High-yield solar photocatalytic CO₂ conversion in dense-phase CO₂ via ZnO/CuO/Ti₃C₂ nanosheet heterojunctions with ionic liquids

Harnessing solar energy to convert liquid carbon dioxide (CO 2 ) into chemical fuels presents a promising solution to address both the greenhouse effect and the fossil fuel crisis. In this study, heterogeneous photocatalysts composed of zinc oxide (ZnO) nanocones and semi-hedgehog-like cupric oxide (CuO) nanoparticles were successfully synthesized via a hydrothermal treatment for efficient photocatalytic reduction of liquid CO 2 . To further enhance performance, two-dimensional Ti 3 C 2 MXene nanosheets (NSs), corresponding to 5 mol% relative to ZnO, were integrated onto the composite photocatalyst surface, enhancing the specific surface area, facilitating interfacial charge transfer, and promoting the separation of photo-generated electron-hole pairs. Furthermore, 1-Ethyl-3methylimidazolium amino-acetate ionic liquid (IL) was utilized to lower the overpotential and enhance CO 2 adsorption and diffusion. This led to a pronounced hydrogenation effect that significantly boosted methane yield in the photocatalytic process. As a result, the ZnO/CuO/Ti 3 C 2 NSs/ILs heterojunction nanocomposite demonstrated significantly enhanced photocatalytic activity for dense-phase CO 2 reduction compared to pristine ZnO nanoparticles. Using water as a hydrogen source, ZnO/0.5CuO/Ti 3 C 2 NSs exhibit a very high total yield for liquid CO 2 reduction (62 bar and 22 °C), reaching 136.9 mmol h⁻¹ g⁻¹ for CO and 30.2 mmol h⁻¹ g⁻¹ for CH₄ under irradiation of a Xe arc lamp. This remarkable production rate marks a significant step forward in the development of efficient CO 2 reduction systems and presents a promising strategy for advancing solar-driven carbon conversion technologies.