Physical aging of polymer of intrinsic microporosity PIM-1 is one of the major obstacles for its application as a commercial membrane material for gas separation. In this work, physical aging of PIM-1 and matrices of this same polymer containing graphene-like materials were studied.Graphene-like fillers resulted from the functionalization of graphene oxide (GO) with two alkyl chains of different lengths, using octylamine (OA) and octadecylamine (ODA), and further chemical reduction. Extents of membrane aging were evaluated through changes in gas permeability over time;the separation of gas mixtures comprising carbon dioxide and methane, which are of great interest for industrial applications such as the production of biogas or the purification of natural gas, was carried out. 50:50 vol. % CO 2 /CH 4 mixtures were used as feed and separation performance analysed for fresh membranes and at intervals of approximately a month up to 155 days. At the end of this testing period, aged PIM-1 membranes showed a CO 2 permeability of (2.0± 0.7) x 10 3 Barrer, which corresponds to a CO 2 permeability reduction of 68 % from the value obtained right after their fabrication. The addition of alkyl-functionalized GO is shown to be an efficient strategy to retard the physical aging of PIM-1 membranes; filler loadings as low as 0.05 wt.% of reduced octylfunctionalized GO showed a CO 2 permeability of (3.5 ± 0.6) x 10 3 Barrer after 5 months, which is almost three quarters higher than that of pure PIM-1 membrane aged for the same time period and represents a reduction of just 39% from its initial value. Moreover, the addition of graphene-like materials to PIM-1 does not affect its mechanical properties. Highlights Physical aging of mixed matrix membranes (MMMs) composed of PIM-1 and graphene-like materials was investigated. A binary CO 2 /CH 4 (50:50 vol.%) gas mixtures was used. Physical aging was reduced by the incorporation of reduced alkyl-functionalized graphene oxide nanosheets into PIM-1 matrices. Low filler loadings led to higher reduction in physical aging.

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Highlights1. PES/GO membranes were prepared in combination with various pore forming agents.2. Higher flux and improved rejection were achieved with the addition of GO.3. Synthetic solutions of protein and dyes were rejected efficiently at 1 bar. 4. Membrane fouling was reduced with the addition of GO.