期刊
MATERIALS
卷 6, 期 9, 页码 3688-3709出版社
MDPI
DOI: 10.3390/ma6093688
关键词
pseudomorphic transformation; silica gel; LiChrospher (R) Si 60; MCM-41 spheres; PFG NMR; diffusion
类别
资金
- Deutsche Forschungsgemeinschaft within the International Research Training Group GRK 1056 Diffusion in Porous Materials
- Top-Level Research Area Multifunctional Materials and Processes from Molecules and Nanodevices at Universitat Leipzig
The pseudomorphic transformation of spherical silica gel (LiChrospher(R) Si 60) into MCM-41 was achieved by treatment at 383 K for 24 h with an aqueous solution of cetyltrimethylammonium hydroxide (CTAOH) instead of hexadecyltrimethylammonium bromide (CTABr) and NaOH. The degree of transformation was varied via the ratio of CTAOH solution to initial silica gel rather than synthesis duration. The transformed samples were characterized by N-2 sorption at 77 K, mercury intrusion porosimetry, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Thus, MCM-41 spheres with diameters of ca. 12 mu m, surface areas >1000 m(2) g(-1), pore volumes >1 cm(3) g(-1) and a sharp pore width distribution, adjustable between 3.2 and 4.5 nm, were obtained. A thorough pulsed field gradient nuclear magnetic resonance (PFG NMR) study shows that the diffusivity of n-heptane confined in the pores of the solids passes through a minimum with progressing transformation. The final product of pseudomorphic transformation to MCM-41 does not exhibit improved transport properties compared to the initial silica gel. Moreover, the PFG NMR results support that the transformation occurs via formation and subsequent growth of domains of <1 mu m containing MCM-41 homogeneously distributed over the volume of the silica spheres.
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