Aqueously Synthesized and Reusable Ce(IV)-Based Metal–Organic Frameworks with Aliphatic Multicarboxylate Linkers for Highly Efficient Pb²⁺ Removal from Water

Abstract

New Ce(IV) metal organic frameworks (MOFs) are reported based on the aliphatic linker butane-1,2,3,4-tetracarboxylic acid (H4BTCA). These materials were prepared using an eco-friendly aqueous-based synthesis, and their structures were elucidated through microcrystal electron diffraction (MicroED) and powder X-ray diffraction (PXRD). They feature an 8-coordinated net with a bcu topology, rarely observed for Ce(IV) MOFs. Interconversion between the MOFs was easily achieved via treatment with basic or formic acid solutions, revealing the breathing of the MOFs’ frameworks. The MOFs were investigated for their ability to sorb Pb2+ under both batch and continuous flow conditions. The results showed relatively high Pb2+ sorption capacities (up to 254 mg Pb/g) and an exceptional capability for the rapid removal (in less than 10 min of MOF-solution contact) of Pb2+ from low initial concentrations from complex solutions and real-world water samples. Notably, the materials in the form of calcium alginate-based beads used as a stationary phase in a column (along with sea sand) demonstrate a remarkable ability to capture Pb2+ under continuous flow, showing decent removal capacities, excellent regeneration efficiency, and reusability. The mechanism of the Pb2+ sorption process was determined via experimental data, indicating strong interactions of the MOF’s functional groups (carboxylate and hydroxide groups) with the Pb2+ ions.