Synthesis and characterization of IPN hydrogels based on HEMA-co-AM/PVA at Low HEMA contents for metal removal applications

This work aimed to synthesize the interpenetrating polymer network (IPN) hydrogels of poly(2-hydroxyethyl methacrylate-co-acrylamide)/polyvinyl alcohol (P(HEMA-co-AM)/PVA). The hydrogels were prepared by the thermal method and microwave irradiation method via a free-radical. The thermal method was synthesized by a two-step reaction in aqueous solution at 50C for 24 h. For the microwave irradiation method, the hydrogels was synthesized by a one-pot reaction in an aqueous solution with varied electric power at 300-600 W and reaction time for 5-17.5 min. After that,P (HEMA-co-AM)/PVA/CS hydrogels were also prepared by the thermal methodin an aqueous at 50 C for 48 h. The IPN hydrogels were crosslinked by glutaraldehyde (GA) and Ethylene glycol dimethacrylate (EGDMA) using ammonium persulfate (APS) as aninitiator. In the first step, (P(HEMA-co-AM) network was synthesized in PVA aqueous solution and then followed by glutaraldehyde crosslinking reagent to form to the semi-IPN structure. Several analytical techniques such Fourier transform infra-red (FT-IR) spectroscopy were used to identify the functional groups in the structure of hydrogel films. Scanning electron microscopy (SEM) and atomic-force microscopy (AFM) were used to characterize the surface microstructure of the hydrogel. X-ray diffraction (XRD) testing was carried out to identify the microstructure of hydrogel structure. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) measurements were performed to investigate the effect of the amount of monomers on the thermal stability of the membranes. This study compared the properties, including water adsorption and heavy metals adsorption ability of hydrogels obtained from different techniques. The swelling behaviors of the hydrogel were measured gravimetrically in distilled water at a room temperature of 28± 2C, and a rapid response. Results showed that the hydrogel prepared by microwave irradiation technique exhibited the higher swelling ratio than 1,200% for 300W at 17.5 min compared with the hydrogels prepared by the conventional thermal method. The adsorption capacities and rates of Pb2+ ions onto IPN hydrogel were evaluated. The maximum adsorption capacity of the metals was found to occur at an initial metal concentration of 750-1000 mg/L. The pseudo-first order and pseudo-second order kinetics were applied to examine the of adsorption behavior. The kinetic experimental data properly correlated with the pseudo-second order kinetic model more than with the pseudo-first order. The Langmuir and Freudlich adsorption models were applied to describe the isotherms and isotherm constants. Adsorption isotherms data of metal ions were likely to follow the Langmuir model. After comparing the adsorption capacity among the hydrogels obtained from the different techniques, it was found that the hydrogel prepared by microwave irradiation technique showed a higher removing efficiency of heavy metal ions than the hydrogels prepared by the conventional thermal method.