Graphene production: new solutions to a new problem.

528 nature nanotechnology | VOL 3 | SEPTEMBER 2008 | www.nature.com/naturenanotechnology Interestingly, the nano-selenium material captured five times more mercury than the maximum predicted on the basis of its surface area, indicating significant penetration of mercury into the nanoselenium matrix. This did not occur in the other sorbent materials. Even so, the amount of mercury sequestered was less than 10% of the potential 1:1 molar stoichiometry for Hg:Se. This means that the binding capacity of nano-selenium can be further improved by optimizing its surface area. The use of elemental selenium to capture elemental mercury to form mercury selenide eliminates the need to first oxidize the mercury into a charged form that can subsequently be sequestered by a partner of opposing charge. The chemistry of mercury and selenium, particularly the readily interactive electron orbitals of elemental selenium (Fig. 1), predisposes its binding to elemental mercury with high affinity. Capture of uncharged gas-phase elemental mercury onto a solid substrate such as elemental selenium has obvious advantages because the mercury selenide forms directly from the initial collision rather than requiring a sequential two-step process. The nano-selenium sorbents are intended for use in protective barrier cloths that can stop the release of mercury from carpets contaminated by broken fluorescent lamps. They can also be applied in containment bags designed for safe disposal of the lamps or other mercurycontaining wastes. Unstabilized nanoselenium in the form of a dry powder or in an impregnated cloth was successfully used in a proof-of-principle test for in situ realtime suppression of mercury vapour escape following the fracture of fluorescent lamps. Mercury’s binding interaction with nano-selenium parallels the interaction that occurs when mercury enters the body. The mechanism of mercury toxicity appears to involve covalent binding of mercury to selenium at the active sites of seleniumdependent enzymes4, such as glutathione peroxidases, as well as other important selenoenzymes including the thioredoxin reductases. Binding of mercury irreversibly inhibits the antioxidant functions of these enzymes and leaves vulnerable tissues such as the brain poorly protected against oxidative damage. Therefore, it is highly appropriate that the small but precious supply of selenium in the body may someday be protected from airborne mercury exposures by using products containing nano-selenium sorbents.