Synthesis and anion exchange properties of a Zn/Co double hydroxide salt

In this study, a ZnCo―SO4 double hydroxide salt (DHS) has been synthesized by the reaction of CoSO4·7H2O with solid ZnO in aqueous solution. The resulting pink ZnCo―SO4 DHS was characterized by X-ray Diffraction, Infrared Spectrometry, UV/Visible Spectrometry and Thermal analysis. Characterizations show that its structure is similar to the one described for the layered Zn Sulfate Hydroxide Hydrate, i.e. brucite layers with 1/4 empty octahedra presenting tetrahedrally coordinated divalent atoms above and below the empty octahedra. Co atoms are located in the octahedra and zinc atoms in tetrahedra and octahedra. In this structure the exchangeable anions are located at the apex of tetrahedra. SEM and TEM observations show that the DHS is composed by aggregates of hexagonal plates of several hundreds of nanometers. Due to its interest for industrial or environmental applications, the exchange of sulfate groups by carbonates has been investigated. Results show a limited exchange capacity and a higher affinity for sulfates compared to affinity for carbonates.