Integration of sulfur nanoparticles as dual electron donors in a photosensitizer-microbe hybrid for photocatalytic CO₂-to-polyhydroxybutyrate conversion.

Despite aligning with circular economy principles, emerging CO2-to-bioplastic photo-biohybrid technology faces critical solar-to-chemical efficiency bottlenecks that threaten ecological/economic viability. This study introduces an innovative ternary hybrid system combining sulfur nanoparticles (SNPs) with the semiconductor graphitic carbon nitride (g-C3N4) and the photosynthetic bacterium Rhodopseudomonas palustris. Our findings reveal SNPs' bifunctional role as (1) a hole scavenger that enhances charge separation in g-C3N4 photocatalysts and (2) a bioavailable electron donor promoting bacterial growth under photoautotrophic conditions. The optimized g-C3N4-SNPs-R. palustris system achieved remarkable poly-β-hydroxybutyrate production titer of 3.19 ± 0.03 g/L with 11.79 % ± 0.93 % quantum efficiency using solely CO2 and SNPs as inputs. Through an economic and environmental assessment, we demonstrate that this sulfur-mediated photobiohybrid strategy effectively bridges two environmental challenges: atmospheric CO2 sequestration and petroleum plastic replacement. This work establishes a circular solar biomanufacturing prototype converting carbon waste streams into biodegradable plastics.