Ultra-small carbon dots boost bioelectricity generation by accelerating extracellular electron transfer

Bioelectrochemical systems incorporating carbon dots (CDs) show promise for both sustainable energy generation and wastewater treatment. The majority of currently available CDs are, however, potentially toxic and improperly sized for bioelectrochemical applications. In this study, ultra-small natural nitrogen-containing CDs were prepared using simple hydrothermal technology and common Hydrocotyle vulgaris leaves as starting material. These CDs, which have an average diameter of ∼1.3 nm, are readily taken up by bacterial cells and show excellent biocompatibility with the cells. When bound to the intracellular components of Shewanella oneidensis MR-1, the CDs substantially improve electron transport channels, leading to enhanced extracellular electron transfer (EET). This interaction not only stimulates the metabolism of S. oneidensis MR-1 but also increases the generation of bioelectricity. Biocells incorporating these CD-modified bacteria shows ∼11.2-, 2.0- and 13.1-fold increases in current, voltage and power output, respectively, compared with biocells incorporating unmodified bacteria. Our findings offer a viable method for producing biomass-based CDs that significantly improve EET, thereby amplifying bioenergy production.