Papers by Keyword: Aerogel

Abstract: The structure and properties of graphene oxide aerogels (GOA), prepared by a modified Hummer’s method followed by a freezing-drying process in addition to a pre-oxidized procedure, were studied through FTIR, Raman, SEM and XDR techniques. FTIR results indicated the existence of -C-O, -C-OH and -C=O function groups on the GOA surface. Therefore, the D band intensity of GOA sample exhibited remarkable increasing in the Raman spectra compared with of graphite; it may be due to change the order-structure of graphite to disorder-structure of GOA. The diffractive peak for the graphite at 2θ of 26.5° vanishes instead the one around 10.0° occurred in the XRD pattern for the GOA supported that the structure and d-spacing changed seriously from graphite to GOA. The SEM images revealed that the micro-structure of graphene layer of GOA was wrinkler and softer than that of graphite, however, the former involved fewer lamellar layer appearance with wrinkles on the edges of the graphene. All the characterized evaluation confirmed that the graphite powder has been transformed into a GOA structure through the modified Hummers’ method.

Abstract: Aerogels based on organic high performance fibers have been attracted great attention due to its excellent thermal and mechanical properties. Here, PBO nanofiber aerogel were prepared from the super-fiber PBO through a top-down process with a sol-gel process and a simple freeze-drying process, followed by thermal cross-linking. The prepared aerogel has a small volume shrinkage, a high specific surface area of 168.9 m² /g and a small pore diameter of 1.356 nm. Because of its 3D porous structure, it results in a low density of 6 to 30 mg/cm³ and a high porosity (98%). The aerogel retains the molecular structure of PBO at the same time, which gives it initial thermal decomposition temperature up to 500 °C and a superior fire-retardant capability. PBO aerogel possesses good compressive properties with a yield stress of 0.44MPa at 80% strain and an elasticity modulus of 1.98 MPa which is higher than SiO₂ and cellulose aerogel reported.

Abstract: Thermal conductivity is an important material property in the energy design process of the buildings. While cement-based materials are the most consumed materials in construction industry, thermal properties of these materials can play a significant role in energy efficiency of the buildings. Cementitious materials with low thermal conductivity can be desirable for using as a part of heat insulation or for thermal bridge calculations. In this study, hydrophobic aerogel granules were used as aggregate and combination of Portland cement and fly ash was considered as the binder in order to achieve a material with low thermal conductivity. Replacement of 50 vol% hardened cement paste (hcp) by aerogel granules led to about 70% reduction in thermal conductivity of air dried samples (from 0.67 W/mK to 0.20 W/mK). However, this reduction was nearly 50% in moist samples submerged in water for three days (from 0.97 W/mK to 0.50 W/mK) due to replacement of air by water in hcp pores, which can be avoided by using hydrophobic agents. The thermal conductivity can be reduced by increasing water-cement ratio as well as aerogel content. This type of composite can be used as cast concrete or on-site 3D printing of wall elements.

Abstract: Agroindustry waste containing cellulose compound, Sorghum stem, was utilized to become cellulose aerogel which was then used as dye absorbent in textile dye wastewater. Cellulose was prepared by sorghum stem powder delignification using 6%w of NaOH solution. The ratio of powder and NaOH was varied in 1:12, 1:15, and 1:20. After this process, the powder was synthesized with NaOH/Urea to produce an aerogel by the freeze-drying method. The result shows that a higher amount of NaOH in the delignification process could increase aerogel density and decrease the porosity. Thermal stability and sorption efficiency of the aerogel was analyzed in this study. Higher porosity of aerogel tends to raise % removal in methylene blue absorption. This study reveals that aerogel three times more effective than activated carbon in dye removal.

Abstract: In recent years, many researchers have focused on the energy efficiency and performance of existing buildings. In order to predict the hygrothermal performance and minimize the risk of moisture damage in retrofit cases, user-friendly moisture calculation tools have been developed. However, concerns have been raised as to how to increase the reliability of such tools. In this context, the present study uses simulation to investigate the retrofit potential of the historical building façades via application of silica aerogels on the external walls. Monitored data provided the basis for generation of a more accurate initial simulation model, as well as the evaluation of the predictive performance of the model.

