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1.
Porous silica was prepared using the sol-gel synthesis with porous carbon matrices as a pore-forming support. Tetraethoxysilane (TEOS) was hydrolyzed in an acid medium in the presence of a substoichiometric amount of water. Various carbon materials were used, among them Sibunit and catalytic filamentous carbon. Carbon matrices were impregnated with hydrolyzed TEOS and dried, then carbon was removed by burning out in air at 873 K. The obtained porous silica samples were studied by adsorption and electron microscopic methods. The specific surface area as high as 1267 m 2g and pore volume as high as 5.7 cm 3/g were determined for some silica samples. Thus deposited SiO 2 was found to cover the carbon surface copying its surface. With CFC used as carbon matrix, silica nanotubes were obtained. Thermostability of such silica is significantly greater as compared to silica gels reported earlier. 相似文献
2.
Compositions containing heteropoly compounds (ammonium phosphoromolybdate (APM) and phosphoromolybdenum acic (PMA)) are synthesized in a porous silica matrix using the sol-gel method. The obtained compositions containing 5–20 w/w % of APM and PMA are studied with the help of the X-ray-phase and differential-thermal analyses, IR and electron spectroscopy, and nitrogen adsorption. The APM and PMA maintain the Keggin structure after being introduced into an oxide matrix. The samples prepared by the sol-gel method have mesoporous and meso-macroporous structures and enhanced photocatalytic activity in comparison to the initial heteropoly compounds. 相似文献
3.
The study discussed the synthesis of silica sol using the sol-gel method, doped with two different amounts of Cu nanoparticles. Cotton fabric samples were impregnated by the prepared sols and then dried and cured. To block hydroxyl groups, some samples were also treated with hexadecyltrimethoxysilane. The average particle size of colloidal silica nanoparticles were measured by the particle size analyzer. The morphology, roughness, and hydrophobic properties of the surface fabricated on cotton samples were analyzed and compared via the scanning electron microscopy, the transmission electron microscopy, the scanning probe microscopy, with static water contact angle (SWC), and water shedding angle measurements. Furthermore, the antibacterial efficiency of samples was quantitatively evaluated using AATCC 100 method. The addition of 0.5% (wt/wt) Cu into silica sol caused the silica nanoparticles to agglomerate in more grape-like clusters on cotton fabrics. Such fabricated surface revealed the highest value of SWC (155° for a 10-μl droplet) due to air trapping capability of its inclined structure. However, the presence of higher amounts of Cu nanoparticles (2% wt/wt) in silica sol resulted in the most slippery smooth surface on cotton fabrics. All fabricated surfaces containing Cu nanoparticles showed the perfect antibacterial activity against both of gram-negative and gram-positive bacteria. 相似文献
4.
The comparative studies for the effect of vinyl-modified silica (VMS) and raw silica (RS) particles on the cell structure, insulation (dielectric and thermal transport) properties, and thermal stability of thermoplastic PMMA-silica nanocomposite (PSN) foams are described. The VMS particles were synthesized by the conventional acid-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) in the presence of 3-(trimethoxysilyl)propyl methacrylate (MSMA) molecules. The as-prepared VMS particles were then characterized through fourier transform infrared (FTIR), solid-state 13C-nuclear magnetic resonance ( 13C-NMR) and 29Si-NMR spectroscopy. Subsequently, the PSN materials were prepared via in-situ bulk polymerization. The dispersion of silica particles in PMMA matrix was observed by transmission electron microscopy (TEM) studies. Gel permeation chromatography (GPC) was used to determine the molecular weights of as-prepared samples. The PSN materials were used to produce foams by a batch process in an autoclave using nitrogen as foaming agent. The effect of VMS and RS particles on the cell structure, insulation properties and thermal stability of PSN foams were investigated by scanning electron microscopy (SEM), LCR meter, Transient plane source (TPS) technique and thermal gravimetric analysis (TGA), respectively. The better dispersion capability of VMS particles in PSN foams was found to lead enhanced nucleation efficiency, thermal stability and decreased dielectric constant (ε′), dielectric loss (ε″) and thermal conductivity ( k). POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers 相似文献
5.
