In Situ Converted High‐Loading Membranes With Molecularly Dispersed Porous Organic Cages for Superior CO₂/N₂ Separation

ABSTRACT

Porous organic cages (POCs) based mixed‐matrix membranes with characteristics of molecular‐size pores and operation efficiency are promising for gas separation; however, the imbalance between high loading and molecular dispersion impedes the further development of POCs in the field of membrane gas separation. Herein, we propose an in situ cage conversion strategy to construct solid‐solution membranes: RCC3, a highly soluble yet nonporous cage, is first synthesized via the reduction reaction, followed by its homogeneous dispersion in PIM‐1 to form a uniform membrane. Paraformaldehyde, involved in situ nucleophilic addition, converts nonporous RCC3 to rigid porous FT‐RCC3 directly in the membrane. FT‐RCC3 membrane exhibits permanent porosity and molecularly dispersed cages with the highest loading (26.6 wt%) achieved ever for POC‐based membranes. Permeation measurements of CO₂ and N₂ gases show that the obtained FT‐RCC3 membrane demonstrates superior CO₂/N₂ separation performance with CO₂ permeability (9321 Barrer) and CO₂/N₂ selectivity (68.9) largely exceeding the 2019 upper bound and other POCs membranes. Both CO₂ permeability and CO₂/N₂ selectivity are substantially enhanced in comparison to pristine PIM‐1 and RCC3/PIM‐1 membranes.

In situ conversion of flexible, nonporous RCC3 into rigid, porous FT‐RCC3 simultaneously achieves high loading and molecular dispersion of POCs within solid‐solution membranes, thereby significantly enhancing CO₂/N₂ separation efficiency.

1. Introduction

Emissions of carbon dioxide (CO₂) from fossil fuel combustion are a major contributor to global warming, rendering efficient CO₂ capture from flue gases an urgent priority [1, 2]. Compared with energy‐intensive conventional separation technologies—such as cryogenic distillation [3], pressure‐swing adsorption [4], and solvent absorption [5]—membrane‐based separation offers an energy‐efficient alternative [6, 7, 8]. Polymer membranes, favored for their ease of processing and scalability, currently dominate the market [9, 10, 11]. Nevertheless, their performance is restricted by the trade‐off between gas permeability and selectivity, often referred to as the Robeson upper bound [12].

To overcome this limitation, porous crystalline materials, including zeolites, metal–organic frameworks (MOFs) [13, 14], covalent organic frameworks (COFs) [15], and so on, have been incorporated into polymers to form mixed‐matrix membranes (MMMs) [16, 17]. However, poor compatibility between the filler particles and the polymer chains leads to non‐selective interfacial defects, which significantly compromise separation efficiency [18, 19]. Porous organic cages (POCs), as an emerging class of discrete porous molecules composed of fully organic linkers, present new opportunities for membrane design owing to their inherent well‐defined cavities, tunable pore structures, and unique solution processability [20, 21, 22].

Solid‐solution membranes (SSMs) consist of POCs as “solutes” and polymer as “solvent,” in which POCs achieve molecular‐level dispersion, thereby circumventing the interfacial issues typical of conventional MMMs [23]. CC3, a molecule of four triazines and six diamines, is one of the most commonly used POCs for constructing SSMs due to its rigid pore structure, good solubility in organic solvents, and ease of post‐synthesis [20]. However, the limited solubility of CC3 POCs in polymer introduces a new challenge: when the loading exceeds a critical value, typically ∼10 wt%, POCs tend to precipitate like a supersaturated solute. Aggregation among molecular cages and the formation of large crystals cause non‐selective interfacial defects and degrade separation performance [24]. In previous work, our group introduced ionic liquid (IL) into CC3 and fabricated SSMs with PIM‐1. Hydrogen‐bonding interactions from the IL improved the compatibility between CC3 and the polymer. Nevertheless, at POCs loadings above 10 wt%, crystallization particles and interfacial defects reemerged, again impairing separation performance [25]. The reversible imine bonds in CC3 can be reduced to form the flexible amine‐linked RCC3 [26, 27]. Owing to their varying degrees of deformation, RCC3 are less prone to self‐assembling into crystalline particles and can be highly loaded as molecular additives within polymers [28]. As a price, their flexible frameworks also prevent gas ingress due to pore contraction [29].

