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1.
The dependence of the stability of SiO2 and Al2O3 sols on the pH of their medium has been studied. Vapor adsorption isotherms on powders were prepared from acidic and basic
sols, the immersion enthalpy (heat) of samples containing preadsorbed water have been determined and, also, the reversibility
of the sol ⇌ xerogel transformation, i.e. the peptizability of the powders, has been investigated.
Based on the flocculation values determined with KCl, the sols have been classified into three groups. The stability of highly
hydrophilic sols (acidic SiO2- and Al2O3-sols) is ensured by a thick continuous diffuse lyosphere formed around the particles, as the continuity principle by Ostwald–Buzágh
suggests. In this case, no electric charge is needed for ensuring stability. These sols are thermodynamically stable (group
1). Sols with medium stability are stabilized by the electrical double layer around the particles and by 1–2 layers of adsorbed
water. The flocculation value of these sols is determined by the electrostatic interaction, whereas the peptizability of the
flocs is related to formation of water layers. Such sols are the basic SiO2- and Al2O3-sols (group 2). Sols of low stability are of hydrophobic nature. Their flocculation value with 1:1 electrolytes is smaller
than 0.1 molkg-1. The transformation process sol ⇒ floccule ⇒ xerogel is mostly irreversible. There are a lot of such sols (group 3). The
existence of a hydrosphere is proved by the almost identical value of the hydration energy for both the acidic and the basic
SiO2 sols, in spite of an order of magnitude difference in the flocculation value. The remnants of adsorbed water after drying
hinders sintering of the particles and ensures the peptizability of powders.
The highly hydrophilic sols (sequence of hydrophilicity: SiO2> Al2O3>FeO OH ⋅ 0.5 H2O) are all oxides which are formed in acidic media.
Received: 25 May 1997 Accepted: 13 October 1997 相似文献
2.
B. G. Ershov 《Russian Chemical Bulletin》2000,49(10):1715-1721
Radiation-chemical reduction of Ni2+ ions in aqueous solutions of Ni(ClO4)2 containing sodium formate or isopropyl alcohol was studied, γ-Irradiation of deaerated solutions in the presence of polyethyleneimine,
polyacrylate, or polyvinyl sulfate gives stable metal sols containing spherical particles 2–4 nm in diameter. The optical
absorption spectra of nickel nanoparticles exhibit a band with a maximum at 215±5 nm (ε215=4.7·103 L mol−1 cm−1) and a shoulder at 350 nm. A mechanism for the radiation-chemical reduction of Ni2+ ions by hydrated electrons and organic radicals (CO2- radical anions in the case of HCOONa and Me2C·OH radicals in the case of PriOH). The redox potentials of the Ni2+/Ni0 and Ni+/Ni0 pairs (Ni0 is a nickel atom) are approximately −2.2 and −1.7 V, respectively. The nanoparticles are readily oxidized by O2, H2O2, and other oxidants. The reactions of these species with silver ions yield relatively stable nanoaggregates containing both
nickel and silver in addition to silver nanoparticles.
Published inIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 1733–1739, October, 2000. 相似文献
3.
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
4.
The Er3+-doped Al2O3 nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC3H7)3]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO3)3·5H2O]. The five phases of γ-(Al,Er)2O3, θ-(Al,Er)2O3, α-(Al,Er)2O3, ErAlO3, and Al10Er6O24 were detected with the 0–20 mol% Er3+-doped Al2O3 nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm
for phase transformation of undoped γ-Al2O3→α-Al2O3 at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with
increase of the Er3+ doping concentration. Infrared absorption spectra of γ-Al2O3 and θ-Al2O3 nanopowders showed the two broad bands of 830–870 and 550–600 cm−1, the three broad bands of 830–870, 750–760, and 550–600 cm−1, respectively. The infrared absorption spectra for the α-Al2O3 nanopowder showed three characteristic bands, 640, 602, and 453 cm−1. The two characteristic bands of 669 and 418 cm−1 for Er2O3 clusters were observed for the Er3+-doped Al2O3 nanopowders when Er3+ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm−1 are the characteristic bands of Al10Er6O24 phase. 相似文献
5.
