No abstract

Thermally stable and 2-D hexagonal super-microporous silicas were obtained utilizing hydrated R-sodium disilicate over a diverse range of surfactant/Si molar ratios. Silica-based mesostructured materials composed of hydrated R-sodium disilicate and hexadecyltrimethylammonium (C 16 TMA) cations were acid-treated, resulting in the formation of 2-D hexagonal mesostructured silica(R)-n (n ) C 16 TMA/Si molar ratio). Although the 2-D hexagonal structure of mesostructured silica(R)-0.2 collapsed at 900°C, those of mesostructured silicas(R)-0.5, -0.7, and -1.0 were retained even after calcination at 1000°C. The retention of the 2-D hexagonal structures was confirmed further by TEM. The higher thermal stability is ascribed to lower Na content in mesostructured silica(R)-n. Higher C 16 TMA/Si molar ratios lowered the pH values in the reaction suspensions, and then interlayer Na ions in the silicates were further exchanged with hydrated protons. Because of the higher thermal stability, ordered super-microporous silicas can be formed in the present system. The condensation of the silicate frameworks proceeded with the rise of the calcination temperature, leading to a further decrease in pore size. The pore sizes of the products calcined at 1000°C were 1.7-1.8 nm (BJH method), smaller than those reported for ordered mesoporous silicas prepared using C 16 TMA cations.

No abstract

Silica-based mesostructured materials are formed using hydrated R-sodium disilicate and hexadecyltrimethylammonium (C 16 TMA) chloride at various C 16 TMA/Si molar ratios, and compared with those from kanemite. When the C 16 TMA/Si ratios are 0.2, 0.5, 0.7, and 1.0, 2-D hexagonal structures are formed from hydrated R-sodium disilicate though the structures are collapsed on calcination. Less ordered hexagonal structures with straight channels arranged in one direction are formed when the C 16 TMA/Si ratio exceeds 1.0. In the case of the reactions of kanemite with C 16 TMA ions, lamellar mesostructures are formed at the ratios higher than 0.5, whereas a 2-D hexagonal structure is formed only at the ratio of 0.2. Mesoporous silica (SSW-1) derived from hydrated R-sodium disilicate is prepared at lower pH without acid treatment when the C 16 TMA/Si ratio is 2.0. The volume occupied by the headgroups of C 16 TMA ions in hydrated R-sodium disilicate should be larger than that in kanemite because the distance between Si-Osites in the bending direction of hydrated R-sodium disilicate is longer than that of kanemite due to the unique layered silicate structure.