Aggregated Nanoparticle Morphology Effects on Membrane Filtration

Abstract

Nanoparticles are considered potential environmental contaminants because of reported toxicity to biota in the environment. As such, there is interest in understanding how to remove nanoparticles from waters. This study investigated membrane filtration behaviors of 70-nm alumina oxide nanoparticle when aggregated under diffusion limited aggregation and reaction limited aggregation regimes. In this study, nanoparticles were aggregated under conditions of high and low ionic strength to form aggregates of different morphology. Aggregates were filtered using a hydrophilic polyvinylidene fluoride membrane with a pore size of 0.22 µm, 100% nanoparticle removal efficiencies were obtained regardless of aggregation conditions used. Aggregate morphology was quantified by measured fractal dimensions. Fractal structure differences coincided with measured filtration resistance values. Low porosity aggregates provided a filtration resistance 43% greater than high porosity aggregates of the same effective size. Model predictions for measured specific resistance values were improved through incorporation of compressibility indexes. In order to obtain a porous structure with less resistance, a fast coagulation process is suggested for nanoparticle removal.

Keywords:

• Aggregated nanoparticles
• Filtration
• Fractal dimension
• Membrane cake layer
• Porosity
• Resistance

Acknowledgments

We are thankful to Dr. Jacinta Conrad, Dr. Jeffrey Rimer, and Matthew Oleksiak of the University of Houston for their help with the fractal dimension measurements.