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2024-11-23 17:57

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Conference: Bucharest University Faculty of Physics 2009 Meeting

Section: Optics, Spectroscopy, Plasma and Lasers

Title:

Spectroscopic characterization of some layered materials of LDH-type. Analysis of the interstitial anions

Authors:

L. Frunza(1), N. Gheorghe(1,2), F. Iova(2), P. Ganea(1), F. Neatu(3), V.I. Parvulescu(3)

Affiliation:

(1)National Institute of Materials Physics, Magurele,

(2) Faculty of Physics, University of Bucharest,

(3) Faculty of Chemistry, University of Bucharest

E-mail

lfrunza@infim.ro

Keywords:

layered materials, interstitial anions, quantitative analysis, FTIR spectra

Abstract:

Layered oxide materials positively charged, with the structure of layered double hydroxides (LDH) and containing in the interlayer space anions (for electroneutrality) and water molecules were studied by spectroscopic methods. A reason of such investigations is related to their applicability in catalytic reactions. Besides, experimental studies probing the interlayer composition and properties, the surface regions and even the detailed structure of the sheets are difficult and still scarcely discussed in the literature. Layered oxide materials have the general formula [M1−x2+Mx3+(OH)2]x+(Az−)x/z·mH2O, where M2+and M3+ are metal cations. In our case M2+ = Zn2+, Mg2+; M3+ = Al3+, Ga3+, Az− represents the anions to balance the positive charge of the layer (here, nitrate NO3- and/or carbonate CO32-). The samples were prepared in laboratory and were further noted Mg3Al-LDH, Mg3Ga-LDH, Zn2Al-LDH and Zn2Ga-LDH. They were characterized by powder X-ray diffraction, FTIR and nitrogen adsorption. XRD diagrams showed that the materials have a layered structure; the basal spacing of (001) was estimated to be ca. 7.8 Å. Vibrational spectra were recorded with a Spectrum BX FTIR spectrometer (Perkin Elmer) by KBr technique. The spectra were analyzed by fitting Gaussians to the data as previously described. The regions of interest were: 400-1400 cm-1 for the framework vibration modes, 1200-2000 cm-1 for the anion modes, 3300-400 cm-1 for the OH stretching mode. The nitrate-carbonate anions were determined using their characteristic frequencies. Quantitative analysis was performed using calibration curves.