Ultrasonic role to activate persulfate/chlorite with foamed zero-valent-iron: Sonochemical applications and induced mechanisms

The novel system, consisting of composite oxidants (persulfate/chlorite, S(2)O(8)(2−)/ClO(2)(−)) and stationary phase activator (zero-valent-iron foam, Fe(0)(f)) driven by ultrasonic (US) field, was applied to treat the triphenylmethane derivative effectively even at low temperature (≈ 289 K). By comparisons of sub-systems, the US roles to S(2)O(8)(2−), ClO(2)(−), and Fe(0)(f) were seriatim analyzed. US made the reaction order of multi-component system tend to within 1 (leading to de-order reaction), and widened pH activating range of the Fe(0)(f) by sonicate-polishing during the process of ClO(2)(−) co-activating S(2)O(8)(2−). US and Fe(0)(f) were affected by fluid eddy on activating S(2)O(8)(2−)/ClO(2)(−). The Fe(0)(f) had slight effect on the temperature of US bubble-water interface but the addition of ClO(2)(−) lowered it. The partitioning capacity of the above US reactive zone increased during the reaction. US and ClO(2)(−) could enrich the kinds of degradation intermediates. The contributions of free radicals (ClO(x)-based radicals, sulfate radicals (SO(4)•(−)), and hydroxyl radicals (•OH)) and non-free radicals (ClO(2), and O = Fe(IV/V) from ionic Fe under “-O-O-” of S(2)O(8)(2−) and cyclic adjustment reaction of ClO(2)(−)) processes by sonochemical induction were equally important by corresponding detection means. Especially, real-time and online high-resolution mass spectrum by self-developing further confirmed the chain transfers of different free radicals due to US role. The findings expanded the application of sono-persulfate-based systems and improved understanding on activation mechanism.