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|Title:||Abrupt structural transformation in hydrotalcite-like compounds mgi-jAltCOHMNOaV/zHiO as a continuous function of nitrate anions|
|Authors:||Xu, Z.P. |
|Source:||Xu, Z.P.,Zeng, H.C. (2001-03-08). Abrupt structural transformation in hydrotalcite-like compounds mgi-jAltCOHMNOaV/zHiO as a continuous function of nitrate anions. Journal of Physical Chemistry B 105 (9) : 1743-1749. ScholarBank@NUS Repository.|
|Abstract:||We report here a systematic XRD/FTIR/CHN/ICP investigation for structural transformation of hydrotalcitelike compounds Mgi-jAlOHMNOaVnFhO 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 Mgi-iAU(OH)2(NO3)x·H2O 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/nm2. 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. © 2001 American Chemical Society.|
|Source Title:||Journal of Physical Chemistry B|
|Appears in Collections:||Staff Publications|
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