A facile method to estimate the effective membrane pore charge density through surface zeta potential measurement

Abstract

In this work, an attempt was made to find a correlation between the effective membrane pore charge density (Xd), which is a non-measurable quantity and the measurable quantities like, the zeta potential of the membrane surface and initial feed concentration (C0). Effects of solution pH and feed electrolyte concentration were included in the measurements of membrane zeta (ζ) potential. Seven membranes were fabricated in the range of molecular weight cut-off between 1 and 5 kDa. Zeta potential, membrane permeability, molecular weight cut off, contact angle, average pore size and Fourier transform infrared spectroscopy were used for membrane characterization. A series of monovalent salt rejection experiments were done at three initial feed concentrations of 2 g/L, 5 g/L and 10 g/L, at pH of 3, 7 and 9, at 276 kPa transmembrane pressure and 50 L/h cross flow rate. A map between Xd, ζ-potential and C0 was generated by solving the Donnan Steric Pore Model (DSPM). The good agreement amid the theoretically calculated Xd and the Xd calculated from the developed correlation allows one to estimate the effective membrane pore charge density for the loose NF/low cut off UF membranes by only measuring the ζ-potential and feed concentration of the solute, eliminating the requirement to solve the entire DSPM model.