In this study, a facilitated transport mixed matrix membrane was fabricated by a surface coating method. Polyvinyl amine (PVAm) and chitosan (Cs) were used as the polymer matrix materials and coated onto a porous polysulfone (PS) support. Graphene oxide (GO) grafted with hyperbranched polyethylenimine (HPEI-GO) was added as the nanofiller. The gas separation tests with CO 2 /N 2 (10:90 v:v) mixed gas suggest that the addition of GO could improve CO 2 /N 2 selectivity. The highest CO 2 permeance was 36 GPU in the membrane with 2.0 wt % HPEI-GO, and the optimal selectivity was 107 in the membrane with 3.0 wt % HPEI-GO. Herein, GO could provide a transport channel for CO 2 and enhance the long-term stability of the membranes. Further gas separation tests under various relative humidities confirmed that facilitated transport was the main mechanism of gas separation through the membrane. The stability test suggests that the membrane has long-term stability. CO 2 transports through the membrane mainly by the facilitated transport mechanism with assistance from the solution-diffusion mechanism, while N 2 transports only by the solution-diffusion mechanism.
Molybdenum disulfide (MoS2) is a graphene-like two-dimensional inorganic material, which has been used for the first time as an inorganic nanofiller to prepare a composite mixed matrix membrane to separate CO2 and N2. Polysulfone (PSf) was used as a support substrate and poly(dimethylsiloxane) (PDMS) was used as the gutter layer. The selective layer was prepared by mixing a CO2-philic copolymer Pebax 1657 with MoS2 nanosheets to enhance CO2 permeance. In addition, a simple drop-coating and evaporation method was developed to prepare the selective layer. Both permeability and selectivity of the MoS2-Pebax membrane have exceeded the pristine Pebax membrane. The permeability and selectivity reached to the maximum values of 64 Barrer and 93, respectively, at 0.15 wt % MoS2 nanosheets loadings. This result has been on the Robeson's upper bound line. The membrane also showed higher stability. The separation mechanism of the membrane is based on the well-known solution-diffusion mechanism. In addition, the stronger adsorption energy of MoS2 nanosheets to CO2 than N2 also provides the enhancement of gas selectivity.
Block copolymer materials have been considered as promising candidates to fabricate gas separation membranes. This microphase separation affects the polymer chain packing density and molecular separation efficiency. Here, we demonstrate a method to template microphase separation within a thin composite Pebax membrane, through the controllable self-assembly of one-dimensional halloysite nanotubes (HNTs) within the thin film via the solution-casting technique. Crystallization of the polyamide component is induced at the HNT surface, guiding subsequent crystal growth around the tubular structure. The resultant composite membrane possesses an ultrahigh selectivity (up to 290) for the CO/N gas pair, together with a moderate CO permeability (80.4 barrer), being the highest selectivity recorded for Pebax-based membranes, and it easily surpasses the Robeson upper bound. The templated microphase separation concept is further demonstrated with the nanocomposite hollow fiber gas separation membranes, showing its effectiveness of promoting gas selectivity.
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