Elucidation of selective adsorption study of Congo red using new Cadmium(II) metal-organic frameworks: Adsorption kinetics, isotherm and thermodynamics

Herein, we report the syntheses, characterization, thermodynamic and kinetic properties and application of two Cd(II) containing metal-organic frameworks, namely [Cd (5-aip) (bpy)] (1) and [Cd (5-hip) (bpy)] (2), where 5-aip ​= ​5-aminoisophthalate ion, 5-hip ​= ​5-hydroxyisophthalalate ion and bpy ​= ​2,2′-bipyridine respectively. Structural analyses showed that both MOFs displayed a two-dimensional (2D) framework structure, anchored with free –NH2 and –OH groups, for 1 and 2 respectively. The dye adsorption behaviors of both MOFs were explored in detail, which showed that both MOFs efficiently and selectively adsorbed anionic dye Congo red (CR) over cationic dyes. Linear as well as nonlinear kinetics and isotherm data of CR removal by MOFs were thoroughly studied to predict the optimum models. The experimental data fitted well with the Langmuir adsorption isotherm model and followed pseudo second order kinetics. A spontaneous and feasible nature of CR adsorption process was elucidated from the thermodynamic parameters. Two new Cd(II) containing metal-organic frameworks have been synthesized and characterized. Both MOFs showed efficient and selective adsorption of anionic dye Congo red over cationic dyes. The Congo red adsorption process is thermodynamically feasible, spontaneous, and based on electrostatic and hydrogen-bonding interactions between the dye and MOFs. [Display omitted] •Two new Cd(II) containing metal-organic frameworks have been synthesized.•Both MOFs were characterized by standard analytical techniques.•Structural analyses showed that both MOFs displayed a two-dimensional (2D) framework structure.•Dye adsorption studies showed that both MOFs efficiently and selectively adsorbed anionic dye Congo red over cationic dyes.•A detailed kinetic study, different thermodynamic parameters, and a plausible mechanism are discussed.