Rational design and synthesis of diimide-based metal-organic frameworks for lanthanides recovery from tailing wastewater

Owing to the importance of lanthanides (Lns), sustainable recovery of low-concentration Lns from secondary resources is a challenge of great significance. Herein, a strategy to construct a series of metal-organic frameworks (MOFs; Cd-PDI-2D, Cd-PDI-3D, and Cd-NDI-3D MOFs) is proposed by introducing appropriate N-heterocyclic building blocks to explore the effects of functional-group types and framework soft basicity on the Ln-adsorption performance of MOFs. In contrast, Cd-PDI-2D shows amino groups along the 110 crystal plane as effective anchors for Lns, exhibiting super-high adsorption capacity and significant selectivity, due to the softer basicity of the two-dimensional framework. Moreover, the Cd-PDI-2D is utilized as column-packing materials to successfully extract ppb-level Lns from ppm-level competing ions of rare-earth tailings, which demonstrates its great promise for Ln recovery from secondary sources. Furthermore, this strategy could be extended for the enrichment of other noble metals in natural samples by rationally designing targeted linking ligands.