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 [RF-(VM-SiO3/2)n-RF/Mag] were prepared by the sol-gel 
reaction of the corresponding fluorinated
oligomer [RF-(CH2CHSi(OMe)3)n-RF; n = 2, 3; RF =
CF(CF3)OC3F7 : RF-(VM)n−RF] 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 RF-(VM-SiO3/2)n-RF/Mag composite fine particles. The RF-(VM-SiO3/2)n-RF/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 RF-(VM-SiO3/2)n-RF/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.