Synthesis of New Layered Double Hydroxide Intercalates

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Layered Double Hydroxides (LDHs),[NM^<2+>_xM^<3+>_<1-x>(OH)_2][A^<n->_<x/n>・yH_2O], consist of positively charged brucite-like layers separated by charge-balancing hydrated gallery anions A^<n->. In this study, polyoxometallate (POM)-pillared LDHs have been prepared by the new techniques.1. Preparation and characterization of silicate-intercalated LDHs via carboxylate-pillared precursorsIntercalation of silicate anions in gallery space of carboxylate-pillared LDH with different layer distance has been investigated by ion exchange method. The intercalation was carried out by adding a starting parent LDH in NaOH solution containing silicic acid granulas with vigorous stirring and by refluxing the reaction mixture at 100 ﾟCSilicate anions were found to be intercalated to from the silicated LDH with basal spacing of 11.4-12.1A^^ﾟ at the conditions of > O.O5 M NaOH and reaction time of 2.5 h. However, the interlayer structure of the silicated LDH was influenced with initial gallery height o … More f the parent LDH and the adipate-pillared LDH having a little bigger basal spacing [d_<003>=13.9A^^ﾟ) has givern the most well-ordered LDH product with two-dimensional silicate anions as the interlayer guest. The crystallinity of the sillicated LDH products was in order: adipate-pillared LDH [d_<003>=13.9A^^ﾟ) > terephthalate-pillared LDH (14.5A^^ﾟ) > sebacate-pillared LDH (16.8A^^ﾟ)> chlorinated LDH (7.8A^^ﾟ) > > laurate-pillared LDH (31.5A^^ﾟ). The silicated LDHs were also investigated by XRD, IR, TG-DTA, MAS-NMR etc.2. Direct synthesis of a polyoxometallate-pillared layered double hydroxide by copreciptationA new method for the preparation of POM-pillared LDH has been accomplished by using the corecipitation reaction as follows. First, alpha-[SiW_<11>O_<39>]^<8-> was dissolved in water and pH the POM solution was adjusted to6.0. Then, the mixed solution of Zn^<2+> and Al^<3+> ions was added drop-wise to the vigorously stirred POM solution at 100 ﾟC. The coprecipita-tion reaction of Zn^<2+> and Al^<3+> ions in moderately acidic alpha-[SiW_<11>O_<39>]^<8-> solution directly was found to afford a LDH derivative with an approxi-mate composition of [Zn_<24>Al_8(OH)_<64>][alpha-SiW_<11>O_<39>] and an exceptionally well-ordered gallery height of 9.8A^^ﾟ. Less