Zirconium organophosphonates as high capacity, selective lanthanide sorbents

• Novel zirconium organophosphonate coordination networks have been synthesised.
• Selective lanthanide sorption from competitive, acidic solutions observed.
• Fast kinetics and high capacity provide commercial viability.
• Materials are hydrolytically and radiolytically stable.
• Porosity and sorption capacity controllable by composition.

Novel and versatile zirconium organophosphonate coordination networks have been developed as sorbent platforms via simple, low-temperature hydrothermal reactions of zirconium propoxide with amino tris(methylene phosphonic acid) (ATMP). The resulting materials exhibited hierarchical porosity and possessed exceptional selectively for lanthanide elements over mono- and divalent metal ions during competitive sorption experiments in 0.1 M HNO3, as well as modest intra-lanthanide selectivity. As such, the present materials have potential as solid phase extractants for lanthanide separations in applications including mining, radioactive waste treatment and environmental remediation. Lanthanide sorption was shown to occur via uncoordinated PO groups in the ATMP molecule. The structure, porosity and sorption properties of the coordination network platform could be tuned through varying the molar ratio of phosphorus to zirconium. Interestingly, the sample with the lowest surface area (<2 m2/g) demonstrated the highest sorption capacity. Optimal compositions demonstrated europium sorption with fast kinetics and very high capacities of up to 0.63 g/mg min and 60 mg/g respectively. As such, these highly stable zirconium organophosphonates, prepared from inexpensive precursor chemicals using one-pot methods, perform comparably to costly commercially available polymer resins.

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