Chitosan was modified by graft copolymerization using acrylamide monomer. The resultant modified chitosan was further subjected to Hofmann degradation in order to convert acrylamide group into free amino groups and carboxylic groups. Infrared spectroscopy and 1H NMR were employed to identify the chemical structures of acrylamide grafted chitosan and Hofmann treated graft chitosan. As a result, the final product was proven to be the vinylamine-co-acrylic acid-co-chitosan. The result of potentiometric titration showed that the final product contained an increase in amount of free amino groups, which was expected to enhance the performance of removal capacity of anioric dye anionic dye and heavy metal ion. The assessment of removal capacity of anionic dyes by modified chitosan indicated that an increase in free amino groups of modified chitosan led to an increase in dye removal capacity. However, its dye removal capacity was much lower than those of virgin chitosan. It was found that the molecular weight of the modified chitosan was significantly lower than that of virgin chitosan due to the degredation of chitosan backbone during Hofmann degradation treatment. This indicated that the molecular weight of chitosan played an important role in anionic dye removal. In the case of heavy metal removal, the results showed that modified chitosan exhibited better performance than virgin chitosan, indicating that the presence of free amino groups and carboxylic groups dominated the formation of chitosan-metal complex not the molecular weight of chitosan itself.
