Friday, September 19, 2008

Chem. Mater., 20 (18), 5787–5795, 2008.

Characterization of Noncrystalline Nanomaterials: NMR of Zinc Phosphate as a Case Study
Marcus Roming,† Claus Feldmann,*† Yamini S. Avadhut,‡ and Jörn Schmedt auf der Günne*‡

Zinc phosphate nanoparticles are prepared via a polyol-mediated synthesis. The nanomaterial turns out to be nonagglomerated and very uniform in size and shape, in particular 20 nm in diameter. X-ray powder diffraction analysis and high-resolution transmission electron microscopy indicate as-prepared nanoparticles to be noncrystalline. To investigate the chemical composition (stoichiometry, material homogeneity, amount of ortho-/metaphosphate, water content, type of surface-allocated adsorbents, differentiation of surface/inner core), X-ray diffraction, NMR-spectroscopy, energy-dispersive X-ray analysis, infrared spectroscopy, and thermal analysis are performed. To validate the local structure and composition, we performed 1H, 13C, and 31P magic angle spinning nuclear magnetic resonance spectroscopy and multidimensional homo- and heteronuclear multiple-pulse solid-state NMR experiments. Moreover, 31P{1H} rotational echo double-resonance experiments for various spin topologies are analyzed analytically and numerically, in order to differentiate between homogeneous nanoparticles and core−shell nanoparticles. The analysis gives a length scale to homogeneity and for bulk materials allows us to differentiate between mono- and dihydrogen phosphates, and phosphate hydrates.

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