Wen Qin,Chengyuan Zheng,Haoming Qin,Yang Song,Yang Zhou,Jin Jiang,Jun Ma
Permanganate/electron shuttle systems for the enhanced transformation of anilines were evaluated. The presence of electron shuttles (2,2’-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS), 1-hydroxybenzotriazole (HBT) and catechol (CAT) accelerated the oxidative transformation of aniline by Mn(VII). In the Mn(VII)/ABTS process, ABTS •+ was partially consumed through fragmentation or polymerization with aniline, while the second-order rate constants ( k app 2 , M −1 s −1 ) of the interaction of ABTS •+ with aniline rose from 86.57 to 140.04 M −1 s −1 with increase in pH from 5 to 8. In the Mn(VII)/HBT system, aniline removal was markedly enhanced under acidic conditions due to the formation of polymerized products via radical cations (HBT • ). Furthermore, the oxidative transformation of aniline (82.5 %) by Mn(VII)/CAT was significantly higher than that by Mn(VII) (65.2 %) because of Michael addition reaction of aniline and ortho-benzoquinone (o-BQ). Moreover, the formation of Mn(III) was confirmed by the overall oxidation state (3.13) and the X-ray Photoelectron Spectroscopy (XPS) spectra of the Mn products in the CAT/Mn(VII) process, revealing a synergistic mechanism between o-BQ and Mn(III) for enhanced aniline degradation.
The permanganate/sulfite (Mn(VII)/sulfite) process has shown promise for degrading recalcitrant organic micropollutants, yet current methods to differentiate the roles of intermediate manganese species (IMS) and sulfate radicals (SO₄ •- ) show limitations. In this study, atrazine (ATZ) - a widely detected and oxidation-resistant herbicide - was used as a probe compound to investigate the reactivity of IMS and SO₄ •- generated in the Mn(VII)/sulfite system. ATZ exhibited negligible degradation by Mn(VII) alone but underwent rapid transformation within seconds in the presence of sulfite, with degradation efficiency increasing at lower pH and optimal [Mn(VII)]/[sulfite] ratios. Using stopped-flow spectrophotometry, pseudo-first-order kinetics were confirmed. Six major transformation products were identified, among which atrazine amide (CDIT) and desethyl-atrazine (DEA) were predominant. The molar ratio of CDIT to DEA ([CDIT]/[DEA]) was evaluated as a mechanistic indicator. A consistent ratio of ~4.8 at low sulfite levels indicated Mn(V)-dominated oxidation, while lower ratios at higher sulfite concentrations reflected increasing contributions from Mn(III) and SO 4 •− . This trend was supported across pH 3, 5, and 7. Water matrix components such as natural organic matter and nitrite were found to inhibit ATZ degradation, likely due to their scavenging of reactive species. This study establishes the [CDIT]/[DEA] ratio as a novel mechanistic indicator in manganese-activated oxidation and highlights the Mn(VII)/sulfite process as an effective strategy for degrading recalcitrant micropollutants in water treatment.
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