In the context of the preservation of cultural heritage, the treatment of paper by an aminoalkylalkoxysilane, or its mixture with dimethyldiethoxysilane (DMDES), gave encouraging results. The condensation experiments presented here, carried out in alcohol medium using aminopropylmethyldiethoxysilane (AMDES) alone or with DMDES, were followed using 1H NMR, 29Si NMR and matrix‐assisted laser desorption ionization time‐of‐flight (MALDI TOF) spectroscopies. The aim was to determine whether DMDES and AMDES could copolymerize under the conditions used. An exchange reaction was observed for AMDES in ethanol in the absence of water, under conditions where no exchange took place for DMDES. In methanol, this reaction proceeded much more rapidly and the reactivity of methoxysilyl groups was higher than that of ethoxysilyl groups. In the same solvent, in the presence of water, hydrolysis, cyclization and oligomerization were observed using NMR and MALDI TOF spectroscopies. In ethanol, a kinetic study of a mixture of DMDES and AMDES showed that the condensation of the two monomers proceeded at comparables rates and MALDI‐TOF analysis gave evidence that mixed oligomers were produced, containing from one to four AMDES units. It was concluded that the co‐oligomerization did not lead to a mixture of homo‐oligomers, which would be due to different hydrolysis and condensation kinetics, but induced the formation of co‐oligomers. Copyright © 2010 Society of Chemical Industry 相似文献
6.
For the first time, the contents of isolated methyl groups, i.e. methyl groups bound to quaternary aliphatic or aromatic carbon, in crude oil samples were determined. As an analytical tool we used the 3J(H,H) modulated 1H-NMR spin echo technique. Weighed amounts of hexamethyldisiloxane (HMDS) containing six isolated methyl groups were added to the samples to determine absolute concentrations. The contribution of isolated methyl carbon to total carbon was in the range of 3.0 to 6.9% methyl groups bound to aliphatic carbon, and 1.2 to 4.6% for methyl bound to aromatic carbon. Model compound mixtures of known composition were prepared to validate the new procedure. The procedure delivers accurate and precise results with regard to relative standard deviations of less than 1%. 相似文献
7.
用丙烯酸丁酯与少量功能单体共聚,合成了分子链侧基带羟基的聚丙烯酸丁酯(PBA)乳液,然后与硅溶胶混合,用溶胶-凝胶法制备了PBA/SiO2杂化材料弹性体;研究了SiO2含量对杂化材料弹性体力学性能及透光率的影响,并用扫描电子显微镜、傅里叶变换红外光谱、差示扫描量热分析和动态力学性能分析对杂化材料弹性体的结构进行了表征。结果表明,PBA/SiO2杂化材料热压后成为一种力学性能优良的具有一定透光率的弹性体。随着SiO2含量的增加,杂化材料弹性体的力学性能提高,透光率和SiO2粒子的粒径增加,PBA基体的玻璃化转变温度和损耗因子下降;PBA共聚物分子链侧基所带羟基与SiO2粒子表面的硅醇基发生了缩合脱水反应,形成了Si—O—C共价键,使PBA基体与SiO2粒子构成的界面结合紧密,从而赋予杂化材料弹性体以优良的性能。 相似文献
8.
以十六烷基三甲基溴化胺(CTAB)稳定过的商业硅溶胶为模板硅源、蔗糖为炭前体、运用溶胶凝胶法制备了多孔炭材料。并采用低温N2等温吸脱附、X射线衍射等对材料的结构进行了测试与表征。结果表明:CTAB的加入使所得的多孔炭孔径分布更加集中,由于炭化温度较低,所得的炭材料仍为无定形结构。 相似文献
9.
Cardinyl acrylate (CA), prepared by the reaction of acryloyl chloride and cardinol, was copolymerized with methyl methacrylate (MMA) in bulk at 80°C using 2% benzoyl peroxide as an initiator. The copolymer composition was determined by 1H-NMR spectroscopy. Three copolymer samples containing 0.0048–0.0838 mol fraction of cardinyl acrylate were obtained. A significant improvement in the thermal stability of MMA was observed by incorporating 0.0048–0.0838 mol fraction of CA in the backbone. The activation energy for decomposition in the temperature range 350–480°C for copolymers was higher than PMMA. © 1992 John Wiley & Sons, Inc. 相似文献
10.
以钛酸丁酯为原料,通过在TiO2溶胶中添加质量分数为49%的硫酸,用溶胶–凝胶法制备了固体超强酸纳米光催化剂SO42?-TiO2,并在此基础上用硝酸银进行了改性。用XRD、IR、UV-vis、BET等手段对所制得的试样进行了表征,同时以甲基橙及苯酚的水溶液为模拟污染物,评价了样品的光催化性能,发现SO42--TiO2的光催化活性最高可达单一TiO2的10倍,SO 42?/Ag-TiO2的液相光催化活性超过P-25。 相似文献
11.
