共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
3.
4.
Gregorio Guadalupe Carbajal Arizaga Jos Eduardo Ferreira da Costa Gardolinski Wido Herwig Schreiner Fernando Wypych 《Journal of colloid and interface science》2009,330(2):352-358
A Zn/Al layered double hydroxide with molar ratio of 3 was prepared by coprecipitation in alkaline pH and used as a matrix to intercalate the ionic complex diaquadioxalatooxoniobate(V) (DDON), derived from NH4[NbO(C2O4)2(H2O)2]2H2O. In a similar way, the layered zinc hydroxide nitrate, Zn5(OH)8(NO3)22H2O, was synthesized, preexpanded with azelate ions (−OOC(CH2)7COO−), and then intercalated with the niobium complex. For both layered matrices, the results from X-ray powder diffractometry, Fourier transform infrared spectroscopy, and thermal analysis (TG/s-DTA) indicate the presence of the oxalate ion. In addition, results from X-ray photoelectron and Raman spectroscopy indicate the presence of the niobium center bonded to oxygen atoms. Finally, diffuse reflectance UV–vis spectroscopy suggests that the niobium centers are coordinated to oxalate ions. This is the first report of the intercalation of niobium into a layered matrix. 相似文献
5.
Surface-charging behavior of Zn-Cr layered double hydroxide 总被引:1,自引:0,他引:1
Rojas Delgado R Arandigoyen Vidaurre M De Pauli CP Ulibarri MA Avena MJ 《Journal of colloid and interface science》2004,280(2):136-441
A Zn-Cr layered double hydroxide (LDH) having the formula Zn(2)Cr(OH)(6)Cl(0.7)(CO(3))(0.15)2.1H(2)O was synthesized and characterized by powder X-ray diffraction, infrared spectroscopy, acid-base potentiometric titration, mass titration, electrophoretic mobility, and modeling of the electrical double layer. Adsorption of alizarin was also performed in order to show some particular features of the HDL. Net hydroxyl adsorption, which increases with increasing pH and decreasing supporting electrolyte concentration, takes place above pH 5. The electrophoretic mobility of the particles was always positive and it decreased when the pH was higher than 9. An isoelectric point of 12 could be estimated by extrapolating the data. The modified MUSIC model was used to estimate deprotonation constants of surface groups and different adsorption models were compared. Good fit of hydroxyl adsorption and electrophoresis could be achieved by considering both OH(-)/Cl(-) exchange at structural sites and proton desorption from surface hydroxyl groups. The modeling, in agreement with alizarin adsorption, indicates that most of the structural positive charge of the LDH is screened at the surface by exchanged anions and negatively charged surface groups. It also suggests that only structural charge sites initially neutralized by chloride ions are active for anion exchange. The remaining sites are blocked by carbonate and do not participate in the exchange. 相似文献
6.
Gursky JA Blough SD Luna C Gomez C Luevano AN Gardner EA 《Journal of the American Chemical Society》2006,128(26):8376-8377
Changes in chemical properties of nanoscale particles include quantum size effect, changes in the cell parameters and lattice symmetry, and surface and interface effects. In the case of layered double hydroxides (LDHs), surface and interface effects dominate for nanoparticles of MgAl LDHs. Using TEM micrographs of nanoparticle-sized LDHs, we have found that the increased number of surface atoms relative to the internal atoms increases the surface-to-surface interparticle attractions. As a result, nanosize LDH particles are able to form continuous oriented films that adhere well to a polar substrate. 相似文献
7.
Ahmet Nedim Ay 《Journal of Thermal Analysis and Calorimetry》2011,103(3):897-902
Thermal decomposition kinetics and mechanism of layered double hydroxides (LDHs) intercalating different amounts and types of borate ions were studied using Coats–Redfern integral and Achar differential methods. The results revealed that the Coats–Redfern integral method is more appropriate than the Achar differential method for evaluation of the nonisothermal thermogravimetric decomposition data. The first-order Avrami-Erofe’ev A1 mechanism was found to be the best fitting kinetic model for almost all samples. In addition to the amount and type of the intercalated borate ion, interlayer orientation was also of importance in determining the chemical and thermal stabilities and hence the decomposition kinetics of the studied compounds. 相似文献
8.
An atomistic model of layered double hydroxides, an important class of nanoporous materials, is presented. These materials have wide applications, ranging from adsorbents for gases and liquid ions to nanoporous membranes and catalysts. They consist of two types of metallic cations that are accommodated by a close-packed configuration of OH- and other anions in a positively charged brucitelike layer. Water and various anions are distributed in the interlayer space for charge compensation. A modified form of the consistent-valence force field, together with energy minimization and molecular dynamics simulations, is utilized for developing an atomistic model of the materials. To test the accuracy of the model, we compare the vibrational frequencies, x-ray diffraction patterns, and the basal spacing of the material, computed using the atomistic model, with our experimental data over a wide range of temperature. Good agreement is found between the computed and measured quantities. 相似文献
9.
