Selective capacitive removal of Pb(II) ions from industrial wastewater using NF/Mn2CoO4@MoO2 electrodes

To achieve targeted removal of Pb 2+ from industrial wastewater, a NF/Mn 2 CoO 4 @MoO 2 composite electrode, synthesised using the hydrothermal method combined with electrodeposition technology, was employed to construct an asymmetric capacitive deionization (CDI) system to selectively electro-adsorb and desorb Pb 2+ ions. The electrode exhibited pseudocapacitive characteristics in solutions containing Pb 2+ , facilitating rapid and reversible redox reactions. The asymmetric CDI system, utilising graphite paper as the positive electrode and NF/Mn 2 CoO 4 @MoO 2 as the negative electrode, displayed exceptional adsorption performance at 1.4 V for 1 h, decreasing the Pb 2+ concentration from 50 ppm to 4 ppb, achieving an adsorption capacity of 156.24 mg g −1 , and displaying outstanding cyclic stability. Moreover, the electrode demonstrated preferential adsorption of Pb 2+ in mixed solutions containing multiple heavy metal ions, with relative removal coefficients of 4.48 − 19.86 compared with other ions. Analysis of the adsorption mechanism indicated that during the adsorption process, Pb 2+ was embedded between MoO 2 layers, disrupting the electron cloud symmetry and triggering an oxidation reaction. Octahedral MoO 2 then lost electrons and transformed into tetrahedral [MoO 4 ] 2- , forming PbMoO 4 with embedded Pb 2+ between the layers, and achieving effective removal of Pb 2+ with high selectivity. Molecular dynamics simulations and density functional theory (DFT) calculations confirmed the high selectivity of the prepared electrode for Pb 2+ ions based on stronger binding of Pb 2+ to MoO 2 than other ions. The electrode has application potential for the capacitive removal of Pb 2+ from industrial effluent through CDI technology.