Design of [BmIm]₃PW₁₂O₄₀ Ionic Liquid Encapsulated-ZIF‑8 Nanocomposite for Cationic Dye Adsorptive Removal: Modeling by Response Surface Methodology

In this study, the modification of metal–organic frameworks with polyoxometalate-based ionic liquids was assessed and their efficient role in the improvement of their adsorption performance was studied. Metal–organic framework ZIF-8 was encapsulated with [BmIm]₃PW₁₂O₄₀, a polyoxometalate-based ionic liquid, through reaction with the ZIF-8 imidazolate groups. The novel ZIF-8-[BmIm]₃PW₁₂O₄₀ nanocomposite was characterized using XRD, FTIR, SEM, EDX, and BET analyses, which confirmed the successful insertion of [BmIm]₃PW₁₂O₄₀ on the surface of the ZIF-8 structure. It was used to study the adsorptive removal of a methylene blue (MB) cationic dye model and showed high adsorption performance between pH 2 and 11 with an optimum sorbent dosage of 4 g/L. The adsorption kinetics corresponded well to the pseudo-second-order kinetic model. Moreover, response surface methodology was used to optimize experimental conditions and determine the highest MB removal percentage. The correlation between variables (time, pH, and sorbent dosage) and responses (removal percentage) were well fitted to the second-order polynomial model (R² = 0.949, Adj. R² = 0.9032, and pred. R² = 0.6129). The optimal conditions were found to be adsorbent amount = 0.04 g/L, pH = 11, and contact time = 45 min. Under these conditions, the highest removal percentage and amount of desirability were found to be 95.75% and 0.9, respectively.