Anionic dye adsorption on ZnAl hydrotalcite-type and regeneration studies based on “memory effect”

Abstract

ABSTRACT Currently, the treatment of wastewater containing dye by the effective adsorbent attracts a great deal of interest. In this work, we report the removal of Congo Red (CR) dye from water using ZnAl-Layered Double Hydroxides (LDH) synthesised by the urea method. Samples characterisation was carried out by X-ray diffraction (XRD), Thermogravimetric/differential thermal analysis (TG/DTA), and Fourier transform infrared spectroscopy (FTIR).The results showed that well-crystallised layer material with uniform particle size was formed. Various parameters influencing the adsorption process, such as dye concentration, adsorbent dosage, contact time, pH and solution temperature were investigated. The adsorption kinetics were evaluated using the pseudo-first-order and second-order kinetic models. According to kinetics studies, the adsorption of CR was instantaneous and fast, which reflects a strong affinity of LDH for dye molecules and follow ideally the pseudo-second order model. Isotherm studies show that the Freundlich isotherm model was appropriate to describe the adsorption of CR onto ZnAl-LDH, with a maximum adsorption capacity of 591.80 mg/g at pH = 3. Based on adsorption study, the amount of CR uptake onto LDH increases with increasing initial dye concentration and temperature from 298 to 318 K. The thermodynamic parameters show that adsorption process of CR was spontaneous and endothermic in nature. Furthermore, we investigated ZnAl-LDH decomposition and structure regeneration based on “memory effect“ from previous calcined sample. After rehydration, layer material with good crystallinity was achieved, revealing that the regeneration process was successfully conducted.