Efficient helium separation of graphitic carbon nitride membrane

An efficient membrane for helium separation from natural gas is quite crucial for cryogenic industries. However, most experimentally available membranes fail in separating helium from small molecules in natural gas, such as H2, as well as in 3He/4He isotopes separation. Using first-principles calculations, we theoretically demonstrated that the already-synthesized graphitic carbon nitride (g-C3N4) has high efficiency in helium separation from the gas molecules (H2, N2, CO and CH4) in natural gas and the noble gas molecules (Ne and Ar). The selectivity of He over H2 molecule at room temperature is calculated to be as high as 107. More interestingly, the g-C3N4 membrane can also serve as a quantum sieving membrane for 3He/4He separation with a predicted transmission ratio of 18 at 49 K, thus offers a combined means of both He and 3He isotope separation.