Kinetic evaluation and comparative study of cationic and anionic dyes adsorption on Zeolitic imidazolate frameworks based metal organic frameworks

In this study adsorption activity of Zeolitic imidazolate frameworks (ZIFs) namely ZIF-67, ZIF-8 and Zn/Co zeolitic imidazole framework, a subclass of metal organic framework is investigated for removal of cationic and anionic dyes from aqueous medium. ZIF-8, ZIF-67 and bimetallic Zn/Co ZIF were synthesized via room temperature and solvothermal route. Morphology, crystal structure, thermal stability and surface area were evaluated through scanning electron microscopy (SEM) x-ray diffraction (XRD), Thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) respectively, while metal-ligand coordination was studied through Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy. Adsorption isotherm and kinetics studies were carried out at ambient conditions of 25 ± 3 °C and contact time of 90 min to determine adsorption capacity of prepared samples. Zn/Co ZIF with removal efficiency of 92% was found to be better competitor for adsorption among all prepared Zeolitic imidazolate frameworks (ZIFs) due to synergic effect of Co and Zn leading to enhanced porosity and high surface area. High R² value illustrates that Langmuir isotherm model was followed in all reactions and adsorption proceeds through chemisorptions process. Kinetic study of adsorption reactions showing high R² values and minute difference between experimental and calculated values of Q_e justify the best fitting of pseudo second order kinetic model. (paper)