Removal of heavy metal ions from an aqueous solution by CS/PVA/PVP composite hydrogel synthesized using microwaved-assisted irradiation

A simple protocol of chitosan/polyvinyl alcohol/polyvinylpyrrolidone (CS/PVA/PVP) hydrogel synthesis using microwave-assisted irradiation to initiate and accelerate network formation was explored. The optimum ratio of CS:PVA:PVP was 0.3:0.6:0.3 g with epichlorohydrin as a cross-linking agent under 600 watts of irradiation for 3 min. The gel swelling degree and gel fraction of the hydrogel were approximately 1627.4% and 42.6%, respectively. The individual metal ion removal efficiency was the highest for Pb(II), followed by Cu(II), Ni(II), and Cd(II) as adsorbed by the CS/PVA/PVP hydrogel. Varying the pH of the solution containing metal ions in the range of 4.0 – 8.0 did not significantly affect the adsorption capacity. However, the order of adsorption capacity of mixed metal ions differed from that of individual ions. The maximum capacities of Pb(II), Cu(II), Ni(II), and Cd(II) ions were 80.02, 33.07, 15.13, and 8.36 mg g−1, respectively. The desorption and reusability study of the CS/PVA/PVP hydrogel revealed that 0.1 M EDTA was a suitable candidate to regenerate the hydrogel as more than 60% of metal ion removal efficiency was still achieved after five adsorption cycles. In addition, the reaction mechanism of the hydrogel network formation derived from infrared spectrometry indicated that network formations were developed through the reaction between the crosslinking agent and hydroxyl and amino functional groups of the starting materials. Adsorption mechanism based on the results obtained from x-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS) was also presented. This study showed that the proposed composite hydrogel could be further developed and used as a platform to efficiently adsorb metal ions.