Enhanced activation of PMS by a novel MnFe2O4@N-PC-GM composite for rapid 1-naphthol degradation: Formation and mechanism of singlet oxygen

A novel magnetic catalyst, MnFe2O4 functionalized N-doped porous carbon/geopolymer (MnFe2O4@N-PC-GM) composite, was synthesized using pine cones and geopolymer as precursors for efficient and sustainable removal of 1-naphthol. Experimental results indicated that MnFe2O4 particles were distributed in in the structure of N-PC-GM carrier, greatly increasing the number of active sites. The removal ratio of 1-naphthol was up to 86.06% in MnFe2O4@N-PC-GM/PMS system, and the degradation process followed pseudo-second-order kinetics (R2 = 0.996). Quenching experiments and EPR analysis validated that 1-naphthol was degraded in MnFe2O4@N-PC-GM/PMS system mainly through a non-radical oxidation pathway dominated by 1O2. X-ray photoelectron spectroscopy (XPS) and degradation experiments in different gas atmosphere demonstrated that the sources of 1O2 were closely related to the existence of oxygen vacancies (OVs), the conversion of dissolved oxygen as well as the introduction of active sites (N, Mn and Fe). Furthermore, the good degradation rate of 1-naphthol in real water confirmed the feasibility of MnFe2O4@N-PC-GM/PMS system in practical application. This work provided a new strategy for the treatment of persistent organic pollutants in water.