A novel insight into the microwave induced catalytic reduction mechanism in aqueous Cr(VI) removal over ZnFe2O4 catalyst
Gaoqian Yuan, Kezhuo Li, Jingzhe Zhang, Zhong Huang, Faliang Li, Haijun Zhang, Junkai Wang, Shaowei Zhang, Quanli Jia, Quanli Jia
Abstract
Aqueous Cr(VI) pollution is an emerging environmental issue. Herein, a sphere-like ZnFe 2 O 4 catalyst with a size of ∼430 nm was prepared by a solvothermal method , by which the aqueous Cr(VI) in a 50 mL solution with concentration of 50 mg/L was completely removed after 10 min-microwave (MW) irradiation. "Surface temperature visualization" tests and COMSOL simulations showed that the surface temperature of the as-prepared ZnFe 2 O 4 catalysts could be as high as > 1000 °C only after 300 s MW irradiation, and the work function calculations and scavenging experiments demonstrated that the excited electrons derived by the “hot spots” effect of the ZnFe 2 O 4 catalysts reduced the Cr(VI) to Cr(III). Kinetic reaction process of the reduction of *Cr 2 O 7 2− to *CrO 3 H 3 over the ZnFe 2 O 4 catalysts was clarified by using DFT calculation, and the results indicated that *Cr 2 O 7 2− 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 ZnFe 2 O 4 catalysts. The present study not only proves that the MW induced ZnFe 2 O 4 catalytic reduction was promising for ultrafast remediation of toxic Cr(VI), but also provides a new insight into the corresponding mechanism.