10.
Frost RL Reddy BJ 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,65(3-4):553-559
Raman and thermo-Raman spectroscopy have been applied to study the natural hydrotalcite manasseite Mg(6)Al(2)(OH)(16)(CO(3)).4H(2)O. Hydrogen bond distances calculated using a Libowitzky-type empirical function varied between 2.61 and 3.00A. Stronger hydrogen bonds were formed by water units as compared to the hydroxyl units. Thermo-Raman spectroscopy enabled the identification of bands attributed to the hydroxyl units. Two Raman bands at 1062 and 1058 cm(-1) are assigned to symmetric stretching modes of the carbonate anion. Thermal treatment shifts these bands to higher wavenumbers indicating a change in the carbonate bonding. 相似文献
11.
Fabrice Leroux Julien Gachon Jean-Pierre Besse 《Journal of solid state chemistry》2004,177(1):245-250
Alginic acid, a biopolymer produced by brown seaweed, is incorporated between the sheets of a layered double hydroxide (LDH) via direct coprecipitation. The growth of the inorganic crystalline seeds over the polymer gives rise to a lamellar structure. The obtained nanocomposite presents a basal spacing in agreement with the ideal picture of the polymer lying perpendicularly to the inorganic sheets. A study using FTIR and 13C CP-MAS spectroscopies suggests that the interaction between the organic guest and the inorganic framework is weak. However, the polymer has a stabilizing effect in temperature, since ZnO is observed at 350°C, whereas it appears at 200°C for the chloride LDH pristine material. 相似文献
12.
13.
The orientation-controlled LDH crystals on Si substrates were intercalated by dicarboxylate ions to give the anisotropic layer expansion. 相似文献
14.
V. Correcher J. Garcia-Guinea Y. Rodriguez-Lazcano 《Journal of Thermal Analysis and Calorimetry》2018,133(3):1253-1257
Layered double hydroxides (LDHs) and many of the related hydrotalcite-like minerals have been well studied from the chemical and structural point of view; however, their luminescence properties have been scarcely studied. We herein report on the thermoluminescence (TL) behaviour of a natural LDH (Mg6Cr2CO3(OH)16·4H2O), previously characterized by X-ray fluorescence, X-ray energy-dispersive spectrometry, electron probe microanalysis, thermogravimetry and differential thermal analysis, that exhibited a very complex green-IR spectral emission. The broad waveband peaked at ~?640 nm can be mainly linked to the 4T1?→?6A1 (at 570 nm), 4A2g?→?2Eg (~?685 nm), 4T1?→?6A1 (~?700 nm), and 1T2g?→?3A2g (green) and 1T2g?→?3T2g (red) transitions due, respectively, to the presence of Mn2+, Cr3+, Fe2+ and Ni2+. The weak red-TL emission can likely be attributed to the quenching effect due to Fe (~?8–11%) ions substituting for Mg2+. 相似文献
15.
Yan D Lu J Ma J Wei M Evans DG Duan X 《Physical chemistry chemical physics : PCCP》2010,12(45):15085-15092
Luminescent benzocarbazole anions (BCZC) intercalated into the interlayer region of Mg-Al-layered double hydroxides (BCZC/LDH) with different layered charge densities (LCD) were prepared. The structure and chemical composition of the composites were characterized by X-ray diffraction, elemental analysis, thermogravimetry and differential thermal analysis (TG-DTA), infrared spectra (FT-IR), UV-vis absorption and fluorescence spectroscopy. The photoemission behavior of BCZC in the LDH matrix with high (Mg/Al ratio = 1.801) and low (Mg/Al ratio = 3.132) LCD is similar to that of BCZC solid and aqueous solution states respectively, indicating that the luminescence performances of the intercalated dye anions can be tuned by adjusting the LCD of the LDH layer. Moreover, the thermal stability and stacking order of BCZC are largely improved upon intercalation, and the BCZC/LDH thin film exhibits well polarized luminescence with the luminescent anisotropy of 0.15-0.20. In addition, molecular dynamics (MD) simulation was employed to calculate the basal spacing and molecular arrangement of the intercalated BCZC within the LDH matrix. The simulation results show that the distribution of BCZC anions is much broader in the gallery of Mg-Al-LDH with high LCD, while BCZC anions exhibit a more ordered arrangement in LDH with low LCD. Furthermore, the radial distribution functions of interlayer water molecules were also studied. Based on the combination of experiment and theoretical simulation, this work provides a detailed understanding of the tunable photoluminescence, orientation and diffusion behavior of the luminescent molecules confined within the gallery of a 2D inorganic matrix. 相似文献
16.
