New Insights into the Microstructure-Separation Properties of Organosilica Membranes with Ethane, Ethylene, and Acetylene Bridges

Abstract

Microporous organosilica membranes with ethane, ethylene, and acetylene bridges have been developed and the extensive microstructural characterization has been discussed in relation with separation properties of the membrane. The organosilica network structure and the membrane performances can be controlled by adjusting the flexibility, size, and electronic structure of the bridging groups. A relatively narrow size distribution was obtained for the novel acetylene-bridged sol by optimizing the sol synthesis. Incorporation of larger rigid bridges into organosilica networks resulted in a looser microstructure of the membrane, which was quantitatively evaluated by N2 sorption and positron annihilation lifetime (PAL) measurements. Molecular weight cutoff (MWCO) measurements indicated that the acetylene-bridged membrane had a larger effective separation pore size than ethane- and ethylene-bridged membranes, leading to a relatively low NaCl rejection in reverse osmosis. In quantum chemical calculations, a more open pore structure and increased polarization was observed for the acetylene-bridged networks, which led to a significant improvement in water permeability. The present study will offer new insight into design of high-performance molecular separation membranes.

Hybrid Materials for Molecular Sieves

“…BTESM is selective in the separation of hydrocarbons with kinetic diameters > 0.4 nm, e.g., C 2 H 6 (0.42 nm), i-C 4 H 10 (0.54 nm) , and the separation of propene (0.46 nm) from propane (0.50 nm) (Kanezashi et al 2012a, b). In agreement with expectation, longer and stiffer bridges lead to larger pores and therefore to lower permselectivities Xu et al 2014).…”

“…Several bridged groups R have already been used in hybrid silica membranes. In general they are linear aliphatic or aromatic bridges, e.g., alkylenes -C n H 2n -(n = 1, 2, 3, 6, 8, and 10), ethenylene -C 2 H 2 -, ethynylene -C C-, and the arylenes p-phenylene -p-C 6 H 4 -, and di-pphenylene -p-C 6 H 4 -p-C 6 H 4 - Paradis et al 2013;Xu et al 2014). More recently, a precursor with a malonamide-functional bridge and a triazine-functional precursor have been reported Ibrahim et al 2014b).…”

Structure–property tuning in hydrothermally stable sol–gel-processed hybrid organosilica molecular sieving membranes

“…There is a small, but considerable fraction of pores [0.4 nm that limits the separation of hydrogen from other larger industrial molecules and that is not present in silica. Longer bridge lengths [12] and stiffer bridges [14] lead to larger pores and therefore to lower permselectivities, although long flexible chains such as -C 8 H 16 -appear to collapse, leading to loss of permeability. On the other hand, BTESM-derived membranes with permselectivities of 15-21 for H 2 /N 2 and 7-9 for H 2 /CH 4 [28] perform only marginally better than BTESE-derived membranes in H 2 separation even though their bridge length is shorter.…”

“…Bridged silsesquioxanes that have already been reported for hybrid organosilica membranes contain aliphatic or aromatic bridging groups [12][13][14]. The precursors referred to in this article are a,x-bis(triethoxysilyl)-R compounds, where R is an alkylene -C n H 2n -(n = 1, 2, 3, 6, 8, or 10), ethenylene (-C 2 H 2 -), ethynylene (-C:C-) or an arylene Fig.…”

Preparation of Bridged Polysilsesquioxane Membranes from Bis[3-(triethoxysilyl)propyl]amine for Water Desalination

“…In fact, membranes prepared from bis(triethoxysilyl)-ethane, -ethene, and -ethyne showed improved water permeability as the bridging units became more rigid and polar in the order of ethane < ethene < ethyne. 12,13 We have introduced hydroxyl, 14 acetoxy, 15 triazine, 16 and triazole 17 units to the membranes to increase water permeability by enhancing hydrophilicity.…”