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.