Oxygen vacancy induced peroxymonosulfate activation by NixZn1−xFe2O4 for the effective degradation of tetracycline in water

Herein, a series of NixZn1−xFe2O4 catalysts with various content of oxygen vacancy were prepared by adjusting the doping content of Ni and applied to activate peroxymonosulfate (PMS) for the degradation of tetracycline (TC). When x = 0.6, Ni0.6Zn0.4Fe2O4 with the most oxygen vacancy presented the highest TC removal efficiency and the maximum apparent rate constant (kapp). In Ni0.6Zn0.4Fe2O4/PMS system, about 95.6% of TC was degraded within 60 min, and the kapp was 0.113 min−1, which was 10.18 and 3.47 times of the ZnFe2O4/PMS and NiFe2O4/PMS systems. Significantly, the role of oxygen vacancy on Ni0.6Zn0.4Fe2O4 surface was investigated. It was found that PMS ([O3S-O-O-H]-) could be adsorbed and captured by oxygen vacancy on Ni0.6Zn0.4Fe2O4 surface, and PMS could be further reduced by the free electrons in oxygen vacancy to generate SO4•- and •OH radicals. The production of 1O2 also be related to the surface oxygen vacancy. TC was attacked and mainly degraded by these three reactive oxygen species (ROS). In addition, TC could be also directly oxidated by donating electrons to the metastable complex that was formed by the reaction between Ni0.6Zn0.4Fe2O4 and PMS.