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Abrupt structural transformation in hydrotalcite-like compounds Mg1-xAlx(OH)(2)(NO3)(x)center dot nH(2)O as a continuous function of nitrate anions
Xu, Z. P. and Zeng, H. C. (2001) Abrupt structural transformation in hydrotalcite-like compounds Mg1-xAlx(OH)(2)(NO3)(x)center dot nH(2)O as a continuous function of nitrate anions. Journal of Physical Chemistry B, 105 9: 1743-1749.
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| Author(s) |
Xu, Z. P.
Zeng, H. C.
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| Title |
Abrupt structural transformation in hydrotalcite-like compounds Mg1-xAlx(OH)(2)(NO3)(x)center dot nH(2)O as a continuous function of nitrate anions
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| Journal name |
Journal of Physical Chemistry B
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| Publication date |
2001
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| Volume number |
105
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| Issue number |
9
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| ISSN |
1520-6106; 1089-5647
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| Start page |
1743
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| End page |
1749
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| Total pages |
7
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| Place of publication |
Washington, DC.
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| Publisher |
American Chemical Society
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| Language |
eng
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| Abstract |
We report here a systematic XRD/FTIR/CHN/ICP investigation for structural transformation of hydrotalcite-like compounds Mg1-xAlx(OH)(2)(NO3)(x). nH(2)O 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). nH(2)O 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 is attributed to a drastic change in nitrate anion arrangement. On the basis of our FTIR observations and Coulombic energy estimation, a "stick-lying" model for nitrate arrangement has been proposed, which is apparently superior to a "tilt-lying" model reported previously. The saturated charge density of the brucite-like layers for the "stick-lying" nitrate anions is about 4 e/nm(2). The sharp decrease in crystallite dimension can be ascribed to the change of nitrate configuration from "flat-lying" to "stick-lying" due to increasing lateral repulsion among the anions and thus discontinuation in the planar growth.
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| Keyword(s) |
Chemistry, Physical
Layered Double Hydroxides
Ion-exchange Properties
Physicochemical Properties
Calcined Hydrotalcites
Aluminum Hydrotalcite
Cobalt Hydroxide
Decomposition
Clays
Temperature
Phases
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