Influence of thermal treatment on the structure and adsorption properties of layered zinc hydroxychloride

Layered zinc hydroxychloride (Zn5(OH)8Cl2·H2O) synthesized by hydrolyzing the ZnO particles in aqueous ZnCl2 solutions at 100 °C for 48 h was outgassed at different temperatures ranging from 100 to 250 °C for 2 h and the structure and adsorption properties of the products were examined by various means. Outgassing at 100–150 °C eliminated the H2O molecules in interlayer of zinc hydroxychloride. The layered structure of zinc hydroxychloride was disintegrated at 175 °C by breaking the OH⋯Cl hydrogen-bond in interlayer to form curled thin films composed of poorly crystallized β-Zn(OH)Cl and ZnO, leading to the increment of the specific surface area from 4 to 39 m2/g. The β-Zn(OH)Cl was decomposed at 225 °C to form ZnO. The crystallinity of ZnO was increased on elevating the outgassing temperature, giving rise to the UV absorption property. The H2O and CO2 adsorption measurements revealed that the zinc hydroxychloride outgassed at 100–150 °C possessed a high H2O and CO2 adsorption selectivity, and the selectivity diminished by the formation of thin films of ZnO above 175 °C.