High-Temperature Synthesis of Stable Ordered Mesoporous Silica Materials by Using Fluorocarbon-Hydrocarbon Surfactant Mixtures

摘要

Highly ordered hexagonal mesoporous silica materials(JLU-20)with uniform pore sizes have been successfully synthesized at high temperature(150-220 deg C)by using fluorocar-bon-hydrocarbon surfactant mixtures.The fluorocarbon-hydrocarbon surfactant mixtures combine the advantages of both stable fluorocarbon surfactants and ordered hydrocarbon surfactants,giving ordered and stable mixed micelles at high temperature(150-220deg C).Mesoporous JLU-20 shows extraordinary stability towards hydrother-mal treatment(100% steam at 800 deg C for 2 h or boiling water for 80 h),thermal treatment(calcination at 1000 deg C for 4 h),and toward mechanical treatment(compressed at 740 MPa).Transmission electron microscopy images of JLU-20 show well-ordered hexagonal arrays of mesopores with one-dimensional(ID)channels and further confirm that JLU-20 has a two-dimensional(2D)hexagonal(P6mm)mesostruc-ture.~(29)Si HR MAS NMR spectra of as-synthesized JLU-20 shows that JLU-20 is primarily made up of fully condensed Q~4 silica units(delta =-112 ppm)with a small contribution from incompletely cross-linked Q~3(delta =-102 ppm)as deduced from the very high Q~4/Q~3 ratio of 6.5,indicating that the mesoporous walls of JLU-20 are fully condensed.Such unique structural features should be directly attributed to the high-temperature synthesis,which is responsible for the observed high thermal,hydro-thermal,and mechanical stability of the mesoporous silica materials with well-ordered hexagonal symmetry.Furthermore,the concept of"high-temperature synthesis"is successfully extended to the preparation of three-dimensional(3D)cubic mesoporous silica materials by the assistance of a fluorocarbon surfactant as a co-template.The obtained material,designated JLU-21,has a well-ordered cubic Im3m meso-structure with fully condensed pore walls and shows unusually high hydro-thermal stability,as compared with conventional cubic mesoporous silica materials such as SBA-16.