Continuous flow supercritical water synthesis and crystallographic characterization of anisotropic boehmite nanoparticles

• Published in: Journal of applied crystallography Vol. 43; no. 4; pp. 858 - 866
• Main Authors: Lock, Nina, Hald, Peter, Christensen, Mogens, Birkedal, Henrik, Iversen, Bo Brummerstedt
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01.08.2010; Blackwell Publishing Ltd
• Subjects: Alignment; Anisotropy; Boehmite; Chemical synthesis; Continuous flow; Crystallites; Crystallography; Morphology; Nanoparticles; supercritical water; Water
• ISSN: 1600-5767; 0021-8898; 1600-5767
• DOI: 10.1107/S0021889810019187

Crystalline boehmite nanoparticles have been prepared in a few minutes from thermal decomposition of aluminium nitrate in near‐ and supercritical water. Highly anisotropic nanoparticles are formed under continuous flow conditions using T‐piece mixing and a large size tube diameter. The shapes and sizes of the synthesized nanocrystals were determined from peak shape analysis of powder X‐ray diffraction data. The crystallite morphology is pressure dependent, and the size increases with temperature for constant reaction time and pressure. The modelled crystallite sizes and anisotropic shapes are in good agreement with transmission electron microscopy studies. At lower synthesis pressures the boehmite crystallite morphology is a mixture of platelets and bar‐shaped crystals. The bar‐shaped crystals align into polycrystalline fibre‐like long thin needles, which again align sidewise in bundles. At higher pressures, only the polycrystalline fibres are formed. Full conversion of dried boehmite to γ‐Al2O3 is observed after short‐term heating to 773 K with an overall conservation of the morphology.