Preparation of fluoroalkyl end-capped vinyltrimethoxysilane oligomer/micro-sized silica composites possessing superoleophilic/superhydrophobic characteristic: application to selective removal of aromatic compounds from aqueous methanol solution by using these composites

Fluoroalkyl end-capped vinyltrimethoxysilane oligomer [R_F-(CH₂–CHSi(OMe)₃)_n-R_F; n = 2, 3; R_F = fluoroalkyl group: R_F-(VM)_n-R_F] was found to undergo the sol–gel reaction in the presence of micro-sized silica particles under alkaline conditions to afford the corresponding fluorinated oligomer/micro-sized silica composites [R_F-(VM-SiO_3/2)_n-R_F/μ-SiO₂]. The obtained composites were applied to the surface modification of glass to reveal a superoleophilic/superhydrophobic characteristic on the modified surface. In contrast, fluoroalkyl end-capped vinyltrimethoxysilane oligomer/silica nanocomposites [R_F-(VM-SiO_3/2)_n-R_F/n-SiO₂], which were prepared in the presence of nanometer-sized silica particles under similar sol–gel reactions, provided an oleophobic/superhydrophobic property on the surface. R_F-(VM-SiO_3/2)_n-R_F/μ-SiO₂ composites were applied to the solid-phase extraction sorbent to isolate the transparent colorless oil from water-in-oil (W/O) emulsion. These composite powders were also applicable to the effective removal of traditional organic dyes, such as rhodamine B, acid red 289, and fluorescein from aqueous methanol solution. Of particular interest, it was demonstrated that R_F-(VM-SiO_3/2)_n-R_F/μ-SiO₂ composites, of whose micro-sized silica gel is surface-functionalized with amino units, can exhibit a similar superoleophilic/superhydrophobic characteristic on the composite surface, giving the selective removal of fluorinated phenol-type aromatic compounds from aqueous methanol solutions, although the removal ability for the corresponding non-fluorinated ones was not observed at all under similar conditions.