Facile green synthesis of organosilica nanoparticles by a generic "salt route"

Colloidal silica has wide applications and the global demand of specialty silica is continually increasing. Therefore, it is significant to develop a synthetic method that is simple, versatile, energy-saving, ecologically benign, and easily scalable. Biomimetic synthesis of colloidal silica represents a promising strategy; however, it often requires the synthesis or extraction of specialized macromolecules. In this paper, we present a novel aqueous, one-pot, and green route for synthesis of organosilica nanoparticles. The reaction systems contain only water, an organosilane precursor, a salt, and a commonly used surfactant or amphiphilic polymer. The reaction was performed at ambient conditions without adding any additional solvent, energy, and harsh chemicals. The key findings include the novel identification of 5 salts (i.e. nitrite, fluoride, dibasic phosphate, acetate, and sulfite) that can catalyze organosilica condensation and the resulting formation of nano-colloids. Moreover, the presence of amphiphilic molecules is essential for salt catalysis at low salt concentrations and at nearly neutral pH. Solid-state NMR and in-situ ATR-FTIR studies confirmed that organosilica condensation is highly efficient under the mild reaction condition. In conclusion, the present study demonstrates that "soft" interaction between salts and surfactants (or polymers) can be utilized to construct an effective platform for synthesis of "hard" organosilica particles. The proposed method is generic and applicable to a wide range of commonly used surfactants (viz. non-ionic, anionic, cationic) and amphiphilic polymers, as well as to organosilanes with various hydrophobic functional groups (e.g. mercaptopropyl, vinyl, and methyl).