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

Abstract

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.

Rapid catalytic oxidation of arsenite to arsenate in an iron(III)/sulfite system under visible light

“…Although SO4 − •-based advanced oxidation processes (S-AOPs) have drawn great attention in recent decades [22,24,25], little is known about the mechanism of As(III) oxidation by S-AOPs and the nature of the reactive oxygen species involved. The system using sulfite (generally expressed as S(IV)) as reactant and iron(II), iron(III), or light as inductor can also produce SO4 − • [26]. Recently, iron(II)/(III)-sulfite systems with or without UV light have been used to decolorize azo dyes, but dye mineralization in such systems is very poor [27][28][29][30].…”

An effective heterogeneous iron-based catalyst to activate peroxymonosulfate for organic contaminants removal

“…Among these various AOPs, activated peroxymonosulfate (PMS) oxidation has been regarded as an interesting treatment method because PMS is more easily activated compared with hydrogen peroxide, which is one of the most commonly used oxidants in AOPs [7,8]. Although some research has demonstrated that heat and UV irradiation can be used to activate PMS to generate powerful radicals, these techniques are restricted in practical application owing to their high energy input [9,10].…”

Comparative Study of the Oxidative Degradation of Different 4-Aminobenzene Sulfonamides in Aqueous Solution by Sulfite Activation in the Presence of Fe(0), Fe(II), Fe(III) or Fe(VI)

“…The photo Fe(III)/sulfite system was also efficient at degrading bisphenol A around neutral pH [31]. Guo et al [29] demonstrated the effective degradation (90%) of 2,4,6-trichlorophenol within 180 min at pH 4 by the UV/Fe(III)/sulfite system. On the other hand, Fe(VI) alone is a powerful oxidant [32] and, in combination with sulfite, enhances the generation of oxidizing species.…”

“…The use of Fe(II)-Fe(III)/sulfite systems are, therefore, good candidates for their use in the detoxification of contaminated water [22][23][24][25][26][27][28][29][30]32,34]. Fe(0) represents an alternative as an activator in radicals generation [35], and the use of Fe(VI) and sulfite produces a synergic effect, speeding up the removal of contaminants [28].…”