Serendipity and 2D nanomaterials: Rediscovering the Synthesis Protocols

With external dimensions or internal structure in the range from 1 nm to 100 nm, nanomaterials are a hot topic of research in the present times. This research domain involves a material-science approach to the field of nanotechnology. Nanomaterials are slowly becoming popular in the commercial market, with applications in manufacturing processes, products, healthcare (biosensing, bioimaging, tumor diagnosis, etc.), paints, insulation, filters, and lubricant additives, in a long list of many others.

Researchers at IIT Gandhinagar have stumbled upon an unexpected discovery that will potentially have significant implications on the existing experimental methodologies utilized to synthesize two dimensional (2D) nanomaterials.

Generally, the conventional protocols require scientists to take a layered parent material in an organic solvent and expose it to very high energy sound waves (ultrasonication) for a specific amount of time. As a result, these sound waves create a lot of shear forces and lead to the formation of 2D nanosheets. These nanosheets are revolutionizing several everyday technologies. For example, graphene (nanosheet layer) from graphite (parent material) finds its use in batteries and the preparation of ultra-strong materials.

During this process of nanosheet synthesis, the common understanding was that these bursts of ultrasonic energy do not affect the organic solvent — meaning it remains stable throughout the entire experimentation.

Dr. Kabeer Jasuja, a professor in Chemical Engineering at the Indian Institute of Technology Gandhinagar, along with his research team, observed an unusual phenomenon where the organic solvent itself was transforming into quantum dots! In simple terms, quantum dots are extremely tiny fluorescent nanostructures, just 2 nm in diameter, which is the same as the diameter of a DNA molecule.

“Earlier, we could not accept the outcome and thought that these quantum dots could be the result of possible contaminations. However, on conducting various experiments in controlled environments and carefully designed setups, we concluded that the organic solvent is indeed converting into carbon quantum dots,” said Dr. Jasuja.

The group is trying to synthesize nanosheets, which are like graphene but made from boron. The reason for picking boron is its notorious chemistry. Several theoretical chemists have predicted its existence in planar forms, but there is no experimental proof till now.

“Since we were using metal diborides, rather than having carbon planes, we had boron planes. Our expectation after the experiment was to obtain boron nanosheets. However, results showed that we also had a nanomaterial similar to graphene, but it was much smaller in its lateral dimensions. We found the presence of this entity in the negative control experiments (with organic solvent only) as well. So, in addition to boron, we also obtained lots of carbon. After reconfirming the outcomes, we arrived at this unique finding. As most of the scientific community works on carbon, this perspective was hidden until now since there was no way to differentiate between the two sources of carbon, viz., parent material and organic solvent,” Dr. Jasuja explained.

On shining laser light through the solvent (negative control) after the experiment, Saroj Kumar Das (a Ph.D. scholar in Dr. Jasuja’s lab) observed the Tyndall Effect. He found that the dispersion exhibited a color different from that of the laser he was shining. Also, when he changed the wavelength of the laser, it displayed other beautiful fluorescent colors. This effect (scattering of light) happens due to the presence of particles in the solvent, which are quantum dots in this case.

To summarize, during the synthesis of 2D nanosheets, two processes are happening simultaneously — first, the parent material is exfoliating, and second, the organic solvent is itself transforming into quantum dots.

The last 40 years saw the discovery of several new nanomaterials, and it is during the previous decade that many of them started getting incorporated into technologies that we use in our day-to-day lives. Among these nanomaterials, the new family of quantum dots is seeking attention worldwide. These are the tiniest nanomaterials imaginable! The very fact that it is possible to work with the matter at such a small scale helps develop new outlooks. Dr. Jasuja’s lab is working with a viewpoint to make these nanomaterials and quantum dots more and more accessible to people in the future.