Synthesis and characterization of layered zinc hydroxychlorides

Layered material of zinc hydroxychlorides (Zn5(OH)8Cl2·nH2O: ZHC), which is one of the basic zinc salts (BZS), was synthesized from ZnO nano-particles aged with aqueous ZnCl2 solutions at different temperatures ranging from 6 to 140 °C for 48 h. X-ray diffraction (XRD) results indicated that the diffraction peaks of ZnO completely disappeared by aging at 6 °C and the ZHC peaks were developed. By increasing the aging temperature, crystallinity of the layered structure was improved. At 6 °C, the ZHC particles were thin hexagonal plate particles with sizes ranging from 1 to 3 μm. The particle size of ZHC was independent of aging temperature. The atomic Cl/Zn ratios of all the ZHC materials were almost 0.2 less than 0.4 of the theoretical ratio, indicating that the synthetic ZHC is Cl-deficient. It seemed that half of Cl atoms in the layer were replaced with HCO3− and/or OH−. The specific surface areas of ZHC estimated from N2 adsorption isotherms were ca. 10 m2 g−1 and were independent of the aging temperature. However, the H2O monolayer adsorption capacity per unit surface area (nw) for all the samples was higher than that of ZnO particles, revealing the high affinity of ZHC to H2O molecules. The nw values were increased by reducing the crystallinity of ZHC. This enhancement of H2O adsorption selectivity was thought to be related with less-crystallized parts of the particles.