Two dimensional (2D) molecular frameworks for rapid and selective adsorption of hazardous aromatic dyes from aqueous phase

Herein, two dimensional metal organic frameworks, [M(ox)(bpy)](n) [H(2)ox = oxalic acid, bpy = 4,4'-bipyridine and M = Cu (1) or Co(2)] are designed under solvothermal condition and characterized thoroughly by FTIR, PXRD, TGA and single crystal X-ray studies. X-ray structure along with topological analysis reveals a two dimensional (2D) framework of the present material with sql topology with metals in square bipyramidal geometry. The two MOFs are employed for adsorption of organic dyes i.e. methylene blue (MB) and methyl orange (MO) considered widely as water pollutants. Interestingly, the molecular frameworks showed selective nature towards methylene blue, the cationic dye. The framework remains stable after adsorption of dye and can be recycled up to five times. At equilibrium, the removal percentage of MB by the frameworks is ultimate (96-98%) with optimum temperature (25 degrees C) and pH (neutral). The kinetic studies are suggestive of the adsorption to proceed via pseudo second order reaction. The key factors or mechanism for enhanced adsorption of MB are electrostatic, pi-pi and hydrogen-bonding interactions existing between the 2D sheets and the dye. Thus, fine structural tuning of the easy-to-prepare two dimensional frameworks could lead to adsorb and remove the hazardous organic aromatic pollutants with high efficiency at low cost in future endeavours.