Cu₂ZnSnS₄–Sporomusa ovata photobiohybrids coupled with Clostridium kluyveri fermentation for CO₂conversion to C₄–C₆fatty acids

The conversion of greenhouse CO₂ into long-chain chemicals remains a major challenge in artificial photosynthesis. Here, we present a novel semi-biological platform that integrates microbial photocatalysis with fermentation to produce fatty acids from CO₂. The process begins with light-driven CO₂ reduction to acetate and ethanol, enabled by a photobiohybrid composed of the earth-abundant, non-toxic semiconductor Cu₂ZnSnS₄ (CZTS) and the CO₂-fixing electrotroph Sporomusa ovata (S. ovata). In this CZTS–S. ovata hybrid, the CZTS nanoparticles act as light absorbers, generating reducing equivalents (electrons/H₂) that drive microbial CO₂ conversion. Under continuous illumination for five days, the system exhibited excellent biocompatibility and reusability, yielding acetate (1.035 ± 0.05 mmol g⁻¹) and ethanol (0.967 ± 0.04 mmol g⁻¹). These C₂ intermediates were subsequently upgraded via microbial chain elongation by Clostridium kluyveri (C. kluyveri), producing C₄ butyric acid (2.78 ± 0.2 µmol), C₆ caproic acid (1.08 ± 0.3 µmol), and H₂ (2.4 ± 0.4 µmol). This integrated photocatalysis–fermentation strategy showcases a sustainable route for solar-to-chemical energy conversion, offering a promising solution for carbon valorisation through the convergence of materials science and biotechnology.