Kinetic and Thermodynamic Studies of Lysozyme Adsorption on Cibacron Blue F3GA Dye-Ligand Immobilized on Aminated Nanofiber Membrane

Abstract

The polyacrylonitrile (PAN) nanofiber membrane was prepared by the electrospinning technique. The nitrile group on the PAN nanofiber surface was oxidized to carboxyl group by alkaline hydrolysis. The carboxylic group on the membrane surface was then converted to dye affinity membrane through reaction with ethylenediamine (EDA) and Cibacron Blue F3GA, sequentially. The adsorption characteristics of lysozyme onto the dye ligand affinity nanofiber membrane (namely P-EDA-Dye) were investigated under various conditions (e.g., adsorption pH, EDA coupling concentration, lysozyme concentration, ionic strength, and temperature). Optimum experimental parameters were determined to be pH 7.5, a coupling concentration of EDA 40 μmol/mL, and an immobilization density of dye 267.19 mg/g membrane. To understand the mechanism of adsorption and possible rate controlling steps, a pseudo first-order, a pseudo second-order, and the Elovich models were first used to describe the experimental kinetic data. Equilibrium isotherms for the adsorption of lysozyme onto P-EDA-Dye nanofiber membrane were determined experimentally in this work. Our kinetic analysis on the adsorption of lysozyme onto P-EDA-Dye nanofiber membranes revealed that the pseudo second-order rate equation was favorable. The experimental data were satisfactorily fitted by the Langmuir isotherm model, and the thermodynamic parameters including the free energy change, enthalpy change, and entropy change of adsorption were also determined accordingly. Our results indicated that the free energy change had a negative value, suggesting that the adsorption process occurred spontaneously. Moreover, after five cycles of reuse, P-EDA-Dye nanofiber membranes still showed promising efficiency of lysozyme adsorption.

Keywords: adsorption; dye affinity ligand; kinetic; lysozyme; nanofibrous membrane; thermodynamic.

Figure 1

Schematic representation of the electrospinning device, including polymer solution stored in syringes, syringe pumps, DC high voltage power supplies, and cylindrical rotating collector.

Figure 2

The chemical synthesis routes of P-COOH, P-EDA, and P-EDA-Dye nanofiber membranes.

Figure 3

FTIR spectra of (a) PAN, (b) P-COOH, (c) P-EDA, and (d) P-EDA-Dye nanofiber membranes.

Figure 4

SEM images of (a) PAN, (b) P-COOH, (c) P-EDA, and (d) P-EDA-Dye nanofiber membranes. Bar scale: 500 nm.

Figure 5

Effects of operating parameters on the binding capacity of P-EDA-Dye nanofiber membranes for lysozyme: (a) adsorption pH, (b) concentration of EDA coupled on P-COOH nanofiber membrane, (c) dye concentration immobilized on P-EDA-Dye nanofiber membrane, and (d) dye immobilization concentration vs. dye loaded.

Figure 5

Effects of operating parameters on the binding capacity of P-EDA-Dye nanofiber membranes for lysozyme: (a) adsorption pH, (b) concentration of EDA coupled on P-COOH nanofiber membrane, (c) dye concentration immobilized on P-EDA-Dye nanofiber membrane, and (d) dye immobilization concentration vs. dye loaded.

Figure 6

Adsorption rate at varying concentrations of lysozyme by P-EDA-Dye nanofiber membrane. (a) Kinetic curves at varying concentrations of lysozyme, (b) pseudo first-order plot of ln(q₁−q_t) against t, (c) pseudo second-order plot of t/q_t against t, (d) Elovich model plot of q_t against ln t, and (e) intra-particle diffusion model plot of q_t against t^0.5.

Figure 7

Adsorption rate at varying concentrations of NaCl by P-EDA-Dye nanofiber membrane. (a) Kinetic curves at varying concentrations of NaCl, (b) pseudo first-order plot of ln(q₁−q_t) against t, (c) pseudo second-order plot of t/q_t against t, (d) Elovich model plot of q_t against ln t, and (e) intra-particle diffusion model plot of q_t against t^0.5.

Figure 8

Adsorption rate of lysozyme at varying temperatures by P-EDA-Dye nanofiber membrane. (a) Kinetic curves at varying temperatures (278 K–308 K), (b) pseudo first-order plot of ln(q₁−q_t) against t, (c) pseudo second-order plot of t/q_t against t, (d) Elovich model plot of q_t against ln(t), (e) intra-particle diffusion model plot of q_t against t^0.5, and (f) Arrhenius plot of ln k₂ against 1/T for the adsorption of lysozyme on the P-EDA-Dye nanofiber membrane.

Figure 9

(a) Effect of temperature on the equilibrium isotherm curves for the adsorption of lysozyme on P-EDA-Dye nanofiber membrane, (b) Langmuir model plot of C/q against C, (c) Freundlich model plot of ln(q) against ln(C), (d) Temkin model plot of q against ln(C), and (e) Van ’t Hoff plot for the adsorption of lysozyme on P-EDA-Dye nanofiber membrane.

Figure 10

Effect of number of the repeated use of the P-EDA-Dye nanofiber membrane on the binding capacity of lysozyme by P-EDA-Dye nanofiber membrane.