In a three-neck circular bottom flask, quantitative amount of deionized and double-distilled
water was added and heated to 80°, then quantitative of AlCl3⋅6H2O (or Al(NO3)3⋅9H2O) was
added piece by piece with stirring. During the reaction, Al powder was added in order to
adjust the aluminum ion concentration. The hydrolysis reaction was, from a to z, carried out
under a refluxing condition. After a transparent and stable sol was obtained, the reaction was
completed.