Preparation and Surface Properties of Low-Density Gels Synthesized Using Prepolymerized Silica Precursors

Mrowiec-Białoń, Julita; Jarzębski, Andrzej B.; Pająk, L.; Olejniczak, Zbigniew; Gibas, Mirosław

doi:10.1021/la0400656

Cited by 13 publications

(10 citation statements)

References 19 publications

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“…They further made postulations from the SAXS results that ES40 xerogels appear to have a higher microstructural homogeneity indicating a thicker and stronger polymeric network which consisted of a highly condensed silica wall on one side with a thick polymeric chain barrier on the other, whereas the TEOS xerogels resulted in a lower homogeneity suggestive of a thinner polymeric chain wall. Further, ES40 xerogels exhibit larger pore size and micropore volume but lower surface area of silica xerogels than those observed in the corresponding TEOS sol-gel formulation2139.…”

Section: Discussionmentioning

confidence: 84%

“…As a consequence, the tendency for the structures to undergo cluster-cluster growth to form very open fractal structures due to a higher degree of condensation is greater in the ES40 sol-gel process. In the 29Si magic-angle spinning NMR study of the silica xerogels, Mrowiec-Bialoń et al 21 presented that the population of Q 3 and Q 4 sites predominated the silica structure in the xerogels prepared by ES40 than that of the TEOS which can only be explained by a greater silanol condensation. They further made postulations from the SAXS results that ES40 xerogels appear to have a higher microstructural homogeneity indicating a thicker and stronger polymeric network which consisted of a highly condensed silica wall on one side with a thick polymeric chain barrier on the other, whereas the TEOS xerogels resulted in a lower homogeneity suggestive of a thinner polymeric chain wall.…”

Section: Discussionmentioning

confidence: 99%

“…This precursor is available commercially, which is industrially derived from TEOS using 40% of the theoretical water concentration, therefore it has 40% of silica by mass21, or 60% of the alkoxide groups. Fig.…”

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confidence: 99%

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Reversible Redox Effect on Gas Permeation of Cobalt Doped Ethoxy Polysiloxane (ES40) Membranes

Miller

Wang

Smart

et al. 2013

Sci Rep

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This work reports the remarkable effect of reversible gas molecular sieving for high temperature gas separation from cobalt doped ethoxy polysiloxane (CoES40) membranes. This effect stemmed from alternating the reducing and oxidising (redox) state of the cobalt particles embedded in the ES40 matrix. The reduced membranes gave the best H2 permeances of 1 × 10−6 mol m−2 s−1 Pa−1 and H2/N2 permselectivities of 65. The reduction process tailored a molecular gap attributed to changes in the specific volume between the reduced cobalt (Co(OH)2 and CoO) particles in the ES40 structure, thus allowing for the increased diffusion of gases. Upon re-oxidation, the tailored molecular gap became constricted as the particles reversed to Co3O4 resulting a lower gas diffusion, particularly for the larger gases ie. CO2 and N2. The ES40 matrix proved to be structurally rigid enough to withstand the reversible redox effect of cobalt particles across multiple cycles.

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Section: Discussionmentioning

confidence: 84%

Section: Discussionmentioning

confidence: 99%

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Reversible Redox Effect on Gas Permeation of Cobalt Doped Ethoxy Polysiloxane (ES40) Membranes

Miller

Wang

Smart

et al. 2013

Sci Rep

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“…In another work, ES40 xerogels and aerogels were analysed by 29 Si NMR and small-angle X-ray scattering method, showing a high concentration of Q 3 and Q 4 species indicating a further degree of crosslinking and siloxane bridges [132]. In these reports, the reduction of silanol formation provides research opportunities to improve the hydrostability of silica membranes.…”

Section: Silica Hydrostabilitymentioning

confidence: 98%

High performance ES40-derived silica membranes for desalination

Wang¹

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Access to potable water has become one of the top 10 global problems facing our contemporary society. Desalination of vast amounts of seawater is a promising measure to ameliorate this stress.Numerous thermal and membrane processes have been employed to desalt seawater, of which reverse osmosis (RO) using polymeric membranes is the most mature technology and has been regarded as the benchmark in current desalination technologies. However, due to the high pressure requirement for RO operation, other membrane processes, such as membrane distillation and pervaporation have been developed as the alternatives to further reduce the energy cost.Furthermore, due to the lack of chemical/thermal stability and high tendency to scaling and fouling of polymeric membranes, novel inorganic membranes, in particular silica derived membranes, are emerging as potential candidates for desalination. The majority of published works on silica membranes utilizes tetraethyl orthosilicate (TEOS) as the silica precursor and interlayers are generally required to reduce the roughness of the porous substrates, followed by 4 to 6 thin-film coatings and calcinations with heating rates of 1-2 º C min -1 to form defect free silica membranes, which consume 10-14 days with extra cost. Therefore, the major target of this research is to produce interlayer-free silica membranes fabricated by rapid thermal processing (RTP) for desalination application.Ethyl silicate 40 (ES40) is used as precursor to prepare silica membranes in this work owing to their superior thermal stability as compared to the TEOS analogous product. Firstly, the sol-gel processing of ES40 was investigated in this thesis. At different temperatures and H 2 O/Si ratios, ES40 underwent various degrees of phase separation behaviour and sol-gel reactions. It was found that the hydrolysis and condensation reactions decreased with decreasing reaction temperature.Dense silica structures were obtained using low H 2 O/Si ratios, whereas higher porosity was produced from a phase-separated sol-gel system with high H 2 O/Si ratios. This tailoring process facilitated further condensation reactions and crosslinking of silica chains, leading to stronger silica matrices which were more resistant to densification.The second part of this work is focused on improvement of the hydrostability of ES40-derived silica membrane materials by adjusting the reactant ratios of sol-gel synthesis process, as the low resistance of silica membranes to water vapor attack, which induce enlargement of the pore size followed by failure in salt rejection, can be detrimental to desalination performance. Investigations were carried out on the effects of reactant ratios on the microstructure of the silica matrices and their hydrothermal stability under harsh conditions (550 °C, 75 mol% vapour). The most hydrothermally stable matrix was obtained by decreasing the ethanol ratio whilst increasing water II and acid ratios. The improved hydrothermal stability was attributed to the further transition of silanol to siloxa...

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“…) branching polymerization instead of a linear chain growth (as is the case with TEOS). Such polymerization behaviour would typically lead to a cluster-cluster growth of silica polymer with more siloxane bridges (Si-O-Si), whereby a thicker and more stable film is achieved (Mrowiec-Białoń et al, 2004;Miller et al, 2013;. These properties are much desired for gas separation applications involving wet gases.…”

Section: Figure 820mentioning

confidence: 99%

Advanced Materials for Polymeric Ultrafiltration Membranes Fabrication and Modification

Muhamad¹,

Nazri²,

Lau³

et al. 2018

Advanced Materials for Membrane Fabrication and Modification

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Preparation and Surface Properties of Low-Density Gels Synthesized Using Prepolymerized Silica Precursors

Cited by 13 publications

References 19 publications

Reversible Redox Effect on Gas Permeation of Cobalt Doped Ethoxy Polysiloxane (ES40) Membranes

Reversible Redox Effect on Gas Permeation of Cobalt Doped Ethoxy Polysiloxane (ES40) Membranes

High performance ES40-derived silica membranes for desalination

Advanced Materials for Polymeric Ultrafiltration Membranes Fabrication and Modification

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