Determination of Coordination Parameters of Cd2+ and Zn2+ with Polyvinyl Alcohol and Chitosan

The apparent coordination numbers and coordination stability constants of polyvinyl alcohol-Cd2+ (PVA-Cd2+), polyvinyl alcohol-Zn2+ (PVA-Zn2+), and chitosan-Zn2+ (CTS-Zn2+) were determined in aqueous solution through the straightforward and effective measurement of the equilibrium metallic ion concentration. The difference of the parameters between these complexes was discussed in detail. The apparent coordination numbers of PVA-Cd2+, PVA-Zn2+, and CTS-Zn2+ complexes were 1.76, 1.36, and 1.44, respectively, which at the molecular level is due to multiple complexes with different coordination constants (1 or 2) being formed. The apparent coordination stability constants of PVA-Cd2+, PVA-Zn2+, and CTS-Zn2+ complexes were 4.0 × 103, 1.2 × 103, and 4.6 × 104, respectively. In comparison with Zn2+, it was easier for Cd2+ to be coordinated with PVA and the apparent coordination constant was closer to 2. In addition, the larger apparent coordination stability constant of CTS-Zn2+ compared with that of PVA-Zn2+ i...