Hydrophobicity and Oleophilicity
The unmodified PU foams showed both hydro and oleophobicity – both water and oil were repelled from the surface of the foam. The addition of both PTFE and NPs, however, changed the properties of the material, which became super-hydrophobic and oleophilic.
The figure on the left shows the behavior of the modified foam when a drop of oil-containing water is deposited on the material surface. It can be seen how the oils (colored with blue dye) are adsorbed, while the water is not – the oil and foam just stays on the surface, waiting to be collected.
Tests performed on this material showed no water uptake at all; the oil, on the contrary, was adsorbed very quickly, with the material reaching the saturation in less than 60 seconds.
Further to these properties, the presence of the NPs apart from turning the material into oleophilic also made it magnetic; this is due to the magnetic properties of the iron oxides themselves. The figure on the side shows how the foam can be directed towards the oil and be moved around using a magnet till the water remains practically clean.
Dr. Athanassia Athanassiou, one of the researchers in this project, told Decoded Science that, “The characteristics of these materials are very important: the combination of super-hydrophobicity and oleophilicity is something very innovative; up to now, no other polymeric porous material showed both properties at the same time at such extent. This ensures an excellent removal of the oils from the water and very high oil absorption efficiency.
The modified foams are very efficient, as they can absorb oil more than 12 times their weight.
Moreover, the magnetic behavior makes it very easy to move and remove these foams from the water; this aspect is very important to employ them in large-scale operation. Additionally, these foams are also light, floating on water surface; this further simplifies the removal procedure.”
Oil-Removing Magnetic Foam: Scaling Up
Will this foam be viable on a large-scale to clean up oil spills? According to Dr. Athanassiou, the researchers still need to study the scale-up process. The good news? She tells us that “…the modification of the commercial PU foams is achieved with simple steps; this makes the scale-up, feasible, simple and economically viable.” That’s great news for the environment!
P. Calcagnile et al. Magnetically Driven Floating Foams for the Removal of Oil Contaminants from Water. (2012). ACS Nano, 6(6), 5413-5419. Accessed August 28, 2012.
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