Nanofiltration membranes modified with alkoxysilanes: Surface characterization using zeta-potential

The characterization of nanofiltration (NF) membranes is necessary for predicting their performance under different operating conditions, and for optimizing the membrane-separation process. A thin-film composite (TFC) polymer membrane for nanofiltration, modified with tri- and tetra-alkoxysilanes, was produced using a sol–gel procedure. The surface charges of the modified membranes were determined at different pHs by means of the zeta-potential. The streaming current was measured for a zeta-potential analysis of the flat-sheet membranes. Knowledge of the zeta-potential is essential for designing and operating membrane processes, and its measurement provides the key to understanding the control of charge-related phenomena. The zeta-potential of modified membranes is distinct from that of an untreated membrane. The isoelectric point was found to be at a higher pH after a treatment with any of the alkoxysilanes. The surfaces of the modified membranes showed an amphoteric behaviour. The homogeneity and stability of the treatment were assessed by a repeated zeta-potential analysis of the same and different membrane samples.