[Mainland China] USTC's -20°C Ultralow-Temperature Interfacial Polymerization Technology Published in *Nature Communications*: Nanofiltration Membrane Water Permeability Increased 4-Fold, Industrial Wastewater Treatment Costs Reduced by 79.1%

Lead Summary: A research team led by Professor Wang Yunkun at the University of Science and Technology of China, in collaboration with researchers at Rice University, published findings in Nature Communications: they proposed a -20℃ ultra-low-temperature liquid-liquid interfacial polymerization strategy that constructs a fully amorphous selective layer by suppressing polyamide crystallization, enabling nanofiltration membranes with water permeability 4 times higher than room-temperature membranes and Cl⁻/SO₄²⁻ selectivity improved by 3 times; life cycle assessment based on real industrial wastewater showed that adopting this membrane can reduce treatment costs by 79.1% and carbon emissions by 26.4%.

Pain Point: The "Crystallization Bottleneck" of Nanofiltration Membranes

Nanofiltration membranes play a critical role in water purification and industrial wastewater treatment, yet their performance has long relied on empirical trial-and-error optimization. In conventional interfacial polymerization processes, the crystallinity of the polyamide selective layer is difficult to control: the presence of microcrystalline regions introduces localized transport barriers and tortuous pathways that impede the efficient permeation of water molecules and solutes, constituting a core bottleneck limiting membrane performance enhancement.

More challenging still, reaction temperature—a key parameter governing polymer chain mobility, relaxation, and crystallization kinetics—has been confined in conventional interfacial polymerization to a narrow window near room temperature, because the aqueous phase readily freezes below 0℃, making it difficult to further lower the synthesis temperature. The concept of "trading temperature for performance" has thus remained unattainable.

Breakthrough: "Molecular Cryo-Quenching" at -20℃

The research team's approach is elegantly simple: by adding 30% methanol to the aqueous phase, the reaction medium remains liquid at -20℃ ultra-low temperature, substantially shifting the interfacial polymerization temperature window downward. The ultra-low temperature effectively suppresses molecular diffusion, establishing a kinetically constrained polymerization environment that enables direct assembly of polyamide chains—suppressing crystallization and forming a smooth, defect-free fully amorphous selective layer.

The team systematically verified the mechanism through molecular dynamics simulations and two-dimensional diffusion-ordered spectroscopy nuclear magnetic resonance (2D DOSY NMR):

• Diffusion-limited—simulations showed that in the room-temperature system, piperazine molecules had diffused to the water-organic interface by the end of the simulation, whereas diffusion in the -20℃ system was clearly restricted, with the diffusion coefficient reduced by 75%;
• Rate-controllable—2D DOSY NMR experiments confirmed that the piperazine diffusion rate at -20℃ was only 10% of that at room temperature; in-situ microplate reader monitoring showed a slow decline in piperazine concentration in the ultra-low-temperature system, confirming effective regulation of the interfacial polymerization reaction rate at ultra-low temperature.

Performance Leap: Permeability ×4, Selectivity ×3, Cost -79.1%

The resulting fully amorphous nanofiltration membrane delivered an exceptional performance record:

• Water permeability improved 4 times—substantially higher than room-temperature control membranes, with significantly increased water production per unit area, implying lower operating pressure and reduced membrane area requirements;
• Cl⁻/SO₄²⁻ selectivity enhanced 3 times—surpassing previously reported high-performance nanofiltration membranes, with stronger rejection and fractionation capability for divalent ions;
• Full life-cycle economic and environmental win-win—life cycle assessment (LCA) based on real industrial wastewater demonstrated that adopting this membrane can reduce treatment costs by 79.1% and carbon emissions by 26.4%.

This study establishes "temperature-controlled chain assembly" as a scalable new strategy for nanofiltration membrane design—one that does not rely on new material systems but rather reconstructs membrane microstructure through the fundamental process variable of temperature.

Industrialization Outlook: A New Variable for Advanced Industrial Wastewater Treatment

For the wastewater treatment and reclaimed water reuse industry, membrane technology serves as the "heart component" of advanced treatment and salt fractionation resource recovery. The simultaneous leap in nanofiltration membrane permeability and selectivity directly compresses two major operating expenditures—high-pressure pump energy consumption and membrane replacement costs. This is particularly significant for the membrane concentration unit in the zero liquid discharge (ZLD) process train for high-salinity industrial wastewater ("pretreatment—membrane concentration—evaporative crystallization")—every incremental improvement in membrane concentration efficiency translates into reduced load and investment in downstream evaporative crystallization.

Industry analysts believe that if this strategy is successfully validated on scaled-up membrane production lines, the adoption rate of nanofiltration in industrial wastewater reuse, high-quality reclaimed water production (e.g., front-end enhancement of the "UF + RO" dual-membrane process), and high-salinity water salt fractionation is poised to accelerate. The findings, jointly completed by Chinese and American teams and published under the title "Suppressing Polyamide Crystallization Unlocks Ultrapermeable and Highly Selective Nanofiltration Membranes," provide a clear technical pathway reference for the development of high-performance domestic separation membranes.

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