Selective capacitive removal of Pb 2+ ions from zinc smelting wastewater using MoO 4 2--intercalated CoFe-LDH electrode

Abstract

To develop efficient, low energy consumption technologies for lead (Pb 2+ ) ion pollution control and lead metal recovery, layered double hydroxides (LDHs) were selected for capacitive deionization (CDI) due to their tunable interlayer spacing, high ion-exchange capacity, low cost, and good environmental compatibility. To address their inherent limitations including poor conductivity and adsorption capacity for Pb 2+ , and insufficient selectivity, a stainless-steel mesh (SS) substrate modified with a Ti₄O₇ film was used. MoO4 2--intercalated CoFe-LDH (CoFe-MoO4 2--LDH) was solvothermally synthesized on the modified substrate surface, yielding the SS/Ti4O7/CoFe-MoO4 2--LDH electrode, which served as the cathode along with graphite paper as the anode to form an asymmetric CDI cell. Evaluation of its Pb 2+ electrosorption performance showed that intercalating MoO4 2significantly enhanced the electrochemical behavior of CoFe-LDH coatings, improving adsorption capacity and selectivity for Pb 2+ . The electrode achieved Pb 2+ adsorption capacity of 199.98 mg•g -1 and excellent cycling stability, and demonstrated outstanding selective adsorption of Pb 2+ in mixed solutions containing various heavy metal ions. Experimental characterization combined with density functional theory (DFT) calculations revealed high selectivity for Pb 2+ originating from strong preferential binding between [MoO4] 2in the LDH gallery under an applied electric field and Pb 2+ ions, generating a PbMoO4 phase. This work provided a promising strategy for treating lead-containing industrial wastewater for both environmental remediation of lead contamination, and recovery of lead as a vital resource.