Efficient adsorptive elimination of organic pollutants from aqueous solutions on ZIF-8/MWCNTs-COOH nanoadsorbents: Adsorption kinetics, isotherms, and thermodynamic study

The removal of organic pollutants was examined by new zeolitic imidazolate framework-8/carboxyl-functionalized multi-walled carbon nanotubes (ZIF-8/MWCNTs-COOH) nanoadsorbents, which were prepared via controlling the reaction sequence of MWCNTs-COOH with the precursors of ZIF-8. Structural morphology and chemical composition characterizations confirmed the successful preparation of ZIF-8/MWCNTs-COOH nanoadsorbents. The obtained samples manifested a preferable adsorption capacity for Congo red with the maximum adsorption capacity of 1185.58 mg g−1 with an adsorption removal rate of 97.93% at equilibrium adsorption. Further analyses indicated that the adsorption process conformed to the pseudo-second-order kinetic model and Langmuir adsorption isotherm. The thermodynamic analyses were depicted as endothermic, entropy-increasing, and spontaneous. The effects of pH value, interfering ions, and dosage on the adsorption properties were systematically explored. The nanoadsorbent can be expediently reused for eight cycles without a prominent reduction in adsorption activity. The improved performance and high reusability can be ascribed to the increasing specific surface, the presence of electrostatic interaction, hydrogen bonding, and π–π interaction between ZIF-8/MWCNTs-COOH and organic molecules. In addition, the prepared composites also showed a better adsorption performance for tetracycline with the equilibrium adsorption capacity of 471.22 mg g−1 compared to pure ZIF-8 and MWCNTs-COOH.