In this work, we establish an effective strategy, termed in situ cage conversion (Figure 1), to construct a CO₂‐separation‐led membrane. This strategy balances well between the dispersion, the loading, and the porosity, compared with traditional methods (Figure 1a). In this strategy, CC3 cages are reduced to form RCC3, which is highly soluble. RCC3 is loaded up to 40 wt% into the polymer of intrinsic microporosity (PIM‐1) to form a solid‐solution membrane. In situ conversion of RCC3 gives rigid and porous cages of FT‐RCC3. The converted FT‐RCC3 retains the molecular monodispersity of cages and enhances the porosity of the membrane. The resulting membrane is tested for gas permeation of CO₂ and N₂, and selective and permeable separation of CO₂ from N₂ is observed (Figure 1b). This strategy enables the construction of high‐performance POC‐based membranes for efficient CO₂/N₂ separation.

FIGURE 1.

(a) Challenges in preparing POCs‐based SSMs. (b) In situ conversion of flexible, nonporous RCC3 to rigid, porous FT‐RCC3, simultaneously achieves high loading and molecular dispersion of POCs within the SSMs, thereby enhancing CO₂/N₂ separation efficiency.

2. Results and Discussion

CC3 with pore structure (5.8 Å) is reduced by sodium borohydride to form flexible and nonporous RCC3, and then reshaped to rigid, highly crystalline FT‐RCC3 with restored internal porosity (4.6 Å) (Figure 2a). This conversion was systematically verified using x‐ray diffraction (XRD), fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), nuclear magnetic resonance (NMR) spectroscopy, electrospray ionization mass spectroscopy (ESI‐MS), and scanning electron microscopy (SEM) (Figures S1–S8). Upon reduction with NaBH₄, RCC3 transforms from a rigid cage‐like structure into a flexible conformation, which weakens π–π stacking. Meanwhile, the introduced secondary amine interacts more strongly with chloroform and increases conformational entropy, thereby making it soluble in chloroform [28]. RCC3 does not readily self‐assemble into crystalline particles and can be incorporated into polymers as a molecular‐level additive at loadings of up to 50 wt%. XRD patterns (Figure S9) of RCC3/PIM‐1 SSMs with loadings ranging from 10 to 50 wt% exhibit only broad peaks within the 7–40° range, with no discernible crystalline peaks. This confirms the molecular‐level dispersion of RCC3 within the PIM‐1 matrix. SEM images (Figure S10 and S11) reveal smooth and continuous surfaces for both pristine PIM‐1 and RCC3/PIM‐1 membranes, even at a loading up to 50 wt%. No visible particles are observed, indicating excellent compatibility and dispersion of the filler. The aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy (AC‐HAADF‐STEM) images were directly confirm the presence of discrete molecular cage structures in the as‐synthesized RCC3/PIM‐1%–40% SSM (Figure S12). Raman mappings (Figures S13 and S14) further corroborate a uniform spatial distribution of RCC3 throughout the PIM‐1 matrix at all loading levels, with no occurrence of local aggregates.

FIGURE 2.

