M2+ ΔH# / kJ mol−1 ΔS# / kJ mol−1K−1 ΔG#298K/ kJ mol−1 Absent Fe2+ Cu2+ 35.56 34.83 30.78 – 0.162 – 0.156 – 0.173 84.13   81.32 82.33

Table 4: Thermodynamic parameters for the reaction between MB+ and SO32− . ([MB+]=20 mg/dm3; [ SO32− ]=1.0 mol/dm3; [Catalyst]=0.3 mg/dm3; pH = 8-9; T = 30°C).