It looks like paper. It feels like paper. It's even made like paper. But this paper, made from metal nanowires, can sit in water for months and never get wet, while soaking up to 20 times its weight in oil.
"You can even print on it and cut it just like paper," said Jing Kong, a researcher at the Massachusetts Institute of Technology and co-author of a study on the paper appearing in this month's issue of Nature Nanotechnology.
The new nanopaper is designed to help clean oil spills, even difficult emulsions, and other environmental toxins.
The nanopaper is made from solid potassium manganese oxide nanowires instead of cellulose, the main ingredient of normal paper. Each nanowire is about 20 nanometers in diameter, and together they naturally clump together to form strands several centimeters long.
After being dissolved in water, the nanometers dry rapidly to create a sheet of nanopaper.
"The process of making the nanopaper is same one you would use to make [normal] paper," said Francesco Stellacci, a study co-author also at MIT.
By itself, the nanopaper sucks up water just like normal paper. But by coating the nanopaper with siloxane vapor, 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.
It's the combination of the nanowires and that coating that creates oil-absorbing nanopaper.
"We tried the polymer coating on different materials," said Kong. "But it doesn't have as much of a dramatic effect as it does on the nanowires."
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 mixed in with the water, that are difficult to clean up.
"There is a huge environmental challenge there," said 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," said Lahann.
The MIT team has patented their nanopaper and plans to commercialize it. Kong estimates that it will be available in a year and a half and will cost about $4 per kilogram.