Metallocene-anchor inducing oriented MOF membrane for helium separation

Abstract

Oriented metal-organic framework (MOF) membranes hold significant promise for advanced helium (He) separation, but their synthesis remains a challenging task. We report the preparation of an oriented MOF membrane using metal-organic polyhedra (MOP) fragment as metallocene-anchor. The metallocene-anchor induces the growth of homoligand Zr-MOF along the c-axis, resulting in the {001}-oriented structure. This orientation increases the transition energy barrier of methane (CH4), enabling precise He/CH4 separation with a selectivity of 77.3 and a He permeance of 695.1 GPU. The membrane exhibits exceptional robustness, demonstrating resistance to high-pressure conditions (up to 40 bar), thermal shock (−25 °C to 85 °C), and long-term stability (1000 h). The separation performance surpasses that of existing MOF membranes and exceeds the Robeson upper bound. Additionally, a three-stage membrane process enables the concentration of low He concentrations of 0.3% up to 99.9%, highlighting the potential of membranes for helium extraction. The successful fabrication of various oriented MOF membranes indicates the universality of this strategy.