Using recent developments in inorganic biomineralization as a guide, we have investigated aqueous Zr-sulfate chemistry to understand the atomic-level structures of oligomeric clusters present in solution and their correspondence with solids that precipitate. Pair distribution functions (PDF)s obtained from high-energy X-ray scattering (HEXS) data, small angle X-ray scattering (SAXS), and Raman spectroscopy are used to quantify Zr correlations in solution. All the solutions studied are consistent with polydisperse oligomers in equilibria although in each case a single moiety is selected as the building unit for the crystals that precipitate. Absent sulfate, tetravalent Zr in acidic aqueous solution forms tetranuclear and/or larger hydrolysis products. Addition of sulfate results in the evolution of larger oligomers, their formation and stability primarily dependent on sulfate concentration. Both HEXS and spectroscopic data obtained from solutions at subequimolar concentrations of Zr:SO42- are consistent with the presence of a large oligomer in solution; a compound containing octadecanuclear units bridged by sulfate is precipitated as a crystalline phase. From solutions with equimolar concentrations of Zr:SO42-  a structure built from hexanuclear [Zr6(OH)4O4]12+ and octadecanuclear [Zr18(OH)xOy]n+ units is observed, decorated by sulfate anions. Further addition of sulfate to the solutions results in the disruption of the polynuclear complexes and precipitation of Zr(SO4)2(H2O)4. The evolution of structural building units and the role of sulfate in the assembly of the larger oligomers will be discussed. These results emphasize the presence of well-formed prenucleation species with well-defined correlations on length scales of < 1 nm, often considered to be within the structurally-amorphous regime. This work is supported by the U.S. DOE, under contract DE-AC02-06CH11357.

Correlations in Zr - sulfate aqueous solutions and their impact on precipitate stoichiometry and structure: Synthesizing new materials by design

246th National Meeting (2013)

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