Researchers at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) have proposed a novel strategy for the controllable fabrication of Turing-patterned polyamide nanofiltration membranes, using ion-track-etched membranes produced by heavy-ion irradiation and chemical etching.

The study was recently published in Chemical Engineering Journal.

Water scarcity and increasingly complex water compositions pose challenges to water treatment. Owing to its low energy consumption, nanofiltration technology is widely used in wastewater reclamation, brackish water softening and industrial water treatment.

Conventional nanofiltration membranes rely on interfacial polymerization to form polyamide selective layers, whose surfaces typically exhibit disordered nodular structures. A long-standing permeability–selectivity trade-off remains a major hurdle: high permeability and high selectivity are difficult to achieve simultaneously.

Turing-patterned membranes are considered a promising solution. Turing structures are periodic, self-organized morphologies that form spontaneously through reaction–diffusion instability. Their distinctive ridge–valley architecture can increase the effective permeation area while preserving the intact crosslinked network of the selective layer. However, precise and controllable preparation of such membranes has remained challenging.

By exploiting ion-track-etched membranes with uniform and precisely tunable pore sizes, the researchers combined the intrinsic exothermic nature of interfacial polymerization with the membrane structure to achieve controllable fabrication of nanofiltration membranes bearing Turing structures.

According to the study, the discrete nanopores of the ion-track-etched membrane alter heat dissipation at the reaction interface. The monomer concentration field couples with the thermal field, jointly inducing thermally coupled reaction–diffusion instability and spontaneously forming a Turing ridge–valley morphology. The entire process requires no additional nanoparticles or polymer additives, enabling additive-free construction of Turing structures.

The team further established a thermally coupled reaction–diffusion theoretical model, revealing the rules governing Turing pattern formation. They found that the diffusion contrast of the reacting species determines the pattern morphology, while the absolute rates of mass and thermal transport determine the characteristic feature size.

By optimizing key parameters, the researchers achieved precise regulation of the Turing structure. The resulting membrane exhibited a highly crosslinked network and a strongly negatively charged surface, removing more than 98% of five representative organic micropollutants, including bisphenol A, norfloxacin and ofloxacin. The membrane also showed favorable antifouling ability and maintained stable performance over 168 hours of continuous filtration.

This work offers a new additive-free route to high-performance nanofiltration membranes and provides theoretical support for designing separation membranes for drinking water safety, industrial wastewater treatment and wastewater resource recovery.

Schematic of the nanopore-mediated reaction-diffusion-thermal coupling strategy for fabricating Turing-patterned polyamide nanofiltration membranes. (Image from IMP)