Gas sorption test
The sorption analysis of pure gases was conducted by using an isothermal equipment “intelligent gravimetric analysis” (IGA) (IGA100C Hiden Isochema Ltd. England) at different temperatures. The gas sorption values were taken volumetrically for pure PDMS and MMMs. Before testing the sorption analysis, the pure PDMS and Ni-ZIF-8 MMMs without PVDF support were placed in the oven at 120°C for 6 h for the complete removal of any adsorbed moisture or solvent from it. The detailed method of the sorption tests is given in supplementary information.
The solubility is the penetrant property to dissolve with the membrane. The solution coefficient expresses the solubility of the component in the medium, which is a dissolution property of components. . The solution coefficient (S) of gas, can be described as the gas concentration divided by pressure of the gas at the equilibrium. So,
\(S=\frac{C}{P}\) (5)
here S , C, and P representing the solution coefficient (cm3 (STP) cm-3 membrane bar-1), gas concentration (cm3 (STP) cm-3membrane), and pressure at equilibrium (bar), respectively. The solution selectivity (а S) was measured by using the following equation,
\(\alpha_{S}=\frac{S_{\text{BD}}}{S_{N2}}\) (6)
here S BD and S N2representing the solution coefficients of butadiene and nitrogen, respectively.
Diffusivity is an important parameter indicative of the penetrant mobility across the membrane based on its concentration difference. The diffusion coefficient expresses the speed of diffusion of components in medium, which is a transfer attribute of components. Through the solution coefficient and permeability values, diffusion coefficient (D ) was measured by using the equation,
\(D=\ \frac{P}{S}\) (7)
here D representing the diffusion coefficient (cm2 s-1) of the gas, P , andS showing the permeability (Barrer) of the gas, and solution coefficient (cm3 (STP) cm-3 membrane cmHg-1), respectively.
The diffusion selectivity (а D) was measured by using the following equation,
\(\alpha_{D}=\frac{D_{\text{BD}}}{D_{N2}}\) (8)
here D BD and D N2 showing the diffusion coefficients of butadiene and nitrogen, respectively.