The aim of this study was to prepare transparent organic–inorganic nanohybrid materials with improved physical properties in comparison with the matrix polymer. Polymerizable silica nanoparticles were synthesized via the reaction of silanol groups on the surface of silica nanoparticles (particle diameter ≈ 12 nm) with isocyanate groups of 2‐(methacryloyloxy)ethyl isocyanate (MOI) in ethyl acetate. In addition, the matrix monomer, urethane dimethacrylate, was prepared by the reaction of an MOI isocyanate group with the hydroxyl group of 2‐hydroxyethyl methacrylate, and novel organic–inorganic nanohybrid materials were obtained at various silica contents with bulk polymerization. The surface treatment of the silica nanoparticles and preparation of the matrix monomer were carried out in a one‐pot reaction. The prepared hybrid materials retained high transparency, and the elastic modulus and surface hardness improved with increasing silica content. Moreover, the strength of the material containing 20 wt % silica was up to 30 MPa higher than that of the matrix polymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
12.
采用溶胶-凝胶法,通过常压干燥制备了疏水型二氧化硅气凝胶。研究了pH、水解时间等因素对二氧化硅气凝胶透光率的影响。以正硅酸乙酯为原料,通过酸(草酸)-碱(氨水)两步催化,采用溶胶-凝胶法常压干燥制备了疏水型介孔二氧化硅气凝胶。正硅酸四乙酯、乙醇、草酸、氨水物质的量比为1∶4∶5∶0.2,草酸和氨水的浓度分别为0.008、0.05 mol/L时,采用二甲基二氯硅烷为改性剂常压制备了二氧化硅气凝胶。透射电镜、扫描电镜测试表明:二氧化硅气凝胶具有纳米介孔结构。接触角测定表明:二氧化硅气凝胶与水的接触角为148°,表现出疏水性。 相似文献
13.
以甲基三甲氧基硅烷(MTMS)和四乙氧基硅烷(TEOS)为混合硅源、甲醇为溶剂,通过酸碱两步催化溶胶-凝胶法制备湿凝胶,经超临界流体干燥得到块状二氧化硅气凝胶。用扫描电镜、氮气吸附脱附测试以及热重分析等手段对气凝胶的微观形貌、比表面积、孔径分布、弯曲性、压缩性、热稳定性等进行研究,结果表明:MTMS/TEOS比例会影响气凝胶的微观结构、弯曲和压缩性以及热稳定性,以MTMS/TEOS=8/1制得的气凝胶密度为0.11 g·cm -3、孔隙率为94.2%、比表面积为693.3 m 2·g -1、最大弯曲角可达92°、最大压缩比例可达41.2%、压缩回弹率为100%。 相似文献
14.
This work prepared the highly transparent photo‐curable co‐polyacrylate/silica nanocomposites by using sol‐gel process. The FTIR and 13C NMR analyses indicated that during the sol‐gel process, the hybrid precursors transform into composites containing nanometer‐scale silica particles and crosslinked esters/anhydrides. Transmission electron microscopy (TEM) revealed that the silica particles within the average size of 11.5 nm uniformly distributed in the nanocomposite specimen containing about 10 wt % of Si. The nanocomposite specimens exhibited satisfactory thermal stability that they had 5% weight loss decomposition temperatures higher than 150°C and coefficient of thermal expansion (CTE) less than 35 ppm/°C. Analysis via derivative thermogravimetry (DTG) indicated that the crosslinked esters/anhydrides might influence the thermal stability of nanocomposite samples. The UV‐visible spectroscopy indicated that the nanocomposite resins possess transmittance higher than 80% in visible light region. Permeability test revealed a higher moisture permeation resistance for nanocomposite samples, which indicated that the implantation of nano‐scale silica particles in polymer matrix forms effective barrier to moisture penetration. Adhesion test of nanocomposite samples on glass substrate showed at least twofold improvement of adhesion strength compared with oligomer. This evidenced that the silica and the hydrophilic segments in nanocomposite resins might form interchains hydrogen bonds with the ? OH groups on the surface of glass so the substantial enhancement of adhesion strength could be achieved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
15.
