共查询到20条相似文献,搜索用时 15 毫秒
1.
Uzma K. H. Bangi M. S. Kavale Seungsu Baek Hyung-Ho Park 《Journal of Sol-Gel Science and Technology》2012,62(2):201-207
The successful incorporation of multiwalled carbon nanotubes (MWCNTs) into silica aerogels prepared by sol–gel method is reported
herein. Pure silica aerogels prepared using sodium silicate precursor by ambient pressure drying are so fragile that they
cannot be used easily. MWCNTs were used as reinforcements to improve the mechanical properties of silica aerogels. Results
show that inserting small amounts of MWCNTs in the gels causes enhanced dimensional stability of silica aerogels. The silica
aerogels were prepared by doping MWCNTs in silica matrix before gelation. The influence of MWCNTs on some microstructural
aspects of silica matrix has been studied using nitrogen adsorption–desorption isotherms. From SEM study it is confirmed that
the silica particles get capped on the surface of MWCNTs suggesting an enhanced toughness. Further, FTIR, Raman, EDAX, thermal
conductivity and hydrophobicity studies of these doped aerogels were carried out. By addition of MWCNTs, silica aerogels were
formed with 706 m2/g BET and 1,200 m2/g Langmuir surface areas and 149o contact angle. Low density (0.052 g/cc) and low thermal conductivity (0.067 W/m K) MWCNTs doped silica aerogels were obtained
for the molar ratio of Na2SiO3::H2O::MWCNTs::citric acid::TMCS at 1::146.67::2.5 × 10−3::0.54::9.46 respectively with improved mechanical strength. 相似文献
2.
Uzma K. H. Bangi A. Parvathy Rao H. Hirashima A. Venkateswara Rao 《Journal of Sol-Gel Science and Technology》2009,50(1):87-97
Experimental results on the physico-chemical properties of ambiently dried sodium silicate based aerogels catalyzed with various
acids are reported. The aerogels were prepared by hydrolysis and polycondensation of sodium silicate followed by subsequent
washings, surface chemical modification and ambient pressure drying using 10 various acid catalysts consisting of strong and
weak acids. The strength and concentration of acids have the major effect on the gelation of sol and hence the physico-chemical
properties of the silica aerogels. Strong acids such as HCl, HNO3 and H2SO4 resulted in shrunk (70–95%) aerogels whereas weak acids such as citric and tartaric acids resulted in less shrunk (34–50%)
aerogels. The physical properties of silica aerogels were studied by measuring bulk density, volume shrinkage (%), porosity
(%), pore volume, thermal conductivity, contact angle with water, Transmission Electron Microscopy (TEM), Atomic Absorption
Spectroscopy (AAS), Fourier Transform Infrared Spectroscopy (FTIR), Thermo Gravimetric-Differential Thermal (TG-DT) analyses
and N2 adsorption–desorption BET surface analyzer. The best quality silica aerogels in terms of low density (0.086 g/cm3), low volume shrinkage (34%), high porosity (95%), low thermal conductivity (0.09 W/m K) and hydrophobic (148°) were obtained
for molar ratio of Na2SiO3:H2O:citric acid:TMCS at 1:146.67:0.72:9.46 with 20 min gelation time. The resulting aerogels exhibited the thermal stability
up to around 420 °C. 相似文献
3.
Interest in improving the optical transmission of sodium silicate-based aerogels by ambient pressure drying led to the synthesis of aerogels using a two-step sol–gel process. To produce optically transparent silica aerogel granules, NH4F (1 M) and HCl (4 M) were used as hydrolyzing and condensation catalysts, respectively. The silica aerogels were characterized by their bulk density, porosity (%), contact angle and thermal conductivity. Optical transmission of as synthesized aerogels was studied by comparing the photos of aerogel granules. Scanning electron microscopic study showed the presence of fractal structures in these aerogels. The degree of transparency in two step sol–gel process-based aerogels is higher than the conventional single step aerogels. The N2 adsorption–desorption analysis depicts that the two step sol–gel based aerogels have large surface areas. Optically transparent silica aerogels with a low density of ∼0.125 g/cc, low thermal conductivity of ∼0.128 W/mK and higher Brunauer, Emmett, and Teller surface area of ∼425 m2/g were obtained by using NH4F (1 M), HCl (4 M), and a molar ratio of Na2SiO3::H2O::trimethylchlorosilane of 1::146.67::9.46. The aerogels retained their hydrophobicity up to 500 °C. 相似文献
4.
