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Chemistry at the core of nanoscience One of the hottest topics in science today is the study of nanomaterials—crystals that measure only a few atoms across. "At present, the wealth of experimental information on these materials stands in contrast to the incomplete understanding of mechanisms underlying their observed properties," says Marion Thurnauer, director of Argonne's Chemistry Division. Thurnauer believes that chemistry will play a major role in understanding nanomaterials and developing practical applications. "Chemistry provides the bridge between behavior at the molecular level and the macroscopic properties of matter. At the nanoscale, properties are dominated by molecular behavior. Chemical knowledge of molecular interactions and processes is a necessary component for the growth of nanoscience." Thurnauer and her colleagues have shown that the natural crystalline structure of titanium oxide—also known as "titania"—becomes distorted in particles less than 20 nanometers in diameter. The experiments compared bonding between titanium and oxygen atoms under three distinct forms of titania: "bulk" or normal-sized crystals, pure nanosized crystals, and nanosized crystals with ascorbic acid—better known as vitamin C—attached. In bulk titania crystals, each titanium atom bonds with six oxygen atoms, forming an octahedron with titanium at the center and oxygen at each corner. A normal crystal of bulk-titania consists of this unit structure repeated millions of times. But when you come to the surface, the repetition has to end, so the titanium attaches to some other chemical group. So in a sense, the surface is a defect. Defects are important because they are the keys to imbuing materials with new properties, including computer chips, transistors and many other commercially important electronic products based on semiconductors. As titania crystals become smaller, the surface defects and distortions become dominant. In fact, at the nanosize scale, the defects are so pronounced that the octahedron becomes a pyramid. But when nanotitania combines with vitamin C, the bonds realign and the unit shape returns to an octahedron, Argonne's researchers learned. This sort of basic research will help scientists learn to control the defect sites, opening up a whole new field of chemistry.
Submitted by DOE's Argonne National Laboratory |