Is amino-modification of HKUST-1 in PEI mixed-matrix membranes always favorable to CO2 separation?

The amino-modification of the filler material is one of the most common strategies for optimization of the performance of mixed matrix membranes, aiming to enhance the interactions between the filler and the organic matrix and accelerate the adsorption of gas molecules by the filler. Herein, we found that the in-situ introduction of amino groups into the HKUST-1 filler would have negative effects on the gas separation performance of the MMMs following the “diffusion-adsorption coupling control” mechanism, which suggests that using MOFs fillers with large aperture size to accelerate the diffusion of small H2 molecules and slow the diffusion of polar CO2 molecules through the adsorption-desorption process. The NH2-HKUST-1 filler caused the blockage and loss of the pore structure, and the interfacial interactions in the PEI-based mixed matrix membranes were not improved. Therefore, the in-situ synthesized NH2-HKUST-1 did not support H2/CO2 separation. This work further investigates the possible “diffusion-adsorption coupling control” mechanism of fillers with large aperture size and contributes to the development of MMMs materials.