Selective capacitive removal of Pb2+ ions from zinc smelting wastewater using a MoO42−-intercalated CoFe-LDH electrode

Abstract

To develop efficient, low energy consumption technologies for lead (Pb²⁺) 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 Pb²⁺ and insufficient selectivity, a stainless-steel (SS) mesh substrate modified with a Ti₄O₇ film was used. MoO₄²⁻-intercalated CoFe-LDH (CoFe–MoO₄²⁻-LDH) was solvothermally synthesized on the modified substrate surface, yielding the SS/Ti₄O₇/CoFe–MoO₄²⁻-LDH electrode, which served as the cathode along with graphite paper as the anode to form an asymmetric CDI cell. Evaluation of its Pb²⁺ electrosorption performance showed that intercalating MoO₄²⁻ significantly enhanced the electrochemical behavior of CoFe-LDH coatings, improving adsorption capacity and selectivity for Pb²⁺. The electrode achieved a Pb²⁺ adsorption capacity of 199.98 mg g⁻¹ and excellent cycling stability and demonstrated outstanding selective adsorption of Pb²⁺ in mixed solutions containing various heavy metal ions. Experimental characterization combined with density functional theory (DFT) calculations revealed high selectivity for Pb²⁺ originating from strong preferential binding between [MoO₄]²⁻ in the LDH gallery under an applied electric field and Pb²⁺ 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.