The nanosponges that have been developed by a joint team of Rice University and Penn State University researchers look pretty exciting (wish I could write a better headline about them). Here’s the researcher describing them,
I find the idea that the sponges can be reused and the oil still put to use quite compelling. From the April 16, 2012 news item on Nanowerk,
… Daniel Hashim, a graduate student in the Rice lab of materials scientist Pulickel Ajayan, said the blocks are both superhydrophobic (they hate water, so they float really well) and oleophilic (they love oil). The nanosponges, which are more than 99 percent air, also conduct electricity and can easily be manipulated with magnets.
To demonstrate, Hashim dropped the sponge into a dish of water with used motor oil floating on top. The sponge soaked it up. He then put a match to the material, burned off the oil and returned the sponge to the water to absorb more. The robust sponge can be used repeatedly and stands up to abuse; he said a sample remained elastic after about 10,000 compressions in the lab. The sponge can also store the oil for later retrieval, he said.
“These samples can be made pretty large and can be easily scaled up,” said Hashim, holding a half-inch square block of billions of nanotubes. “They’re super-low density, so the available volume is large. That’s why the uptake of oil can be so high.” He said the sponges described in the paper can absorb more than a hundred times their weight in oil.
Nanosponges have been made from carbon nan0tubes before now (from the Feb. 8, 2010 article by Michael Berger on Nanowerk),
Carbon nanotubes (CNTs) are ‘strange’ nanostructures in a sense that they have both high mechanical strength and extreme flexibility. Deforming a carbon nanotube into any shape would not easily break the structure, and it recovers to original morphology in perfect manner. Researchers in China are exploiting this phenomenon by making CNT sponges consisting of a large amount of interconnected nanotubes, thus showing a combination of useful properties such as high porosity, super elasticity, robustness, and little weight (1% of water density).
The nanotube sponges not only show exciting properties as a porous material but they also are very promising to be used practically in a short time. The production method is simple and scalable, the cost is low, and the sponges can find immediate use in many fields related to water purification.
“We hope to give an example to industry that this sponge is a real thing they can prepare at low cost, make versatile products with high performance, and solve environmental problems utilizing nanotechnology,” [says] Anyuan Cao, a professor in the Department of Advanced Materials and Nanotechnology at Peking University …
The difference between the nanosponges made in 2010 and the ones made in 2012 is the fabrication process. From the April 16, 2012 news item on Nanowerk,
Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry, said multiwalled carbon nanotubes grown on a substrate via chemical vapor deposition usually stand up straight without any real connections to their neighbors. But the boron-introduced defects induced the nanotubes to bond at the atomic level, which tangled them into a complex network. Nanotube sponges with oil-absorbing potential have been made before (see paper in Advanced Materials: “Carbon Nanotube Sponges”), but this is the first time the covalent junctions between nanotubes in such solids have been convincingly demonstrated, he said.
“The interactions happen as they grow, and the material comes out of the furnace as a solid,” Ajayan said. [emphasis mine] “People have made nanotube solids via post-growth processing but without proper covalent connections. The advantage here is that the material is directly created during growth and comes out as a cross-linked porous network.
By comparison, the team in China used this process (from the Feb. 8, 2012 article),
The scientists synthesized the sponges by a chemical vapor deposition (CVD) process during which the CNTs (multi-walled nanotubes with diameters in the range of 30 to 50nm and lengths of tens to hundreds of micrometers,) self-assembled into a porous, interconnected, three-dimensional framework.
The research team had collaborators from the US, Mexico, Japan, Spain, and Belgium. From the April 16, 2012 news release on EurekAlert,
When he was an undergraduate student of Ajayan’s at Rensselaer Polytechnic Institute, Hashim and his classmates discovered hints of a topological solution to the problem while participating in a National Science Foundation exchange program at the Institute of Scientific Research and Technology (IPICYT) in San Luis Potosí, Mexico. The paper’s co-author, Mauricio Terrones, a professor of physics, materials science and engineering at Penn State University with an appointment at Shinshu University, Japan, led a nanotechnology lab there.
“Our goal was to find a way to make three-dimensional networks of these carbon nanotubes that would form a macroscale fabric — a spongy block of nanotubes that would be big and thick enough to be used to clean up oil spills and to perform other tasks,” Terrones said. “We realized that the trick was adding boron — a chemical element next to carbon on the periodic table — because boron helps to trigger the interconnections of the material. To add the boron, we used very high temperatures and we then ‘knitted’ the substance into the nanotube fabric.”
For anyone who would like to read further about this work (from the April 16, 2012 news release on EurekAlert),
The paper’s co-authors are Narayanan Narayanan, Myung Gwan Hahm, Joseph Suttle and Robert Vajtai, all of Rice; Jose Romo-Herrera of the University of Vigo, Spain; David Cullen and Bobby Sumpter of Oak Ridge National Laboratory, Oak Ridge, Tenn.; Peter Lezzi and Vincent Meunier of Rensselaer Polytechnic Institute; Doug Kelkhoff of the University of Illinois at Urbana-Champaign; E. Muñoz-Sandoval of the Instituto de Microelectrónica de Madrid; Sabyasachi Ganguli and Ajit Roy of the Air Force Research Laboratory, Dayton, Ohio (on loan from IPICYT); David Smith of Arizona State University; and Humberto Terrones of Oak Ridge National Lab and the Université Catholique de Louvain, Belgium.
The article is titled, Covalently bonded three-dimensional carbon nanotube solids via boron induced nanojunctions, and has been published as an open access article in Nature’s Scientific Reports.
I did mention the nanosponges developed in China in my Feb. 9, 2010 posting.