Facile synthesis of zeolitic-imidazole framework-67 (ZIF-67) for the adsorption of indigo carmine dye

This study aims to synthesize ZIF-67 for the adsorption of indigo carmine (I.C.) dye. ZIF-67 materials were synthesized under different conditions and the synthesis condition of ZIF-67 giving the best adsorption efficiency was obtained. In batch adsorption studies, pH, adsorbent amount, contact time, initial dye concentration, and temperature effects were investigated. Adsorption data were applied to Langmuir, Freundlich, and Temkin isotherm models. The best correlation value was obtained in Langmuir isotherm (R² = 0.999). The adsorption of I.C. dye with ZIF-67 occurred in a monolayer with a homogeneous surface according to Langmuir isotherm. The highest adsorption capacity value of ZIF-67 metal–organic framework for I.C. dye was found as 370 mg/g. Kinetic model studies were also performed and pseudo first-order, pseudo second-order, and intraparticle diffusion models were used. Pseudo second-order was the best fitting kinetic model to the data (R² = 0.997). Adsorption mechanisms of ZIF-67 for I.C. dye include electrostatic interaction, π–π interaction, and hydrogen bonding. Thermodynamic studies showed that I.C. removal by ZIF-67 is an exothermic and spontaneous process. ZIF-67 was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), and N₂ adsorption–desorption. The surface area of synthesized ZIF-67 was found 1493 m² g⁻¹. The salt concentration effect on I.C. adsorption by ZIF-67 was also investigated, showing an increase in adsorption capacities with increasing salt concentration. The regeneration study was carried out and after 5 cycles, the reduction in efficiency was 21%.