{"205461":{"#nid":"205461","#data":{"type":"news","title":"Surface Diffusion Plays a Key Role in Defining the Shapes of Catalytic Nanoparticles","body":[{"value":"\u003Cp\u003EControlling the shapes of nanometer-sized catalytic and electrocatalytic particles made from noble metals such as platinum and palladium may be more complicated than previously thought.\u003C\/p\u003E\u003Cp\u003EUsing systematic experiments, researchers have investigated how surface diffusion \u2013 a process in which atoms move from one site to another on nanoscale surfaces \u2013 affects the final shape of the particles. The issue is important for a wide range of applications that use specific shapes to optimize the activity and selectivity of nanoparticles, including catalytic converters, fuel cell technology, chemical catalysis and plasmonics.\u003C\/p\u003E\u003Cp\u003EResults of the research could lead to a better understanding of how to manage the diffusion process by controlling the reaction temperature and deposition rate, or by introducing structural barriers designed to hinder the surface movement of atoms.\u003C\/p\u003E\u003Cp\u003E\u201cWe want to be able to design the synthesis to produce nanoparticles with the exact shape we want for each specific application,\u201d said \u003Ca href=\u0022http:\/\/www.bme.gatech.edu\/facultystaff\/faculty_record.php?id=158\u0022\u003EYounan Xia\u003C\/a\u003E, a professor in the \u003Ca href=\u0022http:\/\/www.bme.gatech.edu\/\u0022\u003EWallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University\u003C\/a\u003E. \u201cFundamentally, it is important to understand how these shapes are formed, to visualize how this happens on structures over a length scale of about 100 atoms.\u201d\u003C\/p\u003E\u003Cp\u003EThe research was reported April 8 in the early online edition of the journal \u003Cem\u003EProceedings of the National Academy of Sciences\u003C\/em\u003E (PNAS). The research was sponsored by the \u003Ca href=\u0022http:\/\/www.nsf.gov\/\u0022\u003ENational Science Foundation\u003C\/a\u003E (NSF).\u003C\/p\u003E\u003Cp\u003EControlling the shape of nanoparticles is important in catalysis and other applications that require the use of expensive noble metals such as platinum and palladium. For example, optimizing the shape of platinum nanoparticles can substantially enhance their catalytic activity, reducing demand for the precious material, noted Xia, who is a \u003Ca href=\u0022http:\/\/www.gra.org\/\u0022\u003EGeorgia Research Alliance\u003C\/a\u003E (GRA) eminent scholar in nanomedicine. Xia also holds joint appointments in the School of Chemistry and Biochemistry and the School of Chemical and Biomolecular Engineering at Georgia Tech.\u003C\/p\u003E\u003Cp\u003E\u201cControlling the shape is very important to tuning the activity of catalysts and in minimizing the loading of the catalysts,\u201d he said. \u201cShape control is also very important in plasmonic applications, where the shape controls where optical absorption and scattering peaks are positioned. Shape is also important to determining where the electrical charges will be concentrated on nanoparticles.\u201d\u003C\/p\u003E\u003Cp\u003EThough the importance of particle shape at the nanoscale has been well known, researchers hadn\u2019t before understood the importance of surface diffusion in creating the final particle shape.\u003C\/p\u003E\u003Cp\u003EAdding atoms to the corners of platinum cubes, for instance, can create particles with protruding \u201carms\u201d that increase the catalytic activity. Convex surfaces on cubic particles may also provide better performance. But those advantageous shapes must be created and maintained.\u003C\/p\u003E\u003Cp\u003ENatural energetic preferences related to the arrangement of atoms on the tiny structures favor a spherical shape that is not ideal for most catalysts, fuel cells and other applications. \u0026nbsp;\u003C\/p\u003E\u003Cp\u003EIn their research, Xia and his collaborators varied the temperature of the process used to deposit atoms onto metallic nanocrystals that acted as seeds for the nanoparticles. They also varied the rates at which atoms were deposited onto the surfaces, which were determined by the injection rate at which a chemical precursor material was introduced. The diffusion rate is determined by the temperature, with higher temperatures allowing the atoms to move around faster on the nanoparticle surfaces. In the research, bromide ions were used to limit the movement of the added atoms from one portion of the particle to another.\u003C\/p\u003E\u003Cp\u003EUsing transmission electron microscopy, the researchers observed the structures that were formed under different conditions. Ultimately, they found that the ratio of the deposition rate to the diffusion rate determines the final shape. When the ratio is greater than one, the adsorbed atoms tend to stay where they are placed. If the ratio is less than one, they tend to move.\u003C\/p\u003E\u003Cp\u003E\u201cUnless the atomic reaction is at absolute zero, you will always have some diffusion,\u201d said Xia, who holds the Brock Family Chair in the Department of Biomedical Engineering. \u201cBut if you can add atoms to the surface in the places that you want them faster than they can diffuse, you can control the final destination for the atoms.\u201d\u003C\/p\u003E\u003Cp\u003EXia believes the research may also lead to improved techniques for preserving the unique shapes of nanoparticles even at high operating temperatures.