## Nanomaterial-Based Membrane
### Polymer Nanocomposites Membranes for Gas Separation
presented the fabrication and characterization of polystyrene-TiO\({}_{2}\) nanoparticles mixed matrix membranes for the separation of CO\({}_{2}\) from nitrogen. The impact of TiO\({}_{2}\) nanoparticles loading was examined on membrane performance. Their study showed that upsurge of feed pressure led to reduction in flux of gases. There was a further confirmation that an excellent separation performance could be attained at TiO\({}_{2}\) nanoparticles loading of 7 wt.% [79]. Carbon nanotubes are prospective functional materials that have recently gained much interest since swift movement of gases in carbon nanotubes was discovered because of low resistance movement in their intrinsic passages [80]. The exceptional features of carbon nanotubes inspire scholars to investigate an excellent penetrable, selective hybrid carbon molecular sieve membranes by embedding carbon nanotubes into membrane precursors [81]. However, the effectual employment of carbon nanotubes in mixed matrix  
Figure 3: Schematic illustration of the membrane separation process using polymer membrane with selective inter-activities of the gas molecules with the pores across the membranes with the aid of Knudsen’s diffusion. membrane greatly depends on the capability to uniformly disperse the carbon nanotubes through the matrix. [PERSON] et al. synthesized polyetherimide/multi-walled carbon nanotubes composite membrane for gas separation; carbon dioxide penetrability was roughly 27 \(\times\) higher than polyetherimide carbon membrane, attaining 1463 Barrer, and O\({}_{2}\)/N\({}_{2}\) perm-selectivity was 24.16 at 26 \({}^{\circ}\)C [82]. The results showed that the multi-walled carbon nanotubes offer an improvement in gas diffusivity by means of broadening the micro-pore volume. [PERSON] et al. [83] successfully fabricated multi-walled carbon nanotubes/carbon nanocomposite thin films by integrating multi-walled carbon nanotubes into polyimide precursor solutions [83]. The membrane displayed excellent CO\({}_{2}\) flux of 866.6 Barrer, which was 2-4 \(\times\) higher than that of pure carbon membrane. [PERSON] et al. [84] produced a mixed matrix membrane embedded with functionalized multi-walled nanotubes using the solution casting technique, whereby the functionalized multi-walled nanotubes were integrated into the polyimide membrane [84]. The influence of nominal multi-walled nanotubes content on the gas separation properties was studied. When likened to a neat polymer membrane, the mixed matrix membranes revealed 100% improvement in CO\({}_{2}\)/CH\({}_{4}\) selectivity. The mixed matrix membrane possesses a high capability of separating gases at the molecular level. In addition, it possesses a high capability of ultimately reducing the energy consumed in modern-day separation processes. It was demonstrated from the study that the addition of carbon nanotubes to polymeric membranes has enhanced separation properties on the membranes to a definite extent. [PERSON] et al. also fabricated mixed matrix membranes comprising of acid-treated functionalized multi-walled carbon nanotubes integrated into polyimide polymer for gas separation [85]. The gas separation performance revealed an increase of 292% CO\({}_{2}\) permeability coefficient when 3 wt.% multi-walled carbon nanotubes was integrated into the mixed matrix membranes. Furthermore, there was an increase of 145% in the selectivity of CO\({}_{2}\)/N\({}_{2}\) and an increase of 144% in the selectivity of CO\({}_{2}\)/CH\({}_{4}\). Generally, carbon membranes attained from the thermal decomposition when polymeric membranes were utilized as precursors are projected as a prospective substitute for the separation of gas, primarily owing to their excellent separation ability when likened to polymeric membranes [86]. [PERSON] et al. obtained carbon molecular sieve membranes by means of well-ordered pyrolysis of polyetherimide mixed with polyimide [87]. The results revealed that the free volume size and the pore size were improved with an upsurge in the polyimide content.