In case of copper ions, the formed complexes between copper
ions and chitosan and chitosan–glycine biosorbents are stable
complexes. That is due to the decrease of Ce by increasing the
immersion time. While, in case of chitosan–chloroacetic acid
modified polymer, the stability of the metal complex decreased
considerably. That is due to the shielding of NH2 groups in the
biosorbent. In addition, the high electronegativity of chloride
substituent decreases the participation of the lone-pair of
electrons of NH2 groups, which decreases the stability of the
formed complex, Fig. 3a–d.