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1.
Sara J. Palmer J. Kristóf Veronika Vágvölgyi Erzsébet Horváth R. L. Frost 《Journal of Thermal Analysis and Calorimetry》2009,96(2):449-454
The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. The thermal decomposition of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer has been studied using controlled rate thermal analysis technology. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 10.9 and 11.1 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. Calculations show dehydration with a total loss of 7 moles of water proving the formula of hexacyanoferrate(II) intercalated hydrotalcite is Mg6Al2(OH)16[Fe(CN)6]0.5·7H2O and 9.0 moles for the hexacyanoferrate(III) intercalated hydrotalcite with the formula of Mg6Al2(OH)16[Fe(CN)6]0.66·9H2O. CRTA technology indicates the partial collapse of the dehydrated mineral. Dehydroxylation combined with CN unit loss occurs in two isothermal stages at 377 and 390°C for the hexacyanoferrate(III) and in a single isothermal process at 374°C for the hexacyanoferrate(III) hydrotalcite. 相似文献
2.
Sara J. Palmer Laure M. Grand Ray L. Frost 《Journal of Thermal Analysis and Calorimetry》2011,103(2):473-478
The aluminate hydrotalcites are proposed to have either of the following formulas: Mg4Al2(OH)12(CO3
2−)·xH2O or Mg4Al2(OH)12(CO3
2−, SO4
2−)·xH2O. A pure hydrotalcite phase forms when magnesium chloride and aluminate solutions are mixed at a 1:1 volumetric ratio at
pH 14. The synthesis of the aluminate hydrotalcites using seawater results in the formation of an impurity phase bayerite.
Two decomposition steps have been identified for the aluminate hydrotalcites: (1) removal of interlayer water (230 °C) and
(2) simultaneous dehydroxylation and decarbonation (330 °C). The dehydration of bayerite was observed at 250 °C. X-ray diffraction
techniques determined that the synthesis of aluminate hydrotalcite with seawater and a volumetric ratio of 4.5 results in
very disordered structures. This was shown by a reduction in the mass loss associated with the removal of interlayer water
due to the reduction of interlayer sites caused by the misalignment of the metal-hydroxyl layers. 相似文献
3.
Ray L. Frost Sara J. Palmer Laure-Marie Grand 《Journal of Thermal Analysis and Calorimetry》2010,101(3):859-863
Insight into the unique structure of layered double hydroxides (LDHs) has been obtained using a combination of X-ray diffraction and thermal analysis. Indium containing hydrotalcites of formula Mg4In2(CO3)(OH)12·4H2O (2:1 In-LDH) through to Mg8In2(CO3)(OH)18·4H2O (4:1 In-LDH) with variation in the Mg:In ratio have been successfully synthesised. The d(003) spacing varied from 7.83 Å for the 2:1 LDH to 8.15 Å for the 3:1 indium containing LDH. Distinct mass loss steps attributed to dehydration, dehydroxylation and decarbonation are observed for the indium containing hydrotalcite. Dehydration occurs over the temperature range ambient to 205 °C. Dehydroxylation takes place in a series of steps over the 238–277 °C temperature range. Decarbonation occurs between 763 and 795 °C. The dehydroxylation and decarbonation steps depend upon the Mg:In ratio. The formation of indium containing hydrotalcites and their thermal activation provides a method for the synthesis of indium oxide-based catalysts. 相似文献
4.
R. L. Frost A. W. Musumeci M. O. Adebajo W. Martens 《Journal of Thermal Analysis and Calorimetry》2007,89(1):95-99
Hydrotalcites of formula Mg6A12(OH)16(PO4)·4H2O formed by intercalation with the phosphate anion as a function of pH show variation in the d-spacing attributed to the size of the hydrated anion in the interlayer. The value changes from 11.91 Å for pH 9.3, to 7.88 Å at pH 12.5. No crystalline hydrotalcites with phosphate in the interlayer were formed at pH 9.3. Thermal decomposition identifies three steps namely dehydration, dehydroxylation and some loss of carbonate during the thermal treatment. The addition of a thermally activated ZnAl-HT to a phosphate solution resulted in the uptake of the phosphate and the reformation of the hydrotalcite. The technology has the potential for water purification through anion removal. 相似文献
5.
