Search

Co-solvent assisted interfacial polymerization (CAIP) has been widely used to increase the water permeability of thin-film composite (TFC) reverse osmosis (RO) membranes. However, its outcomes are often poorly understood or unpredictable. To bridge the gap between conventional wisdom and the real effects of the co-solvent, we report—for the first time, to the best of our knowledge—empirical evidence in terms of the actual interfacial tension between two immiscible solutions used in CAIP. According to our results, dimethyl sulfoxide (DMSO), which is frequently used as a co-solvent, influences IP by interacting with trimesoyl chloride (TMC). The dipole-dipole interaction between DMSO and TMC was estimated to increase the TMC concentration at the interface and, thereby, the reaction rate. Due to the fast reaction, the diffusion barrier forms quickly, reducing the thickness and roughness of the active layer. The cross-linking degree was also determined to decrease due to the incomplete reaction that occurs when one of three acyl chloride groups interacts with Sδ+−Oδ− electrostatic dipoles of DMSO at the interface, as evidenced by the variation in unreacted acyl chloride groups in the active layer and by the nitrogen/oxygen ratio. Such morphological changes were consistent with the trend in the performances of the RO membranes prepared with different amounts of DMSO, and were used to interpret the possible transport phenomena. Image 1 • The interaction between DMSO and TMC was considered as a parameter dictating IP. • DMSO increased the TMC concentration at the interface during IP. • The increase in the TMC concentration led to a faster but incomplete IP reaction. • The faster and incomplete IP changed the morphological features of polyamide films. • A new mechanism was proposed to clarify the DMSO effect based on empirical evidence. [ABSTRACT FROM AUTHOR]

The weak interfacial force among the substrate with polyamide layer is always a non-ignorable issue for the traditional thin-film composite (TFC) membrane during actual operation. To solve this issue, herein, we have proposed an effective strategy, which is enhancing the long-term separation durability of the TFC membrane by fixing the polyamide layer on the substrate through covalent bonding. To start with, an amino-substituted polyethersulfone (PES-NH 2) was synthesized and blended with polyethersulfone (PES) to prepare a hydrophilic PES/PES-NH 2 substrate. Next, the amino group in the substrate could effectively react with a part of acyl chloride groups in the organic phase to form the stable covalent bond with the polyamide layer formed by interfacial polymerization. The prepared PES/PES-NH 2 TFC membrane possessed a denser polyamide layer with a higher cross-linking degree, as well as exhibited greatly increased separation performance at 0.6 MPa. Significantly, the PES/PES-NH 2 TFC membrane still maintained excellent separation performance under a long-term filtration period of 15 days, which is also much longer than the PES TFC membrane. This effective and promising method provides a valuable way to maintain the separation stability of TFC membrane in long-term operation. [Display omitted] • An amino-substituted polyethersulfone (PES-NH 2) resin was successfully synthesized. • The hydrophilic PES/PES-NH 2 substrate membrane containing amino groups was firstly prepared. • The PES/PES-NH 2 TFC polyamide membrane showed good long-term separation stability. • The mechanism of strengthening the interface connection between the substrate and the polyamide layer was elaborated. [ABSTRACT FROM AUTHOR]