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Sol-gel-derived organosilica membranes with different linking groups consisting of 2 carbon atoms (ethane, ethylene, and acetylene) were fabricated using bis(triethoxysilyl)ethane (BTESE), bis(triethoxysilyl)ethylene (BTESEthy), and bis(triethoxysilyl)acetylene (BTESA). No research group has ever proposed tailoring the microstructure and permeation properties of bridged organosilica membranes as a way to control the bond angles. In this study, however, we found that increases in the Si–O–Si and Si–C–C bond angles contributed to the formation of a loose and uniform structure, which was suggested by the blue shift of Si–O–Si and Si–C–C bonds in the FT-IR spectra. BTESA membranes featured a more open and accessible pore structure, which was suitable for the separation of C3H6/C3H8. The present study provides a novel way to design the microstructure and permeation properties of organosilica membranes via controlling the bond angles in the network structure.

TiO2-ZrO2 nanofiltration membranes were successfully prepared using a sol-gel method. Two types of TiO2-ZrO2 sols (polymeric and colloidal sols) with molar ratios of 5/5 were coated onto α-Al2O3 cylindrical porous supports followed by firing at different temperatures. The structures of the membranes were amorphous up to a firing temperature of 500 °C. Measurements of the N2 permeance and water permeability revealed that values for average pore size, N2 permeance, and water permeability (Lp) of the prepared membranes were increased with increases in the firing temperature, and a drastic increase was observed at the temperature of transformation from an amorphous to a crystalline phase. For the membranes fired at 200–600 °C, the average pore size and N2 permeance was 0.5–0.8 nm and 0.14–0.54 × 10−5 mol/(m2 s Pa), respectively; nanofiltration performance showed molecular weight cut-offs (MWCOs) of 200–810 g/mol, and Lp of 2–12 × 10–12 m3/(m2 s Pa), respectively. In the present study, values for the structure and separation performance of the membranes were successfully controlled via the use of different sizes of sols and by manipulating the firing temperature.

This study investigated the effect of acid post-treatment on the filtration performance of organosilica membranes. The membranes were prepared from 1,2-bis(triethoxysilyl)ethane (BTESE) via sol-gel processing with different H2O/BTESE molar ratios. Fourier-transform infrared spectra significant residual ethoxy groups within membranes derived from sols with low H2O/BTESE ratios, after firing at 300 °C in N2. The ethoxy groups within the membranes were hydrolyzed to hydroxide groups by immersing the membranes in hydrochloric acid (HCl). This rendered the membranes more hydrophilic. The hydroxyl groups may have promoted the formation of hydrophilic pores, which would in turn promote water permeation. The HCl-treated membranes showed higher water permeability than the original BTESE-derived membrane. The effect of HCl treatment was more pronounced for the membrane prepared with the lowest H2O/BTESE ratio of 1, resulting in approximately three times higher water permeability than the original membrane. Membranes prepared from sols with low H2O/BTESE ratios showed improved solute rejection and increased water permeability, upon HCl treatment. This was attributed to cross-linking in the organosilica matrix via the condensation of newly-formed hydroxyl groups, that caused the narrowing or blocking of large pores.

Long-chain organosilica bis(triethoxysilyl)propane (BTESP) membranes typically have a flexible non-porous structure. Fluorine was used to tune the network pore structure of BTESP membranes in an effort to improve the gas permeation properties. The network pore size was enlarged and the effect of calcination temperature on the network structure was evaluated based on gel and membrane characterizations. Fluorine-doped BTESP membranes calcined at 350 °C and 650 °C have shown H2 permeance on the orders of 1.2 × 10−6 mol m−2 s−1 Pa−1 and 1.5 × 10−6 mol m−2 s−1 Pa−1 with H2/N2 selectivities of 8 and 6, respectively, which indicates similar pore sizes with lower condensation effect at high temperature of 650 °C, that was suppressed due to the presence of Si–F and C–F bonds. Undoped BTESP membranes, on the other hand, showed H2/N2 selectivity that was significantly lower—from 24 to 11 at 650 °C. FT-IR and N2 adsorption isotherms clearly indicated that fluorine significantly decreased the Si–OH density and increased the surface area and micropore volume. Further water adsorption analysis revealed that fluorine significantly increased the hydrophobicity of the BTESP network structure. Overall, the results of this study endorse the effectiveness of fluorine to control the network pore structure in both wet and dry molecular separation systems.

This work reports the preparation of a carbonized SiO2–ZrO2 composite membrane with enhanced H2 permselectivity via a sol-gel process. The sol-gel synthesis of the precursor SiO2–ZrO2-acetylacetonate composite was optimized by studying the effect that the water/alkoxide molar ratio exerted on the final properties of carbon-SiO2-ZrO2. Characterization by thermogravimetry, XRD, and N2 adsorption revealed that utilizing a water/alkoxide molar ratio of 60 was optimal for the retention of carbon and for promoting the qualities of amorphousness and microporosity. Furthermore, using a Si/Zr ratio of 9/1 in a carbon-SiO2-ZrO2 membrane resulted in a high level of H2 permselectivity. This membrane showed H2 permeance of 16 x 10−7 mol m−2 s−1 Pa−1 and H2/N2 and H2/CH4 ideal selectivities of 75 and 148, respectively. More importantly, the H2 permselectivity of the carbon-SiO2-ZrO2 membrane exceeded that of a similarly pore-distributed unmodified SiO2–ZrO2 membrane with an H2 permeance of 3 x 10−7 mol m−2 s−1 Pa−1. This enhanced H2 permselectivity was attributed to the increase in pore volume contributed by ultra-micropore-bearing carbon nanoparticles.

Hybrid organosilica membranes of silver-doped bis [3-(trimethoxysilyl) propyl] amine (BTPA) were prepared via sol-gel processing followed by coordination reactions to improve the permeability and separation performance. The evolution of silver in two phases as silver ions and as nanoparticles was observed during modification of the aminosilica networks; the silver ions coordinated with amine moieties while the silver nanoparticles developed following reduction on the aminosilica surface. The silver/amine mole ratio was evaluated against the formation of coordinated and particulate species during modification in the range of 0.1–0.5 mol mol−1. The formation of microporosity was successfully developed from 2.36 to 115 m2 g−1 by increasing the silver mole ratio. Furthermore, silver-modified aminosilica membranes showed a hydrogen (H2) permeance of 1.46 × 10−6 mol m−2 s−1 Pa−1, which was 65-fold higher than pure BTPA with excellent selectivity for H2/propane (C3H8) separation of 1500. It is evident that the proposed modification method via the two-phase structural evolution of silver coordination and nanoparticles reorganized the organosilica framework and improved the separation in the dehydrogenation of propane.

