Novel method to treat polluted water

Novel method to treat polluted water

Own Correspondent


TWO National University of Lesotho (NUL) professors, Himanshu Narayan from the Department of Physics and Electronics and Haile Michael Alemu from the Department of Chemistry and Chemical Technology are advancing a very high-tech method to treat polluted water.

They use the freest source of energy, sunlight, to treat water polluted with dye like that produced by Thetsane textile factories.

“Essentially our final intent in this research area is to develop a continuous process in which we input totally polluted water to a system, and get 100 percent clean, reusable water at the output, in a matter of minutes,” Professor Narayan says.

A very enthusiastic professor, Narayan, adds: “Our aim is not just to develop this process of waste water treatment, but we also want to make sure that the costs involved are low and affordable.”

How is this possible?

“Well, with a little effort and meticulous planning, one can cut-off, for example, the requirement of expensive ultraviolet energy and use the freely available sunlight instead,” Narayan said.

“Moreover, one can use catalysts which are known for their ability to regenerate themselves after every use, greatly cutting costs. That is what our research is all about.”

First, the professors started with very small materials; in fact nanomaterials!

How small? Take the thickness of your hair. A nanomaterial is about 1000 times smaller than that thickness. They produce such materials through chemical reactions.

You will surely be perplexed by the names of materials they use to achieve their results. These include, Titanium Oxide, Yttrium Oxide, and Erbium oxide.

Now, hold your breath as we enter deep into the territory where physics and chemistry comfortably meet and merge in solidarity.

In the meantime, don’t go away as Professor Narayan loosens, and lays bare, the mysteries of the universe right before your own eyes.

Prof Narayan narrated this thought-provoking process slowly, as if he didn’t want even a single word to be missed: “We normally start with our favourite material, Titanium Oxide (or titania), as a semiconductor. Since it is a semi-conductor, its electrons sort of jump as they receive energy from outside in the form of light, and this is the key to the destruction of the dye.”

“In the beginning, we thought there was a problem with this semi-conductor, titania.”

The problem was that titania does not absorb visible light (from sunlight).

“So we mixed titania with zinc ferrite,” he says, adding: “Our understanding was that zinc ferrite would help with the provision of energy since it is able to absorb sunlight which will, in turn, set electrons free in titania. The process worked. However, as we were later to prove beyond any doubt, it was not for the reasons we first proposed.”

Further investigations revealed that whatever the impact of zinc ferrite in sunlight absorption was, it was not as important as the fact that the dye (Congo Red) being degraded was itself the one absorbing the light and transferring it to titania, which in turn, thanks the dye by blistering it with a swarm of electrons, thus destroying it.

The results were such that where only 85 percent of the dye was degraded with pure Titania, a combination of both Titania and zinc ferrite was able to degrade up to 90 percent of the dye, which was a slight improvement.

To further prove the theory that maybe it was the dye, rather than zinc ferrite doing the magic here, they mixed titania with another material, Yttrium Oxide.

Nano-sized materials with this combination were synthesized for the very first time, in the labs of NUL. This material, Yttrium Oxide, is far worse than Titania itself in terms of absorbing sunlight. Thus it would not absorb any energy from visible light, and thus, there would be no dye degradation.

“But now the degradation was even better – close to 95 percent. We were stunned,” he says.

Why would a material, not only worse than zinc ferrite but also far worse than Titania itself perform better than zinc ferrite?

They were about to discover an interesting phenomenon. The behaviour did not only prove that it was the dye itself absorbing most of the sunlight. It also proved that Yttrium Oxide was enhancing, rather than inhibiting the process.

But why, any scientist would ask?

When light is absorbed on the semiconductors, it “excites” the electrons which move away from the materials, and with their energy, break down the dye into water, carbon dioxide and some salts, depending on the nature of the dye.

However, negatively charged electrons leave positively charged vacant spaces (called holes) behind, which, due to their own energy, further break the dye.

However, the negatively charged electrons can come back, especially when the particle-size is small as in this case, to the positively charged holes and get neutralised in a process called recombination, thereby significantly plummeting the very process they were meant to start.

But, and here is the key, the presence of Yttrium Oxide supply Yttrium ions with three positive charges per ion. These many positive charges attract negative electrons, preventing them from filling the “holes,” thus leaving the “holes” to continue degrading the dye.

In the end, this one will blow your mind. When they used Neodymium oxide and Erbium Oxide to replace Yttrium Oxide, they got 100 percent and 99 percent dye degradation respectively.

The research is still on.

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