Sung-Woo Hwang Hae-Hyun Jung Sang-Hoon Hyun Young-Soo Ahn 《Journal of Sol-Gel Science and Technology》2007,41(2):139-146
Effective ambient-drying techniques for synthesizing crack-free silica aerogel bulks from the industrial waterglass have been
developed. Silica wet gels were obtained from aqueous colloidal silica sols prepared by ion-exchange of waterglass solution
(4–10 wt% SiO2). Crack-free monolithic silica aerogel disks (diameter of 22 mm and thickness of 7 mm) were produced via solvent exchange/surface
modification of the wet gels using isopropanol/trimethylchlorosilane/n-Hexane solution, followed by ambient drying. The effects of the silica content in sol and the molar ratio of trimethylchlorosilane/pore
water on the morphology and property of final aerogel products were also investigated. The porosity, density, and specific
surface area of silica aerogels were in the range of 92–94%, 0.13–0.16 g/cm3, and ∼675 m2/g, respectively. The degree of springback during the ambient drying processing of modified silica gels was 94%. 相似文献
5.
Rui Yan Minchao Zhang Wangqing Zhang Shuangxi Liu 《Journal of Sol-Gel Science and Technology》2011,59(2):315-326
Temperature dependent synthesis of micro- and meso-porous silica employing the thermo-responsive homopolymer poly(N-isopropylacrylamide) or the random copolymer poly(N-isopropylacrylamide-co-acrylic acid) as structure-directing agent (SDA) and Na2SiO3 as silica source is proposed. The thermo-responsive character of the SDA provides the advantages including (1) temperature
dependent synthesis of microporous silica, hierarchically micro-mesoporous silica, and mesoporous silica just by changing
the aging temperature below or above the low critical solution temperature of the thermo-responsive SDA, and (2) elimination
of the thermo-responsive SDA from silica matrix by water extraction. The synthesis mechanism is discussed, and the effect
of the aging temperature and the weight radio of SDA/Na2SiO3 on the synthesis of micro- and meso-porous silica are studied. Microporous silica, hierarchically micro-mesoporous silica
and mesoporous silica with the surface area at 3.5−9.0 × 102 m2/g and the pore volume at 0.28−1.13 cm3/g and the average pore size ranging from 1.1 to 9.0 nm are synthesized. The strategy affords a new and environmentally benign
way to fabricate porous silica materials, and is believed to bridge the gap between the synthesis of microporous and mesoporous
silica materials. 相似文献
6.
The effect of four ionic liquids on the porous texture of silica aerogels synthesized from mixed tetramethoxysilane and methyltrimethoxysilane
and dried by the CO2 supercritical method, was studied. Two of these ionic liquids were composed of BF4
− anions while the other two included Cl− anions. The synthesis of gels from ionic liquids did not require another acidic catalyst for silica hydrolysis, nor a basic
catalyst for silica condensation. These aerogels were compared with traditional aerogels made according to a double step catalysis,
which first involved hydrolysis with HCl followed by condensation with pH 9 Tris HCl buffer. Gel mass analysis and thermogravimetric
data showed that, when the initial molar of ionic liquid to Si was 1.58, only ~2% (by mass) of the initial ionic liquids consisting
of BF4
− anions and ~10% (by mass) of ionic liquids containing Cl− anions, remained in the aerogels after supercritical drying. Moreover, X-ray diffraction confirmed that in ionic liquids
based on BF4
− anions, evaporation of the volatile components before supercritical CO2 drying led to the formation of regularly ordered mesopores. 相似文献
7.
