A mutually beneficial waste-to-biochar strategy: Mn-mediated dual enhancement of 5-HMF production and catalytic performance

The concept of converting biowaste to energy is popular worldwide; however, overcoming the trade-off between bio-oil recovery and obtaining functional biochar remains challenging. This study investigated the effects of three transition metal ions (Mn 2+ , Cu 2+ and Fe 2+ ) throughout the entire process of recovering 5-hydroxymethylfurfural (5-HMF) from forestry waste and on the catalytic abilities of biochar derived from the oil-extracted residue. The Cu 2+ , Fe 2+ , and Mn 2+ ions significantly increased 5-HMF yields by 93- to 158-fold compared to the metal-free control. However, only marginal improvements in the catalytic ability of the residue-derived biochar for persulfate activation were observed for Cu- or Fe-doped biochar, despite the general benefit of transition metal doping for biochar functionalization. Interestingly, a dual Mn-mediated promotion was achieved beyond enhancing 5-HMF production. The Mn-doped biochar (Mn-Biochar) exhibited excellent peroxydisulfate (PDS) activation capability, enhancing the degradation of the antibiotic sulfamethoxazole (SMX) by 6.6- to 15.0-fold. Characterizations revealed that incorporated nitrogen was responsible for this enhancement. N-doping transformed the Mn species into MnO, which tripled the Mn loading capacity and enhanced the electrical conductivity of the biochar. The formed Mn-N x structure in the biochar (Mn-N-FBBC) facilitated polarization of the O O bond and cleavage of the S O bond in PDS, generating 1 O 2 for SMX degradation. Life cycle assessment (LCA) indicated that this dual Mn-mediated process for 5-HMF recovery and biochar production offers synergistic benefits, realizing the “waste-resource-material-treatment” paradigm in biomass conversion.