N-doped biochar-Fe/Mn as a superior peroxymonosulfate activator for enhanced bisphenol a degradation

Emerging contaminants (ECs) are characterized by their widespread environmental distribution and low concentrations, posing significant challenges for their effective removal from source wastewater. To better deal with the problems associated with ECs, we developed a robust Fe-Mn bimetallic catalyst supported on N-doped biochar (FM@NBC-8) for peroxymonosulfate (PMS)-mediated advanced oxidation system, in which bisphenol A (BPA) was investigated as a typical EC. Particularly, complete degradation of BPA in the FM@NBC-8/PMS system was achieved within 5 min, accompanying with a high TOC removal. The degradation rate of BPA with FM@NBC-8 was 143 times that of the initial biochar (BC-8), 20 and 91 times that of single metal-doped catalysts Fe (F@NBC-8) and Mn (M@NBC-8), respectively. The degradation rate of BPA was enhanced to 1.7337 min^⁻1 with 0.6 g L^⁻1 FM@NBC-8 utilized to activate PMS, achieving a superior performance in BPA degradation compared to most reported results in the literature (0.081∼1.43 min^⁻1). The introduction of Fe, Mn, and N elements dramatically enhanced the specific surface area (from 46.285 to 218.541 m² g^⁻1) of the catalyst, thereby enhancing the adsorption capacity of PMS and pollutants on the catalyst. Moreover, the accelerated electron transfer between the catalyst and PMS favored the formation of low-valent metal intermediates (Fe(II)-O-O-SO₃^- and Mn(II)-O-O-SO₃^-), responsible for the generation of SO₄^•-and ^•OH. And ¹O₂ was generated mainly via the decomposition of SO₅^•- in FM@NBC-8/PMS system, thereby collectively enhancing the pollutant degradation. The stability of the catalyst was attributed to the synergistic effects of nitrogen doping and biochar encapsulation, which ensured effective operation of the FM@NBC-8/PMS system across a broad pH range of 3 to 10, while also providing resistance to interference from ubiquitous anions. This study indicates that the bimetal biochar-based materials for catalytic PMS activation have significant potential for practical application in green environmental remediation.