Sara J. Palmer R. L. Frost T. Nguyen 《Journal of Thermal Analysis and Calorimetry》2008,92(3):879-886
Hydrotalcites containing carbonate, vanadate and molybdate were prepared by coprecipitation. The resulting materials were
characterized by XRD, and TG/DTA to determine the stability of the hydrotalcites synthesized. The thermal decomposition of
carbonate hydrotalcites consist of two decomposition steps between 300 and 400°C, attributed to the simultaneous dehydroxylation
and decarbonation of the hydrotalcite lattice. Water loss ascribed to dehydroxylation occurs in two decomposition steps, where
the first step is due to the partial dehydroxylation of the lattice, while the second step is due to the loss of water interacting
with the interlayer anions. Dehydroxylation results in the collapse of the hydrotalcite structure to that of its corresponding
metal oxides, including MgO, Al2O3, MgAl2O4, NaMg4(VO4)3 and Na2Mg4(MoO4)5. The presence of oxy-anions proved to be beneficial in the stability of the hydrotalcite structure, shown by the delay in
dehydroxylation of oxy-anion containing hydrotalcites compared to the carbonate hydrotalcite. This is due to the substantial
amount of hydroxyl groups involved in a network of hydrogen bonds involving the intercalated anions. Therefore, the stability
of the hydrotalcite structure appears to be dependent on the type of anion present in the interlayer. The order of thermal
stability for the synthesized hydrotalcites in this study is Syn-HT-V>Syn-HT-Mo> Syn-HT-CO3-V>Syn-HT-CO3-Mo>Syn-HT-CO3. Carbonate containing hydrotalcites prove to be less stable than oxy-anion only hydrotalcites. 相似文献
6.
A combination of high resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer has been used to study the thermal decomposition of synthetic hydrotalcites reevesite (Ni6Fe2(CO3)(OH)16·4H2O) and pyroaurite (Mg6Fe2(SO4,CO3)(OH)16·4H2O) and the cationic mixtures of the two minerals. XRD patterns show the hydrotalcites are layered structures with interspacing distances of around 8.0. Å. A linear relationship is observed for the d(001) spacing as Ni is replaced by Mg in the progression from reevesite to pyroaurite. The significance of this result means the interlayer spacing in these hydrotalcites is cation dependent. High resolution thermal analysis shows the decomposition takes place in 3 steps. A mechanism for the thermal decomposition is proposed based upon the loss of water, hydroxyl units, oxygen and carbon dioxide. 相似文献
7.
Frederick L. Theiss Sara J. Palmer Godwin A. Ayoko Ray L. Frost 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1123-1128
The removal of the sulfate anion from water using synthetic hydrotalcite (Mg/Al LDH) was investigated using powder X-ray diffraction
(XRD) and thermogravimetric analysis (TG). Synthetic hydrotalcite Mg6Al2(OH)16(CO3)·4H2O was prepared by the co-precipitation method from aluminum and magnesium chloride salts. The synthetic hydrotalcite was thermally
activated to a maximum temperature of 380 °C. Samples of thermally activated hydrotalcite where then treated with aliquots
of 1000 ppm sulfate solution. The resulting products where dried and characterized by XRD and TG. Powder XRD revealed that
hydrotalcite had been successfully prepared and that the product obtained after treatment with sulfate solution also conformed
well to the reference pattern of hydrotalcite. The d(003) spacing of all samples was found to be within the acceptable region for a LDH structure. TG revealed all products underwent
a similar decomposition to that of hydrotalcite. It was possible to propose a reasonable mechanism for the thermal decomposition
of a sulfate containing Mg/Al LDH. The similarities in the results may indicate that the reformed hydrotalcite may contain
carbonate anion as well as sulfate. Further investigation is required to confirm this. 相似文献
8.
N. Voyer A. Soisnard Sara J. Palmer W. N. Martens R. L. Frost 《Journal of Thermal Analysis and Calorimetry》2009,96(2):481-485
Zn-Al hydrotalcites and Cu-Al hydrotalcites were synthesised by coprecipitation method and analysed by X-ray diffraction (XRD)
and thermal analysis coupled with mass spectroscopy. These methods provide a measure of the thermal stability of the hydrotalcite.
The XRD patterns demonstrate similar patterns to that of the reference patterns but present impurities attributed to Zn(OH)2 and Cu(OH)2. The analysis shows that the d003 peak for the Zn-Al hydrotalcite gives a spacing in the interlayer of 7.59 ? and the estimation
of the particle size by using the Debye-Scherrer equation and the width of the d003 peak is 590 ?. In the case of the Cu-Al
hydrotalcite, the d003 spacing is 7.57 ? and the size of the diffracting particles was determined to be 225 ?.
