A novel hydrogel based on agricultural waste for removal of hazardous dyes from aqueous solution and reuse process in a secondary adsorption

A novel hydrogel based on the orange peel (OP) and N-vinyl-2-pyrrolidone was prepared by free-radical polymerization using gamma irradiation. The effect of radiation dose and hydrogel composition on gel content was studied. The formed hydrogel was characterized by FT-IR, TGA, and SEM. The swelling behavior was determined as a function of swelling time, pH, and OP content. The hydrogel swelling was found to be pH dependent, and the diffusion mechanism of water into the hydrogel was found Fickian. The developed hydrogel was used for the removal of Congo red (CR) and methyl orange (MO) dyes from wastewater. The effects of various operating parameters, such as initial pH, contact time, initial dye concentration, and temperature on the removal of dyes, have been investigated. The Langmuir and the Freundlich adsorption models were applied to study the adsorption isotherm. The pseudo-first-order model was proved compatible for CR adsorption and the pseudo-second-order model well described the adsorption of MO. The adsorption of dyes increased with increasing temperature indicating that the endothermic nature of the adsorption process and the thermodynamic parameters was evaluated. Second, the adsorption cycle of dyes was also examined and discussed utilizing the loaded hydrogel with the other dye and cobalt metal ions.