Seiichi Kondo

Surface silanol groups of mesoporous silica FSM-16

The surface structure of mesoporous silica crystals FSM-16 with a narrowly distributed pore size has been studied by FTIR, measurement of SiOH number and adsorption of N2 and H2O. IR spectra of FSM-16 outgassed at temperatures above 170 °C showed a sharp band at 3740 cm–1 due to free SiOH and a broad shoulder at 3600–3500 cm–1 due to hydrogen-bonded SiOH. The SiOH number, determined by a weight-loss method, amounted to 3.3 groups nm–2, which is less than that of mesoporous silica gels. The amount of H2O adsorbed on FSM-16 decreased with calcination above 800 °C, owing to the dehydroxylation of SiOH. On treating with alcohol, the number of free SiOH decreased, leading to a decrease in H2O adsorption. The crystallinity of FSM-16 was lowered by pressing. With increasing pressure the specific surface area decreased and the SiOH number increased, up to 9.5 groups nm–2.

Physical and chemical properties of inactive surface hydrogen-bonded hydroxyl groups

The physical and chemical properties of surface hydrogen-bonded OH groups, formed by the hydrothermal reaction of silica hydrogels, xerogels, precipitated silicas (made with sodium silicate in the liquid phase at pH 11 and > 373 K) and aerosils, have been studied. In contrast to free OH groups, surface hydrogen-bonded OH groups, having an absorption band at 3500 cm–1, have low enthalpies of adsorption of water, methanol and methyl iodide, can be reversibly dehydroxylated and rehydroxylated by the adsorption of water vapour, and can be easily changed to OD groups by the adsorption of heavy water. These OH groups cannot be methoxylated with chlorotrimethylsilane or methanol. Cations such as Co2+ do not seem to be ion exchanged with the protons of these OH groups.

Fourier-transform infrared spectroscopy of colloidal α-, β- and γ-ferric oxide hydroxides

Fourier-transform infrared spectra and surface properties of colloidal α-, β- and γ-ferric oxide hydroxides [Fe(O)OH], which were synthesized and aged in this laboratory, have been studied. The spectrum of the α phase has a strong absorption band at 3150 cm–1 and two weak ones at 3485 and 3661 cm–1. That of the β phase has a strong band at 3480 cm–1, a weak band at 3659 cm–1 and two very weak bands at 3686 and 3723 cm–1. That of the γ phase has a strong band at 3160 cm–1, a weak band at 3624 cm–1 and a very weak band at 3528 cm–1. The changes of these bands by the adsorption of heavy water, water and methyl iodide molecules and cupric ions have been studied in detail and the various bands were assigned to various OH groups with respect to the crystal structures of these materials.

Heat of immersion of thermally treated silica gel

The heat of immersion of thermally treated silica gel in water, aliphatic alcohols and other organic compounds was studied. Silica gel was heathyphen;treated in the range from ≈ 450 K to the temperature above which a vigorous change in properties occurred by sintering. Heat treatment was performed in gases such as helium, oxygen, air and water, and a vacuum of ≈ 0.1 N m–2; a known amount of Na+ ion impurity was present in silica gel to be treated. The values of heat of immersion in water, aliphatic alcohols, aromatic compounds and compounds with dipole moments were proportional to the number of OH groups per unit surface area in the range 0 to ≈ 4 OH groups per nm2. This relation is discussed with respect to the surface and pore structures of silica gel.

Adsorption of water and methanol on colloidal iron(III) oxide hydroxides by infrared spectroscopy

The surfaces of α-, β- and γ-iron(III) oxide hydroxides have been characterized mainly through the adsorption behaviour of water and methanol by means of F.t.i.r. spectroscopy. In the α-phase two kinds of surface hydroxyl groups with bands at 3485 and 3661 cm–1 are active for the adsorption of these molecules. In the β-phase two surface hydroxyl groups with bands at 3686 and 3723 cm–1 are active for the adsorption of both molecules, but that at 3659 cm–1 is less active. The hydroxyl groups of the γ-phase with a band at 3624 cm–1 are active for water and methanol adsorption. There seem to be reactive adsorption sites other than surface hydroxyl groups.