Separating Oil and Water with Superhydrophobic Vertically Aligned CNT Membranes

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The long-term ecological harm and immense costs, both direct and indirect, of oil spills may soon be a distant memory.   Researchers have been able to show that carbon nanotubes are oleophilic—strong affinity to oil—and that vertically aligned multi-walled carbon nanotubes (VAMWNTs) suitable for superhydrophobic—water repelling—membranes.  Researchers have combined these VAWMNTs with fine stainless steel mesh to create dual-scale membranes that repel water and attract oil.  The membranes are comprised of nanotube needle-like structures on a microporous mesh, creating a membrane with low surface energy.  In laboratory tests, the membranes were easily able to separate diesel fuel from water, even when the emulsions were stabilized with substances designed to reduce the surface tension of the liquid.  The filter was also able to separate high viscosity, very thick, lubricating oils emulsified in water, a feat more comparable to separating heavy crude from water.

These filters were manufactured via thermal chemical vapor deposition (CVD), a method that involves using the fine stainless mesh as a substrate and depositing CNTs on its surface through vapor deposition[fn]http://www.azom.com/article.aspx?ArticleID=1552[/fn].  The process allows the membranes to be fabricated in a simple and cost effective step.  CVD has been used for nanofabrication of CNTs for nearly two decades and is ideal for industrial scale production of multiwall CNTs.

DOI: 10.1016/j.carbon.2010.02.020

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This technology is a generational enhancement over skimming, coagulation-flocculation, centrifugal separation, and other methods of oil separation, allowing for the low-energy, rapid separation of oil and water.

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This technology has the potential to improve environmental quality and increase resource efficiency in industrial processes.

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This technology may pose a risk to biotic life in the event of release of the carbon nanotubes from the mesh substrate. The level of risk will be unknown until the rate of release and fate and transport of the multi-walled CNTs are studied in these membranes. Carbon Nanotubes as with other nanotubes and nanowires have been shown to pierce cell walls; making them potentially cytotoxic. Additionally, there are environmental health and safety risks associated with the CVD process used to align the MWCNTs on the steel mesh. These risks must be addressed based on the precursors used in the vapor and the resultant exhaust gases from the deposition process.

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