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.

Highlights

  • Desirable features of nanofiber membranes intended for use in protein adsorption include low non-specific adsorption, high adsorption capacity, high adsorption rate, good biocompatibility, and high chemical/mechanical stability; these characteristics can be achieved by manipulation of chemical composition and synthesis operation that result in high porosity, large specific adsorption area, and good hydrophilicity of nanofiber membranes [6,9–13]

  • Our results suggested that the optimal pH for lysozyme adsorption on P-EDA-Dye nanofiber membrane is pH 7.5

  • The values of kinetic parameters associated with the adsorption mechanism of lysozyme were determined in a batch stirred tank system

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Summary

Introduction

Electrospun nanofiber membranes have been intensively researched in fields [1], such as tissue engineering [2], drug delivery [3], biosensing [4], antibacterial membranes [5], filtration and adsorptive membranes [6,7], and wastewater treatment [8]. Desirable features of nanofiber membranes intended for use in protein adsorption include low non-specific adsorption, high adsorption capacity, high adsorption rate, good biocompatibility, and high chemical/mechanical stability; these characteristics can be achieved by manipulation of chemical composition and synthesis operation that result in high porosity, large specific adsorption area, and good hydrophilicity of nanofiber membranes [6,9–13]. Polyacrylonitrile (PAN) membranes have superior mechanical strength and chemical stability [14,15], but their hydrophobic nature makes them less suitable for application in protein adsorption, as compared with the cellulose membranes that have good hydrophilicity [16,17]. Introduction of the hydrophilic groups on the PAN membrane surface could combine the advantages offered by both hydrophilic and hydrophobic membranes

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