(a) N₂ sorption isotherms and pore size distributions at 77 K of CC3, RCC3, and FT‐RCC3. (b) CO₂ adsorption isotherms at 298 K of PIM‐1, RCC3/PIM‐1%–40% and converted FT‐RCC3/PIM‐1%–40% membranes. (c) Pore size distributions of CO₂ adsorption isotherms at 273 K of PIM‐1, RCC3/PIM‐1%–40%, and converted FT‐RCC3/PIM‐1%–40% membranes. (d) ESI‐MS spectra of RCC3/PIM‐1%–40% and converted FT‐RCC3/PIM‐1%–40% membranes. (e) ¹H NMR spectra of RCC3/PIM‐1%–40% and converted FT‐RCC3/PIM‐1%–40% membranes. (f) Content of FT‐RCC3 and RCC3, and conversion rate in converted FT‐RCC3/PIM‐1 with various filler loadings based on ¹H NMR spectra.

To achieve the in situ conversion of nonporous RCC3 into porous FT‐RCC3 in SSMs, the RCC3/PIM‐1 membranes treated with a paraformaldehyde/methanol solution at 70 °C for 48 h. CO₂ adsorption measurements at 298 K verify the successful restoration of porosity after the conversion (Figure 2b). Due to pore collapse, the RCC3/PIM‐1%–40% (40% here denotes the loading) membrane shows 13.9% lower CO₂ uptake than pristine PIM‐1. In contrast, the transformed FT‐RCC3/PIM‐1%–40% membrane exhibits an increased CO₂ adsorption capacity by 21.3%, confirming that a portion of the flexible and nonporous RCC3 has been effectively converted into rigid and porous FT‐RCC3 within the SSMs. This will be beneficial for the CO₂ adsorption and diffusion in membranes, thereby enhancing SSMs’ CO₂ permeability and selectivity [30]. As shown in Figure 2c, the original RCC3/PIM‐1%–40% membrane possesses fewer pores around 0.6 nm relative to pristine PIM‐1, consistent with pore blocking by RCC3. After conversion, the FT‐RCC3/PIM‐1%–40% membrane displays a narrower pore‐size distribution and increased porosity, resulting from the recovered microporosity of FT‐RCC3.

ESI‐MS analyses (Figure 2d) of the dissolved RCC3/PIM‐1%–40% and converted FT‐RCC3/PIM‐1%–40% membranes confirm the structural transformation: while the spectrum of the original membrane shows a characteristic peak at m/z 1142.27 corresponding to RCC3, the converted membrane exhibits two distinct peaks at m/z 1142.50 and 1214.55, attributable to residual RCC3 and converted FT‐RCC3, respectively (Figures S4 and S5). Further evidence from ¹H NMR spectra (Figure 2e) reveals an additional signal at 4.00 ppm assigned to FT‐RCC3, alongside the original RCC3 signal at 3.81 ppm. Quantitative integration of these chemical shifts (Figures S15–S19) indicates conversion degrees of 30.3%, 41.8%, 41.5%, 63.7%, and 52.6% for SSMs with RCC3 loadings of 10, 20, 30, 40, and 50  wt%, respectively, giving 3.2, 8.8, 13.1, 26.6, and 27.5 wt% of FT‐RCC3 in respective converted SSMs. Therefore, the calculated actual contents of FT‐RCC3 and RCC3 in the converted SSMs are shown in Figure 2f and Table S1.

FTIR spectra (Figure S20) reveal the changes in chemical bonds following SSMs conversion. The enhanced characteristic peak at 3327 cm⁻¹ in the RCC3/PIM‐1%–40% membrane is attributed to N‐H of RCC3. In contrast, the converted FT‐RCC3/PIM‐1%–40% membrane exhibits a characteristic peak at 1037 cm⁻¹, attributed to the C‐O stretching vibration of the hydroxymethyl group due to paraformaldehyde incorporation. Building on the confirmed conversion, TGA further reveals a substantial enhancement in the thermal stability of the converted SSMs (Figure S21). This improvement originates from the hydroxymethyl groups introduced via the reaction of paraformaldehyde with secondary amines. The increased steric hindrance of these groups restricts C─N bond rotation, thereby reinforcing the conformational rigidity of the molecular cages. Moreover, the hydroxymethyl groups serve as strong hydrogen‐bonding sites, establishing an extensive and robust intermolecular hydrogen‐bonding network [30].

