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

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 center dot 6H(2)O was found to be the main hydrolysis product of the AlCl3 containing ionic liquids. The as- prepared AlCl3 center dot 6H(2)O 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 center dot 6H(2)O 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 degrees C. The formation of pseudoboehmite and gamma-Al2O3 as intermediates are observed at 200 degrees C and 550 degrees C, respectively. The obtained pseudoboehmite is mesoporous with an average pore diameter of 3.8 nm and a high surface area of 226 m(2) g(-1). The chloroaluminite obtained by hydrolysis of the homogenous mixture of 1M AlCl3-[ BMP] TFSA undergoes thermal decomposition yielding amorphous alumina at 200 degrees C, which transforms completely to well crystallized alpha- Al2O3 at 1000 degrees 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.