Synthesis and characterization of novel β-cyclodextrin xanthate hydrogel/nickel oxide nanocomposites: adsorption isotherm, kinetic, thermodynamic, photocatalytic activity and reusability studies

β-Cyclodextrin xanthate hydrogel/nickel oxide (NiO) nanocomposites (β-CDXHs/NiO NCs) have been prepared using free radical polymerization technique along with the incorporation of NiO nanoparticles (NPs) within β-CDXHs hydrogel matrix through hydrothermal method. The prepared β-CDXHs/NiO NCs have been characterized by various techniques, including UV, FTIR, TGA, ΔpHpzc, GPC, XRD, SEM and EDAX analyses. Methylene blue (MB) dye removal has been found to be highly pH dependent, and showed a maximum removal of 99.23% for MB dye at optimum adsorbent dosage of 1.2 g, pH of 7, stirrer rate of 400 rpm, solution temperature of 25 °C, initial concentration of 100 mg/L and contact time of 30 min. The adsorption isotherm data were fitted to the Langmuir and Freundlich adsorption model with adsorption capacity 310.55 mg/g for MB dye. The plots of isotherms indicated that both physisorption and chemisorption were possible. The adsorption rate of MB dye onto β-CDXHs/NiO NCs is controlled through pseudo-first- and second-order kinetic models. The negative ΔH and ΔG values exhibit that the MB dye adsorption process was exothermic and spontaneous in nature. It was observed from the desorption studies that about 76.72% of the adsorbent had been regenerated for fifth cycle, exhibiting good reusability. The MB dye degradation was found to be 93.09% in the presence of β-CDXHs/NiO NCs. Hence, the experimental results suggest that the β-CDXHs/NiO NCs act as an efficient photocatalyst that can be used for the treatment of wastewater containing MB dye.

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