High-temperature synthesis of stable ordered mesoporous silica materials using mesoporous carbon as a hard template

Replicated mesoporous silica materials from CMK-3 (denoted as RSC-3-X, X stands for synthesis temperature) have been successfully synthesized in acidic media at high temperatures (160-240°C) and subsequently characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen sorption isotherms, and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy. XRD patterns and nitrogen sorption isotherms exhibit the highly hydrothermal stable mesostructure of RSC-3 samples. Transmission electron microscopy images of RSC-3-220 show ordered hexagonal arrays of mesopores with 1D channels and further confirm the 2D hexagonal (p6mm) mesostructure of RSC-3-220. ²⁹Si MAS NMR spectra indicate that as-synthesized RSC-3 samples are primarily made up of fully condensed Q⁴ silica units (δ = -112 ppm) with a small contribution from incompletely cross-linked Q³ (δ = -102 ppm) as deduced from the high Q⁴/Q ³ ratio of 5.5-9.5, implying the fully condensed walls of RSC-3. Such unique structural features should be attributed directly to the high-temperature synthesis, which could be responsible for the observed highly hydrothermal stability of RSC-3.