Effect of partially neutralized aluminum solutions on the texture and pore structure of silica

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Physicochemical and engineering aspects, 1996-10, Vol.117 (1), p.131-141
• Main Authors: Selim, S.A., El Shafei, G.M.S., Mekewi, M., Stone, W.E.E., Vielvoye, L.
• Format: Article
• Language: English
• Subjects: Aluminium; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Pore structure; Porous materials; Silica; Texture
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/0927-7757(96)03646-1

N 2 adsorption measurements at 77 K were performed on two types of silica of different porosities, and on their products obtained by soaking in partially neutralized aluminum solutions of varying R = [OH] [Al] = 0.5–2.0 (pH 3–4). TG analysis showed that the Al taken by the mesoporous silica was accompanied by its hydroxyls, but with the predominantly microporous silica it was stripped of some of them, where a strong potential field in the narrow pores compensated for any charge differences. IR spectral analysis showed that for microporous silica the peak (due to SiO stretching of surface OH) is located at 950 cm −1 instead of approximately 970 cm −1 in the case of mesoporous silica, which seems to results from the strong perturbation between hydroxyls at close range in the narrow pores. A reduction in this peak takes place upon Al treatment that increases with R, with the probable formation of a surface complex of the type SiOAl. Uptake of Al ions produced a narrowing of the pores, that increased with the increase in Al content. From pore structure analysis, the micropore fraction could be sorted into ultramicropores (⩽10 Å) and supermicropores (10–20 Å). The volume of the former is almost unaffected by any change in Al content. The sizes of the supermicropores and mesopores (⩾20 Å) are crucial to the Al uptake. Changes in pore sizes at R ⩾ 1.0 facilitate the initial attack of the large Al polymeric species.