Boehmite nanocrystals with tridimensional shape were synthesized by lengthening the aging time of the hydrothermal processing. Boehmite was first precipitated at pH 10 and at 100°C from an aqueous Al 3+ solution, and subsequently hydrothermally annealed at 200°C over the range time between 24 and 168 h. The crystalline structure of all the boehmite nanocrystals prepared showed no significant modifications. On the contrary, its microstructure strongly depended on the aging time, as the growth of the nanoparticles showed two clearly different steps: In the first one, crystallites grew mainly along the ⟨101⟩ directions, usually referred as basal, whereas in the second one the growth was along the baxis, i.e., in the [010] direction. This led to an increase of the proportion of lateral faces parallel to the b-axis in the total surface area of the nanoparticles with an increase of the annealing time. The higher proportion of lateral faces increased the total surface charge of the nanoparticles. Thus, important properties as the stabilization of the boehmite nanocrystals in suspension or their potential functionalization by grafting of organic molecules on these surfaces could be controlled applying the described methodology. ■ INTRODUCTIONNanomaterials technology has attracted great interest in the last two decades. One of the subjects more dealt with in this field is the preparation of inorganic nanoparticles with desired size and morphology, 1 as these materials present interesting properties allowing a number of new applications in fields such as catalysis, 2 biomedicine, 3 and ceramics. 4 Boehmite is one of the polymorphs of the aluminum oxyhydroxide, namely, γ-AlOOH, which is widely used as a precursor for the so-called transitional aluminas, the main one being γ-Al 2 O 3 , and for corundum (α-Al 2 O 3 ), both materials of industrial interest in the catalyst and ceramic fields, respectively. Moreover, and taking advantage of the biocompatibility of aluminum oxide, the only metal oxide approved for intramuscular injections, 5 new applications far beyond its role as vaccine adjuvant 6 are being developed in the medical field. Some examples found in the literature deal with the entrapment of proteins in boehmite, 5 which enhanced their thermal stability, or its use in bone-implant applications, taking advantage of its enhanced osteoblast functions with respect to classic metallic or ceramic materials. 7 Previous works carried out in this group reported the functionalization of boehmite nanoparticles with different molecules to develop potential sensors for cations and anions in aqueous solution by fluorescence spectroscopy 8 as well as potential contrast agents for NMR imaging. 9,10All the above-mentioned applications are based on strict control of the size, shape, and crystallinity of the nanoparticles of boehmite or alumina. It is therefore of capital importance to understand the process giving rise to these materials by the different available methodologies. One of the most used preparation procedures for boehmit...

Control of size, morphology and dispersability in water of the boehmite nanoparticles prepared with additives by a hydrothermal method.

Mesocrystalline TiO2 nanoparticles were synthesized using a hydrothermal approach. A simple two-step procedure at low temperature (<140 °C) allowed the nucleation of primary particles sized 2-4 nm and their subsequent assembly as almost spherical aggregates sized ≈20 nm. X-ray powder diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) studies, and HRTEM studies confirmed anatase as the unique TiO2 crystalline phase. The mesocrystalline structure of the anatase aggregates was clearly evidenced by HRTEM and SAED results. The mesocrystalline nanopowders exhibit a mesoporous structure with a surface area and pore volume of 63.5 m2 g-1 and 0.22 cm3 g-1, respectively. Ultraviolet (UV) and visible light (Vis) absorption ability were recorded. The combined high effectiveness and selectivity for the NOx abatement of the new mesocrystalline photocatalyst are reported. It is worth remarking that the maximised selectivity values reached for the NOx process are reported for the first time and could be associated with the mesoporous nature of the anatase photocatalyst.

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