Effects of molar ratio and calcination temperature on the adsorption performance of Zn/Al layered double hydroxide nanoparticles in the removal of pharmaceutical pollutants

Abstract This work focuses on the development of zinc/aluminum layered double hydroxides (LDHs) phases intercalated by carbonates ions (Zn-Al-CO 3 ) and their use in the removal of pharmaceutical pollutants. The materials were synthesized by the co-precipitation method at different Zn/Al molar ratios (r = 1, 3 and 5). Each synthesized material was calcined at 300, 400, 500 and 600 °C to increase their performance. Samples were characterized by various physicochemical techniques including XRD, FTIR, ICP-AES and TEM-EDX. The as-synthesized and calcined products were used for the removal of salicylic acid (SA) as a model of pharmaceutical pollutants. The results obtained show that the Zn/Al molar ratios and calcination temperatures have a great influence on the adsorption capacity. The optimum adsorption efficiency was found to be 94.59% for Zn/Al molar ratio of 3 and a calcination temperature of 300 °C. Kinetics of the adsorption takes place in two steps; the first fast rapid step can be interpreted by the adsorption on the external surface of the crystallites, while the second slow step could be due the reconstruction phenomenon of LDHs structure “memory effect”. After the adsorption processes, XRD patterns show that the calcined product (r = 3, T  = 300 °C) was reconstructed by a salicylic acid. The adsorption performance was slightly decreased with regeneration cycles.