A. De Roy

Ion exchange of different phosphate ions into the zinc-aluminium-chloride layered double hydroxide

A well-crystallised [Zn–Al–Cl] layered double hydroxide was prepared by coprecipitation at constant pH. The chloride ion of this solid was then exchanged in solution with a series of phosphate ions having different sizes and charges; namely, PO3−, H2PO4−, HPO42−, PO43−, P2O74− and P3O105−. Powder X-ray diffraction and Fourier transform infrared spectroscopy have allowed a correlation to be made of the structural features of the precursor and the exchanged materials.

Structural approach and conductivity of lamellar hydroxides Zn2Cr(OH)6X.nH2O (x = anion) by xanes, exafs and X-ray diffraction

Abstract Powder diffractograms of Zn 2 Cr(OH) 6 X.nH 2 O (X = anion) are characteristic of lamellar and ill-organized materials. A structural approach has been investigated using XANES and EXAFS analysis of the K edge spectra of Cr, Zn and Br. Results of X-ray absorption analysis indicates an octahedral coordination for Cr and Zn and a delocalisation of X anion. At 293 K we measured conductivities in the range 3.10 −3 to 2.10 −6 Ω −1 . cm −1 . The fact that these materials can be obtained as strongly oriented thick layers suggests possible applications in microionic technology, particularly in the development of hydrogen sensors.

Evolution of protonic conduction in some synthetic anionic clays

Abstract The conductivity of some lamellar double hydroxides (LDHs) of general formula: [MII(1−x)MIIIx(OH)2]x+ [Xx/m ·nH2O]x-( x≈ 1 3 ; M= Cr, Cu, Zn ; X m- = Cl - , Br - , NO 3 - , 1 2 CO 3 2- , 1 2 SO 4 2- ) is studied by the complex impedances method. The measurements are performed in an airtight cell. The samples are previously equilibrated with a 50%RH atmosphere. The results of conductivity measurements show clearly that the mobility of charge carries depends on both the nature of the intercalated anions and the hydroxylated framework composition. The protonic nature of the conduction process is controlled by potentiometric measurements at room-temperature in an electrochemical gas cell.

Chloride-hydrogenophosphate ion exchange into the zinc–aluminium–chloride layered double hydroxide

The ion exchange of chloride by hydrogenophosphate in the [Zn–Al–Cl] layered double hydroxide was investigated by using X-ray diffraction and infrared spectroscopy. The effects of [Zn2+/[AI3+] ratio in [Zn–Al–Cl], anion concentration in the solution, aging time and temperature of the solution on the ion exchange were studied. The best sample in terms of crystallinity and extent of ion exchange was obtained by carrying out the exchange reaction at 25°C in a 0.01 M HPO42− solution at pH 8 with at least 5 h of aging time. A sample prepared under these conditions was further characterized by X-ray microanalysis.

[Cu-Cr] Layered Double Hydroxides Pillared by CrO42-and Cr2O72-Oxometalates

Abstract The grafting of CrC4 2- and Cr2O7 2- oxometalates has been evidenced on [Cu-Cr] layered double hydroxides by a PXRD study under moderate heating and by Infrared spectroscopy.

Preparation of a well-ordered layered nanocomposite from zinc–aluminum–chloride layered double hydroxide and hydrogenophosphate by ion exchange

The ion exchange of hydrogenophosphate ion in Zn–Al–chloride layered double hydroxides was investigated. The chloride precursors prepared by coprecipitation at pH 10 preserved their lamellar structure following ion exchange. It was found that the aging time is important in controlling the crystallization of the phosphate-exchanged compounds; long aging times of more than 8 h lead to poorly crystallized phases. The grafting of the anion onto hydroxylated sheets by moderate thermal treatment was confirmed by a combination of several techniques, including powder X-ray diffraction (XRD), infrared (IR) spectroscopy, and thermal analyses.

A new two-dimensional approach to molecular-based magnets: Nickel(II)-Chromium(III) double hydroxide systems

Abstract We present a new approach to get two-dimensional materials with tunable T c temperatures obtained from molecular precursors by soft, low-temperature synthetic methods. Experimental results are presented about the synthesis and the magnetic properties of two series of materials: two-dimensional arrays derived from Ni(OH) 2 . Ferrimagnetic materials with rather high Curie temperatures were obtained. We propose perspectives in the synthesis of materials with higher T c .

Evolution of protonic conduction in [Zn–Al–Cl] Lamellar Double Hydroxide phases with temperature and trivalent metal content

Abstract The conduction properties of a series of [Zn–Al–Cl] Lamellar Double Hydroxides (LDHs) with different amounts of trivalent metal are studied by impedance spectroscopy. The structural evolution of these samples is characterized by Rietveld analysis on powder X-ray diffraction diagrams. The conduction properties appear clearly related to the structural evolution of the interlayer domains.

Protonic conductivity of hydrotalcite-type compound thick films: Application to a humidity sensor

Abstract A new type of realization of the hydrotalcite-type lamellar protonic superconductor Zn 2 Al(OH) 6 Cl· n H 2 O (henceforth called [Zn-Al-Cl] is described, using an original ink composed of a concentrated aqueous suspension of [Zn-Al-Cl] which, when applied by the screen-printing technique, permits to elaborate very satisfactory deposits. X-ray patterns show a high orientation of the (001) reticular planes in a direction parallel to the substrate; this must produce a strong anisotropy of the material conductivity. The electrical properties related to the hydration of the [Zn-Al-Cl] compound are such as to permit the fabrication of a humidity sensor; two types of sensor are realized, one working with direct current (dc sensor), the other with alternating current (ac sensor). The performance of each device is studied by means of specific experiment. Results are interpreted and compared.

Nuclear magnetic resonance analysis of protons in the hydrotalcite type compound Zn23Al13 (OH)2Cl13·n(H2O)

Abstract In the lamellar compound Zn 2 3 Al 1 3 (OH) 2 Cl 1 3 ·n(H 2 O) the 1H NMR line shapes as a function of the hydration state and temperature clearly reveal the existence of two kinds of protons characterized by very different mobilities. The relaxation times measured as a function of temperature and frequency also suggest an interpretation of the proton motion in accordance with structural and conductivity data.