Microwave/ultrasound-assisted synthesis of an Fe(III)-coordinated oxazolone–polyamide metallopolymer for coordination-driven Cu(II) removal from water

This study investigated the microwave/ultrasound-assisted synthesis of a new O/N-rich oxazolone–polyamide framework and its Fe(III)-coordinated metallopolymer for Cu(II) removal from aqueous solution. The oxazolone precursor was prepared using microwave irradiation at 300 W for 10-15 min, followed by ultrasound activation at 40 kHz for 20 min, giving a yield of approximately 70%, while the reduced diamine monomer was obtained in 66% yield. The resulting NH-OXAZAM-CO polymer was further coordinated with Fe(III) to produce Fe-(NH-OXAZAM-CO), containing abundant amide, oxazolone, carbonyl, and nitrogen donor sites. The prepared materials were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, and density functional theory calculations. Cu(II) adsorption was evaluated using synthetic CuSO 4 solutions under controlled conditions: adsorbent dose 1.0 g L −1 , particle size 125–250 μm, initial Cu(II) concentration 10–50 mg L −1 , pH 5.5 ± 0.1, ionic strength 0.01 M NaNO 3 , and temperature 25 ± 1 °C. The Langmuir model provided the best fit, with a maximum adsorption capacity of 54.9 mg/g, a Langmuir constant of 0.1689, a separation factor of 0.10, and a correlation coefficient of R 2 = 0.9999, confirming favorable monolayer adsorption on finite active sites. The Temkin model also showed acceptable fitting (R 2 = 0.9701), indicating adsorbent–adsorbate interactions, whereas the Dubinin–Radushkevich model gave an adsorption energy of 1.16 kJ mol −1 , suggesting that weak physical interactions contribute to the initial uptake stage. Spectroscopic evidence from infrared and X-ray photoelectron analyses confirmed Cu(II) binding through oxygen and nitrogen donor sites, while computational descriptors supported the role of electron-rich coordination centers in metal-ion capture. Overall, the study demonstrates that Fe(III)-modified oxazolone–polyamide metallopolymers are promising coordination-based adsorbents for Cu(II)-contaminated water treatment.