共查询到20条相似文献,搜索用时 15 毫秒
1.
A new solvent-less sol-gel route for silica film elaboration is presented. TEOS polymerization is induced by ozone bubbling
through the initial sol composed of TEOS and water with the molar ratio R = [H2O]/[Si]. Replacing ozone by pure oxygen allows for demonstrating the specific effects of ozone. With ozone bubbling, a comparison
of certain film properties is made between R = 0 and R = 5 with HCl aqueous solution (pH = 1.8). The opto-geometrical properties of the films are studied by spectroscopic ellipsometry,
the surface topography by atomic force microscopy and the chemical content by infra-red spectroscopy. The huge influence of
the R value on sol and film properties is shown. 相似文献
2.
MCM-41 mesoporous silica has been functionalized with two kinds of macrocylic calixarene derivatives Calix[4] and Calix[4]Br (Calix[4]=P-tert-butylcalix[4]arene, Calix[4]Br=5.11,17.23-tetra-tert-butyl-25.27-bihydroxy-26.28-bibromopropoxycalix[4]arene) through condensation approach of tetraethoxysilane (TEOS) in the presence of the cetyltrimethylammonium bromide (CTAB) surfactant as a template. Novel organic-inorganic mesoporous luminescent hybrid containing RE3+ (Eu3+, Tb3+) complexes covalently attached to the functionalized ordered mesoporous MCM-41, which are designated as RE-Calix[4]-MCM-41 and RE-Calix[4]Br-MCM-41, respectively, are obtained by sol-gel process. It is found that they all have high surface area, uniform in the mesostructure and good crystallinity. Measurement of the photoluminescence properties show the mesoporous material covalently bonded Tb3+ complexes (Tb-Calix[4]-MCM-41 and Tb-Calix[4]Br-MCM-41) exhibit the stronger characteristic emission of Tb3+ and longer lifetime than the corresponding Eu-containing materials Eu-Calix[4]-MCM-41 and Eu-Calix[4]Br-MCM-41 due to the triplet state energy of modified organic ligands Calix[4]-Si and Calix[4]Br-Si match with the emissive energy level of Tb3+ very well. 相似文献
3.
A.I. Karacolak F.M. Emen D. Kılıç E. Kutlu M.A. Ali N. Körözlü R.E. Demirdogen 《Materials Today Chemistry》2021
The spherical mesoporous MCM-41 coated with a novel Ca2MoO5:Eu3+ phosphor layer was prepared for the first time. The obtained Ca2MoO5:Eu3+-MCM-41 was characterized via XRD and FT-IR. The crystal system of the Ca2MoO5 phase was determined to be orthorhombic, and its space group was found to be Ima2 (46), and its cell parameters were a = 16.175, b = 5.1514, c = 5.6977 A°; α = β = γ = 90°. The particle dimensions of MCM-41 and Ca2MoO5:Eu3+-MCM-41 nanoparticles were determined to be 260 nm and 229 nm via scanning electron microscopy analysis. Bortezomib was loaded into the Ca2MoO5:Eu3+-MCM-41 nanoparticles under scCO2 at 200 bars and 40 °C. The results of the TG analysis showed that the amount of drug-loaded to MCM-41 and Ca2MoO5:Eu3+-MCM-41 nanoparticles were determined to be 14.02% and 3.02%, respectively. The BET analysis showed that while the specific surface area and pore volume of MCM-41 and Ca2MoO5:Eu3+ before Bortezomib (BTZ) loading were 1,506 m2/g and 267 m2/g, respectively, after drug loading these values were found to decrease to 488 m2/g and 7.883 m2/g. It was determined that BTZ was released from the nanoparticles in a sustained manner over 66 h. The R2 value, which was calculated to be 0.9739, indicated that the release kinetic of BTZ followed the Korsmeyer–Peppas model. 相似文献
4.