A molecular sieving membrane was fabricated using triethoxyfluorosilane (TEFS), which contains Si–F bonds and is categorized as a pendant-type alkoxysilane. The hydrothermal stability and hydrocarbon (C3H6, C3H8) permeation properties were evaluated for TEFS membranes. When a fluorine-induced silica membrane had a Si–F bond in the amorphous structure, the reaction of steam and Si-F groups during steam treatment formed Si-OH groups, which slightly decreased the gas permeance. Even though gas permeance slightly decreased under a steam atmosphere, a TEFS membrane calcined at 350 °C had networks that were looser and more uniform than those of a conventional SiO2. In addition, the formation of adsorption sites (Si-OH groups) under steam treatment enhanced both interactions with the π-bonds (C=C double bond) of C3H6 and the C3H6/C3H8 permeation properties (C3H6 permeance: 2.2 × 10−7 mol m−2 s−1 Pa−1, C3H6/C3H8 permeance ratio: 42 at 35 °C). The hydrothermal stability was dramatically enhanced by calcination temperatures as high as 750 °C due to the presence of fewer Si-OH and Si–F bonds in the amorphous structure, although the network pore size of a TEFS membrane was the same whether it was calcined at 750 °C or at 350 °C.

The use of inexpensive porous polymers instead of conventional ceramics to support silica-based membranes can potentially minimize the cost of membrane synthesis. To develop polymer-supported silica-based membranes, lowering the high synthesis temperature of the silica-based top layer is essential. In this study, we explore the application of atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) for synthesizing polymer-supported silica-based membranes. The deposition of a continuous silica-based layer on an asymmetric polysulfone ultrafiltration membrane using hexamethyldisiloxane as an organosilicon precursor was achieved at ambient temperature and pressure via AP-PECVD. The gas permeation properties of the AP-PECVD-derived polymer-supported membranes strongly depended on the deposition duration, as prolonged deposition could reduce the remaining defects by covering the entire surface of the support with the plasma-deposited layer. The membranes showed increased selectivities for H2/N2 and H2/SF6 from 2.9 to 9.5, and from 4.5 to 184, respectively, exhibiting gas permeation dominated by molecular sieving. The present study demonstrates that AP-PECVD is a promising strategy for the fabrication of polymer-supported silica-based membranes for gas separation.

We developed a series of molecule-scale hybrid amine-silica membranes synthesized from organoalkoxysilane precursors of 3-(triethoxysilyl)propan-1-amine (PA-Si) and 3-(triethoxysilyl)-N-methylpropan-1-amine (SA-Si), and made these functional using either unhindered amines or a 3-(triethoxysilyl)-N,N-dimethylpropan-1-amine (TA-Si) that is sterically hindered. CO 2 adsorption-desorption measurements of amine-silica powdered xerogels were conducted to observe the effect of amine type on CO 2 adsorption and desorption/diffusion properties. The results revealed that TA-Si xerogel powders demonstrated faster kinetics for both adsorption and desorption processes compared with those of the PA-Si and SA-Si samples due to the steric hindrance effect of the amine, which reduced the CO 2 binding energy and thereby boosted both the forward and reverse reaction rates of CO 2 -amine. In single-gas permeation performances, all the membranes exhibited excellent molecular sieving at higher temperatures and all the gases considered, except CO 2 , tended to permeate the membranes via activated diffusion. The effect of amine type on CO 2 separation performance was compared using CO 2 permeance, CO 2 /N 2 selectivity, activation energy for permeation ( E p ) of CO 2 [ E p (CO 2 ) ], and differences in E p between CO 2 and N 2 [ E p (CO 2 )-E p (N 2 ) ]. The TA-Si membrane demonstrated superior CO 2 separation performance, and achieved the highest values for both CO 2 permeance and selectivity. A relatively smaller difference in CO 2 separation performance was observed between PA-Si and SA-Si membranes despite some differences in basicity. This suggests that, rather than the basicity, it was the steric hindrance effect that played the greatest role in CO 2 transport performance across amine-silica membranes.

In this study, molecular simulation was used to explore the structural characteristics and transport performances of cyclic peptide nanotubes (CPNTs). A molecular dynamics (MD) technique was used to construct four different molecular models of nanotubes: an octamer prototypical cyclic peptide (8CP); and, three cyclic peptides modified by replacing one or two L-Lysine or L-Leucine groups with an aromatic amino acid, 3-amino-2-methylbenzoic acid (γ-Mba-OH). MD simulation was used to explain how the hydrophobic modification of functional group affects the structure, channel volume, interior affinity, and transportation behavior of water in CPNTs. The Monte Carlo (MC) method was adopted to investigate the sorption behaviors in these four types of CPNTs. The internal diameter, channel morphology, and volume analyses indicated that modified functional groups disrupted the symmetry of cyclic peptides and changed the structural characteristics of the nanotubes. The hydrogen bond distribution and interaction energy analyses suggested that the modified γ-Mba-OH functional groups reduced the interior affinity between water molecules and nanotubes, which led to hydrophobic properties. The adsorption analysis revealed that a greater number of modified functional groups in CPNTs resulted in a lower affinity for water molecules, which lowered the adsorption amount in low-pressure regions. The modified γ-Mba-OH functional groups lowered the attractive forces and enlarged the channel volume, which was reflected in the diffusion calculation that showed improvements in water diffusivity in most cases. The results of the structure and water transport properties of CPNTs, as shown by the MD technic and MC methods, provided useful information that would have been difficult to obtain in an actual experiment. The simulation techniques can assist in the analysis of nanotube structural properties and in the transport behavior of the molecules in CPNTs.

SiO 2 -ZrO 2 (5/5, 3/7) nanofiltration membranes with a low molecular weight cut-off (MWCO) were fabricated by coating different Si/Zr molar ratios of 5/5 and 3/7 sols from large to small colloidal sol sizes on cylindrical α-alumina porous supports with firing at 550 °C. The pore sizes of the membranes were controlled by the SiO 2 -ZrO 2 colloidal sol sizes used for the top layer. SiO 2 -ZrO 2 membranes with a MWCO of less than 60, and 160–180 for neutral solutes, showed water permeabilities of (0.2–0.4)×10 –12 and (1.9–2.7)×10 –12 m 3 /(m 2 s Pa), respectively. The solute rejections were strongly dependent on the type of solute; the rate of rejection for alcohols was much higher than that for either glycols or sugars. SiO 2 -ZrO 2 membranes with a low MWCO showed hydrothermal stability and high nanofiltration performance in water at 90 °C. The water permeabilities of membranes increased from 2.5×10 –12 to 11.9×10 –12 m 3 /(m 2 s Pa) in operating temperatures from 25 to 90 °C, while the MWCO increased slightly from 150 to 210. This indicates that SiO 2 -ZrO 2 membranes with a low MWCO showed excellent nanofiltration performance at high temperatures. The permeation properties for nanofiltration membranes were analyzed using the Spiegler-Kedem equation.