The dispersion states of cages in converted FT‐RCC3/PIM‐1 SSMs were investigated. XRD patterns of the converted FT‐RCC3/PIM‐1 SSMs with loadings ranging from 10 to 50 wt% (Figure 3a) remain similar to those before conversion, displaying only broad, amorphous halos in the 7°–40° range and no discernible crystalline peaks. This confirms that the converted FT‐RCC3 also attains molecular‐level dispersion inside the PIM‐1 matrix, with no signs of agglomeration and/or long‐range order. SEM images (Figures 3b and S22) show that the surface of the converted FT‐RCC3/PIM‐1 SSMs remains fully continuous, without crystallization or defect formation. Cross‐sectional SEM images (Figures 3b and S23) likewise reveal no crystalline particles of FT‐RCC3. Raman imaging (Figure 3c; Figures S24 and S25) further corroborates a uniform spatial distribution of FT‐RCC3 throughout the PIM‐1 matrix across all loading levels, with no signal of local aggregation. HRTEM has been explored as a useful technique to reveal microstructures and porosity that are difficult to characterize in amorphous or molecularly dispersed systems [31, 32, 33]. AC‐HAADF‐STEM images directly visualize discrete molecular cage structures embedded in the transformed SSMs (Figure 3d). More TEM images at different locations and corresponding elemental (C, N, and O) mappings are provided in Figure S26 and S27, showing the uniform distribution of the cage. Together, XRD, SEM, Raman mapping, and AC‐HAADF‐STEM combinatorially provide multiscale evidences, consistently demonstrating that the in situ conversion process preserves molecular‐level dispersion of POCs even under high filler loadings, while maintaining a uniform and defect‐free SSM structure.

FIGURE 3.

(a) XRD patterns of FT‐RCC3/PIM‐1 SSMs with varied RCC3 loadings. (b) Top‐view and cross‐section SEM images of FT‐RCC3/PIM‐1%–40% SSM. (c) Raman mapping of FT‐RCC3/PIM‐1%–40% SSM at 1488.84 cm⁻¹. (d) AC‐HAADF‐STEM image of FT‐RCC3/PIM‐1%–40% SSM.

The gas separation performance at 2 bar and 25°C of PIM‐1 and RCC3/PIM‐1 SSMs with cage loadings ranging from 10 to 50 wt% was systematically evaluated using a CO₂/N₂ (50/50, v/v) mixed gas. As shown in Figure S28 and Table S2, neat PIM‐1 displays a CO₂ permeability of 4138  Barrer and CO₂/N₂ selectivity of 25.1. After incorporating nonporous RCC3, the separation performance of RCC3/PIM‐1 membranes decrease progressively with increasing RCC3 loadings, exhibiting both lower CO₂ permeability and moderately reduced CO₂/N₂ selectivity. This decline stems from the nonporous nature of RCC3 (Figure 2a), which cannot provide selective transport pathways via internal cavities, while acting as physical barriers that hinder gas diffusion through the polymer matrix (Figure S29a). Nevertheless, RCC3 shows excellent solubility in PIM‐1 and remains uniformly dispersed even at 50  wt% loading, effectively avoiding cage aggregation or crystallization that commonly occurs in most SSMs, thus preserving morphological homogeneity at high filler loadings (Figure S10).