Poonam M. Shewale A. Venkateswara Rao A. Parvathy Rao S. D. Bhagat 《Journal of Sol-Gel Science and Technology》2009,49(3):285-292
In the present paper, attempts have been made to produce transparent silica aerogels with low density and better hydrophobicity
by controlled sol–gel route and subsequent atmospheric pressure drying. The hydrogels were prepared by hydrolysis and polycondensation
of sodium silicate (Na2SiO3) in the presence of acetic acid catalyzed water followed by several washing steps with water, methanol and hexane, respectively.
The surface modification of the wet gel was carried out using a mixture of hexamethyldisilazane (HMDS) in hexane. Since, the
sol–gel chemistry provides a straightforward method to control the physical and optical properties of the aerogels, the influence
of various sol–gel parameters viz. gel washing time, molar ratios of CH3COOH/Na2SiO3 and HMDS/Na2SiO3 and silylation period on the physical and optical properties of the aerogels have been investigated. The aerogels have been
characterized by bulk density, Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric and Differential Thermal
Analysis (TG-DTA), Atomic Absorption Spectroscopy (AAS), Scanning Electron Microscopy (SEM) studies and Contact angle measurements. 相似文献
8.
In the present paper, we report the synthesis of tetrapropoxysilane (TPOS)-based silica aerogels with high surface area and large pore volume. The silica aerogels were prepared by a two-step sol-gel process followed by surface modification via a simple ambient pressure drying approach. In order to minimize drying shrinkage and obtain hydrophobic aerogels, the surface of the alcogels was modified using trichloromethylsilane as a silylating agent. The effect of the sol-gel compositional parameters on the polymerization of aerogels prepared by TPOS, one of the precursors belonging to the Si(OR)4 family, was reported for the first time. The oxalic acid and NH4OH concentrations were adjusted to achieve good-quality aerogels with high surface area, low density, and high transparency. Controlling the hydrolysis and condensation reactions of the TPOS precursor turned out to be the most important factor to determine the pore characteristics of the aerogel. Highly transparent aerogels with high specific surface area (938 m2/g) and low density (0.047 g/cm3) could be obtained using an optimized TPOS/MeOH molar ratio with appropriate concentrations of oxalic acid and NH4OH. 相似文献
9.
Ann M. Anderson Mary K. Carroll Emily C. Green Jason T. Melville Michael S. Bono 《Journal of Sol-Gel Science and Technology》2010,53(2):199-207
Hydrophobic silica aerogels have been prepared using the rapid supercritical extraction (RSCE) technique. The RSCE technique
is a one-step methanol supercritical extraction method for producing aerogel monoliths in 3 to 8 h. Standard aerogels were
prepared from a tetramethoxysilane (TMOS) recipe with a molar ratio of TMOS:MeOH:H2O:NH4OH of 1.0:12.0:4.0:7.4 × 10−3. Hydrophobic aerogels were prepared using the same recipe except the TMOS was replaced with a mixture of TMOS and one of
the following organosilane co-precursors: methytrimethoxysilane (MTMS), ethyltrimethoxysilane (ETMS), or propyltrimeth-oxysilane
(PTMS). Results show that, by increasing the amount of catalyst and increasing gelation time, monolithic aerogels can be prepared
out of volume mixtures including up to 75% MTMS, 50% ETMS or 50% PTMS in 7.5–15 h. As the amount of co-precursor is increased
the aerogels become more hydrophobic (sessile tests with water droplets yield contact angles up to 155°) and less transparent
(transmission through a 12.2-mm thick sample decreases from 83 to 50% at 800 nm). The skeletal and bulk density decrease and
the surface area increases (550–760 m2/g) when TMOS is substituted with increasing amounts of MTMS. The amount of co-precursor does not affect the thermal conductivity.
