Impact of the structure of the equivalent number of molecules of additive aliphatic amines used during interfacial polymerization on the structure and desalination performance of the co-polyamide membranes

The current study aimed to investigate how the structure and number of amino groups present in the aliphatic additive amines impact the structure and performance of the membranes while keeping the number of molecules of each additive amine the same during membrane fabrication. This was readily achieved using 0.1 equivalent moles of three aliphatic amines to meta-phenylenediamine (MPD). The aliphatic amines, including ethylenediamine (2A), diethylenetriamine (3A), and N, N-bis(3-aminopropyl)ethylenediamine (4A), were used as additives. Ethylenediamine (2A) has two primary amino; diethylenetriamine (3A) has two primary and one secondary amino and N, N-bis(3-aminopropyl)ethylenediamine (4A) has two primary and two secondary amino groups per molecule. Four membranes were fabricated by interfacial polymerization (IP) using four different aqueous phases, including one MPD solution and three MPD+0.1 equivalent additive amines. In contrast, trimesoyl chloride (TMC) was used as an organic phase. Owing to the differences in the composition of the aqueous phase used during IP, the surface charge of the co-polyamide membranes became significantly positively charged compared to the control MPD/TMC membrane. The co-polyamide MPD-4A/TMC and MPD-2A/TMC membranes possessed isoelectric points (IEPs) of 9.2 and 9.6, respectively, compared to an IEP of around 3.8 for the control MPD/TMC membrane. The MPD-4A/TMC membrane showed an improved pure water permeate flux of 47.1 L m^-2 h^-1 compared to 30.0 L m^-2 h^-1 for the control MPD/TMC membrane at 30 bar. Moreover, the MPD-4A/TMC membrane showed a rejection of 98.3% and 96.0% for CaCl₂ and NaCl, compared to 95.6% and 95.2% for the control MPD/TMC membrane. The MPD-4A/TMC membrane also showed stable desalination performance using 10,000 ppm NaCl feed and antifouling properties using 10,000 ppm NaCl and 100 ppm bovine serum albumin (BSA) feeds.