Tailoring the structure of a sub-nano silica network via fluorine doping to enhance CO2 separation and evaluating CO2 separation performance under dry or wet conditions

Rana, Ikram; Nagasawa, Hiroki; Tsuru, Toshinori; Kanezashi, Masakoto

doi:10.1016/j.memsci.2022.120735

Cited by 7 publications

(5 citation statements)

References 43 publications

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“…The incorporation of fluorine into hydrophobic pendant–type organosilica further improved the hydrophobic/hydrophilic properties. Several studies have reported similar results of increased hydrophobicity with the addition of fluoride ions into silica matrix by showing the very low amount of H 2 O adsorbed by comparison with undoped samples [ 26 , 36 , 37 ].…”

Section: Resultsmentioning

confidence: 63%

The Effect of C/Si Ratio and Fluorine Doping on the Gas Permeation Properties of Pendant-Type and Bridged-Type Organosilica Membranes

et al. 2022

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A series of pendant–type alkoxysilane structures with various carbon numbers (C1–C8) were used to fabricate sol–gel derived organosilica membranes to evaluate the effects of the C/Si ratio and fluorine doping. Initially, this investigation was focused on the effect that carbon-linking (pendant–type) units exert on a microporous structure and how this affects the gas-permeation properties of pendant–type organosilica membranes. Gas permeation results were compared with those of bridged–type organosilica membranes (C1–C8). Network pore size evaluation was conducted based on the selectivity of H2/N2 and the activation energy (Ep) of H2 permeation. Consequently, Ep (H2) was increased as the C/Si ratio increased from C1 to C8, which could have been due to the aggregation of pendant side chains that occupied the available micropore channel space and resulted in the reduced pore size. By comparison, these permeation results indicate that pendant–type organosilica membranes showed a somewhat loose network structure in comparison with bridged–type organosilica membranes by following the lower values of activation energies (Ep). Subsequently, we also evaluated the effect that fluorine doping (NH4F) exerts on pendant−type [methytriethoxysilane (MTES), propyltrimethoxysilane (PTMS)] and bridged-type [1,2–bis(triethoxysilyl)methane (BTESM) bis(triethoxysilyl)propane (BTESP)] organosilica structures with similar carbon numbers (C1 and C3). The gas-permeation properties of F–doped pendant network structures revealed values for pore size, H2/N2 selectivity, and Ep (H2) that were comparable to those of pristine organosilica membranes. This could be ascribed to the pendant side chains, which might have hindered the effectiveness of fluorine in pendant–type organosilica structures. The F–doped bridged–type organosilica (BTESM and BTESP) membranes, on the other hand, exhibited a looser network formation as the fluorine concentration increased.

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Section: Resultsmentioning

confidence: 63%

The Effect of C/Si Ratio and Fluorine Doping on the Gas Permeation Properties of Pendant-Type and Bridged-Type Organosilica Membranes

et al. 2022

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“…Figure illustrates the relationship between the apparent activation energies ( E p ) for CO 2 and N 2 as a function of APTES concentration in TEOS–APTES (TFA) membranes calcined at 250 °C under a N 2 atmosphere, calculated using eq . In particular, eq describes the relationship between gas permeance ( P ), temperature ( T ), and activation energy of permeation ( E p ): where P is the gas permeance, k 0 is the permeation constant, M is the molecular weight of gas [kg mol –1 ], R is the gas constant [J mol –1 K –1 ], T is the absolute temperature [K], and E p is the activation energy of permeation [J mol –1 ] P = k 0 M R T exp [ − E normalp R T ] …”

Section: Resultsmentioning

confidence: 99%

“…In particular, eq 3 describes the relationship between gas permeance (P), temperature (T), and activation energy of permeation (E p ): where P is the gas permeance, k 0 is the permeation constant, M is the molecular weight of gas [kg mol −1 ], R is the gas constant [J mol −1 K −1 ], T is the absolute temperature [K], and E p is the activation energy of permeation [J mol −1 ]. 21…”

Section: Gas Permeation Properties and Co 2 Separation Performance Of...mentioning

confidence: 99%

“…However, the CO 2 adsorption properties of fluorine-induced silica network structures are compromised as CO 2 -philic sites (Si−OH), which are replaced by hydrophobic Si−F groups. 21 The CO 2 separation efficiency of silica membranes depends on the pore size, and the CO 2 affinity with the membrane surface is considered an essential parameter because preferentially adsorbed CO 2 on the philic surface can block the permeance of other gases (N 2 , CH 4 , etc.). 22 Therefore, 3aminopropyltriethoxysilyl (APTES) as an amine source, which exhibits strong CO 2 affinity, has been utilized extensively to functionalize silica because the defect-free surface was found difficult to obtain with pure APTES owing to the faster condensation rate of amine−organic−silane.…”

