Highly efficient light-gated COF membrane for precise multistage molecular separation

Membrane technology is crucial for the separations in chemical and biochemical industries because of its flexibility and reliability. However, conventional multistage separation requires multiple membranes with different pore sizes, leading to low efficiency and high energy consumption. Inspired by the light-responsive behavior of stomata in natural leaves, we successfully fabricated a highly efficient light-gated covalent organic framework (COF) membrane by using click reaction to incorporate 53.5 weight % azobenzene into the nanochannels, where the pore size of this membrane could be dynamically switched between 0.73 and 0.93 nanometers because of the reversible trans-cis isomerization of azobenzene. Notably, the light-gated COF membrane enabled efficient multistage separations of cannabidiol oil (a high-value pharmaceutical), limonene, and chlorophyll in hemp oil as well as gold, silver, and iron ions in simulated natural ores. The separation process remained stable over 100 trans-cis-trans cycles as a result of the formation of stable triazole bonds. Thus, this work provides an instructive strategy to develop light-gated COF membranes for precise molecular separations.