SiOC membranes were fabricated by a sol-gel method using three types of silica precursors: vinyltrimethoxysilane (VTMS), triethoxysilane (TRIES), and 1,1,3,3-tetramethyldisiloxane (TMDSO). The timing of the addition of TMDSO was evaluated via single-gas permeation for its effect on formation of the SiOC structure and on membrane performance. The effect that VTMS compounding exerted on membrane performance and on oxidation stability was also evaluated. The network size of SiOC membranes was precisely tailored by controlling the timing of the addition of TMDSO during the sol preparation process. There was no significant change in the network pore size either before or after thermally induced hydrosilylation (Si–C=C + Si–H → Si–CH2–CH2–Si) and the cross-linking of Si–CH3 groups (Si–CH3 + Si–CH3 → Si–CH2–Si + CH4). These SiOC membranes were highly selective of H2 over larger molecules such as CF4 and SF6. The effect of VTMS compounding on network pore size was small, but the oxidation stability of the SiOC structure at 500 °C was dramatically enhanced.

The aim of this work was to study how the structural and permeation properties of BTESE membranes were affected by the simultaneous influences of water ratios (WRs) in sol preparation, defined as (H 2 O)/ bis(triethoxysilyl)ethane (BTESE), ranging from 3 to 240, and the firing atmosphere (under N 2 and/or air, firing temperature 100–300 °C) for gas permeation (GS) and reverse osmosis (RO) applications. The thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and N 2 adsorption results revealed that the ethoxide groups in the pore networks of BTESE membranes were almost completely hydrolyzed and the silica networks became dense when the WR was increased from 3 to 240 regardless the firing environment. Based on the FTIR, most of the organic peaks for samples fired under N 2 were more intense than the samples fired under air. Hence, the samples fired under N 2 were more hydrophobic than the samples fired under air, as proven by the contact angle and H 2 O adsorption. This demonstrates that the firing of BTESE membranes under N 2 slowed down the decomposition of organic bonds in the sample, and made the structures within the networks more intense and rigid. In terms of separation performance, the permeance of gases and H 2 O was clearly dependent on the WR. Increasing the WR decreased the permeance of both gases and H 2 O via the pore network of BTESE membranes. On the other hand, the firing environments also affected the permeance of gases and H 2 O. BTESE membranes fired under air exhibited a higher permeance of gases and H 2 O. In addition, we also investigated the relationship between gas and liquid permeance correlation using He gas as the predictor of water permeance. Increasing the He permeance resulted in increases in water permeance. Based on these results, it was suggested that the WR was a primary factor in controlling the pore size and solute rejections, and the firing environments played a primary role in deciding the hydrophilicity and hydrophobicity of membrane surfaces and pore networks during the fabrication of BTESE membranes.

Triethoxysilane (TRIES), which consists of three ethoxy groups and a Si-H bond as a pendant-type alkoxysilane, was utilized as a Si precursor for the fabrication of a gas separation membrane. The effect of membrane fabrication parameters such as sol preparation conditions and calcination temperatures on Si-H groups and network structures was evaluated. The degree of dehydrogenation of Si-H groups in aqueous solution was independent of the H 2 O/Si molar ratio in the sol, but the degree of hydrolysis and polymerization of ethoxy groups (-OEt) depended on the H 2 O molar ratio. TRIES membranes calcined at 550 °C under N 2 showed a decrease in network size with an increase in the H 2 O/Si molar ratio in the sol. The TRIES-derived network pore size also depended on the calcination temperature, and the network size was decreased under lower calcination temperatures. For example, a TRIES membrane calcined at 550 °C showed high selectivity for He/N 2 and H 2 /N 2 at approximately 1000 and 600, respectively, however, in the case of calcination at 300 °C, Knudsen diffusion dominated for small molecules (H 2 /N 2 selectivity: 4.3) and molecular sieving favored large molecules (H 2 /CF 4 : >100, H 2 /SF 6 : >400). When a TRIES membrane was fabricated by calcination at 300 °C, most Si-H groups were still present in the networks, the estimated network pore size for the TRIES membrane was 0.577 nm, which was larger than that of a tetraethoxysilane (TEOS) membrane calcined at 350 °C (0.426 nm). On the other hand, when TEOS and TRIES membranes were fabricated at 550 °C, both membranes showed approximately the same network pore size (TEOS: 0.385 nm, TRIES: 0.382 nm), due to the dehydrogenation of Si-H groups in the formation of Si-OH groups as well as for the forming of a Si–O–Si bond.

SiO 2 -ZrO 2 nanofiltration membranes were fabricated by coating different molar ratios of SiO 2 , SiO 2 -ZrO 2 (9/1, 7/3, 5/5, 3/7), and ZrO 2 sols onto α-alumina porous tubes and firing at 200 and 550 °C. The SiO 2 and SiO 2 -ZrO 2 (9/1, 7/3, 5/5) membranes fired at 200 and 550 °C showed pore diameters ranging from 0.65 to 0.80 nm, while SiO 2 -ZrO 2 (3/7) and ZrO 2 membranes fired at 550 °C showed larger pores than those fired at 200 °C due to the formation of crystalline structures in the ZrO 2 . SiO 2 -ZrO 2 membranes with a zirconia content larger than 50 mol% showed high hydrothermal stability in hot water (90 °C). After treating SiO 2 -ZrO 2 (5/5) membranes in hot water, the water permeability (L p ) increased dramatically while the rejection was unchanged. On the other hand, the L p for SiO 2 -ZrO 2 (3/7) membranes decreased while the rejection increased. This can be ascribed to the balance between the dissolution of Si and the generation of OH groups, which amounts to pore sizes and hydrophilicity. Moreover, SiO 2 -ZrO 2 (5/5, 3/7) membranes showed stable water permeability and molecular weight cut-off values for as long as 4 weeks at pH values of 2 and 12, confirming a high level of chemical stability in strongly acid and alkaline solutions.

Microporous silica membranes with high permselectivity are fabricated by atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) using hexamethyldisiloxane as the precursor in plasma working gases of pure argon, and mixture of argon with oxygen or nitrogen. A silica membrane grown using plasma composed of a mixture of argon and nitrogen displays highly efficient gas separation, with selectivities for He/N 2 and He/SF 6 of 196 and 820, respectively, and He permeance of 1.1×10 −7 mol m −2 s −1 Pa −1 at 50 °C. Characterization of the membranes by FTIR and X-ray photoelectron spectroscopies reveals a relatively high concentration of carbon remains in the membrane grown using a mixture of argon and nitrogen. Annealing at elevated temperature after plasma deposition improves the permselectivity of the membranes. After annealing at 300 °C, the permeance of He at 50 °C increased to 4.0×10 -7 mol m -2 s -1 Pa -1 with no marked decrease of selectivity (He/N 2 =98, He/SF 6 =770). The annealed membrane also exhibits remarkable permselectivity for CO 2 , showing selectivities for CO 2 /N 2 and CO 2 /CH 4 of 46 and 166, respectively, with CO 2 permeance of 1.9×10 -7 mol m -2 s -1 Pa -1 at 50 °C. AP-PECVD shows great promise to fabricate microporous silica membranes highly permselective for gas separation.

