Aim of the study:
In this paper the research was described, in which a hybrid hydrogel had been prepared, characterized by various instrumental techniques, and used as effective adsorbent for the removal of Congo Red dye (CRd) from an aqueous solution.

Material and methods:
The hydrogel was prepared using sodium polyacrylate and clay as raw materials. A batch adsorption approach was employed to evaluate the effects of pH, contact time, initial CRd concentration, adsorbent dosage, and temperature on the adsorption.

Results and conclusions:
To gain insight into the adsorption mechanism, kinetic studies were performed. The pseudo second-order model best fit the experimental data, with regression coefficient close to 1. Among the applied isotherm models – Langmuir, Freundlich, and Temkin – the Langmuir isotherm model provided the best fit for the equilibrium data, with the correlation coefficient close to unity (0.989). Thermodynamic analysis, considering enthalpy (ΔH°), Gibbs free energy (ΔG°) and entropy (ΔS°), has indicated that the adsorption process is exothermic, spontaneous, and feasible, with increase in randomness at the solid-solution interface. The adsorbent is effective in removal of selected dye from water and could serve as the best alternative to activated carbon. Further experiments are recommended to validate these results.