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1.
SiO2/Sb2O3 (SiSb), having a specific surface area, S BET, of 788 m2 g−1, an average pore diameter of 1.9 nm and 4.7 wt% of Sb, was prepared by the sol-gel processing method. Meldola's blue (MeB), methylene blue (MB) and toluidine blue (TB) were immobilized on SiSb by an ion exchange reaction. The amounts of the dyes bonded to the substrate surface were 12.49, 14.26 and 22.78 μmol g−1 for MeB, MB and TB, respectively. These materials were used to modify carbon paste electrodes. The midpoint potentials (E m) of the immobilized dyes were −0.059, −0.17 and −0.18 V vs. SCE for SiSb/MeB, SiSb/MB and SiSb/TB modified carbon paste electrodes, respectively. A solution pH between 3 and 7 practically did not affect the midpoint potential of the immobilized dyes. The electrodes presented reproducible responses and were chemically stable under various oxidation-reduction cycles. Among the immobilized dyes, MeB was the most efficient to mediate the electron transfer for NADH oxidation in aqueous solution at pH 7. In this case, amperometric detection of NADH at an applied potential of 0 mV vs. SCE gives linear responses over the concentration range of 0.1–0.6 mmol L−1, with a detection limit of 7 μmol L−1.  相似文献   

2.
This article presents the results of our investigation on the obtaining of Ni0.65Zn0.35Fe2O4 ferrite nanoparticles embedded in a SiO2 matrix using a modified sol–gel synthesis method, starting from tetraethylorthosilicate (TEOS), metal (FeIII,NiII,ZnII) nitrates and ethylene glycol (EG). This method consists in the formation of carboxylate type complexes, inside the silica matrix, used as forerunners for the ferrite/silica nanocomposites. We prepared gels with different compositions, in order to obtain, through a suitable thermal treatment, the nanocomposites (Ni0.65Zn0.35Fe2O4)x–(SiO2)100–x (where x=10, 20, 30, 40, 50, 60 mass%). The synthesized gels were studied by differential thermal analysis (DTA), thermogravimetry (TG) and FTIR spectroscopy. The formation of Ni–Zn ferrite in the silica matrix and the behavior in an external magnetic field were studied by X-ray diffraction (XRD) and quasi-static magnetic measurements (50 Hz).  相似文献   

3.
TiO2–SiO2 composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO2–SiO2 composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO2–SiO2) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO2–SiO2 composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO2–SiO2 composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO2–SiO2 core surface via surface functionalized reaction. The particle size of TiO2–SiO2 composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO2–SiO2 composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO2–SiO2 composite nanoparticles are well dispersed in the PU matrix.  相似文献   

4.
Nanosized TiO2 and nano-anatase TiO2 decorated on SiO2 spherical core shells were synthesized by using a sol–gel method. The synthesized pure TiO2 nano particle and TiO2 grafted on SiO2 sphere with various ratios have been characterized for their structure and morphologies by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrophotometry (FTIR) and transmission electron microscopy (TEM). Their surface areas were measured using the BET method. The photocatalytic activity of all nanocomposites was investigated using methylene blue as a model pollutant. The synthesized TiO2/SiO2 particles appeared to be more efficient in the degradation of methylene blue pollutant, as compared to pure TiO2 particles.  相似文献   

5.
Stable SiO2 and TiO2 organosols were prepared by hydrolyzing tetraethyl orthosilicate (TEOS) in the presence of 6–12 M NH3 and titanium(IV) isopropylate (TTIP) in reverse microemulsions of 0.12–0.25 M bis(2-ethylhexyl) sulfosuccinate (Aerosol OT, AOT) in n-decane with the aqueous pseudophase content of 2–3 vol %, 0.018–0.090 M TEOS, and 0.15–0.55 vol %, 0.003–0.025 M TTIP. The degree of hydrolysis was monitored by IR spectroscopy (for TEOS) and spectrophotometry (for TTIP). Oxide nanoparticles were characterized by photon-correlation spectroscopy (PCS) (D h = 8–100 nm) and laser electrophoresis (ζ-potential = 7.4–11.6 mV). The occurrence of surface potential made it possible to separate the oxides from the excess of surfactant by nonaqueous electrophoresis and to determine particle sizes (7–40 nm) by means of transmission electron microscopy (TEM).  相似文献   

