Liquid metal interface enables glassy MOF membranes with defect-mediated CO₂ transport.

Glassy metal-organic frameworks (MOFs) combine structural disorder with thermal processability, yet their use as membranes has been hindered by difficulties in fabricating thin, continuous and defect-free films. Here we show a float glass-inspired strategy in which liquid gallium guides the vitrification of ZIF-62 into freestanding glassy MOF membranes. By matching surface energy between melt and bath, dewetting is suppressed, enabling uniform membranes with tunable thickness. In pure glassy MOF membranes, uncoordinated nitrogen sites generated during melting enhance CO₂ diffusion, experimentally validating a sorption-assisted transport mechanism. Post-synthetic methylation of these sites reverses CO₂/H₂ selectivity and raises activation energy. We further identify a glassy impurity phase of ZIF with zni topology that emerges under specific conditions, diminishing CO₂ uptake and membrane performance. These results establish how interfacial control and defect engineering together enable high-performance glassy MOF membranes and provide an experimental foundation for probing structure-transport relationships in disordered porous materials.