Gregorio Guadalupe Carbajal Arizaga Fernando Wypych Oscar Edel Contreras Lopez 《Journal of solid state chemistry》2010,183(10):2324-2328
A zinc/aluminum LDH was precipitated with recycled ammonia from a chemical vapor deposition reaction. The LDH presented a crystalline phase with basal distance of 8.9 Å, typical for nitrate-containing LDHs, and another phase with a basal distance of 13.9 Å. Thermal treatment at 150 °C eliminated the phase with the bigger basal distance leaving only the anhydrous nitrate-intercalated LDH structure with 8.9 Å. Intense N-H stretching modes in the FTIR spectra suggested that the expansion was due to intercalation of ammonia in the form of [NH4(NH3)n]+ species. When additional samples were precipitated with pure ammonia, the conventional LDH nitrate structure was obtained (8.9 Å basal distance) at pH=7, as well as a pure crystalline phase with 13.9 Å basal distance at pH=10 due to ammonia intercalation that can be removed by heating at 150 °C or by stirring in acetone, confirming a unusual sensu stricto intercalation process into a LDH without exchanging nitrate ions. 相似文献
17.
Gago S Pillinger M Valente AA Santos TM Rocha J Gonçalves IS 《Inorganic chemistry》2004,43(17):5422-5431
A Zn,Al layered double hydroxide (LDH) with Zn/Al = 1.45 and containing nitrate anions was prepared by coprecipitation and characterized by powder X-ray diffraction, Zn K-edge extended X-ray absorption fine structure spectroscopy (EXAFS), thermogravimetric analysis, FTIR and FT Raman spectroscopy, and (27)Al MAS NMR spectroscopy. Three Zn...O and four Zn...M (M = Zn, Al) shells could be fitted to the low-temperature (40 K) EXAFS spectrum, in accordance with a model for an ordered cationic sheet. The nitrate anions were easily exchanged by 2,2'-bipyridine-5,5'-dicarboxylate anions, resulting in an increase in the basal spacing from 9 to 18 A. The basal spacing of the pillared derivative indicates that the anions are arranged with their longest dimension nearly perpendicular to the host layers. This material exhibits a high encapsulating ability, as evidenced by its interaction with a dichloromethane solution of the dioxomolybdenum(VI) complex MoO(2)Cl(2)(THF)(2). A material with a metal loading of 11.2 wt % was obtained. Molybdenum K-edge EXAFS analysis could not substantiate the formation of a supported complex of the type MoO(2)Cl(2)(N-N) but instead indicated the formation of unidentate-bridged entities of the type [O(2)Mo-O-MoO(2)] with a metal-metal separation of 3.29 A. The molybdenum-containing LDH was active as a catalyst for the liquid-phase epoxidation of cis-cyclooctene, 1-octene, and trans-2-octene using tert-butyl hydroperoxide as the oxygen source, yielding the corresponding epoxides as the only products. For reactions carried out with no additional solvent (other than n-decane) or in the presence of 1,2-dichloroethane, the solid catalyst could be recycled with no major loss of activity. Other tests confirmed that the systems functioned as true heterogeneous catalysts. 相似文献
18.
We report the first controlled synthesis of a layered double hydroxide (LDH) in a water-in-oil reverse microemulsion system. This synthesis of Mg2Al-LDHs was carried out in the reverse microemulsion of NaDDS (sodium dodecyl sulfate)-water-isooctane with water/surfactant molar ratio = 24. This enables us to obtain nanometer sized LDH platelets typically with a 40-50 nm diameter and 10 nm thickness. Further modification of the reverse microemulsion using triblock copolymers during crystallization allowed us to express different growth orientations of the LDH structure. These data show that the aspect ratio of LDHs can be flexibly adjusted over a wide range. 相似文献
19.
Touati S Mansouri H Bengueddach A de Roy A Forano C Prevot V 《Chemical communications (Cambridge, England)》2012,48(57):7197-7199
Aerogels of layered double hydroxides were prepared by a simple and eco-friendly method involving a quick coprecipitation followed by supercritical CO(2) drying. Such aerogels display high surface areas and enhanced adsorption behavior. 相似文献
20.
O. B. Belskaya N. N. Leont’eva T. I. Gulyaeva V. A. Drozdov V. P. Doronin V. I. Zaikovskii V. A. Likholobov 《Kinetics and Catalysis》2011,52(5):761-769
A layered aluminum-magnesium hydroxide of the hydrotalcite type containing interlayer carbonate counterions (HT-CO3) and activated hydrotalcite containing interlayer OH− ions (HT-OH) were studied for the subsequent use as the precursors of supports for platinum catalysts. It was found that
the nature of an interlayer anion in the composition of an aluminum-magnesium layered hydroxide is an important factor affecting
both the formation of the oxide support and its texture characteristics. The replacement of the interlayer CO32− anion by OH− resulted in changes in the structural parameters of the initial double hydroxide: a decrease in the interlayer distance with
the retention of the Mg/Al ratio and an increase in the imperfection of the layered material. X-ray diffraction studies in
the temperature range of 30–900°C showed that HT-OH is characterized by the ability to form low-temperature spinel at 375°C.
As a result, two types of aluminum-magnesium oxide supports, which were characterized by different pore space organizations
at the same Mg: Al ratio, were obtained from the given layered hydroxides. 相似文献