Synthesis, characterization, and adsorption mechanism of clay/cobalt-based MOF nanocomposites for enhanced removal of methylene blue

In this work, a cobalt-based metal-organic framework (MOF), ZIF-67, and its composite derivatives incorporating sepiolite (Sep-ZIF-67) and halloysite (Hal-ZIF-67) clays were prepared and explored for methylene blue (MB) adsorption from aqueous solutions. The structural and morphological characteristics of the prepared sorbents were systematically studied via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared spectroscopy (FTIR) analyses. The influence of several operational parameters including the solution pH, adsorbent dosage, contact time, and initial dye concentration on the adsorption efficiency was investigated and optimized. The incorporation of natural clay supports significantly improved the adsorption efficiency of ZIF-67 owing to their high surface area and abundant surface functional groups. Among the different adsorbents, Sep-ZIF-67 had the highest adsorption capacity (94.34 mg g − 1 ), followed by Hal-ZIF-67 (65.36 mg g − 1 ) and pristine ZIF-67 (49.92 mg g − 1 ). The equilibrium data were best fitted by the Langmuir isotherm model, indicating that monolayer adsorption occurred, whereas the kinetic data closely followed the pseudo-second-order model, suggesting chemisorption as the dominant mechanism. Moreover, the used adsorbents can be regenerated successfully up to six times. These findings confirm that clay-modified ZIF-67 composites, particularly Sep-ZIF-67, offer promising platforms for wastewater treatment applications.