CAS Institute of Modern Physics Achieves Controllable Fabrication of Turing-Structure Nanofiltration Membrane, Removing Over 98% of Typical Organic Micropollutants

Researchers at the Materials Research Center of the Institute of Modern Physics, Chinese Academy of Sciences, have reported new progress in structural control and performance optimization of nanofiltration (NF) membranes for water treatment. Using ion-track-etched membranes produced by heavy-ion irradiation followed by track etching as substrates, the team proposed a thermally coupled nanopore-mediated interfacial polymerization strategy that enables controllable fabrication of polyamide NF membranes with Turing ridge-valley surface patterns, showing strong potential for efficient removal of organic micropollutants. The results were published in the international chemical engineering journal Chemical Engineering Journal.

Water scarcity and increasingly complex water composition are pressing challenges for treatment processes. Nanofiltration, valued for its low energy consumption, is widely used in wastewater reclamation, brackish water softening and industrial water treatment. Mainstream NF membranes rely on interfacial polymerization (IP) to form a polyamide separation layer, but diffusion-reaction kinetics typically produce a disordered nodular surface, creating a long-standing permeability-selectivity trade-off.

Turing structures-periodic self-organized patterns formed by reaction-diffusion instability-offer continuous ridge-valley undulations that enlarge effective water-transfer area while preserving a fully crosslinked separation layer, making them an attractive route to break the trade-off. However, previous work focused almost exclusively on diffusion differences between chemical species, overlooking the exothermic nature of the amidation reaction itself and how the spatial distribution of reaction heat at the interface shapes pattern formation.

To address this, the team exploited the uniform, precisely tunable pores of the ion-track membrane. Discrete nanopores alter interfacial heat dissipation-local polymerization heat cannot spread evenly, producing a non-uniform interfacial temperature field-while also regulating enrichment and transport of the aqueous monomer piperazine (PIP). Coupling of the monomer concentration field and the thermal field induces a thermally coupled reaction-diffusion instability, spontaneously generating Turing ridge-valley morphologies, with no added nanoparticles or polymeric additives.

The team further built a thermally coupled reaction-diffusion model and used two-dimensional finite-difference simulations to reveal the governing rules: diffusion contrast determines the final pattern morphology, while absolute mass- and heat-transfer rates determine the characteristic feature size. Experimentally, by tuning substrate pore size, aqueous monomer concentration and IP reaction time, the membrane's ridge-valley feature size could be flexibly adjusted across a wide range of 117.7 nm to 608.5 nm.

Key performance of the optimized membrane:

• Molecular weight cut-off: 320 Da
• Water permeance: 9.11 L m⁻² h⁻¹ bar⁻¹
• Na₂SO₄ rejection: up to 99.67%
• Organic micropollutant removal: above 98% for neutral and charged species including bisphenol A, tetracycline and norfloxacin, via combined size sieving and electrostatic repulsion
• Operational stability: no significant performance decay after 168 h of continuous filtration

By treating heat transport as a key variable for steering self-organized interfaces rather than considering material diffusion alone, the work establishes a complete mass-heat coupling framework for interfacial polymerization morphology control. It provides an additive-free fabrication route for high-performance NF membranes and theoretical and technical groundwork for next-generation separation membranes in drinking water safety, industrial wastewater treatment and wastewater reclamation. The study was supported by the National Natural Science Foundation of China and other programs.