Theoretical design of a strain-controlled nanoporous CN membrane for helium separation

Designing an efficient membrane for He purification is quite crucial in scientific and industrial applications. Ultrathin membranes with intrinsic pores are highly desirable for gas purification because of their controllable aperture and homogeneous hole distribution. Based on the first-principles density function theory and molecular dynamics simulations, we demonstrate that the compressively strained graphitic carbon nitride (CN) can effectively purify He from Ne and Ar. Under a -6% strain, the CN monolayer with a suitable pore size presents an easily surmountable barrier for He (0.11 eV) but formidable for Ne (0.51 eV) and Ar (2.45 eV) passing through the membrane, and it exhibits exceptionally high selectivity of 5.17*10^6 for He/Ne and 1.89*10^39 for He/Ar, as well as excellent He permeance of 1.94*10^7 GPU at room temperature, superior to those of porous graphene and C2N membrane. Our results confirm that strain-tuned CN membrane could be potentially utilized for He separating from other noble gases.