共查询到20条相似文献,搜索用时 15 毫秒
1.
Marcela Stoia Mircea Stefanescu Thomas Dippong Oana Stefanescu Paul Barvinschi 《Journal of Sol-Gel Science and Technology》2010,54(1):49-56
The paper presents a study on the preparation of Co2SiO4/SiO2 nanocomposites by a new modified sol–gel method. We have prepared gels starting from tetraethylorthosilicate (Si(OC2H5)4), cobalt nitrate Co(NO3)2·6H2O and some diols: ethylene glycol (C2H6O2), 1,2propanediol (C3H8O2) and 1,3propanediol (C3H8O2), for a final composition: 30% CoO/70% SiO2. During the heating of the gels at 140 °C, a redox reaction takes place between NO3
− ions and diol with formation of some carboxylate anions. These carboxylate anions react with the Co(II) ions to form coordination
compounds embedded in silica matrix, as evidenced by FT-IR spectrometry and thermal analysis. These Co(II) coordinative compounds
thermally decompose in the range 250–300 °C to the corresponding oxides: CoO and/or Co3O4 inside the matrices pores. When CoO results, it reacts with SiO2 at low temperature leading to Co2SiO4, which crystallizes at 700 °C. XRD patterns of the samples annealed at temperatures lower than 700 °C were characteristic
to amorphous phases. The samples annealed at temperatures ≥700 °C, contain Co2SiO4 (olivine) as unique crystalline phase inside the amorphous silica matrix, according to XRD patterns. As evidenced by TEM
images, Co2SiO4 nanoparticles are homogenously dispersed inside the silica matrix. 相似文献
2.
Petr Brázda Daniel Nižňanský Jean-Luc Rehspringer Jana Poltierová Vejpravová 《Journal of Sol-Gel Science and Technology》2009,51(1):78-83
ε-Fe2O3/SiO2 nanocomposite was prepared by novel solgel method using single precursor for both nanoparticles and matrix. This method allows to prepare the samples free of α-Fe2O3 with 40% of Fe2O3 in SiO2. Nanoparticles of 12 nm diameter were obtained by annealing at 1,000 °C. The samples were characterized by powder X-ray diffraction and transmission electron microscopy. Mössbauer spectroscopy identified ε-Fe2O3 as the only magnetically ordered phase at room temperature. Magnetic measurements revealed progressive necking of hysteresis loops measured at 300 and 2 K. In both cases the intrinsic coercivity reaches only 0.25 T. Measurements up to 14 T shows monotonous decreasing trend of saturated magnetization with increasing temperature. 相似文献
3.
Thin films being composed of a nanoporous SiO2 network and silica nanoparticles were prepared on glass substrates by sol–gel processing. The surfaces combine anti-reflective
(AR) and anti-soiling properties as demonstrated in laboratory testing and long term outdoor exposure. Films were characterized
by scanning electron microscopy (SEM). It is shown that both, the structure of the nanoporous matrix as well as the particle
density, contribute to this effect, the influence of relative humidity (RH) during dust exposure was investigated. Due to
their generally improved solar transmittance and dust-repellant properties the coatings are believed to have a vast potential
for many photovoltaic and solar thermal applications. 相似文献
4.
Composites containing vitamin B12 (cyanocobalamin) dispersed in amorphous silica xerogel were studied structurally as a function of annealing temperature.
Silica xerogel samples were prepared by the sol–gel method using an ethanol:H2O:TEOS molar ratio of 4:11.6:1 and loaded with cyanocobalamin. We found that the structure of the cobalamin is unaltered,
although decoordination of the benzimidazole nucleobase of B12, whereas the amorphous quartz structure of the matrix is maintained under heat-treatment without low-cristobalite phase transformation,
typically of this kind of materials. We found in our samples partial crystallization of the glass matrix in form of stishovite
obtained at very lower pressure than those specified by the phase diagram, and temperatures about 400 °C due to the presence
of vitamin B12. The presence of stishovite is corroborated by the Rietveld refinement method. 相似文献
5.
6.
K. P. Lopes L. S. Cavalcante A. Z. Simões R. F. Gonçalves M. T. Escote J. A. Varela E. Longo E. R. Leite 《Journal of Sol-Gel Science and Technology》2008,45(2):151-155
NiTiO3 (NTO) nanoparticles encapsulated with SiO2 were prepared by the sol–gel method resulting on core-shell structure. Changes on isoelectric point as a function of silica
were evaluated by means of zeta potential. The NTO nanoparticles heat treated at 600°C were characterized by X-ray diffraction,
transmission electron microscopy (TEM) and energy dispersive X-ray analysis. TEM observations showed that the mean size of
NTO is in the range of 2.5–42.5 nm while the thickness of SiO2 shell attained 1.5–3.5 nm approximately. 相似文献
7.
