Removal of Congo red by two new zirconium metal–organic frameworks: kinetics and isotherm study

Abstract

Two metal–organic frameworks based on zirconium with high stability were synthesized by the hydrothermal method. Zirconium salt, benzene-1,4-dicarboxylic acid, and benzene-1,3,5-tricarboxylic acid were used to produce Zr6O4(OH)4(BDC)6 and Zr6O4(OH)4(OAc)6(BTC)2 metal–organic frameworks, respectively. The potential of adsorption of Congo red by synthesized metal–organic frameworks was investigated. The results of X-ray diffractometry, Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis methods state that the metal–organic frameworks have a high capacity to adsorb Congo red in a short time. Kinetic and isotherm data of Congo red were discussed using pseudo first- and second-order equations. The results show that adsorption follows the second-order kinetic model. The equilibrium adsorption data of Congo red on the synthesized samples were analyzed by Langmuir, Temkin, and Freundlich isotherm models, suggesting adsorption follows the Langmuir model and provides the maximum adsorption capacity of 340 and 870 mg g−1 for Zr6O4(OH)4(BDC)6 and Zr6O4(OH)4(OAc)6(BTC)2, respectively.