(381aa) Comparison of Methods of Incorporating Silver into Ultrafiltration Membranes to Prevent Biofouling

Biofouling on ultrafiltration membranes used for water purification can lower flux and shorten membrane lifespan. Prior work has shown that biofouling can be reduced by incorporating silver into the membranes, either as nanoparticles or in ionic form. This is due to the anti-microbial properties of silver. This project compares the effectiveness of various methods of incorporating silver into the membranes and how well each method prevents silver leaching. Ultrafiltration membranes are fabricated by phase inversion of a solution of cellulose acetate (CA) and polyvinyl alcohol (PVA) dissolved in n-methylpyrrolidone (NMP). Four methods of silver incorporation are tested. In two methods, 50 nm and 200 nm silver nanoparticles are added to the polymer solution prior to phase inversion. We expected the 50 nm silver nanoparticles to show a stronger initial anti-microbial effect than the 200 nm silver nanoparticles, but to dissolve and lose their anti-microbial effectiveness more rapidly. In the third method, silver nitrate is added to the polymer solution prior to phase inversion. We expected this to result in more rapid release of silver ions compared to when large nanoparticles are added. In the fourth method, a CA/PVA membrane is cast, then is functionalized with iminodiacetic acid (IDA), then is soaked in a 0.05M silver nitrate solution to allow silver ions to bind to the IDA. We expected the chelating action of IDA to slow the release of silver ions. Membranes are characterized with X-ray photoelectron spectroscopy (XPS) to confirm the presence of silver, infrared (IR) spectroscopy to determine functional groups present, and scanning electron microscopy (SEM) to examine the pore morphology of the membranes. To measure membrane performance, flux is calculated from dead-end filtration tests with deionized water and a 2 mg/mL solution of bovine serum albumin (BSA). Preliminary data show that IDA functionalization followed by silver nitrate addition improves pure water flux from 5.2 L/(m^2*h) to 35.0 L/(m^2*h), improves flux from 3.4 L/(m^2*h) to 24 L/(m^2*h) for filtration with BSA solution, and improves BSA rejection from 90.3% to 98.2% compared to an unfunctionalized CA/PVA membrane. The rate of silver leaching is determined by using atomic absorption spectrometry (AAS). Inductively coupled plasma mass spectrometry (ICP-MS) is used to measure the change in concentration of silver in the effluent over time during dead-end filtration. Antimicrobial performance is tested by the membrane’s ability to kill E. coli over a period of time. Additionally, this project investigates predictive models of the phase inversion. The effects of PVA concentration and silver presence on pore morphology are modeled with molecular dynamics simulations and phase field simulations of the phase inversion process. The Flory-Huggins solution theory will be used to model the thermodynamics of the phase inversion process. We will investigate whether simulation results qualitatively agree with the experimental observations.