Advanced Pyrene Copolymer/rGO Hydrogels for Efficient Congo Red Removal from Aqueous Systems

This study investigates the use of hydrogel semi-interpenetrating polymer networks (semi IPN) as efficient adsorbents for removing the dye congo red (CR) from aqueous solutions. Specifically, three hydrogel semi IPN, namely AH0–AH2, were synthesized through redox polymerization of acrylamide, polyethylenimine, polyhydroxylethylmethacrylate and (pyren-1-yl)methyl methacrylate/2-acrylamido-2-methylpropane-1-sulfonic acid copolymer (pyrene−AMPS) using a reduced graphene oxide (RGO)-N,N’-methylene-bis(acrylamide) (MBA)-based crosslinker (GABC). Results indicated that these hydrogels were efficient in removing CR at pH 6.73, with the adsorption behaviour conforming to the Langmuir isotherm. This suggests a monolayer adsorption pattern, indicating a chemical nature. Thermodynamic analysis supports the practical feasibility of this process. The negative Gibbs free energy of adsorption (ΔG̊) indicates that adsorption is spontaneous and favorable. Conversely, the positive standard entropy of adsorption (ΔS̊) suggests an increase in molecular randomness during the process. Additionally, the standard enthalpy change (ΔH̊) suggests an endothermic activation energy for the binding process. Response Surface Methodology (RSM), utilizing four variables was employed to optimize the removal of CR. The model demonstrated high R2-values and strong agreement between experimental and projected results, affirming its reliability. AH1 and AH2 showed significant efficacy in removing CR dye from aqueous solutions, underscoring their potential application in wastewater remediation.