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Posted: Jan 09, 2017
Efficient nanowire solution for a big-name pollutant
(Nanowerk News) Winter cold snaps often bring tragic stories of Americans killed by carbon monoxide, a colorless, odorless gas present in the emissions of gas-powered generators and vehicles. Several thousand more people are treated for carbon monoxide poisoning each year. While we currently rely on carbon monoxide detectors, new research points the way to a new approach: direct elimination of the gas.
The arrows represent a schematic illustration of the multiple reaction regimes for carbon monoxide (CO) oxidation with the PtFe-FeOx/TiO2 system. The dashed arrows represent reaction pathways that utilize the PtFe and FeOx interface, while the solid arrow represents a reaction pathway that uses the nanowire (NW) and TiO2 interface. The inset shows a scanning electron transmission micrograph of the nanowires, with platinum (Pt, green) in the core of the NW and iron (Fe, red) drawn to the surface. (Image: Zhu et al., J. Am. Chem. Soc. 137, 10156 (2015))
This work could lead to a highly efficient and cost-effective method to remove carbon monoxide. More broadly, the scientists showed how to maximize the activity of the tiny wires made from platinum and iron using an encased structure. This result provides insight towards the development of advanced catalysts, which could impact an incredibly large number of applications, such as fuel cell reaction systems.
Carbon monoxide (CO) is a colorless and odorless gas that is potentially fatal at elevated concentrations due to the prevention of oxygen flow to organs and tissues. Though CO concentrations in the atmosphere have remained below the national safety standard for several decades, this gas still poses a threat to humans when elevated concentrations build up in enclosed areas. Though we currently rely on detectors to alert us of dangerous CO levels, the technology may soon exist to remove CO from indoor air instead.
Collaborators from Oak Ridge National Laboratory, the University of Tennessee, Zhejiang University of Technology, and the Center for Functional Nanomaterials have teamed up to develop uniquely structured nanowires (NWs) that remove CO with a 100 percent conversion efficiency at room temperature.
These one-dimensional nanostructures consist of a PtFe-FeOx core-shell composition and are supported on titanium dioxide (TiO2). Although the structures of these NWs seem rather complex, they are surprisingly simple to create. The team began by assembling PtFe NWs onto the TiO2 support.
Then, they simply heated the NWs in air to cause Fe to diffuse to the surface of the NWs, thus creating the PtFe-FeOx core-shell structure. This structure serves to maximize the interfacial synergy of the system and to improve catalytic performance. Through the use of isotope mass spectrometry, the researchers identified three unique mechanisms for CO conversion.
Two of the mechanisms involve the interface between the PtFe and FeOx phases of the NWs, with the remaining mechanism involving the interface between the NWs and the TiO2. All three of these reactions combine to give the NWs the extremely efficient 100 percent conversion of CO.
Additionally, the presence of Fe and FeOx on Pt helps to prevent poisoning of the catalyst (deactivation through occupied binding sites). Upon application of slight heating (40°C), NWs that had begun to decrease in activity due to poisoning were rejuvenated and resumed catalytic function at 100 percent conversion. The NWs remained stable and active through this process for many cycles, thus also illustrating their durability.
This research can ideally be developed into a method for CO abatement, although the design of these unique NWs will also serve as inspiration for the design of advanced catalysts used in many different applications.