Leaching of CuO Nanoparticles from PES Ultrafiltration Membranes

Recent studies have incorporated nanoparticles such as CuO, ZnO, and TiO₂ to improve membrane physical and filtration properties. However, one of the major concerns about membrane modification with nanoparticles is the possible leaching of the nanoparticles leading to further contamination of source waters. Therefore, this study investigated the effects of prolonged exposure of polyethersulfone (PES) membranes incorporated with CuO nanoparticles, to different cleaning solutions. The cleaned membranes were extensively characterized for both material properties and separation performance, which enabled a closer look at particle leaching effect through a prolonged exposure. After 840 h of exposure, the presence of CuO in the cleaning solutions was confirmed using dynamic light scattering (DLS), energy-dispersive X-ray spectroscopy (EDS), and inductively coupled plasma mass spectroscopy (ICP-MS) techniques. Nanoparticle leaching resulted in changes in membrane hydrophobicity, surface roughness, pure water permeability, and salt rejection properties. Through comparison with the bare PES membranes, it was shown that cleaning solutions also degraded the membrane polymer. However, the marked effect was less pronounced compared to combined leaching of nanoparticles and degradation of the polymer noted with PES membranes incorporated with CuO nanoparticles. Therefore, when membranes incorporated with nanoparticles are used, a polishing step may be required to remove potentially leached nanoparticles. Leached nanoparticles may result in secondary pollution and pose a health risk concern to nontarget organisms. This work provides insights into the stability of nanocomposite membranes, and the achieved results can be extrapolated to other nanoparticles such as TiO₂ and ZnO because they possess similar physicochemical behavior.