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–N 4 coordination. For ozonation, 100% of 50 ppm 4-nitrophenol could be rapidly degraded within 30 min with negligible Mn leaching (∼0.04 mg/L), better than lots of commercial MnO x catalysts. Compared with nitrogen-doped biomass carbon (BNC), introduction of atomic Mn will convert the dominated reactive oxidation species (ROSs) from · OH into O 2 · – with longer lifespans. According to DFT calculations, O 3 will be first adsorbed on the catalyst to form Mn–N 4 –O* ad intermediate, which will react with H 2 O to generate · OH on BNC and react with dissolved O 3 to produce O 2 · – on the Mn–N 4 sites, thus revealing a different O 3 activation mechanism on Mn–N–C catalysts.