The use and application of synthetic zeolites for ion exchange, adsorption and catalysis has shown enormous potential in industry. In this study, X-ray fluorescence (XRF) analysis was used to determine Si and Al in fly ash (FA) precipitates. The Si and Al contents of the fly ash precipitates were used as indices for the alkaline hydrothermal conversion of the fly ash compounds into zeolites. Precipitates were collected by using a co-disposal reaction wherein fly ash is reacted with acid mine drainage (AMD). These co-disposal precipitates were then analysed by XRF spectrometry for quantitative determination of SiO2 and Al2O3. The [SiO2]/[Al2O3] ratio obtained in the precipitates range from 1.4 to 2.5. The [SiO2]/[Al2O3] ratio was used to predict whether the fly ash precipitates could successfully be converted to faujasite zeolitic material by the synthetic method of [J. Haz. Mat. B 77 (2000) 123]. If the [SiO2]/[Al2O3] ratio is higher than 1.5 in the fly ash precipitates, it favours the formation of faujasite. The zeolite synthesis included an alkaline hydrothermal conversion of the co-disposal precipitates, followed by aging for 8 h and crystallization at 100 °C. Different factors were investigated during the synthesis of zeolite to ascertain their influence on the end product. The factors included the amount of water in the starting material, composition of fly ash related starting material and the FA:NaOH ratio used for fusing the starting material. The mineralogical and physical analysis of the zeolitic material produced was performed by X-ray diffraction (XRD) and nitrogen Brunauer-Emmett-Teller (N2 BET) surface analysis. Scanning electron microscopy (SEM) was used to determine the morphology of the zeolites, while inductively coupled mass spectrometry (ICP-MS), Fourier transformed infrared spectrometry (FT-IR) and Cation exchange capacity (CEC) [Report to Water Research Commission, RSA (2003) 15] techniques were used for chemical characterisation. The heavy and trace metal concentrations of the zeolite products were compared to that of the post-synthesis filtrate and of the precipitate materials used as Si and Al feed stock for zeolite formation, in order to determine the trends (increase or decrease) and ultimate fate of any toxic metals incorporated in the co-disposed precipitated residues. 相似文献
5.
Yao Xu Dong Wu Yuhan Sun Hongchang Gao Hanzhen Yuan Feng Deng 《Journal of Sol-Gel Science and Technology》2007,42(1):13-20
Liquid-state 29Si NMR was used to investigate the hydrolysis and condensation kinetics of ammonia-catalyzed tetraethoxysilane (TEOS) in methanol
system. The reactive rate constants were calculated by applying first-order reaction approximation and the steady state approximation
theory. The reaction orders with respect to TEOS, ammonia and water were derived, as well as the activation energies and the
Arrhenius constants. It was found that the formation of intermediate species Si(OH)(OEt)3 was the rate-limiting step and its reaction rate equation was r
TEOS=7.41×10−3[TEOS][NH3]0.333[H2O]0.227. Higher reactive temperature benefited the hydrolysis of TEOS. The results presented here indicated quantificationally that
the formation of colloidal SiO2 particles was controlled by the initial hydrolysis of TEOS. 相似文献
6.
A. Kamyabi-Gol S. M. Zebarjad S. A. Sajjadi 《Journal of Sol-Gel Science and Technology》2009,51(1):92-101
The present work deals with the synthesis of Ni–SiO2–Al2O3 nanocomposites fabricated by embedding nickel oxide particles, obtained from hexahydrated nickel nitrate [Ni(NO3)2 · 6H2O], in matrixes with different molar percents of Silica/Alumina, through sol–gel method based on hydrolysis and condensation
of tetraethylorthosilicate (TEOS) and Aluminum Isopropoxide [Al(OC3H7)3] alkoxides. Due to the various factors, e.g., pH, EtOH/TEOS/H2O ratio, Si/Ni ratio etc., influencing the nickel grain size of the nanocomposites, Taguchi robust design method of system
optimization was used to determine the percent of contribution (%ρ) of each factor. The nanocomposites were reduced in a flow
of hydrogen and nitrogen gas at 700 °C for half an hour. The nickel grain size in the nanocomposites was determined by utilizing
Scherrer`s method and XRD patterns. The smallest nickel grain size obtained from the Taguchi orthogonal array was about 24 nm,
later confirmed by TEM observations. After optimization of the controlling factors, a nickel grain size of 15.4 nm was obtained.
