Exchange of interlayer terephthalate anions from a Mg–Al layered double hydroxide: formation of intermediate interstratified phases

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 CO32− and SO42− but only partly by Cl− and NO3−. 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.