The development of robust membranes able to withstand harsh environments such as oxidative conditions would improve the sustainability of several separation processes. Therefore, organosilica and ceramic non-commercial membranes were characterized and their performances were compared before and after contact with hydrogen peroxide. The organosilica membrane showed a high level of solute rejection coefficients (0.928 for NaCl and 0.969 for MgCl 2 ), but low permeability (5.04·10 –13 m 3 /m 2 s Pa, equivalent to 0.181 L/m 2 h bar). The ceramic membrane, however, showed low solute rejection (0.187 for NaCl and 0.649 for MgSO 4 ), but high membrane permeability (7.05·10 –12 m 3 /m 2 s Pa, equivalent to 2.538 L/m 2 h bar). While the organosilica membrane was quite sensitive to the presence of hydrogen peroxide, the chemical stability of the ceramic membrane in 30% hydrogen peroxide solution was very satisfactory. A Kedem-Katchalsky membrane transport model and a logistic decay model were applied to successfully test the performance of the membranes and to characterize the evolution of the organosilica membrane, respectively.

Organosilica microporous membranes were fabricated from 1, 2-bis (triethoxysilyl) ethane (BTESE)-derived sols prepared in acidic pH via the pH-swing method. This method includes two steps whereby a specific amount of NH3 was added into the acid sols and switched to acid after a reaction of several minutes. We found that the size of the BTESE-derived sols by pH-swing could be controlled via the H2O/BTESE molar ratio and the reaction time in alkali. Under the same H2O/BTESE ratio of 60, the BTESE-derived sols prepared in the pH-swing method showed an increase sol size in contrast with the acid method, and the sol size was easily controlled by the dominating reaction in alkali pH – the condensation reaction. Gas permeation results showed that some gases (He, H2, N2, C3H8, SF6) permeated the membrane that was prepared using the pH-swing sols (pH-swing membrane) at approximately twice the rate shown by the membrane prepared using acid sols (acid membrane); H2 permeance levels of the pH-swing membrane and the acid membrane were 3.4×10−6 and 1.6×10−6 mol m−2 s−1 Pa−1 at 200 °C, respectively. The pH-swing membrane also maintained similar H2/C3H8 permeance ratios of ranging from 2600~5800, confirming that pH-swing processing is an innovative method for improvement in the gas permeance of BTESE-derived organosilica membranes. One possible reason for these results could be that the membranes prepared using the pH-swing sols increased the size of the sols, which reduced the sol penetration into the intermediate layer. Moreover, the high cross-linking that was caused by pH-swing increased the thermostability of the BTESE-derived organosilica networks. The CO2/CH4 and CO2/N2 permeance ratios for the pH-swing membrane were as high as 90 and 28, respectively, at 50 °C.

To examine the prospect of a future application of organosilica membranes to steam recovery under hydrothermal conditions, we proposed a novel concept that involved a hydrothermally stable intermediate layer derived from colloidal 1,2-bis(triethoxysilyl)ethane (BTESE) sols with a BTESE-derived separation top layer. In this work, a BTESE-derived nanoporous intermediate layer (i-BTESE) was prepared from a BTESE-derived colloidal sol without pinholes or cracks, and then a BTESE-derived sub-nanoporous separation layer was formed on the i-BTESE to obtain a BTESE/i-BTESE membrane. The BTESE/i-BTESE membrane showed excellent water permeance as high as 5 × 10-6 mol/(m2 s Pa), and a high level of permeance was maintained for as long as 361 h at 200°C under vapor pressure of 200 kPa (abs.). In addition, the membrane achieved an H2O/N2 permeance ratio that reached as high as 350 even after 361 h. On the other hand, the permeance of a conventional BTESE-derived membrane that used a silica-zirconia intermediate layer (BTESE/i-SiO2-ZrO2) decreased gradually, which suggested a degradation of the BTESE/i-SiO2-ZrO2 membrane. The high and stable performance of the BTESE/i-BTESE membrane confirmed the proposed concept whereby a hydrothermally stable intermediate layer could significantly improve the hydrothermal stability that is required in order to use organosilica membranes in steam recovery.

F-BTESM membranes were fabricated by doping a fluorine source into bis(triethoxysilyl)methane (BTESM), which is an organosilica precursor composed of Si–CH2–Si bonds. Pore size controllability and C3–C4 hydrocarbon permeation properties for F-BTESM membranes with different concentrations of fluorine were evaluated using single-gas permeation and N2/C3–C4 hydrocarbon binary separation. The pore size of an organosilica membrane can be precisely controlled via doping with the correct concentration of fluorine. The molecular sieving properties for C3/C4 hydrocarbon separation such as that for C3H6/iso-C4H8 was dramatically enhanced with the addition of a fluorine concentration of F/Si = 0.05, and this membrane showed a C3H6/iso-C4H8 permeance ratio of 388 at 50 °C. The permeance of hydrocarbon gases was increased with an expansion of the pore size, and F-BTESM (F/Si = 0.15) showed a high level of C3H6 permeance (>5.0 × 10−7 mol m−2 s−1 Pa−1). The results of hydrocarbon adsorption and single permeation properties showed that the carbon number of the hydrocarbons and the presence of unsaturated bonds enhanced the adsorption affinity to silica-derived materials. In the binary separation of N2/C3–C4 hydrocarbons, N2 permeance was remarkably decreased by comparison with single-gas permeation, which was due to a blocking effect by the hydrocarbons adsorbed inside the pores. Hydrocarbon gases with a stronger affinity tended to inhibit the permeation of N2.

The evolution of the physicochemical properties of allylhydridopolycarbosilane (AHPCS) was systematically investigated via DLS, TG, FTIR, XRD, and EDS. AHPCS-derived membranes were prepared by coating AHPCS sols onto porous substrates, which was then followed by pyrolysis at 300–800 °C. The pre-crosslinking by thermal curing significantly increased the colloidal sol size of AHPCS in toluene solutions, which effectively reduced penetration into substrates and enhanced the gas permeation. Furthermore, the pore structure of AHPCS-derived membranes could be precisely tailored by the pyrolysis temperatures, and the results indicated that the structure of membranes could be roughly classified into one of three types: a dense polymer structure, a loose transitional structure, and a denser ceramic structure (here, the term ‘dense/denser’ refers to the small/smaller pore structure, while the ‘loose’ refers to the large pore structure). AHPCS-derived membranes prepared at 300–800 °C under a N2 flow displayed superior H2 permeance of (0.2–5) × 10−6 mol/(m2 s Pa) at 200 °C with good H2/N2 selectivity of 12–56. Ceramic SiC membranes prepared at 700 °C showed an attractive H2 permeance of (2–4) × 10−6 mol (m2 s Pa)−1 at 200 °C with H2/N2 selectivity of 16–22, H2/SF6 selectivity higher than 10,000, and N2/SF6 selectivity higher than 800. Moreover, the structure of the ceramic SiC membranes was highly stable with good oxidation resistance at 500 °C under air. AHPCS membranes prepared at 300–800 °C had different pore structures that exhibited a high level of quality and a variety of permeation properties that could provide many options for membrane materials over a wide range of applications.

