Fe@Fe2O3 core-shell nanowires enhanced Fenton oxidation by accelerating the Fe(III)/Fe(II) cycles

• Fe@Fe2O3 core–shell nanowires can accelerate the Fe(III)/Fe(II) cycles during Fenton oxidation.
• Fe(III)/Fe(II) cycles are accelerated by superoxide radicals generated by Fe@Fe2O3 core–shell nanowires at pH > 4.
• Fe@Fe2O3 core–shell nanowires and ferrous ions decompose H2O2 to produce more hydroxyl radicals.

In this study we demonstrate Fe@Fe2O3 core–shell nanowires can improve Fenton oxidation efficiency by two times with rhodamine B as a model pollutant at pH > 4. Active species trapping experiments revealed that the rhodamine B oxidation enhancement was attributed to molecular oxygen activation induced by Fe@Fe2O3 core–shell nanowires. The molecular oxygen activation process could generate superoxide radicals to assist iron core for the reduction of ferric ions to accelerate the Fe(III)/Fe(II) cycles, which favored the H2O2 decomposition to produce more hydroxyl radicals for the rhodamine B oxidation. The combination of Fe@Fe2O3 core–shell nanowires and ferrous ions (Fe@Fe2O3/Fe2+) offered a superior Fenton catalyst to decompose H2O2 for producing OH. We employed benzoic acid as a probe reagent to check the generation of OH and found the OH generation rate of Fe@Fe2O3/Fe2+ was 2–4 orders of magnitude larger than those of commonly used iron based Fenton catalysts and 38 times that of Fe2+. The reusability and the stability of Fe@Fe2O3 core–shell nanowires were studied. Total organic carbon and ion chromatography analyses revealed the mineralization of rhodamine B and the releasing of nitrate ions. Gas chromatograph-mass spectrometry was used to investigate the degradation intermediates to propose the possible rhodamine B Fenton oxidation pathway in the presence of Fe@Fe2O3 nanowires. This study not only provides a new Fenton oxidation system for pollutant control, but also widen the application of molecular oxygen activation induced by nanoscale zero valent iron.

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