Study on the synthesis of mesoporous materials with liquid crystals formed in SDS/CTAB/NaBr/1-Hexanol/H2O as templates

Abstract

Mesoporous silica materials were synthesized using tetraethoxysilane (TEOS) as precursor and liquid crystals (LCs) formed in mixtures of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) with additions of NaBr and 1-hexanol as templates. For this purpose, the formation of LCs in the mixtures under different conditions was first studied. It was found that the additions of 1-hexanol and NaBr can synergistically weaken the electrostatic interaction between CTAB and SDS and promote the growth of the ordered assemblies, leading to the significant expansion of the LC phase areas in both SDS excess area and CTAB excess area, respectively. The effects of 1-hexanol concentrations, surfactant concentrations, and pH values on the phase diagram and hence the structures of LCs were subsequently studied. These LCs are well-structured templates for the syntheses of mesoporous silica materials that were characterized using nitrogen adsorption/desorption analysis and scanning electron microscopy (SEM). It was shown that 1-hexanol played an important role in the formation of LC templates and hence effectively improved the specific surface area and order of mesoporous materials. The BET specific surface area was high up to 937 m2/g and the average pore diameter increased to 2.5 nm when the total concentration of CTAB and SDS was 0.2 mol/L, the molar fraction of CTAB in the mixture was 0.82, the concentration of 1-hexanol was 0.4 mol/L, and pH value was 2. These studies shed light on the syntheses of mesoporous materials with large specific surface area and highly ordered structure for multiple applications.