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In this study, we report the adsorption process of Congo Red (CR) dye by calcined Layered Double Hydroxide (ZAC) at 550°C. The urea hydrolysis method was applied to produce highly crystalline Zn2Al-LDH. Samples characterisation was carried out by X-ray diffraction (XRD), Thermogravimetric/differential thermal analysis (TG/DTA), and Fourier transform infrared spectroscopy (FTIR). The results show that the adsorption of CR on calcined ZnAl-LDH was accompanied by the reconstruction of the layered structure. The ZAC showed higher adsorption efficiency versus other adsorbent under investigation and optimum conditions of contact time, adsorbent dose, pH and temperature were found to be 50 min, 0.02 g, 7 and 318 K, respectively. Isotherm studies show that the Langmuir isotherm model was appropriate to describe the CR adsorption data compared with Freundlich and Temkin isotherm models, with a higher correlation coefficient (R2 > 0.99) and maximum adsorption capacity of 406.5 mg/g. The thermodynamic parameters revealed that the adsorption process was spontaneous, endothermic, and governed by chemisorption. To further facilitate the recovery process in CR adsorption, we test the feasibility of applying ZnAl-LDH and its calcined product at 550°C entrapped in alginate beads. Experimental results indicate that alginate-coated ZAC beads, which exhibited remarkable adsorption performance, were more stable and require less effort to pull and separate than the alginate/ZnAl-LDH composite beads. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]