZnAl2O4: Bridge-type hot carrier transfer and reaction kinetics in the photodegradation of catechol

Z-scheme heterojunction catalysts are novel photocatalytic materials with wide application prospects because of their promise for the engineering of band structure to achieve high-speed hot carrier-transfer and strong redox tunability. A bridged-Au Z-scheme heterojunction catalyst (ZnO-Au-ZnAl2O4) was synthesized using layered double hydroxides (LDHs) as the backbone. The atomistic and architectural structures, elemental composition and and visible-light absorption of as-prepared photocatalysts were systematically investigated and characterized. The presence of Z-scheme heterojunctions in ZnO-Au-ZnAl2O4 can significantly improve the photocatalytic activity under visible light irradiation with a reaction rate constant of 0.5503 h (ZnO-Au(2%)-ZnAl2O4), 27.2 times that of pure ZnO (0.0202 h(-1)) and 9.8 times that of ZnO-ZnAl2O4 (0.0389 h(-1)). We further investigated the reaction kinetics of the heterostructure catalyst in the photodegradation of catechol, where the effect of the catalyst dosage, initial pH, irradiation intensity and reaction temperature were discussed. Based on the mechanism study in the capture and detection of photo-generated radicals and the calculation of band structures by DFT (work function), the successful construction of bridged-Au Z-scheme heterojunction was further proven. Au nanoparticles sandwiched between ZnO and ZnAl2O4 play a vital role for the formation of a built-in electric field (BIEF) between ZnO and ZnAl2O4, which can significantly facilitate the transfer of hot carriers in the photocatalytic system.