The role of phase transfer catalysts on properties of polyamide thin-film composite forward osmosis membranes

Abstract In this article, 1,3,5-benzenetricarbonyl trichloride (TMC), m-phenylenediamine (MPD) and phase transfer catalysts (PTCs) were used to produce polyamide thin-film composite (TFC) forward osmosis (FO) membranes through interfacial polymerization (IP) reaction. The effects of dodecyl trimethyl ammonium chloride (DTAC), sodium dodecyl sulphate (SDS) and dodecyl dimethyl betaine (BS12) on the polyamide molecular aggregation structures, surface morphology and FO separation performance of the membranes were systematically investigated. In the FO process, concentrated 1.0 M NaCl aqueous solution was chosen as the draw solution and 0.1 M NaCl aqueous solution was used as the feed solution (at room temperature). Separation performance included the water flux (Jw) and reverse salt rejection (reverse solute flux, RS). The experiment proved that PTCs can regulate the molecular chain aggregation state and surface morphology of polyamide, which can lead to a relatively definite improvement in water flux (11.5 L m−2 h−1) (DTAC-polyamide). Simultaneously, the polyamide surface morphology was found to play a major role in the water permeability of the FO membrane rather than the density of the skin layer (i.e., degree of cross-linking), and we found that a relatively smooth surface is more conducive to weakening the external concentration polarization (ECP) phenomenon that occurs in the FO process. We attribute this mechanism on polyamide to the size effect and charge interaction of PTCs. In the current study, the balanced effect of the synergistic interaction of the molecular structure and rough surface of polyamide on FO separation performance should be comprehensively considered.