Photodriven Carbon Nitride Nanosheet-Bacterium Biohybrid with an Encapsulation Structure for CO₂ to C₄ Bioplastic Conversion

Converting CO2 into multicarbon products with high value and energy density is hindered by technical bottlenecks, including low efficiency and poor selectivity. The biohybrid combining photocatalysts with the bacterium Ralstonia eutropha presents the potential to synthesize the C4 Bioplastic polyhydroxybutyrate (PHB) from CO2. However, existing nonmetallic biohybrids rely on supplementary additives and exhibit limited PHB yields. To overcome these challenges, we designed a biohybrid composed of carbon nitride nanosheets (CNNS) and R. eutropha that operated without any sacrificial agents or auxiliary additives. This biohybrid utilized CO2 to produce PHB under weak indoor light, achieving a PHB production rate of 37.25 ± 0.9 mg L–1 day–1, surpassing the reported performance of both metal-based biohybrids and additive-assisted nonmetallic biohybrids. Distinct from bulk aggregation structures, CNNS-R. eutropha formed an encapsulation structure with CNNS enveloping bacterial cells. This configuration enhanced the contact area at the abiotic–biotic interface, enabling efficient integration and promoting interfacial material transport. The biohybrid structure reduced charge transfer resistance and enhanced electron–hole separation efficiency. The mechanisms of CO2 conversion and electron transfer within the CNNS-R. eutropha biohybrid were proposed. Upon light excitation, CNNS generated photoexcited electrons that reduced H2O to produce H2. The evolved H2 interacted with either soluble hydrogenases or membrane-bound hydrogenases, facilitating the synthesis of reducing equivalent NADPH and energy carrier ATP. These drove the Calvin cycle, converting CO2 into key carbon metabolic intermediates, ultimately resulting in PHB synthesis. This work presents a high-yield biohybrid system, offering a sustainable and economical approach for multicarbon production from CO2.