Preparation of small-pore UF membranes with high porosity by modulating the size of nano-CaCO3 in a casting solution

High-performance ultrafiltration (UF) membranes show significant potential for high selectivity and permeation. In the present study, small-pore polyethersulfone (PES) UF membranes with narrow size distributions and high surface porosities were successfully prepared from PES casting solutions that contained nano-CaCO₃ particles of different sizes and were coagulated in a HCl solution. The nano-CaCO₃ particles with different sizes (22.8–6.3 nm) were produced by modulating the HCl/nano-CaCO₃ molar ratio in the casting solution. The size of the nano-CaCO₃ particles and the amount of CaCl₂ produced synergistically affected the viscosity of the casting solution; in addition, these factors regulated the structure and performance of the PES UF membranes. The obtained membranes exhibited small pore sizes with narrow pore size distributions and high surface porosities, as well as high water flux and bovine serum albumin (BSA) rejection. The optimized membrane had a surface pore size of 9.8 nm with an FWHM of 5.5 nm and a high surface porosity of 12.8%. The membrane also exhibited a high water permeance of 737.2 L·m⁻²·h⁻¹·bar⁻¹ with a BSA rejection of 99.3%, which surpassed those reported for PES membranes in the literature. This work provided a simple and effective method for preparing high-performance UF membranes.