Preparation and properties of fluorinated aliphatic alcohols/silica nanocomposites – Application to the encapsulation of anatase titanium oxide nanoparticles into these composite cores

A variety of fluorinated aliphatic alcohols [RF-CH2CH2OH; RF = CF3(CF2)3CH2(CF2)5, CF3(CF2)n; n = 3, 5, 7] were applied to the preparation of the corresponding fluorinated alcohols/silica nanocomposites [RF-CH2CH2OH/SiO2] through the sol–gel reactions with tetraethoxysilane (TEOS) and silica nanoparticles under alkaline conditions. RF-CH2CH2OH/SiO2 nanocomposites thus obtained have a good dispersibility and stability in not only water but also traditional organic solvents such as methanol, ethanol, 1,2-dichloroethane and tetrahydrofuran. FE–SEM (field emission scanning electron microscopy) and dynamic light scattering (DLS) measurements show that these composites are nanometer size-controlled fine particles in methanol. These fluorinated nanocomposites were also applied to the surface modification of glass to exhibit a superhydrophilic characteristic with a superoleophobicity on the modified surface. Interestingly, RF-CH2CH2OH/SiO2 nanocomposites were found to exhibit no weight loss behavior corresponding to the contents of the alcohols in the composites even after calcination at 800 °C. In addition, anatase TiO2 nanoparticles (an-TiO2) were effectively encapsulated into RF-CH2CH2OH/SiO2 nanocomposite cores under the similar sol–gel reactions to give the corresponding fluorinated alcohol/SiO2/an-TiO2 nanocomposites. These obtained nanocomposites can give a higher photocatalytic activity even after calcination at 1000 °C for the decolorization of methylene blue under UV light irradiation than that of the an-TiO2 nanoparticles under the similar conditions, although the parent TiO2 nanoparticles after calcination were unable to give a photocatalytic activity.