6.
Phase equilibria in a miscibility gap of the SiO2-TiO2 system were studied. A visual polythermal analysis and annealing of samples were performed in a Galakhov microfurnace. The microstructure and composition of the obtained samples were investigated by scanning electron microscopy and electron probe microanalysis. A critical analysis of the experimental data was made. Thermodynamically optimized based on the sub-regular solution model, a phase diagram of the SiO2-TiO2 system was constructed.  相似文献   

7.
Nickel nanoparticles supported on silica were prepared by hydrazine reduction in aqueous medium. The obtained solids were characterized by X-ray diffraction (XRD), Transmission Electronic Microscopy (TEM), Electron Diffraction (ED), hydrogen chemisorption, and Temperature Programmed Desorption of hydrogen (H2-TPD). The catalytic properties were evaluated for benzene hydrogenation in the temperature range 75–230 °C. XRD patterns reveal presence of the metallic nickel particles with fcc structure. Metal dispersion and hydrogen storage increase with decreasing metal particle size. The H2-TPD profiles exhibit two domains, one due to desorption of hydrogen from Ni metal and another due to spillover from metal to the support. The catalytic activity strongly depends on the metal loading. It increases with decreasing metal loading. This is attributed to metal surface area, which also increases with decreasing metal loading. Kinetic studies of benzene hydrogenation on the Ni catalysts showed that the benzene partial order is around −2. This significant negative value is ascribed to a strong adsorption of benzene on the catalyst surface.  相似文献   

8.
Reverse micellar microemulsions were utilised to synthesise stable lead titanate colloids from typical sol–gel type molecular precursors. The particles of a few nanometres in diameter that formed by hydrolysis in the micelle cores demonstrated a nanocrystalline texture without the need for thermal treatment. In a chemical solution deposition routine based on the nanoparticle dispersions, ferroelectric PbTiO3 thin films showing excellent remanent polarisation of more than 50 μC cm−2 were derived. The electrical characteristics of the layers were correlated to their microstructure which was controlled by the precursor composition and the annealing conditions. A columnar morphology that was realised by spinning on coatings of up to 100 nm in individual thickness proved most favourable with respect to the ferroelectric performance of the films.  相似文献   

9.
FePО4/SiO2 supported catalysts with a different content of iron phosphate are prepared. The properties of the catalyst are changed by the introduction of alkali metal compounds (Na or Cs) on its surface. The samples obtained are characterized by X-ray diffraction, low-temperature nitrogen adsorption, temperatureprogrammed reduction by hydrogen, and temperature-programmed desorption of ammonia. The catalytic properties are investigated in the reaction of gas-phase propylene glycol oxidation. It is shown that the selectivity of methylglyoxal formation on the unmodified catalysts is determined by the state of the supported active component and by its reduction–oxidation ability under the action of a reaction mixture.  相似文献   

10.
Silica and core–shell structured titania/silica (TiO2/SiO2) nanoparticles with particles size ranging from tens to hundreds of nanometers were prepared and deposited onto cotton fabric substrates by sol–gel process. The morphologies of the nanoparticles were characterized by field-emission scanning electron microscope (FE-SEM). The photocatalytic decomposition properties as well as UV-blocking properties of the fabrics treated with SiO2 and TiO2/SiO2 nanoparticles were investigated.  相似文献   

