This looks like a fairly normal piece of stainless steel mesh, but it's coated with a special substance which allows it to block oil while allowing water through.
Developed by researchers at Ohio State, the coating is apparently inspired by lotus leaves, which do the opposite: repelling water but not oil. The team attempted to replicate the bumpy surface of the lotus leaf by spraying silica nanoparticles onto steel mesh, then added a polymer coating that has surfactant molecules embedded within it. Surfactants are typically used to lower the surface tension between two liquids, making them easier to separate.
The resulting mesh was tested by pouring thoroughly mixed water and oil through it. When the mixture hits the mesh, oil collects on the surface (that's the red stuff in the image above) while water passes through; the oil can then be poured off into another container. The results are published in Scientific Reports.
The coating is just a few nanometres thick, and the researchers estimate that the mesh could be made for less for around 50 pence per square foot. If that's possible the applications are promising. "If you scale this up, you could potentially catch an oil spill with a net," explained Bharat Bhushan, one of the researchers, to PhysOrg. [Scientific Reports via PhysOrg]