Effect of fluorine doping on the network pore structure of non-porous organosilica bis(triethoxysilyl)propane (BTESP) membranes for use in molecular separation

Rana, Ikram; Nagasawa, Hiroki; Yamamoto, Kazuki; Gunji, Takahiro; Tsuru, Toshinori; Kanezashi, Masakoto

doi:10.1016/j.memsci.2021.120083

Cited by 3 publications

(5 citation statements)

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“…On the other hand, a peak was detected as Si–F (688 eV) in all fluorine–containing organosilica network structures. The existence of fluorine as Si–F and C–F bonds has also been reported in bridged organosilica (BTESM, Si–C 1 –Si; and BTESP, Si–C 3 –Si) network structures [ 26 , 27 ].…”

Section: Resultsmentioning

confidence: 93%

“…The results indicating a slight decrease in silanol groups (Si–OH) after fluorine doping were obtained for both forms of pendant–type organosilica network structures. It should be noted that various studies have reported that fluorine significantly decreases the silanol density (Si–OH) of conventional silica (TEOS) and bridged–type organosilica (BTESM, BTESP) network structures [ 25 , 26 , 27 ]. This effectiveness of fluorine is associated with a decrease in the silanol density (Si-OH) perturbed by the presence of Si–F and C–F groups in the bridged–type organosilica network structures [ 35 ].…”

Section: Resultsmentioning

confidence: 99%

“…A high uptake of N 2 adsorption was observed in fluorine-doped BTESP samples, whereas undoped BTESP samples showed a non-porous structure. This change in the microporous properties of F–BTESP samples is associated with a decrease in silanol density (Si–OH), which was perturbed by Si–F and C–F bonds and the subsequent network structure resulted in a high surface area and micropore volume [ 27 ]. Thus far, these results are consistent with the observation of physicochemical properties (FT–IR), where a small change in silanol density (Si–OH) was seen in fluorine-induced pendant–type organosilica samples, and F–doped gels simultaneously showed improved N 2 adsorption properties.…”

Section: Resultsmentioning

confidence: 99%

“…Long–chain organosilica membranes are known to block pores due to space occupation, and these are not considered effective for the fabrication of highly permeable gas–separation membranes. After fluorine (NH 4 F) incorporation, improved permeation properties have been reported irrespective of the organic linking units, which demonstrated an enlarged network pore size that was caused by Si–F and C–F bonds [ 27 , 35 ]. H 2 /N 2 selectivity and E p (H 2 ) decreased as the fluorine concentration increased (F/Si = 0–5/5), which indicates a loose network formation.…”

Section: Resultsmentioning

confidence: 99%

“…Kanezashi et al reported the effect of fluorine on conventional silica (TEOS) and bridged organosilica (BTESM) membranes and both membranes showed enlarged network pore size that was affected by Si–F and C–F bonds [ 25 , 26 ]. Fluorine-doped long–chain organosilica membranes with flexible organic linking units (BTESP, Si–C 3 –Si) have demonstrated an enlarged pore size with permeation properties (H 2 permeance; 10 −6 mol m −2 s −1 Pa −1 ) that are at least one order of magnitude higher than those of undoped BTESP membranes (10 −7 mol m −2 s −1 Pa −1 ) [ 27 ]. To the best of our knowledge, no one has reported the effect of fluoride ions on pendant-type organosilica structures.…”

Section: Introductionmentioning

confidence: 99%

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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: 93%