A Parametric Study on Protein-Membrane-Ionic Environment Interactions for Membrane Fouling

This work reports on protein-membrane-ionic environment interactions on the basis of chemical and electrochemical features of ultrafiltration membranes and the protein in the solution that affects the extent of protein adsorption onto the membrane, which is a measure of membrane-fouling. Bovine serum albumin (BSA) was chosen as the model protein; and 10 kDa of hydrophobic polyethersulfone (PES) and hydrophilic cellulose triacetate (CTA) ultrafiltration membranes at the solution pH values of 3.78, 4.78, and 6.80, and ionic-strengths of 0.01 M and 0.1 M were employed. Isotherms for BSA adsorption on both types of membranes were correlated by the Freundlich equation. More BSA was adsorbed on hydrophobic PES membranes than was adsorbed on hydrophilic CTA membranes. The highest degree of adsorption on PES membranes was obtained at pH=3.78 whereas the minimum adsorption occurred at the isoelectric point (IEP) (pH=4.78) of BSA. With increasing ionic strength, the adsorbed protein on both membranes decreased. The zeta-potentials of the membranes and protein were determined by streaming potential measurements and theoretical calculations, respectively; and the electrostatic interactions and van der Waals energies between the membranes and the protein were calculated using the Deryagin-Landau/Verivey-Overbeek (DVLO) theory. To detect the structural changes that occurred, membrane surfaces were analyzed by Fourier transform infrared-attenuated total reflectance (FTIR-ATR) measurements, and scanning electron microscopy (SEM) and atomic force microscope (AFM) images.