Solvent-free vapor-phase healing drives UiO-66 membranes beyond the H2/CH4 upper bound

Abstract

Vapor-phase post-synthetic defect healing (VPDH) is shown to convert inherently defect-rich UiO-66 into a truly size-selective molecular sieve suitable for industrial hydrogen purification. Exposing polycrystalline UiO-66 to terephthalic-acid vapor at 260 degrees C lowers the missing-linker density from 1.24 to 0.09 per Zr6 node without the solvents that swell or degrade the framework. The resulting membranes display sharply narrowed pores and deliver single-gas H2/CH4 and H2/C3H8 selectivities of 61 and 99, respectively, while a mixed-gas H2/CH4 selectivity of 143 at 180 degrees C exceeds the Robeson upper bound by nearly a factor of two. Performance is retained up to 3 bar, after 60 days of ambient storage, and after mechanical sonication; exposure to humid 10 ppm SO2 at 180 degrees C causes less than 10% loss in hydrogen flux, whereas pristine UiO-66 and ZIF-8 fail catastrophically. The solvent-free, one-step VPDH route therefore offers a scalable, environmentally benign path to chemically and mechanically robust MOF membranes that meet the temperature, pressure and contaminant challenges of nextgeneration hydrogen purification.