Development of nanofiltration membranes based on rigid star amphiphiles

The objective of this study was to develop new NF membranes capable of providing higher water permeability and higher rejection for a wide range of contaminants compared to commercial NF membranes. Rigid star amphiphiles (RSAs), synthesized as part of this study having various range of hydrophobicity, were used as active layer material. Characterization study by atomic force microscopy (AFM), and Rutherford backscattering spectrometry (RBS) showed that the RSA membranes have uniform, ultrathin (∼16.5 nm) active layers. Performance characterization showed that RSA membranes had water permeability 1.3-3.1 times higher than that of commercial NF membranes (ESNA and TFC-S) while providing comparable rejection of the organic contaminant surrogate Rhodamine WT(R-WT). However, the rejection of arsenious acid (H₃AsO₃) by most RSA membranes was found to be lower than that by the commercial membranes. The RSA with highest hydrophilicity provided the highest rejection of R-WT. In contrast, optimum As(III) rejection, comparable to that of commercial NF membranes was obtained for RSAs with intermediate hydrophilicity. Polymerization of RSA is now under study to improve RSA membrane performance.