Surface Area Of Silica Aerogels Research Articles

Effects of several additives on silica aerogel properties and adsorption performance for n-hexane, carbon tetrachloride and toluene

In this work, hydrophobic and monolithic silica aerogels were prepared at ambient pressure by using β-cyclodextrin, cetyltrimethylammonium bromide and ethylene glycol as additive. The aerogels were characterized and used for adsorption of n-hexane, carbon tetrachloride and toluene. These additives have different effects on the morphology and specific surface area of silica aerogels. Compared to cetyltrimethylammonium bromide and ethylene glycol, introducing β-cyclodextrin into silica aerogel could increase adsorption capacity for of n-hexane, carbon tetrachloride and toluene more effectively.

Fabrication and characterization of Aerogel-Polydimethyl siloxane (PDMS) Insulation Film

The building has a large impact on the space heating demand and the indoor environment is affected by climate or daylight. Hence, silica aerogel has generally used as a film to reduce the coefficient of the window in the building. Silica aerogel is a suitable material to apply for insulation material with lower thermal conductivity than that of air to save interior energy. However expensive precursor and drying process were the main issue of the silica aerogel synthesis and practical usage. We attempt to fabricate aerogel insulation film for energy saving through the economic process under ambient pressure. Silica aerogel was synthesized from rice husk ash, which was an agricultural waste to be able to recycle. Taguchi design was used to optimize the parameters (amount of rice husk ash, pH, aging time) controlling the surface area of silica aerogel. The silica aerogel is prepared by sol-gel processing through acidic treatment and aging. The silica aerogel was obtained by modification of silica hydrogel surface and dry at ambient pressure. Finally, aerogel film was respectively fabricated by the different content of aerogel in polydimethylsiloxane (PDMS). Silica aerogel obtained 21 – 24nm average particle size was analyzed by SEM and silica aerogel with high surface area (832.26 m2/g), pore size ( 3.30nm ) was characterized by BET. Then silica Aerogel – PDMS insulation film with thermal conductivity (0.002 W/mK) was analyzed by thermal wave system. The study demonstrates an eco-friendly and low-cost route toward silica – PDMS insulation film with low thermal conductivity (0.002 W/mK).

Synthesis and characterization of silica aerogel as a promising drug carrier system

In the past years, use of aerogel in drug carrier systems has been of great interest among researchers because of its amorphous structure, significant porosity, and other special properties. In this study, the effects of physical characteristics of silica aerogels on the efficient medical application are investigated. To this end, silica aerogels with several densities were synthesized by using a two-stage sol-gel procedure and dilution by acetonitrile in gelation step. Physical characteristics of produced silica aerogels were analyzed by BET and BJH methods. Results reveal that the pore diameter and the surface area of silica aerogel are functions of its density. Using supercritical CO2 method, the efficiency of drug (Ketoprofen) loading on aerogels with respect to aerogel density was investigated. Cell viability and cell growth on silica aerogels were evaluated by MTT assay and SEM analysis, respectively. The drug-loaded materials were characterized by using of FT-IR, XRD, UV-Spectroscopy, and FE-SEM analysis. Results show that the effective density of silica aerogel for a drug carrier system is 0.12 g/cm3.

The effect of process variables on the properties of nanoporous silica aerogels: an approach to prepare silica aerogels from biosilica

