New insights into the formation and transformation of active species in nZVI/BC activated persulfate in alkaline solutions

In this study, a nanocomposite material synthesized by loading nanoscale zerovalent iron (nZVI) onto biochar (BC, gasification plant byproduct) was successfully prepared, and the nZVI/BC5 (mass ratio 1:5) exhibited oxidative resistance, reutilization and stability via COD removal experiments. The nZVI/BC5 nanocomposites was used in persulfate (PS) activation for the synergistic degradation of aromatic pollutants in alkaline wastewater. The nZVI/BC5 selectively adsorbed aromatic pollutants through π-π, π-π-metal (BCsurface-OFeO) bonding interactions in textile dyeing wastewater (TDWW), and make the free radicals easier to react to aromatic pollutants. FTIR, XPS and EPR analyses showed that some PFRs generated through the reaction between nZVI and the surface functional groups of BC, the other PFRs were transformed from the BCsurface-OFeO species. The chemisorption provided electrons for the BCsurface-O-Fe(III)O- to produce the BCsurface-Ȯ··Fe(II)-O- (persistent free radicals, PFRs). The formation and transformation of the BCsurface-OFeO species were the dominant processes in the radical pathways, they could quickly and sustainably produce SO4·- and ·OH through heterogeneous catalytic oxidation of water (mediator) and S2O82- (from 0.81 to 0.02 g/L). Finally, a favorable synergistic combined process was initiated via chemisorption and degradation of aromatic pollutants. The BCsurface-OFeO species offer a new understanding of synergistic heterogeneous degradation in alkaline solutions. The byproduct BC could be reused and applied in wastewater pretreatment by this new feasible strategy.