The thermal decomposition steps can be broken down into 4 sections for both of these hydrotalcites. The first step decomposition
below 100°C is caused by the dehydration of some water absorbed. The second stage shows two major steps attributed to the
dehydroxylation of the hydrotalcite. In the next stage, the gas CO2 is liberated over a temperature range of 150°C. The last reactions occur over 400°C and involved CO2 evolution in the decomposition of the compounds produced during the dehydroxylation of the hydrotalcite. 相似文献
9.
Ray L. Frost Henry J. Spratt Sara J. Palmer 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,72(5):984-988
Near-infrared (NIR), X-ray diffraction (XRD) and infrared (IR) spectroscopy have been applied to hydrotalcites of the formula Mg6 (Fe,Al)2(OH)16(CO3)·4H2O formed by intercalation with the carbonate anion as a function of divalent/trivalent cationic ratio. Such hydrotalcites were found to show variation in the d-spacing attributed to the size of the cation. In the IR (1750–4000 cm−1), the position of all bands except those at approximately 3060 cm−1 shift to higher wavenumbers as the cation ratio increases. Conversely, at wavenumbers below 1000 cm−1, the bands shift to lower wavenumbers as the cation ratio increases. A water bending mode at higher wavenumbers was also observed which indicates that the water is strongly hydrogen bonded. In the NIR spectrum between 8000 and 12,000 cm−1, there is a broad feature which is attributed to electronic bands of the ferrous ion and low intensity sharp bands due to overtones of the OH stretching vibrations. It is also apparent from this region that Fe2+ substitutes for Mg2+. The intensity of bands at 7750 and 5200 cm−1 increases as the cation ratio increases in the NIR spectrum. Hydrotalcites with a magnesium amount 3 and 4 times greater than that of aluminium and iron combined, in the lower wavenumber region of the NIR spectrum, have very similar spectral profiles. This work has shown that hydrotalcites with different divalent/trivalent ratios can be synthesised and characterised by infrared spectroscopy. 相似文献
10.
Laure-Marie Grand Sara J. Palmer Ray L. Frost 《Journal of Thermal Analysis and Calorimetry》2010,100(3):981-985
The hydrotalcite based upon manganese known as charmarite Mn4Al2(OH)12CO3·3H2O has been synthesised with different Mn/Al ratios from 4:1 to 2:1. Impurities of manganese oxide, rhodochrosite and bayerite at low concentrations were also produced during the synthesis. The thermal stability of charmarite was investigated using thermogravimetry. The manganese hydrotalcite decomposed in stages with mass loss steps at 211, 305 and 793 °C. The product of the thermal decomposition was amorphous material mixed with manganese oxide. A comparison is made with the thermal decomposition of the Mg/Al hydrotalcite. It is concluded that the synthetic charmarite is slightly less stable than hydrotalcite. 相似文献
11.
The thermal decomposition of natural iowaite of formula Mg6Fe2(Cl,(CO3)0.5)(OH)16·4H2O was studied by using a combination of thermogravimetry and evolved gas mass spectrometry. Thermal decomposition occurs over
a number of mass loss steps at 60°C attributed to dehydration, 266 and 308°C assigned to dehydroxylation of ferric ions, at
551°C attributed to decarbonation and dehydroxylation, and 644, 703 and 761°C attributed to further dehydroxylation. The mass
spectrum of carbon dioxide exhibits a maximum at 523°C. The use of TG coupled to MS shows the complexity of the thermal decomposition
of iowaite.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
R. L. Frost A. W. Musumeci J. Theo Kloprogge M. L. Weier M. O. Adebajo W. Martens 《Journal of Thermal Analysis and Calorimetry》2006,86(1):205-209
The thermal decompositions of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer have been studied using thermogravimetry combined with mass spectrometry. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 11.1 and 10.9 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. XRD was also used to determine the products of the thermal decomposition. For the hydrotalcite decomposition the products were MgO, Fe2O3 and a spinel MgAl2O4. Dehydration and dehydroxylation take place in three steps each and the loss of cyanide ions in two steps. 相似文献
13.
