In situ Surface Functionalization of Hydrophilic Silica Nanoparticles via Flame Spray Process

Hydrophobic silica nanoparticles grafted with a high amount of organic molecules were successfully prepared by an in situ functionalization method in flame spray pyrolysis (FSP) process. Hydrophilic SiO2 nanoparticles were converted into hydrophobic ones by silylation between 3-methacryloxypropyltrimethoxyl silane (MPS) and silica's surface hydroxyl groups. The freshly formed silica nanoparticles in flame were continuously functionalized by a fine spray of 3-methacryloxypropyltrimethoxyl silane (MPS) solution at a preferred temperature. The functionalization extent, morphology structure and size of silica nanoparticles were characterized by transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectronic spectroscopy (XPS). The influence of concentration, pH value and pre-activation of organic silane solution on the surface grafting density was investigated in detail. The obtained silica nanoparticles had a higher MPS functional content of 15.0 wt% (an average density of 2.7 MPS molecule/nm2) than that of the silica modified by wet chemistry route, showing an excellent, stable hydrophobic property. The results have demonstrated that the in situ FSP functionalization process is a simple, effective and promising route for the scalable preparation of advanced, hydrophobic nanomaterials.