Novel Photo-Sulfite System: Toward Simultaneous Transformations of Inorganic and Organic Pollutants

An efficient and green advanced oxidation process (i.e., photo-sulfite reaction) for the simultaneous oxidation of sulfite and organic pollutants in water is reported. The photo-sulfite system (UV–Fe(III)–sulfite) is based on the Fe-catalyzed sulfite oxidation and photochemistry of Fe(III) species. SO4 •– and •OH radicals were identified in the photo-sulfite system with radical scavenging experiments using specific alcohols. This novel technology was consistently proven to be more favorable than the alternative Fe(III)–sulfite systems for the degradation of 2,4,6-trichlorophenol (2,4,6-TCP) and other organic pollutants at all conditions tested. The reactivity of photo-sulfite system was sustained due to the spontaneous switch of photoactive species from Fe(III)–sulfito to Fe(III)–hydroxo complexes with the depletion of sulfite and the decrease in pH. In contrast, in the absence of light the performance of the Fe(III)–sulfite system was greatly diminished after the consumption of sulfite. The formation of the Fe(III)–sulfito complex is a necessary step for initiating the photo-sulfite reaction. Inhibition of the oxidation of 2,4,6-TCP and methyl orange (MO) was observed in the presence of ligands that can stabilize one or more of the reactants: Fe(III), Fe(II), or sulfite. Our study provides a new facile route for the generation of SO4 •– and simultaneous removal of organic and inorganic pollutants.