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Enhancement of Membrane Filtration Process via Nanomaterial Coatings for the Generation of Electrostatic Forces, Oil Barriers, and Joule Heating


Water scarcity exasperated by global climate change and growing population is a growing challenge for many regions of the world. The water shortages are prompting regions to look for new water sources to supplement their dwindling water supplies ranging from wastewater reuse to saline ground water desalination. Membrane filtration is one of the few technologies that can treat these water sources but suffers from fouling, and complicated system designs. Herein we present methods to address problems faced by membrane filtration through use of nanomaterial-based thin films that actively address key problems faced by membrane filtration processes.

Organic contaminants commonly found in surface waters, ground water, and wastewater rapidly foul membranes, leading to decline in their performance. We demonstrate that application of electrical potentials to electrically conductive and robust carbon nanotube (CNT) thin films deposited on UF membranes generates strong electrostatic repulsive forces. We demonstrate that these artificially generated electrostatic forces can reduces membrane fouling during treatment of synthetic wastewaters and model organic foulants, with the results being qualitatively explained by the solution of modified Poisson-Boltzmann equation. Although our results demonstrate electrostatics forces are effective at preventing organic fouling, their efficacy suffers in saline waters such as produced, flow back, and industrial wastewaters. These waters can contain oil emulsions made up of small and stable oil droplets that can rapidly foul UF membranes. We take advantage of the nano-magnetite properties, which cause the nano-particles to form a film at the water-oil interphase. The nano-magnetite films create a physical barrier that prevents oil droplets from interacting with the membrane surface or coalesce during filtration. The fouling prevention is explored as a function of nano-particle and membrane hydrophilicity with a developed theoretical framework qualitatively explaining our experimental results. Finally, we demonstrate that the previously prepared CNT films when deposited on hydrophobic membranes can be used to drive membrane distillation (MD) process via Joule heating effect. We explore the stability of the CNT films using electrical impedance spectroscopy (EIS) under different frequencies and salinities and demonstrate that they can be used to achieve exceptionally high single pass recoveries in MD.

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