Effect of the synthesis pH, the nature of the divalent cations and the metal salt concentration on the formation of layered double hydroxides for removal of Cochineal Red A dye from aqueous solutions

Abstract

In this research work, removal of Cochineal Red A dye from aqueous solution was studied using layered double hydroxide materials prepared by a coprecipitation method at variable pH. The effects of the synthesis pH, the nature of the divalent cations and the total metal salt concentration on the formation of layered double hydroxides and their application to the removal of Cochineal Red A dye from aqueous solution were investigated. The structure of the materials prepared was characterized by X-ray diffraction and Fourier transform infrared. It was found that the nature and content of the bi- and trivalent metal ions in the layered double hydroxide influenced the adsorption. Ni–Fe had 0.96 to 1.70 times more adsorption capacity before reaching its equilibrium adsorption than Zn–Fe prepared at pH 7–9 with 2.2 M of total metal salt concentration. No difference was observed in the amount of Cochineal Red A dye adsorbed onto Zn–Fe prepared at both pH 7–9 and pH 10–11 in the range 1.1–3.3 M of total metal salt concentration. The results show that the increase in the precipitation pH leads to decreasing adsorption capacity. The Cochineal Red A dye adsorption follows the Temkin model for the Ni–Fe and Zn–Fe prepared at pH 7–9 and follows the Langmuir model for the Zn–Fe synthesized at pH 10–11 with high coefficient correlation. The adsorption kinetics data fitted the pseudo-second-order model. A thermodynamic study indicates that the adsorption process is both spontaneous and endothermic in nature.