Intrinsic peroxidase-like activity of dissolved black carbon released from biochar

Dissolved black carbon (DBC) is an important constituent of the natural organic carbon pool, influencing the global carbon cycling and the fate processes of many pollutants. In this work, we discovered that DBC released from biochar has intrinsic peroxidase-like activity. DBC samples were derived from four biomass stocks, including corn, peanut, rice, and sorghum straws. All DBC samples catalyze H₂O₂ decomposition into hydroxyl radicals, as determined by the electron paramagnetic resonance and the molecular probe. Similar to enzymes that exhibit saturation kinetics, the steady-state reaction rates follow the Michaelis-Menten equation. The peroxidase-like activity of DBC is controlled by the ping-pong mechanism, as suggested by parallel Lineweaver-Burk plots. Its activity increases with temperature from 10 to 80 °C and has an optimum at pH 5. The peroxidase-like activity of DBC is positively correlated with its aromaticity as aromatics can stabilize the reactive intermediates. The active sites in DBC also involve oxygen-containing groups, as inferred by increased activity after the chemical reduction of carbonyls. The peroxidase-like activity of DBC has significant implications for biogeochemical processing of carbon and potential health and ecological impacts of black carbon. It also highlights the need to advance the understanding of the occurrence and role of organic catalysts in natural systems.