Ultrafast activation of peroxymonosulfate by reduction of trace Fe³⁺ with Ti₃C₂ MXene under neutral and alkaline conditions: Reducibility and confinement effect

Ultrafast activation of peroxymonosulfate (PMS) by reduction of trace Fe³⁺ at the μg L^-1 level with the ecofriendly Ti₃C₂ MXene under neutral and alkaline conditions was achieved for the first time. Complete removal of model pollutant sulfamethoxazole (SMX) was accomplished within about 5 min and 10 min at pH 7.0 and 9.0, respectively. The degradation rate of SMX in Fe³⁺/PMS/MXene process was increased by 72 times compared with that in the absence of Ti₃C₂ MXene (pH = 7). Methanol/tert-butanol quenching experiment and electron spin resonance (ESR) measurement demonstrated that hydroxyl radical (^•OH) and sulfate radical (SO₄^•–) were the primary reactive species. The strong reducibility of Ti₃C₂ MXene played the key role in triggering the Fe(III)/Fe(II) cycle and accelerating PMS activation. The reducibility of Ti₃C₂ MXene towards Fe³⁺ was measured to be 3.35:1–5.03:1 (mol:mol), far higher than that of hydroxylamine (1:1). Because the confinement effect of MXene inhibited the hydrolysis of iron ions, Fe³⁺/PMS/MXene process exhibited excellent performance even under neutral and alkaline conditions. This study improved the understanding of MXene in Fenton-like reaction and provided an ideal Fenton-like process with ultra-low metal consumption, high efficiency and broad pH range.