Layered double hydroxides (LDHs), [M²⁺_1-x M³⁺_x (OH) ₂][A^n-_x/n·yH₂O], 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 (NO₃) ₂-Al (NO₃) ₃ mixed solution was added into each guest anion (Cl^-, CO3^2-, NO₃^- or SO₄^2-) solution under a nitrogen atmosphere at 40°C. The intercalation 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°C. 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 (d₀₀₃=0.78 nm) and NO₃/Mn-Al LDH (d₀₀₃=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 Mn²⁺ 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, don, was expanded to 2.86 nmfor 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 role. In particular, the intercalated surfactants were decomposed at lower temperature (200°C) 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.

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Recent developments in the study of the intercalation of organoammonium ions into smectites are reviewed. The new developments of the applications of the organoammonium exchanged smectites include the selective adsorption of harzardous organic compounds from water, the immobilization of photo and electroactive species to construct novel photo and electrofunctional materials, the complexation with organic polymers for the enhancement of the mechanical properties. The novel controlled properties of smectites achieved by the modification with the adsorption of organoammonium ions open up new opportunities to tailor the properties of the smectite-organic intercalation compounds. The effects of organoammonim ions and the nature of smectites on the properties of the resulting functional intercalation compounds were discussed.

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