Organic groups influencing microporosity in organosilicas

Abstract

The micropore structure of a series of organosilica materials with various organic groups in bridging (methylene, ethylene, hexylene, octylene, p-phenylene) and terminal (methyl, n-propyl) positions was analyzed and compared to that of inorganic amorphous silica. Vapor thermogravimetry with water, methanol, 1-propanol and cyclohexane vapors was used to measure accessible pore volumes, pore entrance sizes and surface chemistries. Gas pycnometry with He, Ar and N2 was used to measure skeletal densities, semi-quantitative surface-to-volume ratios and surface areas, pore entrance sizes and semi-quantitative pore cavity sizes. Conventional adsorption isotherms were measured for N2 at -196 °C to check for mesoporosity and for CO2 at 0 °C to obtain Brunauer-Emmett-Teller surface areas for comparison. The known classification of 1) short or rigid organic bridges that open up the pore structure, 2) longer and more flexible bridges that cause pore filling and 3) terminal organic groups that reduce pore formation is further specified. The incorporation of any organic group in the silica network increased the dispersity in micropore entrance sizes as compared to inorganic silica in the probed size range. A critical discussion is given of the commonly accepted 'spacing concept' of organic bridges.

Bis(triethoxysilyl)ethane (BTESE)–Organosilica Membranes for H2O/DMF Separation in Reverse Osmosis (RO): Evaluation and Correlation of Subnanopores via Nanopermporometry (NPP), Modified Gas Translation (mGT) and RO Performance

“…Hiroshima University’s successful strategy for controlling the water ratio (WR) to design the pore networks of BTESE membranes for both gas separation and reverse osmosis applications has been demonstrated through studies [ 11 , 13 , 20 ]. Additionally, there are many who conducted research on multiple generations of organoalkoxysilanes, such as bis(triethoxysilyl)methane (BTESM) and 1,3-bis(triethoxysilyl)propane (BTESP), 1,4-bis[2-(triethoxysilyl)vinyl]benzene (BTES-VB), and 2,5-bis[2-(triethoxysilyl)vinyl]pyridine (BTESVP) to tailor the pore size of organosilica membranes for gas separation (GS), pervaporation (PV), and RO applications [ 9 , 10 , 11 , 12 , 13 , 20 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ].…”

Development of an acetylacetonate-modified silica-zirconia composite membrane applicable to gas separation

“…Silica membranes exhibit moderately high flux and excellent selectivity [15,17,18], but size control and instability under hydrothermal conditions are known problems [15]. To develop silica and silica-based membranes with high perm-selectivity, pore size tunability, and hydrothermal stability, many researchers have studied various techniques such as spacer methods [19,20], templating methods [21], anion and cation doping [6,17,23], and hybridization of silica with other metal oxides such as Al2O3 [12,24], TiO2 [25,26], and ZrO2 [5,22].…”

Pore size tuning of bis(triethoxysilyl)propane (BTESP)-derived membrane for gas separation: Effects of the acid molar ratio in the sol and of the calcination temperature

“…In particular, bridged-type organosilica membranes have a loose network structure because organic linking units between the Si atoms assume the role of a spacer, and the Si atomic distance can remain large [19,20]. The effects that a spacer species of bridgedorganoalkoxysilane exerts on microporous structures and gas permeation properties have recently been discussed [29][30][31][32][33][34][35][36]. Organosilica with short linking units (CnH2n, n = 1, 2) creates a rigid silica network, and membranes with a microporous structure and molecular sieving properties have dominant gas permeation properties similar to conventional silica membranes.…”