Regulating activation pathway of Cu/persulfate through the incorporation of unreducible metal oxides: Pivotal role of surface oxygen vacancies

In this paper, we surprisingly found that the incorporation of unreducible metal oxides MxOy (M = Mg, Zn, Ca, Ba, Al) onto CuO hybrid magnetic nano ferric oxide (Cu@Fe3O4) may alter the reaction pathway in persulfate activation, and increase the reaction rate constant. The activation of peroxymonosulfate (PMS) by Cu@Fe3O4 led to a classic sulfate radical based oxidation process (SR-AOP) with an acetaminophen (ACE) degradation rate constant of 0.004 min(-1), while O-1(2)-dominated nonradical oxidation process was disclosed in CuM@Fe3O4 with wildly fluctuated reaction rate constants from 0.003 to 0.242 min(-1). Mechanism studies indicated that singlet oxygen (O-1(2)) derived from the direct oxidation of superoxide anions radicals (O-2(center dot-)) or the recombination of O-2(center dot-) was the main reactive oxygen species (ROS) in CuM@Fe3O4/PMS system. A series of characterization experiments (pH(pzc) tests, XPS, H-2-TPR, et al.) and DFT calculation disclosed that the addition of an unreducible metal M yielded many positive effects: (1) the formation of surface oxygen vacancies (O-V) raised the zero point charge (pH(pzc)) of CuM@Fe3O4, thus enhanced the adsorption and activation of PMS; (2) promoting the generation of a new Cu species (Cu3+) on the surface of CuM@Fe3O4, which then participated in the generation of O-1(2). The different reducibility of Cu3+ led to differences in the catalytic properties of CuM@Fe3O4. In addition, the effects of various water matrix species and the results of reusability experiment, mineralization experiment, and ecotoxicity test exhibited that CuM@Fe3O4/PMS system possessed excellent practical application value.

Automated summary

The study found that incorporating unreducible metal oxides into CuO hybrid magnetic nano ferric oxide can alter the reaction pathway and increase the reaction rate in persulfate activation. In the CuM@Fe3O4/PMS system, O-1(2) dominates the nonradical oxidation process, indicating the importance of singlet oxygen in the system.