ANION-EXCHANGE REACTIONS OF HYDROXY DOUBLE SALTS

Hydroxy double salts (HDS's) comprise a class of layered materials which are similar to layered double hydroxides (LDH's) and show a comparable intracrystalline reactivity. All samples described in this paper were prepared by reacting a solid oxide MeO with a solution of a nitrate M(NO3)2: ZnO with solutions of Ni(NO3)2.6H2O, Co-(NO3)2.6H2O, and Cu(NO3)2.3H2O; NiO with Cu(NO3)2-3H2O; and CuO with Ni(NO3)2.6H2O, Co(NO3)2.6H2O, Zn(NO3)2.6H2O, and Cu(NO3)2.3H2O. Typical compositions of HDS's are [(Me,M)2(OH,NO3)4] and [(Me,M)5-(OH)8](NO3)2. The hydroxy double salts easily exchange anionic surfactants for the interlayer nitrate anions. Toward short-chain acid anions the HDS's are less reactive than the LDH's. The anion exchange capacity is due to the exchange of anions incorporated in the hydroxide layer (as in the basic copper nitrate [CU2(OH)3NO3]) or of anions bound as gegenions of the positively charged hydroxide layer. The positive charge originates from an excess of the divalent metal ions as in basic zinc salts [Zn5(OH)8](NO3)2.2H2O or [Zn5(OH)8]Cl2.H2O. The arrangement of long-chain alkyl sulfate ions in the interlayer space is deduced from basal spacing measurements. In many HDS's the surfactant anions are largely tilted to the hydroxide layers and are aggregated in bilayers. Technical secondary alkanesulfonates which are mixtures of isomers are arranged in the bimolecular film in a way that a constant interlamellar separation is attained. The organic derivatives of the HDS's adsorb neutral molecules between the layers. Typical is the interlamellar adsorption of primary 1-alcanols such as hexanol, octanol, and decanol by the alkyl sulfate derivatives.