Adsorptive removal of the hazardous anionic dye congo red and mechanistic study of zif-8

Abstract

A metal–organic framework zeolitic imidazolate framework-8 (ZIF-8) nanosorbent was successfully prepared using a facile method under mild conditions. ZIF-8 was characterized using X-ray diffraction, Fourier transform infrared, scanning electron microscopy, X-ray photoelectron spectroscopy, and Brunauer–Emmet–Teller, and the material was used to remove Congo red (CR) from aqueous media. The adsorption kinetics, isotherms, and effects of pH and ionic strength were studied. The results showed that pseudo-second-order kinetics model and Langmuir isotherm matched well with CR adsorption on ZIF-8. The optimal conditions for CR removal occurred at neutral pH (6–8). Thermodynamics parameters of adsorption (free energy, enthalpy, and entropy) were also evaluated and indicated that the sorption process was spontaneous and exothermic. The possible mechanisms of CR adsorption onto ZIF-8 were attributed to electrostatic attractions, pore-filling effects, π–π interactions, and hydrogen bonding interactions. Regeneration of the adsorbent was also demonstrated using ethanol, and the adsorbent maintained good performance. The outstanding reusability and superior CR dye adsorbent capability of ZIF-8 demonstrated its potential application in wastewater treatment.