Insights into Mn-doped biochar induce peroxymonosulfate activation for phenol degradation: The overlooked significance of C-O-Mn

Abstract

Understanding the metal bonding types in biochar and their effects on peroxymonosulfate (PMS) activation is essential for selecting appropriate biomass and developing efficient catalysts. This study reports a dual-pathway non-radical oxidation system activated by Mn-doped biochar (P-Mn-TPs-900). In the P-Mn-TPs-900/PMS system, phenol degradation reached 100 % within 60 min across a broad pH range (5 −10). Additionally, this oxidation system exhibited excellent stability (5 cycles), maintaining at least 74 % degradation efficiency in the presence of background ions or humic acid. Experimental results and density functional theory (DFT) calculations identified: i) C-O-Mn sites as the primary active sites for PMS activation, facilitating the formation of singlet oxygen (¹O₂) which was the key reactive oxygen species for phenol degradation; ii) phenol adsorbed on the P-Mn-TPs-900 surface was degraded via an electron transfer process between sulfate groups and phenol. DFT calculations showed strong hybridization between the Mn 3d-orbital, the O 2p-orbital, and the corresponding 2p-orbitals of carbon, which enhanced biochar's catalytic capability. This study provides insights into the role of the C-O-Mn site in PMS activation and offers guidance for selecting suitable biomass for developing practical Fenton-like systems in wastewater treatment.