Intercalation of Nanosized Fe₃C in Iron/Carbon To Construct Multifunctional Interface with Reduction, Catalysis, Corrosion Resistance, and Immobilization Capabilities

As a robust reducing system in industrial wastewater treatment, iron/carbon (Fe/C) microelectrolysis suffers from surface passivation and low utilization efficiency. Herein, we introduced Fe₃C into the Fe/C system to develop a core-shell Fe⁰/Fe₃C/C nanorod with a multifunctional interface (Fe₃C/C) providing reduction, catalysis, adsorption, and corrosion resistance. The results proved that the fabricated Fe⁰/Fe₃C/C possesses 5.6 times higher reduction capacity (220 mg/g) for Cr(VI) reduction but a relatively lower Fe leakage (2.7 mg/L) than Fe/C. On the basis of the results of electrochemical characterization (Tafel polarization curves and electrochemical impedance spectroscopy), the corrosion-resistant Fe₃C/C shell can significantly prevent surface passivation of the Fe⁰ core, whereas Fe₃C efficiently catalyzes electron transfer from the inner Fe⁰ to the external carbon surface. Moreover, the reductive species involved in Cr(VI) removal were identified as hydrogen atoms, adsorbed Fe(II) ions, and electrons tunneling from Fe⁰. STEM, XPS, and Mössbauer spectroscopies were further adopted to characterize the interface reaction of Fe⁰/Fe₃C/C during the Cr(VI) removal process. Finally, the reaction mechanism for Cr(VI) reduction over Fe⁰/Fe₃C/C was proposed, and the distribution of active sites was inferred.