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• The novel Fe 2 CoTi 3 O 10 -MXene composite was successfully synthesized for PMS activation. • Fe 2 CoTi 3 O 10 -MXene composite exhibited excellent catalytic performance for the 2,4-D removal. • A ternary synergistic degradation was investigated based on Fe, Co and Ti species. • The possible activation mechanism and degradation pathway of 2,4-D were proposed. In this study, a novel Fe 2 CoTi 3 O 10 -MXene (FCT-M) composite was synthesized and employed as a heterogeneous catalyst for the oxidative degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) based on peroxymonosulfate (PMS) activation. The effects of catalyst dosage, PMS dosage, pH of the initial solution, 2,4-D concentration, and the co-existing inorganic ions (HCO 3 − and Cl−) and humic acid (HA) were systematically evaluated. The catalyst with the Fe 2 CoTi 3 O 10 loading (FCT-M-2) of 6.72% demonstrated superior catalytic performance. The results showed that around 98% of 2,4-D degraded in 15 min on using 0.2 g/L FCT-M-2 composite, 0.2 g/L PMS, and 20 mg/L 2,4-D with an initial pH of 7. The co-existence of sulfate radicals (SO 4 −) and hydroxyl radicals (OH) was confirmed based upon electron paramagnetic resonance spectroscopy and radical scavenger tests, while SO 4 − was identified as the main reactive species in the FCT-M/PMS catalytic system. The superior performance of FCT-M based on PMS activation was achieved due to remarkable synergistic effect of the active sites of three transition metals (Fe, Co, and Ti) on the catalyst surface. According to the identified intermediates, a possible 2,4-D degradation pathway is proposed. Overall, this study widens the scope of employing heterogeneous catalysts towards PMS activation and sheds light on the degradation of organic pollutants in aqueous solutions. [ABSTRACT FROM AUTHOR]

[Display omitted] • FeII/EDDS/UV/PAA was more effective than its subordinate processes in NAP degradation. • UV photoreduction and EDDS chelation assisted the FeII/FeIII cycle. • FeII/FeIII cycle in FeII/EDDS/UV/PAA process dominated the PAA activation. • A four-stage degradation model in FeII/EDDS/UV/PAA system was established. • Effects of Cl-/Br-, HCO 3 –/CO 3 2– and HA were comprehensively evaluated. The application of the integrated FeII/EDDS/UV/PAA (FEUP) process (EDDS = ethylenediamine- N,N' -disuccinic acid; PAA = peracetic acid) as a novel advanced oxidation process (AOP) for the degradation of a model contaminant, namely, naproxen (NAP), at neutral pH was investigated. The enhanced NAP degradation in this system at pH 7 was primarily attributable to the continuous activation of PAA via the UV-assisted FeII/FeIII cycle. A four-phase conceptual process of NAP degradation was established. The instantaneous degradation stage (IDS), in which FeII and PAA instantaneous react within 1 s, resulted in the degradation of ~ 20% of NAP. The rapid degradation stage (RDS), in which the regenerated FeII rapidly activates PAA to produce the hydroxyl radicals (•OH) and organic radicals including CH 3 C(O)O•, CH 3 C(O)OO•, CH 3 OO• and •CH 3 (defined as R-C•) without being scavenged by the FeII/FeIII-EDDS complexes, contributed to the degradation of ~ 55% of NAP. The slow degradation stage (SDS), during which FeII/FeIII-EDDS complexes started competing for radicals, and resulted in the degradation of ~ 15% of NAP. The continuous degradation stage (CDS), in which hydrogen peroxide (H 2 O 2) was the only oxidant because PAA was exhausted, corresponded to the degradation of another ~ 10% of NAP. The effect of water matrices including Cl-/Br-, HCO 3 –/CO 3 2–, and humic acid (HA) was evaluated: Br-, HCO 3 –/CO 3 2–, and HA exhibited an inhibiting effect on NAP degradation, while Cl- showed no influence on NAP degradation in the FEUP process. A superior degradation performance was achieved under a low FeII dosage and neutral conditions, demonstrating the great potential of the FEUP process for practical applications. [ABSTRACT FROM AUTHOR]