Fe₂O₃ nanorods on carbon nanofibers induce spontaneous reductive transformation of inorganic contaminants in ambient aerated water

This work reports an unconventional example that Fe₂O₃ nanorods loaded on carbon nanofiber sheet (Fe₂O₃/CNF) enable the spontaneous reductive transformation of recalcitrant inorganic contaminants (e.g., CrO₄^2-, Fe(CN)₆^3-, IO₃^-, HSO₅^-, ClO₃^-, BrO₃^-, Ag⁺, and Pt⁴⁺) in ambient aerated solutions without using any external energy and chemicals. Fe₂O₃/CNF exhibited notable reductive activities for a variety of inorganic ions and transition metal ions (13 inorganic substances) which could be spontaneously reduced whereas Fe₂O₃ or CNF alone did not induce any conversion. The quantitative conversions to reduced products on Fe₂O₃/CNF were demonstrated for the cases of Fe(CN)₆^3-, IO₃^-, ClO₃^-, and BrO₃^-. The reductive transformation was further confirmed by measuring the cathodic current generation on Fe₂O₃/CNF electrode upon spiking the target inorganic species. The spontaneous reductive processes were little hindered by the presence of dissolved O₂, which makes the application practically viable as it does not require an energy-consuming deaeration process. The surface characterizations suggest that the spontaneous electron transfer is initiated upon introducing reducible inorganic substrates which electrons are transferred from the oxygen-containing functional groups on CNF to the inorganic substrates through Fe₂O₃ nanorods. The Fe₂O₃/CNF nanocomposite that reductively removes various inorganic substrates is proposed as a novel reactive nanomaterial that can control low-level contaminants.