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Journal ArticleDOI

Synthesis and physicochemical properties of cobalt aluminium hydrotalcites

01 Mar 1995-Journal of Materials Science (Kluwer Academic Publishers-Plenum Publishers)-Vol. 30, Iss: 6, pp 1462-1468
TL;DR: In this article, a coprecipitation method was used to obtain cobalt aluminium hydrotalcites with different compositions under low supersaturation conditions, which were characterized by X-ray diffraction (XRD), infrared absorption (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and surface area measurements.
Abstract: Cobalt aluminium hydrotalcites with different compositions were prepared by a coprecipitation method under low supersaturation conditions. The compounds were characterized by X-ray diffraction (XRD), infrared absorption (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and BET surface area measurements. XRD and IR studies revealed that all the compounds are single-phase crystallized under a hydrotalcite-like network. Hydrothermal treatments given to the aged sample increased the crystallinity of the samples. TG studies showed two stages of weight loss, the first due to the removal of interlayer water and the second ascribed to the removal of water molecules from the brucite sheet and CO2 from the interlayer carbonate anion, whose transition temperature depends on the Co/Al atomic ratio. Thermal calcination of these materials results in the formation of high surface area non-stoichiometric spinel phase whose crystallinity increases with increase in the calcination temperature attributed to the sintering of the particles.
Citations
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Journal ArticleDOI
TL;DR: In this paper, a systematic XRD/FTIR/CHN/ICP investigation for structural transformation of hydrotalcite-like compounds Mg1-xAlx(OH)2(NO3)x·nH2O as a continuous function of nitrate anions (x = 0.18−0.34).
Abstract: We report here a systematic XRD/FTIR/CHN/ICP investigation for structural transformation of hydrotalcite-like compounds Mg1-xAlx(OH)2(NO3)x·nH2O as a continuous function of nitrate anions (x = 0.18−0.34). With seven finely divided steps in x value, a clear relationship between basal spacing and nitrate anion content (and thus trivalent cation content) has been found. In particular, we have been able to “arrest” an intermediate hydrotalcite-like phase that situates at the midpoint of an abrupt structural transformation. Unlike that of normal hydrotalcites, the relationship revealed in our nitrated Mg1-xAlx(OH)2(NO3)x·nH2O samples is much more complicated. While the lattice parameter a decreases with increase of nitrate content, the parameter c decreases slightly over x = 0.18−0.22, rises abruptly with a further increase of nitrate anions at x = 0.26, and then reaches maximums at x = 0.31−0.34. The compound at x = 0.26 also shows a sharp decrease in mean crystallite dimension. The abrupt structural change i...

294 citations

Journal ArticleDOI
TL;DR: In this article, a review examines sorption processes on mineral surfaces for nine trace elements (Cr, Co, Ni, Cu, Zn, Sr, Cd, Hg, Pb), focusing on the results of modern x-ray spectroscopic studies.
Abstract: The partitioning (or sorption) of trace elements from aqueous solutions onto mineral surfaces and natural organic matter (NOM) has played a major role in determining the trace element content of natural waters. This review examines sorption processes on mineral surfaces for nine trace elements (Cr, Co, Ni, Cu, Zn, Sr, Cd, Hg, Pb), focusing on the results of modern x-ray spectroscopic studies. Such studies provide unique information on the structure and composition of sorption products, including their mode of attachment to mineral surfaces or functional groups in NOM under in situ conditions (i.e., with aqueous solution present at 25°C). The types of chemical reactions (acid-base, ligand exchange, redox, dissolution/reprecipitation) that can occur at mineral-aqueous solution interfaces are also reviewed, and some of the factors that affect the reactivity of mineral surfaces are discussed, including changes in the geometric and electronic structures of mineral surfaces when they first react with aqueous so...

257 citations

Journal ArticleDOI
TL;DR: In this article, a simplified structural model for the decomposition of hydrotalcite is presented, and the presence of oxidizable Co2+ cations and the diffusion of Co3+ to the octahedral sheets and the stability of the solid solution of Co-spinels formed are identified as key factors in the low thermal stability of a hydrotarcite precursor in air.
Abstract: High temperature X-ray diffraction (HT-XRD), thermal analysis (TGA-DTA), mass spectrometry (MS), in situ Fourier transform infrared (FT-IR) spectroscopy, and in situ Raman spectroscopy have been used to characterize the thermal decomposition of Co–Al hydrotalcite, [Co6Al2(OH)16](CO3)·4H2O, in air and inert atmospheres. In the first decomposition step, water is removed from the structure, a process which is complete at 150–200 °C. This transition is followed by dehydroxylation and decarbonation, as well as carbonate reorganization in the interlayer space. These processes require higher temperatures under inert atmospheres than in air. The transition temperatures also depend on the nature of the technique applied (static vs. dynamic operation). An intermediate metastable mixture of phases is identified, which contains the dehydrated layered structure and an emerging spinel-like mixed oxide phase. This phase is formed in the region of 150–175 °C in air and was not observed under inert atmospheres. Dehydroxylation leads to the collapse of the hydrotalcite phase and is complete at 250–300 (air) and 350–400 °C (inert gas). Carbonate removal is coupled with the dehydroxylation process, although removal of carbonate groups is only complete at 450 (air) and 600 °C (inert gas). Thermal treatment in air finally leads to a solid solution of cobalt spinels [Co(Co,Al)2O4]. Mixtures of CoO and CoAl2O4 are formed upon treatment under inert atmospheres. Based on the analytical results, a simplified structural model for the decomposition process is presented. The presence of oxidizable Co2+ cations in the octahedral sheets and the diffusion of Co3+ to the interlayer space in the dehydrated layered structure, and the stability of the solid solution of Co-spinels formed are identified as key factors in the low thermal stability of the hydrotalcite precursor in air.

