Mist based interfacial polymerization technique for graphene oxide modified thin film composite nanofiltration membrane

Abstract

Among the major issues faced by thin film composite membrane used in nanofiltration (NF) application are the fouling behaviour and the trade-off effect between water permeability and salt rejection. This study aimed to develop a new type of nanomaterials-modified thin film nanocomposite (TFN) membrane with enhanced surface characteristics by employing a new interfacial polymerization (IP) technique based on the mist method. Particularly, the objectives of this work are to investigate the effects of different mist-based interfacial polymerization conditions on the polyamide (PA) selective layer properties of membranes, to evaluate the impacts of plasma-enhanced chemical vapour deposition (PECVD)-modified graphene oxide (GO) interlayer on the characteristics of TFN membrane made of optimized mist-based IP conditions, and to investigate the influences of organic solution temperature during IP process on the properties of GO-modified TFN membrane for NF applications. The results show that in addition to forming thinner and looser PA structure, the piperazine (PIP) solution required in the mist-based IP (MIP) reaction was significantly reduced, i.e., 17 times lower than conventional IP. The microdroplet dispersion approach in MIP could form a higher crosslinked PA due to the high polymerization interface, besides forming a higher free volume selective layer due to the disruption in the PA repeat structure. The newly developed membrane could achieve 9.08 L/m2 hbar pure water permeability (PWP) and 97.2% Na2SO4 rejection coupled with complete flux recovery rate. Following this, a new TFN membrane incorporating GO was fabricated using the developed MIP technique. GO was surface-functionalized using greener PECVD approach to improve its dispersibility. Compared to the control GO, acrylic acid-modified GO (AA/GO) was able to improve PWP of TFN membrane by 6.6%, reaching 11.34 L/m2 hbar. Its PWP was also higher compared to TFC membrane (~25% enhancement) owing to enhanced membrane hydrophilicity coupled with formation of thin yet highly crosslinked PA upon AA/GO incorporation. By varying the temperature of organic solvent (0 to 55 °C) during IP, the TFN 0 membrane with the thinnest and smoothest PA layer was able to be produced, recording 12.14 L/m2 hbar PWP, 93% Na2SO4 rejection and 16% NaCl rejection. This membrane with the smoothest surface aided in its low protein adsorption, demonstrating great antifouling potential. Meanwhile, the TFN 55 membrane achieved a water-salt permselectivity ratio of 11.0, which was found to be >2 folds compared to the commercial NF3 membrane (4.88) owing to its enhanced crosslinking. Both TFN 55 and TFN 0 membrane showed great short-term (12 h) stability and retained more than 95% of the AA/GO nanosheets after a 5-day agitation period. Overall, the mist-based IP fabrication of TFN membrane at low temperature can overcome the limitations of the conventional IP technique to produce a smooth and defect-free TFN membrane with improved filtration performance and reduced protein adsorption.