Nanotechnology Now

Our NanoNews Digest Sponsors





Heifer International

Wikipedia Affiliate Button


android tablet pc

Home > Press > Surface diffusion plays a key role in defining the shapes of catalytic nanoparticles

Transmission electron microscope (TEM) images show four distinctive types of nanocrystals that were obtained at different reaction temperatures during Georgia Tech experiments to study the effects of surface diffusion.

Credit: Images courtesy of Younan Xia
Transmission electron microscope (TEM) images show four distinctive types of nanocrystals that were obtained at different reaction temperatures during Georgia Tech experiments to study the effects of surface diffusion.

Credit: Images courtesy of Younan Xia

Abstract:
Shape changers

Controlling 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.

Surface diffusion plays a key role in defining the shapes of catalytic nanoparticles

Atlanta, GA | Posted on April 8th, 2013

Using systematic experiments, researchers have investigated how surface diffusion - a process in which atoms move from one site to another on nanoscale surfaces - 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.

Results 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.

"We want to be able to design the synthesis to produce nanoparticles with the exact shape we want for each specific application," said Younan Xia, a professor in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University. "Fundamentally, 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."

The research was reported April 8 in the early online edition of the journal Proceedings of the National Academy of Sciences (PNAS). The research was sponsored by the National Science Foundation (NSF).

Controlling 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 Georgia Research Alliance (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.

"Controlling the shape is very important to tuning the activity of catalysts and in minimizing the loading of the catalysts," he said. "Shape 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."

Though the importance of particle shape at the nanoscale has been well known, researchers hadn't before understood the importance of surface diffusion in creating the final particle shape. Adding atoms to the corners of platinum cubes, for instance, can create particles with protruding "arms" that increase the catalytic activity. Convex surfaces on cubic particles may also provide better performance. But those advantageous shapes must be created and maintained.

Natural 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.

In 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.

Using 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.

"Unless the atomic reaction is at absolute zero, you will always have some diffusion," said Xia, who holds the Brock Family Chair in the Department of Biomedical Engineering. "But 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."

Xia believes the research may also lead to improved techniques for preserving the unique shapes of nanoparticles even at high operating temperatures.

"Fundamentally, it is very useful for people to know how these shapes are formed," he said. "Most 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."

Xia's 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.

In 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.

The research is part of a long-term study of catalytic nanoparticles being conducted by Xia's research group. Other aspects of the team's work addresses biomedical uses of nanoparticles in such areas as cancer therapy.

"We are very excited by this result because it is generic and can apply to understand and control diffusion on the surfaces of many systems," Xia added. "Ultimately we want to see how we can take advantage of this diffusion to improve the catalytic and optical properties of these nanoparticles."

The 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.

This 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.

####

For more information, please click here

Contacts:
John Toon

404-894-6986

Copyright © Georgia Institute of Technology

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

Imaging

Berkeley Lab Researchers Demonstrate First Size-based Chromatography Technique for the Study of Living Cells April 22nd, 2014

More effective kidney stone treatment, from the macroscopic to the nanoscale April 17th, 2014

Catching the (Invisible) Wave: UC Santa Barbara researchers create a unique semiconductor that manipulates light in the invisible infrared/terahertz range, paving the way for new and enhanced applications April 11th, 2014

News and information

Berkeley Lab Researchers Demonstrate First Size-based Chromatography Technique for the Study of Living Cells April 22nd, 2014

PETA science consortium to present hazard testing strategy at nanotoxicology meeting: High tech field ripe for use of sophisticated non-animal testing strategies April 22nd, 2014

Harris & Harris Group Notes the Receipt of Proceeds From the Sale of Molecular Imprints' Semiconductor Business to Canon April 22nd, 2014

National Space Society Congratulates SpaceX on the Success of CRS-3 and the First Flight of the Falcon 9R April 22nd, 2014

Chemistry

Thinnest feasible membrane produced April 17th, 2014

Targeting cancer with a triple threat: MIT chemists design nanoparticles that can deliver three cancer drugs at a time April 15th, 2014

Govt.-Legislation/Regulation/Funding/Policy

Cloaked DNA nanodevices survive pilot mission: Successful foray opens door to virus-like DNA nanodevices that could diagnose diseased tissues and manufacture drugs to treat them April 22nd, 2014

