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排序方式: 共有78条查询结果,搜索用时 36 毫秒
41.
Over the past decade sol–gel methods have become increasingly popular alternatives to the solid state synthesis of metal oxides.
In many cases sol–gel synthesis is preferred due to desirable physical properties such as high surface area, high porosity,
and small crystallite size. Monolithic zinc ferrite aerogels were produced by the epoxide addition sol–gel method. It was
observed that addition of propylene oxide to 2-propanol solution of either the hydrated metal nitrate salts or the hydrated
metal chloride salts resulted in the formation of stable red–brown gels. Aerogels were characterized using powder X-ray diffraction,
high resolution scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption/desorption analysis.
The metal salt used in the synthesis was found to significantly influence the properties of the aerogel. All aerogels synthesized
exhibited low densities and high surface areas (>340 m2/g). Annealing of the aerogel at relatively low temperatures (below 450 °C) yielded a highly crystalline porous material which
is composed of nanometer sized particles. 相似文献
42.
Mesoporous silica films have been synthesized by a modified sol-gel method in the presence of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers as structure-directing agents. Influence of synthetic conditions on the formation of mesoporous silica films has been investigated. Porosity of samples can be controlled by block copolymer concentration and aging time of precursor solutions, while the block length of block copolymers affects mesoporous structures. Post-deposition chemical treatment using vaporized ammonia makes it possible to control and stabilize the mesoporous structures. Cooperation interaction mechanism can be considered as an acceptable model for the structural formation in the synthesis of mesoporous silica films. 相似文献
43.
以无机金属盐为前驱体,采用环氧丙烷添加法结合CO2超临界流体干燥和热处理工艺,制备了不同锑掺杂浓度的二氧化锡(ATO)气凝胶.所得气凝胶为深蓝色块体,平均密度约为600 mg?cm-3,锑掺杂浓度在5%到20%(x)之间.电子显微镜图片显示ATO气凝胶的骨架由粒径约为数十纳米的颗粒堆积而成,而这些颗粒又由数纳米的初级球形颗粒构成.X射线衍射谱表明,样品的主要晶相为SnO2四方相金红石结构,锑的掺杂仅引起微小的晶格畸变.X射线光电子谱显示锡元素以+4价态存在,而锑则具有+3和+5的混合价态.四探针电阻率测试仪的结果表明,ATO气凝胶的电阻率在2.7-40Ω?cm之间变化,其中在锑掺杂浓度(x)为12%时具有最低电阻率. 相似文献
44.
The work presents a synthetic approach that combines methods of metal vapor synthesis (MVS), gelation and supercritical drying in order to obtain chitosan aerogels containing silver nanoparticles. On the first stage, two types of silver organosols were prepared via the eco-sustainable MVS method. Then the prepared silver organosols were used to modify chitosan powders for producing metal-chitosan powder composites. Gelation of the powder composites was performed in oxalic acid at elevated temperatures. Supercritical drying of the gels was implemented in order to preserve the formed porous structures. Thus, the chitosan powders modified with MVS-produced silver nanoparticles were used to prepare metal-chitosan aerogels. Characterization of the structure and the morphology of both powder and aerogel silver-chitosan composites was conducted by means of low temperature nitrogen adsorption, X-ray photoelectron spectroscopy, X-ray powder diffraction, small-angle X-ray scattering, SEM and TEM. Changes in the structure and morphology of silver nanoparticles between powder and aerogel composites were analyzed. 相似文献
45.
The large amount of microplastic pollution in the aquatic environment has been regarded as a major challenge facing the world. Although some traditional water treatment processes can effectively remove microplastics in the millimeter range, research is still needed to solve the problem of removing smaller microplastics. Here, we made a durable zinc metal-organic framework-based composite material ZIF-8@Aerogel by in situ growing ZIF-8 on wood aerogel fibers, which can successfully remove microplastics in simulated water and seawater. The removal efficiencies on micro/nano plastics including poly(1,1-difluoroethylene)(60-110 nm) and polystyrene(90-140 nm) reached 91.4% and 85.8%, respectively. This work is expected to provide a new and efficient way to remove small-sized microplastic particles in the environment. 相似文献
46.
Zulhelmi Alif Abd. Halim Muhamad Azizi M. Yajid M. Hasbullah Idris Halimaton Hamdan 《Journal of Macromolecular Science: Physics》2018,57(6):479-496
Rice husk is rich in amorphous silica which has found various applications as a filler in rubbers and plastics. In the research described here silica was extracted from rice husk ash in the form of sodium silicate which was used to produced amorphous precipitated silica (PS) and silica aerogel (SA) using a sol – gel process and supercritical drying. These materials were then physically mixed with unsaturated polyester (UP) resin and cured at room temperature to form polymer composites. The experimental results showed that the UP composites with 30% (volume percent) of SA filler had lower density and better thermal insulation than the composites with the same amount of PS. Thermogravimetric analysis (TGA) results showed that the Tonset of the PS and SA composites were slightly delayed by 15 and 10°C, respectively. The tensile stress-strain curves showed that addition of the fillers reduced the tensile strength, but increased the elastic moduli of the UP matrix. PS filled UP composites exhibit higher moduli (higher stiffness) than that of SA filled UP composites. This was due to agglomeration and poor adhesion of the SA particles to the UP matrix while better dispersion was observed for the PS filled composite. 相似文献
47.
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49.
Graphene oxide (GO)-gelatin (G) aerogels were synthesized via the physical interactions between GO-oxygenated groups and G amine groups to obtain potential hemostatic devices. The influence of the aerogel synthesis conditions—acid and basic GO suspensions—was used to evaluate their clotting performance. These materials were also characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, and thermogravimetric analysis, and their properties of absorption, stiffness, porosity, surface charge, and pore size were measured and compared. The clotting activity of the materials was evaluated by prothrombin time, activated partial thromboplastin time, soluble human P-selectin, and in vitro dynamic clotting assays, as well as their cytotoxicity. GO-G aerogels presented heterogeneous microporous structures with porosities higher than 90% and a high PBS absorption capacity, 49.6 ± 3.8 gPBS/gaerogel for positively charged aerogels (15.63 ± 0.5 mV) and 42.75 ± 2.38 gPBS/gaerogel for negatively charged aerogels (?20.53 ± 1.07 mV). Comparatively, positively charged aerogels had superior structural properties to negatively charged aerogels, such as stiffness, porosities, and pore sizes, because they promote H bonding. In regard to hemostatic activity, negatively charged aerogels had higher clotting performance, reaching 95.6% clotted blood, and therefore provide a suitable structure for the coagulation process and promote clot formation without using common mechanisms. In addition, negatively charged aerogels were not cytotoxic and promoted fibroblast proliferation. Therefore, negatively charged GO-G aerogels may be a potential hemostatic device that can be used as a wound dressing. 相似文献
50.