Synthesis and characterization of ZnO nanoparticles via zeolitic imidazolate framework-8 and its application for removal of dyes

Zinc oxide (ZnO) nanoparticles were obtained via calcination of zeolitic imidazolate framework-8 (ZIF-8). The activities of prepared ZnO nanoparticles at different temperature 450, 550, and 650 degrees C were investigated for the adsorption of acid red 57 (AR57) and remazole red (RR) dye. The synthesized ZnO nanoparticles were characterized by different spectroscopic studies such as FTIR, X-ray diffraction, energy-dispersive X-ray spectroscopy, N-2 adsorption-desorption and pH titration for determination of Zero-point charge (pH(ZPC)). The mechanism of adsorption behavior of AR57 and RR are studied with respect to temperature, pH and concentration. Experimental data indicated that the adsorption capacity of ZnO for AR57 and RR was higher in acidic rather than in basic solutions. The activation energy of adsorption was also evaluated for the adsorption of AR57 and RR onto ZnO nanoparticles. Langmuir and Freundlich adsorption models were also applied to describe the equilibrium isotherms and the isotherm constants. The pseudo-first-order and pseudo-second-order model equations were used to analyze the kinetics of the adsorption process. The adsorption efficiency of ZnO nanoparticles was found in the order: 450 > 550 > 650 degrees C. The activation energy, enthalpy, change of free energy and entropy of adsorption were also evaluated for the adsorption of AR57 and RR onto ZnO nanoparticles. The thermodynamics of the adsorption indicated spontaneous and exothermic nature of the process. (C) 2020 Elsevier B.V. All rights reserved.