G. M. Rozantsev S. M. Vavilova L. V. Zaslavskaya 《Russian Journal of Inorganic Chemistry》2010,55(3):446-453
Processes occurring in Nb6O198−-WO42−-H+-H2O system where c
Nb: c
W = 4: 2, c
Nb+W0 = 5 × 10−3, 2.5 × 10−3, or 10−3 mol/L, and ionic strengths I = 0.01–0.14 are created by NaCl background electrolyte were studied by pH titration and mathematical modeling. Solute ion
species distribution diagrams were obtained for $
Z = \frac{{c_{H^ + }^0 }}
{{c_{Nb + W}^0 }} = 0 - 1.5
$
Z = \frac{{c_{H^ + }^0 }}
{{c_{Nb + W}^0 }} = 0 - 1.5
. The concentration constants and thermodynamic constants of formation were calculated for isopolyniobotungstate anions (IPNTAs).
H
x
Nb4W2O19(6−x)−, (x = 1–5), ions were shown to appear in solution only after Nb6O198− was protonated and aquapolytungstate anions were formed. The results of modeling were supported by the synthesis of Tl3H3Nb4W2O19 · 16.5H2O, Tl2H4Nb4W2O19 · 11H2O, and NaTl3(H4Nb4W2O19)2 · 22H2O salts, which were identified by chemical analysis and IR spectroscopy. 相似文献
6.
Michel A. Aegerter Cesar O. Avellaneda Agniezska Pawlicka Mohamed Atik 《Journal of Sol-Gel Science and Technology》1997,8(1-3):689-696
Electrochromism is defined as the persistent but reversible optical change (usually transmission) produced electrochemically.
The preparation by the sol-gel process of thin films made of amorphous or crystalline nanoparticles of WO3, V2O5, Nb2O5, TiO2, CeO2, Fe2O3 and mixed compounds such as WO3−TiO2, CeO2−TiO2, CeO2−SnO2, have opened remarkable new opportunities for obtaining electrochromic layers exhibiting large optical transmission variation
in the UV, visible or infrared range and acceptable kinetics under H+ or Li+ insertion. In this paper we give an overview of what has been recently achieved in this field, with emphasis for cathodic
electrochromic coatings of Nb2O5 and TiO2 composition. Finally we stress the future developments in this fast growing field. 相似文献
7.
Milos Hayer Vlastimil Matejec Daniela Berkova Ivan Kasik Jiri Kanka Pavel Peterka Pavel Honzatko 《Journal of Sol-Gel Science and Technology》2000,19(1-3):293-296
The paper reports effects of high-temperature treatment of silica layers doped with Al2O3, P2O5, Yb and Er ions, which are coated inside silica substrate tubes and transformed through viscous flow into the core of a preform, on properties of these cores. The gel layers are applied inside the silica substrate tubes from sols based on tetraethoxysilane and corresponding chlorides in isopropanol by controlled lowering the column of the sol. The layers are thermally treated at 500°C and subject to high-temperature treatment from 1000 to 1300°C. The tube with the layers is collapsed into a preform from which fibers are drawn at about 1950°C. The results of concentration measurements show that during the high-temperature treatment the content of silica in the layer increases at least five times in comparison with that of the sol composition. This effect depends on the sol composition and the number of the coated gel layers. Measurements show that in the prepared fibers there is some remaining unsaturated absorption of erbium ions at 1535 nm, which is related to quenching of the erbium ions. 相似文献
8.
WU Hongbo WANG Xiao & CHEN Jianmin Department of Environmental Science Engineering Fudan University Shanghai China 《中国科学B辑(英文版)》2005,48(1):31-37
Carbonyl sulfide (COS) is one of the most abun-dant sulfur containing gases in the troposphere andlower stratosphere[1,2]. It is relatively inert in the tro-posphere and can be transported into the stratosphere,where it dissociates under the solar ultravi… 相似文献
9.
