Atomic Structure Analysis of Nanocrystalline Boehmite AlO(OH)

Nanocrystalline n -AlO(OH) (Disperal P2, Sasol) was investigated by means of the atomic pair distribution function (PDF). The PDF is derived from powder diffraction data, and an ideally resolved PDF is obtained from a synchrotron source which provides a large maximal scattering vector length Q max > 300 nm −1 . Here, however, we were able to reveal atomic structure details of the ∼4 nm particles from in-house diffraction data ( Q max = 130 nm −1 ): PDF least-squares model refinements show that n -AlO(OH) is of the layered Boehmite structure type (oC16, Cmcm ), but the structure is uniformly distorted in domains of ∼2 nm within the nanoparticles. The hydrogen bonds between the layers are widened significantly by +13 pm, accounting for the higher reactivity when compared to microcrystalline Boehmite. Our results from only one “nanocrystallographic” experiment are consistent with a trend that was found via the Rietveld technique on a series of AlO(OH) of different crystallite sizes ( Bokhimi et al. J. Solid State Chem.2001, 159, 32−40 ). In addition, the PDF contains information on structural distortion as a function of (coherence) domain size within the nanoparticles.