Simultaneous Spin-Coating and Interfacial Polymerization for Overcoming the Gas Permeability-Selectivity Trade-off of Thin-Film Nanocomposite Membranes

The spin-coating technique at various spin rates was integrated into the conventional interfacial polymerization (CIP) method to fabricate thin film nanocomposite (TFN) membranes with polyamide (PA) layers containing pristine unmodified halloysite nanotube (HNT). Physiochemical properties and morphology of the TFNs were analyzed using techniques such as FTIR, XRD, AFM, Raman spectroscopy, and SEM. Due to the strong centrifugal force provided by spin-coating in the dynamic IP (DIP) technique, HNTs were arranged and oriented in the PA layer. Therefore, compared to the CIP-prepared PA layer, the DIP-prepared layer was thinner and smoother, while it was more crystalline. As a result of these features as well as the continuous transport pathways provided by the oriented HNTs, the DIP-prepared TFN membrane showed a CO2 permeance of 55 GPU (at a feed gas pressure of 5 bar and a spin-coating rate of 4000 rpm), which was 4.5-times higher than that of the corresponding TFN prepared by CIP. Moreover, CO2/N-2 and CO2/CH4 selectivities of the DIP-prepared TFN at the same operational conditions were 5- and 5.5-times, respectively, higher than those of the corresponding CIP-prepared one. Finally, the CO2/gas selectivities of CIP-prepared membranes decreased, while those of the membranes prepared at spin rates greater than 1000 rpm increased by increasing the feed gas pressure. This study demonstrates how through such a facile DIP method, HNTs improve both the CO2 permeance and CO2/gas selectivity of TFNs without additional need for nanotube surface modification.