A group of American chemists have successfully synthesised ‘ultrastable’ silver nanoparticles which are more stable than their gold counterparts. In an article published in Nature this week, the authors describe the use of the sulfur-containing p-mercaptobenzoic acid to stabilise the nanoparticles in quantitative yield in relatively large quantities from a fairly straightforward synthetic procedure.
Silver nanoparticles are of great interest at the moment, due to their possible applications in fields such as catalysis, sensing, photochemistry and medicine. They’re particularly well-known for their antibacterial properties, and you may have seen various wound dressings in the supermarket utilising this particular property.
Stable silver nanoparticles are more desirable than gold as silver is cheaper and more abundant. However, they have proven difficult to synthesise for decades as silver is more prone to oxidation than gold, leading to tarnishing which limits their application and development. This is why this article is so important, and is how it’s found its way into one of the world’s leading publications.
The authors report the particles as having a discrete molecular structure, which is impressive, as most synthetic techniques for forming metal nanoparticles lead to a range of different sizes of product. These particles then need to be separated, costing time and materials. Interestingly, these particles are so stable that when new silver nanoparticles are synthesised alongside them, they remain completely intact, and don’t aggregate to larger particles, as typical silver nanoparticles would. Because of this, large-scale synthesis of these particles is possible, with scales of 140 g being achieved so far. This is 3 times larger than typical nanoparticle preparations!
X-ray crystallography revealed the structure of the particles, which was shown to have extremely high symmetry. The silver core consists of an icosahedron within a dodecahedron, with an outer core containing the organic stabilising ligand leading to an overall octahedral structure. It’s a completely unique and fascinating structure, and is unlike anything seen in gold or silver nanoparticles previously. It is this exceptional structure which gives the particles their astounding stability.
After decades of intensive research, these highly-stable particles are a real breakthrough, and this is an exciting step forward in this field of chemistry. No doubt research will now explode around this area, which could have massive impacts on materials science as new products are made exploiting the remarkable stability of these particles.