Filtration membrane switches between filtering oil and water

Sometimes, people want to clean up polluted water, by removing spilled oil from its surface. Other times, they want to purify oil-based fuel, by removing water from it. An inexpensive new "smart" membrane created at Canada's University of British Columbia can switch between doing both.

Developed by a team led by chemical engineering master's student Chun Haow (Bryan) Kung, the reusable membrane is made up of a fine copper mesh.

In a quick and scalable process, this is initially immersed in an electrolyte solution, then subjected to a succession of two small voltages for a total of two minutes.

When the membrane is subsequently used to filter an oil/water mixture, only oil can pass through it, holding back any water that's present within that oil.

This is due to the rough surface structure of the mesh and the copper oxides that are bound to it.

If the membrane is subjected to just a few seconds' worth of voltage from an ordinary alkaline battery, however, that current alters the surface structure.

As a result, water can now pass through the membrane, but oil is held back.

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(Image Credit: University of British Columbia)