Synthesis and characterization of novel thin film nanocomposite reverse osmosis membranes with improved organic fouling properties for water desalination

Abstract

In this study, a new type of thin film nanocomposite (TFN) reverse osmosis (RO) membranes was prepared by incorporating different amounts of halloysite nanotubes (HNTs) into the polyamide (PA) selective layer via in situ interfacial polymerization. The effect of HNTs incorporation into the PA selective layer on the surface morphology, separation performance and antifouling properties of the membranes were thoroughly investigated and discussed. The presence of HNTs in PA layer was verified using EDX, XRD and FTIR analysis. The “leaf-like” outgrowth morphology of PA layer was observed using FESEM. Upon addition of HNTs, the hydrophilicity, surface roughness and water flux of TFN membranes have all increased. The water flux enhancement can be ascribed to higher hydrophilicity and additional water pathways through porous HNTs in TFN membranes. It is noteworthy that the TFN membrane that was embedded with 0.05 wt/v% HNTs (labeled as TFN0.05) could exhibit water flux as high as 36 L m⁻² h⁻¹ (at 15 bar gauge) with NaCl rejection maintained at 95.6%. In comparison to the control thin film composite (TFC) membrane, the water flux of TFN0.05 membrane was 90% higher. Although further increase in HNTs loading to 0.1 wt/v% could result in greater water flux, its RO performance was compromised by a significant decrease in NaCl rejection. Besides offering greater water flux, the TFN0.05 membrane also showed better antifouling affinity than HNTs-free TFC membrane. It is most probably due to the increase in hydrophilicity as well as surface negative charge upon addition of HNTs. Based on the results obtained in this work, it can be concluded that incorporating an appropriate amount of HNTs into PA rejection layer could potentially improve the performance of TFC membrane during RO applications.