In this study, we introduced molecular imprinting combined with electrochemical method to determine trace 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide in standard solution and actual samples. For this purpose, we synthesis of vinyl silica coated MWCNTs in alkaline environment with surfactant, molecularly imprinted polymers were prepared on the surface of MWCNTs by free radical polymerization, following the composite materials were dissolved in chitosan solution and dropped on the glassy carbon electrode. The functionalized materials were characterized by fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetry and nitrogen adsorption desorption. Electrochemical performance of molecularly imprinted membrane was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry. Selectivity, stability and reproducibility of the sensors were also studied and discussed. A good linear relationship for supervising 2,4-D from 1.0?×?10?4 to 1.0?×?10?8 mol L?1 with the correlation coefficient of 0.994 and a low LOD of 4.270?nmol?L?1 (S/N?=?3). The electrochemical sensor has been successfully applied to detect 2,4-D with a recovery rate ranges from 96.2 to 102.4% and a relative standard deviation of less than 4.74%. This work provides potential ideas for detection of trace 2,4-D in real samples. 相似文献
16.
A series of composites consisting of commercial waterborne polyurethane (PU) and silica were prepared by in situ synthesis (sol-gel method) and compared to those prepared by the addition of commercial silica (blending method). Adhesion resistance, mechanical resistance, small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) measurements were performed in order to evaluate the effect of silica addition. The adhesion resistance reached a maximum at 3 wt.% of added silica. Comparing the sol-gel composites with the analog composites obtained by the addition of commercial nanosilica, it was observed that although the composites containing commercial silica displayed higher mechanical resistance, better adhesion was obtained with the in situ method. The DSC results showed increasing crystallinity with increasing silica addition. 相似文献
17.
Molecular dispersions of amorphous siliceous materials doped with organic molecules were prepared by a sol-gel process in which Si(OC 2H 5) 4 was hydrolyzed in neutral or acidic solution. An amorphous silica which was doped with quinizarin on the order of 5×10 −5 mol/mol SiO 2 showed photochemical hole burning at ∼4 K. 相似文献
18.
Reduced graphene oxide (rGO) scaffoldings are used as templates to create lightweight 3D rGO/silica and rGO/silico-aluminate hybrids by a simple impregnation route and the sol-gel method. The printed rGO assemblies are infiltrated by the corresponding alkoxide precursor solution and gelled by exposure to ammonia vapours, producing an hybrid replica of the rGO structure. The hybrids show a significant prevalence of mesopores, with total porosity above 94 %, density of ~ 0.1 g?cm ?3 and high specific surface area (≥ 190 m 2?g ?1). As a result, the 3D composite materials show enhanced water adsorption capacity and hydrophilicity, display compressive strengths in the range 0.1 – 0.4 MPa, which scale with the proportion of silica (or Al-modified silica) on the hybrid scaffold, and electrical conductivities are above 60 S?m ?1. These properties are very attractive for applications in the removal of pollutants, water filtering, catalysis, drug delivery, or energy production and storage. 相似文献
19.
Organic-inorganic hybrid materials were prepared starting from tetraethoxysilane and α- or α,ω-triethoxysilane terminated poly(ε-caprolactone) (PCL-Si) using the sol-gel process. In all cases the formation of nanocomposites with a high level of interpenetration between organic and inorganic phases was noted. Poly(methyl methacrylate) slabs were dip-coated with PCL-Si/silica hybrids and a very strong increase of the flame resistance (also after UV irradiation) was noted for all coating compositions without marked differences with respect to hybrid compositions. This behavior was attributed to a preferential segregation of silica onto the outer surface, as evidenced by XPS analysis. 相似文献
20.
Organic/inorganic hybrid silica membranes were prepared from 1,1,3,3‐tetraethoxy‐1,3‐dimethyl disiloxane (TEDMDS) by the sol‐gel technique with firing at 300–550°C in N 2. TEDMDS‐derived silica membranes showed high H 2 permeance (0.3–1.1 × 10 ?6 mol m ?2 s ?1 Pa ?1) with low H 2/N 2 (~10) and high H 2/SF 6 (~1200) perm‐selectivity, confirming successful tuning of micropore sizes larger than TEOS‐derived silica membranes. TEDMDS‐derived silica membranes prepared at 550°C in N 2 increased gas permeances as well as pore sizes after air exposure at 450°C. TEDMDS had an advantage in tuning pore size by the “template” and “spacer” techniques, due to the pyrolysis of methyl groups in air and Si? O? Si bonding, respectively. For pore size evaluation of microporous membranes, normalized Knudsen‐based permeance, which was proposed based on the gas translation model and verified with permeance of zeolite membranes, reveals that pore sizes of TEDMDS membranes were successfully tuned in the range of 0.6–1.0 nm. © 2011 American Institute of Chemical Engineers AIChE J, 2011 相似文献
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