Removal of Azo Dyes: Intercalation into Sonochemically Synthesized NiAl Layered Double Hydroxide

A sonochemical method was employed in the synthesis of nickel aluminum layered double hydroxides (NiAl-LDH) and the materials were used as adsorbents for the removal of the reactive azo dye, Remazol Brilliant Violet (RBV-5r). The experimental data obtained for microstructure were compared and both the arrangement and orientation of the intercalated dye species were examined using molecular dynamics (MD) simulations. The obtained materials were characterized by X-ray diffraction (XRD), nitrogen sorption (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Fourier transformation infrared spectroscopy (FTIR). The adsorption characteristics were studied in a batch process by optimizing different parameters such as calcination temperature, contact time, initial dye concentration, solution pH, and solution temperature. NiAl-LDH material synthesized by sonochemical (SC) methods and calcined at 250 degrees C (NiAl-C250SC) showed the best dye removal efficiency (100% removal in 6 min) with an adsorption capacity of 150 mg/g at 25 degrees C and at pH = 6. The reusability of the dye loaded material was investigated by replicating the adsorption desorption cycle. The results show that the material could regenerate without significant loss of the adsorption capacity. The regenerated adsorbent showed 95.9%, and 95.7% of the initial adsorption capacity after the first and the second regeneration cycles, respectively. XRD and FTIR results for LDH before and after the dye adsorption showed removal of the dye is due to intercalation of the organic dye molecule into the LDH structure where a net increase in the basal spacing from 7.48 to 8.71 angstrom is observed. Molecular dynamics (MD) simulations further suggest that the dye molecules arrange in the interlayer space as a monolayer with the main axis horizontal to the layer plane. The calculated d-spacing values were in good agreement with the experimental results.