Russian scientists clean nanodiamonds with table salt and heat — no acid needed

Researchers from the Baikov Institute of Metallurgy and Materials Science and the Lebedev Physical Institute of the Russian Academy of Sciences have developed a method to clean nanodiamonds using ordinary table salt (NaCl). The study was published in the journal Diamond and Related Materials.

Synthetic nanodiamonds, after production, are typically covered with a layer of graphite and other impurities. Removing this layer is essential for their use, but traditional chemical cleaning with strong acids and oxidizers can damage the diamond core or alter the composition and geometry of its surface.

The new technique, named NOSAP (Non-Oxidative Salt-Assisted Purification), avoids these issues. The process begins by mixing nanodiamond particles with a sodium chloride solution. The mixture is then freeze-dried. Next, the dried material is heated to 500°C. During heating, sodium and chlorine ions penetrate between the layers of the graphite shell. After cooling, the salt is dissolved in water, and the graphite shell separates along with it. Instead of fine soot, the researchers obtain large flakes measuring 250–500 micrometers.

A key finding of the experiment is the absence of significant oxidative destruction of the shell. The method removes graphite without oxidizing carbon or damaging the crystals. This approach could offer a more efficient and environmentally friendly alternative for industrial nanodiamond purification, preserving the integrity of the diamond surface.