X-ray structural modeling and gas adsorption analysis of cagelike SBA-16 silica mesophases prepared in a F127/butanol/H2O system

A detailed characterization of large-pore cagelike mesoporous SBA-16 silica materials with tailored pore dimensions is reported. The materials were synthesized in a EO106PO70EO106 (F127)-butanol-H2O system under mildly acidic conditions, and the pore diameters were tailored by varying the hydrothermal treatment temperature. Structural information was acquired by full-profile analysis of powder X-ray diffraction (XRD) patterns. High-resolution diffraction data were obtained for all the materials using synchrotron radiation as the X-ray source, enabling a comprehensive XRD modeling supplemented with the generation of electron density distribution maps. The structural parameters derived from the XRD modeling were compared with data obtained from nitrogen and argon physisorption experiments performed at -196 degrees C. An excellent agreement was found between the XRD modeling results and those obtained by a new nonlocal density functional theory (NLDFT) kernel developed for pore size analysis based on gas adsorption in spherical pores, while NLDFT analysis based on a cylindrical pore model was shown to systematically underestimate the pore dimensions by about 30% which exceeds previous expectations. Furthermore, the Barrett-Joyner-Halenda model was shown to give errors up to about 45% in the pore size range above 4 nm. The structure of the surfactant-silica hybrid materials was also analyzed by XRD, which shed more light on the structural changes accompanying the thermal surfactant removal process. The present study is expected to provide a reference source for the accurate characterization of large cagelike mesoporous silica materials, on the basis of a direct comparison of suitable data collected independently by gas physisorption and comprehensive XRD modeling.