Anion exchange in layered double hydroxides by surfactant salt formation

In this paper a method of anion exchange in layered double hydroxides (LDHs) based on the formation of a salt between an anionic and a cationic surfactant, which is extracted from aqueous solution into an organic unmixed phase, is discussed. Two Zn(II)–Cr(III) LDHs, synthesised by direct coprecipitation under constant pH intercalated with dodecylsulfate (DS) and dodecylbenzenesulfonate (DBS), were used as starting materials (precursors). By this method various inorganic and organic anions can be intercalated by exchange with the surfactant anion in the interlamellar domain, resulting in new intercalated materials. The kinetics of such exchange and the possibility of controlled partial exchange are also discussed. The exchanged materials obtained showed phase purity and considerable high crystallinity. Another advantage of this method is related to the conditions in which the precursor and the final products can be obtained, i.e. the precursors are very easy to synthesise and no further treatments for use in this exchange, such as hydrothermal treatment, are required in either case. Moreover, the kinetic study showed that the anion exchange is very quick. An advance on anion exchange process in LDHs is also demonstrated by the possibility of controlled quantitative substitution.