Investigating the efficacy of 1,2,4-oxadiazole decorated cross-linked polyamidoxime-based macromolecular networks in metal ions remediation

Crosslinked polyamidoximes (PAOs) were synthesized using terephthaloyl chloride (TPC) as a crosslinking agent, which interacted with the pendant amidoxime groups on the polymer chains. The incorporation of a stiff 1,2,4-oxadiazole bridging unit was achieved by reacting TPC with PAOs in tetrahydrofuran (THF) under reflux. The linkage was verified using FTIR spectroscopy to identify the characteristic functional groups in the crosslinked polyamidoximes. X-ray diffraction (XRD) patterns indicated improved chain alignment due to crosslinking. Additionally, the thermal stability of crosslinked PAOs increased significantly to a range of 515–593 °C, compared to 426–489 °C for non-crosslinked PAOs. These crosslinked PAOs were tested for their effectiveness in removing metal ions through a batch process. Optimal conditions resulted in maximum adsorption efficiencies of 86% for Cd (II) and 88% for Pb (II) at pH 6, with a contact time of 3 h, a feed concentration of 40 mg/L, and 0.1 g of adsorbent. The adsorption mechanism conformed more closely to the Langmuir isotherm than the Freundlich model. In competitive adsorption, the order of metal uptake was Fe (II) > Pb (II) > Cd (II) > Cu (II). Consequently, this class of crosslinked polyamidoximes shows potential for use in water treatment applications for removing heavy metal ions.