T. V. Kon’kova M. G. Gordienko M. B. Alekhina N. V. Men’shutina 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2017,91(3):468-471
The high efficacy of iron-containing catalysts based on SiO2–Al2O3 systems obtained via sol–gel method in the oxidative destruction of carmoisine azo dye in aqueous solutions is demonstrated. It is found that the stability of the catalysts with respect to the leaching of iron ions into a solution during catalysis grows along with the aluminum content in the composition of aluminosilicate supports. It is concluded that the synthesized catalysts are promising materials for purifying wastewaters contaminated with organic dyes. 相似文献
8.
M. Kamal I. K. Battisha M. A. Salem A. M. S. El Nahrawy 《Journal of Sol-Gel Science and Technology》2011,58(2):507-517
A sol–gel process for producing monolithic silica–phosphate (SiO2–P2O5) system different concentrations of P2O5, starting with tetra-ethoxysilane TEOS, and triethyl-phosphate as sources of SiO2 and P2O5 was performed. The gels were heat-treated at temperatures ranging from 100 up to 900 °C. The structural and chemical analyses
of the samples were determined by using X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). It was
found from the XRD that the existence of phosphorus enhances the crystallization of silica gel, while the FTIR indicated the
main functional groups of silica–phosphate. It is important to study the effect of hydroxyl in silica–phosphate glass. The
results obtained are promising to use the prepared samples in a variety of applications, ranging from traditional application
such as lighting products) to the modern application (such as optical fibers. Optical studies were measured by using the spectrophotometer
in wavelength range 0.2–2.5 μm. The refractive index (n) was calculated for the prepared samples, it was found to be strongly affected by structural rearrangement resulting from
the elimination of the solvent and the Si–OH, Si–O–Si and Si–O–OH bonding by phosphate and aluminum and it increases by increasing
phosphate concentrations. The weight losses have investigated for prepared samples. 相似文献
9.
M. Baikousi S. Agathopoulos I. Panagiotopoulos A. D. Georgoulis M. Louloudi M. A. Karakassides 《Journal of Sol-Gel Science and Technology》2008,47(1):95-101
Magnetic bioglasses in the system CaO–SiO2–P2O5 were prepared by interaction of acetic acid vapors with iron nitrate dispersed on the surface of sol–gel derived porous silicate
network. Upon pyrolysis, the created iron acetate species transform into magnetic iron oxide nanoparticles. X-ray diffraction
(XRD), FT-infrared (FT-IR) spectroscopy and surface area measurements (BET) were employed to monitor the evolution of glass
structural features during the synthetic pathway as well as the structure and the texture of the resultant glasses. XRD, Raman
spectroscopy and vibration magnetic measurements (VSM) revealed the features of magnetic phases, developed in the form of
γ-Fe2O3 and magnetite. The obtained glasses exhibit in vitro bioactivity, expressed by spontaneous formation of hydroxyapatite on
their surface after immersion in SBF at 37 °C, confirmed with μ-Raman and FT-IR spectroscopies. 相似文献
10.
Elisa Marenna Carmela Aruta Elza Bontempi Antonio Cassinese Paolo Colombi Laura E. Depero Pasquale Pernice Antonio Aronne 《Journal of Sol-Gel Science and Technology》2009,49(1):106-111
The morphological and electrical characterization of transparent nanostructured LiNbO3–SiO2 thin films synthesized by a novel sol–gel route is reported. Films annealed at different temperatures exhibit different size
of the nanocrystals, as demonstrated by Atomic Force Microscopy and Glancing Incidence X-ray diffraction. The dc electrical
measurements performed on planar devices reveal electrical bistability. A clear relationship between the electrical bistability
and the size of LiNbO3 nanocrystals embedded in the matrix is observed. 相似文献
11.
Martina Dinelli Elena Fabbri Federica Bondioli 《Journal of Sol-Gel Science and Technology》2011,58(2):463-469
To enhance the poor scratch resistance of polycarbonate, a silica (SiO2) and titania (TiO2) transparent inorganic coatings was designed and synthesized using a microwave assisted sol–gel heating. Due to the transparency
of PC to microwave, the idea was to obtain a localized heating only on the coating film. The obtained films were fully characterized
to mainly evaluate the effect of titania content, added both as nanoparticles and from tetraethyl orthotitanate, TEOT, on
scratch resistance and surface morphology. Particular attention was paid to preserve the transparency of the final product.
The results allowed to define that TEOT addition enhances the adhesion between coating and polycarbonate, even if the optimized
quantity have to be defined in order to avoid a decrease of coating mechanical resistance. In this work optimized TEOT level
results to be the associated to 5 wt% of TiO2, which enable the better balancing between adhesion and mechanical resistance performances. 相似文献
12.
