Title: Gasseparation with binary-cooperative heterogeneous membranes

Authors: Bo Wang, Chen Zhang, Junrui Zhang, Ji-kun Yin, Xiaomin Song, Haochen Ye, Qing-hua Li, Jun-chao Lao, Tie Wang

First author and affiliation: Bo Wang (Professor), Tianjin University of Technology

Corresponding authors and affiliation: Bo Wang (Professor), Tie Wang (Professor), Tianjin University of Technology

Link:https://www.nature.com/articles/s41467-026-69949-1

1. Research Background

Polymer membranes hold great promise in the field of gas separation. However, designing a polymer membrane that simultaneously achieves high separation performance and structural stability remains challenging. In practical applications, membrane separation technology often needs to operate under harsh conditions such as high pressure, which can easily lead to compaction or plasticization of polymer chains, thereby destroying the membrane structure and reducing gas separation efficiency. Although enhancing interchain interactions (e.g., hydrogen bonding, metal coordination bonding) can improve membrane structural stability, this often sacrifices the free volume of the polymer and inhibits gas molecule transport. In nature, animal bones are composed of rigid hydroxyapatite and flexible collagen arranged alternately. This "rigid-flexible" synergy endows bones with excellent mechanical properties. Inspired by this, we aim to construct independent heterogeneous functional domains within a polymer network, leveraging their synergistic effect to enhance gas separation performance while maintaining membrane structural stability.

2. Brief Introduction

Recently, the team of Tie Wang & Bo Wang from the Tianjin Key Laboratory of Life and Health Intelligent Detection, Tianjin University of Technology, published a research paper titled "Gas separation with binary-cooperative heterogeneous membranes" in Nature Communications. This work proposes a micro-zone interfacial polymerization strategy to reconstruct the polymer network and fabricate heterogeneous membranes with acrumpledmorphology. The study reveals that the heterogeneous membrane exhibits microphase separation: thepeakregions are enriched with amide groups, serving asCO₂-affinity sites and forming fastCO₂transport channels; thevalleyregions are enriched with rigid groups, which not only enhanceCO₂diffusion but also endow the membrane with excellent pressure resistance. The synergistic effect of these dual-functionalpeakandvalleyregions enables the membrane to exhibit outstanding CO₂permeance and CO₂/N₂selectivity under 1.0 MPa pressure. This research provides a new design strategy for developing high-durability polymer membranes suitable for harsh environments.

3. Research Content

3.1 Construction of Heterogeneous Structure

Using a micro-zone interfacial polymerization technique, the organic phase monomer (trimesoyl chloride, TMC) was anchored in the swollen micropores of polydimethylsiloxane (PDMS) and then reacted with the aqueous phase monomer (piperazine, PIP) to construct the heterogeneous membrane. By adjusting the "holding time" after decanting the TMC solution, membranes with different morphologies were obtained: short holding times (e.g., 30-120s) resulted in liquid-liquid micro-zone interfacial polymerization, forming heterogeneous membranes withcrumpled(peak/valley) morphologies (PT-1, PT-2, PT-3); holding times>160sled to liquid-solid interfacial polymerization, forming smooth-surfaced homogeneous membranes (PT-4, PT-5). A key discovery came from atomic force microscopy-infrared spectroscopy (AFM-IR) characterization. By imaging the spatial distribution of functional groups, the research team observed microphase separation in the heterogeneous membrane (Figure 1): signals corresponding to amide groups (C=O,C–N) were mainly enriched in thepeakregions of the undulating structure, while signals corresponding to benzene ring groups (C=C, C–H) were mainly concentrated in thevalleyregions.

Figure 1 Schematic diagram of heterostructure construction and AFM-IR characterization.

3.2 Formation Mechanism of the Heterogeneous Structure

To reveal the formation mechanism of this microphase-separated structure, Raman scanning spectroscopy was employed. During the formation of the heterogeneous membranes (PT-1,PT-2,PT-3) via liquid-liquid interfacial polymerization, the solvent (n-hexane) swollen in the PDMS micropores continuously delivered TMC monomers to the interface, promoting the continuous growth and fusion of the polyamide membrane, ultimately forming the undulating structure. Raman spectra acquired in fixed-focus mode showed that the signal corresponding to the benzene ring appeared early on the substrate surface (valleypositions) and then gradually weakened, indicating that the polyamide membrane (peakpositions) grew and covered the substrate. In contrast, during the formation of the homogeneous membranes (PT-4,PT-5) via liquid-solid interfacial polymerization, the lack of solvent in the micropores hindered continuous TMC monomer supply, preventing full growth and fusion of the polyamide membrane, resulting in a densely packed smooth surface.

3.3 Mechanical Properties of the Heterogeneous Structure

Owing to the distinct chemical compositions and microstructures of thepeakandvalleyregions, the heterogeneous membrane exhibits excellent mechanical properties (Figure 2). In horizontal tensile tests, the heterogeneous membrane (PT-1,2,3) utilized a stress-relief effect through its undulating deformation, showing no visible cracks after 100 tensile cycles, while the homogeneous membranes (PT-4,5) developed significant cracks after only 5 cycles. In verticalstresstests, nanomechanical mapping by AFM revealed that thepeakregions have a lower Young's modulus (more "flexible"), effectively releasing vertical pressure through deformation, while thevalleyregions have a higher Young's modulus (more "rigid"), demonstrating excellent pressure resistance. Gold nanoparticlecoveragetestsshowed that the width of thepeaks decreased with increasing pressure, confirming the deformation-based pressure release process.

Figure 2 Testing and analysis of mechanical properties of the heterogeneous membrane.

3.4 Gas Separation Performance of the Heterogeneous Structure

Benefiting from the synergistic effect of the "flexible"peakand "rigid"valleydual-functional regions, the heterogeneous membrane exhibits outstanding gas separation performance under high pressure. At 1.0 MPa, the PT-3 membrane shows the best performance, with a CO₂permeance of approximately 3000 GPU and significantly improved CO₂/N₂selectivity compared to homogeneous membranes (PT-4 and PT-5). Compared with membranes reported in the literature, the heterogeneous membrane in this work shows notable advantages in both CO₂permeance and selectivity. Gold nanoparticle coverage experiments and COMSOL simulations both confirmed that the diffusion rate of gases in thepeakregions of the heterogeneous membrane is much higher than that in thevalleyregions.

4. Conclusions and Outlook

In this study, a heterogeneouscrumpledpolymer membrane structure with microphase separation was constructed using micro-zone interfacial polymerization. Thepeakandvalleyregions are enriched with different functional groups, providing dual functions of gas transport and pressure resistance, respectively. This binary-cooperative effect enables the membrane to withstand high pressure while simultaneously achieving a significant increase in gas permeability and selectivity, effectively addressing the trade-off between separation performance and structural stability in traditional polymer membranes. This work not only provides a high-performance membrane material for CO₂capture but also demonstrates a generalizable strategy for membrane structural design. In the future, by changing the monomers or preparation conditions, more opposing yet synergistic functional domains (e.g., hydrophilic-hydrophobic, ordered-disordered, polar-nonpolar) can be introduced into the membrane, potentially enabling efficient separation of challenging systems such as isomers and expanding membrane applications to more harsh environments involving high temperatures, acids, and alkalis.