For comparison, conventional MMMs were prepared by physically blending pre‐synthesized CC3 (26.6 wt%) and FT‐RCC3 (26.6 wt%) with PIM‐1. The XRD pattern of this membrane (Figure S30) reveals that both CC3 and FT‐RCC3 remain in a crystalline state within the PIM‐1 matrix. Corresponding SEM images clearly show crystalline particles of CC3 and FT‐RCC3 incorporated in the membrane (Figures S31 and S32). In this work, the Raman mapping image (Figure 3c) of the converted FT‐RCC3/PIM‐1%–40% membrane appears uniformly green because the cage molecules are uniformly dispersed within the polymer. In contrast, the Raman mapping of the directly physically blended FT‐RCC3/PIM‐1‐26.6% membrane differs. Due to the presence of FT‐RCC3 crystals in the membrane, the Raman signal intensity in the particulate regions is stronger, resulting in the appearance of partial red regions in the Raman mapping (Figure S33). Gas separation performance at 2 bar and 25°C (Figure 4a and Table S3) indicates that the CC3/PIM‐1‐26.6% MMM exhibits a CO₂ permeability of 6872 Barrer and a CO₂/N₂ selectivity of 35.3, while the FT‐RCC3/PIM‐1‐26.6% MMM shows a CO₂ permeability of 7356 Barrer and a CO₂/N₂ selectivity of 39.4 (same loading of 26.6% in respective CC3 and FT‐RCC3 membranes). Although these values are notably higher than those of the pristine PIM‐1 membrane and the RCC3/PIM‐1%–40% MMM, they remain substantially lower than those of the in situ converted FT‐RCC3/PIM‐1%–40% SSM, which delivers a CO₂ permeability of 9321 Barrer and a CO₂/N₂ selectivity of 68.9. This performance gap is primarily attributed to interfacial defects still arising from the aggregation of crystalline filler particles in the former two cases of CC3 and FT‐RCC3 MMMs. The comparison clearly demonstrates that conventional blending methods cannot prevent filler agglomeration and interfacial incompatibility at high loadings. In contrast, our strategy—which first achieves uniform dispersion of the soluble, nonporous precursor RCC3, followed by its in situ conversion to porous FT‐RCC3—ensures molecular‐level dispersion of the porous filler. By avoiding cage‐molecule aggregation and interfacial defects, this approach enables enhanced and stable separation performance even under high loadings of cage‐like fillers (the latter FT‐RCC3 SSM membrane).

FIGURE 4.

(a) Mixed gas permeation results of PIM‐1, CC3/PIM‐1‐26.6%, RCC3/PIM‐1%–40%, FT‐RCC3/PIM‐1‐26.6%, and converted FT‐RCC3/PIM‐1%–40% membranes at 2 bar and 25°C. (b) Mixed gas permeation results of converted FT‐RCC3/PIM‐1 SSMs with varied filler loadings at 2 bar and 25°C. (c) Mixed gas permeation results of FT‐RCC3/PIM‐1%–40% at varied temperatures and 2 bar. (d) Mixed gas permeation results of FT‐RCC3/PIM‐1%–40% at varied pressures and 25°C. (e) 30‐day anti‐aging property test of FT‐RCC3/PIM‐1%–40%. (f) Comparison of CO₂/N₂ separation performance of FT‐RCC3/PIM‐1%–40% with the performances of other reported MMMs.

