Temperature-regulated non-radical to radical oxidation of organic pollutants by peroxymonosulfate: A tale of ice and fire

It is generally assumed that the degradation efficiency of thermally activated peroxymonosulfate (TAP) oxidation processes is constrained at lower temperatures. This study explores the degradation of organic pollutants using peroxymonosulfate at −40 °C to 80 °C. The oxidative destruction of organic pollutants appeared to follow pseudo first-order kinetics, and an N-shaped degradation profile was observed for Acid Yellow 17 (AY17) as well as for other pollutants. The total organic carbon of AY17 was reduced after 4 h by 23.9 % at −20 °C and by 18.1 % at 80 °C. The direct oxidation of organic pollutants by peroxymonosulfate was significantly enhanced at −20 °C, attributed to the freezing concentration effect. At T ≥ 5 °C, an increase in temperature promoted the oxidation of organic substrates. The involvement of free radicals ([rad]OH and/or SO₄[rad]⁻) was verified at T ≥ 60 °C. The degradation rates of pollutants were markedly accelerated in the presence of chloride ions across the tested temperature range, as the freezing concentrated peroxymonosulfate (FCP) and TAP processes may facilitate the generation of hypochlorous acid (HClO). These findings contribute to a deeper understanding of the significant role that temperature plays in modulating the oxidation pathways of persulfate-based processes.