It was found that the SiO2/Al2O3 molar ratio of the matrix had the most influence on the nickel grain size (29.22%) and the Water/TEOS molar ratio stood in
second place (21.44%). It was illustrated that the starting temperature of the aluminum isopropoxide had the least influence
on the nickel grain size. 相似文献
7.
Xabier Rios Paula Moriones Jesús C. Echeverría Asunción Luquín Mariano Laguna Julián J. Garrido 《Adsorption》2011,17(3):583-593
The mild synthetic conditions provided by the sol-gel process and the versatility of the colloidal state allow for the mixing
of inorganic and organic components at the nanometre scale in virtually any ratio for the preparation of hybrid materials.
Our interest in hybrid xerogels focuses on combining their porosity with other properties to prepare optic-fibre sensors.
The specific aim of this paper is to synthesise hybrid xerogels in acid media using methyltriethoxysilane (MTEOS) and tetraethoxysilane
(TEOS) as silica precursors and to investigate the effect of the MTEOS molar ratio on the structure and porous texture of
xerogels. Gelation time exponentially increased as the MTEOS molar ratio increased. Increasing the MTEOS molar ratio yielded
xerogels with lower density and lower particle size. The incorporation of MTEOS resulted in new FTIR bands at 1276 and 791 cm−1, which was attributed to vibrational modes of methyl group. The band around 1092 cm−1 associated with siloxane bonds shifted to lower wavenumbers and split into two bands. The 29Si spectra only showed the Q
n
(n=2, 3, 4) signal in xerogels with 0% MTEOS and the T
n
(n=2, 3) signal in xerogels with 100% MTEOS; hybrid xerogels showed both Q and T signals. From XRD peaks at 2θ around 9°, we inferred that xerogels (>70% MTEOS) consisted of nanocrystalline CH3–SiO3/2 species. Increasing the MTEOS molar ratio produced xerogels with lower pore volumes and lower average pore size. The integration
of methyl groups on the surface decreased the surface polarity and, in turn, the characteristic energy. 相似文献
8.
HPWA/MCM-41 mesoporous molecular sieves of appropriate ratios were prepared by loading HPWA on siliceous MCM-41 by the wet impregnation method. The prepared HPWA/MCM-41 materials were characterized by X-ray diffraction analysis (XRD) and BET surface area and FT-IR measurements. The morphology of mesoporous materials was studied by TEM observation. The catalytic activity of the above materials was tested for the condensation of dimedone (active methylene carbonyl compound) and various aromatic aldehyes under liquid phase conditions at 90 °C. The products were confirmed by FT-IR, 1H NMR and 13C NMR studies. HPWA supported MCM-41 catalysts catalyses efficiently the condensation of dimedone and aromatic aldehydes in ethanol and other solvents under liquid phase conditions to afford the corresponding xanthenedione derivatives. Activities of the catalysts follow the order: HPWA/MCM-41(20 wt.%) > HPWA/MCM-41(30 wt.%) > H3PW12O40·nH2O > HPWA/MCM-41(10 wt.%) > HPWA/SiO2 (20 wt.%) > HM (12) > Hβ (8) > Al-MCM-41 (50). Various advantages associated with these protocols include simple workup procedure, short reaction times, high product yields and easy recovery and reusability of the catalyst. 相似文献
9.
The variation of surface properties of SiMCM-41 and AlMCM-41 nanoporous materials as function of synthesis time was examined.
