Adsorption capability for Congo Red on exfoliated graphene-decorated CoFe2O4 nanocomposite: Kinetic, isotherm, thermodynamic and recyclability studies

In the present work, we investigated kinetics and isotherms of the adsorption process of EG@CoFe2O4 adsorbent toward Congo Red dye in aqueous solution. Four kinetic models (pseudo first-order, pseudo second-order, Elovich, and Bangham) and four isotherm models (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich) were estimated elucidate the adsorption mechanism. Current results show that the pseudo second-order model is the most appropriate kinetics for the adsorption and that the monolayer behavior (Langmuir model), rather than multilayer behavior (Freundlich equation), is more suitable to describe the adsorption. The adsorption process was confirmed to be endothermic and spontaneous via thermodynamic study. On the other hand, via Boehm's titration we confirmed that EG@CoFe2O4 can contain functional groups (carboxylic, phenolic, laconic groups and basic groups) with the respective amount of 0.020, 0.044, 0.032, and 0.156 mmol/g. The EG@CoFe2O4 showed high maximum adsorption capacity (98.60mg/g), and good recyclability.