Zhijie Li Wenzhong Shen Zhiguo Wang Xia Xiang Xiaotao Zu Qiangmin Wei Lumin Wang 《Journal of Sol-Gel Science and Technology》2009,49(2):196-201
SnO2/SiO2 composite nanoparticles were prepared by sol–gel-hydrothermal process and their physico-chemical structure and photocatalytic
property were investigated. The results of XRD, TEM and FT-IR indicated that SnO2 crystallites with the tetragonal rutile structure were well-developed directly during hydrothermal process. The SnO2/SiO2 composite nanoparticles owned narrow size distribution, large specific surface area, and good thermal stability. As the presence
of 25.0 wt% SiO2, the SnO2 nanoparticles were about 4.0 nm in diameter and the specific surface area was 259.0 m2/g. After calcination at 800 °C, the crystalline grain size maintained 16.2 nm and the surface area still remained 132.6 m2/g. The SnO2/SiO2 composite nanoparticles showed better photocatalytic activity than pure SnO2 nanoparticles. 相似文献
13.
Aiju Zhang Zhihong Li Zicheng Li Yumei Zhu 《Journal of Sol-Gel Science and Technology》2009,49(1):6-11
SiO2–Al2O3–Na2O glass coated cubic boron nitride (cBN) abrasive particles were prepared by sol–gel technique. The results indicated that
SiO2–Al2O3–Na2O glass was excellent material for oxidation protection of cBN abrasive grains because coefficient of thermal expansion of
this glass closely matched that of cBN materials. The single particle compressive strength and impact toughness of this glass
coated cBN abrasive particles were significantly increased. For the application of glass coated cBN abrasives to vitrified
grinding wheels, it was evident that the glass coating provided high bonding strength between cBN abrasive grains and vitrified
bond system. 相似文献
14.
I. Prakash N. Nallamuthu P. Muralidharan M. Venkateswarlu Manjusri Misra Amar Mohanty N. Satyanarayana 《Journal of Sol-Gel Science and Technology》2011,58(1):24-32
In situ base catalyst assisted sol–gel process is used for the synthesis of nanocrystalline CoFe2O4 deposition on SiO2 particles. The SiO2 particles were prepared using base catalyst assisted sol–gel process and the consecutive formation and deposition of nanocrystalline
CoFe2O4 on SiO2 particles was monitored using Powder X ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Thermo Gravimetric
And Differential Thermal Analysis (TG/DTA), Scanning Electron Microscopy and Energy Dispersive X ray Spectroscopy (SEM–EDS)
and High Resolution Transmission Electron Microscopy (HRTEM). The crystallite size of CoFe2O4 is calculated using Scherrer’s formula and it is found to be 8 nm. The HRTEM images and selective area electron diffraction
(SAED) results confirmed the formation of nanocrystalline CoFe2O4 particles deposited over SiO2 spheres. 相似文献
15.
C. K. Ghosh S. R. Popuri T. U. Mahesh K. K. Chattopadhyay 《Journal of Sol-Gel Science and Technology》2009,52(1):75-81
Nanocrystalline powders of CuAlO2 were synthesized through sol–gel method using nitrate-citrate route and also through solid state reaction method. We used
a new set of precursor materials for the synthesis of CuAlO2 through sol–gel route which were not reported in the past. A little lowering of the synthesis temperature (1,000 °C) was
observed in case of sol–gel process compared to the solid state reaction method (1,100 °C) and also at shorter time duration.
The particle size of the synthesized powders was determined through small angle X-ray scattering. It has been observed that
the particle size prepared by nitrate-citrate technique is less than the particle size prepared by the solid-state reaction
method. Chemical states of the atomic species were determined by X-ray photoelectron spectroscopy. The formation of phase
pure CuAlO2 were also confirmed by Fourier transformed infrared spectroscopy. A number of solvents were also used for finding the best
possible combinations for obtaining phase pure CuAlO2 at 1,000 °C and it was observed that only the combination of nitrate salts, citric acid and ethanol resulted phase pure CuAlO2. 相似文献
16.
Wen Wang Jian-Cun Rao Hua Ke Ming Feng Rui-Lin Xia Qing-Chang Meng De-Chang Jia Yu Zhou 《Journal of Sol-Gel Science and Technology》2010,56(1):87-92
We report the independent invention of perovskite ferroelectric nanowires strontium bismuth tantalate (SrBi2Ta2O9, SBT). Electrophoretic sol–gel techniques have been used successfully. The morphology and structures are analyzed via SEM,
TEM and XRD. SBT nanowires and nanoparticles filled template revealed 30 and 40 μm long, respectively. SBT are proved to be
a single phase of orthorhombic perovskite structure. As it indicated, SBT nanowires has been crystallized at 700 °C. To minimize
surface polarity, SBT nanowires oriented preferentially along the growing axis (c axis) by translation and rotation of atomic clusters of SBT. 相似文献
17.
