Rice University Opens Graphene for Organic Chemistry
Rice University researchers have found a highly controllable way to attach organic molecules to pristine graphene. The work opens the door for a new class of chemical sensors, thermoelectric devices and metamaterials.
Rice University’s Tour Lab has made a a superlattice with patterns of hydrogenated graphene.
Until this work, there was no way to attach molecules to the basal plane of a sheet of graphene, according to Tour, "They would mostly go to the edges, not the interior. But with this two-step technique, we can hydrogenate graphene to make a particular pattern and then attach molecules to where those hydrogens were,” he said in a statement.
Tour and researchers Zhengzong Sun and Rice graduate Cary Pint (now at Intel) demonstrated that graphene can be made suitable for novel types of chemistry.
"This is useful to make, for example, chemical sensors in which you want peptides, DNA nucleotides or saccharides projected upward in discrete places along a device. The reactivity at those sites is very fast relative to placing molecules just at the edges. Now we get to choose where they go."
The first step in the process involved creating a lithographic pattern to induce the attachment of hydrogen atoms to specific domains of graphene's honeycomb matrix. This restructure, Tour said, turned it into a two-dimensional, semiconducting superlattice called graphane. Hydrogen atoms were generated by a hot filament using an approach developed by Robert Hauge, a distinguished faculty fellow in chemistry at Rice and co-author of the paper.
The lab demonstrated it could dot graphene with finely wrought graphane islands using a fluorescence quenching microscopy (FQM), which allowed the researchers to see patterns with a resolution as small as one micron.
Next, the lab exposed the material to diazonium salts that spontaneously attacked the islands' carbon-hydrogen bonds. The salts also eliminated the hydrogen atoms, leaving a structure of carbon-carbon sp3 bonds that are more amenable to further functionalization with other organics.
The work takes graphene from Rice’s graphene-graphane superlattice to a hybrid, a more complicated superlattice," Sun said. In the future, the team intends to make further functional changes to materials where it can control the position, the bond types, the functional groups and the concentrations.
"In the beginning, there was very little organic chemistry you could do with graphene. Now we can do almost all of it. This opens up a lot of possibilities," Sun added.
The work appeared this week in the online journal Nature Communications. Co-authors include: graduate students Daniela Marcano, Gedeng Ruan and Zheng Yan, former graduate student Jun Yao, postdoctoral researcher Yu Zhu and visiting student Chenguang Zhang, all of Rice.
The work was supported by the Air Force Office of Scientific Research, Sandia National Laboratory, the Nanoscale Science and Engineering Initiative of the National Science Foundation and the Office of Naval Research MURI graphene program.