Efficient degradation of metronidazole by peroxodisulfate through triboelectric effect of water eddy: Electrocatalytic promotion of Fe3+/Fe2+ cycling

Abstract

In order to address the problem of permeable reactive barrier (PRB) clogging due to the generation of substantial iron sludge resulting from the release of excess Fe³⁺ ions from zero-valent iron in groundwater pollution control, we had introduced electrocatalytic technology to form a Fe³⁺/Fe²⁺ cycle in order to improve the clogging of PRB. On the other hand, the power source of Fe³⁺ reduction becomes the limiting factor for efficiency. The principle of triboelectricity has been expanded to solid–liquid frictional electrification and innovative electric energy harvesting applications. The mechanical energy converts into electrical energy under hydraulic conditions, and the generated electrons drive the Fe³⁺ reduction. We synthesized a contact-electro-catalyst, iron-loaded mesoporous carbon (Fe/OMC), which induced solid–liquid friction at the Fe/OMC interface under water eddy, and investigated its triboelectric response through electrochemical methods. The electrons generated by triboelectric effect form a Fe³⁺/Fe²⁺ cycle on the catalyst surface through electron transfer. Fe/OMC as a contact-electro-catalyst synergized with peroxodisulfate (PDS) to remove 91 % of metronidazole in 60 min under water eddy conditions. The system promoted the generation of free radicals by PDS and their oxidation of MNZ (>80 % for ${\mathrm{S}\mathrm{O}}_4^{·-}$ and ·OH). Cycling experiments and simulated column experiments demonstrated the cyclic regeneration performance and repair longevity of Fe/OMC increased more than 2 times compared to the theoretical life. The content of iron ions was detected and the Fe³⁺/Fe²⁺ cycling mechanism was verified by material characterization and cyclic voltammetry curves. This study contributes to the understanding of the water eddy friction triggering mechanism and provides new insights for the development of contact-electro-catalysis in the field of low-energy environment treatment.