A. B. Shishmakov L. S. Molochnikov D. O. Antonov Yu. V. Mikushina O. V. Koryakova L. A. Petrov 《Russian Journal of Inorganic Chemistry》2016,61(9):1085-1091
ZrO2–SiO2 xerogels have been synthesized through hydrolysis of a mixture of tetrabutoxyzirconium and tetraethoxysilane in a desiccator in a vapor of a 15% aqueous NH3 atmosphere. ZrO2–SiO2–Cu(II) xerogels were synthethized analogously through joint hydrolysis of a mixture of the organometallic precursors and copper(II) chloride. The effect of synthesis conditions on the physical and chemical properties of the resulting material has been studied. 相似文献
18.
MgNb2O6 nanocrystalline powders have been synthesized at a low temperature by improved citrate sol–gel method in this paper. The
high quality solution of Nb5+ was prepared using Nb2O5 as the starting material. The crystal structure and microstructure of MgNb2O6 powders were characterized by XRD and SEM techniques, and the effects of preparation craft including pH value and the proportion
of citric acid to the niobium ions on the crystal structure and microstructure of powders were also investigated. XRD and
TG/DTA results show that the single phase of MgNb2O6 for synthesized powders can be obtained by calcining the precursor at 700 °C. SEM results indicate that the average particle
size of MgNb2O6 exhibits a significantly dependence on the pH values and the proportion of citric acid to the niobium ions, where it was
found that particle size of a 20 nm can be obtained for the MgNb2O6 powders by sol–gel process. 相似文献
19.
S. V. Ingale P. B. Wagh A. K. Tripathi A. S. Dudwadkar S. S. Gamre P. T. Rao I. K. Singh Satish C. Gupta 《Journal of Sol-Gel Science and Technology》2011,58(3):682-688
The degradation of nitro aromatics like trinitrotoluene (TNT) released in the waste water from explosive process plants is
the serious problem due to toxic and explosive nature of TNT. The poor response of TNT to biodegradation enhanced the gravity
of the problem. We have demonstrated that high specific surface area TiO2–SiO2 nano-composite aerogel is promising photo catalyst in successful treating of TNT contaminated aqueous solution. The TiO2–SiO2 composite aerogel with nominal content of 20 and 50% TiO2, used as catalyst, were prepared by co-precursor sol–gel method using titanium isopropaxide and tetramethylorthosilicate
as source of titania and silica, respectively. The XRD studies confirmed formation of anatase phase of crystalline TiO2 with nano sized crystallites. The TiO2–SiO2 aerogel showed specific surface area of 1,107 and 485 m2/g for the aerogels containing 20 and 50% TiO2, respectively. The 100 ppm TNT solution was treated, in 700 ml capacity reaction vessel, using H2O2 oxidizer and TiO2–SiO2 aerogel catalyst in presence of UV light (8 W UV lamp). Using TiO2–SiO2 (50/50) aerogel with surface area of 485 m2/g, we succeeded to reduce the TOC to 1 ppm within 3.5 h where as using TiO2/SiO2 (20/80) aerogel with surface area of 1,107 m2/g, the TOC was reduced to about only 7 ppm in the same time. It revealed that the combination of high TiO2 content and high specific surface area is an important factor to achieve effective and faster degradation of TNT for complete
mineralization. 相似文献
20.
Shengqiang Xu Qingming Huang Yanting Xu Zhuoliang Ye Xiaohui Chen 《Research on Chemical Intermediates》2017,43(12):7055-7071
The phosphorus (P) modified MoO3–Bi2SiO5/SiO2 catalyst was prepared by a simple co-impregnation method and investigated in the epoxidation of propylene by molecular oxygen. The catalyst was characterized by X-ray diffraction (XRD), N2 adsorption–desorption analysis, NH3-temperature-programmed desorption (NH3-TPD), transmission electron microscopy, and Raman spectroscopy. It was found that the P-modified MoO3–Bi2SiO5/SiO2 catalyst with a P/Mo molar ratio of 0.5 exhibits the best catalytic performance for epoxidation of propylene by O2, the TOFs for propylene oxide (PO) formation was four times higher than that of the unmodified one at 633 K. The modification by P could promote the dispersion of MoO3 nanoparticles and increase the number of weak and moderate acid sites with respect to the phosphorus-free MoO3–Bi2SiO5/SiO2 catalyst, which were beneficial to the formation of PO. Moreover, the introduction of P also could protect the mesoporous structure by inhibiting the formation of Bi2Mo3O12, which was beneficial to the dispersion of active species. We suppose that the phosphorus, bismuth and molybdenum species of P-modified MoO3–Bi2SiO5/SiO2 catalyst play important roles for propylene epoxidation by molecular oxygen. 相似文献