Blending Silver Nanoparticles in a Membrane to Reduce Biofouling during Filtration

Membranes have been effectively used in water treatment for the separations of contaminants. During filtration, rejected materials are sent to the waste stream or accumulate on the surface of the membrane, with the latter leading to fouling. When microorganisms, such as bacteria, accumulate on the membrane, biofouling occurs. Silver nanoparticles have anti-microbial behaviors due to the reported release of reactive oxidative species. Reactive oxidative species are free radicals that are created after penetration to the cell, which cause toxicity in the microbial cells. By embedding silver nanoparticles in a membrane, biofouling build up on membranes can be minimized or even prevented. The membranes in this research were formed from a dope solution comprised of polysulfone dissolved in bioderived co-solvents Rhodiasolv® PolarClean and gamma-valerolactone (GVL).

Once the silver nanoparticles are added to the membrane, the silver can potentially leach into the water during filtration. Silver is not allowed in water, as the regulations require the silver concentration not to exceed 0.1 mg/L. Therefore, adding a polymer to coat, stabilize, and prevent the leaching of the silver nanoparticles was the goal of this study. The coating polymers studied were polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and polydopamine (PDA) due to their charge attraction. Characterization testing was then performed to ensure the polymers were coating the nanoparticles and attaching to the membrane polymer. After the coated nanoparticles were created, Fourier transform infrared (FTIR) was used to confirm the coating process was complete. There were no significant differences between the polymer and coated nanoparticles. Dynamic Light Scatter (DLS) was then used to measure the coated nanoparticle size and zeta potential or charge of the particle. The coated nanoparticles size increased and there was less of a charge comparably to the pristine nanoparticles. Then, UV-vis spectrophotometry was used to measure the particles’ light absorption. The results showed the coated nanoparticles had absorbed less light than the pristine nanoparticles. After characterization testing was performed, x-ray photoelectron spectroscopy (XPS), Drop Shape Analyzer, and scanning electron microscope (SEM) were employed to measure the different characteristics of the coated nanoparticle membranes.