O. A. Gapurenko T. N. Gribanova R. M. Minyaev V. I. Minkin 《Russian Chemical Bulletin》2007,56(5):856-862
The energy characteristics and geometric parameters of the dodecahedrane endohedral complexes X@C20H20 (X = C4−, N3−, O2−, F−, Ne) were studied by the density functional theory B3LYP method with the 6-311G(d,p), 6-311+G(d,p), and 6-311G(df,p)) basis
sets. In all structures the central atoms X are characterized by a coordination number of 20. The energy of formation of the
complexes decreases in the order X = C4−, N3−, O2−, F−, Ne. The coordination number of the central atom remains unchanged upon adding Li+ counterions to anionic systems.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 824–830, May, 2007. 相似文献
10.
A 3D infinitely extended structural rare earth coordination compound with a formula of K3{[Sm(H2O)7]2Na[α-SiW11O39Sm(H2O)4]2}·14H2O has been synthesized by reaction of Sm2O3, HClO4, NaOH with α-K8SiW11O39·nH2O, and characterized by IR, UV spectra, ICP, TG-DTA, cyclic voltammetry, variable-temperature magnetic susceptibility and
X-ray single-crystal diffraction. X-ray single-crystal diffraction indicates that the title compound crystallizes in a triclinic
lattice, Pī space group, with a = 1.2462(3) nm, b = 1.2652(3) nm, c = 1.8420(4) nm, α = 87.45(3)°, β = 79.91(3)°, γ= 82.57(3)°, Z = 1, R1 = 0.0778, wR2 = 0.1610. Structural analysis reveals that Sm3+(1) coordination cation has incorporated into the vacant site of [α-SiW11O39]8− entity, forming the [α- SiW11O39Sm(H2O)4]5− subunit. The two adjacent [α-SiW11O39Sm(H2O)4]5− subunits are combined with each other through two Sm(1)-O-W bridges accompanying the formation of dimmer structural unit
[α-SiW11O39Sm(H2O)4]2
10− of the title compound. The neighboring dimmer structural units [α-SiW11O39Sm(H2O)4]2
10− are linked to form the 1D chainlike structure by means of two Sm3+(2) and a Na+(1) coordination cations. The K+(1) cations connect the 1D packing chains constructing the 2D netlike structure, and adjacent netlike layers are also grafted
by K+(2) cations to build the novel 3D infinitely extended structure. The result of TG-DTA curves manifests that the decomposition
temperature of the title polyanionic framework is 554°C. The cyclic voltammetry measurements show that the title polyanion
has the two-step redox processes in aqueous solution with pH = 3.1. Variable temperature magnetic susceptibility indicates
the title compound obeys the Cruie-Weiss Law in the higher temperature range from 110 to 300 K, while in the lower temperature
range from 2 to 110 K the comparatively strong antiferromagnetism interactions can be observed. 相似文献
11.
E. Yu. Matveev G. A. Razgonyaeva V. N. Mustyatsa N. A. Votinova K. Yu. Zhizhin N. T. Kuznetsova 《Russian Chemical Bulletin》2010,59(3):556-559
The reaction of the [B10H9O2C4H8]−, [B10H9OC4H8]−, and [B10H9OC5H10]− anions with negatively charged S-nucleophiles, such as SH−, SCN−, and S2O3
2−, resulted in the ring opening of the cyclic substituent and the formation of derivatives with the terminal thiol, thiocyanate,
and thiosulfate groups. The structures of the products were confirmed by the IR, mass, and 1H, 11B, and 13C NMR spectra. 相似文献
12.
Glaubitt Walther Watzka Winfried Scholz Hermann Sporn Dieter 《Journal of Sol-Gel Science and Technology》1997,8(1-3):29-33
Structural ceramic oxide fibers like α-Al2O3, MgAl2O4 (spinel), Y3Al5O12 (YAG) and eutectic Al2O3−Y3Al5O12 as well as the functional Pb(Zr1−xTix)O3 (PZT) fibers were successfully prepared by sol-gel processing. All precursors are based on metal oxohydroxopropionates. A
comparative study of sol-gel routes leading to spinnable sols demonstrates the key role of propionic acid as an excellent
agent for controlling hydrolysis and condensation reactions. 相似文献
13.
