Delayed Linker Addition (DLA) Synthesis for Hybrid SOD ZIFs with Unsubstituted Imidazolate Linkers for Propylene/Propane and n‐Butane/i‐Butane Separations

We present a novel synthesis strategy termed delayed linker addition (DLA) to synthesize hybrid zeolitic‐imidazolate frameworks containing unsubstituted imidazolate linkers (Im) with SOD topology (hereafter termed Im/ZIF‐8). Im linker incorporation can create larger voids and apertures, which are important properties for gas storage and separation. To date, there have been only a handful of reports of Im linkers incorporated into ZIF‐8 frameworks, typically requiring arduous and complicated post synthesis approaches. DLA, as reported here, is a simple one‐step synthesis strategy allowing high incorporation of Im linker into the ZIF‐8 framework while still retaining its SOD topology. We fabricated mixed‐matrix membranes (MMMs) with 6FDA‐DAM polymer and Im/ZIF‐8 obtained via DLA as a filler. The Im/ZIF‐8‐containing MMMs showed excellent performance for both propylene/propane and n‐butane/i‐butane separation, displaying permeability and ideal selectivity well above the polymer upper bound. Moreover, highly detailed molecular simulations shed light to the aperture size and flexibility response of Im/ZIF‐8 and its improved diffusivity as compared to ZIF‐8.