(541f) Thin Film Composite (TFC) Membranes with Copper Nanoparticles: Preparation and Antibacterial Characteristics

Membrane biofouling has been a challenging problem that could severely restrict its applications in water desalination process. Copper is known for its antimicrobial properties and is abundantly available with low cost. In this paper, copper nanoparticles (Cu-NPs) with a mean diameter of 15nm were synthesized by the reduction of copper (II) chloride with sodium borohydride (NaBH₄), using cetyl trimethylammonium bromide ((C₁₆H₃₃)N(CH₃)₃Br, CTAB) as a capping agent. After purification of CuNPs by dialysis, the particles were successfully immobilized onto the surface of thin film composite (TFC) membranes via either electrostatic interactions or by covalent bonding with cysteamine as a linker. The electrostatic method entailed simply dipping the newly-fabricated TFC membranes to the Cu-NPs suspension. The presence of CTAB created a cationic bilayer outside the Cu-NPs, which allowed the Cu-NPs be attached to the negatively-charged membrane surface through electrostatic interactions. The covalent bonding method utilized cysteamine (C₄H₁₂N₂S₂) to activate the thin film layer with thiol functional groups, which then allowed attachment of Cu-NPs onto the membrane via a stable covalent bonding. The resulting membranes by these two methods were labeled as TFC-CuNPs and TFC-S-CuNPs, respectively, in this study.  Scanning electron microscopy (SEM) imaging and associated energy-dispersive X-ray spectroscopy (EDS) showed that a significant amount of Cu-NPs existed on both types of membranes. Surface hydrophilicity of the membranes was enhanced by the attachment of CuNPs, as indicated by the measured contact angle of 63.3 ± 0.8^o for TFC, 38.6 ± 0.2^o for TFC-CuNPs, and 58.0 ± 3.4^o for TFC-S-CuNPs. At 300psi trans-membrane pressure and feed NaCl concentration of 2000 mg/L, the corresponding water flux was increased from 47.1 L/m²/h for TFC, 49.4 L/m²/h for TFC-CuNPs, and 69.1 for TFC-S-CuNPs. The salt rejection was slightly decreased from 94.4% for TFC to 92.4% for TFC-CuNPs and 92.3 for TFC-S-CuNPs. The TFC membranes with CuNPs both exhibited excellent antibacterial properties against P. aeruginosa based on the disk incubation test and the SEM observation. Moreover, TFC-S-CuNPs with covalently-bound CuNPs were shown to be more stable and with better anti-bacterial properties than the TFC-CuNPs.