Ultrathin Film Composite Membranes Fabricated by Novel In Situ Free Interfacial Polymerization for Desalination

Abstract

Ultrathin polyamide nanofilms are desirable as the separation layers for the highly permeable thin-film composite (TFC) membranes, and recently, their lowest thickness limits have attracted a lot of attention from researchers. Due to the interference of the underlying substrate, preparing a defect-free, ultrathin polyamide nanofilm directly on top of a membrane substrate remains a great challenge. Herein, we report a novel fabrication technique of TFC membranes, named in situ free interfacial polymerization (IFIP), where the IP reaction occurs at the uniform, free oil–water interface dozens of microns above the substrate, and then the resulting nanofilm spontaneously assembles into the TFC structure without extra manual transfer. This IFIP method not only overcomes the limitations of conventional IP, succeeding in preparing ultrathin–nanofilm composite membranes for nanofiltration and reverse osmosis application, but also enables scale membrane manufacturing that is not feasible via previously reported free-standing IP. Based on the IFIP method, the thickness of the polyamide nanofilm was successfully reduced to ca. 3–4 nm, which we believe is close to the ultrathin limit of the polyamide nanofilm for separation application. Meanwhile, the structure–performance relationship revealed that the strategy of increasing TFC membrane permeance by reducing polyamide layer thickness also had a limit. Besides, the IP mechanisms in regard to the formation of surface morphology and film growth were explored by combining experimental and molecular simulation methods. Overall, this work is expected to push forward the fundamental study and practical application of the ultrathin–film composite membrane.

Electrostatic-modulated interfacial polymerization toward ultra-permselective nanofiltration membranes

“…This mechanism is further supported by the increased thickness of Fe 3+ -screened and NaCl-screened eIP-3 membranes ( Figure S17 ). Besides, we also observed diverse nanostructure on the surface of eIP membranes ( Figures S18−S20 ), which may be attributed to the aqueous template effect on the hydrophilic substrate ( Jiang et al., 2019 , 2020 ). These nanostructures of the eIP membranes only induce a very limited increasement of surface area in the range of 2%–9% ( Figure S21 ), exerting insignificant influence on membrane performance.…”

Regulating the Crystallization Morphology of Poly(vinylidene fluoride‐chlorotrifluoroethylene) Ultrathin Film by Changing Temperature and Substrate

“…The height difference between the surfaces of film and substrate was recorded as the film's thickness (Figure S4, Supporting Information). [47] All samples have been undergone an amorphous treatment before isothermal crystallization. The detailed steps are described as follows: The ultrathin film samples were heated to 135 °C on a hot stage (50 °C min -1 ) and then kept for 5 min to fully melt.…”

“…The height difference between the surfaces of film and substrate was recorded as the film's thickness (Figure S4, Supporting Information). [ 47 ]…”

Ultrathin Membranes for Separations: A New Era Driven by Advanced Nanotechnology

“…a) A plot of NaCl rejection versus water permeance of state‐of‐the‐art sub‐50 nm RO membranes; data a–m are taken from refs. [ 4,42,43,46,77,92,124,131,174,247–249 ]; b) NaCl rejection versus water permeance of state‐of‐the‐art commercial RO membranes; c) a plot of Na 2 SO 4 rejection versus water permeance of state‐of‐the‐art sub‐50 nm NF membranes; data a–w are taken from refs. [ 29,40,45,49,65,104,105,118–123,126–129,133,137,174,213,250–254 ]; d) MgSO 4 rejection versus water permeance of state‐of‐the‐art commercial NF membranes.…”