Al2O3 nanoporous membranes for nanofiltration were successfully prepared from nanofiber sols (4 nm in diameter and 1400 nm in length) by controlling the number of sol coats and the firing temperature of the membrane. The effects of the number of sol coats and the firing temperature were characterized via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption, scanning electron microscope (SEM), transmission electron microscopy (TEM), nanopermporometry, and nanofiltration. A crack-free and continuous separation layer of the membranes, which is composed of Al2O3 nanofibers overlapping in the same direction on the membrane surface, was achieved. A greater number of sol coats greatly reduced the N2 permeance and water permeability of the membrane, but had no significant effect on either the average pore size or the molecular weight cut-off (MWCO). Meanwhile, firing temperature greatly affected the structure and separation performance of the membranes due to a transformation of the crystalline phase from boehmite to γ-Al2O3 under high temperatures. Al2O3 nanofiber-derived membranes had an average pore size and a MWCO that tended to be constant at 1.0 nm and 870–990 g/mol via firing at 200 °C, irrespective of the number of sol coats. Those values were increased, however, with increases in the firing temperature.

Membrane-based separation technologies are considered an effective process for the capture of CO2 due to advantages such as high levels of energy efficiency with inexpensive levels of investment. It remains challenging, however, to develop a membrane with high levels of both permeance and selectivity with the ability to capture CO2 in a highly efficient manner. Herein, we report amino-decorated organosilica membranes that are based on a facile and effective co-polymerization strategy that uses bis(triethoxysilyl)acetylene (BTESA) and (3-aminopropyl) triethoxysilane (APTES) precursors. This co-polymerization strategy simultaneously endows the resultant membranes with a controlled pore size and enhanced CO2-philic properties that have significantly improved CO2 separation performance. These composite membranes display CO2 permeance that ranges from 2550–3230 GPU and a range for CO2/N2 selectivity of 31–42 in the separation of CO2/N2 mixtures, which outperforms most state-of-the-art membranes and exceeds the target for post-combustion CO2 capture operations. A satisfying performance was achieved with a CO2 permeance of 8 ✕ 10−7 mol m−2 s−1 Pa−1 (2390 GPU) and CO2/CH4 selectivity of 70. The present study highlights an elegant decoration strategy for the production of membranes with ultrahigh CO2 capture capacities, which can also be extended to other organosilica precursors for target-oriented separations by varying the bridged or side-chain groups.

Membrane-based separation of organic/organic mixtures is of great importance in the chemical and petrochemical industries, but remains very challenging owing to the harsh working conditions. Herein, ultrathin and chemically stable Bis(triethoxysilyl)acetylene (BTESA)-derived organosilica membranes were reproducibly prepared, and for the first time they were utilized in the pervaporation separation of methanol/organic azeotropes. The as-prepared BTESA membranes exhibited exceptional pervaporation performance in a 10 wt%/90 wt% methanol/dimethyl carbonate (DMC) mixture, and showed a high separation factor of approximately 120 with a permeation flux of 2–4 kg m-2 h-1 at 50 °C. This impressive performance was primarily the result of the preferential sorption of methanol and the efficient size sieving of DMC. In addition, the effects of feed concentration and temperature on methanol/DMC pervaporation performance were thoroughly investigated. Importantly, a generalized solution-diffusion model successfully described the pervaporation performance of BTESA membranes, and the usefulness of this model was further confirmed via the pervaporation of methanol/methyl acetate and methanol/methyl tert-butyl ether (MTBE) mixtures. This work demonstrates the great potential of organosilica membranes for high-performance organic/organic pervaporation.

The management of oily wastewater produced in the petrochemical industries poses an immense challenge from both practical and environmental points of view. Filtration using ceramic membranes has been considered a promising technology to remove stable emulsions from oily wastewater; however, the separation performances are severely limited by membrane fouling. In this study, we evaluated the filtration performance of porous ceramic membranes for the treatment of oil/water emulsions. Porous ceramic membrane, having different pore sizes (0.1–1.4 μm) and made from various materials (Al2O3, TiO2–ZrO2, TiO2, and SiC), were tested in a crossflow microfiltration system using oil/water emulsions. The emulsions were stabilized by anionic and cationic surfactants. The fouling caused by filtration is discussed in terms if membrane and emulsion properties. Pore size and surface charge were the two most important prominent fouling factors during the oil/water emulsion filtrations. For membranes with small pores, serious fouling was observed, irrespective of the type of surfactant; however, these membranes exhibited excellent oil rejection. The fouling was caused by the accumulation of oil droplets on the membrane surface, which subsequently led to the formation of a cake layer and/or a continuous oil layer. The effect of surface charge became significant regarding membranes of larger pore sizes, especially when membrane pore sizes were comparable to that of the droplet sizes. When the membrane and oil droplets had the same charge, electrostatic repulsion occurred, preventing the penetration of oil droplets into the pores. Although some of the small oil droplets could enter the pores, they would be trapped at the narrowing and/or flexing inside the pores because droplet deformation was inhibited by the electrostatic repulsion. Therefore, fouling occurred on the membrane surface and inside. As a result, a severe decline in water permeation was observed, together with a moderate oil rejection. By contrast, when the membrane and oil droplets were oppositely charged, oil droplets were deformed and entered the pores, resulting in permeation through the membrane. Therefore, water permeation was high, but oil rejection was sacrificed. These results indicate that both pore size and surface charge of membranes should be optimized to achieve better filtration performance.

Membrane-based separation techniques are responsible for great advances in the separation of propylene/propane mixtures. In this study, bis(triethoxysilyl)acetylene (BTESA) was selected as the precursor in the fabrication of organosilica membranes for use in propylene/propane separation. We proposed an effective strategy to finely engineer the pore subnano-environment of BTESA membranes for highly selective propylene/propane separation via controlling the calcination temperatures. Measurement of the surface energy, the 29Si-NMR spectra, and the gas sorption isotherms clearly indicated that low-temperature calcined BTESA materials with a greater number of silanol groups showed an enhanced affinity to propylene molecules. BTESA membranes calcined at 150 °C featured a promisingly high C3H6/C3H8 selectivity of 52 and a C3H6 permeance of 1.7 ✕ 10−8 mol m−2 s−1 Pa−1 at 50 °C. These values were approximate to those reported for ZIF-8 membranes and higher than the standards for commercialization. The high level of C3H6/C3H8 separation performance was believed to be accounted by the synergetic effects of both controlled pore size and enhanced affinity to propylene molecules. Moreover, compared with traditional organosilica membranes that were calcined at ~350 °C, low-temperature calcination (150 °C) for BTESA membranes efficiently reduced the energy consumption and fabrication cost.

