Controlled Morphology Synthesis of Nanostructured β‑AlF3–x(OH)x with Tunable Specific Surface Area

In this work, the synthesis of β-AlF3–x(OH)x nanoparticles with very high specific surface area (SSA) using a microwave-assisted solvothermal process is reported. The influence of synthesis parameters on the morphology and SSA was investigated, and the nature of the solvent is shown to have the greatest impact. Five samples prepared using different solvent mixtures were deeply characterized by thermogravimetric analysis (TGA), N2 sorption, powder X-ray diffraction, transmission electron microscopy (TEM), and 19F and 27Al high-field solid-state NMR. Their SSAs range from 25 to 345 m2·g–1 with an associated OH content slightly increasing from ≈16% (AlF2.52(OH)0.48) to ≈19% (AlF2.42(OH)0.58), as estimated by TGA and 27Al high-field solid-state NMR. Compared to previous reference work [Dambournet, D., Chem. Mater. 2008, 204 1459−1469], β-AlF3–x(OH)x nanoparticles with SSAs up to 4 times larger were obtained. TEM revealed the formation of hollow nanostructures except when the surface exceeds 300 m2·g–1, in which case isolated nanoparticles are observed. The sample with the highest SSA also displaying an appealing cumulative pore volume of 0.060 cm3·g–1, its hydrogen adsorption capability was evaluated to show that β-AlF3–x(OH)x nanoparticles have a potential interest for hydrogen storage applications.