Berkeley Lab Researchers Demonstrate First Size-based Chromatography Technique for the Study of Living Cells April 22nd, 2014

Progress made in developing nanoscale electronics: New research directs charges through single molecules April 21st, 2014

'Exotic' material is like a switch when super thin April 18th, 2014

Discoveries

Like a hall of mirrors, nanostructures trap photons inside ultrathin solar cells April 22nd, 2014

Nanomaterial Outsmarts Ions April 22nd, 2014

Vacuum Ultraviolet Lamp of the Future Created in Japan: First Solid-State Vacuum UV Phosphor, Described in APL-Materials, Promises Smaller, Safer, Longer Lasting, Low Power Lamps for Industrial Applications April 22nd, 2014

Berkeley Lab Researchers Demonstrate First Size-based Chromatography Technique for the Study of Living Cells April 22nd, 2014

Announcements

Berkeley Lab Researchers Demonstrate First Size-based Chromatography Technique for the Study of Living Cells April 22nd, 2014

PETA science consortium to present hazard testing strategy at nanotoxicology meeting: High tech field ripe for use of sophisticated non-animal testing strategies April 22nd, 2014

Harris & Harris Group Notes the Receipt of Proceeds From the Sale of Molecular Imprints' Semiconductor Business to Canon April 22nd, 2014

National Space Society Congratulates SpaceX on the Success of CRS-3 and the First Flight of the Falcon 9R April 22nd, 2014

Tools

MRI, on a molecular scale: Researchers develop system that could one day peer into the atomic structure of individual molecules April 20th, 2014

Oxford Instruments Asylum Research Introduces the MFP-3D InfinityTM AFM Featuring Powerful New Capabilities and Stunning High Performance April 18th, 2014

More effective kidney stone treatment, from the macroscopic to the nanoscale April 17th, 2014

Aerotech X-Y ball-screw stage for economical high performance Planar positioning April 16th, 2014

Energy

Like a hall of mirrors, nanostructures trap photons inside ultrathin solar cells April 22nd, 2014

Global leader in solar cell manufacturing eyes New York for major expansion outside of Japan: CNSE and Solar Frontier Explore $700 Million Investment, Job Creation in New York State April 22nd, 2014

Nanoreporters tell 'sour' oil from 'sweet': Rice University's hydrogen sulfide nanoreporters gather intel on oil before pumping April 22nd, 2014

High-temperature plasmonics eyed for solar, computer innovation April 17th, 2014

Automotive/Transportation

Relieving electric vehicle range anxiety with improved batteries: Lithium-sulfur batteries last longer with nanomaterial-packed cathode April 16th, 2014

Tiny particles could help verify goods: Chemical engineers hope smartphone-readable microparticles could crack down on counterfeiting April 15th, 2014

Nanotech Business Review 2013-2014 April 9th, 2014

Heat-conducting polymer cools hot electronic devices at 200 degrees C March 31st, 2014

Fuel Cells

University of Surrey collaborates with India and Tata Steel to revolutionise renewable energy March 26th, 2014

Novel membrane reveals water molecules will bounce off a liquid surface: Study may lead to more efficient water-desalination systems, fundamental understanding of fluid flow March 16th, 2014

Big Step for Next-Generation Fuel Cells and Electrolyzers: Researchers at Berkeley and Argonne National Labs Discover Highly Promising New Class of Nanocatalyst February 27th, 2014

Research and applications of iron oxide nanoparticles February 26th, 2014

Research partnerships

University of Waterloo Visits China to Strengthen Bonds With Research Partners April 21st, 2014

Novel stapled peptide nanoparticle combination prevents RSV infection, study finds April 17th, 2014

Scientists Capture Ultrafast Snapshots of Light-Driven Superconductivity: X-rays reveal how rapidly vanishing 'charge stripes' may be behind laser-induced high-temperature superconductivity April 16th, 2014

Scalable CVD process for making 2-D molybdenum diselenide: Rice, NTU scientists unveil CVD production for coveted 2-D semiconductor April 8th, 2014

NanoNews-Digest
The latest news from around the world, FREE







  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More














ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







© Copyright 1999-2014 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE