Synthesis, structure and characterization of ZrPOF-DEA, a microporous zirconium phosphate framework material

A microporous zirconium phosphate material with the chemical composition |(C4H12N+)6(H3O+)2(H2O)2|[Zr32P48O176F8(OH)16] (ZrPOF-DEA) has been synthesized ionothermally using diethylammonium chloride and oxalic acid to form the deep eutectic solvent. It is closely related to the analagous ethylammonium material ZrPOF-EA, which has already been shown to discriminate very well between CO2 and CH4. The framework structures, with two different 8-ring channels running parallel to the x-axis, one of which intersects a 7-ring channel running parallel to the z-axis, proved to be identical. Only the positions of the non-framework cations and water molecules differ. The structure of ZrPOF-DEA (Pbam, a = 20.03757(1) Å, b = 37.19099(1) Å, c = 6.62488(1) Å) was solved from synchrotron powder diffraction data using the charge-flipping algorithm in Superflip. Difference Fourier analyses were then used to locate the non-framework species in the channels. Rietveld refinement of the final structure converged with RF = 0.037 and Rwp = 0.138. Although this material, like ZrPOF-EA, is stable up to 410 °C, it does not discriminate as well between CO2 and CH4. Thermogravimetric analysis shows that not all of the organic species have been removed at 410 °C, and this is presumably the reason for the poorer adsorption results.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Microporous zirconium phosphate material that can distinguish between CO2 and CH4. ► Zirconium phosphate framework produced via ionothermal synthesis. ► Full structure of ZrPOF-DEA elucidated from synchrotron powder diffraction data.