Bonus material for Metals’ Hidden Strengths, by Roberta Baxter Two additional discoveries may significantly impact our lives in the future Scientists at Cornell University, Ithaca, N.Y., have created a new type of material made from the metal platinum that could help reduce the toxicity of car exhaust more efficiently At Queensland University of Technology, Brisbane, Australia, researchers have discovered that gold, in combination with light, can help reduce air pollution More efficient catalytic converters A catalytic converter is a device that removes pollutants from motor vehicle exhaust Located between a vehicle's engine and tailpipe, it converts exhaust pollutants such as carbon monoxide, nitrogen oxides, and hydrocarbons into gases such as nitrogen, oxygen, and carbon dioxide The chemical reactions involved consist of two oxidation reactions, in which oxygen is captured by one of the reactants, and one reduction reaction, in which oxygen is released by one of the reactants: Oxidation of hydrocarbons (CxH2x+2): CxH2x+2 + 2x O2 → x CO2 + 2x H2O (where x is an integer) Oxidation of carbon monoxide: CO + O2 CO2 Reduction of nitrogen oxides: NOx x O2 + N2 (where x = or 2) The catalytic converter contains a chemical called a catalyst that speeds up these conversion reactions but is not involved in them The catalyst is often a precious metal, such as platinum, palladium, or rhodium But these metals are costly, so scientists and engineers usually try to make the most of them One way to so is to use them in the form of a powder instead of a solid, because the total surface area of the powder particles is larger than the total surface area of a solid that would be made of these particles This is a general principle in chemistry: Each time you want to maximize use of a material in a chemical reaction, it is better to break it down in smaller pieces to increase the amount of surface area available for the chemical reaction (and when the surface area is increased, more reactants will bind to the metal molecules, making the chemical reaction between these reactants more efficient) Researchers at Cornell University have taken this principle a step further They have made a honeycomb-like structure made of platinum The tiny spaces in that structure are about 10 nanometers across (one nanometer is one billionth of a meter), thus providing even more surface area for chemical reactions to occur If converters were manufactured with this type of catalyst, they would more with less, that is, they would remove pollutants faster with less amounts of platinum Earlier experiments had produced honeycomb-like metals with 2- to 4-nanometer pores, but this size was too small for gases to flow through the honeycomb, which reduced the amount of pollution removed This time, the scientists, led by Cornell professor of materials science and engineering Uli Wiesner, tried a new method in which they mixed tiny particles of platinum, also called nanoparticles and containing a few hundreds of atoms each, with polymers—molecules made of long chains of mostly carbon and hydrogen atoms The polymers directed the platinum nanoparticles into the desired honeycomb-like structure The resulting material was heated at high temperatures without air, which converted the polymer into a carbon scaffold This scaffold prevented the platinum nanoparticles from fusing together, which would have destroyed the desired honeycomblike structure The scaffold was subsequently allowed to cool, and the platinum nanoparticles maintained their regular patterns Then, the scaffold was removed with acid, leaving a honeycomb-like structure of platinum nanoparticles Honeycomb-like platinum structure developed at Cornell University [Courtesy of Scott Warren & Uli Wiesner, Cornell University] This new finding may usher in a new era of more efficient and cheaper catalysts in other applications, such as fuel cells—devices that generate electricity by combining a fuel and oxygen—and “plasmonic” surface structures that can carry more information across microchips than conventional wires “These new structures open a completely novel playground, because no one has been able to structure metals in bulk ways using polymers,” Wiesner says “In principle, if you can it with one metal you can it with others or even mixtures of metals.” Cleaner air with gold Scientists have found a new use for gold Huai Yong Zhu, professor of chemistry at Queensland University, and colleagues found that very small clumps of gold atoms called nanoparticles act as a catalyst to pull apart organic molecules and air pollutants called volatile organic chemicals (VOCs) These gold particles—which are a few millionths of a millimeter in size—catalyze the oxidation reaction of organic molecules, breaking them down into carbon dioxide (CO2) and water (H2O), by absorbing visible and ultraviolet light The generic chemical reaction is: Organic molecule + O2 Au (catalyst) and light CO2 + H2O In one experiment, a sample of an organic compound called formaldehyde (HCHO)— which is one of many VOCs—was placed in a vessel along with gold nanoparticles supported by zirconium dioxide (ZrO2) When the scientists directed blue light toward the vessel, the concentration of formaldehyde decreased by 64% over hours Zhu and colleagues found that formaldehyde had been broken into carbon dioxide by the gold particles after they were activated by the blue light (The zirconium compound did not take part in the reaction; it acted only as a support material for the gold.) The scientists did the same experiment with sunlight and found that the concentration of formaldehyde decreased by 8% over hours “If gold and sunlight can be used to catalyze reactions to purify the air, we can make the air cleaner without using energy,” Zhu says This discovery could boost the use of gold in industrial applications seeking to purify the air from pollutants, such as VOCs, both indoors and outside Future technology may also use gold and sunlight to drive chemical reactions that occur at ambient temperatures —Roberta Baxter ... concentration of formaldehyde decreased by 64% over hours Zhu and colleagues found that formaldehyde had been broken into carbon dioxide by the gold particles after they were activated by the blue... it acted only as a support material for the gold.) The scientists did the same experiment with sunlight and found that the concentration of formaldehyde decreased by 8% over hours “If gold and... experiment, a sample of an organic compound called formaldehyde (HCHO)— which is one of many VOCs—was placed in a vessel along with gold nanoparticles supported by zirconium dioxide (ZrO2) When the scientists