Preparation of hydroxyl group containing bridged organosilica membranes for water desalination

Development of Highly Water-Permeable Robust PSQ-Based RO Membranes by Introducing Hydroxyethylurea-Based Hydrophilic Water Channels

Copolymerization of bis[3-(triethoxysilyl)propyl]amine (BTESPA) and N-(2-hydroxyethyl)-N'-[3-(triethoxysilyl)propyl]urea (HETESPU) provided highly permeable robust reverse osmosis (RO) membranes that have an organically bridged polysilsesquioxane (PSQ) structure. The RO experiments with NaCl aqueous solution (2000 ppm) indicated that the introduction of hydroxyethylurea groups markedly improved the permeability of water (1.86 × 10^-12 m³/m²sPa) to approximately 19 times higher than that of a membrane prepared via the BTESPA homopolymerization, with NaCl rejection remaining nearly unchanged (96%). This is the highest water permeability obtained so far for PSQ-based membranes that show higher than 90% NaCl rejection. The improvement of water permeability is likely due to aggregation through hydrogen bonding in the PSQ layer, which can be regarded as a hydrophilic water channel.

Robust and Transparent Antifogging Polysilsesquioxane Film Containing a Hydroxy Group

Poly(glycidyloxypropyl)silsesquioxane (PGPS) was successfully synthesized by hydrolysis and polycondensation using the nitrogen flow method. A poly(3-(2,3-dihydroxypropoxypropyl)silsesquioxane) (PSQ-OH) film was prepared via two routes. In route A, PSQ-OH was prepared by the hydrolysis of the epoxy group of PGPS in an aqueous hydrochloric acid (HCl)/tetrahydrofuran solution, affording a diol group; then, PSQ-OH was coated on a glass substrate and heated. The antifogging performance of the PSQ-OH film was evaluated in terms of water uptake (WU) and scratch resistance. The obtained PSQ-OH film exhibited a low WU of 5% and a scratch resistance of 1.6. In route B, PGPS was coated on a glass substrate and immersed in a 0.5 mol/L aqueous sulfuric acid solution for 1-15 h at room temperature, producing a diol group. The solid-state ¹³C nuclear magnetic resonance spectrum indicated that the epoxy group was completely hydrolyzed after immersion for 15 h. The WU of the PSQ-OH film prepared via route B increased from 5 to 19% with the increase in the immersion time and was higher than that of the PSQ-OH film prepared via route A. The PSQ-OH film on a glass substrate retained transparency under water vapor exposure at 60 °C. The PSQ-OH film prepared via route B exhibited a high scratch resistance of 2.7-3.6, similar to that of a poly(3-(2-aminoethylaminopropyl)silsesquioxane) film. The scratch resistance of the PSQ-OH film was 5-7 times higher than that of the poly(vinyl alcohol) film. The PSQ-OH film was uniform with no pinholes and cracks. The PSQ-OH film was transparent and colorless and exhibited a high transmittance of >90% in the wavelength range of 400-800 nm. Overall, the prepared PSQ-OH film exhibits good antifogging, transparency, and mechanical properties.

Organosilica-Based Membranes in Gas and Liquid-Phase Separation

Organosilica membranes are a type of novel materials derived from organoalkoxysilane precursors. These membranes have tunable networks, functional properties and excellent hydrothermal stability that allow them to maintain high levels of separation performance for extend periods of time in either a gas-phase with steam or a liquid-phase under high temperature. These attributes make them outperform pure silica membranes. In this review, types of precursors, preparation method, and synthesis factors for the construction of organosilica membranes are covered. The effects that these factors exert on characteristics and performance of these membranes are also discussed. The incorporation of metals, alkoxysilanes, or other functional materials into organosilica membranes is an effective and simple way to improve their hydrothermal stability and achieve preferable chemical properties. These hybrid organosilica membranes have demonstrated effective performance in gas and liquid-phase separation.