Clean fuel thanks to nanoparticles?

The shape and size of the particles determines their suitability for desulfurization

Multi-walled MoS2 nano-octahedron © Forschungszentrum Dresden-Rossendorf
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Nanoparticles of molybdenum disulfide (MoS2) could in the future ensure that fuels can be desulfurized more effectively. Researchers have now discovered that in addition to size, the shape of the particles is important for use in fuel desulfurization. These results were discussed in the journals Angewandte Chemie and Nature Nanotechnology.

It has long been known that very small, sulfur-rich MoS2 platelets can desulfurize fuel and that this ability increases very rapidly as the particle size decreases. This effect was attributed to the special structure along the edges of these regular triangular nanoparticles. In contrast to the semiconducting MoS2 solid these edges are electronically conductive like a metal.

"Nano confetti" on gold

Since the binding of sulphurous impurities of the fuel takes place only at the edges of the triangular plates, an international team of scientists from the Technical University of Dresden, the Forschungszentrum Dresden-Rossendorf and the Weizmann Institute in Rehovot, Israel, were interested in the binding properties of larger MoS2 molecules. Nanoparticles with many, long and easily accessible edges.

Above all, three-dimensional particles, they found, promise a high potential for the desulphurisation and detoxification of car exhaust gases. Such octahedral particles of the shape of a double pyramid are less expensive to produce than the very small platelets in use, which must be produced on a gold layer, much like nano-confetti.

Size and structure decide on properties

For the first time, the researchers were able to show that the ability to desulfurize fuel does not have to be restricted to the smallest MoS2 particles, but that similar effects also occur with larger nanoparticles. In addition to the particle size, so the result, the three-dimensional structure of MoS2 nanoparticles determines the chemical and physical properties in a crucial way. display

As an important result of the joint studies, the relationship between particle size and shape on the one hand and the electronic properties on the other was recorded over several orders of magnitude. MoS2 nanoparticles such as platelets, fullerenes and even nanotubes with dimensions of more than ten nanometers are semiconducting extended MoS2 crystal. In contrast, in the diameter range of three to seven nanometers, there are regular three-dimensional structures composed of eight equilateral triangles each. For the edges and corners of these nano-octahedra, the calculations of the Dresden scientists predict similar metallic properties as were found for the smaller, catalytically active nanoplates.

Single-walled nano-octahedra with a few hundred atoms are, according to the calculation, unstable and have not been observed so far. Multi-walled octahedra, nested in one another like a matryoshka doll, can be produced stably and promise similar abilities as the smaller, catalytically active nanoplates. These materials were investigated using various experimental and theoretical techniques (transmission electron microscopy, quantum mechanical simulation).

(Technical University Dresden, 07.02.2007 - NPO)