Synthesis of hydrophilic and hydrophobic xerogels with superior properties using sodium silicate

Sarawade, Pradip B.; Kim, Jong-Kil; Hilonga, Askwar; Quang, Đặng Viết; Kim, Hee Taik

doi:10.1016/j.micromeso.2010.10.030

Cited by 68 publications

(28 citation statements)

References 47 publications

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“…2 and 3) which were previously also observed for APD waterglass based silica aerogels [52,58,59]. In contrast, there is no difference in the bulk density with different aging times for SCD silica aerogels because the supercritical drying process eliminates the capillary stresses and forces during drying and hence, leads to very little shrinkage, regardless of the strength of the gel network.…”

Section: Discussionsupporting

confidence: 59%

“…In summary, most of these studies indicate that long aging times and several solvent exchanges before drying are typically employed during the synthesis of silica aerogels. The effect of both aging and drying processes on the final physico-chemical properties of silica aerogels was investigated for SCD TEOS based silica aerogels [55,57] and for APD water-glass based silica aerogels [52,58,59].…”

Section: Introductionmentioning

confidence: 99%

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Effect of aging on silica aerogel properties

Iswar

Malfait

Balog

et al. 2017

Microporous and Mesoporous Materials

136

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Silica aerogels' unique physical and chemical properties make them fascinating materials for a wide variety of applications. In addition to hydrophobization by silylation, aging is very important in the synthesis of silica aerogel by ambient pressure drying. Here we systematically study the effect of aging on the physico-chemical properties of silica aerogel with emphasis on ambient dried materials. Silica gels were aged for different times and at different temperatures in their gelation liquid (without solvent exchange), hydrophobized in hexamethyldisiloxane and subsequently dried either at ambient pressure or from supercritical CO 2 . Dynamic oscillatory rheological measurements demonstrate that aging reinforces the alcogels, particularly at high strain. The specific surface area decreases with increasing aging time and temperature as a consequence of Ostwald ripening processes during aging. With increasing aging time and temperature, the linear shrinkage and bulk density decrease and the pore size and pore volume increase for the ambient dried gels, but remain nearly constant for supercritically dried gels. Small-Angle X-ray scattering does not detect significant structural changes at length scales smaller than about hundred nanometers, but hints at systematic variations at larger length scales. The findings of this study highlight the importance of aging to increase the ability of the gel particle network to withstand irreversible pore collapse during ambient pressure drying.

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Section: Discussionsupporting

confidence: 59%

Section: Introductionmentioning

confidence: 99%

Effect of aging on silica aerogel properties

Iswar

Malfait

Balog

et al. 2017

Microporous and Mesoporous Materials

136

View full text Add to dashboard Cite

show abstract

“…Next, the TMS group, which is a hydrophobic substituent of the DMS group, is generated when TMCS or DMDCS reacts with silanol that resides on the particle surface of the hydrogel, as shown by Eqs. (5) and (6).…”

Section: Hydrophobization Of Hydrogels and Ambient Pressure Drying Ofmentioning

confidence: 99%

“…Methods for synthesizing silica aerogels from waterglass include a method in which alkali is added to acidic sol, with the sodium ions removed using an ion-exchange resin 5) and a method in which acid is added directly to the waterglass. 6),7) The ion-exchange method has a significant impact on the environment due to the large amount of water used for cleansing and regenerating the ion-exchange resin and, for these reasons, processes that are friendlier to the environment and that minimize the use of water are desired.…”

Section: Introductionmentioning

confidence: 99%

Effect of organic hydrophobic groups on the pore structure and thermal properties of waterglass-based silica xerogels

Oikawa

Toyota

Sakatani

et al. 2017

J. Ceram. Soc. Japan

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Hydrophobic silica xerogels containing trimethylsilyl (TMS) and dimethylsilyl (DMS) organic hydrophobic functional groups were synthesized using waterglass as the starting material. Five types of hydrophobic silica xerogels with varying surface coverages of the TMS and DMS groups were synthesized by changing the molecular structure of siloxane, which was used to introduce the hydrophobic moieties into the hydrogel and to investigate the resultant surface structures and thermal characteristics. The results revealed that the relative area of silica xerogels was smaller with a higher coverage of DMS groups. In addition, the thermal decomposition temperature of the silyl group shifted to higher temperatures, and the weight reduction during heating was also relatively limited in the above samples.

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“…) and C-C vibration peak (968 cm À1 ) appeared (Ghoshal and Manjare, 2003;Sarawade et al, 2011Sarawade et al, , 2013, manifesting the enhanced hydrophobicity of SG-2.…”

mentioning

confidence: 95%

Adsorption performance of hydrophobically modified silica gel for the vapors of n-hexane and water

Huang

Wang

et al. 2017

Adsorption Science & Technology

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An ordinary silica gel (SG-1) was chosen as the raw material and hydrophobically modified with trimethylchlorosilane under different microwave exposure. The orthogonal experiment was designed to screen the optimized modification method. The hydrophobic properties modified silica gel (SG-2) was analyzed by comparing the difference changes of surface chemistries. Then, the adsorption capacities of SG-1 and SG-2 to the n-hexane vapor and water vapor, respectively, were investigated and compared with the capacities of activated carbon and SG-3 (hydrophobically modified using the same composite modifier without microwave exposure). Meanwhile, there cyclable adsorptions of SG-2 to the two vapors were conducted while the desorptions of vacuum and heat was observed. The results showed that the effect of hydrophobic modification to SG-1 under microwave exposure was obvious and SG-2 also had a very good effect of adsorption for the n-hexane vapor. The modified silica gel shows great potential and effect for the recovery of volatile organic compounds with high content of water.

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Synthesis of hydrophilic and hydrophobic xerogels with superior properties using sodium silicate

Cited by 68 publications

References 47 publications

Effect of aging on silica aerogel properties

Effect of aging on silica aerogel properties

Effect of organic hydrophobic groups on the pore structure and thermal properties of waterglass-based silica xerogels

Adsorption performance of hydrophobically modified silica gel for the vapors of n-hexane and water

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