Eco-friendly fabrication of ZnO–Co₃O₄/C S-scheme photocatalyst from bimetallic ZIF for sunlight-powered H₂ generation and CO₂-to-fuel conversion

The efficiency of photocatalytic fuel generation continues to be constrained by swift electron-hole recombination and inadequate harvesting of visible-range photons in monocomponent semiconductors. In this study, we describe an environmentally benign approach to prepare a ZnO-Co₃O₄/C S-scheme photocatalyst, starting from a Zn/Co bimetallic ZIF that undergoes regulated pyrolysis at 600 °C in an inert N₂ environment. The bimetallic ZIF was synthesized through a water-ethanol solvothermal process with a low environmental impact score (E-factor: 3.2), completely eliminating hazardous organic solvents from the procedure. Powder XRD, EM imaging, and XPS collectively verified the development of an intimately integrated ZnO-Co₃O₄/C junction while preserving the porous architecture inherited from the parent ZIF. A suite of characterization tools including Mott-Schottky plots, attenuated PL emission, reduced EIS arc radii, and ESR spin-trapping signatures all point toward operation via an S-scheme charge migration pathway. Under optimized conditions, the composite photocatalyst delivered H₂ at 2340 ± 45 µmol per gram per hour (AQY reaching 8.2% under 450 nm illumination) while concurrently converting CO₂ to CO at 58.7 ± 2.1 µmol g⁻¹ h⁻¹, maintaining 95.5% of its initial catalytic activity across five consecutive reuse cycles. Our findings illustrate that sustainable, scalable synthesis of MOF-based S-scheme photocatalysts is achievable and can simultaneously drive two distinct solar-to-fuel conversion processes.