F- assistant synthesis of ultra-hydrothermally stable mesoporous silica by using nonionic organosilicon surfactant as templates

Mesoporous silica with thick pore wall (designated ECT) was synthesized in the presence of fluoride anions by using nonionic organosilicon surfactant (K903) as template. According to the results from XRD patterns and N-2 adsorption-desorption analysis, the addition of fluoride has a strong effect on the pore diameter and pore wall thickness of the ECT samples. Si-29 MAS NMR indicates that the degree of silicate condensation is greatly enhanced by adding fluoride ions. The hydrothermal stability of the mesoporous silica (ECT) synthesized in the presence of fluoride was found to be greatly improved compared to that of the sample without addition of fluoride ions. When F/Si = 0.045, the mesostructure of the sample could still remain after refluxed in boiling water even for 20 days. The ultra hydrothermal stability could be attributed to its thick pore wall, less defects in the silica framework and high degree of polymerization of silicate. Moreover, results from SEM reveal that the addition of fluoride anions also has great effect on the morphology structure of ECT sample. (C) 2009 Elsevier Inc. All rights reserved.