Very insightfully was it stated, in the early stages of my interview with IIT Ropar PhD doctoral student and metallurgical engineer, Sagarika Bhattacharjee, that science is about more than finding solutions to difficult-looking problems on paper - it’s about our world, us people, and the phenomena that affect either and all. And this provides an easy segue to Ms. Bhattacharjee’s master thesis on Degradation of Dyes using Photocatalytic Materials to lower water pollution due to industrial influents.

Having gotten her Masters of Technology degree at SRM University, Tamil Nadu, Ms. Bhattacharjee had firsthand witnessed the issue of excessively polluted waters due to huge amounts of factory waste being dumped directly into the water bodies. “There’s a lot of dyeing mills and tie-and-dye factories.” She says, when talking about how she’d come up with her project in the first place. “As much as you’d expect, of course, from the Land of the famous Kanjivaram.” What was to be regretted however was the state that it had left the coastal waters in, with non-degradable dyes and other waste contaminating the bay more and more as the years went by. The greatest problem, in her opinion, had been that these dyes can never be broken down in sunlight like other biodegradable, relatively harmless waste in the waters, and thus, they stagnate and pile up and progressively make the situation worse. And therefore, the solution had to be to figure out a way that made it possible for these dyes to degrade naturally, and preferably, by a mechanism completely autonomous and recurring. So this is exactly what Ms. Bhattacharjee did, by synthesizing a ZnO/Au/g-C3N4 Nanocomposite Multi-junction, for efficient photo-catalytic application.

Photocatalysis is a series of chemical reactions usually induced by electromagnetic irradiation. Essentially, sunlight falling on certain materials can cause excitation of atoms, which results in radicals that affect the surroundings. And what Ms. Bhattacharjee aimed to find was a way to ensure this process happens cyclically, that is, the electrons fall back to their ground state only to jump back up upon receiving more energy in the form of light, resulting in a loop of photocatalysis and simultaneous degradation of the material owing to the generated energy. This was made possible by her using a nanocomposite of zinc oxide, gold, and graphitic C3N4. Heterogeneous photocatalysis on metal oxide semiconductors has proven to be effective in degrading organic pollutants for some time now. At the same time, a promising candidate was found in g-C3N4 which possessed a band gap fairly similar to that of ZnO. Au, in contrast, is brought in for its fairly small band gap, which enables it to be used in the middle of the two to keep the process looped.

What actually happens is that electrons from the valence bands of ZnO and in g-C3N4 jump to their respective conduction bands on being exposed to sunlight. This results in the creation of holes in the valence bands - which is simultaneously responsible for minor side processes like photooxidation. Moreover, the electrons in the conduction band of g-C3N4 tend to fall into the conduction band of ZnO because it is at lower energy and electrons have a tendency to seek stability. This results in an excess of electrons in the conduction band of ZnO which is responsible for formation of O-radicals from oxygen gas in the atmosphere, which eventually leads to the degradation of required materials. Subsequently, the excited electrons also fall back to their ground state (and some pass through Au’s VB-CB system to fall into g-C3N4’s valence band as well, and this leads to generation of some energy which reincites the entire process. Thus, degradation of dyes is achieved using photocatalysis of a nanocomposite of ZnO/Au/g-C3N4.

The determination of these concepts and elements is the interesting part, in Ms. Bhattacharjee’s opinion. The real hardship, and ironically, real scientistic labor lies in the characterization of them. This involves the synthesis of the nanocomposite, which is requisite for the verification of hypotheses in the first place, and then the various kinds of testing to ensure validity of what was synthesized. There’s dozens of processes to mix and match for the creation of any nanocomposite, ranging from centrifugation and magnetic stirring to bath sonication and calcination - definitely not necessarily in that order. Moreover, there’s several tests, such as X-Ray Diffraction (XRD), scanning electron microscopy, and optical absorbance spectroscopy. If you thought studying atoms in sixth grade was hard, because you couldn’t see them and that seemed to be it back then, then you’re in for a surprise! When it comes to nanoparticles, not even most microscopes do a good enough job of seeing these. Plus, she goes on to elaborate, one of the biggest problems with nanoscience, brilliant as it is, is that in spite of all the theorizing, there’s a considerable lag in the practical aspect of things, and not enough reliable data, causing scientists to have to perform these tests repeatedly till the exactly desirable result is achieved. And sometimes these processes accidentally end up causing coagulation and turning them into macroparticles; and one must start all over again. However, despite this being the biggest roadblock on her path, Ms. Bhattacharjee looks back at the memory of it fondly, for it all played a part in leading her to her final success, and the fruits of her labor and knowledge that she’s been able to do her bit for the environment because of it, makes all of the journey worth it.

In the concluding phase of our interview, we talked about the future of her project. She mentioned how photocatalysis can play a part in several other schemes as well, such as O2 reduction, hydrogen production and fuel cells. It could also be used to create food safety devices because it prevents antibacterial activity. A comparative study of the photocatalytic activity of ZnO, ZnO/g-C3N4 and ZnO/Au/g-C3N4 was also on the books for her, but there was both a time and resources constraint due to the COVID-19 pandemic. In fact, her project and masters’ degree were both completed through online medium in mid-2020, and the subtle incompleteness stays with her as a reminder of it.

However, her work was most extraordinary despite the circumstances, and provides a new outlook of addressing environmental crises entirely. Once again reiterating her thoughts on the true impact of science, she emphasizes how it’s about picking the right problems, choosing the best route of many to the same goal, and keeping it both simple and replicable. All her projects have been similar in this manner - they have been centered around environmental or societal issues. Her belief that science and technology exists as a way to help each other and the planet, and that our responsibility as students of it must be to do the same rather than collect degrees or chase after accolades, is perfectly reflected in one of her ending quotes, “Perhaps I’m an engineer first, and a scientist second.” She aspires to continue to contribute in preventing environmental crises and leaving a positive impact in meaningful and innovative ways.

Accumulation of dyes at shores — water pollution at its worst.
Mechanism of photocatalysis as described
How photocatalysis works generally