Search

The reaction of a nitrilotriacetate-intercalated Mg-Al layered double hydroxide in a lanthanum nitrate solution is studied. La3+ is incorporated into the interlayer through the formation of a chelate complex. NO3 − is also taken up as a charge-balancing anion. During chelation the interlayer repeat increases from 11.9 A to 13.9 A. Chemical analysis suggests that 1:1 and 1:2 metal:chelate complexes are formed within the interlayer. Calcination of the La3+-containing double hydroxide results in the formation of LaAlO3.

The formation, by coprecipitation, of a Mg-Al layered double hydroxide (LDH) intercalate containing nitrilotriacetate (NTA) anions has been observed. The intercalated LDH has a basal spacing close to 12 A (gallery height 7.2 A). The rehydration of a Mg-Al mixed oxide (formed by calcination at 500 °C of a Mg-Al carbonate-containing LDH) in the presence of NTA also results in the formation of a NTA intercalated LDH, indicating the ability of the mixed oxide for adsorptive removal of NTA. It was further shown that nitrate-containing LDHs may be ion-exchanged by NTA, whereas for carbonate-containing materials exchange is difficult. In some cases the formation of the intercalate is accompanied by considerable sequestration of the magnesium and aluminium cations. It is proposed that NTA may exist in the interlayer of the LDH as a trivalent or a divalent anion or under certain circumstances as a [Mg-NTA] – complex.

The exchange of interlayer terephthalate (TA) anions from a Mg–Al layered double hydroxide (LDH) by carbonate, sulfate, chloride and nitrate anions is reported. It is shown that TA is readily exchanged by CO 3 2− and SO 4 2− but only partly by Cl − and NO 3 − . We demonstrate that during the exchange process interstratified phases are observed. Such interstratification has previously been reported only for directly synthesised materials. The origin of the interstratification is believed to be associated with two preferred orientations of TA anions within the layers, i.e. vertical or horizontal to the clay sheets. Two models for the possible exchange mechanism which is operating in these systems are proposed.