A novel insight into the microwave induced catalytic reduction mechanism in aqueous Cr(VI) removal over ZnFe2O4 catalyst.

Abstract

Aqueous Cr(VI) pollution is an emerging environmental issue. Herein, a sphere-like ZnFe2O4 catalyst with a size of ∼430nm was prepared by a solvothermal method, by which the aqueous Cr(VI) in a 50mL solution with concentration of 50mg/L was completely removed after 10min-microwave (MW) irradiation. "Surface temperature visualization" tests and COMSOL simulations showed that the surface temperature of the as-prepared ZnFe2O4 catalysts could be as high as >1000°C only after 300sMW irradiation, and the work function calculations and scavenging experiments demonstrated that the excited electrons derived by the "hot spots" effect of the ZnFe2O4 catalysts reduced the Cr(VI) to Cr(III). Kinetic reaction process of the reduction of *Cr2O72- to *CrO3H3 over the ZnFe2O4 catalysts was clarified by using DFT calculation, and the results indicated that *Cr2O72- adsorbed on the Fe atoms was more easily to be reduced, and that Fe atoms played more significant roles than the Zn and O atoms in ZnFe2O4 catalysts. The present study not only proves that the MW induced ZnFe2O4 catalytic reduction was promising for ultrafast remediation of toxic Cr(VI), but also provides a new insight into the corresponding mechanism.