Effects of Cation on the Morphology of Boehmite Precipitated from Alkaline Solutions by Adding Gibbsite as Seed

Abstract

Regulation of boehmite morphology is important for improving its performance in applications. In this paper, the dependence of boehmite morphology on cation ions was studied by XRD, SEM, TEM, FTIR, and zeta-potential, together with calculation of ion degree of association. Boehmite was respectively precipitated from sodium, potassium, lithium, or barium alkaline solution by adding gibbsite as seed at 180 °C for 2 h. Cation concentration and species determined the boehmite morphology. Increase in cation concentration or precipitation in K+, Na+, Li+, and Ba2+ alkaline solution correspondingly precipitated rhombic, hexagonal, and elliptical morphology for boehmite. Al(OH)4– was predominantly found in filtrate solution by Raman spectra, whereas red shift of FTIR was observed in alkaline solution containing Ba2+, Li+, Na+, and K+ cations. The degree of association of Mn+[Al(OH)4–]nn− increased in the following order: Ba2+[Al(OH)4–]2 > Li+Al(OH)4– > K+Al(OH)4– > Na+Al(OH)4– in the same concentration of cation solution. This finding agreed with the variations in FTIR change and zeta potential. Meanwhile, increasing cation and Al(OH)4– concentration or precipitation in lithium or barium alkaline solution caused the (202) facet of boehmite to gradually disappear and the (200) facet to be exposed. Therefore, the selective adsorption of ion pairs on the (202) and (200) facet of boehmite mainly accounted for the boehmite morphology.