Roles of oxysulfur radicals in the oxidation of acid orange 7 in the Fe(III)-sulfite system

The Fe(III)-sulfite system has been regarded as a new alternative for the systems containing persulfate or peroxymonosulfate in the oxidation of organic contaminants in water or wastewater. Here, a detailed theoretical analysis was made on the inhibitory activities of the inhibitors (ethanol, tert-butyl alcohol, 1-hexanol, aniline, diphenylamine, and pyrogallol (PA)) to examine the roles of oxysulfur radicals in the oxidation of the azo dye acid orange 7 (AO7) in the Fe(III)-sulfite system. Experimental results confirm the expected concentration of inhibitors for the complete inhibition of specific radicals and establish that the combination of 1-hexanol and PA was suitable for analyzing the role of [GRAPHICS] and [GRAPHICS] . [GRAPHICS] and [GRAPHICS] contributed 57.1% and 42.9%, respectively, to the oxidation in the presence of oxygen at pH 3, which means that [GRAPHICS] makes comparable contribution as [GRAPHICS] in the oxidation of specific organic pollutants like AO7 in this system. [GRAPHICS] reacts with AO7 only in the absence of oxygen. The second-order rate constants for the reaction of AO7 with [GRAPHICS] or [GRAPHICS] were determined to be 1.2 x 10(7) and 2.1 x 10(6) M-1 s(-1), respectively. The proper combination of inhibitors should be taken into account when probing the roles of multiple radicals.