SiO 2 –ZrO 2 membranes were successfully prepared by coating SiO 2 –ZrO 2 (molar ratio 5/5) sols on cylindrical α-alumina porous supports with average pore sizes of 2.1, 2.9 and 3.6 μm followed by firing at 550 °C. The pore sizes of the SiO 2 –ZrO 2 membranes, which were evaluated by nanopermporometry using hexane, were 1.20 and 0.65 nm after coating with SiO 2 –ZrO 2 sols of 35 and 19 nm in diameter, respectively. The membrane pore sizes were not affected by the pores of the supports, but, instead, were controlled by the colloidal sizes of the SiO 2 –ZrO 2 sols that made up the top layer. The average pore sizes of SiO 2 –ZrO 2 membranes fired at 200, 300, 400 and 550 °C increased slightly from 0.60 to 0.70 nm with an increase in the firing temperature while water permeability ( L p ) tended to decrease with increases in the firing temperature that ranged from (3.3–0.8)×10 −12 m 3 /(m 2 s Pa). The decreased water permeability was ascribed to chemical and physical changes by firing temperature such as hydrophilicity/hydrophobicity, porosity, etc. The water permeabilities of SiO 2 –ZrO 2 membranes showed stable flux due to the addition of zirconia into the silica sol, showing improved stability in water. Nanofiltration performance was evaluated using aqueous solutions and showed molecular weight cut-offs ranging from 200 to 350.

Bis(triethocysilyl)ethane (BTESE)-derived organosilica membranes were applied for the dehydration of aqueous isopropanol (IPA) solutions in pervaporation and vapor permeation. The stability of the membranes under high-water-content systems was demonstrated in pervaporation and vapor permeation. The membranes showed excellent stability in the long-term pervaporation of a 50 wt% IPA aqueous solution at 75 °C. The membranes were also stable in vapor permeation with a high-water-content stream (IPA concentration of 50 wt%) at 100 °C. These results clearly demonstrated that BTESE-derived organosilica membranes are applicable for the dehydration of high-water-content mixtures. The effect of the feed component and operating temperature on dehydration performance was also investigated. An analysis of the permeation resistance through the membranes was conducted based on a simple series-resistance modeling approach and revealed that the permeation resistance of the support layer strongly inhibited the water permeability, particularly when the water content in the feed was high.

Ceramic membranes were newly developed with hydrophobic intermediate layers to achieve high gas permeance in the presence of water vapor. Me-SiO 2 sols, which were prepared by co-precursors of tetraethoxysilane (TEOS) and methyltrimethoxysilane (MTMS) were coated as intermediate layers. Two types of organosilica sols prepared with bis(triethoxysilyl)ethane (BTESE) and bis(triethoxysilyl)octane (BTESO) were used for the top layers. By characterization of nanopermporometry using hexane and water as condensable vapors, Me-SiO 2 layers showed pore diameter of approximately 1.5 nm and exhibited hydrophobic properties and that SiO 2 –ZrO 2 layers were hydrophilic. BTESE- and BTESO-derived sols were coated on hydrophobic Me-SiO 2 layers, referred to as BTESE/Me-SiO 2 and BTESO/Me-SiO 2 , and on hydrophilic SiO 2 –ZrO 2 layers, which are referred to as BTESE/SiO 2 –ZrO 2 and BTESO/SiO 2 –ZrO 2 . Gas permeation was examined for four types of membranes under a dry and a wet atmosphere. Under dry conditions, BTESO/Me-SiO 2 showed a gas permeation trend that was similar to that of BTESO/SiO 2 –ZrO 2 . The selectivity of H 2 /SF 6 for BTESE/Me–SiO 2 (334) was much lower than that of BTESE/SiO 2 -ZrO 2 (>20,000) due to the inhomogeneous coatings of BTESE on the Me-SiO 2 layers. Under humidified conditions, BTESE/Me–SiO 2 and BTESO/Me-SiO 2 with hydrophobic intermediate layers, exhibited less of a decrease in CO 2 permeance compared with either BTESE/SiO 2 -ZrO 2 or BTESO/SiO 2 –ZrO 2 , both of which had hydrophilic intermediate layers. The water vapor resulted in a negligible effect on gas permeance for totally hydrophobic BTESO/Me-SiO 2 , while a little larger decrease was observed for hydrophilic top layers of BTESE/Me–SiO 2 , showing that membranes with hydrophobic surface chemistry can effectively resist water vapor condensation or adsorption during gas permeation.

Organosilica membranes were fabricated under controlled sol-preparation conditions such as the ratio of triethoxysilane (TRIES) and vinyltrimethoxysilane (VTMS) and the hydrosilylation temperature. The single-gas permeation properties and hydrothermal stability of organosilica membranes were evaluated to clarify the relationship between hydrothermal stability and organosilica structure. Pt-catalyzed and thermally cured hydrosilylation was applied to evaluate the effect that hydrosilylation temperature exerts on the properties of membranes. Organosilica membranes (Pt-catalyzed hydrosilylation at 40 °C) showed H 2 permeance of approximately 10 −6 mol m −2 s −1 Pa −1 with H 2 selectivity (H 2 /CH 4 :15, H 2 /CF 4 :950) at 500 °C, and were stable under an oxidative atmosphere at 500 °C. The organosilica network size derived by thermal curing at 500 °C was smaller than that by Pt-catalyzed hydrosilylation, even though the units (Si–C–C–Si, Si–O–Si) were the same. Hydrosilylation reactivity derived by thermal curing (500 °C, N 2 ) strongly depended on the TRIES/VTMS (= H / V ) ratio in the SQ sol, and an H / V ratio of 1.25 showed a higher level of hydrosilylation reactivity. Its hydrothermal stability was better than that of amorphous silica membranes, due to the incorporation of Si–(CH 2 ) 2 –Si units in the networks via hydrosilylation, based on the decreased ratio of He and H 2 permeance, the He/H 2 permeance ratio, and the activation energy before/after steam treatment.

A novel layered-hybrid membrane consisting of a thin and defect-free organosilica separation layer deposited onto a flexible polymeric nanofiltration membrane was successfully developed via a simple sol–gel, spin-coating, low-temperature, heat-treatment process. This marked the first application of this type of a layered-hybrid membrane to the reverse osmosis (RO) desalination of a 2000 ppm NaCl solution. The optimal heat-treatment temperature for the membrane preparation was also investigated. These layered-hybrid membranes displayed good stability and reproducibility in the RO process, and showed a stable and high degree of water permeability (approximately 1.2×10 −12 m 3 m −2 s −1 Pa −1 ) with salt rejection that was competitive (96%) with conventional processing. Moreover, this layered-hybrid membrane also showed good hydrothermal stability at operating temperatures ranging from 25 to 60 °C and stable RO performance during a continuous RO desalination process that lasted for more than 160 h.

A pore network of bis(triethoxysilyl)ethane (BTESE) organosilica membranes was controlled by adjusting the molar ratios of BTESE/H2O/acid=1/x/0.2 (x=3 and 240). The mechanisms for solute transport in the BTESE RO membrane were investigated using three different aqueous solutions of sodium chloride (NaCl), ethanol (EtOH) and isopropanol (IPA). The pressure and temperature were varied from 0.4 to 1 MPa and from 25 to 80 °C, respectively. Water flux and rejection increased for both alcohols and electrolyte with an increase in the applied pressure. It was noteworthy that the rejection of alcohols decreased with an increase in the RO operating temperature, while the electrolyte rejection remained almost constant. The BTESE membranes exhibited high thermal robustness under the long-term testing conditions, delivering salt rejections >98% until the end of the testing period (50 h). The BTESE membranes could also be regenerated after use in the gas and RO experiments, thus demonstrating robust properties.

