Ni/Fe and Mg/Fe layered double hydroxides and their calcined derivatives: preparation, characterization and application on textile dyes removal

In this study, Mg/Fe and Ni/Fe layered double hydroxides (LDHs) with molar ratio (M2+/Fe3+) of 3 and intercalated with carbonate ions were synthesized by co-precipitation method. The as-synthesized materials and their calcined products (CLDHs) were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric and differential thermal analyses (TGA-DTA), transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM-EDX), inductively coupled plasma (ICP) and elemental chemical analysis CHNSO. The materials were used as adsorbents for the removal availability of textile dyes from aqueous solution. Methylene blue (MB) and malachite green (MG), representative of cationic dyes, and methyl orange (MO) representative of anionic dyes were used as model molecules. Adsorption experiments were carried out under different parameters such as contact time, temperature, initial dyes concentration and solution pH. Experimental results indicate that CLDHs had much higher adsorption capacities compared to LDHs. Adsorption kinetic data fitted well the pseudo-second order kinetic model. The process was spontaneous, endothermic for cationic dyes and exothermic for the anionic dye. Equilibrium sorption data fitted the Langmuir model instead of Freundlich model.