Silica aerogel, a nanoporous material, was produced by using rice husk ash via sol–gel method. The aim of the study is to examine effects of the acid type (acetic, hydrochloric, nitric, oxalic and sulfuric acid), dryer type (air, freeze, oven and vacuum) and the addition of tetraethyl orthosilicate on the structural and physical properties of aerogels produced from rice husk ash. In addition, this is the first study investigating the effect of vacuum oven drying on the structure of rice husk based silica aerogel. Specific surface area and pore size of obtained silica aerogels have been analyzed by the N2 adsorption and desorption measurements at 77 K via Brunauer–Emmett–Teller (BET) and Barrett–Joiner–Halenda (BJH) methods, respectively. Surface functional groups were determined with fourier transform infrared spectroscopy (FTIR). Surface morphology was examined with scanning electron microscopy (SEM). Moreover, density was calculated by tapping method. The results showed that all of the variables had remarkable effects on the final properties of the silica aerogel. The BET specific surface area of the silica aerogels increased with the addition of tetraethyl orthosilicate, while the tapping density decreased. The BET specific surface area and pore size of silica aerogels varied between 140.7–322.5 m2 g−1, and 5.38–12.05 nm, respectively. Silica aerogel which was obtained by using oxalic acid, tetraethyl orthosilicate addition and air dryer had the highest BET specific surface area (322.5 m2 g−1).

Preparation of aerogel-eicosane microparticles for thermoregulatory coating on textile

Aerogel/eicosane microparticles were prepared by dispersing nanoporous silica aerogel powder in a liquid of phase change material (PCM), eicosane. Melt-infiltration (M), solvent-dissolving (D) and combined melt-dissolving (MD) for particle dispersion were investigated. Differential Scanning Calorimetric thermograph indicated that microparticle M has maximum heat capacity of 198J/g whereas the heat capacity of microparticles D and MD was found to be 139J/g and 144J/g, respectively. FT-IR and SEM analyses of the microparticles revealed that the eicosane infiltrated and coated the fine aerogel particles but the microparticles still remained in the powder form. The nanoporous aerogel structure held the infiltrated eicosane while the ultra-high specific surface area of silica aerogel kept the surrounding eicosane in situ by surface tension. Infrared thermal imaging showed that the eicosane did not drip out from the microparticles even at 120°C, whereas the pure PCM completely changed phase to fluid when heated. The developed microparticles provide ease of coating application in room temperature for thermal protective textiles. The coated fabric showed significantly improved thermal resistance over the speculated phase transition period of the PCM. This opens up the opportunity for the developed microparticles to be utilised as a thermal protective coating additive in a wide temperature range without melting or dripping out from the applied substrates.

Effect of water content on properties of one-step catalyzed silica aerogels via ambient pressure drying

Tetraethylorthosilane was hydrolyzed and condensed in methanol as solvent, and catalytic aqueous ammonium fluoride and different amounts of water as co-solvent. The prepared gels were aged and solvent exchanged by n-hexane. The surfaces of the gels were modified using trimethylchlorosilane. Finally ambient pressure drying was performed. The surface area of the samples was determined by BET analysis and the pore size distributions were measured using the BJH method. FT-IR spectroscopy was used to confirm surface silylation. Compressive properties were investigated before drying. By increasing the amount of water, gelation time decreased significantly and compression modulus rose by increasing water content. Specific compression modulus (modulus/density) of the samples exhibited decrease with larger water content. The BET and BJH results showed that at first by adding more water, the specific surface area of silica aerogels decreased, this declination is more significant for the sample with 3 molar parts of water and after that, the surface area again increased slightly. The FE-SEM micrographs showed the pearl necklace structure for prepared samples.

Effective preparation of crack-free silica aerogels via ambient drying

Effective ambient-drying techniques for synthesizing crack-free silica aerogel bulks from the industrial waterglass have been developed. Silica wet gels were obtained from aqueous colloidal silica sols prepared by ion-exchange of waterglass solution (4–10 wt% SiO2). Crack-free monolithic silica aerogel disks (diameter of 22 mm and thickness of 7 mm) were produced via solvent exchange/surface modification of the wet gels using isopropanol/trimethylchlorosilane/n-Hexane solution, followed by ambient drying. The effects of the silica content in sol and the molar ratio of trimethylchlorosilane/pore water on the morphology and property of final aerogel products were also investigated. The porosity, density, and specific surface area of silica aerogels were in the range of 92–94%, 0.13–0.16 g/cm3, and ∼675 m2/g, respectively. The degree of springback during the ambient drying processing of modified silica gels was 94%.