Construction of manganese ferrite/zinc ferrite anchored graphene-based hierarchical aerogel photocatalysts following Z-scheme electron transfer for visible-light-driven carbon dioxide reduction

Herein, atomic-level interfacial coupling between spinel-type MnFe₂O₄ (MFA) and ZnFe₂O₄ (ZFA) was achieved via a sol–gel method combined with phase separation. These composites were then anchored onto a three-dimensional graphene aerogel (GA) through ethylenediamine-assisted hydrothermal self-assembly, forming a hierarchically porous MFA/ZFA@GA with a high surface area (191.06 m²/g). The optimized MFA/ZFA@GA exhibited a CO production rate of 21.14 μmol·g⁻¹·h⁻¹ (96 % selectivity, 94 % stability) under visible light, a 3.87-fold enhancement over single-component systems. The in-situ MFA/ZFA heterojunction and graphene-enhanced electron transfer synergistically prolonged photogenerated electron lifetime by 10 times. The hierarchical pores also boosted CO₂ adsorption (7.66 wt%), the appreciable saturation magnetization intensity (37.49 emu/g) enabled magnetic separation recovery, and *COOH monitoring confirmed rapid desorption kinetics for high CO selectivity. Experiments combined with theoretical calculations revealed a Z-scheme mechanism: MnFe₂O₄’s reductive electrons (−0.79 V vs. NHE) drove CO₂ reduction, while ZnFe₂O₄’s oxidative holes (1.50 V vs. NHE) facilitated H₂O oxidation. Strategic integration of heterostructures, carbon hybridization, and aerogel architectures offered an efficient pathway for monolithic photocatalyst design.