Intercalation of Macrocyclic Crown Ether into Well-Crystallized LDH: Formation of Staging Structure and Secondary Host-Guest Reaction

A carboxyethyl substituted azacrown ether derivative (CSAE) was intercalated as it second host into a parent host of well-crystallized crystal of Mg-Al layered double hydroxide (MgAl-LDH) by it CSAE/NO3- ion-exchange reaction. The influence of intercalation temperature on the structures and compositions of CSAE-LDH nanocomposites Was investigated. The composites obtained at the temperatures below 70 degrees C had almost the same CASE contents and layered structures with a basal spacing of about 1.6 nm, corresponding to the vertical orientation 2 of CSAE plane to the LDH layer. The chemical analysis showed that a considerable amount of CO32- (with CO32-, CSAE molar ratio of 1.4) was incorporated in the interlayer of LDH. The CSAE content decreased while CO32- content increased with an increase of the intercalation temperature in the region above 70 degrees C. At 100 degrees C, a second staging phase of 2.33 nm appeared, attributed to the ordered stacking of the 1.6 nm phase and it 0.77 nm phase produced by the CO32-/CSAE exchange, At higher temperatures, a new phase with a basal spacing of 1.18 nm appeared, which corresponds to the tilt/twisted orientation of CSA E anions in the interlayer. The other second staging phase of 2.08 nm appeared obviously at 150 degrees C, due to the regular stacking of the 1.18 and 0.77 nm phases. The adsorptive properties for transition metal ions were studied using the 70 and 150 degrees C reacted composites. The 70 degrees C reacted one showed higher adsorptivity toward transition metal ions; the adsorptive capacity increased in the sequence of Cu2+ > Ni2+ > Co2+ > Zn2+ and distribution coefficient for Cu2+ was markedly higher than those for the other ions. However, the 150 degrees C reacted one showed little adsorptivity toward these ions. The adsorption for transition metal ions was accompanied by the intercalation of nearly equivalent amount of nitrate ions. This shows that the interlayer CSA E ions in the 1.6 rim phase act as a second host, but those in the 1.18 nm phase do not.