Reactive oxygen species dependent degradation pathway of 4-chlorophenol with Fe@Fe2O3 core–shell nanowires

• DTPA was first used to promote the aerobic 4-chlorophenol degradation with Fe@Fe2O3 nanowires.
• TOC removal rate in the Fe@Fe2O3/DTPA/4-CP/Air system was much faster than the case of EDTA.
• Both DTPA and 4-CP could be rapidly mineralized by hydroxyl radicals.
• DTPA could inhibit the hydrogen evolution through the reduction of proton by Fe@Fe2O3.
• The 4-CP degradation pathways were dependent on the generated reactive oxygen species.

In this study, an environmentally benign polyaminocarboxylic ligand diethylenetriamine pentacetate (DTPA) was first used to promote the aerobic 4-chlorophenol (4-CP) degradation with Fe@Fe2O3 core–shell nanowires, and then compared with the most used counterpart ethylenediamine tetraacetate (EDTA) of poor biodegradability. Although the 4-CP removal rate in the Fe@Fe2O3/DTPA/Air system was slower owing to the preferential degradation of DTPA, the total organic carbon removal rate in the Fe@Fe2O3/DTPA/4-CP/Air system was much faster than that in the Fe@Fe2O3/EDTA/4-CP/Air system. We interestingly found that hydroxyl radicals could more easily react with DTPA to produce DTPA radicals than with EDTA to produce EDTA radicals. Ligands (DTPA or EDTA) could significantly accelerate the hydroxyl radicals production with Fe@Fe2O3, while more hydroxyl radicals were generated in the Fe@Fe2O3/DTPA/Air system. We also employed gas chromatography-mass spectrometry and ion chromatography to detect organic intermediates and chloride ions to probe the 4-chlorophenol degradation pathways, and found its degradation pathways were dependent on the reactive oxygen species generated in the different systems. This study can clarify the roles of polyaminocarboxylic ligands on the molecular oxygen activation with nanoscale zero-valent iron, and also provide a green chlorophenols removal method.

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