Rapid Electron Transfer at the Organo–OrganicInterface: Black Carbon-Mediated Electron Shuttling Enhances ROS Generation during Solid Organic Matter Oxidation

Black carbon (BC) is produced by incomplete biomass combustion and serves as a key electron shuttle in subsurface environments, where it coexists with reduced solid organic matter (SOM_red). However, the role of BC’s abundant redox moieties in mediating electron transfer from SOM_red to O₂ during redox fluctuations remains unexplored. In this study, four BC types were prepared from distinct biomass precursors (pine wood and zein) at different pyrolysis temperatures (500°C and 800°C). BC enhanced hydroxyl radical (•OH) production by 1.2–1.8 fold compared with SOM_red alone. Notably, a two-electron transfer pathway dominated •OH formation in both systems. BC amplified •OH production mainly by promoting electron release from the solid phase of SOM_red. Characterization and model experiments revealed that graphite crystallites accelerated electron transfer, while quaternary N groups increased electron release from SOM_red, as demonstrated by electrochemical analysis and DFT calculation. This •OH-enhancement process further facilitated As(III) removal. These findings highlight BC’s significant potential to mediate solid-phase electron transfer in SOM-rich environments.