A two dimensional Co(II) metal–organic framework with bey topology for excellent dye adsorption and separation: Exploring kinetics and mechanism of adsorption

Abstract Removal of organic pollutants (dyes) by using metal-organic frameworks from the wastewater is emergent hey days owing to the harmful effects of them on environment and water bodies. Herein this work, a 2D metal–organic framework, namely [(1,2-DPE)Co2Cl2]n (HT-1) has been prepared under solvothermal condition using 1,2-di(4-pyridyl)ethylene (1,2-DPE) as a ligand. The HT-1 is characterized by various analytical, spectral and single-crystal X-ray studies. The topological analysis ascertains the bey topology of the MOF with the Co(II) ion present in a tetrahedral environment. We further explored the MOF for its material importance as dye adsorbent using a cationic dye such as methylene blue (MB) as well as an anionic dye such as methyl orange (MO) in aqueous medium. It is concluded that HT-1 has the excellent ability to adsorb cationic dye molecules with excellent efficiency. The highest adsorption of the dye by the MOF was observed at neutral (optimum) pH and room temperature with highest efficiency for removal of MB i.e, 97%. The mechanism behind the better adsorption is cation-π interaction along with other non-covalent contacts existing between the MOF and MB. The presence of any inter-particle diffusion has been ruled out with N2 adsorption isotherm. Moreover, the negligible magnitude of the zeta potential (determined at varying pH) observed at the surface of the MOF suspension also excluded the adsorption phenomenon due to electrostatic interaction between the MOF and the dye. Henceforth, the non-covalent contacts are revealed to be solely responsible for the adsorption process following the pseudo-second order kinetics. Thus, the present MOF comes out as a better model for adsorption and separation of methylene blue in aqueous phase employing non-covalent interactions and this structure-activity tuning of the framework could be used for adsorbing specific dyes in future endeavours.