Organosilica membranes for gas separation were prepared by plasma-enhanced chemical vapor deposition (PECVD) using three different types of silicon precursors: hexamethyldisiloxane (HMDSO), trimethylmethoxysilane (TMMOS), and methyltrimethoxysilane (MTMOS). Based on gas permeation measurement, the MTMOS-derived membrane showed the highest He/N2 selectivity, followed by the TMMOS-derived and HMDSO-derived membranes. FT-IR characterization indicated that the HMDSO-derived membrane had the highest content of methyl group and the lowest Si O Si, while the methyl group content for the MTMOS-derived membrane was the lowest and Si O Si was the highest. These results suggest that the pore size of organosilica membranes could be tuned by changing the chemical structure of the silicon precursor. The MTMOS-derived membrane was further heat-treated to determine the effect of thermal annealing on gas-permeation properties. The gas permeances were drastically improved by the thermal annealing. After heat-treatment at 500 °C, the membrane showed a high H2 permeance of 6.5×10−7 mol/(m2 s Pa) with a H2/SF6 selectivity of 410 at 200 °C, and 5.6×10−7 mol/(m2 s Pa) with a H2/SF6 selectivity of 360 at 50 °C.

We developed a procedure that saves significant amounts of energy during the separation of organic liquids via organic solvent reverse osmosis (OSRO). The proof-of-concept was confirmed using theoretical calculation to demonstrate energy-consumption at less than 1/100th and 1/10th that of conventional distillation and pervaporation (PV), respectively. Bis(triethoxysilyl)acetylene (BTESA)-derived organosilica membranes consisting of a SiO2–ZrO2 intermediate layer and an α-Al2O3 support were evaluated by challenging a series of azeotropic mixtures of methanol/toluene, methanol/methyl acetate, methanol/dimethyl carbonate (DMC), and methanol/methyl tert-butyl ether (MTBE). BTESA membranes showed excellent size- and/or shape-sieving properties and remarkable levels of organic-tolerance with an ultrahigh methanol flux that outperforms state-of-the-art polymeric membranes. In particular, the robust ceramic support and rigid organosilica networks endowed the resultant membranes with the ability to withstand transmembrane pressures as high as 18 MPa.

The separation of azeotropic mixtures such as methyl acetate and methanol via a membrane is an interesting and challenging issue, since the membrane must be able to withstand these harsh solvents and provide good flux and selectivity. SiC-based membranes have attracted a great deal of interest due to their high mechanical strength, structural stability, and corrosion resistance at elevated temperatures. Herein, we describe the first use of polytitanocarbosilane (TiPCS), which is known as a precursor of continuous Si–Ti–C–O fibers (Tyranno), in the preparation of Ti-incorporated SiC-based membranes for the pervaporation (PV) removal of water or methanol, and describe the evaluation of hydrothermal stability. For this study, the physical and chemical properties of TiPCS-derived materials during pyrolysis were characterized via TG-MS, ATR-FTIR, XPS, XRD, and N2 adsorption-desorption isotherms. The pore characteristics and surface areas of TiPCS-derived ceramic powders revealed that the titanium components in TiPCS inhibit and/or reduce the densification of the network structures at elevated temperatures. The network structure of TiPCS-derived, SiC-based membranes showed trends similar to those of TiPCS-derived ceramic powders. The membrane prepared at 750 °C featured reproducibility and attractive selectivities for the PV removal of water or methanol from liquid mixtures.

The aim of this work was to study the fouling and cleaning behavior of bis(triethoxysilyl)ethane (BTESE)-derived organosilica membranes, which is a new class of RO membranes that feature chlorine tolerance and thermal stability. The foulants used in this study included bovine serum albumin (BSA) and sodium alginate (SA), which are typical examples of effluent organic matter (EOM). Sodium dodecyl sulfate (SDS) and dodecyltrimethyl ammonium bromide (DTAB) surfactants served as typical industrial waste. With the EOM foulants, BSA fouling occurred at a pH that approximated its iso-electric point (IEP), and the fouling became more severe with the addition of electrolytes into the SA solution. In both cases, however, the fouled BTESE membrane was recovered with the use of deionized water (DIW). The fouling was more pronounced in the presence of DTAB by comparison with SDS surfactants. Surprisingly, in all tests, within 30 min and without the need of chemical agents, the integrity of the fouled BTESE membranes was recovered by applying water at a temperature of at least 80 °C.

Ceramic microfiltration membranes with superior chemical and mechanical stability for sustainable operation under harsh conditions have demonstrated great potential for industrial wastewater treatment. In this study, low-cost ceramic microsheet membranes with a thickness of sub-0.5 mm that possess superhydrophilic and underwater superoleophobic properties were fabricated from an Al2O3-rich Al2O3/polysulfone composite slurry via a phase inversion/sintering strategy. The cross-sectional morphologies of these phase inversion-induced composite films appear as ceramic green bodies that can be precisely controlled by tuning the operation parameters during the classic phase-inversion process of a polymer, which allows the morphology to withstand a subsequent high-temperature (1250 °C) sintering process. The thinner nature ( 99% and a much higher emulsion permeability of ~3,000 L/(m2 h bar), which is 2 orders of magnitude higher than most commercially available microfiltration membranes that are capable of similar levels of separation performance. This process resulted in a favorable membrane that combines robustness under complex chemical environments with low cost for both materials and processing approaches, which should facilitate its practical application in the industrial treatment of oily wastewater.

In this study a new type of layered hybrid membrane was fabricated. This new membrane consisted of a thin organically bridged silica separation layer deposited onto the surface of a flexible polymeric membrane, NTR-7450 (Nitto Denko, Japan), and was comprised of a sulfonated polyethersulfone top layer and a porous polysulfone support. Using 1,2-bis(triethoxysilyl)ethane (BTESE) as a precursor, a continuous and defect-free BTESE separation layer was deposited onto the surface of a polymeric nanofiltration membrane via a facile, reproducible and scalable sol–gel spin-coating and low-temperature curing process. First, the optimal preparation conditions were established, which included the curing temperature and the spin-coating cycles. The membranes were then used for the vapor permeation dehydration of isopropanol-water solutions, and showed a stable water flux of 2.3 kg/(m2 h) and an improved separation factor of about 2500, which was an increase of approximately 5-fold compared with that of a polymeric nanofiltration membrane. In addition, single-gas permeance through this membrane was also discussed and a modest H2/N2 selectivity of 26 was obtained, which approximated the performance of ceramic-supported BTESE-derived silica membranes.

