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 (NiFeMoS x ) was anchored in-situ on nickel foam as a cathode to activate CaSO 3 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 NiFeMoS x . The beneficial performance came from the synergistic activation of CaSO 3 by simultaneous rapid redox cycles of Fe(II)/Fe(III) and Ni(II)/Ni(III) on the NiFeMoS x cathode. Specifically, the primary intermediates Fe(II)-HSO 3 - and Ni(II)-SO 3 2- triggered a series of radical chain reactions, accompanied the reduction of Ni(III)/Fe(III) by electrochemistry and electron donor of Mo(IV) and S 2- 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 as  SO 4 ∙ − , ·OH, O 2 ∙ − and 1 O 2 , of which 1 O 2 and O 2 •- 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.