Controlled synthesis and osmotic properties of ionosilica nanoparticles

Abstract

Abstract Ionosilica nanoparticles are original ionic nano-objects at the interface of ionic liquids and mesoporous silica. Ionosilica nanoparticles' synthesis was achieved via sol-gel procedures exclusively from ionic trialkoxysilylated precursors without any silica source. However, the knowledge about the main synthesis parameters for a controlled synthesis of ionosilica nanoparticles remained fragmental so far. In this work, we present a systematic study for ionosilica nanoparticle formation starting from a virtually cationic silylated ammonium precursor. Due to their ionic nature, the behavior of ionic precursors considerably differs from that of conventional molecular silylated precursors. Here, we screened several reaction parameters for ionosilica nanoparticles’ formation such as solvent polarity, precursor and surfactant concentrations, and temperature. Our results allow controlling the textures and architectures of ionosilica nanoparticles in terms of porosity (specific surface area) and particle size. The formed ionosilica nanoparticles were thoroughly characterized by means of nitrogen sorption, elemental analysis, electron microscopies, dynamic light scattering (DLS), and solid state NMR measurements. Liquid 1H NMR spectroscopic measurements allowed monitoring the kinetics of the hydrolysis-polycondensation reactions. It appeared that the hydrolysis is relatively fast (30–120 min) whereas the polycondensation reaction requires more time (1–2 days). Finally, we used Forward Osmosis (FO-) experiments as a valuable tool to monitor a possible evolution of the nanoparticles in aqueous media. We observed that the ionosilica nanoparticles showed decreasing osmotic properties in successive FO-regeneration cycles. We attribute these results either to the exchange of the osmotically active halide anions or to particle agglomeration. Ionosilica nanoparticles therefore show limited long-term stability in aqueous media that limit their potential as draw solute in forward osmosis.