Circumstances of La, Eu, Dy, and Yb Cations Intercalated via Ion Exchange in γ-Zirconium Phosphate

Abstract

Both α- and γ-zirconium phosphate were examined for use as ion exchangers for recovery of rare earth elements. Trivalent rare earth elements can be partially substituted for protons in the interlayer space, and γ-zirconium phosphate shows a much better ion exchange competency than α-zirconium phosphate. The exchanged cation of the rare earth elements might be related to different amounts of oxygen from P–OH and H2O, and these rare earth elements were thus positioned at a different separations from the zirconium phosphate layer. The radial structure function (RSF) curve from extended X-ray absorption fine structure data implied that the calibrated M–O distance and coordination number changed with the ionic radius. The calibrated M–O distances from RSF were 2.52, 2.42, 2.38, and 2.28 for La, Eu, Dy, and Yb, respectively. The coordination numbers of oxygen for Yb were approximately 7 and greater than 10 for La and Eu, respectively. These smaller coordination numbers for smaller cations may result from the strong interaction between the cations and the zirconium phosphate layer. The Debye–Waller factor also increased with an increase in the ionic radius. These factors show a strong relation to the coordination state of rare earth elements in the unit cell of the γ-zirconium phosphate and to the interaction strength.

Metastable Zirconium Phosphate under Nanoconfinement with Superior Adsorption Capability for Water Treatment

“…However, with respect to ZrP@MPS, its adsorption capacities toward heavy metal cations are less disturbed by Ca II , i.e., ≈100%, >70%, and >40% for Pb II , Cd II , and Ni II respectively even when m Ca/heavy metal reaches 80. These results suggest that the inner‐sphere coordination between ZrP@MPS and heavy metal cations results in much higher adsorption selectivity than the nonspecific electrostatic attraction between α‐ZrP (or D001) and heavy metal cations under strong competing conditions 12. The reason is that inner‐sphere coordination usually takes place between the lone pair electrons of oxygen atoms and the d‐ or f‐ orbitals of heavy metals (e.g., Pb II , Cd II and Ni II );29 while alkali or alkaline‐earth metals (e.g., Na I , Ca II , and Mg II ) do not possess d‐orbitals for inner‐sphere coordination with ZrP@MPS.…”

“…These results suggest that the inner-sphere coordination between ZrP@MPS and heavy metal cations results in much higher adsorption selectivity than the nonspecific electrostatic attraction between α-ZrP (or D001) and heavy metal cations under strong competing conditions. [12] The reason is that inner-sphere coordination usually takes place between the lone pair electrons of oxygen atoms and the d-or f-orbitals of heavy metals (e.g., Pb II , Cd II and Ni II ); [29] while alkali or alkaline-earth metals (e.g., Na I , Ca II , and Mg II ) do not possess d-orbitals for inner-sphere coordination with ZrP@MPS. The results of another set of experiments, comparing the adsorption of ZrP nanoparticles with similar size but different phase composition, show that the crystalline structure rather than the crystal size contributes for the selective adsorption (see Figure S8 and S9 in the Supporting Information with accompanying discussion).…”

“…α‐ZrP has an interlayer distance of 0.76 nm and possesses monohydrogen phosphate group (HPO 4 ) sharing three oxygen atoms with three Zr(IV) atoms 11a. With respect to γ‐ZrP, the layers with distance of 1.22 nm are constructed by the alternative distribution of the dihydrogen phosphate groups (H 2 PO 4 ) sharing two oxygen atoms with Zr(IV) atoms and the phosphate groups (PO 4 ) sharing four oxygen atoms with Zr(IV) atoms 12. In both structures, the protons in HPO 4 or H 2 PO 4 groups act as the BrÖnsted acid sites for ion exchange with cations.…”

“…ZrP has been widely utilized for the adsorption of toxic metals, radioactive and rare earth elements due to its superior ion exchange capability 11a,12,13. In practical water treatment application, the ZrP nanoparticles need to be loaded onto various substrate materials including activated carbon, silicates, biomass, and polymer,14 in order to prevent loss of materials and particle aggregation, and to facilitate sample recycling.…”

Selective potassium uptake via biocompatible zeolite–polymer hybrid microbeads as promising binders for hyperkalemia

“…Specific ion-exchange/detection/storage ability has been verified in various agents, including zeolites [ [9] , [10] , [11] ], sodium zirconium cyclosilicate [ 12 ], layered phosphates [ 13 , 14 ], carbon-based materials [ 15 , 16 ], polymer-based materials [ 17 , 18 ], crown ethers [ 19 , 20 ] and their graphene derivatives [ 21 , 22 ]. Among them, zeolites are considered as the main trial materials in consideration of production cost and specific binding ability.…”