Mo4+-Pb2+ redox triggers self-enhanced removal and recovery of Pb2+ with superselectivity

Abstract

Membrane-based electrodeposition (MED) has emerged as a promising approach for reversible removal-recovery of toxic but valuable Pb²⁺. However, limited by the low specificity of membrane deposition toward various heavy metal ions in MED, the selective removal of Pb²⁺ remains an obstacle. Inspired by the soft-hard acid-base theory, here we developed a Pb²⁺-affinity electroactive membrane by incorporating MoS₂ with the cation exchange membrane (CEM) to achieve a tandem Pb²⁺ selective adsorption-deposition process. CEM@MoS₂ achieved nearly 100 % Pb²⁺ removal selectivity even in the presence of diverse competing cations, with a remarkable distribution coefficient (1.3 × 10⁷ mL·g⁻¹) and treatment capacity (2580.4 mg·g⁻¹), resulting in a high-purity Pb²⁺ concentrate recovery. Importantly, a spontaneous Mo⁴⁺-Pb²⁺ redox reaction was found, which triggered Pb²⁺ reduction to metallic Pb. This surficial Pb° formation decreased the energy barrier for subsequent membrane H₂O splitting and Pb²⁺ reduction, accounting for the unexpected self-enhanced Pb²⁺ removal scenario. Additionally, the exhausted Mo⁴⁺ species was facilely regenerated via a cathodic reduction method, demonstrating excellent stability and reusability. The work is expected to provide a viable strategy for selective removal-recovery of heavy metal ions using MED.