11.
With tetraethoxysilane as the organic precursor, gradient density aerogels were fabricated by three different methods: layer-by-layer gelation, sol-co-gelation and continuous formation technics. Through layer-by-layer method, a 5-layer graded density silica aerogel whose density ranges from 50 to 200 mg/cm3 was obtained, but it existed a dense skin between adjacent layers which could result in density mutation in the interface. In order to optimize its interface character, sol-co-gelation technique was created to improve the interdiffusion and smooth out the density mutation via a self-built device. Finally, on the base of the device and sol-co-gelation technics, a continuous formation process was developed to fabricate the completely gradient density silica aerogel. Optical microscope and X-ray phase contrast method were used to characterize the samples prepared by three different technics and comparatively research their interface feature.  相似文献   

12.
Electronic structure of (SiO2)3 clusters was calculated by the density functional method. Charge states were determined using various functionals, bond lengths and total energies of clusters were estimated.  相似文献   

13.
SiO2/TiO2 hybrid nanofibers were prepared by electrospinning and applied for photocatalytic degradation of methylene blue (MB). The phase structure, specific surface area, and surface morphologies of the SiO2/TiO2 hybrid nanofibers were characterized through thermogravimetry (TG), X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), etc. XRD measurements indicated that doping of silica into TiO2 nanofibers can delay the phase transition from anatase to rutile and decrease the grain size. SEM and BET characterization proved that silica doping can remarkably enhance the porosity of the SiO2/TiO2 hybrid nanofibers. The MB adsorption capacity and photocatalytic activity of the SiO2/TiO2 hybrid nanofibers were distinguished experimentally. It was found that, although increased silica doping content could enhance the MB adsorption capacity, the intrinsic photocatalytic activity gradually dropped. The SiO2 (10 %)/TiO2 composite nanofibers exhibited the highest MB degradation rate, being superior to SiO2 (20 %)/TiO2 or pure TiO2.  相似文献   

14.
The Ni/ZrO2/SiO2 aerogels catalysts were synthesized via three different routes: (i) impregnation ZrO2–SiO2 composite aerogels with a aqueous solution of Ni(NO3)2, (ii) impregnation SiO2 aerogels with a mixed aqueous solution of Ni(NO3)2 and ZrO(NO3)2 · 2H2O, (iii) one-pot sol–gel procedure from precursors Ni(NO3)2/ZrO(NO3)2 · 2H2O/Si(OC2H5)4. These catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), ammonia temperature-programmed desorption (NH3-TPD), N2 adsorption–desorption isotherms and Fourier transform infrared (FT-IR). The Liquid-phase hydrogenation of maleic anhydride (MA) was performed over these catalysts. The results revealed that the different preparation routes result in a difference between the obtained samples, concerning the crystal structure and composition, surface acidity, mixed level of each component, texture, and catalytic selectivity.  相似文献   

15.
The photoluminescence properties of xZnO–(100−x)SiO2 (x = 0, 5, 10, 20) containing 1% Eu2O3 prepared by a sol–gel method were systematically investigated. The results indicated that the relative proportion of f–f transitions to charge transfer (CT) absorption decreased with the increase of ZnO concentration. The intensity of 5D07FJ transitions of Eu3+ ions was enhanced with the increase of ZnO content due to local structure changes and decreased quantities of Eu3+ ions clusters. The results of fluorescence line narrow (FLN) spectra indicated that Eu3+ ions occupied one site in SiO2 glass and two sites in ZnO–SiO2 glasses. The second-order crystal field parameters were calculated. B20 and B22 for site 1 increased with excitation energy, while ones hardly changed for site 2.  相似文献   

16.
We have investigated the processes occurring within titanium dioxide powders heated and modified by silicon dioxide nanoparticles at 150, 400, and 800 °C. It has been figured out that the mentioned modification stipulates the increase in the powders’ radiation resistance. While investigating, we employed methods of the near-/mid-infrared regions spectrophotometry, derivatography, and mass spectrometry. The research results show that the increase in the radiation resistance at the heating is stipulated by a number of factors, namely (1) the desorption of the physically/chemically bound gases, (2) upfilling of the released bonds with the oxygen molecules, and (3) the improvement of titanium dioxide stoichiometry on the surface. The after-modification radiation resistance increases excessively (as opposed to the heating) due to the fact that the electron–hole pairs relaxate on the nanoparticles, which precipitate onto the surface of titanium dioxide powder.  相似文献   

