Thermodynamic functions of metal–sericin complexation in ultrafiltration study

• Mathematical modeling was presented to evaluate metal–sericin complex constant.
• Effect of temperature on R% was elaborated in ultrafiltration of heavy metals.
• Thermodynamic functions were discussed by mathematical modeling in ultrafiltration.

A scientific attempt was made to exclusively bridge the gap between theoretical modeling and experimental evaluation of thermodynamic parameters exhibiting the removal efficiency of biopolymer in membrane supported ultrafiltration. The d-election deficient metal ions are chelated by naturally occurring biopolymer sericin containing polypeptides of several amino acids. Thermodynamically, an equilibrium is established between chelated metal ions in retentate on one side and escaped metal ions in permeate solution on other side of membrane due to metal–sericin complexation in ultrafiltration cell. The amount of metal ions entrapped on account of metal–sericin complexation (MSC) is the function of rejection percentage R% in polymer supported ultrafiltration. A novel theoretical model or relationship between R% and metal–sericin complexation constant Kf was developed at Donnan equilibrium followed by the evaluation of thermodynamic functions such as ΔG0, ΔH0 and ΔS0 in sericin-facilitated ultrafiltration. High rejection percentage (R>90%) of Cu(II) and Zn(II) implies the significant stability of MSC for these metal ions at three different temperatures 293 K, 303 K and 313 K. Greater values of R% were observed at lower concentration of each metal ion on account of enhanced chelating power of applied biopolymer sericin which is susceptible to concentration of metal ions. In addition, rejection data were statistically elaborated to support the argument based on developed novel model.

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