Quaternary Ammonium-Based Ionosilica Hydrogels as Draw Solutes in Forward Osmosis

Abstract

In the last few years, forward osmosis (FO) has attracted increasing interest as a sustainable technique for water desalination and wastewater treatment. However, FO remains as an immature process principally due to the lack of efficient and easily recyclable draw solutes. In this work, we report that ionosilica hydrogels based on quaternary ammonium halide ionosilica are efficient draw solutes in FO. Fluidic ionosilica hydrogels were obtained via hydrolysis-polycondensation reactions of a trisilylated quaternary ammonium precursor in slightly acidic water/ethanol solvent mixtures. The liquid-to-gel transition of the precursor and the kinetics of the formation of hydrogels were monitored by liquid NMR measurements. The formed hydrogels were shown to generate osmotic pressure up to 10.0 atm, indicating the potential of these hydrogels as efficient draw solutes in FO. Our results suggest that iodide anions are the osmotically active species in the system. Regeneration of the hydrogels via ultrafiltration (UF) was successfully achieved, allowing the development of a closed FO-UF process. However, the osmotic performances of the ionosilica hydrogels irreversibly decreased along the successive FO-UF cycles, probably due to anion exchange processes.

Textural control of ionosilicas by ionic liquid templating

“…33 Ionosilicas are highly modulable functional materials featuring a large range of surface and interface properties. 34,35 They found applications in water treatment and upgrading, 36,37 separation 38,39 and drug delivery. 40–42 Due to the high chemical similarity between ionosilicas and ILs and with the aim of studying the confinement of ILs within an ionosilica matrix, we recently focused on the formation of nanocomposites via hydrolysis–polycondensation reactions of ionosilica precursors in the presence of ILs.…”