Boosting light-driven CO2 reduction towards solar fuels: Mainstream avenues for engineering ZnO-based photocatalysts.

Abstract The realization of artificial photosynthesis in the photocatalytic CO2 transformation into valuable chemicals or solar fuels (such as CO, CH4, HCOOH, and CH3OH) by solar-light harvesting is a promising solution to both global-warming and energy-supply issues. Recently, zinc oxide (ZnO) has emerged as an excellent oxidative photocatalyst among non-titanium metal oxide due to its availability, outstanding semiconducting and optical properties, non-toxicity, affordability, and ease of synthesis. However, its wide bandgap and inability to absorb in the visible region has demanded particular modification for its practical use as a sustainable photocatalyst. This review provides a panorama of the latest advancement on ZnO photocatalysis towards CO2 reduction with an overview of fundamental aspects. Various modification strategies such as transition metal and non-metal doping, loading of plasmonic metals, and surface vacancy engineering for tunning the properties and improving the performance of ZnO are elaborated. Composites or hetero-structuralization-based Z-scheme formation is also presented along with an in-depth photocatalytic reduction mechanism. Moreover, a new novel Step-scheme (S-scheme) heterostructure modification with a charge transfer pathway mechanism is also highlighted. Finally, the key challenges and new directions in this field are proposed to provide a new vision for further improvement for ZnO-based photocatalytic CO2 conversion.