The series of RCC3/PIM‐1 SSMs was treated with a paraformaldehyde/methanol solution to activate the porosity of FT‐RCC3, and the gas‐separation performance at 2 bar and 25°C of the resulting FT‐RCC3/PIM‐1 SSMs was subsequently evaluated. As shown in Figure 4b and Table S4, the FT‐RCC3/PIM‐1%–10% membrane exhibits increased CO₂/N₂ selectivity but reduced CO₂ permeability compared to pristine PIM‐1. This is because the membrane contains only 3.2 wt% porous FT‐RCC3, while the remaining 6.9 wt% nonporous RCC3 still acts as a diffusion barrier (Figure 2a). With increasing the filler loading, the CO₂ permeability of the converted membrane rises. The FT‐RCC3/PIM‐1%–40% membrane delivers an optimal combination of CO₂ permeability (9321 Barrer) and CO₂/N₂ selectivity (68.9). This enhancement stems from the in situ formation of more rigid, porous FT‐RCC3 within the PIM‐1 matrix, and such a porous cage provides efficient, selective pathways for CO₂ transport (Figure S29b). However, at 50 wt% loading, both CO₂ permeability (8603 Barrer) and selectivity (59.6) decline slightly. According to Figure 2f and Table S4, the actual contents of porous FT‐RCC3 in the 40 and 50 wt% membranes are similar (26.6 vs. 27.5 wt%), but the latter contains significantly more nonporous RCC3 (23.3 vs. 14.3 wt%) within the membrane layer; possibly due to the kinetically unfavorable reaction of RCC3 with paraformaldehyde in the restricted space of the membrane layer. The higher fraction of nonporous filler not only impedes gas diffusion but may also partially block the pore windows of FT‐RCC3, thus reducing both permeability and size‐sieving ability. Overall, the superior performance of the FT‐RCC3/PIM‐1%–40% membrane highlights the advantage of the in situ conversion strategy: it guarantees the molecular dispersion properties of highly‐loaded porous molecular cages in SSMs, thereby enhancing the gas separation performance. We also conducted the PIM‐1 membrane using the same solution treatment and performed GPC analysis. The results (Table S5) show that the number‐average molecular weight (M_n) of PIM‐1 before and after treatment was 46977 and 45823, respectively, with a PDI of 1.6 in both cases, indicating no significant degradation or cross‐linking of PIM‐1. Gas separation results at 2 bar and 25°C (Table S4) show that the CO₂ permeability of the treated PIM‐1 membrane was 4289 Barrer, compared to 4138 Barrer for the original membranes, and the CO₂/N₂ selectivity was 24.7 compared to 25.1 for the original ones, with changes falling within the experimental error range.

Figure 4c and Table S6 illustrate the separation performance at 2 bar of the FT‐RCC3/PIM‐1%–40% membrane as a function of operating temperature (25°C–75°C). With increasing temperature, the permeability of CO₂ increases, while the CO₂/N₂ selectivity declines. This trend is attributed to the enhanced thermal energy of gas molecules, which accelerates their diffusion through the membrane [34]. Notably, when the temperature is cycled back to 25°C, the membrane's performance is fully recovered, confirming that no irreversible structural damage occurs during thermal operation. The influence of feed pressure on gas separation was also examined (Figure 4d and Table S7). Mixed‐gas permeation tests were conducted at 2, 4, 6, and 8 bar (at 25°C) to evaluate the membrane's resistance to CO₂‐induced plasticization. The FT‐RCC3/PIM‐1%–40% membrane exhibits highly stable performance across the investigated pressure range, maintaining a CO₂/N₂ selectivity of 63.2 even at 8 bar. This exceptional pressure stability underscores the positive role of the rigid POC in restricting polymer‐chain mobility, thereby effectively suppressing the membrane plasticization.

The influence of conversion conditions on the gas separation performance of SSMs was systematically investigated. Treatment of RCC3/PIM‐40% membrane with a paraformaldehyde/H₂O solution at 70°C for 48  h yielded no FT‐RCC3 characteristic peaks in the ¹H NMR spectrum (Figure S34), indicating an ineffective cage conversion. These membranes show poor separation performance, with a CO₂ permeability of 1084 Barrer and a CO₂/N₂ selectivity of 14.6 (Table S8). This is attributed to water‐induced pore blocking and polymer swelling [35] as well as the poor contact between hydrophobic RCC3 and aqueous paraformaldehyde. In contrast, using a paraformaldehyde/methanol conversion solution enables an efficient reaction due to the good solubility of RCC3. At 70°C, the membranes after different conversion time of 36 h, 48 h, and 60 h were compared. The 36 h‐treated membrane exhibits weak FT‐RCC3 signals and modest performance (CO₂ permeability: 2135 Barrer, CO₂/N₂ selectivity: 28.0) (Figure S35 and Table S8). Although the 60 h‐treated membrane shows clear FT‐RCC3 peaks and improved performance (CO₂ permeability: 8766 Barrer, CO₂/N₂ selectivity: 43.0) (Figure S36 and Table S8), the 48 h‐treated membrane achieves the best balance, delivering a high CO₂ permeability of 9321 Barrer and CO₂/N₂ selectivity of 68.9. Therefore, considering conversion efficiency, separation performance, and process economy, the optimal conversion conditions are identified as paraformaldehyde/methanol solution at 70°C for 48h.

