Interstitial Compound Fe₃C-Doped Fe(0) Nanoparticles Embedded in Mesoporous Carbon Efficiently Boosting Cr(VI) Removal

Abstract

The high reactivity of Fe(0) with Cr(VI) makes it the best choice for Cr(VI) removal. Interstitial compound Fe3C was produced during the carbothermic reduction of mesoporous phenolic resin/ferric ions to form Fe(0)/Fe3C nanoparticles embedded in mesoporous carbon (Fe(0)/Fe3C@MesoC). Fe3C accelerates the electrochemical corrosion process of α-Fe(0) in solution, and the positive/negative equipotential interface that is formed by iron–carbon (Fe–C) microelectrolysis of Fe(0)/Fe3C@MesoC induces the capture of Cr(VI) anions and Cr(III) cations as a result of this process. Cr(VI) was completely reduced to Cr(III) by the Fe(0)/Fe3C@MesoC catalyst with a high electron efficiency (40.5%) relative to nanosized zero-valent iron (1.9%) and Fe@MesoC (32.7%). Surface ferrous ions are the principal reactive species responsible for Cr(VI) reduction (at least 64%); Fe(0)/Fe3C and undetectable surface ferrous ions account for a small part of Cr(VI) reduction (around 28%), and only 8% of Cr(VI) ions are reduced by active hydrogen (H*). The proposed structure of Fe(0)/Fe3C@MesoC provides new insight into iron–carbon material preparation and application in in situ chemical reduction.