Spectroscopic and thermal studies of poly[(N-vinylimidazole)-co-(maleic acid)] hydrogel and its auaternized form

BACKGROUND: In this study, poly[ (N-vinylimidazole)-co-(maleic acid)] (poly(VIm/MA)) hydrogels were prepared by gamma-irradiation of ternary mixtures of N-vinyhmidazole-maleic acid-water using a Co-60 gamma-source. Spectroscopic and thermal analyses of these hydrogels as a function of protonation showed that the results are consistent with the existence of an H-bridged complex when the imidazole rings are partially protonated. Finally, the efficiency and binding trends of Cu2+, Co2+, Cd2+ and Pb2+ ions with both protonated and unprotonated poly(VIm/MA) hydrogels were determined. RESULTS: Gelation of 90% was reached at around 180 kGy dose at the end of irradiation. The poly(VIm/MA) hydrogels synthesized were further protonated in HCl solutions with different concentrations. Hydrogels originally showed 450% volumetric swelling; this ratio reached 1900% after protonation at pH = 5.0. Fourier transform infrared spectral changes in the N+-H stretching region (3200-3600 and 1173 cm(-1)) and the ring mode deformation at 915 cm(-1) are consistent with the formation of an H-bridged complex between the protonated and unprotonated imidazole rings upon partial protonation. Similar changes were obtained from NMR spectra of both the protonated and unprotonated forms of the hydrogels. CONCLUSION: Protonated and unprotonated hydrogels have been used in heavy metal ion adsorption studies for environmental purposes. Adsorption decreased with decreasing pH value due to the protonation of the VIm ring. The adsorption of Me2+ ions decreased in the order Cu2+ > CO2+ > Cd2+ > Pb2+, which is related to the complexation stability as well as the ionic radius of the metal ions. These results show that P(VIm/MA) hydrogels can be used efficiently to remove heavy metal ions from aqueous solutions. However, the protonated form is a bad choice for heavy metal ion adsorption due to electrostatic repulsion forces; it can nevertheless be assumed to be a good choice for anion adsorption from environmental waste water systems. (c) 2007 Society of Chemical Industry.