3.3 Gas separation performance
In order to identify the most suitable gas separation system, the single
gas permeation experiment was first performed on the tubular MXene/SS
membrane. As shown in Figure 9A, different gases were tested and the
ideal selectivity of each gas was calculated. According to the
experimental data, the permeance of H2,
CO2, N2, CH4, and
C2H4 were 1450 GPU, 22 GPU , 61 GPU, 45
GPU, and 8 GPU, respectively, while the corresponding ideal selectivity
of S(H2/CO2),
S(H2/N2),
S(H2/CH4) and
S(H2/C2H4) were 65, 24,
33, and 186, which were all larger than the Knudsen selectivity.
Obviously, the MXene/SS membrane showed a cut-off between
H2 and CO2 molecules. Moreover, the
effect of different electrophoretic deposition time on the gas
separation performance of the tubular MXene/SS membranes was also
investigated. As shown in Figure 9B, for better comparison, the
H2 gas permeance of the bare stainless steel substrate
and the substrate after modification were tested to be 5323 GPU and 4908
GPU with similar H2/CO2 selectivity of
~5, respectively. The comparable results indicated the
use of filamentous CNTs as surface fillers could only modify the
substrate surface without reducing the gas permeance of the original
substrate, which was a promising candidate as a substrate modification.
With the prolongation of electrophoresis time, the MXene membrane grew
thicker, resulting in fewer defects, so the hydrogen permeance of the
tubular MXene/SS membrane became lower, while the gas selectivity
increased initially and then stayed almost unchanged. When the
electrophoresis time was 2.5 min, the
H2/CO2 selectivity of the membrane
reached the maximum of 55 with comparable hydrogen permeance of 1290
GPU, thus the tubular MXene/SS2.5 membrane was the
optimal one in this study.