SEM imaging shows significant differences in the nanostructure for the most hydrophobic surfaces. 相似文献
10.
Je Kyun Lee George L. Gould Wendell Rhine 《Journal of Sol-Gel Science and Technology》2009,49(2):209-220
Less fragile lightweight nanostructured polyurea based organic aerogels were prepared via a simple sol–gel processing and
supercritical drying method. The uniform polyurea wet gels were first prepared at room temperature and atmospheric pressure
by reacting different isocyanates with polyamines using a tertiary amine (triethylamine) catalyst. Gelation kinetics, uniformity
of wet gel, and properties of aerogel products were significantly affected by both target density (i.e., solid content) and
equivalent weight (EW) ratio of the isocyanate resin and polyamine hardener. A supercritical carbon dioxide (CO2) drying method was used to extract solvent from wet polyurea gels to afford nanoporous aerogels. The thermal conductivity
values of polyurea based aerogel were measured at pressures from ambient to 0.075 torr and at temperatures from room temperature
to −120 °C under a pressure of 8 torr. The polyurea based aerogel samples demonstrated high porosities, low thermal conductivity
values, hydrophobicity properties, relatively high thermal decomposition temperature (~270 °C) and low degassing property
and were less dusty than silica aerogels. We found that the low thermal conductivities of polyurea based aerogels were associated
with their small pore sizes. These polyurea based aerogels are very promising candidates for cryogenic insulation applications
and as a thermal insulation component of spacesuits. 相似文献
11.
Eduardo Marafon Lauro T. Kubota Yoshitaka Gushikem 《Journal of Solid State Electrochemistry》2009,13(3):377-383
SiO2/ZrO2/C carbon ceramic material with composition (in wt%) SiO2 = 50, ZrO2 = 20, and C = 30 was prepared by the sol–gel-processing method. A high-resolution transmission electron microscopy image
showed that ZrO2 and the graphite particles are well dispersed inside the matrix. The electrical conductivity obtained for the pressed disks
of the material was 18 S cm−1, indicating that C particles are also well interconnected inside the solid. An electrode modified with flavin adenine dinucleotide
(FAD) prepared by immersing the solid SiO2/ZrO2/C, molded as a pressed disk, inside a FAD solution (1.0 × 10−3 mol L−1) was used to investigate the electrocatalytic reduction of bromate and iodate. The reduction of both ions occurred at a peak
potential of −0.41 V vs. the saturated calomel reference electrode. The linear response range (lrr) and detection limit (dl)
were: BrO3
−, lrr = 4.98 × 10−5–1.23 × 10−3 mol L−1 and dl = 2.33 μmol L−1; IO3
−, lrr = 4.98 × 10−5 up to 2.42 × 10−3 and dl = 1.46 μmol L−1 for iodate. 相似文献
12.
Hikaru Morimoto Marie Minato Tomohiko Nakagawa Masahide Sato Yoshio Kobayashi Kohsuke Gonda Motohiro Takeda Noriaki Ohuchi Noboru Suzuki 《Journal of Sol-Gel Science and Technology》2011,59(3):650-657
A preparation method for gadolinium compound (Gd) nanoparticles coated with silica (Gd/SiO2) is proposed. Gd nanoparticles were prepared with a homogeneous precipitation method at 80 °C using 1.0 × 10−3 M Gd(NO3)3 and 0.5 M urea in the presence of 1.0 g/L stabilizer. Among stabilizers examined. Sodium n-dodecyl sulfate (SDS) was suitable
as the stabilizer for preparing small Gd nanoparticles, and consequently Gd nanoparticles with a size of 46.2 ± 12.4 nm were
prepared using the SDS. Silica-coating of the Gd nanoparticles was performed by a St?ber method at room temperature using
0.013 M TEOS and 2.0 × 10−3 M NaOH in water/1-propanol solution in the presence of 1.0 × 10−3 M Gd nanoparticles, which resulted in production of Gd/SiO2 particles with an average size of 64.2 ± 14.4 nm. The Gd/SiO2 particles were surface-modified with 3-aminopropyltrimethoxysilane and succinic anhydride. It was confirmed by measurement
of electrophretic light scattering that amino group or carboxyl group was introduced onto the Gd/SiO2 particles. The gadolinium concentration of 1.0 × 10−3 M in the as-prepared colloid solution was increased up to a gadolinium concentration of 0.4 M by centrifugation. The core–shell
structure of Gd/SiO2 particles was undamaged, and the colloid solution was still colloidally stable, even after the concentrating process. The
concentrated Gd/SiO2 colloid solution showed an X-ray image with contrast as high as a commercial Gd complex contrast agent. Internal organs in
a mouse could be imaged injecting the concentrated colloid solution into it. 相似文献
13.
