Activation of sulfite by metal-organic framework-derived cobalt nanoparticles for organic pollutants removal.

Sulfite (SO32-) activation is one of the most potential sulfate-radical-based advanced oxidation processes, and the catalysts with high efficiency and low-cost are greatly desired. In this study, the cobalt nanoparticles embedded in nitrogen-doped graphite layers (Co@NC), were used to activate SO32- for removal of Methyl Orange in aqueous solution. The Co@NC catalysts were synthesized via pyrolysis of Co2+-based metal-organic framework (Co-MOF), where CoO was firstly formed at 400℃ and then partially reduced to Co nanoparticles embedded in carbon layers at 800℃. The Co@NC catalysts were more active than other cobalt-based catalysts such as Co2+, Co3O4 and CoFe2O4, due to the synergistic effect of metallic Co and CoxOy. A series of chain reaction between Co species and dissolved oxygen was established, with the production and transformation of SO3•-, SO52-, and subsequent active radicals SO4•- and HO•. In addition, HCO3- was found to play a key role in the reaction by complexing with Co species on the surface of the catalysts. The results provide a new promising strategy by using the Co@NC catalyst for SO32- oxidation to promote organic pollutants degradation.