Abstract: Melamine/graphene (GO/MF) aerogel composite was prepared through a simple one-step hydrothermal route, freeze-drying, and subsequent carbonization with graphene oxide (GO) and melamine resin. The structure, morphology and electrochemical performance of the composites were characterized by SEM, TEM, XRD-ray, Raman spectroscopy, and electrochemical tests. GO/MF aerogel possessed 3D porous structure and enlarged surface like aerogel materials for efficient ionic diffusion and transport. Melamine resin was used as N-doping agent, and the electrochemical performance of GO//MF was improved effectively. GO/MF aerogel shows a higher capacitance of 106 F/g at a current density of 0.1 A/g comparing to reduce graphen oxide (rGO). Not only the macroporous structure but also the N-doping agent had a significant impact on the capacitive behavior of graphene. These results provide a new method to prepare high performance electrode material as supercapacitors.

Abstract: In this research aerogels were synthesized by homogenization of carbon nanotubes and chitosan under ultrasonic treatment and active magnetic stirring, followed by freeze-drying in order to remove the liquid from its structure. Freeze-drying is characterized by a certain ratio of pressure and temperature at which the solid phase, in our case - the ice, turns into a gas without passing through a liquid phase. Freeze-drying was carried out at a temperature of-5 ° C and a pressure of 30-80 Pa. After freeze-drying which lasted for 20 hours, the as-obtained aerogels were carbonized at temperature of 800 °C in an inert atmosphere. Surface morphology of resulting aerogels was studied using scanning electron microscopy. The hydrophobicity and sorption capacity of these aerogels to organic liquids characterized by different densities were investigated. In addition, composite aerogels with the presence of graphene layers in the structure were obtained and the influence of introduction of graphene on aerogel’s properties was analyzed. It was found that composite aerogels based on graphene and carbon nanotubes with chitosan as a glue matrix are characterized by a better-developed porosity of surface with a smaller pore sizes, and their sorption capacity for organic liquids is also higher compared with the aerogels based on carbon nanotubes.

Abstract: The cellulose-silica composite aerogels (CAs) were fabricated through a permeation sol-gel process in the regenerated cellulose hydrogels followed by freeze drying. The precursor Na₂SiO₃ instead of traditional organic precursor was diffused in the cellulose matrix followed by permeating the catalyst into the cellulose nanofibers network gradually to promote the in situ condensation of Na₂SiO₃ to form a SiO₂ gel skeleton from outside to inside. The obtained CAs displayed the interpenetrating network (IPN) structure of the regenerated cellulose nanofibers network and the SiO₂ gel skeleton in nanoscale. In the IPN structure, the flexible cellulose nanofibers network was supported by the hard inorganic network effectively to sustain the compression and the silica gel skeleton protect the cellulose nanofibers to avoid the remodeling of their shape in the process of solvent replacement before freeze drying. Due to the synergic effects of the different network, the IPN structure endows the CAs with high compression modulus (as high as 15.48 MPa), high specific surface area (as high as 621 m² g^-1) and low density (less than 0.182 g cm^-3).

Abstract: Quartz fiber composites filled with nanosized SiO₂ were prepared by sol-gel method with vacuum impregnation , supercritical drying and surface modification. The silica sol for vacuum impregnated were made from tetraethyl orthosilicate (TEOS), anhydrous ethanol, water and acid catalyst as the starting materials. The water adsorption rate, apparent porosity and electrical properties of composites were investigated by means of archimedes method and waveguide method while the surface area and pore size of the aerogel samples were tested by BET, the mechanism of hydrophobicity was also discussed. The results showed that the moisture absorption rate of products was decreased to 1.21% from 17.36% that without filled with nanosized SiO₂, with a decreasing range of 93%. Additional coating could make the rate even as low as 0.052%.The dielectric constant had no significant change while the loss tangent decreased from 3.1╳10^-3 to 1.4╳10^-3,with a decreasing range of 51.2%.

Abstract: Cellulose nanomaterials processing for aerogel preparation has received considerable attention among the scientific community due to its fascinating properties. In this work, we report on the preparation of cellulose nanocrystals (CNCs) aerogel from wastepaper using a freeze-drying technique. Structural analysis of the cellulosic particles extracted was investigated by Fourier Transform Infrared Spectroscopy (FTIR). Morphological analysis of the extracted cellulose and CNCs were carried out by Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) respectively. We achieved density of aerogel down to 0.012 g/cm³ which is comparable with typical values of cellulosic aerogels. The preparation of the CNCs aerogel might offers a wide range of aerogel applications through an environmentally friendly conversion of wastepaper material.