Zirconium phosphonate sorbents with tunable structure and function

Abstract

Porous zirconium phosphonate materials have been produced via template-free hydrothermal synthesis of a zirconium precursor and amino tris(methylenephosphonic acid). To provide insights into the final structure and function of these materials and how the material properties can be influenced by the synthesis parameters, a variety of samples were prepared. Synthesis conditions were varied by changing P/Zr molar ratios, Zr precursors, pH and temperature. The resulting porous, amorphous zirconium phosphonate materials were characterised via x-ray diffraction, elemental analysis, nitrogen porosimetry, electron microscopies, nuclear magnetic resonance, small angle x-ray scattering and extended x-ray absorption fluorescence spectroscopy. The ultimate functional behaviour of the materials was also measured via competitive metal ion sorption experiments. The resultant materials were found to be selective lanthanide sorbents with capacities dependent on the synthesis conditions. Inducing crystallinity through addition of potassium fluoride during synthesis was shown to produce materials with reduced capacity and selectivity. Characterisation of the porosity of these materials demonstrated that in some cases different structures existed when the samples were wet versus dry and that this was dependent on the synthesis conditions used. All of the synthesis parameters investigated impacted the chemical structure, porosity and sorption properties of the resulting zirconium phosphonate materials.