Well-designed ZnFe2O4/Ag/TiO2 nanorods heterojunction with Ag as electron mediator for photocatalytic CO2 reduction to fuels under UV/visible light

Spinel ZnFe2O4 microspheres coupled with Ag/TiO2 nanorods (NRs) to develop Z-scheme heterojunction were fabricated using a facile hydrothermal approach and were tested for photocatalytic CO2 conversion to fuels. ZnFe2O4/Ag/TiO2 NRs composite presents remarkably improved CO2 photo-activity for CO production, which was 1.49 folds higher than ZnFe2O4/TiO2 NRs and 4.12 times that using pristine ZnFe2O4 microspheres. Similar trends were obtained to produce methane and methanol over composite catalyst. Selective CO and hydrocarbon fuels production was obviously due to double charge transfer approach in indirect Z-scheme heterojunction with superior charge carrier separation and high visible light absorption. Interestingly, CO evolution under visible-light with ZnFe2O4/Ag/TiO2 NRs was declined by 7.48 folds than using UV-light irradiation. This was apparently due to the inappropriate VB position of ZnFe2O4 for stimulating CO2 reduction under visible light irradiation. Comparing morphological effects, coupling TiO2 NRs with Ag/ZnFe2O4, production of CO was 1.40 folds higher than using TiO2 NPs with Ag/ZnFe2O4 composite due to 1D TiO2 NRs and ZnF2O4 were beneficial for promoting charge carrier separation. This work provides a new approach for preparing ZnFe2O4 based structured Z-scheme hetero-junction for stimulating photocatalytic conversion of CO2 to selective fuels and would be promising for energy application.