Constructing Fe2O3 nanoparticles in nitrogen-doped carbon materials to enhance the electrochemical sensing performance of Pb2+ and Cd2+

Abstract

N-doped carbon materials are known for their high conductivity, rich N content, and high adsorption activity. When combined with Fe₂O₃ to form nanocomposites, they can improve the conductivity of Fe₂O₃ and cause significant changes in the electrochemical sensing interface with the influence of their unique electronic structure. In this work, N-doped carbon nanocomposites (Fe₂O₃@NCNPs-x) modified with Fe₂O₃ nanoparticles (Fe₂O₃ NPs) were synthesized by a simple emulsion polymerization method and carbonized under Ar at a high temperature. X-ray photoelectron spectroscopy indicated that compared with undoped Fe₂O₃ NPs, the π bond of Fe₂O₃@NCNPs-1.5 was negatively charged due to the lone pair of electrons near the N atom, acting as an electron donor that enhanced the interaction with HMIs and electron transport, therefore generating more active sites on the surface of Fe₂O₃@NCNPs-1.5. The obtained Fe²⁺/Fe³⁺ ratio was about two times higher than that of undoped Fe₂O₃ NPs (Fe₂O₃@NCNPs-1.5: Fe²⁺/Fe³⁺ = 1.24; Fe₂O₃ NPs: Fe²⁺/Fe³⁺ = 0.61). The surface oxygen vacancy (OV) concentration reached the maximum level (Fe₂O₃@NCNPs-1.5: OVs/O1s = 41.7%; Fe₂O₃ NPs: OVs/O1s = 22%). Fe₂O₃@NCNPs-1.5/GCE also showed enhanced electrochemical performance for detecting Pb²⁺ and Cd²⁺, with a limit of detection (LOD, S/N = 3) of 4.92 and 18.79 nM, respectively. Electrochemical adsorption tests suggested that Fe₂O₃@NCNPs-1.5/GCE had the strongest adsorption capacity for Pb²⁺ and Cd²⁺ in comparison with other modified electrodes, suggesting that different N contents led to different absorbability for heavy metal ions (HMIs). Therefore, when the metal oxide nanoparticles are loaded on compatible carriers, the jointly constructed nanocomposites can be used as the active materials for efficiently detecting HMIs, providing a new concept for designing highly active electrochemical sensors.