Frost R. L. Martens W. Ding Z. Kloprogge J. T. 《Journal of Thermal Analysis and Calorimetry》2003,71(2):429-438
A combination of DSC and high resolution DTG coupled to a gas evolution mass spectrometer has been used to study the thermal
properties of a series of Mg/Zn hydrotalcites of formulae MgxZn6-xAl2(OH)16(CO3) ·4H2O where x varied from 6 to 0. The effect of increased Zn composition results in the decrease of the endotherms and mass loss steps
to lower temperatures. Evolved gas mass spectrometry shows that water is lost in a number of steps. The interlayer carbonate
anion is lost simultaneously with hydroxyl units.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
R. L. Frost W. N. Martens Kristy L. Erickson 《Journal of Thermal Analysis and Calorimetry》2005,82(3):603-608
Summary A combination of thermogravimetry and hot stage Raman spectroscopy has been used to study the thermal decomposition of the
synthesised zinc substituted takovite Zn6Al2CO3(OH)16·4H2O. Thermogravimetry reveals seven mass loss steps at 52, 135, 174, 237, 265, 590 and ~780°C. MS shows that the first two mass
loss steps are due to dehydration, the next two to dehydroxylation and the mass loss step at 265°C to combined dehydroxylation
and decarbonation. The two higher mass loss steps are attributed to decarbonation. Raman spectra of the hydroxyl stretching
region over the 25 to 200°C temperature range, enable identification of bands attributed to water stretching vibrations, MOH
stretching modes and strongly hydrogen bonded CO32--water bands. CO32- symmetric stretching modes are observed at 1077 and 1060 cm-1. One possible model is that the band at 1077 cm-1is ascribed to the CO32- units bonded to one OH unit and the band at 1092 cm-1is due to the CO32- units bonded to two OH units from the Zn-takovite surface. Thermogravimetric analysis when combined with hot stage Raman spectroscopy
forms a very powerful technique for the study of the thermal decomposition of minerals such as hydrotalcites.</o:p> 相似文献
15.
By means of single-crystal X-ray diffraction of nondecomposed, partly, and fully decomposed artinite (Mg2(OH)2CO3·3H2O), it has been shown that the intermediate product of decomposition, Mg2(OH)2CO3, is not amorphous. Its unit cell has been determined and a model of its structure has been deduced, which can account for both the lattice parameters and the relative orientations of the unit cells of artinite, intermediate product, and magnesium oxide found experimentally. The decomposition reaction can be described as a topotactic process with conservation of chains in both and additional conservation of layers in the second step. 相似文献
16.
Methods of preparation of novel composites of poly(ϵ‐caprolactone) and a modified Mg/Al hydrotalcite
Loredana Tammaro Mariarosaria Tortora Vittoria Vittoria Umberto Costantino Fabio Marmottini 《Journal of polymer science. Part A, Polymer chemistry》2005,43(11):2281-2290
12‐Hydroxydodecanoate (HD) anions were intercalated, via an ion‐exchange procedure, onto a Mg/Al hydrotalcite‐like compound with the formula [Mg0.65Al0.35(OH)2](NO3)0.35·0.56H2O. The obtained intercalate, characterized by chemical and thermal analyses, X‐ray powder diffraction, and Fourier transform infrared spectroscopy, had the formula [Mg0.65Al0.35(OH)2](NO3)0.08(HD)0.28·0.56H2O and an interlayer distance of 2.27 nm. Structural considerations indicated that the charge‐balancing HO? (CH2)11? COO? anions were accommodated in the interlayer region as a monofilm of partially interdigitated alkyl chains in a trans planar conformation and bearing the alcoholic group. The organically modified hydrotalcite was used to prepare novel composites based on poly(?‐caprolactone) (PCL) with different procedures: (1) solvent casting, (2) ring‐opening polymerization of ?‐caprolactone, and (3) blending of precursors consisting of a PCL intercalated oligomer with a high‐molecular‐weight PCL. Microcomposites were obtained by the solvent casting of a mixture of a high‐molecular‐weight PCL and the modified hydrotalcite. The ring‐opening polymerization of ?‐caprolactone initiated by the ? OH groups of the alkyl chains intercalated in the hydrotalcite led to hybrid materials in which a low‐molecular‐weight PCL was in part intercalated into the modified hydrotalcite. Nanocomposites containing exfoliated hydrotalcite were obtained through the mixing, in different weight ratios, of hybrids consisting of PCL oligomers and modified hydrotalcite with a commercial high‐molecular‐weight PCL. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2281–2290, 2005 相似文献
17.
