Papers by Keyword: Supercritical Drying

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Authors: Xiao Dong He, He Xin Zhang, Yao Li, Chang Qing Hong
Abstract: Highly Nano-porous SiO2-ZrO2 aerogels were manufactured with tetraethylorthosilicate (TEOS) and zirconyl nitrate dihydrate (ZrO(NO3)2 .5H2O) by the sol-gel method followed by supercritical drying technique. The prepared aerogels are performed by SEM, FT-IR and BET to characterize and analyze the morphology and pore structure of SiO2-ZrO2 aerogels. The results showed that:(i) The areogels are the typical of nano pores in the interval between 1
Authors: Zhi Chen, Yi Long Xie, Jin Xing Qiu, Zhong He Chen
Abstract: ZrO2 support has been prepared by sol-gel and coprecipitation method. CuO and NiO were supported on the supports and they were the activity metals for the catalysts. The CO conversion was tested. The light-off temperature of CO oxidation was 22°C and CO conversion efficiency was up to 50% at 169°C. The prepared catalysts of Cu, Ni supported on ZrO2-A had a high activity for CO oxidation at low temperature.
Authors: Xiu Yan Li, Jun Shen, Ai Du, Zhi Hua Zhang, Hui Yu Yang
Abstract: A simple and clean route to synthesize nano-scale mesoporous silver-silica composite aerogels was described here. The composite aerogels were obtained by adding a silver colloid to an about-to-gel silica sol prepared and then dried in supercritical anhydrous ethyl alcohol. The silver colloid and composite aerogels with silver content of 0wt%, 0.5wt%, 1wt% and 3.5wt% were characterized by UV-visible absorption spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD) and N2 Brunauer-Emmett-Teller (BET). The results show that silver nanoparticles with size about 40nm are successfully impregnated into the spongy porous structure of silica. The surface area decreases from 845 to 443m2/g with the increase of silver content. And the nanoscopic surface and bulk properties of each component are retained in the solid composite.
Authors: Yong Gang Jiang, Yan Qing Qin, Jun Zong Feng, Jian Feng, Lin Xu
Abstract: Monolithic SiO2-TiO2 aerogels were prepared via supercritical drying using tetraethoxysilane and tetrabutyltitanate as precursors and ethanol as solvent. Influence of the heat-treatment on the microstructure and properties of SiO2-TiO2 aerogels were investigated in detail. The results showed that the as-prepared SiO2-TiO2 aerogels had low densities, high specific surface areas, small average pore diameters, and three-dimensional nanoporous structures. The anatase TiO2 phase of SiO2-TiO2 aerogels could form during supercritical drying process, and the transition to rutile TiO2 phase occurred after experiencing 1200°C for 2 h. SiO2-TiO2 aerogels containing 30 wt% TiO2 (ST3) still presented relatively high specific surface area of 451 m2/g even they undergo the treatment of 1000°C for 2 h. And the SEM images indicated that the agglomerated particles derived from ST3 appeared gradually to some extent. The glassy luster of ST3 heat-treated at 1200°C for 2 h illuminates SiO2 started to vitrify. Besides, the thermal conductivity of ST3 at room temperature is up to 0.03257 W·m-1·K-1.
Authors: Xiao Hong Chen, Shuang Xi Yang, Huai He Song
Abstract: A novel organic and inorganic hybrid aerogel of RF/SiO2 is synthesized by one-step method of sol-gel polycondensation reaction using resorcinol-formaldehyde and tetramethoxysilane (TMOS) in ethanol solution, followed by supercritical drying with petroleum ether. The influence of the ratio of raw material on the structure and properties of samples was studied by high resolution electron microscope (HREM), nitrogen adsorption-desorption and infrared ray technology (IR). The results showed that the network structures of RF/SiO2 hybrid aerogels were constituted by an intercross framework of RF and SiO2. The hybrid aerogels can be tuned in bulk density from 0.098 g/cm3 to 0.062 g/cm3 according to the ratio of raw materials. The data of nitrogen adsorption-desorption showed that BET specific surface area was changed from 254 cm2/g to 545 cm2/g, and the pore size of aerogels was in the wide range of 2-10 nm. The investigation of IR spectrum analysis exhibited that there were no chemical bonds formed between SiO2 and RF aerogel.
Authors: Miao Lv, Guo Tong Qin, Wei Wei
Abstract: TiO2 aerogel fibers have been fabricated by electron span combined supercritical drying technique. Polyvinylpyrrolidone (PVP)/TiO2 composite fibers are prepared by electrospinning PVP and TiO2 precursor Ti (OC4H9)4. TiO2 aerogel fibers are obtained by supercritical drying PVP/TiO2 composite fibers using ethanol as media. Structural of the aerogel fibers was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and N2 adsorption at 77 K. The effect of mass ratio of PVP/TiO2 was investigated. SEM shows that pore structure of nanofibers was well developed, with the diameter of nanofibers about 2 μm. N2 adsorption/desorption data show that the highest surface area of aerogel fibers reached 241.6 m2/g with the average pore diameter about 10 nm. The aerogel fibers were anatase type TiO2.
Authors: Cheng Chen, Jian Li
Abstract: This paper reports a new method to prepare a new lignocellulose aerogel that is made from two kinds of wood powder through dissolution/regeneration of cellulose in ionic liquids. The obtained gel was washed with ethanol, liquid carbon dioxide and finally dried by releasing the carbon dioxide from the net structure at supercritical temperature to obtain the aerogel wood. All aerogels were compressible and consisted of nanofibrillar biomaterial network with open-pore structure. The range of density meets a criterion with aerogel density. Infrared spectrum shows that the pre-and post-treatment characteristic absorption peak of wood powder remained unchanged, and the ionic liquid played a mesomeric role among the physical reaction.
Authors: Fang He, Hai Lei Zhao, Xian Hui Qu, Wei Hua Qiu, Wei Jiang Wu
Abstract: Silica aerogels were synthesized from hybrid silicon sources of TEOS and acid silica sol by two-step sol-gel method and supercritical drying. Different chemical compositions of the starting solution were altered in order to make an insight into the relationship between process parameters and the microstructural characteristics of resulting silica aerogels. The results indicate that a certain amount of acid silica sol may promote the gelation process while excessive nano-scaled silica particles easily result in dense structure and low specific surface area. The gelation time increases with the increasing water amount. Excessive water will lead to weak network structure of silica gels and thus larger shrinkage and lower porosity of the resulting silica aerogels.
Authors: Jian Li, Jian Qiu, Yi Xing Liu, Hai Peng Yu
Abstract: Based on the fast-growing and abundant lightwood as ground mass, the study applies the formation principle of aerogel, uses such low-carbon treatment technologies as sol-gel method, Lowry method and supercritical drying method, prepares and forms an environment-friendly aerogel-type wood. The result of study shows that the new type of material not only has the natural biological structure of wood, but also has some fine features of aerogel, and is easily accepted by the environment.
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