Sulfur-doped crown ether graphane for enhanced helium separation

Efficient helium (He) separation is essential for its application in high-tech industries, but existing separation membranes often exhibit limited selectivity and efficiency. This study proposes an effective strategy to enhance He separation performance using a sulfur-doped crown ether graphane membrane (CG-S6). Through first-principles calculations, we systematically assessed the separation barriers and selectivity of CG-S6 against five common atmospheric gases (He, Ne, Ar, N₂, and CH₄). The results show that CG-S6 retains excellent thermodynamic stability and features a reduced band gap of 2.73 eV, a 29% decrease compared to the original CG-6, primarily due to the electronic contributions of sulfur atoms near the Fermi level. Optically, CG-S6 exhibits enhanced ultraviolet absorption with a broader range and a notable redshift compared to CG-6. Importantly, CG-S6 demonstrates a He separation barrier of 0.20 eV, significantly lower than those for Ne (0.50 eV), Ar (1.97 eV), N₂ (1.52 eV), and CH₄ (3.12 eV). Remarkably, the selectivity of He over the other gases ranges from 331.15 to 1 × 10²⁰ across the temperature range of 0-600 K, effectively overcoming the selectivity limitations of the original CG-6 membrane and outperforming several established porous materials. These results suggest that CG-S6 is a promising candidate for He separation. Moreover, sulfur doping proves to be an effective strategy for tuning the separation properties of membrane materials, providing a new theoretical perspective for the development of high-performance He-selective membranes.