Adsorptive and Catalytic Removal of Methylene Blue Using Modified Bentonite: Experimental and DFT Study

ABSTRACT This research studies the purification of montmorillonite from natural Iraqi bentonite clay (NIBC). Montmorillonite was characterized using XRD, SEM‐EDX, TEM, FTIR, DRS, and UV–vis spectrophotometry. The purified montmorillonite is then employed as an adsorbent and the catalytic degradation of organic aqueous pollutants, specifically Methylene Blue (MB). The results show that the selected organic pollutant MB was removed using both adsorption and catalytic degradation. Different isotherms were applied, including Langmuir, Freundlich, and Temkin. Kinetic and thermodynamics were also studied; MB adsorption followed the pseudo‐second‐order model, and the heat of adsorption for MB was (Δ H ° = −19.1 kJ/mol), indicating a physical process. The catalytic degradation was examined utilizing different redox agents, including H 2 O 2 , NaBH 4 , and KBrO 3 . Box‐Behnken Design (BBD) was applied to study the catalytic degradation; hence, ANOVA analysis shows the significant role of H 2 O 2 concentration ( p = 0.0141), and the synergistic effects were observed for H 2 O 2 ‐NaBH 4 ( p = 0.0082) and NaBH 4 ‐KBrO 3 ( p = 0.0012) interactions. Furthermore, Density Functional Theory (DFT), DFTB+, and molecular dynamic (MD) were applied to get a better understanding of the molecular level. Theoretical calculations, including HOMO–LUMO analysis, electron density difference (EDD), global reactivity descriptors, and Density of States (DOS), were all employed. The montmorillonite exhibits a narrow HOMO–LUMO gap (0.05 eV), high electrophilicity (ω = 18.71), and low hardness (η = 0.0242), indicating excellent electron‐transfer capability. DOS shows the availability of Fe‐d orbitals and Si‐p orbitals near the Fermi level, which facilitate the oxidation and reduction process. These results could provide a mechanistic insight into montmorillonite catalytic performance in catalytic environmental remediation.