Zirconium and hafnium hydrogen monothiophosphates H2Zr(PO3S)(2) and H2Hf(PO3S)(2). Syntheses and selective ion-exchange properties of sulfur-containing analogues of H2M(PO4)(2) (M = Zr, Hf)

The reactions between aqueous solutions of M4+ (M = Zr, Hf) and PO3S3- each result in the precipitation-of a white gel that can be dried to a powder. Elemental analysis results for the white polycrystalline product yield a st oichiometry of H2M(PO3S)(2) These new compounds are characterized by therma l analysis (DSC, TG-MS), vibrational spectroscopy (FT-IR, FT-Raman), P-31 M AS NMR spectroscopy energy-dispersive spectroscopy (EDS), and powder X-ray diffraction (XRD). On the basis of the characterizations and the results of trialkylamine intercalation experiments, we conclude that the H2M(PO3S)(2) compounds have a layered structure that is likely similar to that of alpha -H2Zr(PO4)(2).H2O. The interlayer spacing for both H2M(PO3S)(2) compounds, determined by XRD, is similar to9.4 Angstrom. Our characterization results suggest that the sulfur atom of each PO3S3- group is preferentially pointe d into the interlayer region df the compound and is protonated. Two of the many potentially interesting properties of H2Zr(PO3S)(2), its ion-exchange capacity and selectivity, are investigated. H2Zr(Po3S)(2) is demonstrated t o be an effective and recyclable ion-exchange material for both Zn2+(aq) an d Cd2+(aq). Mass balance experiments indicate that the removal of Cd2+(aq) and Zn2+(aq) ions by solid H2Zr(PO3S)(2) occurs by an ion-exchange process. Ion exchange results in the formation of the new compounds H0.2Cd0.9Zr(PO3 S)(2) and H0.50Zn0.75Zr(PO3S)(2). The extraction of metal ions is monitored by XRD, vibrational spectroscopy, and elemental analysis. H2Zr(PO3S)(2) re versibly intercalates Zn2+(aq) ions through three complete cycles of interc alation and deintercalation without any loss of ion-exchange Capacity.