Studies on the synthesis of nano-alumina in air and water stable ionic liquids

• Published in: Journal of materials chemistry Vol. 18; no. 4; pp. 442 - 449
• Main Authors: Farag, Hala K., Endres, Frank
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2008
• Subjects: Chemical synthesis methods; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Materials science; Methods of nanofabrication; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Physics; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Aluminium oxide; Thermal decomposition; Porous materials; Template reaction; Amides; Calcination; Mesoporosity; Ionic liquid; Hydrolysis; Nanoparticles; Pore size; Aluminium chloride; Crystal growth from solutions; Surface area; Microstructure; Alumina; Nanostructured materials; Nanomaterial synthesis
• ISSN: 0959-9428; 1364-5501
• DOI: 10.1039/B711704C

In this paper we report on the synthesis of aluminium oxide nanoparticles in two different air and water stable ionic liquids namely, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide [BMP]TFSA and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide [EMIm]TFSA. The ionic liquids [BMP]TFSA and [EMIm]TFSA exhibit biphasic behaviour beginning with an AlCl3 concentration of 1.6 mol L-1 and 2.5 mol L-1, respectively. Different aluminium oxides were prepared by the hydrolysis of AlCl3 dissolved in the employed ionic liquids, followed by calcinations. AlCl3*6H2O was found to be the main hydrolysis product of the AlCl3 containing ionic liquids. The as-prepared AlCl3*6H2O is subject to thermal decomposition producing different forms of transition oxides, depending on the original liquid composition. Alumina was also obtained by hydrolysis of as-prepared AlCl3*6H2O by NH4OH solution. Hydrolysis of the upper phase of the biphasic mixture of 3 M AlCl3-[EMIm]TFSA with NH4OH produces transparent alumina which is converted into alpha-Al2O3 with a low amount of delta-Al2O3 after calcinations at 1000 deg C. The formation of pseudoboehmite and gamma-Al2O3 as intermediates are observed at 200 deg C and 550 deg C, respectively. The obtained pseudoboehmite is mesoporous with an average pore diameter of 3.8 nm and a high surface area of 226 m2 g-1. The chloroaluminite obtained by hydrolysis of the homogenous mixture of 1 M AlCl3-[BMP]TFSA undergoes thermal decomposition yielding amorphous alumina at 200 deg C, which transforms completely to well crystallized alpha-Al2O3 at 1000 deg C. The obtained alpha-alumina is porous with an average pore size of about 10 nm. This suggests that the ionic liquid [BMP]TFSA acts as a template and that it decomposes thermally at elevated temperature producing pores.