Section: Introductionmentioning

confidence: 99%

“…Another promising strategy involves the incorporation of fluoride ions (F – ) into the silica network structure, resulting in a loose network formation with improved gas permeation and hydrothermal stability. However, the CO 2 adsorption properties of fluorine-induced silica network structures are compromised as CO 2 -philic sites (Si–OH), which are replaced by hydrophobic Si–F groups …”

Section: Introductionmentioning

confidence: 99%

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Impact of Trifluoroacetic Acid on Tetraethoxysilane and Amine-Functionalized Tetraethoxysilane Silica Membranes for CO₂ Separation

Rana,

Moriyama,

Nagasawa

et al. 2024

Ind. Eng. Chem. Res.

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Amorphous silica derived from tetraethoxysilane (TEOS) is known for its remarkable properties, including high chemical and thermal stabilities. However, its inherent structure presents challenges for effective CO 2 /N 2 separation, owing to the difficulty in controlling the silica pore size, considering the similar sizes of CO 2 (0.33 nm) and N 2 (0.36 nm) molecules. In this study, we investigated the impact of trifluoroacetic acid (TFA) and amine (APTES: 3-aminopropyltriethoxysilyl) concentrations, aiming to leverage tailored silica structures with enhanced CO 2 affinity. Specifically, a two-stage investigation was conducted by first examining the influence of TFA on the pore structure of the TEOS networks, followed by an analysis of the CO 2 separation performance using composite TEOS−APTES membranes in the presence of TFA. While the TEOS (TFA) membrane exhibited a CO 2 permeance of 10 −6 mol m −2 s −1 Pa −1 , its CO 2 /N 2 permselectivity remained low. However, introducing TFA into the TEOS−APTES structure resulted in a notable transformation of the primary amine (NH 2 ) groups into amide (−NHCOCF 3 ) functionalities, along with improved microporous properties. This was confirmed by FT-IR spectroscopy, reversible CO 2 adsorption/desorption, and the high uptake of adsorbed N 2 . The resulting composite TEOS−APTES (TFA) membranes with APTES concentrations of 2 and 5 mol % demonstrated enhanced CO 2 permeation properties, achieving a CO 2 /N 2 selectivity of 15 and 35, respectively. This improvement is attributed to the increased pore volume and the introduction of amide functionalities (−NHCOCF 3 ), which exhibit mild affinity for CO 2 . These findings suggest that the developed composite (TEOS−APTES) membranes are promising for industrial applications that require efficient CO 2 separation.

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CO2 Capture by Membrane

Duan,

Meng,

Seshimo

et al. 2024

Handbook of Climate Change Mitigation and Adaptation

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Tailoring the structure of a sub-nano silica network via fluorine doping to enhance CO2 separation and evaluating CO2 separation performance under dry or wet conditions

Cited by 7 publications

References 43 publications

The Effect of C/Si Ratio and Fluorine Doping on the Gas Permeation Properties of Pendant-Type and Bridged-Type Organosilica Membranes

The Effect of C/Si Ratio and Fluorine Doping on the Gas Permeation Properties of Pendant-Type and Bridged-Type Organosilica Membranes

Impact of Trifluoroacetic Acid on Tetraethoxysilane and Amine-Functionalized Tetraethoxysilane Silica Membranes for CO₂ Separation

CO2 Capture by Membrane

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Tailoring the structure of a sub-nano silica network via fluorine doping to enhance CO2 separation and evaluating CO2 separation performance under dry or wet conditions

Cited by 7 publications

References 43 publications

The Effect of C/Si Ratio and Fluorine Doping on the Gas Permeation Properties of Pendant-Type and Bridged-Type Organosilica Membranes

The Effect of C/Si Ratio and Fluorine Doping on the Gas Permeation Properties of Pendant-Type and Bridged-Type Organosilica Membranes

Impact of Trifluoroacetic Acid on Tetraethoxysilane and Amine-Functionalized Tetraethoxysilane Silica Membranes for CO2 Separation

CO2 Capture by Membrane

Contact Info

Product

Resources

About

Impact of Trifluoroacetic Acid on Tetraethoxysilane and Amine-Functionalized Tetraethoxysilane Silica Membranes for CO₂ Separation