Enhancing CO₂ photoreduction efficiency with MXene-modified ZnO@Co₃O₄ double heterojunction

The photocatalytic reduction of CO₂ into energy carriers holds significant industrial appeal, but achieving this process kinetically remains challenging due to the lack of well-designed catalysts. This study presents a novel 2D/3D nanostructured photocatalyst, developed by attaching a few-layer Ti₃C₂ MXene to polyethylenimine (PEI)-modified ZnO@CO₃O₄ nanocages, which are derived from a bimetallic zinc-cobalt ZIF. The resulting Mx-PEI-ZnO@Co₃O₄ catalyst achieved impressive yields of CO and CH₄ at 594.37 and 42.67 μmol g⁻¹ h⁻¹, respectively, without the need for sacrificial agents and photosensitizers, and maintained remarkable stability across multiple cycles. These yields represent the highest performance for ZnO-based catalysts to date, with quantum efficiency at 380 nm reached up to 25.06 %. The unique S-scheme and Schottky junctions, along with enhanced CO₂ adsorption and hydrogen-bond interactions facilitated by the conductive PEI within the Ti₃C₂/ZnO/Co₃O₄ double heterojunctions, effectively inhibit electron-hole recombination and significantly enhance CO₂ photoreduction performance. This study underscores the combined benefits of double heterojunction engineering, PEI-functionalized CO₂ uptake, and MXene co-catalyst integration within a single system, proposing a new approach for designing highly efficient photocatalysts for solar-driven CO₂ reduction in energy-efficient fuel production.