Engineering Fe–N–C sites onto Fe nanoparticles for synergistically boosting Cr(vi) reduction: performance, mechanism, and applications

Abstract

Hexavalent chromium (Cr(VI)) is well known for its high toxicity to humans and the environment. It is of utmost significance to develop robust and effective materials for removing this hazardous compound. Fe nanoparticles (Fe_NPs) play an important role in the reduction and neutralization of environmental pollutants; however, they still face considerable challenges in performance. Herein, we first propose an encapsulation-pyrolysis strategy to engineer atomically dispersed Fe–N–C sites on the surface of Fe_NPs (Fe_NPs@Fe_SAsNC) as synergistic active sites to increase Cr(VI) reduction. Characterization results confirmed that Fe_NPs@Fe_SAsNC was developed by both encapsulation and pyrolysis processes. The Fe_NPs@Fe_SAsNC composite demonstrated a promoted reduction of Cr(VI) to Cr(III) with an initial activity of 2036.81 mg (g_reductant h L)⁻¹ and the removal capacity of 0.259 g_Cr g_reductant⁻¹, compared with those of Fe_NPs/CN (26.91 mg (g_reductant h L)⁻¹ and 0.024 g_Cr g_reductant⁻¹). Spectroscopic tests and theoretical calculations indicated that both electron-rich C/N atoms and low energy barrier for electron transfer in Fe–N–C sites assist in the adsorption and reduction of Cr(VI) on the surface of Fe_NPs@Fe_SAsNC. Moreover, Fe_NPs@Fe_SAsNC exhibits superior reusability and biocompatibility in practical applications, and the encapsulation-pyrolysis strategy was effective in activating other Fe-based reductants. To summarize, this work provides an approach to engineering Fe–N–C sites on the surface of Fe_NPs for the remediation of Cr(VI)-contaminated water.