Adsorption of anionic azo dye Congo Red from aqueous solution by Cationic Modified Orange Peel Powder

This study investigated the adsorption of Congo Red (CR), an anionic azo dye, from aqueous solution by using Cationic Modified Orange Peel Powder (CMOPP). The optimum conditions were determined by investigating the effects of pH, contact time, initial dye concentration and temperature. The adsorbent was characterized by FTIR analysis. The equilibrium data were analyzed using Langmuir and Freundlich isotherm models. The maximum adsorption capacity of CR on CMOPP was estimated as 107, 144, and 163 mg/g, respectively, at different temperatures (298, 308 and 318 K). Langmuir model fitted the equilibrium data better than the Freundlich isotherm. The kinetic results demonstrated that the adsorption of CR onto CMOPP was well described by pseudo-second-order kinetic model. The activation energy of adsorption (E_a) was found to be 30 kJ/mol by using the Arrhenius equation. The calculated thermodynamic parameters (ΔG^o, ΔH^o and ΔS^o) showed that the adsorption of CR onto CMOPP was feasible, spontaneous and endothermic. Desorption experiments were carried out to explore the feasibility of regenerating the adsorbent and the adsorbed CR from CMOPP was desorbed using 0.1 M NaOH. The results indicated that CMOPP can be considered as a potential adsorbent for the removal of CR from aqueous media.