Fe­(VI) has received increasing attention since it can decompose a wide range of trace organic contaminants (TrOCs) in water treatment. However, the role of short-lived Fe­(IV) and Fe­(V) in TrOC decomposition by Fe­(VI) has been overlooked. Using methyl phenyl sulfoxide (PMSO), carbamazepine, and caffeine as probe TrOCs, we observed that the apparent second-order rate constants (k app) between TrOCs and Fe­(VI) determined with the initial kinetics data were strongly dependent on the initial molar ratios of TrOCs to Fe­(VI). Furthermore, the k app value increases gradually as the reaction proceeds. Several lines of evidence suggested that these phenomena were ascribed to the accumulation of Fe­(IV) and Fe­(V) arising from Fe­(VI) decay. Kinetic models were built and employed to simulate the kinetics of Fe­(VI) self-decay and the kinetics of PMSO degradation by Fe­(VI). The modeling results revealed that PMSO was mainly degraded by Fe­(IV) and Fe­(V) rather than by Fe­(VI) per se and Fe­(V) played a dominant role, which was also supported by the density functional theory calculation results. Given that Fe­(IV) and Fe­(V) have much greater oxidizing reactivity than Fe­(VI), this work urges the development of Fe­(V)/Fe­(IV)-based oxidation technology for efficient degradation of TrOCs.

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Complete dechlorination and mineralization of chlorophenols via the reduction−oxidation-mediated electro-Fenton process with a composite bulk cathode is first proposed. The in situ formation of a PdFe nanoalloy and carbon defects as key active sites is mutually induced during the formation of a carbon aerogel-based electrode. Specifically, the PdFe nanoalloy promotes the generation of [H] ads as reduction sites and improves the electron transfer via an electrical circuit, while the carbon defects selectively favor the 2e − oxygen reduction pathway. Notably, this work implies a novel electrocatalytic model for the formation of •OH via (2 + 1)e − oxygen reduction by a consecutive reaction with carbon defects and a PdFe nanoalloy. Complete total organic carbon removal and dechlorination of 3-chlorophenol were performed after 6 h. The kinetic rate constant for removing haloacetamides (HAMs) in drinking water was 0.21−0.41 h −1 , and the degradation efficiency was selfenhanced after electrolysis for 2 h because of the increased concentration of [H + ]. The specific energy consumption was ∼0.55 W•h• g −1 at 100% removal of some HAMs, corresponding to a power consumption of 0.6−1.1 kW•h for complete dehalogenation per ton of drinking water in waterworks. Moreover, the PdFe alloy/CA exhibited extreme mechanical and electrochemical stability with limited iron (∼0.07 ppm) and palladium (0.02 ppm) leaching during the actual application.