Investigation of two cationic dyes adsorption on Algerian MK-KOH Metakaolin: Kinetic, thermodynamic, and computational modeling via DFT approach

This work investigates the adsorption performance of KOH-activated metakaolin (MK-KOH) on the removal of two cationic dyes, methyl violet (MV) and methylene blue (MB), using both experimental and density functional theory (DFT) approaches. MK-KOH was prepared by thermal activation of kaolin followed by KOH alkaline activation. The MK-KOH material was thoroughly characterized to assess its physicochemical properties, and BET measurements revealed a specific surface area of 58.17 m²/g. Batch adsorption experiments were carried out under varying conditions, including contact time (5–120 min), initial dye concentration (10–70 mg·L⁻¹), and temperature (20–60 °C) to evaluate the adsorption performance. MK-KOH had strong absorption capabilities for both dyes, removing MB and MV at maximal levels of 55.01 and 63.99 mg/g, respectively. The MK-KOH adsorption of two dyes is an endothermic process as indicated by the respective positive ΔH° and ΔS° values (74.95 kJ·mol⁻¹ and 39.57 kJ·mol⁻¹) and (54.39 J·mol⁻¹·K⁻¹ and 195.08 J·mol⁻¹·K⁻¹) for MB and MV. DFT computations were used to better examine the adsorption mechanism. The findings demonstrated that the map of electrostatic potential, electronic structure, and frontier molecular orbital distribution indicated that the adsorption of dye molecules on the aluminosilicate surface was driven by electrostatic interaction and π–π stacking. The experimental data was supported by the theoretical findings. According to the results, MK-KOH is affordable and effective adsorbent for eliminating organic dyes from aqueous solutions.