Adsorption of food dye Acid red 18 onto polyaniline-modified rice husk composite: isotherm and kinetic analysis

In this study, the removal of food dye Acid red 18 from aqueous solution by polyaniline/HCl-modified rice husk (polyaniline/HCl-MRH) composite was studied. Properties of synthesized composite were analyzed and confirmed by SEM and FTIR. Results show that Langmuir adsorption isotherm has the best compatibility with the results of experiments. Kinetic analysis using pseudo-first-order model, pseudo-second-order, and the intra-particle diffusion model was carried out. Results also confirmed that adsorption process is compatible with the pseudo-second-order kinetic model. Thermodynamic parameters such as Gibbs free energy changes (ΔG°), Enthalpy changes (ΔH°), and Entropy changes (ΔS°) were calculated. Negative value of ΔG° and positive value of ΔH° show that adsorption of Acid red 18 on polyaniline/HCl-MRH is a spontaneous process also endothermic.