## 3 Results and Discussion
### Ideal CO2 Separation Performance  
The gravimetric sorption results demonstrate the materials with a strong affinity for CO2 and increased CO2 permeabilities. However, the accuracy of the gravimetric sorption data decays at pressures below 1 bar, resulting in lower reliability of the performance parameters that are calculated indirectly: \(D_{i}\) and \(P_{i}\). ESI Figure S3 demonstrates a similar trend in CO2 solubility between the investigated materials if we compare it to the adsorption runs of the gravimetric sorption measurements. The CO2 sorption capacity decreases in the following order: \(\mathbf{P_{9}IL_{0}Zn_{0}}>\mathbf{P_{9}IL_{6}Zn_{1}}>\mathbf{P_{9}IL_{6}Zn_{9 }}>\mathbf{P_{9}IL_{6}Zn_{0}}\). This trend is due to the reduction in FFV with addition of IL to PIL, which is only moderately improved by further supplementary Zn[Tf2N]2. Although some deviations are observed for \(\mathbf{P_{9}IL_{6}Zn_{1}}\) and \(\mathbf{P_{9}IL_{6}Zn_{9}}\), all data points fit the linear Henry model well or the dual-mode sorption model at low pressures, where \(b\cdot p<<1+b\cdot p\), and thus the CO2 concentration or the CO2 sorption capacity increases with increasing CO2 partial pressure. These results confirm the solubility governed CO2 transport in PIL/IL/Zn2+ composites. ESI Figure S4 reveals that CO2 sorption capacities of all investigated materials decrease with increasing temperature. Importantly, the Henry's constant \(k_{D}\) decreases slightly with increasing temperature, following the Arrhenius equation up to approximately 50 \({}^{\circ}\)C (ESI Figure S5). This is in agreement with the constant material-gas system composition if assumed that partial molar enthalpy and entropy of the penetrant are not temperature dependent [77]. The gas transport through the dense membranes synthesized from \(\mathbf{P_{9}IL_{0}Zn_{0}}\), \(\mathbf{P_{9}IL_{6}Zn_{0}}\), \(\mathbf{P_{9}IL_{6}Zn_{1}}\) and \(\mathbf{P_{9}IL_{6}Zn_{9}}\) follows the solution-diffusion mechanism. ESI Table S1 reports the permeability (\(P\)), diffusion (\(D\)) and solubility (\(S\)) coefficients and the respective ideal selectivities with respect to nitrogen (\(P_{x}/P_{\text{N}_{\text{2}}}\); \(D_{x}/D_{\text{N}_{\text{2}}}\); \(S_{x}/S_{\text{N}_{\text{2}}}\)). Time lag experiments using single gases showed that when IL was added to PIL (\(\mathbf{P_{9}IL_{6}Zn_{0}}\)), the CO2 permeability increased by 22 times, raising to 166 Barrer from 7.6 Barrer  
Figure 5: CO2/N2 permeability selectivity calculated from single gas sorption experiments at 20 \({}^{\circ}\)C. The black dotted curves provide guides for eyes. for (**P\({}_{9}\)IL\({}_{0}\)n\({}_{0}\)**). This behavior is due to the faster diffusion of CO\({}_{2}\) molecules through the less viscous segments of IL and is in accordance with previous reports [16]. Further Zn[Tf\({}_{2}\)N]\({}_{2}\) salt incorporation in the PIL/IL composite counteracted the advantage of IL presence resulting in a lower permeability in the two PIL/IL/Zn\({}^{2+}\) composites of 80.9 Barrer and 20.2 Barrer for **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{1}\)**, and **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{9}\)**, respectively. The ideal CO\({}_{2}\)/N\({}_{2}\) permeability selectivity reveals an opposite trend compared to the one estimated from the gravimetric sorption experiments. The values obtained in the time-lag measurements increase in the following order: **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{1}<\)P\({}_{9}\)IL\({}_{0}\)Zn\({}_{0}<\)P\({}_{9}\)IL\({}_{6}\)Zn\({}_{9}<\)P\({}_{9}\)IL\({}_{6}\)Zn\({}_{0}\)**. In the case of **P\({}_{9}\)IL\({}_{0}\)Zn\({}_{0}\)**\(D_{\rm N_{2}}>D_{\rm CO_{2}}\) which is unusual for glassy polymers and supports the discussion about the gravimetric sorption results in Section 3.2.