Cr2O72-/ MnO4-based novel adsorbents: Applicable for removal of cationic and anionic organic dyes from waste water

This study presents the synthesis of two new metal-organic ionic frameworks (MOIFs) and their potential utility as adsorbents for deleterious organic dyes. The frameworks were created through an ion-exchange process in aqueous conditions, employing K2Cr2O7/KMnO4 and 4-[(4-methylpiperazin-1-yl)methyl]-N-(4-methyl-3-{[4(pyridin-3-yl)pyrimidin-2-yl]amino}phenyl)mesylate (Im) as reactants. Structural characterization of the MOIFs was conducted using powder XRD, UV/Vis spectroscopy, and FTIR spectroscopy, enabling precise identification. Differential scanning calorimetry (DSC) analysis provided insights into critical properties such as activation energy, enthalpies of crystallization/melting, and specific heat capacity (0.4318 J per kelvin). These thermal characteristics were further correlated with the MOIFs' structural attributes. The activation energy for MOIF was determined using the Coats-Redfern model with TGA data (-0.85 kJ/M). Anionic dyes (Methyl orange/Congo red/Nigrosine) exhibited significantly higher adsorption rates (almost 100 %) compared to cationic dyes (70-80 %) such as safranin and crystal violet. Kinetic analysis indicated that the adsorption mechanism of MOIFs followed a pseudo first-order model. Overall, the adsorption analysis suggested that MOIFs strongly adsorb anionic dyes in comparison to cationic ones.