Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Tiny porphyrin tubes developed by Sandia may lead to new nanodevices

21.03.2005


Research could result in clean, inexpensive hydrogen fuel

Sunlight splitting water molecules to produce hydrogen using devices too small to be seen in a standard microscope. That’s a goal of a research team from the National Nuclear Security Administration’s Sandia National Laboratories. The research has captured the interest of chemists around the world pursuing methods of producing hydrogen from water.

"The broad objective of the research is to design and fabricate new types of nanoscale devices," says John Shelnutt, Sandia research team leader. "This investigation is exciting because it promises to provide fundamental scientific breakthroughs in chemical synthesis, self-assembly, electron and energy transfer processes, and photocatalysis. Controlling these processes is necessary to build nanodevices for efficient water splitting, potentially enabling a solar hydrogen-based economy."



The prospect of using sunlight to split water at the nanoscale grew out of Shelnutt’s research into the development of hollow porphyrin nanotubes. (See "Porphyrin nanotubes versus carbon nanotubes" below.) These light-active nanotubes can be engineered to have minute deposits of platinum and other metals and semiconductors on the outside or inside of the tube.

The key to making water-splitting nanodevices is the discovery by Zhongchun Wang of nanotubes composed entirely of porphyrins. Wang is a postdoctoral fellow at the University of Georgia working in Shelnutt’s Sandia research group. The porphyrin nanotubes are micrometers in length and have diameters in the range of 50-70 nm with approximately 20 nm thick walls. They are prepared by ionic self-assembly of two oppositely charged porphyrins - molecules that are closely related to chlorophyll, the active parts of photosynthetic proteins. These hollow structures are one member of a new class of nanostructures made of porphyrins that Shelnutt and his team are developing. The porphyrin building blocks (tectons) can be altered to control their structural and functional properties.

Shelnutt says these porphyrin nanotubes have "interesting electronic and optical properties such as an intense resonance light scattering ability and photocatalytic activity." When exposed to light, some porphyrin nanotubes can photocatalytically grow metal structures onto tube surfaces to create a functional nanodevice. For example, when the nanotubes are put into a solution with gold or platinum ions and exposed to sunlight, their photocatalytic activity causes the reduction of the ions to the metal. Using this method the researchers have deposited platinum outside the nanotube and grown a nanowire of gold inside the tube.

The nanotube with the gold inside and platinum outside is the heart of a nanodevice that may split water into oxygen and hydrogen. The research team has already demonstrated that the nanotubes with platinum particles on the surface can produce hydrogen when illuminated with light. To complete the nanodevice that splits water, a nanoparticle of an inorganic photocatalyst that produces oxygen must be attached to the gold contact ball that naturally forms at the end of the tube. The gold nanowire and ball serve as a conductor of electrons between the oxygen- and hydrogen- producing components of the nanodevice. The gold conductor also keeps the oxygen and hydrogen parts separate to prevent damage during operation.

"Laboratory-scale devices of this type have already been built by others," Shelnutt says. "What we are doing is reducing the size of the device to reap the benefits of the nanoscale architecture."

Shelnutt says the nanodevice could efficiently use the entire visible and ultraviolet parts of the solar spectrum absorbed by the tubes to produce hydrogen, one of the Holy Grails of chemistry.

These nanotube devices could be suspended in a solution and used for photocatalytic solar hydrogen production.

"Once we have functional nanodevices that operate with reasonable efficiency in solution, we will turn our attention to the development of nanodevice-based solar light-harvesting cells and the systems integration issues involved in their production," Shelnutt says. "There are many possible routes to the construction of functional solar cells based on the porphyrin nanodevices. For example, we may fabricate nanodevices in arrays on transparent surfaces, perhaps on a masked free-standing film. However, we have a lot of issues to resolve before we get to that point."

Water-splitting is just one of the possible applications of the nanodevices based on porphyrin nanostructures. Shelnutt expects the tubes to have uses as conductors, semiconductors, and photoconductors, and to have other properties that permit them to be used in electronic and photonic devices and as chemical sensors.

The work was partially funded by a grant to the University of Georgia from the Department of Energy, Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences.

Porphyrin nanotubes versus carbon nanotubes

Porphyrins are light-absorbing molecules related to chlorophyll, the active part of photosynthetic proteins and light-harvesting nanostructures (chlorosomal rods). They are the active molecules in many other proteins such as hemoglobin, which gets its intense red color from a porphyrin.

Porphyrin nanotubes are made entirely of oppositely charged porphyrin molecules that self-assemble in water at room temperature. The more well-known carbon nanotubes are formed at high temperatures and have covalent bonds between carbon atoms. Porphyrin nanotubes lack the high mechanical strength of the carbon tubes but possess a wider range of optical and electronic properties that can be exploited in making nanodevices. In fact, carbon nanotubes are often modified by attaching porphyrins to increase their utility. This is unnecessary for the porphyrin nanotubes, which can be tailored to specific purposes like water-splitting by varying the type of porphyrin incorporated into the nanotube itself to obtain the desired properties.

Other porphyrin nanostructures such as nanofibers and rectangular cross-section nanotubes have been made and can also be used in the fabrication of nanodevices.

Chris Burroughs | EurekAlert!
Further information:
http://www.sandia.gov

More articles from Power and Electrical Engineering:

nachricht Improved stability of plastic light-emitting diodes
19.04.2018 | Max-Planck-Institut für Polymerforschung

nachricht Intelligent components for the power grid of the future
18.04.2018 | Christian-Albrechts-Universität zu Kiel

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

Im Focus: Like a wedge in a hinge

Researchers lay groundwork to tailor drugs for new targets in cancer therapy

In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Magnetic nano-imaging on a table top

20.04.2018 | Physics and Astronomy

Start of work for the world's largest electric truck

20.04.2018 | Interdisciplinary Research

Atoms may hum a tune from grand cosmic symphony

20.04.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>