High-Density Single-Atomic Mn-N-C Site in Hierarchical Porous Biochar for Superoxide Radical-Dominated Ozonation

In this work, biomass-derived single-atomic (Mn-N-C) materials with hierarchical porous structures are synthesized through a double-anchoring strategy. Expandable biomass of semen sterculia lychnopherae is used with strong adsorption ability for Mn precursors. High contents of atomic Mn (7.8 wt %) is bonded with astonishing doped N (20.74 at %) to form pyridinic-type Mn-N4 coordination. For ozonation, 100% of 50 ppm 4nitrophenol could be rapidly degraded within 30 min with negligible Mn leaching (similar to 0.04 mg/L), better than lots of commercial MnOx catalysts. Compared with nitrogen-doped biomass carbon (BNC), introduction of atomic Mn will convert the dominated reactive oxidation species (ROSs) from center dot OH into O2 center dot- with longer lifespans. According to DFT calculations, O3 will be first adsorbed on the catalyst to form Mn-N4-O*ad intermediate, which will react with H2O to generate center dot OH on BNC and react with dissolved O3 to produce O2 center dot- on the Mn-N4 sites, thus revealing a different O3 activation mechanism on Mn-N-C catalysts.