The fluorination of silica by ammonia fluoride in several organic solvents has been studied by diffuse reflectance Fourier transform infrared spectroscopy with in situ thermal treatment, 19F magic angle spinning nuclear magnetic resonance, 1H → 29Si and 19F → 29Si cross-polarization techniques, and temperature-programmed analysis followed mass spectrometrically. The extent of surface fluorination and the type of fluorinated species depend on the solvent and treatment procedure. The silicas that were studied show evidence of the formation of two types of surface-fluorinated silicon species:  suface-bonded tetrahedral species with a general formula of O n -Si(OH)4   -   n   -   m F m and, to a lesser extent, octahedral species [F n Si(OH)6   -   n ]2-, which were formed already at low temperature. The thermal decomposition of [F n Si(OH)6   -   n ]2- leads to the removal of corresponding silicon fluorides and hydroxyfluorides, and surface-bonded O3Si−F and O−SiF3 can be additionally formed. Heating to 500−600 °C causes the surface migration of fluorine in O3Si−F over siloxane bridges and the formation of silicon fluorides and their subsequent removal from the surface (complete removal at 600 °C). The hydrophobic nature of fluorinated silica has been shown by infrared spectroscopy and by the thermal dependence of water desorption from the surface.

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Mesoporous molecular sieves Si-MCM-41 (purely siliceous) and Ti-MCM-41 (partly covered with a surface layer of TiO2) were functionalized with phosphate groups by treatment with POCl3 (denoted -MCM-41(P)and Ti-MCM-41(P), respectively). With the use of TEM, X-ray diffraction, and N2 adsorption, it was shown that the initial hexagonal structure, the high specific surface area, and porosity are retained in the functionalized materials but are not as good as in the starting materials. 1H MAS NMR and 31P MAS NMR revealed that the surface of Si-MCM-41(P) consists of silicon phosphate and pyrophosphate species. That of Ti-MCM-41(P) additionally contains titanium dihydro-, hydro-, and pyrophosphate species, the latter being predominant. TPD of adsorbed ammonia for Si-MCM-41(P) and Ti-MCM-41(P) showed that functionalization leads to the creation of moderate and strong acid sites. A combination of mesoporous structure with acidic properties makes the MCM-41 functionalized with phosphate groups promising for use as solid acid catalysts.