High H-abstraction efficiency of Ni(II)-Ni(III)-Ni(II) cycle mediated oxidation of aromatic contaminants by peroxydisulfate

Abstract

Peroxydisulfate (PDS) activation has attracted great attention for the treatment of aromatic contaminants in wastewater. In this study, the synthesized β-Ni(OH)2 exhibits remarkable reactivity in the catalytic oxidation of aromatic contaminants of phenol and aniline under alkaline conditions at a low molar ratio of 2:1 between the initial PDS and aromatic contaminants, indicating that the aromatic contaminants have not been completely mineralized into CO2 and H2O. By means of quenching experiments, LSV analysis and various characterizations, we rule out the primary contributions of •OH, SO4•−, O2•−, 1O2 or the non-radically activated PDS complexes to the oxidation processes. Instead, the oxidation cycle of Ni(II)-Ni(III)-Ni(II) plays the predominant role. DFT calculations further reveal the strong adsorption of phenol (-1.217 eV) and aniline (-1.166 eV) on β-NiOOH surface, which subsequently initiates H-abstraction from phenol and aniline by β-NiOOH with low interaction barriers of 0.119 eV and 0.467 eV, respectively. The produced aromatic radicals then undergo polymerization to produce phenol and aniline polymers. This work provides new insight on PDS activation and offers an effective and cost-saving approach for the removal, recycling, and synthesis of aromatic polymers.