Bhawana Gupta Suresh Magotra Sushil K. Pandey 《Monatshefte für Chemie / Chemical Monthly》2008,44(10):747-752
O,O′-Ditolylphosphorodithioates of phosphorus(III), [(o-, m-, or p-CH3C6H4O)2PS2]
n
PCl3−n
, and phosphorus(V), [(o-, m-, or p-CH3C6H4O)2-PS2]
n
POCl3−n
, (n = 1, 2, and 3) were isolated as colorless viscous liquids by the reaction of PCl3 and POCl3 with sodium ditolylphosphorodithioate, (o-, m-, or p-CH3C6H4O)2PS2Na, in 1:1, 1:2, and 1:3 molar ratios in toluene. These compounds were characterized by elemental analyses, molecular weight
measurements, IR, and NMR (1H, 31P, and 13C) spectroscopic studies, which indicated a less common monodentate linkage of dithiophosphate moieties in both phosphorus(III)
and phosphorus(V) derivatives leading to a tetrahedral geometry around the phosphorus atom. 相似文献
14.
Takashi Kamegawa Masaya Matsuoka Masakazu Anpo 《Research on Chemical Intermediates》2008,34(4):427-434
A highly dispersed Cr6+-oxide species on silica (Cr/SiO2) was found to act as an efficient photocatalyst for the selective oxidation of CO into CO2 with O2 in the presence of H2 under visible (λ>420 nm) or solar light irradiation at 293 K. UV-Vis, photoluminescence and FT-IR investigations revealed
that the selective reactivity of the photoexcited tetrahedral Cr6+-oxide species ([Cr5+−O−]*) with CO, as well as the high reactivity of the photoreduced Cr6+-oxide species (Cr4+-oxide species) with O2 both play significant roles in this reaction. 相似文献
15.
The relative enthalpies, ΔHo (0) and ΔHo (298.15), of stationary points (four minimum and three transition structures) on the •O3H potential energy surface were calculated with the aid of the G3MP2B3 as well as the CCSD(T)–CBS (W1U) procedures from which
we earlier found mean absolute deviations (MAD) of 3.9 kJ mol−1 and 2.3 kJ mol−1, respectively, between experimental and calculated standard enthalpies of the formation of a set of 32 free radicals. For
CCSD(T)-CBS (W1U) the well depth from O3 + H• to trans-•O3H, ΔHowell(298.15) = −339.1 kJ mol−1, as well as the reaction enthalpy of the overall reaction O3 + H•→O2 + •OH, ΔrHo(298.15) = −333.7 kJ mol−1, and the barrier of bond dissociation of trans-•O3H → O2 + •OH, ΔHo(298.15) = 22.3 kJ mol−1, affirm the stable short-lived intermediate •O3H. In addition, for radicals cis-•O3H and trans-•O3H, the thermodynamic functions heat capacity Cop(T), entropy So (T), and thermal energy content Ho(T) − Ho(0) are tabulated in the range of 100 − 3000 K. The much debated calculated standard enthalpy of the formation of the trans-•O3H resulted to be ΔfHo(298.15) = 31.1 kJ mol −1 and 32.9 kJ mol −1, at the G3MP2B3 and CCSD(T)-CBS (W1U) levels of theory, respectively. In addition, MR-ACPF-CBS calculations were applied
to consider possible multiconfiguration effects and yield ΔfHo(298.15) = 21.2 kJ mol −1. The discrepancy between calculated values and the experimental value of −4.2 ± 21 kJ mol−1 is still unresolved.
Note added in proof: Yu-Ran Luo and J. Alistair Kerr, based on the discussion in reference 12, recently presented an experimental
value of ΔfHo(298.15) = 29.7 ± 8.4 kJ mol−1 in the 85th edition of the CRC Handbook of Chemistry and Physics (in progress). 相似文献
16.
