Researchers from Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bengaluru, have developed a new type of gold in the form of very small crystals — microcystallites. The microcrystal gold has been found to be nobler than gold — it do not dissolve in mercury and Aqua regia (a mixture of nitric acid and hydrochloric acid), and showed the least interaction with copper.
The microcystallites were synthesised by decomposing an organic complex containing gold and other ions under controlled conditions. The newly formed microcystallites, about 3 micrometre in length were found to be of a different crystal structure. Normal gold has a (face-centered) cubic structure, while the new ones exhibit deformed cubic structure — tetragonal and orthorhombic cells.
Copper growth
The researchers then examined copper growth on these gold crystals when subjected to plating without the use of electrodes. Electron microscopy images revealed that thick copper got deposited on normal gold within minutes, while no detectable copper was seen on the central portion of the new crystals even after an hour. “We found deposition of copper only on the tips of the new crystallites while the rest of the crystal surface was devoid of copper. This may be due to the different arrangement of the new facets,” explains Chaitali Sow, Ph.D student at JNCASR and one of the authors of the paper published recently in Angewandte Chemie.
The researchers then investigated the stability of the gold microcystallites using corrosive agents like mercury and Aqua regia. While normal gold disappeared in a matter of minutes when immersed in mercury and also in aqua regia, the gold crystallites remained intact. Microscopy imaging showed that the surface was undamaged.
“All these properties make our new crystallites an ideal candidate for catalytic purposes. Gold in itself is not a catalyst but the new gold microcystallites have very active surfaces. Compared with other catalysts like palladium and ruthenium, gold is cheaper and it can also be easily recovered,” explains Prof. Giridhar U. Kulkarni, Director at the Centre for Nano and Soft Matter Sciences (CeNS), Bengaluru and corresponding author of the paper. “Though the production cost of the crystallites is a little high, we are optimising it to bring down the cost. More studies are needed to understand them fully in the context wide range of applications in the offing,” he added.
