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Nanopaper soaks up oily spills

A mat of nanowires with the touch and feel of paper could be used to clean-up oil spills or as a low cost water filter, according to US researchers.

The water-resistant nanopaper, which has the ability to soak up to 20 times its weight in oil, appears in this month's issue of Nature Nanotechnology.

Assistant Professor Jing Kong, a researcher at the Massachusetts Institute of Technology (MIT) and co-author of the paper, says the nanopaper is very similar to traditional writing paper.

"You can even print on it and cut it just like paper," he says.

Unlike normal writing paper, which is made from cellulose, nanopaper is made from solid potassium manganese oxide nanowires. Each nanowire is about 20 nanometres in diameter, and together they naturally clump together to form strands several centimetres long.

After being dissolved in water, the nanowires dry rapidly to create a sheet of nanopaper.

"The process of making the nanopaper is the same one you would use to make [normal] paper," study co-author and MIT Associate Professor Francesco Stellacci says.

Polymer coating

By itself, the nanopaper sucks up water just like normal paper. But by coating the nanopaper with siloxane vapour, a common polymer, the researchers turned it from a super hydrophilic material into a super hydrophobic material, repelling water while attracting oil.

The oil is soaked up and stored in the microscopic nooks and crannies between the individual nanowires, known as capillaries.

The combination of the nanowires and the polymer coating helps the nanopaper absorb oil.

"We tried the polymer coating on different materials," says Kong.

"But it doesn't have as much of a dramatic effect as it does on the nanowires."

Cleaning up

After an oil spill, workers would lay the paper in the contaminated area. In areas of heavy contamination, the nanopaper would be saturated with oil in about five minutes.

The nanopaper would then be collected and boiled. The oil would be re-captured and the nanopaper re-used.

It's a common maxim that oil and water don't mix, but they do form emulsions, where the oil breaks up into tiny particles making it difficult to clean up.

"There is a huge environmental challenge there," says Assistant Professor Joerg Lahann, a researcher at the University of Michigan who was not involved in the MIT work.

"They are able to separate oil from water even in an emulsion, which is very hard," says Lahann.

The MIT team has patented their nanopaper and plans to commercialise it.

Kong estimates that it will be available in a year and a half and will cost about US$4 (A$4.18) per kilogram.