Insights into the mechanism of redox pairs and oxygen vacancies of Fe2O3@CoFe2O4 hybrids for efficient refractory organic pollutants degradation

Abstract

The core-shell Fe2O3@CoFe2O4 hybrids microspheres with abundant oxygen vacancies were synthesized through in-situ ion exchange-calcination method and employed to induce peroxymonosulfate (PMS) to eliminate organic pollutants. The superior catalytic activity and stability of Fe2O3@CoFe2O4 were attributed to the synergistic effects of M2+/M3+ (M denotes Co or Fe) redox cycles. SO4·-, ·OH, O2·- and 1O2 were proved to be the main reactive oxygen species (ROS) involved in the phenol degradation process through quenching experiments and EPR measurements, while the surface-bound SO4·- played a dominant role. Trace metal ions leached during the reaction enhanced the PMS activation, and the oxygen vacancies electron transfer process played a critical role in the formation of O2·-/1O2 and the cycle of M2+/M3+ redox pairs. The formation of ROS and function of 1O2 were also revealed from bulk reaction and interface reaction. This study highlighted the simultaneous evolution of PMS reduction and oxidation to generate ROS, which provided an insight into the efficient catalytic degradation of persistent organic pollutants (POPs).