Layered double hydroxide of cobalt-zinc-aluminium intercalated with carbonate ion: preparation and Pb(Ⅱ) ion removal capacity

摘要

Ternary layered double hydroxide (Co-Zn-Al LDH) intercalated with carbonate was synthesised via a simple co-precipitation method at pH ≥10. It was characterised using the Fourier transform infrared (FTIR) spectrometer, X-ray diffractometer (XRD), surface area and porosity analyser, Thermo-gravimetric/differential thermal analysis (TGA-DTA), and Scanning Electron Microscope (SEM). The Pb(Ⅱ) adsorption properties, mechanism, and possible reuse of the LDH were also investigated by the batch technique. The characterisation results showed the presence of hydroxyl group as well as the intercalated carbonate anions within the well-defined LDH crystal structure. The TGA-DTA results confirmed the presence of these anionic groups which were liberated from the structure at ≈200 and 300°C, respectively. The LDH-specific surface area, pore diameter and width are 54.0 m~2/g, 41.3 and 25.1 nm, respectively. Adsorption results showed that Pb(Ⅱ) equilibrium could be achieved in 120 min, and adsorption increased with concentration and temperature. A Pb(Ⅱ) adsorption capacity of 130.34 mg/g was reached for this LDH, and the adsorption process was spontaneous, endothermic and mainly electrostatic with most of the adsorption occurring within the pores. Desorption test suggested that approximately 90% of the adsorbed Pb(Ⅱ) could be desorbed; hence, the Co-Zn-Al-CO_3 LDH may be reused.