Add time:07/12/2019         Source:sciencedirect.com

This paper discusses the modification of polyamide thin-film composite (TFC) membranes with amino- and diethylamino-cyclodextrins (CDs). An in situ modification procedure was carried out using different concentrations of amino and diethylamino functionalised CDs (both α- and β-CDs) dispersed in m-phenylenediamine in water. These aqueous solutions were then reacted with trimesoyl chloride on polyethersulphone (PES) ultrafiltration support membranes through the interfacial polymerisation process. Contact-angle measurements demonstrate that the TFC membranes have improved hydrophilic properties due to additional OH functional groups of the CDs. The incorporation of the amino- and diethylamino-CDs within the membrane selective layer improved water permeability which was rationalised by the increased hydrophilicity and additional water channels in the modified membranes. Modified membranes exhibited significantly improved water permeability (33.92 ± 2.00 l m−2 h−1) and maintained a high NaCl rejection (99.21% ± 0.65%). The unmodified membranes, however, had a flux of 1.12 ± 0.5 l m−2 h−1 and a NaCl rejection of 95.69% ± 0.87%, at 6.89 bar. Membranes modified with diethylamino-CDs had a smoother surface while the unmodified membranes and membranes modified with amino-CDs had rough surfaces. The membranes modified with diethylamino-CDs had a compact and dense cross-linked polyamide thin-film structure while membranes modified with amino-CDs had a less compact cross-linked structure. This is due to the CC chain of the diethylamino functionality that allowed for a maximum exposure of the pendent group to the trimesoyl chloride during the interfacial polymerisation; as a result, the diethylamino-CDs were less subjected to steric hindrance than the amino-CDs. The pendent group of the amino-CDs was close to the molecule, making it difficult to reach during the interfacial polymerisation due to steric hindrance.

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