Electron tomography reveals key transport pathways in reverse osmosis and nanofiltration membranes

Membranes play key roles in water purification, gas separations and biopharmaceutical processing, and could transform industrial chemical separations and critical mineral extraction. The field has relied on intricate control of membrane properties through systematic perturbations to membrane chemistries and processing, yet many fundamental questions remain on the mechanisms that govern flux and separations. We have leveraged advances in multi-modal electron microscopy to generate new insights on membrane structure and function. For example, we combined energy-filtered transmission electron microscopy with electron tomography from scanning transmission electron microscopy images to map the variation in density of polyamide films used in reverse osmosis and nanofiltration membranes. Quantitative analyses of imaging products are key to extract mechanistic details that govern water transport and separations. With the various recent advances in instrumentation, the field is poised to fundamentally advance how we characterize membranes.