\u003C\/p\u003E\u003Cp\u003E\u201cFundamentally, it is very useful for people to know how these shapes are formed,\u201d he said. \u201cMost of these structures had been observed before, but people did not understand why they formed under certain conditions. To do that, we need to be able to visualize what happens on these tiny structures.\u201d\u003C\/p\u003E\u003Cp\u003EXia\u2019s research team also studied the impact of diffusion on bi-metallic particles composed of both palladium and platinum. The combination can enhance certain properties, and because palladium is currently less expensive than platinum, using a core of palladium covered by a thin layer of platinum provides the catalytic activity of platinum while reducing cost.\u003C\/p\u003E\u003Cp\u003EIn that instance, surface diffusion can be helpful in covering the palladium surface with a single monolayer of the platinum. Only the surface platinum atoms will be able to provide the catalytic properties, while the palladium core only serves as a support.\u003C\/p\u003E\u003Cp\u003EThe research is part of a long-term study of catalytic nanoparticles being conducted by Xia\u2019s research group. Other aspects of the team\u2019s work addresses biomedical uses of nanoparticles in such areas as cancer therapy.\u003C\/p\u003E\u003Cp\u003E\u201cWe are very excited by this result because it is generic and can apply to understand and control diffusion on the surfaces of many systems,\u201d Xia added. \u201cUltimately we want to see how we can take advantage of this diffusion to improve the catalytic and optical properties of these nanoparticles.\u201d\u003C\/p\u003E\u003Cp\u003EThe research team also included Xiaohu Xia, Shuifen Xie, Maochang Liu and Hsin-Chieh Peng at Georgia Tech; and Ning Lu, Jinguo Wang and Professor Moon J. Kim at the University of Texas at Dallas.\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThis research was supported by the National Science Foundation (NSF) under grant DMR-1215034 and by startup funds from Georgia Tech. Any conclusions expressed are those of the principal investigator and may not necessarily represent the official views of the NSF.\u003C\/em\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ECITATION\u003C\/strong\u003E: Xia, Xiaohu, et al., \u201cOn the role of surface diffusion in determining the shape or morphology of noble-metal nanocrystals,\u201d (Proceedings of the National Academy of Science, 2013). \u003Ca href=\u0022http:\/\/www.pnas.org\/content\/early\/2013\/04\/05\/1222109110\u0022\u003Ehttp:\/\/www.pnas.org\/content\/early\/2013\/04\/05\/1222109110\u003C\/a\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EResearch News\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EGeorgia Institute of Technology\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003E177 North Avenue\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EAtlanta, Georgia\u0026nbsp; 30332-0181\u0026nbsp; USA\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cbr \/\u003E\u003Cstrong\u003EMedia Relations Contact\u003C\/strong\u003E:\u0026nbsp; John Toon (404-894-6986)(\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E).\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EControlling the shapes of nanometer-sized catalytic and electrocatalytic particles made from noble metals such as platinum and palladium may be more complicated than previously thought.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"A new study shows the importance of surface diffusion in forming catalytic nanoparticles."}],"uid":"27303","created_gmt":"2013-04-09 10:40:14","changed_gmt":"2016-10-08 03:13:59","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2013-04-09T00:00:00-04:00","iso_date":"2013-04-09T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"205451":{"id":"205451","type":"image","title":"Surface diffusion in nanocatalysts","body":null,"created":"1449179977","gmt_created":"2015-12-03 21:59:37","changed":"1475894861","gmt_changed":"2016-10-08 02:47:41","alt":"Surface diffusion in nanocatalysts","file":{"fid":"196714","name":"catalyst-shapes.jpg","image_path":"\/sites\/default\/files\/images\/catalyst-shapes_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/catalyst-shapes_0.jpg","mime":"image\/jpeg","size":461612,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/catalyst-shapes_0.jpg?itok=0OFWBHh8"}}},"media_ids":["205451"],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"141","name":"Chemistry and Chemical Engineering"},{"id":"144","name":"Energy"},{"id":"145","name":"Engineering"},{"id":"154","name":"Environment"},{"id":"149","name":"Nanotechnology and Nanoscience"}],"keywords":[{"id":"2506","name":"catalyst"},{"id":"14219","name":"Coulter Department of Biomedical Engineering"},{"id":"2044","name":"Fuel Cell"},{"id":"63631","name":"nanocatalyst"},{"id":"2054","name":"nanoparticle"},{"id":"107","name":"Nanotechnology"},{"id":"169567","name":"surface diffusion"},{"id":"24841","name":"Younan Xia"}],"core_research_areas":[{"id":"39451","name":"Electronics and Nanotechnology"},{"id":"39531","name":"Energy and Sustainable Infrastructure"},{"id":"39471","name":"Materials"}],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003EJohn Toon\u003C\/p\u003E\u003Cp\u003EResearch News\u003C\/p\u003E\u003Cp\u003E\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E\u003C\/p\u003E\u003Cp\u003E(404) 894-6986\u003C\/p\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}