Anion-exchange and thermal change of layered zinc hydroxides formed in the presence of Al(III)

Zinc hydroxide chloride particles of ZHC (simonkolleite, Zn5(OH)8Cl2·H2O) and layered double hydroxides (LDH, Zn–Al–Cl) were prepared by hydrolysis of ZnCl2 solutions dissolving AlCl3 at Al/Zn = 0.1 and 0.6 in atomic ratio, respectively. The anion-exchange and thermal change of ZHC and LDH were investigated by XRD, TEM, FTIR, analysis of Zn, Al, and Cl and gas adsorption of N2, H2O, and CCl4. The formed ZHC and LDH particles were hexagonal thin plates and irregularly shaped thin plates, respectively. LDH was more easily ion-exchanged with CO32− and SO42− compared to ZHC. The layered structure of LDH was damaged by the ion-exchange with SO42− but not CO32−, whereas that of ZHC was kept after the ion-exchange with both the anions. The TEM observation of the ZHC and LDH particles outgassed at different temperatures of 75–400 °C revealed that exfoliation takes place on outgassing ZHC at 100–150 °C but not occurs in LDH. ZHC showed a high H2O adsorption selectivity when outgassed below 100 °C, however the adsorption selectivity completely disappeared above 125 °C where the exfoliation took place. On the other hand, LDH exhibited less adsorption selectivity than ZHC though the selectivity was held after outgassed at 400 °C. The facilitated delamination of ZHC indicates that ZHC exhibits weaker interlalyer attractive force than LDH in vacuo.