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High-performance semi-permeable membranes play a vital role in the membrane-based separation technology for seawater and brackish water desalination. Herein, plasticizer-assisted interfacial polymerization (PAIP) was implemented to fabricate aromatic polyamide layers with improved water flux and comparable salt rejection for the first time. Specifically, plasticizer (i.e., diethyl phthalate, DEP) was introduced into the organic phase to perform interfacial polymerization. Effective regulation of the desalination performance was achieved via meticulously adjusting plasticizer concentration. With the addition of 0.5 wt% DEP, water flux promoted from 1.06 L m−2 h−1 bar−1 of the pristine membrane to 2.85 L m−2 h−1 bar−1, with NaCl rejection decreasing from 98.3% to 98.2%. With the addition of 1.5 wt% and 2.0 wt% DEP, water flux improved to 4.82 L m−2 h−1 bar−1 and 5.95 L m−2 h−1 bar−1, respectively, more than 4.5 and 5.5 times that of the pristine membrane. Nevertheless, NaCl rejection decreased to 96.6% and 95.9%, respectively. The infrared detection revealed that the introduction of DEP disrupted the original intermolecular hydrogen bonding between polyamide chains, thereby enhancing the softness of the polyamide layer, which was demonstrated by the decreased Young's modulus. As a result, the water diffusion efficiency through the polyamide layer was promoted, leading to the significant enhancement of water flux. These findings pave a new route for the synthesis of the aromatic polyamide layer with excellent desalination performance to expand the application of membrane technology. Image 1 • Plasticizer-assisted interfacial polymerization was developed to prepare RO membranes. • Polyamide chain flexibility improved substantially in the presence of plasticizer. • Disruption of inter chain hydrogen bonding caused enhancement of chain flexibility. • Water flux enhanced due to more efficient transport channels for water molecules. [ABSTRACT FROM AUTHOR]

The considerable permeability of fully-aromatic polyamide reverse osmosis (RO) membranes is believed to be strongly dependent on the presence of a mount of internal voids within the polyamide separation layer, which provides additional permeation channels in addition to diffusion through the polyamide matrix. Based on this understanding, herein, we reported a novel strategy of developing highly permeable RO membranes via introducing a void-tailoring agent, (3,3,3-trifluoropropyl)trichlorosilane (TFPTCS) into the traditional interfacial polymerization (IP) system composed of m-phenylenediamine and trimesoyl chloride. During IP process, the fast and violent hydrolysis and aminolysis of TFPTCS caused a significantly increasing pore size and porosity of the incipient polyamide film, which resulted in the formation of double- or multi-layer void structures with higher void fraction in the polyamide film. As a result, the TFPTCS added membrane showed a dramatic enhancement in water permeability, and the optimum condition was observed at the 0.03 wt% of TFPTCS concentration with 3.74 L m−2 h−1 bar−1, which was 2.8 times higher than that of the pristine membrane, while the salt rejection was almost unchanged (around 97.0%). These findings demonstrate the feasibility of void-tailoring inside the polyamide film, and encourage further exploration of new alternative void-tailoring agents to prepare highly permeable polyamide RO membranes for water desalination, which were seldom studied previously. • TFPTCS was introduced into the traditional MPD-TMC IP system to tune the internal void structure of the formed PA films. • The addition of TFPTCS led to an increase in the void volume within PA films, the pore size and porosity of PA back face. • The modified membrane showed a 2.8-fold improvement in water permeability without the loss of salt rejection. [ABSTRACT FROM AUTHOR]

Soluble aromatic polyamide films were prepared with different molar ratios of 2,2′-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (APAF) and 3,3′-dihydroxy-4,4′-diaminobiphenyl (HAB), and then in-situ treated at different temperature to obtain thermally rearranged polybenzoxazole (TR-PBO) membranes with ultra-high gas permeability. Compared to polyamide precursors, the obtained TR-PBO membranes exhibited bimodal cavity distribution. The size of smaller cavities, ranging from around 3.3 Å to around 4.1 Å, increased with APAF content. And the larger cavities of 5.6–6.0 Å were almost constant in size, irrespective of thermal treatment temperature or precursor structure. It was found that increasing thermal treatment temperature could prompt smaller cavities to coalesce into bigger ones, thus resulting in better gas permeability. Higher APAF content results in higher gas permeability but inferior resistance to CO 2 plasticization, however, too low APAF content is also not beneficial to plasticization resistance due to the lower thermal conversion ratio caused by close-packed array of HAB-TPC. It was found that with APAF/HAB molar ratio of 5/5, the prepared TR-PBO membranes exhibited better resistance to CO 2 plasticization as well as comparable mechanical properties and stable permeation performance. • Solubility and mechanical properties are optimized by tuning monomer ratio. • Precursor structure only influences the size of smaller cavities. • Increasing TR temperature prompts smaller cavities to coalesce into bigger ones. • TR-PBO membranes display superior resistance to plasticization and physical aging. [ABSTRACT FROM AUTHOR]