Fabrication of mesoporous ZnO nanosheets from precursor templates grown in aqueous solutions 总被引:1,自引:0,他引:1
Keita Kakiuchi Eiji Hosono Toshio Kimura Hiroaki Imai Shinobu Fujihara 《Journal of Sol-Gel Science and Technology》2006,39(1):63-72
Mesoporous ZnO nanosheets were successfully prepared by pyrolytic transformation of zinc carbonate hydroxide hydrate, Zn4CO3(OH)6·H2O. The nanosheets were initially formed as assemblies on glass substrates during chemical bath deposition (CBD) in aqueous
solutions of urea and zinc acetate dihydrate, zinc chloride, zinc nitrate hexahydrate, or zinc sulfate heptahydrate at 80°C.
It was key to induce heterogeneous nucleation of Zn4CO3(OH)6·H2O by promoting a gradual hydrolysis reaction of urea and controlling the degree of supersaturation of zinc hydroxide species.
Morphology of Zn4CO3(OH)6·H2O was largely influenced by the anions present in the CBD solutions. The Zn4CO3(OH)6·H2O nanosheets were transformed into wurtzite ZnO by heating at 300°C in air without losing the microstructural feature. 相似文献
18.
O. N. Krasnobaeva I. P. Belomestnykh T. A. Nosova T. A. Elizarova G. V. Isagulyants V. P. Danilov 《Russian Journal of Inorganic Chemistry》2013,58(6):644-649
A method was developed for introducing gallium into Mg-Al hydrotalcites—precursors of oxide catalysts for oxidative dehydrogenation of alkanes. Samples of oxide catalysts were synthesized that contained gallium oxide and also oxides of magnesium, aluminum, chromium, vanadium, molybdenum, and niobium in various combinations. The catalytic properties of the produced catalysts were studied in the oxidative dehydrogenation of ethane, propane, isobutane, and hexane. It was established that the addition of gallium to catalysts increases the ethylene and propylene yields in the oxidative dehydrogenation of ethane and propane. New hydroxo salts with a layered structure of the hydrotalcite type were synthesized: ternary magnesium gallium aluminum hydroxonitrate of variable composition [Al1 ? n Ga n Mg m (OH)3 + 2m ? 1][NO3 · nH2O] and quaternary magnesium gallium chromium aluminum hydroxonitrate of the composition [AlGaCrMg1.8(OH)11.6][NO3 · nH2O]; these salts were found to be isostructural. 相似文献
19.
O. N. Krasnobaeva I. P. Belomestnykh V. M. Kogan T. A. Nosova V. M. Skorikov T. A. Elizarova V. P. Danilov 《Russian Journal of Inorganic Chemistry》2014,59(7):693-698
For the first time, a method was developed for introducing indium into Mg-Al hydrotalcites—precursors of oxide catalysts for oxidative dehydrogenation of alkanes. Samples of oxide catalysts were synthesized that contained indium oxide and also oxides of magnesium, aluminum, chromium, vanadium, molybdenum, and niobium in various combinations. The catalytic properties of the produced catalysts were studied in the oxidative dehydrogenation of ethane, propane, and isobutane. It was established that the introduction of indium into catalysts increases the selectivity and the yields of desired products. New hydroxo salts with a layered structure of the hydrotalcite type were synthesized: [Al1 ? n In n Mg m (OH)3 + 2m ? 1][(NO3) · nH2O] and quaternary magnesium indium chromium aluminum hydroxonitrate of the composition [Al0.5In0.5Cr0.5Mg2.5(OH)8.5][(NO3) · nH2O]; these salts were found to be isostructural. The obtained compounds were studied as catalyst precursors. 相似文献
20.
Ray L. Frost Anthony W. Musumeci Thor Bostrom Moses O. Adebajo Matt L. Weier Wayde Martens 《Thermochimica Acta》2005,429(2):179-187
The thermal decomposition of hydrotalcites with chromate, molybdate and sulphate in the interlayer has been studied using thermogravimetric analysis coupled to a mass spectrometer measuring the gas evolution. X-ray diffraction shows the hydrotalcites have a d(0 0 3) spacing of 7.98 Å with very small differences in the d-spacing between the three hydrotalcites. XRD was also used to determine the products of the thermal decomposition. For the sulphate-hydrotalcite decomposition the products were MgO and a spinel MgAl2O4, for the chromate interlayered hydrotalcite MgO, Cr2O3 and spinel. For the molybdate interlayered hydrotalcite the products were MgO, spinel and MgMoO4. EDX analyses enabled the formula of the hydrotalcites to be determined. Two processes are observed in the thermal decomposition namely dehydration and dehydroxylation and for the case of the sulphate interlayered hydrotalcite, a third process is the loss of sulphate. Both the dehydration and dehydroxylation take place in three steps each for each of the hydrotalcites. 相似文献