The main properties studied were: surface area, pore diameter, pore volume, mesoporous parameter, and wall thickness. Siliceous
MCM-41 molecular sieves were synthesized starting from hydrogels with the following molar compositions: 4.58SiO2:0.435Na2O:1 CTMABr:200 H2O for SiMCM-41, and 4.58SiO2:0.485 Na2O:1 CTMABr:0.038 Al2O3:200 H2O, for AlMCM-41. Cetyltrimethylammonium bromide (CTMABr) was used as the structural template. The crystallographic parameters
were obtained from XRD data and by nitrogen adsorption using the BET and BJH methods. The results obtained showed a significant
variation of the surface properties of the MCM-41 materials as a function of the synthesis time reaching silica wall thickness
of ca. 2 nm on the fourth day. 相似文献
10.
Dr. Zhihua Xu Prof. Jiaguo Yu Dr. Wei Xiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(29):9592-9598
Mesoporous ferrihydrite/SiO2 composites were synthesized according to a water‐in‐oil microemulsion method and characterized by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, nitrogen‐adsorption/desorption, and by X‐ray photoelectron spectroscopy. The as‐prepared porous ferrihydrite/SiO2 composites showed an excellent adsorption performance for formaldehyde (HCHO) removal from indoor air at ambient temperature. It was found that the aging time during the synthesis had a significant impact on the pore structure, surface area, and HCHO adsorption of these materials. The ferrihydrite/SiO2 composite that was aged for 3 h in the presence of tetraethyl orthosilicate (TEOS) exhibited a relatively high HCHO adsorption capacity, as well as good recyclability, which was attributed to a relatively large BET surface area, optimal pore size, a suitable Si/Fe atomic ratio, and a synergistic effect between ferrihydrite and SiO2. This work not only demonstrates that porous ferrihydrite/SiO2 composites can act as an efficient adsorbent toward HCHO, but suggests a new route for the rational design of cost‐effective and environmentally benign adsorbents with high performance for indoor air purification. 相似文献
11.
In this work the acid properties of a series of HZSM-12 zeolites with different Si/Al ratio were studied. The ZSM-12 crystals
were synthesized by the hydrothermal method starting from a gel with the following molar composition: 20MTEA:10Na2O:x Al2O3:100SiO2:2000H2O, with x = 0.50, 0.67, 1, 1.25 and 2, respectively. The gels were crystallized at 140∘C for 6 days, then washed, dried and calcined to remove the MTEA template. The samples were ion-exchanged with an ammonium
chloride solution and calcined again to obtain the zeolites in the acid form. The materials thus obtained were characterized
by XRD, SEM, BET, TG and n-butylamine adsorption. The Si/Al ratio in the reaction mixture affects the amount of zeolite produced and the size of the
particles. The XRD analysis indicated that the ZSM-12 zeolite crystallizes in a pure form only with Si/Al ratio above 33.
The SEM analysis showed the presence of crystallites with very well defined prismatic shapes. The removal of the MTEA of the
pores of the ZSM-12 by TG indicated that there are two kinds of internal sites occupied by MTEA inside the structure. The
BET area of the ZSM-12 decreases proportionally with the crystallinity of materials. The desorption of n-butylamine showed
that the acid site density is proportional to aluminum content, but the Si/Al ratio shows little influence on the relative
strengths of these sites. 相似文献
12.
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
13.
M. J. van Bommel P. M. C. ten Wolde T. N. M. Bernards 《Journal of Sol-Gel Science and Technology》1994,2(1-3):167-170
The influence of MPS on the hydrolysis and condensation process of TEOS is studied by means of hydrolysis time (t
H) and gelation time (t
G) curves. The addition of MPS to a mixture of TEOS, ethanol and water results in a substantial increase in t
G. The increase is most pronounced when adding takes place in the acid step of the sol-gel process of TEOS.In acid environment hydrolysis of MPS will be dominant compared to hydrolysis of TEOS. This results in an effective decrease of the amount of water available for the hydrolysis of TEOS. However, this decrease in water concentration cannot explain the complete effect of the addition of MPS. The hydrolysed MPS will also be incorporated in the gel network and will strongly influence the cross-linking ability. The lesser functionality of MPS compared to TEOS and the steric hindrance of the acrylate group results in a large increase in t
G. 相似文献
14.
