Novel Al₂O₃/GO/halloysite nanotube composite for sequestration of anionic and cationic dyes

In this study, an Al₂O₃/graphene oxide/halloysite nanotube (Al₂O₃/GO/HNT) nanocomposite has been synthesized and used as an adsorbent for the sequestration of cationic methylene blue (MB) and anionic congo red (CR) dyes from wastewater. The properties of the synthesized Al₂O₃/GO/HNT were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Various factors such as pH, contact time, initial concentration and temperature have been investigated for evaluation of the optimum adsorption in the batch sorption experiment and experimental results showed the highest adsorption capacity was found to be 329.8 mg g^-1 for CR and 258.4 mg g^-1 for MB at an initial concentration of 500 mg l^-1 which was three times higher than the individual Al₂O₃ GO and HNT concentrations. Freundlich and Langmuir adsorption isotherm models were fitted to the experimental data and the results implied that the adsorption of MB well described with Langmuir and CR is related to the Freundlich isotherm model. The kinetics data of CR and MB adsorption was well fitted to pseudo-first-order. The calculated values for thermodynamic parameters indicated that the MB and CR adsorption process were spontaneous and exothermic in nature. The effectiveness of the Al₂O₃/GO/HNT composite was also tested for adsorption of Cu(ii), oxytetracycline (OTC) antibiotic, and 2-chlorophenol (2CP) and the results revealed that the Al₂O₃/GO/HNT composite is a promising adsorbent for the dyes as well as heavy metals and other organic pollutants.