Breaking the trade-off of permeability-selectivity: Strain-assisted T-C3N2 membranes for high-efficient helium separation and purification from gas mixture

Abstract

Developing efficient membranes for He separation and purification is a key application-oriented technology for future innovative engineering. The He separation performance of the T-C₃N₂ monolayer from gas mixture (He, Ne, Ar, CO, N₂, CO₂, H₂O, and CH₄) was systematically investigated by a combination of MD simulations and DFT calculations. It is found that the pure T-C₃N₂ monolayer exhibits high He permeability but poor selectivity for He/Ne and He/CO₂, which motivates us to introduce biaxial compressive strain in the T-C₃N₂ to improve the He separation performance. Under the biaxial compressive strain of 5 % at 300 K, the T-C₃N₂ membrane has high He permeability of 1.46 × 10⁷ GPU) without other gases escaping from the membrane. However, with temperatures over 400 K, some Ne still migrate outside, which significantly hinder the high selectivity of He. Attractively, the membrane with 5.5 % strain engineering could improve He separation capability at 300 K with permeability of 1.53 × 10⁷ GPU and further enhance selectivity of He over other gases, such as He/Ne (5.2 × 10⁵), He/Ar (3.2 × 10³⁷), He/CO (1.7 × 10¹⁹), He/N₂ (2.5 × 10²²), He/CO₂ (1.5 × 10⁹), He/H₂O (3.1 × 10³²), and He/CH₄ (10⁶⁰), which are far beyond other 2D helium separation membranes. These results indicate that the strain-assisted T-C₃N₂ membrane can synchronously own high permeability and selectivity for He separation, which means that the trade-off of permeability-selectivity of the T-C₃N₂ membrane may be broken via the strain engineering. Our results reveal that the strain engineering can remarkably manage the helium separation performance of the T-C₃N₂ membrane, and provide a promising strategy for designing and screening industrial He separation membranes at room temperature.