Cu2ZnSnS4-Sporomusa ovata photobiohybrids coupled with Clostridium kluyveri fermentation for CO2 conversion to C4-C6 fatty 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.