B. G. Ershov 《Russian Chemical Bulletin》1998,47(10):1905-1909
The radiation-chemical reduction of Co2+ ions in an aqueous solution of Co(ClO4)2 containing sodium formate was studied. Stable metal sols containing spherical particles with a diameter of 2–4 nm are formed
under γ-irradiation in the presence of polyacrylate as the stabilizing additive. An aqueous solution of colloidal cobalt has
an optical absorption that increrases smoothly in the UV region without a maximum to 200 nm (ɛ200=1.3·104 mol-1 L cm-1). It is established that the radiation-chemical reduction of the Co2+ ions occursvia an autocatalytic mechanism. The metal sols catalyze the reduction of the Co2+ ions by Co2
− radical ions formed under irradiation. The properties of the sols were studied, and it is shown that they are readily oxidized
by hydrogen peroxide and other oxidants. The mechanism of chemical reactions involving the sols is discussed.
Tranalated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1959–1964, October, 1998. 相似文献
17.
Manuela Sales Carla Valentin Javier Alarcón 《Journal of Sol-Gel Science and Technology》1997,8(1-3):871-875
The aim of this paper was to study the synthesis and characterization of spinel-containing mullite based materials, using
sol-gel techniques. Several gels were prepared, with nominal compositions 3(Al2−2xMx TixO3)·2SiO2 and 3(Al2−xMxO3)·2SiO2, with M=Ni+2 or Co+2 and 0.0≤x≤0.2, by hydrolysis and condensation of mixtures of aluminum, silicon and titanium alkoxides and nickel chloride.
Dried gels were homogeneous and displayed a glass transition at around 750°C, which indicated that the system could be described
as an amorphous silicoaluminate network.
Crystallization pathway of gels were followed using differential thermal analysis and X-ray diffraction patterns of samples
thermal treated at temperatures in the range between 800 and 1400°C. A two-phase aluminate spinel-mullite arrangement was
detected at temperatures around 1200°C. The microstructure of the final product was interesting, because the minor secondary
phase was homogeneously dispersed in the mullite matrix.
Chemical and thermal resistance of diphasic materials were tested and the results indicate that these materials can be used
as high temperature ceramic pigments. 相似文献
18.
I. V. Mironov 《Russian Chemical Bulletin》1998,47(10):1864-1867
The influence of the ion background (NaClO4, LiClO4, and HClO4) on the kinetics of the reaction PtdientH2O2++X−→PtdientX++H2O(X=Cl, Br, I, SCN, and N3) was studied at 25°C by spectrophotometry. Changes in the rate constant with increase in the ionic strength are described
by the Debye-Hückel and Gosh-Bjerrum equations. The reaction PtdienCl++H2O→PtdientH2O2++Cl− was studied by potentiometry and its rate constant was established to depend weakly on variations of the medium.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1918–1921, October, 1998. 相似文献
19.
A new compound C17H20FN3O32+·CuBr42−·H2O is synthesized in the crystal form, where C17H18FN3O3 (CfH, ciprofloxacin) is 4-oxo-7-(1-piperazinyl)-6-fluoro-1-cyclopropyl-1,4-dihydroquinoline-3-carboxylic acid. Crystallographic
data of ciprofloxacinium tetrabromocuprate(II) monohydrate, C17H22Br4CuFN3O4: a = 8.214(1) ?, b = 10.781(2) ?, c = 13.703(2) ?, α = 85.144(2)°, β = 79.119(2)°, γ = 84.018(2)°, V = 1182.5(4) ?3, P
[`1]\bar 1 space group, Z = 2. Supramolecular architecture of the crystal differs from that established for C17H20FN3O32+·CuCl42−·H2O by the absence of π-π interactions of the aromatic rings of CfH32+ ions and also the structural motifs formed by intermolecular hydrogen bonds. 相似文献
20.
Bhawana Gupta Nidhi Kalgotra Savit Andotra Sushil K. Pandey 《Monatshefte für Chemie / Chemical Monthly》2012,39(5):1087-1095