Mn-Al系層状複水酸化物の合成とその熱分解挙動

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Layered double hydroxides (LDHs), [M^<2+>_<1-x>M^<3+>_x(OH)_2][A^<n->_<x/n>・yH_2O], is well known as anionic clay by its anion-exchange property. In this paper, a noble LDH, the Mn-Al LDH, was synthesized by the coprecipitation in which Mn(NO_3)_2-Al(NO_3)_3 mixed solution was added into each guest anion (Cl_-, CO_3^<2->, NO_3^- or SO_4^<2->) solution under a nitrogen atmosphere at 40℃. The intercaiation of anionic surfactants (sodium dodecylbenzenesulfonate: DBS and sodium laurate: LA) into the Mn-Al LDH was also carried out by the ion-exchange in which Cl/Mn-Al LDH was added into DBS or LA solution under a nitrogen atmosphere at 25℃. Moreover, the thermal decomposition of the resulting various Mn-Al LDHS has been examined. The solid products by the coprecipitation were found to have a LDH structure and only Cl/Mn-Al LDH (d_<003>=0.78 nm) and NO_3/Mn-Al LDH (d_<003>=0.89nm) were obtained as a single phase. In addition, the crystallinity of Cl/Mn-Al LDH was remarkably decreased with an increase in drying temperature because Mn^<2+> ion in the hydroxide host layer was oxidized by air during drying. On the other hand, DBS/Mn-Al LDH and LA/Mn-Al LDH were obtained by the ion-exchange. The basal spacing, d_<003>, was expanded to 2.86 nm for DBS/Mn-Al LDH and 4.01 nm for LA/Mn-Al LDH, respectively. DBS and LA ions in the gallery space of the LDH were thought to be arranged obliquely or vertically for the hydroxide host layer as bilayer. During the thermal decomposition, Mn ion in the host layer was found to play as catalytic ro1e. In particular, the intercalated surfactants were decomposed at lower temperature (200℃) than that of surfactants only. The oxidation number of Mn ion in the host layer was also remarkably changed in +2.00〜+3.00 range after the thermal treatment and was increased with an increase in temperature of the thermal treatment under air flow, whereas was decreased under nitrogen flow. Thus, the oxidation number of Mn ion in the host layer was effected by the thermostability of the intercalated guest anion and the atmosphere. In conclusion, we succeeded the synthesis of various kinds of Mn-Al LDH and found the catalytic action of Mn ion in the host layer in the thermal decomposition of guest anions.
日本粘土学会の論文
2000-06-01

Mn-Al系層状複水酸化物の合成とその熱分解挙動

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