Preparation of Zeolite 4A for Adsorptive Removal of Methylene Blue: Optimization, Kinetics, Isotherm, and Mechanism Study

In this study, we have reported a facile preparation of zeolite 4A from Ethiopia kaolin for the adsorptive removal of methylene blue (MB) dye. The formation of highly crystalline and pure phase zeolite 4A with cubic morphology was confirmed by powder X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis. The efficiency of zeolite 4A for abatement of MB was investigated at varying adsorption parameters. Response surface methodology coupled with Box Behnken Design (RSM-BBD) was employed to optimize adsorption parameters. High regression (R 2 = 0.9947) and the low probability ( p value <0.0001) values signify the validity of the quadratic model to predict the removal (%) of MB. The maximum MB removal (%) was 99.37% at the optimum combination of 50 mL of 10 mg/L of MB, 39.05 mg zeolite 4A, and 179.82 contact time (min). The adjusted R-square (R 2 adj ) and standard deviations (SD) were validated the best fitting of pseudo-second-order kinetics and the Langmuir isotherm model for experimental values. The maximum adsorption capacity (Q max ) of zeolite 4A towards MB was found to be 44.35 mg g −1 . Electrostatic interaction, hydrogen bond, and n to π bond formation are predicted to be the plausible interaction mechanism of MB to the surface of zeolite 4A. The Fukui function and vibration analysis based on the density functional theory (DFT) further strengthened the proposed mechanism.