Equilibrium, Kinetic and Thermodynamic studies of adsorption of cationic dyes from aqueous solution using ZIF-8

Zeolitic imidazolate framework-8 (ZIF-8) is one type of (MOFs) that has been synthesized and characterized and detailed analysis of Crystal violet (CV) and Malachite Green (MG) adsorption behaviour. Impact of different variables on batch method as a function of solution pH, concentration of CV and MG, dose of ZIF-8, Contact time and temperature were analyzed and optimal test conditions were determined. Scanning electron microscopy (SEM) was used to measure surface alterations of the ZIF-8. The surface area and volume of the pores were found to be 495.199 m2g–1 and 0.026 cm3g−1, respectively as determined by the Brunauer-Emmett-Teller (BET) test. ZIF-8 point of zero charging (pHPZC) was calculated and was found 7.9. Adsorption data were modeled on isotherms for adsorption of Langmuir, Freundlich, Dubinin–Radushkevich and Temkin. Equilibrium data from the adsorption processes showed that the Langmuir is fitted with CV and MG adsorption. Pseudo-first order, pseudo-second order, kinetic models Weber and Morris and Elovich were used to analyze the kinetic data obtained at different initial dye concentrations. The kinetics of adsorption showed that the action in adsorption adopted the processes of pseudo-second - order kinetic model and chemisorption. The thermodynamic parameter such as ∆G, ∆S and ∆H has been determined. Study of thermodynamics for adsorption indicated the reaction was endothermal and spontaneous.