A systematic investigation to understand the effect of altering the active layer chemistry on the desalination potential of nanofiltration membranes by incorporating varied aliphatic multi-amines during interfacial polymerization

The current study employs a systematic approach to enhance the desalination performance of polyamide (PA) thin film composite (TFC) membranes by modifying the chemistry of the PA active layer. Four aliphatic amines containing two to five primary/secondary amino groups in the amine structure were used. These aliphatic amines include ethylene diamine (2A), diethylene triamine (3A), 1,3-bis(2-aminoethylamino)propane (4A), and tetraethylenepentamine (5A). The aliphatic amines (XA; X=2, 3, 4, and 5) were added in a fixed percentage of 0.2wt% to 1.8wt% of PIP, and hence, four different aqueous phases were prepared. Interfacial polymerization (IP) between PIP/XA on a polysulfone support yielded four PA-TFC membranes. The yielded membranes showed variations in features, such as surface morphologies and wettabilities attributed to varied chemistry. The membranes showed an increase in hydrophilicity with an increase in the chain length of the aliphatic amine with water contact angles of 51o, 42o, 25o, and 26° for PIP/2A-TMC, PIP/3A-TMC, PIP/4A-TMC, and PIP/5A-TMC membranes, respectively. Among different membranes, the behavior of the 3A and 5A amines was similar in terms of PA growth and performance of the membrane. However, in terms of optimized desalination performance, the PIP/3A-TMC membrane proved to be better than the other membranes, with a permeate flux of 65±4 LMH at 20bar with Na2SO4 and MgSO4 rejection rates of 97%, followed by 95% rejection of CaCl2. The PIP/3A-TMC membrane showed the highest flux recovery among other membranes, reaching a value of 96%.