Particle-Size Effects on Gas Transport Properties of 6FDA-Durene/ZIF-71 Mixed Matrix Membranes

A series of 6FDA-Durene-ZIF71 mixed matrix membranes (MMMs) comprising three different ZIF-71 particle sizes (i.e., 30, 200, and 600 nm) have been fabricated to investigate the effects of particle size on the gas separation performance of MMMs. Compared to MMMs containing ZIF-71 particle size > 200 nm, ZIF-71 embedded MMMs with particle sizes of ≤ 200 nm exhibited significantly enhanced gas separation performance. The O₂ and N₂ permeability of MMMs comprising ZIF-71 with particle sizes ≤ 200 nm have higher permeability than the predicted ones using the Maxwell model. By considering the inefficiently packed polymer chain and the sieve-in-a-cage phenomena, the modified Maxwell model displayed comparable permeability over the experimental results suggesting the nonideal nature of MMMs. For the first time, it was found that 200 nm ZIF-71 generated the best MMM for gas separation, particularly for H₂/CH₄ systems. Therefore, a trade-off between ZIF-71 particle size vs gas separation performance must be taken into account when designing an MMM suitable for industrial gas separation applications.