Kirsten Moritz Reinhard Herbig Tanja Damjanovi Christos Argirusis Günter Borchardt 《Colloids and surfaces. A, Physicochemical and engineering aspects》2009,350(1-3):13-21
Mullite and mullite/Al2O3 precursor sols have been developed for the deposition of oxidation barrier coatings on carbon fibre reinforced composites using a combination of sol–gel synthesis and electrophoresis.The sols were synthesised by controlled hydrolysis and condensation of TEOS (tetraethoxysilane) and Al(OBus)3 (aluminium tri-sec-butylate). The main objective was the definition of synthesis conditions which yield sols suitable for the electrophoretic deposition (EPD). Measurements of the Electrokinetic Sonic Amplitude were used to investigate the electrokinetic properties of the sols in the as-prepared state and depending on the later addition of H2O. 29Si CP/MAS NMR spectra of dried precursor samples were recorded to study the homogeneity of Al/Si mixture. The progress of crystallisation with increasing temperature of heat treatment was examined by XRD. Oxidation protection coatings on C/C–SiC composites were prepared by EPD.Whereas a low H2O to TEOS ratio during the sol synthesis was advantageous for a low mullite formation temperature, a high H2O to TEOS ratio was necessary to enable the EPD. The synthesis of a sol with a low H2O to TEOS ratio in the first step and the later modification of this sol by the addition of water was a successful method to combine the required electrokinetic properties and mullitisation temperatures below 1200 °C. 相似文献
15.
Jyoti L. Gurav A. Venkateswara Rao Digambar Y. Nadargi 《Journal of Sol-Gel Science and Technology》2009,50(3):275-280
The experimental results on the study of thermal conductivity and effect of humidity on HMDZ modified TEOS based aerogels
dried at ambient pressure, are reported. Silica sol was prepared by keeping the MeOH/TEOS molar ratio, Acidic water (Oxalic
acid) and basic water (NH4OH) concentrations constant at 16.5, 0.001 and 1 M, respectively throughout the experiments and the HMDZ/TEOS molar ratio
(h) was varied from 0.34 to 2.1. Finally, the surface modified wet gels were dried at an ambient pressure. The thermal conductivity
of the aerogel samples was measured. Further, the humidity study was carried out in 80% humid surrounding at 30 °C temperature
over 80 days. The best quality aerogels in terms of low bulk density, thermal conductivity and durability (no moisture absorption)
with an only 2% of weight gain were obtained for TEOS: MeOH: Acidic H2O: Basic H2O: HMDZ molar ratio at 1:16.5:0.81:0.50:0.681, respectively. The thermal stability and hydrophobicity of the aerogel have
been confirmed with Thermo gravimetric and Differential Thermal (TG–DT) analyses and Fourier Transform Infrared Spectroscopy
(FTIR), respectively. Microstructural studies were carried out by Scanning Electron microscopy (SEM). 相似文献
16.
M. Ştefănescu M. Stoia O. Ştefănescu A. Popa M. Simon C. Ionescu 《Journal of Thermal Analysis and Calorimetry》2007,88(1):19-26
Hybrid organic-inorganic materials,
silica – polyols (ethylene-glycol – EG; 1,2 propane diol –
1,2PG; 1,3 propane diol – 1,3PG and glycerol – GL), were prepared
by a sol-gel process starting from tetraethylorthosilicate (TEOS) and polyols,
in acid catalysis. The resulting materials were studied by thermal analysis
(in air and nitrogen), FTIR and solid state 29Si-NMR
spectroscopy. These techniques evidenced the presence of polyols in the silica
matrix both hydrogen bounded and chemically bounded in the silica network.
The thermal analysis proves to be the most appropriate technique to evidence
the organic chains linked in the matrix network and to follow the thermal
evolution of the gels to the SiO2 matrix. 相似文献
17.
