Fabrication of poly (1, 4-dioxa-7, 12-diazacyclotetradecane-8, 11-dione) macrocyclic functionalized hydrogel for high selective adsorption of Cr, Cu and Ni

Synthesis of hydrogel adsorbent for high selectivity and strong chelate removal of transition metals Cr, Cu and Ni was accomplished via sol-gel method using ligand monomers maleic acid and (2, 2′ ethylenedioxy) bis (ethylamine) reagent. We obtained a 14-membered macrocyclic functional unit called poly (1, 4-dioxa-7, 12-diazacyclotetradecane-8, 11-dione) as the main active sites for metal adsorption. The new adsorbent's cross-linked polymer chains was clearly visualized using SEM spectroscopy; whereas the FTIR, ¹³C NMR and EDX techniques demonstrated its structural and functional groups. With an improved chelating power, this macrocyclic hydrogel was able to ignore non-target substrates, instead showing high specificity for only Cu, Cr and Ni from both single and multi-ion competitive aqueous solutions, in the order Cr > Cu > Ni. Pseudo-second order kinetic model aptly described the adsorption process, revealing chemisorption as the main mechanism which proceeded based on the host-guest chelation principle of metal ions onto the gel's macrocyclic active sites. Thus a high performance, high selectivity adsorbent system was achieved using active sites bearing substrate recognition and isolation properties.