Impact of adding nitro-substituted aromatic acyl chlorides on the structure and desalination performance of polyamide thin film composite membranes

Generally, reverse osmosis (RO) membranes are optimized by adjusting the composition of the aqueous phase during interfacial polymerization (IP). This is a highly convenient strategy as the mixing of the additives to the aqueous phase provides a significant freedom owing to the ease of miscibility or dispersibility of the additives in the aqueous solutions. The impact of adding additives to the organic phase is not much like that of the aqueous phase for the sake of tuning the performance of the polyamide thin film composite (PA-TFC) membranes. Given the high importance of the organic phase during interfacial polymerization, the current study explored the impact of adding a minor amount of nitro group-substituted acyl chlorides, 4-nitrobenzoyl chloride (NBC)/3,5-dinitrobenzoyl chloride (DNBC) to the organic phase containing trimesoyl chloride (TMC) during interfacial polymerization for the sake of tuning the performance of the thin film composite polyamide membranes. Because the acyl chloride group reacts with the amino groups of m-phenylenediamine (MPD), the NBC/DNBC reagents reacted with MPD in a manner analogous to the acid chlorides of TMC. However, the NBC/DNBC does not generate a three-dimensional crosslinked polyamide network, as with TMC. Therefore, membranes developed by incorporating minor quantities of NBC/DNBC have altered polyamide growth, unlike the control NBC/DNBC-0 membrane. The membranes containing NBC/DNBC showed an improvement in permeate flux (DNBC membrane flux = 30.5±0.14 L m^-2 h^-1 and NBC membrane flux = 26.4±0.15 L m^-2 h^-1) in comparsion to the NBC/DNBC-0 (control MPD/TMC) membrane (flux = 16.7 ± 0.12 L m^-2 h^-1) and a slight decline in NaCl rejection, which remained within the acceptable range.