Enhanced Performance of Polyurethane Hybrid Membranes for CO₂ Separation by Incorporating Graphene Oxide: The Relationship between Membrane Performance and Morphology of Graphene Oxide

Abstract

Polyurethane hybrid membranes containing graphene oxide (GO) with different morphologies were prepared by in situ polymerization. The separation of CO2/N2 gas mixtures was studied using these novel membranes. The results from the morphology characterization of GO samples indicated that the oxidation process in the improved Hummers method introduced oxygenated functional groups into graphite, making graphite powder exfoliate into GO nanosheets. The surface defects on the GO sheets increased when oxidation increased due to the introduction of more oxygenated functional groups. Both the increase in oxygenated functional groups on the GO surface and the decrease in the number of GO layers leads to a better distribution of GO in the polymer matrix, increasing thermal stability and gas separation performance of membranes. The addition of excess oxidant destroyed the structure of GO sheets and forms structural defects, which depressed the separation performance of membranes. The hybrid membranes containing well-distributed GO showed higher permeability and permeability selectivity for the CO2. The formation of GO aggregates in the hybrid membranes depressed the membrane performance at a high content of GO.

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“…From the TEM images, GO nanosheets became highly transparent, which indicates that the morphology consisted of a monolayer or just a few layers of GO. This was also in agreement with the AFM results and the results in our former work [21]. Fig.…”

“…S1 and S2 (Supporting Material). From the results of AFM analysis, the average lateral dimension of the GO nanosheets was 0.697 nm; this is in accordance with the thickness of single-layer graphene ($1 nm) proved by previous work [21,32]. From the TEM images, GO nanosheets became highly transparent, which indicates that the morphology consisted of a monolayer or just a few layers of GO.…”

“…The content of GO in all hybrid membranes was 1.0 wt%, which showed the optimal stability and the most homogeneous distribution in polymer matrix, thus the highest separation performance in our previous work [21]. Different Ag-GO samples were dispersed in 12 mL of DMAC by using an ultrasonic probe (KQ-300TDE; 300 W, 80 kHz) for 40 min.…”

“…GO was synthesized through oxidation of graphite powder by using improved Hummers method according to previous reports [21,27]. The mixture of graphite powder (5.0 g) and NaNO 3 (2.5 g) was added with concentrated H 2 SO 4 (115 mL) and cooled to 0°C.…”

“…The dispersion of nanomaterials, such as GO, in the polymer matrix is mainly determined by its morphology and surface properties and is crucial in improving the separation performance of the resulting hybrid membranes [20][21][22]. Hydrophilic groups on the surface of GO nanosheets and the presence of van der Waals force in the lamellar structure complicates the homogeneous dispersion of the nanosheets in the polymer matrix.…”