High yield precipitation of crystalline a-zirconium phosphate from oxalic acid solutions

Microcrystalline zirconium phosphate (ZrP) has been synthesized by precipitating a Zr(IV) salt (i.e., zirconium propionate, chloride, or oxide chloride) with H3PO4 from aqueous solutions of oxalic acid (H2C2O4) at 80 C. Independent of the Zr(IV) salt, crystalline materials have been obtained with reaction yields >90% and reaction time of one day for the following molar ratios: H3PO4/Zr = 6 and H2C2O4/Zr = 10. The material prepared from Zr propionate (ZrPprop) has been further investigated by scanning electron microscopy, thermogravimetry, and ion exchange titrations. Structural characterization has been performed by X-ray powder diffraction and solid state 1H-31P 2D correlation NMR experiments. Structural parameters obtained by Rietveld analysis of powder diffraction data agree with those reported in the literature for single crystal determinations. Moreover, NMR data show that the closest proton environment of the phosphorus atom in ZrPprop is the same as in ZrP samples of similar crystallinity prepared according to literature methods.