17.
This paper describes the synthesis and properties of a new type of ceramic fillers for composite polymer gel electrolytes. Hybrid TiO2-SiO2 ceramic powders have been obtained by co-precipitation from titanium(IV) sulfate solution using sodium silicate as the precipitating agent. The resulting submicron-size powders have been applied as fillers for composite polymer gel electrolytes for Li-ion batteries based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF/HFP) copolymeric membranes. The powders, dry membranes and gel electrolytes have been examined structurally and electrochemically, showing favorable properties in terms of electrolyte uptake and electrochemical characteristics in Li-ion cells.  相似文献   

18.
Perfluorinated 2-methyl- and 2-ethylbenzocyclobutenones on heating in SbF5 underwent isomerization into perfluoroindan-1-one and perfluoro(2-methylindan-1-one), while their reaction with SiO2—SbF5 gave perfluorinated 3-methyl- and 3-ethylphthalides, respectively. Perfluorinated 2-ethyl-2-methyl- and 2,2-diethylbenzocyclobutenones reacted with SbF5 to produce perfluorinated 2-(but-2-en-2-yl)- and 2-(pent-2-en-3-yl)-benzoic acids, and their transformations in SbF5 over SiO2 afforded 5,6,7,8-tetrafluoro-1-oxo-3-trifluoromethyl-1H-isochromene-4-carboxylic acid and perfluoro(4-ethyl-3-methyl-1H-isochromen-1-one), respectively.  相似文献   

19.
Nanostructure luminescent ZnO and SnO2 materials are prepared by a two-step solid-state method based on the solution preparation of the macromolecular precursors ZnCl2·Chitosan and SnCl2·Chitosan having different ratios (1:1, 1:5 and 1:10), their pyrolysis under air at 800 °C. The pyrolytic ZnO and SnO2 nanomaterials show a dependence of the particle size, morphology and luminescent properties with the ratio [metal/polymer] in the MCl2·Chitosan precursors. Thus, ZnO semiconductor materials exhibit luminescence spectra with several emission at 440 nm corresponds to a radiative transition of an electron from the shallow donor level of oxygen vacancies, and the zinc interstitial, to the valence band. On the other hand, the photoluminescence spectrum of the nanostructured SnO2 shows an intense blue luminescence at a wavelength of 420 nm which may be attributed to oxygen-related defects that have been introduced during the growth process of the nanoparticles. Additionally, whereas SnO2 was successfully incorporated into SiO2 structure (SnO2//SiO2) by pyrolysis of solid-state mixtures of the precursors SnCl2·Chitosan in the presence of SiO2, the same reaction carried out with ZnCl2·Chitosan precursors led to a mixture of Zn2SiO4 and SiO2. Thus, this new methodology yields nanostructured semiconductor materials, ZnO and SnO2, suitable for optoelectronic and sensor solid-state devices.  相似文献   

20.
Nanophase silica-titania particles were prepared by two different synthetic routes, namely, sol–gel and hydrothermal processing. The crystallinity and crystallographic phases, particle size and surface area of the materials were controlled by varying the calcination temperature, and/or the ratio of Si to Ti. It was determined by XRD that the crystallite sizes of SiO2-TiO2 prepared by sol–gel and hydrothermal processing decreased from 11 to 6 nm and 12 to 9 nm, respectively, as the mole fraction of silica was increased from 0.1 to 0.4. It is proposed that the presence of the amorphous silica suppresses the growth of anatase TiO2 grains and their phase transformation to rutile. The photocatalytic decomposition rate of 1,4-dichlorobenzene (DCB) in aqueous solution with the sol–gel derived SiO2-TiO2 powder prepared at 750 °C was about 10 ± 5% higher than that observed with Degussa P25, whereas the SiO2-TiO2 samples prepared by hydrothermal processing at 250 °C showed a slightly lower decomposition rate than P25.  相似文献   

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