Long‐term operational stability is another critical parameter for assessing the practical viability of gas separation membranes. The FT‐RCC3/PIM‐1%–40% membrane, converted in paraformaldehyde/methanol solution, was subjected to continuous testing for 30 days under 2 bar and 25 °C. As shown in Figure 4e, the membrane exhibits excellent stability, maintaining a CO₂ permeability of average 8592 Barrer and CO₂/N₂ selectivity of 67.9 throughout the testing period. This indicates that the converted membrane retains its structural integrity and separation function during the anti‐aging test. CO₂ adsorption tests (Figure S37 and Table S9) on PIM‐1, RCC3/PIM‐1%–40%, and FT‐RCC3/PIM‐1%–40% before/after permeation and after 6 weeks of air exposure show that pure PIM‐1 aged significantly, with capacity drops of 14.0% and 31.2%, respectively. RCC3/PIM‐1%–40% also aged (16.2% and 30.8%), indicating nonporous flexible fillers cannot suppress aging. FT‐RCC3/PIM‐1%–40% exhibited much smaller drops (only 5.4% and 7.3%), demonstrating greatly reduced aging. Thus, in situ converted FT‐RCC3 provides inherent rigid porosity and molecular‐level restriction of PIM‐1 segment motion, effectively mitigating physical aging. The separation performance of the FT‐RCC3/PIM‐1%–40% membrane exceeds the 2008 and 2019 Robeson upper bounds, as well as other reported CO₂/N₂ separation membranes (Figure 4f). Moreover, its performance is notably superior to that of other MMMs documented in the literature (Table S10), highlighting the effectiveness of the in situ conversion strategy for the fabrication of high‐performance membranes.

3. Conclusion

In summary, this study developed an in situ conversion strategy to fabricate SSMs with high‐loading POCs. This approach involved the uniform dispersion of the highly soluble but nonporous RCC3 within PIM‐1, followed by its in situ conversion into porous FT‐RCC3 inside the SSMs. Even at 40 wt% loading, the POCs retained their molecular‐level dispersions in the membrane. The resulting membrane exhibited concurrent improvements in both the CO₂ permeability (125.3%) and the CO₂/N₂ selectivity (174.5%) compared to pristine PIM‐1. This strategy effectively addressed the key issue of POCs aggregation and precipitation at high loadings in SSMs. Future work will focus on optimizing the conversion efficiency without cage aggregation via more precise organic reactions and scaling up the process through continuous membrane manufacturing, offering a pathway for designing next‐generation high‐performance SSM for CO₂ capture.

Author Contributions

Liting Yu: methodology, data curation, investigation, and writing – original draft. Jia Pang: methodology, software, investigation, and formal analysis. Yanxi Wu: data curation, investigation, and formal analysis. Yuxuan Yin: methodology and software. Junchao Dong: validation and investigation. Caiyan Zhang: software and validation. Lu Qiao: validation. Peipei Zhou: validation. Meng Wang: validation. Lili Fan: resources. Daofeng Sun: project administration. Zixi Kang: conceptualization, supervision, writing – review, and editing. Jialu Li: supervision, investigation, writing – review, and editing. Hailing Guo: validation, project administration, writing – review, and editing. Xiaoqin Zou: conceptualization, supervision, writing – review, and editing.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File: anie72816‐sup‐0001‐SuppMat.docx.

Data Availability Statement

The data that support the findings of this study are available in the Supporting Information of this article.