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 (ζ)-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.