Solvothermal synthesis and characterization of a layered silicate including a large quantity of Al atom and its mesoporous derivatives

Abstract A layered silicate K-LDS (K 4 H 4 Si 8 O 20 ) analog including a large quantity of Al atom was synthesized by the solvothermal reaction of layered silicate H-RUB-18, potassium ethoxide, and aluminum isopropoxide. The overall Si/Al ratio of the layered compound (ca. 6) was much lower than other Al-substituted layered silicates (typically Si/Al > 50). The presence of four- and six-coordinate Al nuclei was identified by 27 Al MAS NMR spectra, and the relative ratio of AlO 4 :AlO 6 was nearly 4:5. In contrast, the framework Si atoms presented only the Q 3 ( Si–OH) local structure. It was suggested that a large quantity of Al atoms was distributed over the crystal K-LDS surface as amorphous alumina. Mesoporous aluminosilicate derivatives were prepared by the treatment of Al-K-LDS with cationic surfactants (C 16 TMACl and C 22 TMACl). The products had foam-like mesopores with 2.4–3.7 nm pore diameters and high Al contents with Si/Al = 2–3. The mesoporous derivatives could be presumed as aluminosilicates because of their uniform Al distribution, and they exhibited high hydrophilicities owing to the presence of Al atoms or silanols. In addition, their ability to adsorb lysozyme into the mesopores was demonstrated under low equilibrium concentration conditions. The amount of lysozyme adsorbed and the adsorption velocity of these derivatives were considerably superior to those of typical mesoporous silica such as SBA-15, SBA-16, and FSM-16.