Poly (1, 4-diazocane-5, 8-dione) macrocyclic-functionalized hydrogel for high selectivity transition metal ion adsorption

We present a method of synthesizing macrocyclic hydrogel systems using sol-gel polymerization and for high selectivity adsorption works. The hydrogel was fabricated using maleic acid and ethylene diamine ligand and characterized using FTIR, Raman, SEM/EDX, 13C NMR and SAXS techniques. It was revealed that 1, 4-diazocane-5, 8-dione were the principal active sites of this adsorbent. These macrocyclic sites provided defined zones which limited capture and chelation of transition metal ions such that from single ion solutions, only ion substrates of between 1.23 and 1.29 Å ionic size were mainly adsorbed; whereas in case of metal-metal competitive solutions, then only 1.29 Å sized substrates would be adsorbed. This adsorption specificity required that aqua metals of these sizes be of octahedral configurations for more optimum host-gest chelation with the gel active sites. Since Fe(aq) effectively met these criteria, the gel adsorbent displayed outstanding specificity for Fe(aq) adsorption from different levels of competitive environments. Present adsorbent showed that macrocyclic chelate sites can be infused directly into the hydrogel network without any grafting, and facilitates a shape-based, size-limited adsorption. This hydrogel is a promising candidate for applications in heavy metal pollution remediation, drug development and fuel cell catalysts, where high specificity adsorptions are desirable.