Three-dimensionally structured, silica based, organic–inorganic hybrid nanoparticles (NPs) were prepared by a simple and feasible
water-in-oil (W/O) microemulsion method and a promising platform for bioelectrochemical analysis was obtained. The commonly
used phenathiazine organic compound, toluidine blue (TB) was readily captured in the three-dimensional cage of the inorganic
SiO2 network, which was considered to serve as a protective “shell” toward the embedded TB. A TEM image indicated the size of
the thus prepared TB-doped SiO2 (TB@SiO2) NPs was 21 ± 3 nm. UV–visible and IR spectroscopy confirmed successful formation of the organic–inorganic composite and
possible interaction between TB and SiO2, which favored enhanced stability of the hybrid. A sensitive amperometric sensor for hemoglobin (Hb) biomolecules based on
TB@SiO2 NPs conjugated with a biopolymer chitosan (CHIT) membrane was then developed. The surface of the silica NPs was highly biocompatible
and the TB captured inside maintained its high electron-transfer efficiency. Dye leakage of TB from the TB@SiO2 hybrid was proved to be minimal, owing to the inorganic SiO2 network and the force of interaction between TB and SiO2. The amperometric sensor had a detection limit of 2.5 × 10−9 mol L−1 (S/N = 3) with a linear range from 5.0 × 10−9 to 3.0 × 10−6 mol L−1 for Hb. When it was applied to determine the concentration of a clinical blood sample, satisfactory results were obtained
which were in good agreement with those obtained by the standard method. 相似文献
14.
Y. Kobayashi H. Kakinuma D. Nagao Y. Ando T. Miyazaki M. Konno 《Journal of Sol-Gel Science and Technology》2008,47(1):16-22
This paper describes a method for fabrication of silica-coated Co–Pt alloy nanoparticles in a liquid phase process. The Co–Pt
nanoparticles were prepared from CoCl2 (4.2 × 10−5 M), H2PtCl6 (1.8 × 10−5 M), citric acid (4 × 10−4 M) and NaBH4 (1.2 × 10−2 M) with a Co:Pt mole ratio of 7:3. The silica coating was performed in water/ethanol solution with a silane coupling agent,
3-aminopropyltrimethoxysilane (8 × 10−5 M), and a silica source, tetraethoxyorthosilicate (7.2 × 10−4 M) in the presence of the Co–Pt nanoparticles. Observations with a transmittance electron microscope and a scanning transmission
electron microscope revealed that the Co-rich and Pt-rich nanoparticles were coated with silica. According to X-ray diffraction
measurements, core particles were crystallized to metallic Co crystallites and fcc Co–Pt alloy crystallites with annealing
in air at 300–500 °C. Magnetic properties of the silica-coated particles were strongly dependent on annealing temperature.
Maximum values of 11.4 emu/g-sample for saturation magnetization and 365 Oe for coercive field were obtained for the particles
annealed at 300 and 500 °C, respectively. Annealing at a temperature as high as 700 °C destroyed the coating structures because
of crystallization of silica shell, resulting in reduction in saturation magnetization and coercive field. 相似文献
15.
