Preparation of nanoparticle-filled polymeric membranes: Synthesis of biofouling resistant Ag-polysulfone composite ultrafilters
- Graduate student: Julian Taurozzi (Environmental Engineering, MSU)
- Primary Adviser: Dr. Volodymyr Tarabara (Environmental Engineering , MSU)
- PERMEANT collaboration: Dr. Anatoly Burban (UKMA), Volodymyr Bosak (UKMA)
Biological fouling of membranes remains a major factor that increases the cost of the application of membrane technology in water treatment. Using materials that possess biocidal properties to prepare or modify membranes is a promising approach to biofouling mitigation. Silver, both in ionic and nanoparticle form, has been extensively investigated with respect to its bacteriostatic and bactericidal properties. Studies have shown silver nanoparticles to disrupt essential cellular functions, while silver ions cause protein denaturation and possibly affect cellular replication by interacting with DNA macromolecules upon exposure. Incorporating silver into the membrane during membrane preparation is one way to make membranes more resistant to biofouling.
A well established method for the synthesis of asymmetric membranes is phase inversion. In this method, a homogeneous polymer solution composed of the polymer, an organic solvent and (optionally) a pore forming agent, is cast into a thin film of tunable thickness. Once cast, the solvent can be allowed to partially evaporate prior to submersion of the film into a nonsolvent bath. This process results in phase separation of the film and finally yields an asymmetric membrane.
We study the incorporation of silver nanoparticles/ions into the polymeric structure of ultrafiltration polysulfone (PS) membranes produced by phase inversion.Two alternative routes for the incorporation of Ag nanoparticles into the PS matrix are being developed. The first approach involves the addition of Ag/dimethylformamide (DMFA) organosol into a PS/dimethylacetamide (DMA)/polyethyleneglycol (PEG) casting mixture. Upon homogenization of all added components, the resulting mixture is used to cast silver modified membranes. The second approach involves an in-situ reduction of ionic Ag by DMFA, the latter being a component of the casting mixture. Silver nitrate is first dissolved in DMFA at room temperature and this solution is then added to a PS/DMA/PEG casting mixture and heated under intense stirring to initiate the reduction of silver ions upon addition of the Ag/DMFA solution, yielding silver modified membranes.
The obtained membranes are characterized with respect to their hydraulic and bactericidal properties. Clean water flow tests and rejection tests are conducted to assess the impact of modification on the hydraulic performance of membranes. TEM/EDX analysis is performed for qualitative analyses of nanoparticle inclusion in the polymeric matrix. To assess the bactericidal properties of modified membranes, bacteria suspensions are filtered through silver modified membranes and non-modified PS controls and incubated at constant temperature for 48 hours. Preliminary results demonstrate strong inhibition of bacterial growth on the surface of silver-modified membranes, as opposed to controls. Work is on-going on the quantification of the extent of biofouling inhibition, the optimization of the modification parameters, and a better understanding of the underlying physico-chemical processes occurring throughout the modification processes. We are also studying the extent and rate of silver leaching from the membranes, and how this is affected by the preparation method. Strategies for replenishing the membranes' silver loading and therefore ensure a sustained biocidal capacity will also be studied.
Figure 1: SEM micrographs of the cross-section of non-modified (top) and silver modified (bottom) polysulfone membranes.