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, S₂O₈²⁻/ClO₂⁻) and stationary phase activator (zero-valent-iron foam, Fe⁰_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 S₂O₈²⁻, ClO₂⁻, and Fe⁰_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 Fe⁰_f by sonicate-polishing during the process of ClO₂⁻ co-activating S₂O₈²⁻. US and Fe⁰_f were affected by fluid eddy on activating S₂O₈²⁻/ClO₂⁻. The Fe⁰_f had slight effect on the temperature of US bubble-water interface but the addition of ClO₂⁻ lowered it. The partitioning capacity of the above US reactive zone increased during the reaction. US and ClO₂⁻ could enrich the kinds of degradation intermediates. The contributions of free radicals (ClO_x-based radicals, sulfate radicals (SO₄[rad]⁻), and hydroxyl radicals ([rad]OH)) and non-free radicals (ClO₂, and O = Fe^IV/V from ionic Fe under “-O-O-” of S₂O₈²⁻ and cyclic adjustment reaction of ClO₂⁻) 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.