Dynamics of Butane and 1-Butene in ZIF-8 Probed by Solid-State 2H NMR
Abstract
We present a detailed 2H NMR characterization of molecular mobility of 1-butene and n-butane propagating through the microporous ZIF-8, a zeolitic imidazolate framework renowned for its outstandingly high stability and separation selectivity of various. The experimental characterization of n-butane and 1-butene diffusivity in ZIF-8 on the molecular scale is provided for the first time. With 2H NMR spin relaxation analysis we have elucidated the motional mechanism for 1-butene and n-butane guests trapped within ZIF-8 framework and derived kinetic parameters for each type of motion. The characteristic times for microscopic translational diffusion and activation barriers (EC4H10 = 34 kJ mol-1, EC4H8 = 32 kJ mol-1) for n-butane and 1-butene diffusivities have been elucidated. Finally, we show that 2H NMR technique is capable to provide reliable information on microscopic diffusivity in the ZIF-8 MOF even for molecules with slow diffusion rates (<10-14 m2 s-1).