Urchin-like Ni-Fe-Mo sulfide: An effective electrochemical calcium sulfite activator for tetracycline degradation

Sulfite is deemed as a promising precursor to produce highly reactive species for contaminants remediation. Herein, the urchin-like Ni-Fe-Mo sulfide (NiFeMoSx) was anchored in-situ on nickel foam as the cathode to activated CaSO3 for efficient degradation of tetracycline (TC) under natural condition. The degradation efficiency reached 92.7% within 60 min, which was about 1.81 times higher than that of the electro-Fenton process based on NiFeMoSx. The beneficial performance came from the synergistic activation of CaSO3 by simultaneous rapid redox cycles of Fe(II)/Fe(Ⅲ) and Ni(II)/Ni(Ⅲ) on the NiFeMoSx cathode. Specifically, the primary intermediates Fe(Ⅱ)-HSO3- and Ni(Ⅱ)-SO32- triggered a series of radical chain reactions, accompanied the reduction of Ni(Ⅲ)/Fe(Ⅲ) by electrochemistry and electron donor of Mo(Ⅳ) and S2- on the surface of the catalyst. The regeneration of the Fe(Ⅱ)/Ni(Ⅱ) was quickly realized and subsequently triggered the chain reactions, which would accelerate the formation rate of reactive species, such asSO4∙−, ·OH, O2∙− and 1O2, of which 1O2 and O2•- played important roles on degradation TC. This work provides a promising application for the efficient removal of persistent organic pollutants by metal sulfide activated sulfite.