Highly selective capture of lead(II) by a barium-zinc-antimony-oxo cluster-based material: Ion-exchange pathway with single-crystal-to-single-crystal structural transformation

Abstract

Efficient removal of Pb²⁺ from wastewater is of great significance for human health and environmental protection. However, Pb²⁺ capture from complex wastewater is still very challenging due to the strong competition with other metal ions. Herein, the highly selective removal of Pb²⁺ has been achieved by a cluster-based material, namely H_1.03Ba_2.485(H₂O)₁₅[Zn₂Sb₁₂(μ₃-O)₈(μ₄-O)₃(tta)₆]·8H₂O (H₄tta = tartaric acid) (FJSM-BZA). FJSM-BZA exhibits high adsorption capacity (199.29 ± 5.86 mg/g) and fast kinetic response (kinetic equilibrium is reached in 20 min) for Pb²⁺. In particular, even in the presence of competing ions Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Cd²⁺, FJSM-BZA maintains excellent selectivity for Pb²⁺ with removal rate much higher than that of other metal ions. The material after Pb²⁺ adsorption could be regenerated by a simple elution method. The unprecedented single-crystal-to-single-crystal (SC to SC) structural transformations during Pb²⁺ adsorption and elution are unveiled, which helps directly elucidate the distinctive mechanisms of ion exchange between Ba²⁺ and Pb²⁺. It is revealed that the strong coordination interactions of the active carboxyl groups at the periphery of the cluster with Pb²⁺ ions are the intrinsic driving forces for the ion-exchange. This work highlights the design and synthesis of crystalline metal-oxo cluster-based materials for highly selective removal of Pb²⁺.