Activation of peroxymonosulfate by graphitized hierarchical porous biochar and MnFe2O4 magnetic nanoarchitecture for organic pollutants degradation: Structure dependence and mechanism

Three novel graphitized hierarchical porous biochar (MX) and MnFe2O4 magnetic composites (MnFe2O4/MX) have been prepared for degrading organic pollutants by peroxymonosulfate (PMS) activation. MX including MS, ML, MC synthesized using corn stems (S), leaves (L) and cores (C) as raw materials, respectively, possesses hierarchical porous structure, graphitization domains and tremendous surface area. The orange II removal effects of MX and MnFe2O4/MX outperform the corresponding carbonization products, despite that adsorption probably undertakes the major removal efficiency for MX and degradation contributes the most for MnFe2O4/MX. A structure-dependent degradation efficiency is discovered for MX and MnFe2O4/MX, among of which both MS and MnFe2O4/MS present the best removal effect, by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The lowest EIS owning to its better balance between graphitization degree and specific surface area and micropore volume of MnFe2O4/MS among MnFe2O4/MX explains its best catalytic activity. The catalytic degradation occurs by the following three ways. First, the radical-induced oxidation is attained by surface-bound SO4− and OH on MnFe2O4 nanoclusters and hierarchical porous carbon nanosheets generated by one-electron reduction of PMS under the participating and coupling of Mn(III)/Mn(II), Fe(III)/Fe(II), O2/O2−, and active sites on carbon surface. Second, non-radical pathway involves the contribution of 1O2, which is produced in a large quantity by promoted self-decomposition of PMS in presence of MnFe2O4/MS. Third, non-radical pathway is achieved through electron transfer from organic compounds as electron donator to PMS as electron acceptor mediated by graphitization structures. Taking into consideration the excellent degradation performance, easy magnetic separation, and bulk availability of MnFe2O4/MS, this work is expected to pave a new way for precision utilization of corn biomass-based biochar for environmental application.