Accelerated oxidation of micropollutants in the frozen Fenton-like processes at ultra-low-dose catalyst

The application of homogeneous Fenton-like processes based on peracetic acid (PAA) is seriously constrained by the sluggish reaction kinetics and the requirement for acidic pH. This work proposes a freezing-induced strategy that markedly accelerates PAA activation by Fe(III) even at ultra-low dosages. A striking 152.0-fold increase was observed in the pseudo-first-order rate constant for sulfamethoxazole (SMX) degradation upon transitioning the PAA-Fe(Ⅲ) system from room temperature to frozen conditions at neutral pH. Mechanistic investigation revealed that SMX oxidation in the frozen system was predominantly governed by nonradical pathway, specifically high-valent metal species, rather than conventional radical process. Confocal Raman spectroscopy further confirmed that contaminant degradation occurred primarily in the liquid channels between ice crystals. Theoretical calculations demonstrated that the ice-water interface enriched reactant concentrations locally, lengthened bonds, and lowered crucial reaction energy barriers, accelerating the Fenton-like reaction. In addition, a kinetic model quantitatively captured the time-resolved evolution of iron species, identifying Fe(V) as the dominant reactive intermediate, contributing 77.49% to SMX oxidation. Importantly, the frozen system maintained effective degradation performance in real wastewater. This study offers a promising avenue for overcoming the kinetic limitations of conventional Fenton-like systems, establishing a new paradigm for cold-region water remediation.