Modulating NFO@N-MWCNTs/CC Interfaces to Construct Multilevel Synergistic Sites (Ni/Fe-O-N-C) for Multi-Heavy Metal Ions Sensing

A hierarchical heterogeneous composite electrode of NiFe₂O₄@nitrogen-doped multi-walled carbon nanotubes/carbon cloth (NFO@N-MWCNTs/CC) is prepared via a dip-coating method, followed by a hydrothermal process. The flexible carbon cloth (CC) substrate provides robust support and the cross-linked nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) on the CC form a highly porous network with a large specific area that facilitates electron-transfer. The stable support strengthens the framework and prevents pore structure disorder within the porous network, that could lead to the structural instability of the active sites. The decorated NiFe₂O₄ nanoparticles offer abundant active sites for enhanced electrocatalytic activity. Benefiting from the synergistic effect of the 3D hierarchical heterogeneous microstructure and multilevel bimetallic oxide active site (Ni/Fe-O-N-C) constructs, the NFO@N-MWCNTs/CC electrode achieves stable detection of multiple heavy metal ions (HMIs) with high reproducibility. The modified electrode allowed stable detection of multiple heavy metal ions with high reproducibility. The sensitivities of the electrode for Cd(II), Pb(II), Bi(III), and Hg(II) are 344.98, 441.02, 176.484, and 371.099 µA µm⁻¹, respectively. The assay recoveries ranged from 95.3% to 106.8%, highlighting its practical applicability. This study provides innovative composites and theoretical insights to facilitate further advances in the simultaneous high-performance detection of heavy metal ions.