7th August 2019 World's thinnest gold: 0.47 nanometres Scientists at the University of Leeds have created a new form of gold, just two atoms thick, measured at 0.47 nanometres. In addition to being the thinnest unsupported gold ever produced, it functions 10 times more efficiently as a catalytic substrate than larger gold nanoparticles. The material is classed as two-dimensional, as it comprises just two layers of atoms sitting on top of one another. All atoms are surface atoms, so there are no 'bulk' atoms hidden beneath the surface. It could have large-scale applications in the medical device and electronics industries, and also as a catalyst to speed up chemical reactions in a wide range of industrial processes. The researchers involved believe it could also form the basis of artificial enzymes for potential use in rapid, point-of-care medical diagnostic tests and in water purification systems. The synthesis of this ultra-thin metal is described in the journal Advanced Science. "This work amounts to a landmark achievement," said the paper's lead author, Dr Sunjie Ye, from Leeds' Molecular and Nanoscale Physics Group and the Leeds Institute of Medical Research. "Not only does it open up the possibility that gold can be used more efficiently in existing technologies, it is providing a route which would allow material scientists to develop other 2D metals. This method could innovate nanomaterial manufacturing." The research team is now looking to work with industry on ways of scaling-up the process.
Synthesising the gold nanosheet takes place in an aqueous solution and starts with chloroauric acid, an inorganic substance that contains gold. It is reduced to its metallic form in the presence of a "confinement agent" – a chemical that encourages the gold to form as a sheet just two atoms thick. Because of the gold's nanoscale dimensions, it appears green in water, and given its frond-like shape, the researchers describe it as "gold nanoseaweed". Images taken from an electron microscope reveal the way its atoms have formed into a highly organised lattice structure. Professor Stephen Evans heads the Leeds' Molecular and Nanoscale Research Group and supervised the research. He said the considerable gains that could be achieved from using ultra-thin gold sheets were down to their high surface-area-to-volume ratio: "Gold is a highly effective catalyst. Because the nanosheets are so thin, just about every gold atom plays a part in the catalysis. It means the process is highly efficient. "Our data suggests that industry could get the same effect from using a smaller amount of gold, and this has economic advantages when you are talking about a precious metal."
The flakes are also flexible, meaning they could form the basis of electronic components for bendable screens, electronic inks and transparent conducting displays. Professor Evans thinks there will inevitably be comparisons made between the 2D gold and the first 2D material ever created – graphene, which was fabricated at the University of Manchester in 2004. "The translation of any new material into working products can take a long time – and you can't force it to do everything you might like to. With graphene, people have thought that it could be good for electronics or for transparent coatings, or as carbon nanotubes that could make an elevator to take us into space because of its super strength," said Professor Evans. "I think with 2D gold, we have got some very definite ideas about where it could be used, particularly in catalytic reactions and enzymatic reactions. We know it will be more effective than existing technologies – so we have something that we believe people will be interested in developing with us."
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