Sensitive fluorescent probes for determination of hydrogen peroxide and glucose based on enzyme-immobilized magnetite/silica nanoparticles 总被引:2,自引:0,他引:2
Qing Chang Lihua Zhu Guodong Jiang Heqing Tang 《Analytical and bioanalytical chemistry》2009,395(7):2377-2385
Sensitive fluorescent probes for the determination of hydrogen peroxide and glucose were developed by immobilizing enzyme
horseradish peroxidase (HRP) on Fe3O4/SiO2 magnetic core–shell nanoparticles in the presence of glutaraldehyde. Besides its excellent catalytic activity, the immobilized
enzyme could be easily and completely recovered by a magnetic separation, and the recovered HRP-immobilized Fe3O4/SiO2 nanoparticles were able to be used repeatedly as catalysts without deactivation. The HRP-immobilized nanoparticles were able
to activate hydrogen peroxide (H2O2), which oxidized non-fluorescent 3-(4-hydroxyphenyl)propionic acid to a fluorescent product with an emission maximum at 409 nm.
Under optimized conditions, a linear calibration curve was obtained over the H2O2 concentrations ranging from 5.0 × 10−9 to 1.0 × 10−5 mol L−1, with a detection limit of 2.1 × 10−9 mol L−1. By simultaneously using glucose oxidase and HRP-immobilized Fe3O4/SiO2 nanoparticles, a sensitive and selective analytical method for the glucose detection was established. The fluorescence intensity
of the product responded well linearly to glucose concentration in the range from 5.0 × 10−8 to 5.0 × 10−5 mol L−1 with a detection limit of 1.8 × 10−8 mol L−1. The proposed method was successfully applied for the determination of glucose in human serum sample. 相似文献
16.
Evaggelos Economopoulos Theophilos Ioannides 《Journal of Sol-Gel Science and Technology》2009,49(3):347-354
Tetraalkylammonium fluoride salts have been employed as catalysts for the synthesis of silica aerogels by a two-step, sol–gel
method. Aerogel materials were characterized by N2 physisorption and SEM. The effect of the type of catalyst on the optical transparency of obtained aerogels has been examined.
It has been found that such compounds allow the synthesis of silica aerogels with the highest optical transmittance ever reported
for such materials. The optimal catalysts are tetrabutyl and tetraoctyl ammonium fluoride, with which aerogels with transparency
as high as 96% and extinction coefficient as low as 3.5 m−1 can be prepared. 相似文献
17.
Digambar Y. Nadargi Sanjay S. Latthe A. Venkateswara Rao 《Journal of Sol-Gel Science and Technology》2009,49(1):53-59
The properties of silica aerogels are highly dependent on the post-treatment steps like gel washing, gel aging and gel drying.
The experimental results of the studies on one of the post-treatment steps i.e. gel aging effect on the physical and microstructural
properties of methyltrimethoxysilane (MTMS) based silica aerogels, are reported. These hybrid aerogels were prepared by two
step sol–gel process followed by supercritical drying. The molar ratio of MeOH/MTMS (M) was varied from 7 to 35 by keeping
the H2O/MTMS (W) molar ratio constant at 4. The as prepared alcogels of different molar ratios were aged from 0 to 5 days. It was
observed that 2 days of gel aging period is the optimum gel aging period for good quality aerogels in terms of low density,
less volume shrinkage and high porosity. The well tailored network matrix with low density (0.04 g/cm3), less volume shrinkage (4.5%), low thermal conductivity (0.05 W/mK) and high porosity (98.84 %) was obtained for 2 days
of gel aging period of M = 35. Further, the gelation time varied from 8 to 1 h depending on the M values. The gelation time was being more for lesser
M values. The aerogels were characterized by bulk density, porosity, volume shrinkage, thermal conductivity, Scanning Electron
Microscopy and the Fourier Transform Infrared spectroscopy. 相似文献
18.