Reihaneh Malakooti Zeinab Parsaee Rahele Hosseinabadi Hossein A. Oskooie Majid M. Heravi Mina Saeedi Maryam Amrollah Akram Fallah 《Comptes Rendus Chimie》2013,16(9):799-806
A novel [Cu(bpdo)2·2H2O]2+-supported SBA-15 catalyst (bpdo = 2,2′-bipyridine,1,1′-dioxide) was prepared by the impregnation method. The catalyst was characterized by XRD, TEM, and BET nitrogen adsorption–desorption method, FT-IR, UV–vis, and chemical analysis. XRD patterns and TEM analysis of [Cu(bpdo)2·2H2O]2+/SBA-15 showed highly ordered hexagonal mesoporous silica, even after immobilization. Also, nitrogen adsorption–desorption isotherms exhibited type-IV isotherms and H1 hysteresis loops according to the IUPAC classification of mesoporous materials. This green support was tested for the synthesis of benzoxanthenone and benzochromene derivatives under solvent-free conditions, with high yield of products via a simple experimental and work-up procedure. 相似文献
18.
Summary Materials obtained by polycondensation of [Rh(CO)ClL2] [L=PPh2CH2CH2Si(OEt)3] with tetraethoxysilane (TEOS) irreversibly take up CO to give monomeric or dimeric [cis-Rh(CO)2ClL']: (L'=PPh2CH2CH2SiO3/2·xSiO2) (2). The polymeric metal complex (2) is also obtained by CO treatment of [Rh2(CO)2Cl2L'2] (4) or by polycondensation ofin-situ prepared (monomeric or dimeric) [Rh(CO)2ClL] with TEOS. Unlike comparable complexes in solution,(2) is extremely stable in respect to CO loss, even at higher temperatures andin vacuo.Part I of this series, ref. (1). 相似文献
19.
High-quality cubic MCM-48 is successfully synthesized using a new silica source known as silatrane and cetyltrimethylammonium
bromide (CTAB) as the structure-directing agent via sol–gel process. The effects of synthesis parameters, viz. crystallization
temperature, crystallization time, surfactant concentration, quantity of NaOH, and silica source, on the product structure
are investigated. The synthesized samples are characterized using X-ray diffractometer (XRD), N2 adsorption–desorption isotherms, and electron microscopy. Optimally, this product is synthesized from samples crystallized
at 140°C for 16 h with a CTAB/SiO2 ratio of 0.3 and NaOH/SiO2 ratio of 0.5. The XRD result exhibits a well-resolved pattern, corresponding to the Ia3d space group of MCM-48. The BET surface area of this product is as high as 1,300 m2/g with a narrow pore-size distribution of 2.86 nm. The scanning electron microscopic (SEM) images also show the truncated
octahedral shape and well-ordered pore system of MCM-48 particles. 相似文献
20.
正硅酸乙酯水解过程的半经验量子化学研究 总被引:15,自引:0,他引:15
通过半经验量子化学方法研究了正硅酸乙酯的最优化分子几何结构并推断了催化水解机理。通过用MNDO方法求得正硅酸乙酯在不同条件下水解反应过程的位能曲线,研究了不同催化剂对正硅酸乙酯水解反应过程的影响。计算结果表明,碱催化过程是一个放热过程,硅原子可从原先的4配位的正四面体结构向6配位的八面体结构转变。而在酸性条件下,水合质子作为亲电试剂,可以使正硅酸乙酯的烷氧基质子化,从而增加了正硅酸乙酯的亲电能力。质子化后的正硅酸乙酯容易被亲核试剂所进攻,进攻过程是一个SN2亲核取代反应过程。计算结果表明,在有氟离子参与的反应过程中,氟离子对正硅酸乙酯亲核进攻所形成的6配位结构易与亲核试剂水分子发生亲核反应。这些结论对实验研究将起到很重要的指导意义。 相似文献