Sustainable synthesis of nano-crystalline and heterostructural Zr MOF@Bentonite composite, as a novel adsorbent for methylene blue adsorption

Creating high-performance materials that are abundant in nature is an important area of current research to satisfy the growing need for sustainable, high-availability, low-cost functional adsorbents for industrial pollution removal systems. The natural bentonite collected from Abu Tartur area, Western Desert, Egypt is used as a precursor in the synthesis of ZrMOF@Bentonite composite. The synthesized material was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transformer infrared (FT-IR), and nitrogen sorption at liquid nitrogen temperature. The already prepared adsorbent was used in the removal of methylene blue dye from polluted water. Various impacts were discussed viz., adsorbent dose, solution pH, contact time, and initial concentration of the adsorbate in order to access the equilibrium criteria. The maximum removal reached 99.8% when a pH value equal to 5 and 0.17 g of adsorbent was used, While at pH = 6, the % removal was 90%. Moreover, the maximum adsorption capacity was found to be 13.7 mg/g at time 180 min. This result goes parallel with the calculated q_e one. The inspected kinetic models were examined in order to arrive at the adsorption mechanism. The overall different kinetic models were examined and have the best value of R² ≥ 0.96 indicating the adsorption process proceeds through a physisorption nature. The experiment data were analyzed by Langmuir and Freundlich isothermal models exhibiting a high correlation coefficient belonging to the two models (R² ≥ 0.96). The maximum experimental q_e is 29 mg/g which matches very well with the theoretically calculated one (q_max 32.28 mg/g).