Fe(III)-exchanged zeolites as efficient electrocatalysts for Fenton-like oxidation of dyes in aqueous phase

Electrochemical oxidation, a powerful tool for the conversion of several of organic dye compounds using metal-exchanged zeolite modified electrodes, has shown great potential due to its capability of high efficiency degradation, a global priority for a sustainable environment. In this study, the role of the Fe(III)-exchanged-zeolite-modified electrodes using two different zeolite structures (such as FAU (Y) and MFI (ZSM-5)) on the Fenton-like oxidation of Congo Red dye (C32H22N6Na2O6S2) was investigated at room temperature. To clarify the electrocatalytic trend observed by constant potential electrolysis, the surface acidity of the catalysts prepared by ion-exchange method was determined by microcalorimetric measurements of ammonia adsorption. The different acid properties deriving from the presence of different cations (NH4+, H+ and Na+) in the case of MFI structure were found to enhance the ion-exchange capacity as well as the oxidation reaction. MFI catalysts - Fe(Na)ZSM-5, Fe(H)ZSM-5 and Fe(NH4)ZSM-5 - exhibited excellent activity and stability at the end of the electrolysis (within 60min), with a total dye degradation and an higher mineralization on Fe(H)ZSM-5 (64% of TOC), compared with Fe(Na)Ynano, which takes twice as long (120min) for total degradation, with 19% of TOC removal. This work provides an effective route for the development of stable Fe(III)-zeolite-modified electrodes for electro-Fenton oxidation, with a better stabilization of Fe3+ ions within the framework, without the aggregation of iron and the addition of H2O2, at room temperature.Z.B. thanks to ERASMUS+ Program for the mobility PhD grant. This research work has been funded by national funds funded through FCT/MCTES (PIDDAC), (Fundação para Ciência e Tecnologia, FCT) over the projects: LA/P/0045/2020 (ALiCE), UIDB/50020/2020 and UIDP/50020/2020 (LSRE-LCM), Centre of Chemistry (UID/QUI/0686/2020) and project BioTecNorte (operation NORTE-01-0145-FEDER 000004), supported by the Northern Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF).