Effect of synthesis conditions on the non-uniformity of nanofiltration membrane pore size distribution

The uniformity of membrane pore sizes, which is essentially determined by the membrane synthesis conditions, significantly affects the rejection performance of nanofiltration (NF) membranes. In this study, we applied two modeling methods, i.e., the DSPM (Donnan Steric Pore Model) and the log-normal distribution methods, for the determination of the average membrane pore size and pore size uniformity of lab-made NF membranes. The synthesis conditions included concentration of monomers (e.g., piperazine and trimesoyl chloride), (thermal) curing temperature and time, and activation solvent type and duration. Results showed that both high piperazine (PIP) concentration (≥0.5 wt%) and curing temperature (≥40 °C) could enhance the membrane pore size uniformity. Although the average membrane pore size calculated by the DSPM method was higher than that by the log-normal distribution method, they significantly correlated. It appears that the log-normal distribution method could more directly characterize membrane pore size uniformity. Obviously, the pore uniformity of NF membranes affected the rejection of small molecules, such as trace organic compounds. These insights provided a theoretical foundation for the characterization of membrane pore size distribution with more accuracy and the fabrication of membranes with higher pore size uniformity.