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151.
152.
An essential feature of the ambient pressure dried aerogel manufacturing process is the end-capping of the reactive silanol groups in the silica wet gel. In this report, we have presented the effect of two different trimethyl silylating agents viz. trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) on the hydrophobic and physical properties of ambient pressure dried silica aerogels. The hydrogels were prepared by sol-gel processing of sodium silicate precursor (Na2SiO3) in the presence of acetic acid catalyst followed by vapour passing treatment and different solvent exchanging steps. The silylating agent in hexane was used for end-capping of the silanols present on the silica surface of the gel. To study silylation behavior silylating agent/Na2SiO3 molar ratio was varied from 2.4 to 5.6. The aerogels have been characterized by density, % of volume shrinkage, porosity, % of optical transmission, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermo-gravimetric and Differential Thermal Analysis (TG-DTA) and contact angle measurements. 相似文献
153.
Magdalena Krcisz Bogdan Stpie Marta Pasawska Jarosaw Poposki Kinga Dulak 《Molecules (Basel, Switzerland)》2021,26(15)
The aim of this study was to determine the effects that the type of impregnating solution and drying method (freeze drying (FD) and vacuum drying (VD) at 45 °C and convective drying (CD) at 50, 60, and 70 °C) had on the physicochemical and quality properties of courgettes. Courgette slices were vacuum-impregnated (6 kPa) in freshly squeezed onion, kale, and onion and kale (50:50) juices with 3% NaCl solution (N). The application of vacuum impregnation (VI) with impregnating solutions from freshly squeezed onions and kale had a beneficial effect on the bioactive values of courgette. The highest contents of quercetin (41.84 μg/g d.m.) and carotenoids (276.04 μg/g d.m.) were found in courgette impregnated with onion juice after freeze drying. The highest values of lutein and zeaxanthin (216.42 μg/g d.m.) were recorded for courgette impregnated with kale juice and convective dried. By analysing the kinetics of convective drying, the best matching of the logistic model was found. Increasing the drying process temperature from 50 to 70 °C reduced the drying time from 15% to 36%, depending on the type of impregnating solution used. Water activity < 0.6 was recorded for courgette dried by freezing, vacuum, and convection at 60 and 70 °C. Conclusions: The vacuum impregnation process and the impregnation solutions from freshly squeezed vegetables can be used to develop new snacks with high levels of bioactive compounds. The FD method is the most appropriate considering both the bioactive compounds content and the obtained colour and water activity. 相似文献
154.
Mohammad Sirousazar Homa Khadivi Saba Delir 《Journal of Macromolecular Science: Physics》2020,59(5):309-330
AbstractPolyvinyl alcohol and egg white bionanocomposite hydrogels loaded with montmorillonite clay were fabricated by a freezing-thawing technique. The bionanocomposite hydrogels showed an exfoliated morphology and they had a more interconnected and dense network as compared with the clay-free sample. The montmorillonite layers acted as multifunctional crosslinkers and the bionanocomposite hydrogels had nanoscale, slit-shaped pores. The swelling ratios of the bionanocomposite hydrogels were increased either by decreasing the content of incorporated montmorillonite or by increasing the pH of the swelling medium. It was found that the bionanocomposite hydrogels having a higher content of montmorillonite exhibited a slightly slower drying process with a longer drying duration. Using the Ritger-Peppas model, it was shown that the swelling and drying mechanisms for all bionanocomposite hydrogels were non-Fickian diffusion. According to the Peppas-Sahlin model, it was found that the absorption of the swelling agent molecules during the swelling process and also the removal of water molecules during the drying process in the early stages of the processes occurred mostly due to their diffusion. At higher swelling or drying times, the contribution of the relaxation (for swelling) and shrinkage (for drying) of the polyvinyl alcohol polymeric chains and egg white protein chains was increased. 相似文献
155.
156.
Alessandro Allegri Valeriia Maslova Magda Blosi Anna Luisa Costa Simona Ortelli Francesco Basile Stefania Albonetti 《Molecules (Basel, Switzerland)》2020,25(22)
The photocatalytic oxidation of biomass-derived building blocks such as 5-hydroxymethylfurfural (HMF) is a promising reaction for obtaining valuable chemicals and the efficient long-term storage of solar radiation. In this work, we developed innovative TiO2-based materials capable of base-free HMF photo-oxidation in water using simulated solar irradiation. The materials were prepared by combining microemulsion and spray-freeze drying (SFD), resulting in highly porous systems with a large surface area. The effect of titania/silica composition and the presence of gold-copper alloy nanoparticles on the properties of materials as well as photocatalytic performance were evaluated. Among the lab-synthesized photocatalysts, Ti15Si85 SFD and Au3Cu1/Ti15Si85 SFD achieved the higher conversions, while the best selectivity was observed for Au3Cu1/Ti15Si85 SFD. The tests with radical scavengers for both TiO2-m and Au3Cu1/Ti15Si85 SFD suggested that primary species responsible for the selective photo-oxidation of HMF are photo-generated electrons and/or superoxide radicals. 相似文献
157.
通过竞争反应与海水晒盐2个案例,阐述了在化学原理教学过程中运用建模思想,可以使复杂的过程变得简洁、抽象,从而明晰现象背后的原理、规律。 相似文献
158.
Hydrochloric acid (HCl) used as catalyst for the preparation of RF-aerogels leads to organic aerogels in very short gelation
times. The gelation time can be varied from a few seconds to minutes. The wet gels can be dried under ambient conditions.
By variation of the sol composition or catalyst concentration the microstructure of the dry gels can be modified. The aerogel
densities are in the range of 210–410 kg/m3. The particle sizes, determined by scanning electron microscopy (SEM), are in the range of 700–1,500 nm. The particles look
essentially spherical and their size spectrum can be close to monodisperse. The specific surface is measured by nitrogen adsorption
(BET). Thermogravimetry (TGA) is employed to study the drying process, annealing reactions and decomposition of the aerogel
into a carbon aerogel. 相似文献
159.
The effect of heat-treatment on the physico-chemical properties of silica aerogel prepared by sub-critical drying technique 总被引:3,自引:0,他引:3
K. Balkis Ameen K. Rajasekar T. Rajasekharan M. V. Rajasekharan 《Journal of Sol-Gel Science and Technology》2008,45(1):9-15
Synthesis of transparent and crack-free monoliths of silica aerogel by sub-critical drying technique is reported in the present
article. Silane ageing with 50% tetraethylorthosilicate:ethanol followed by solvent exchange using ethanol was adopted. The
effect of heat-treatment on the textural and physical characteristics of silica aerogel was evaluated. The chosen composition
resulted in a high surface area silica aerogel of 1,000 m2 g−1 and a pore volume of 1.4 cm3 g−1 at room temperature. The aerogel heat-treated at 900 °C possessed a surface area of 450 m2 g−1 with a pore volume of 0.4 cm3 g−1. The decrease in surface area and pore volume was associated with the sintering process. The present technique seems advantageous
in preserving the high surface area of the material at high temperatures. The XRD studies showed that the amorphous nature
of aerogel matrix was retained till 1,400 °C, beyond which it crystallized to phase pure crystoballite. 相似文献
160.
Yicen Liu 《Molecular physics》2016,114(16-17):2373-2381