Improvement of Polyamide Thin Film Nanocomposite Membrane Assisted by Tannic Acid-Fe^III Functionalized Multiwall Carbon Nanotubes

Tannic acid-Fe^III functionalized multiwall carbon nanotubes (TA-MWNTs) were successfully obtained through a simple and rapid procedure by forming a stable TA-Fe^III complex coating on the MWNT surface. Hydrophilic TA-MWNTs can disperse well in the aqueous phase and help the formation of a polyamide (PA) thin film nanocomposite (TFN) membrane through interfacial polymerization. TA-MWNT concentration in the aqueous phase was adjusted to achieve the optimal water flux and salt rejection of the TFN membrane. The results reveal that, when 0.03% of TA-MWNTs are added, the optimized water flux of the TFN membrane reaches up to 31.4 L/m²h, 2.36 times of that of the neat PA membrane, along with a well-maintained Na₂SO₄ rejection. Furthermore, the as-prepared TFN membrane shows improved antifouling ability and good long-term stability. A significantly enhanced chlorine resistant capability of the TFN membrane is also presented, which can be ascribed to the radical capturing capability of phenol groups of TA as well as more oxidation-stable polyester bonds produced by the interaction between the phenol groups of TA and the acyl chloride groups of TMC. Assisted by TA-MWNTs, the TFN membrane is found to have prominent advantages over PA and MWNTs/PA TFN membranes.