Preparation of fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/magnetite composites - Application to separation of oil and water

Fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/magnetite composites [R-F-(VM-SiO3/2)(n)-R-F/Mag] were prepared by the sol-gel reaction of the corresponding fluorinated oligomer [R-F-(CH2CHSi(OMe)(3))(n)-R-F; n = 2, 3; R-F = CF(CF3)OC3F7 : R-F-(VM)(n)-R-F] in the presence of magnetite (Fe3O4: Mag) nanoparticles under alkaline conditions at room temperature. Transmission Electron Microscopy (TEM) images showed that Mag nanoparticles can be effectively encapsulated into the fluorinated oligomeric silica nanoparticle cores to afford the R-F-(VM-SiO3/2)(n)-R-F/Mag composite fine particles. The R-F-(VMSiO3/2)(n)-R-F/Mag composite powders thus obtained were applied to the surface modification of glass to exhibit a superoleophilic/superhydrophobic characteristic on the modified surface. Interestingly, it was demonstrated that these composite powders were able to adsorb effectively oil droplets spread on the water interface under a magnetic field (permanent magnet). A good recyclability of the fluorinated composite powders was observed for the adsorption and desorption of the oil even after 5 cycle by the use of the similar magnetic separation technique. In addition, the R-F-(VM-SiO3/2)(n)-R-F/Mag composite powders were applied to the demulsification of W/O emulsion to isolate the transparent colorless oil under a magnetic field, and a reusability of the composite powders was also observed for the demulsification with a higher efficiency over 97% even after 5 cycle.