Purifying water with pencils - making catalysis simple

Researchers are looking at ways to make water purification simple by developing pencils that can draw cleansing catalysts on any surface – and can be transported to where they are needed safely, cheaply and easily.

Dr Peter Sherrell and his team of chemical engineers from the University of Melbourne’s Faculty of Engineering and Information Technology are using advanced 2D crystal technology to develop a pencil with special lead that can treat contaminated water.

With global water scarcity expected to worsen over the coming decades, diseases linked to poor water sanitation are likely to become more prominent. Contaminated water can lead to acute illnesses such as diarrhea (often linked to organic contaminants and bacteria) and serious long-term diseases, which
can be caused by heavy metals accumulating in the body.

With $40,000 initial funding from the philanthropic CASS Foundation, the team is working to develop an effective way to fabricate, store and transport the water cleaning catalysts, and develop proof of concept to take the research to the next stage.

Catalysts increase the rate of a chemical reaction without undergoing any permanent chemical change themselves. Almost everything in your daily life depends on catalysts, from vinegar, to detergent, to beer.

Building on new research that shows certain catalysts, minerals and materials can break down pollutants and kill bacteria essentially turning contaminated water into safe, drinkable water without the need for sophisticated devices the researchers are tapping the potential of 2D crystals to achieve a practical solution.

“2D crystals are the Lego of the nanoscale, each with a different chemical and electronic property. But what makes these crystals so powerful is their ability to be stuck together – or pulled apart – to build something different,” Dr Sherrell says.

“What’s more, when 2D crystals are stacked together, they create something with completely different catalytic properties. For example, imagine if you stacked a green and a black 2D crystal together, you would get something that is blue or orange instead of something green and black. And
with over 2000 different known crystals, you can create catalysts for nearly every catalytic reaction.”

Dr Sherrell and his team have developed a pencil with special lead made from 2D crystals. Although ordinary pencil lead is made from graphite – a common type of 2D crystal – pencil lead can also be made from other 2D crystals. The process is tricky, but it can offer a multitude of benefits.

“Packaging the crystal in pencil form solves the big challenge of storage and transportation,” Dr Sherrell says.

“If the crystals are stored in a liquid, like a solvent, they would take up a lot more space, while being susceptible to photocatalysts like sunlight, which could damage the crystal. Pencils are easy to transport safely, and easy for people to use. For handling, the plastic casing is durable like
a pen.”

If successful, the pencils could prove to be an efficient solution to drinking water contamination. A bottle of contaminated water could be purified simply by drawing a centimetre square on a piece of paper and dropping it into a contaminated bottle of water, for instance.

“It should be possible to create a box of pencils that could purify drinking water by removing heavy metals, breaking down organic pollutants from agriculture or industrial run off, and killing bacteria. Simply drawing lines from different pencils on top of each other would create a brand-new
catalyst for a different reaction,” Dr Sherrell said.

“Users would be shipped out a testing kit containing a combination of different catalyst pencils that let them determine what contaminants are in their water, and then, based on that result, receive instructions on which combination of pencil catalysts will remediate the pollutants.”

In countries such as Pakistan or India where there is considerable heavy metal contamination in drinking water, or other countries where there are organic pollutants in drinking water, these pencils could one day save lives.

“Our aspiration is to demonstrate the ability to create pencils with multiple 2D crystal chemistries and ‘colour’ the same surface with two different catalysts to target specific pollutants, bacteria, or chemical reactions really simply,” Dr Sherrell says.

Read more:

Purifying water with a simple powder (Pursuit, Sept 2021).

First published on 1 June 2022.

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