Vacuum-assisted MPD loading toward promoted nanoscale structure and enhanced water permeance of polyamide RO membrane

Thin-film composite (TFC) reverse osmosis (RO) membranes fabricated by interfacial polymerization (IP) have been widely applied in seawater desalination. Nevertheless, their separation performance is limited by the permeance-selectivity upper bound. Compared to conventional synthesis/modification techniques, the manipulation of amine monomer distribution for the IP reaction has been far less investigated. In this study, we systematically investigated three classical approaches for m-phenylenediamine (MPD) loading during the IP reaction, i.e., vacuum filtration (TFC-V), roller (TFC-R), and air gun (TFC-A). Our results suggested that the vacuum-assisted approach can greatly enhance the availability of MPD monomers, which could, in turn, result in enhanced “ridge-and-valley” morphology of the polyamide rejection layer as a result of the enhanced nanofoaming effect. Furthermore, the TFC-V membrane demonstrated the highest water permeance of 2.8 ± 0.4 L m^-2 h⁻¹ bar⁻¹ compared to TFC-R and TFC-A membranes of 2.1 ± 0.2 L m^-2 h⁻¹ bar⁻¹ and 2.1 ± 0.4 L m^-2 h⁻¹ bar⁻¹, respectively. This study provided mechanistic insights to facilitate an improved understanding of membrane synthesis–structure–performance relationships.