A commercially available thin film composite (TFC) polyamide (PA) nanofiltration (NF) membrane was chemically modified to improve its rejection capacity for selected organic micro-pollutants categorized as endocrine disrupting chemicals (EDCs) and pharmaceutically active compounds (PhACs): bisphenol-A (BPA), ibuprofen, and salicylic acid. The raw NF membrane was altered using the following modification sequence: graft polymerization (methacrylic acid (MA)-membrane); cross-linking of grafted polymer chains (ethylene diamine (ED)-membrane); and, substitution of functional groups (succinic acid (SA)-membrane). Attenuated total reflective Fourier transform infrared (ATR-FTIR) was used to verify each modification in the sequence: the formation of amide bonds; graft polymerization and cross-linking; and, increased carboxylic acids on the modified membrane. Based on zeta-potential and contact angle measurements, graft polymerization increased the negative charge and hydrophilicity of the raw membrane, while cross-linking replaced carboxylic acid with amide bonds, which made the modified membrane almost neutral at pH 6.5. The water fluxes of the ED- and SA-membranes were similar to that of the raw membrane; however, the water flux of the MA-membranes varied with polymerization time (the membrane polymerized for 15 min revealed ≥20% higher flux than the raw membrane). BPA rejection by the raw membrane was substantially improved from 74% to ≥95% after this series of modifications. However, the rejection capacity of the ED-membrane for ibuprofen and salicylic acid was slightly reduced compared with those of the MA-membrane, which was polymerized for 15 min, due to the lack of an electrical repulsion mechanism. The SA-membrane recovered its negative surface charge and showed a clear enhancement in the rejection of all pollutants.
Bibliographical noteFunding Information:
This work was supported by a Korea Science and Engineering Foundation (KOSEF) grant funded by the Korean government (MOST) (No. R01-2005-000-10517-0 (2007)). The authors wish to thank the SAEHAN Co. Ltd., Korea, for providing the NF membrane.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physical and Theoretical Chemistry
- Filtration and Separation