Self-Assembled Melaminium Adipate Lamellae for Adsorptive Removal of Anionic Dyes from Wastewater

The growth in industrialization worldwide has resulted in continual discharge of organic dyes that contaminate the aquatic ecosystem. Common adsorbents employed for dye removal are often expensive and non-biodegradable, causing a problem of secondary waste generation on their disposal. Thus, the design of biocompatible, economical adsorbents is of utmost importance. Bis(melaminium)adipate adipic acid solvate (BMA), an ionic organic material, was synthesized from commercially available melamine and adipic acid. Extensive hydrogen bonding stabilizes BMA sheets that are interlinked by lattice adipic acid molecules, resulting in the lamellar morphology. Though BMA is electrically neutral, positive zeta (zeta)-potential, due to the presence of melaminium moieties on the surface, aids in the adsorptive removal of anionic dyes from wastewater. BMA demonstrated a preference for the adsorption of anionic dyes irrespective of the solution pH, owing to the availability of multiple protonation-deprotonation sites. The Freundlich isotherm model proved to be suitable in describing the equilibrium adsorption of Congo red, owing to the surface heterogeneity in BMA. The adsorbed dye could be recovered and reused, as dye desorption ensued in methanol at room temperature. BMA is reusable for several adsorption-desorption cycles. Its biodegradability ensures that the spent adsorbent is not detrimental to the environment. Thus, the wastewater treatment with BMA generates minimal waste, underlining its viability in practical effluent management.