211 citations

Book ChapterDOI
TL;DR: The layered double hydroxides (LDH) have many physical and chemical properties that are surprisingly similar to those of clay minerals, such as variable layer charge density, ion-exchange properties, reactive interlayer space, swelling in water, and rheological and colloidal properties.
Abstract: Publisher Summary This chapter describes layered double hydroxides. Among the group of minerals referred to as nonsilicate oxides and hydroxides, the layered double hydroxides (LDH) have many physical and chemical properties that are surprisingly similar to those of clay minerals. Their layered structure, wide chemical compositions (because of variable isomorphous substitution of metallic cations), variable layer charge density, ion-exchange properties, reactive interlayer space, swelling in water, and rheological and colloidal properties make LDH clay-like. However, because of their anion-exchange properties, LDH were referred to as “anionic clays.” Most metals in the first transition series can be incorporated into the hydroxyl sheet of the hydrotalcite-like structure. Thus, the formation of mixed metal-Al secondary precipitates may be a general reaction mechanism for transition metal adsorption to clay minerals.

146 citations

Journal ArticleDOI
TL;DR: In this article, the physicochemical properties of ZnAlAn-like compounds were studied using powder X-ray diffraction (PXRD), infrared (IR) and laser Raman (LR) spectra, thermogravimetry (TG), differential scanning calorimetry, evolved gas analysis (EGA), 27Al MAS NMR, and pore-size determination.
Abstract: Zinc–aluminium hydrotalcite-like compounds (ZnAlAn-–HT) with a Zn/Al atomic ratio 2.0 and An- = CO2-3, Cl-, NO-3 and SO2-4, were synthesized by coprecipitation under low supersaturation. Their physicochemical properties were studied using powder X-ray diffraction (PXRD), infrared (IR) and laser Raman (LR) spectra, thermogravimetry (TG), differential scanning calorimetry (DSC), evolved gas analysis (EGA), 27Al MAS NMR, BET surface area and pore-size determination. The PXRD of the synthesized samples showed that the crystallinity was affected by the nature of the anions present in the interlayer space. The IR and LR studies revealed that except the NO-3 ion, the symmetry of these interlayer anions was reduced upon intercalation. The TG, DSC and EGA results showed two or three stages of weight loss corresponding to the removal of the interlayer water, structural water and the anion, respectively. The activation energy, Ea, for the decomposition process was found to decrease in the order ZnAlCO3–HT>ZnAlSO4–HT>ZnAlCl–HT>ZnAlNO3–HT. Formation of a pentacoordinated Al (AlV) in addition to the octahedral (AlVI) and tetrahedral Al (AlIV) was the special feature noticed in the 27Al MAS NMR of the calcined samples. Thermal calcination around 500 °C resulted in the formation of non-stoichiometric ZnO whose crystallinity decreased in the order ZnAlNO3–CHT>ZnAlCl–CHT>ZnAlSO4–CHT>ZnAlCO3–HT while their extent of solid solubility was found to be the reverse. The crystallinity of the calcined samples was also correlated with surface area and pore-size determination.

132 citations

References
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Book
01 Jan 2001

19,319 citations


"Synthesis and physicochemical prope..." refers methods in this paper

  • ...The particle sizes of these materials were calculated employing the X-ray linebroadening technique using the Debye-Scherrer equation, t = 0.9 )~/13cos 0, where t is the particle thickness, )~ is the wavelength of the radiation used, 13 is full width at half maximum (tad) and 0 is the Bragg diffraction angle [ 20 ], and the values are given in Table II. It is clearly evident from this table that the particle size of the hydrothermally treated ......

    [...]

Book
01 Jan 1956
TL;DR: In this article, the authors present a chemical analysis of X-ray diffraction by Xray Spectrometry and phase-diagram Determination of single crystal structures and phase diagrams.
Abstract: 1. Properties of X-rays. 2. Geometry of Crystals. 3. Diffraction I: Directions of Diffracted Beams. 4. Diffraction II: Intensities of Diffracted Beams. 5. Diffraction III: Non-Ideal Samples. 6. Laure Photographs. 7. Powder Photographs. 8. Diffractometer and Spectrometer. 9. Orientation and Quality of Single Crystals. 10. Structure of Polycrystalline Aggregates. 11. Determination of Crystal Structure. 12. Precise Parameter Measurements. 13. Phase-Diagram Determination. 14. Order-Disorder Transformation. 15. Chemical Analysis of X-ray Diffraction. 16. Chemical Analysis by X-ray Spectrometry. 17. Measurements of Residual Stress. 18. Polymers. 19. Small Angle Scatters. 20. Transmission Electron Microscope.

17,428 citations

Journal ArticleDOI
TL;DR: Ion exchange isotherms between hydrotalcite-like (HT) ions were determined and the spacing and width of the 003 reflection were measured as a function of HT composition as mentioned in this paper.
Abstract: Ion-exchange isotherms between hydrotalcite-like (HT) of the NO3-, CI-, and SO4- forms and F , 0% Br , I , OH-, SO42-, CO3 z-, and Naphthol Yellow S (NYS 2-) ions were determined, and the spacing and the width of the 003 reflection were measured as a function of HT composition The ion-exchange equilibrium constant for HTs of monovalent anions are in the sequence OH- > F > Cl > Br- > NO3- > I , those for divalent anions are in the sequence CO3 ~- > NYS z- > SO42- The ion-exchange equilibrium constants tend to increase as the diameters of the anions decrease, and the crystallite size in the 001 direction tends to increase with anions having higher selectivity The OH-form of HT has the smallest basal spacing and the largest crystallite size in the 001 direction

1,522 citations