Preparation of monolithic fluoroalkyl end-capped vinyltrimethoxysilane oligomer /methyltrimethoxysilane/magnetite composites: Application to selective removal of fluorinated aromatic compounds from aqueous methanol solution under magnetic field

Abstract

Monolithtic fluoroalkyl end-capped vinyltrimethoxysilane oligomer /methyltrimethoxysilane/magnetite composites [RF-(VM-SiO3/2)n-RF/MeSiO3/2/Mag] were prepared through two simple processes which consist of the sol-gel reaction of the corresponding oligomer [RF-(CH2CHSi(OMe)3)n-RF: n = 2, 3; RF = CF(CF3)OC3F7: RF-(VM)n-RF] with methytrimethoxysilane (MTMS) under acidic conditions, and successively the sol-gel reaction in the presence of magnetic fine particles (Mag) under alkaline conditions. TEM (Transmission Electron Microscopy) pictures show that Mag particles can be effectively encapsulated into fluorinated oligomeric composite cores to produce the expected composites [RF-(VM-SiO3/2)n-RF/MeSiO3/2/Mag]. In addition, field emission scanning electron micrographs (FE-SEM) indicate that the obtained composites consists of monolithic structures to afford an extremely lower bulk specific gravity (0.32 g/cm3); although the corresponding RF-(VM-SiO3/2)n-RF/Mag composites prepared under similar conditions and the RF-(VM-SiO3/2)n-RF oligomeric particles prepared by the sol-gel reaction of the oligomer under alkaline conditions afforded the relatively higher values: 0.68 and 0.50 g/cm3, respectively. The surface wettability of the RF-(VM-SiO3/2)n-RF/MeSiO3/2/Mag composite particles was studied by the dodecane and water contact angle measurements to exhibit a superoleophilic/superhydrophobic characteristic on their surface. Interestingly, these composite particle powders were applied to the facile removal of aromatic compounds such as bisphenol A, bisphenol AF, 4, 4′-biphenol, octafluoro-4, 4′-biphenol, acetophenone, 2′, 3′, 4′, 5′, 6′-pentafluoroacetophenone, trans-cinamic acid and trans-2,3,4,5,6-pentafluorocinamic acid from aqueous methanol solution under a magnetic fields. More interestingly, it was demonstrated that we can observe the more efficient removal ability for the fluorinated aromatic compounds, compared to that of the corresponding non-fluorinated ones. Especially, such monolithic composites were found to provide the higher removal ability for these aromatic compounds than that for the usual RF-(VM-SiO3/2)n-RF/Mag composite powders under similar conditions.