Synthesis and properties of porous ester-silica nanoparticles

Ester-silica nanoparticles (NPs) were prepared using a facile two-surfactant synthesis route in neutral medium involving silica (tetraethyl orthosilicate, TEOS) and organosilica (3-(trimethoxysilyl)propyl 5-(trimethoxysilyl)pentanoate, PMe) precursors. The ester hydrolysis generates carboxylic acid groups, which confer a strongly negative zeta potential to the NPs at neutral pH. The extent of hydrolysis during the synthesis was quantified by FTIR. The NP size was shown to be highly dependent on hydrodynamic factors such as stir bar size and stirring speed, enabling to fine-tune the NP diameter. The textural properties of the NPs could be monitored using appropriate fraction x of silica precursor, x = [TEOS]/([TEOS]+2 [PMe]). For NPs with a silica fraction x higher than 0.5, a significant porosity could be observed, with mesoporosity appearing for x ≥ 0.7. The physicochemical and textural properties of the prepared materials open applications for water pollution abatement of specific organic compounds. This is exemplified by the efficient adsorption of rhodamine B from the liquid phase by the prepared NPs due to their physicochemical and textural parameters, including a high specific surface area and porosity, strong electrostatic forces and lipophilicity of the pore walls.