Krzysztof Miecznikowski James A. Cox Adam Lewera Pawel J. Kulesza 《Journal of Solid State Electrochemistry》2000,4(4):199-204
We describe a sol-gel approach by which iron hexacyanoferrate is immobilized in silica in a manner suited to investigation
by electrochemistry in the absence of a contacting liquid phase. Such physicochemical parameters as concentration of redox
sites (C
o) and apparent (effective) diffusion coefficient (D
app) are estimated by performing cyclic voltammetric and potential step experiments in two time regimes, which are characterized
by linear and spherical diffusional patterns, respectively. Values of D
app and C
o thereby obtained are 2.0 × 10−6 cm2 s−1 and 1.4 × 10−2 mol dm−3. The D
app value is larger than expected for a typical solid redox-conducting material. Analogous measurements done in iron(III) hexacyanoferrate(III)
solutions of comparable concentrations, 1.0 × 10−2 and 5.0 × 10−3 mol dm−3, yield D
app on the level of 5–6 × 10−6 cm2 s−1. Thus, the dynamics of charge propagation in this sol-gel material is almost as high as in the liquid phase. The residual
water in the silica, along with the pore structure, are important to the overall mechanism of charge transport, which apparently
is limited by physical diffusion rather than electron self-exchange. Under conditions of a solid state voltammetric experiment
which utilizes an ultramicroelectrode, encapsulated iron hexacyanoferrate redox centers seem to be in the dispersed colloidal
state rather than in a form of the rigid polymeric film.
Received: 8 April 1999 / Accepted: 13 August 1999 相似文献
19.
Yoshio Kobayashi Takuya Nozawa Tomohiko Nakagawa Kohsuke Gonda Motohiro Takeda Noriaki Ohuchi Atsuo Kasuya 《Journal of Sol-Gel Science and Technology》2010,55(1):79-85
This paper describes a method for direct coating of fluorescent semiconductor nanoparticles with silica shell. The fluorescent
semiconductor nanoparticles used were CdSe
x
Te1–x
nanoparticles coated with ZnS and succeedingly surface-modified with carboxyl groups, or quantum dots (Q-dots). The Q-dots
were silica-coated by performing sol–gel reaction of tetraethyl orthosilicate (TEOS) using NaOH as a catalyst in the presence
of the Q-dots. Quasi-perfect Q-dots/silica core-shell particles were formed at 5.0 M H2O and 4.0 × 10−4 M NaOH. Under these concentrations of H2O and NaOH, the particle size of Q-dots/silica particles could be varied from 20.1 to 38.1 nm as the TEOS concentration increased
from 2.5 × 10−4 to 50 × 10−4 M. The Q-dots/silica particles showed fluorescence as well as the uncoated Q-dots. 相似文献
20.
Yin Gao Geng Chen Zhijun We Bowei Chen Chuangchuang Huang Xuan Luo Ruizhuang Yang Yutie Bi Lin Zhang 《Journal of Sol-Gel Science and Technology》2014,69(2):407-411
The Cu-doped SiO2 composite aerogels were successfully prepared by sol–gel process and subsequently supercritical drying with ethanol and CO2. The Cu-doped SiO2 composite aerogels had porous texture, low density (<100 mg cm?3) and high specific surface area (>800 m2 g?1), which were investigated by FESEM and nitrogen adsorption desorption porosimetry. The FTIR spectra of the aerogels showed that the ethanol-dried aerogels had been modified by ethyl while the corresponding CO2-dried aerogels had more Si–OH groups. The phase structure and thermal stability were investigated by XRD and TGA, respectively. Due to the reducibility of ethanol, the copper was crystalline in ethanol-dried sample. The Cu-doped SiO2 composite aerogels dried with supercritical ethanol had larger pore diameter and better thermal stability under 400 °C in comparison with CO2-dried composite aerogels. The structures and properties of Cu-doped SiO2 composite aerogels are obviously affected by supercritical drying conditions. The effect research could instruct the synthesis of different state of Cu in composite aerogels. 相似文献