High-temperature synthesis of stable ordered mesoporous silica materials by using fluorocarbon-hydrocarbon surfactant mixtures.
Highly ordered hexagonal mesoporous silica materials (JLU-20) with uniform pore sizes have been successfully synthesized at high temperature (150-220 degrees C) by using fluorocarbon-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 (150-220 degrees C). Mesoporous JLU-20 shows extraordinary stability towards hydrothermal treatment (100 % steam at 800 degrees C for 2 h or boiling water for 80 h), thermal treatment (calcination at 1000 degrees 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 (1D) channels and further confirm that JLU-20 has a two-dimensional (2D) hexagonal (P6 mm) mesostructure. 29Si HR MAS NMR spectra of as-synthesized JLU-20 shows that JLU-20 is primarily made up of fully condensed Q4 silica units (delta=-112 ppm) with a small contribution from incompletely cross-linked Q3 (delta=-102 ppm) as deduced from the very high Q4/Q3 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, hydrothermal, 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 mesostructure with fully condensed pore walls and shows unusually high hydrothermal stability, as compared with conventional cubic mesoporous silica materials such as SBA-16.
Department of Chemistry & State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023, China.
Defeng
D
Li
Yu
Y
Han
Jiangwei
J
Song
Lan
L
Zhao
Xianzhu
X
Xu
Yan
Y
Di
Feng-Shou
FS
Xiao