Fabrication of Fe3O4 and graphitized porous biochar composites for activating peroxymonosulfate to degrade p-hydroxybenzoic acid: Insights on the mechanism

The novel Fe3O4 and porous biochar originated from Myriophyllum aquaticum composites (Fe3O4/MC) with graphitized structure, hierarchical porous and strong magnetism were used as efficient catalysts for degradation of organic pollutants in the presence of peroxymonosulfate (PMS). Three types of catalysts pyrolyzed at 600, 700, 800 °C manifested quit different PMS activation effect with the much better p-hydroxybenzoic acid (HBA) degradation efficiency at 700 and 800 °C than that of 600 °C, which was assigned to the high graphitization degree and mesopores ration of catalysts pyrolyzed at higher temperature. Based on radicals quenching experiments and electron paramagnetic resonance (EPR) analyses, the radical pathway dominated by surface-bound SO4− was the prevailing way while the non-radical pathway performed as electro-transfer was the recessive way during the degradation process. The large amount of surface-bound SO4− radicals were produced through the reduction of PMS by Fe(II), which was regenerated by participation of O2−/O2. The non-radical pathway was achieved by the graphitized structure which acted as electron transfer bridges accepting electrons form organic pollutants and denoting electrons to PMS. Six HBA intermediates were detected and the possible HBA degradation pathway was proposed tentatively. Consequently, the conversion of Myriophyllum aquaticum to composite catalyst provides a brand-new idea for efficient utilization of waste biomass in a high value-added way and simultaneously achieving the contaminants elimination.