Removal of evans blue by using nickel-iron layered double hydroxide (LDH) nanoparticles: Effect of hydrothermal treatment temperature on textural properties and dye adsorption

The use of low-cost adsorbent has been investigated as a replacement for the current expensive methods of removing dyes from wastewater. The sorption of add dye (Evans Blue) from aqueous effluents onto anionic clays (hydrotalcite-like) has been studied. Hydrotalcite may be an effective adsorbent of organic molecules due to its hydrophobic nature and the accessibility of its interlayer region. Ni/Fe layered double hydroxide (LDM), with a molar ratio of 3, were synthesised by coprecipitation followed by hydrothermal treatment at different temperatures (85, 100 and 140°C) for 4 days. The materials were characterised by X-ray powder diffraction (XRD), infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N ₂ adsorption-desorption (BET). The diffractograms and FT-IR spectroscopy of the fresh materials showed that the hydrotalcite is present in all samples. The XRD pattern obtained was typical of a hydrotalcite, where the interlayer anion is CO₃^2-, XRD and Infrared spectroscopy complemented each other by showing that with treatment the degree of order increased regardless of the type of treatment. Furthermore, it was shown that aging at increased temperature and pressure increased crystallinity. TEM showed that crystal size increased with aging temperature, so that growth occurred on the edges resulting in the formation of hexagonal plate shaped hydrotalcite crystals. The surface area decreased with increasing the hydrothermal treatment temperature. The effects of various parameters such as hydrothermal treatment temperature, crystallite size, contact time and calcination on the extent of adsorption were investigated. The studies of the removal efficiency of the reactive textile dye: Evans Blue (Direct Blue 53) by NiFeCO₃ HDLs showed that the effect of hydrothermal treatment temperature on adsorption increases with aging temperature. The Evans Blue (EB) removal percent increased with increasing contact time. Above the 70%, 50% and 20% of EB adsorption occurred in the first 2 min for HDL-140, HDL-100 and HDL-85°C respectively. Furthermore, it was found that the calcined materials are much more effective than the original LDH in removing Evans Bleu dye from an aqueous solution.