The sol–gel method was applied to the fabrication of Al-doped bis (triethoxysilyl) methane (BTESM)-derived membranes. The single-gas permeation properties for Al-doped BTESM-derived membranes were examined to evaluate the effect of aluminum concentration on amorphous silica network sizes. Each permeance was decreased with an increase in the Al concentration, and the H 2 /CH 4 and H 2 /C 3 H 8 permeance ratios increased with an increase in Al concentration. For example, an Al-doped BTESM (Si/Al=8/2) membrane fabricated at 200 °C showed a H 2 permeance of 4.4×10 −7 mol m −2 s −1 Pa −1 , which was approximately 1/10th that of a BTESM membrane fabricated at 200 °C. The H 2 /CH 4 and H 2 /C 3 H 8 permeance ratios were 60 and 2700 with Al doping, but 30 and 1000 without Al-doping, respectively. The activation energy of He, H 2 , N 2 , and CH 4 permeation was increased with an increase in the Al concentration, indicating that the pore size of BTESM-derived networks was decreased with an increase in Al concentration. The decrease in BTESM-derived network sizes that resulted from an increase in the Al concentration can be ascribed to the absolute amount of Al incorporated into BTESM-derived networks and/or coordinated with Si-OH groups, as suggested by 27 Al MAS NMR. High C 3 H 6 /C 3 H 8 permeance ratios of approximately 40 for Al-doped BTESM (Si/Al=9/1) membranes fabricated at 200 °C were achieved through the precise control of the silica network size via a spacer method using Si–C–Si units as well as the incorporation of Al in BTESM-derived networks.

Using 1,2-bis(triethoxysilyl)ethane (BTESE) as a single precursor, a uniform, defect-free and perm-selective organosilica layer was successfully deposited onto porous polysulfone ultrafiltration (PSF-UF) supports via a simple sol–gel spin-coating and thermal-treatment process. The layered hybrid membranes, where BTESE-derived SiO2 is deposited on polymer supports, were applied to the vapor permeation dehydration of isopropanol–water (90/10 wt%) solutions at 105 °C, and demonstrated a water flux of 1.6 kg/m2 h and a separation factor of 315 with no selectivity for a PSF-UF support. Long-term stability testing of vapor permeation also confirmed the excellent stability of these BTESE/PSF-UF layered hybrid membranes. Moreover, compared with porous PSF-UF supports, this layered hybrid membrane also showed improved gas separation performance and a moderate (≈10) separation factor for H2/N2.

Sol–gel derived microporous amorphous TiO 2 –ZrO 2 –organic composite membranes were prepared by two different types of chelating ligands, diethanolamine (DEA) and isoeugenol (2-methoxy-4-propenylphenol, ISOH) as reaction inhibitors for hydrolysis and condensation of Ti- and Zr-alkoxide. The structural properties of the composite gels were characterized via a thermogravimetric study (TG), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and N 2 adsorption analysis; and the optimized calcination atmosphere and temperature conditions for a microporous membrane were examined. A crack-free thin (50 nm) TiO 2 –ZrO 2 –organic layer for gas separation was formed on a SiO 2 –ZrO 2 intermediate layer (150 nm) supported on a macroporous α-Al 2 O 3 substrate as an asymmetric membrane. Compared with DEA, more of the ISOH and its remnants effectively remained after calcination, which promoted higher permeance and selectivity as a microporous gas separation membrane by forming bimodal microporous structures that narrowed the original TiO 2 –ZrO 2 pores. A TiO 2 –ZrO 2 membrane with ISOH calcined at 350 °C under a N 2 atmosphere showed He and CO 2 permeances of 1.0×10 −6 and 2.0×10 −7 mol m −2 s −1 Pa −1 , respectively, at 200 °C. The CO 2 /N 2 permeance ratio was 6.4 at 200 °C and 46 at 35 °C.

High-performance organic–inorganic hybrid silica membranes were developed for use in membrane reactors for methylcyclohexane (MCH) dehydrogenation to toluene (TOL). The membranes were prepared via sol–gel processing using bis(triethoxysilyl)ethane (BTESE). In particular, the effect of hydrolysis conditions (H2O/BTESE molar ratio) on membrane performance was extensively investigated. Characterization based on TG-MASS, FTIR, N2 adsorption and positron annihilation lifetime (PAL) measurements of BTESE-derived silica gels revealed that the ethoxides of BTESE were almost completely hydrolyzed and the silica networks became dense by increasing the H2O/BTESE molar ratio from 6 to 240. BTESE-derived silica membranes showed a hydrogen permeance that was higher than 1×10−6 mol/(m2 s Pa). H2/TOL selectivity increased from 100 to 10,000 by increasing the H2O/BTESE molar ratio from 6 to 240, while keeping a hydrogen permeance of more than 1×10−6 mol/(m2 s Pa). In MCH dehydrogenation, a BTESE-derived silica membrane reactor with a Pt/γ-Al2O3/α-Al2O3 bimodal catalytic layer achieved MCH conversion of 75% that was higher than the equilibrium conversion of 60%, and a hydrogen purity in the permeate stream of more than 99.9% at 230 °C.

The removal of water vapor from humid gas streams is important for steam recovery in power plants and reaction enhancement in a membrane reactor that produces water as a by-product, and so on. The prospect of future applications for organosilica membranes in these fields prompted the present investigation of humid gas separation properties via 1,2-bis(triethoxysilyl)ethane (BTESE)-derived membranes. In this work, binary humid gas separation (H2O/H2 and H2O/N2) was performed on BTESE-derived membranes at temperatures ranging from 80 to 200 °C under feeds of water mole fractions ranging from 0.1 to 0.9. Permeance and the permeance ratios of H2O/H2 and H2O/N2 were confirmed to be dependent on temperature and vapor pressure, and found to be correlated using the water adsorption potential, which accounted for both the temperature and the vapor pressure. The highest levels of water permeate flux, permeance, and permeance ratios of H2O/H2 and H2O/N2 were 37 kg/(m2 h), 5.5 × 10−6 mol/(m2 s Pa)), and 84 and infinity (>6700), respectively, at 150 °C where the partial pressure difference of water across the membrane was 107 kPa. The high performance of BTESE-derived organosilica membranes shows promise for their future applications in humid gas separation at moderate-to-high temperatures.

Ultrathin, defect-free organosilica membranes on porous commercialized polymeric nanofiltration membranes (polythersulfone, PES) were fabricated via flow-induced deposition (FD) with a rinse step. Herein, we compare the FD approach with and without the rinse step and describe the effect on the formation of BTESE layers, along with separation performances during the vapor permeation (VP) dehydration of isopropanol (IPA)/water solutions (IPA: 90 wt%). The rinse strategy of reducing the BTESE layer (less than 100 nm) effectively enhanced the membrane permeance without compromising selectivity. The rinsed membrane showed high water permeance (1.8 × 10 −6 mol m −2 s −1 Pa −1 ) that almost equaled that of a polymeric support (2.0 × 10 −6 mol m −2 s −1 Pa −1 ), and a separation factor of about 800 for this VP process at 105 °C (1.1 wt% IPA in the permeate side). Moreover, these membranes demonstrated stable permeation properties under surroundings that included both vapor and liquid for the VP and pervaporation dehydration of IPA/water mixtures under high temperature. The membranes also demonstrated fine flexibility in a vast array of bending radii (more than 1.5 mm). This work has shown that the rinse process is an effective strategy for fabricating an ultrathin organosilica top layer on porous polymeric supports via the FD approach.