For the first time ever, chemists have used benzene, a common hydrocarbon, to make a new kind of molecular nanotube. This novel structure can be made with planned ‘defects’ along its walls which allows it to carry other molecules giving it a wide range of potential uses.
The research team is based at the University of Tokyo and explain the significance of nanotubes made from benzene on the university website. They write that, “Typical carbon nanotubes are famous for their perfect graphite structures without defects, but they vary widely in length and diameter. Our team wanted a single type of nanotube, a novel form with controlled defects within its nanometer-sized cylindrical structure allowing for additional molecules to add properties and functions.”
Although chemical synthesis of the benzene nanotubes is complicated in places, the process has a success rate of over 90%. This is due in part to the symmetry of the structure, which makes bonding additional benzenes (as many as 40) relatively simple. Once this has happened, the benzenes, sometimes referred to as phenines, are used as panels to form the walls of the nanotube cylinder, creating intentional, evenly spaced defects.
The result, as the team explain in the peer-reviewed journal Science, is a, “… cylindrical carbon compound composed of 40 benzene rings bonded to one another at the 1, 3, and 5 positions to leave regular void spaces in the walls.”
Reporting on the discovery, the online scientific journal Phys.org describes how, “The researchers’ novel process of synthesis starts with benzene, a hexagonal ring of six carbon atoms. They use reactions to combine six of these benzenes to make a larger hexagonal ring called a cyclo-meta-phenylene (CMP). Platinum atoms are then used which allow four CMPs to form an open-ended cube. When the platinum is removed, the cube springs into a thick circle and this is furnished with bridging molecules on both ends enabling the tube shape.”
The key advantage to the new structure is that its defects allow for other chemicals to be inserted inside the tube. This creates a nanotube with great potential, especially for use in the field of semiconductors. As Hiroyuki Isobe, a professor at the Chemistry Department at the University of Tokyo and one of the key researchers observes, “The pNT molecules are aligned and packed in a lattice rich with pores and voids. These nanopores can encapsulate various substances which imbue the pNT crystal with properties useful in electronic applications. One molecule we successfully embedded into pNT was a large carbon molecule called fullerene (C70).”
The team clearly have a passion for their discovery and acknowledge its attractive shape. As Isobe states, “A team lead by Kroto/Curl/Smalley discovered fullerenes in 1985. It is said that Sir Harold Kroto fell in love with the beautiful molecule. A few decades after the discovery, this beautiful molecule, fullerene, has found various utilities and applications.”
Adding that, “We feel the same way about pNT. We were shocked to see the molecular structure from crystallographic analysis. A perfect cylindrical structure with fourfold symmetry emerges from our chemical synthesis. We hope that the beauty of our molecule is also pointing to unique properties and useful functions waiting to be discovered.”