Different synthesis methods for ordered mesoporous silicas and their characteristics comparison

Abstract

Ordered mesoporous silica were synthesized under different conditions: hydrothermal synthesis in basic medium, room temperature synthesis in acid medium and sol-gel synthesis in neutral medium, and pore structure, specific surface area and pore size distribution of samples were studied and compared in detail by means of SAXRD, HRTEM, BET, FT-IR. The results show that the mesopores in the samples obtained via above three methods all possess uniform hexagonal arrays in short range. Mesoporous silica obtained in acid medium possesses narrow pore size distribution centered around 1.24 nm with specific surface area of 1220 m²·g⁻¹; Mesoporous silica obtained in basic medium by hydrothermal synthesis at 160°C possesses narrow pore size distribution centered around 1.90 nm with specific surface area of 542.8 m²·g⁻¹; and mesoporous silica obtained in neutral medium by sol-gel synthesis possesses broader pore size distribution centered around 4.01 nm, specific surface area of 485.0 m²·g⁻¹. Therefore, ordered mesoporous silicas with different pore sizes can be prepared using various synthetic methods and conditions. After heat treatment, Si-O-Si bending vibration strengthens and the adsorption peak of asymmetrical Si-O-Si stretching vibration broadens, and the crosslinking and condensation reaction of silica skeleton strengthen, meanwhile the amount of active centers of hydroxyl group on the surface of mesopores may be influenced, thus chemical assembly activity of mesopores may also be influenced.