Thanks to Engineers, Cleaning Up Water Pollution May be Done with Sunlight 

While having the capability to harm us humans, sunlight gives us plenty of the good stuff too, like free vitamin D, crops to eat, and oxygen from plants. But that’s not all.  

Researchers from Michigan Technological University have developed a singlet oxygen model to calculate how particular chemicals break down in surface water. Meaning, sunlight can break down chemicals in streams, lakes, and rivers. 

Most surface water around us is yellowish or brown. The color comes from leaf and bark debris that make tannins, which are polyphenols. They’re basically natural organic compounds in plants.  

This debris absorbs sunlight and creates the singlet oxygen that degrades contaminants, which the researchers explored. 

What’s singlet oxygen? 

Being an absolute commoner, I thought this meant a tiny particle of oxygen but that’s not it. It’s a reactive species of oxygen that causes photochemical transformation. 

It’s a process where light and oxidizing materials produce chemical reactions. Understanding how long it takes for a particular chemical to break down under this transformation was something that this study tried to do. 

When researchers understand how many hours or days it takes a particular contaminant to break down, it helps scientists to protect the waterways. 

Knowing a particular chemical’s half-life helps resource managers estimate whether or not that chemical is building up in the environment. 

To do so, asociate professor at Michigan Tech Daisuke Minakata developed a comprehensive reactive activity model. This model shows how singlet oxygen’s reaction mechanisms perform against a diverse group of contaminants and computes their half-life in a natural aquatic environment. 

Minakata said, “We tested 100 different organic, structurally diverse compounds. If we know the reactivity between singlet oxygen and contaminants, we can say how long it will take to degrade one specific structure of a contaminant down to half the concentration.” 

 

Red glow of singlet oxygen passing into triplet state. Photo by Nekitmm Wikimedia Commons

 

The one when the sun shines 

Now, the rate of indirect-sunlight-initiated chemical oxidation won’t be the same in each type of body of water. Every lake, river, or stream has its own unique compound of organic matter. 

And because the process does not occur in the dark, the amount of sunlight a water body receives also affects reactions. For instance, singlet oxygen plays a partial role in degrading the toxins in harmful algal blooms and in breaking down the excess nitrogen and phosphorus produced by agricultural runoff. 

“Singlet oxygen can be used for disinfection of pathogens. It can oxidize chemicals in drinking water or wastewater treatments. There are many ways to use this strong chemical oxidant for many purposes in our lives,” said Minakata. 

Aiming for byproducts after knowing the reactions 

After getting an understanding of calculations from Minakata’s model, the researchers wanted to conduct a further study. They want to know the byproducts produced by singlet oxygen/chemical reactions. 

They want to know and predict whether the byproducts themselves will be toxic. By understanding the stages of degradation, Minakata and his team can develop an expanded model to predict the formation of sun-worn byproducts and how the interactions start again. 

So this discovery is still at its very early stage. However, I think we should credit the research team nevertheless. Thanks to them, we now at least know that ensuring clean water for human use can happen by recreating what’s happening in nature. 

And of course, this research can always be the base for other, more advanced, and more practical study or findings in the future. 

If you want to read more of this study, you can find it in the journal Environmental Science and Technology. 

 

A reusable system that purifies water 

In a similar finding, Penn State researchers have discovered and developed a material that could remove persistent pollutants from water.  

The research team firstly found that in nature, the interaction of molecules at the boundary of different liquids can lead to new structures. Those molecules, which are self-building, are important to the development of all life on Earth. 

But, the scientists could engineer them to perform specific functions.  

Corresponding author Scott Medina said, “We took inspiration from biological systems to see if we can get similar phenomena to emerge with non-biological molecules,” 

Incorporating fluorine 

When they first experimented on this research, the team incorporated fluorine into an amino acid and mix it with a fluorinated oil to guide its molecular organization. Now, fluorine is not a common element in nature. 

The result was that it formed a bead comprised of the fluorine droplet surrounded by an amino acid coating. When the researchers tried to expose the bead into air, its components rearranged to form a film. 

Inside the film is a thin layer of fluorinated oil surrounded by two layers of microscopic amino acid crystalline structures. When agitated, this film could rearrange itself into the bead and take other fluorinated molecules with it. 

Medina said, “Fluorines don’t play well with others, so if you put them together there are very strong interactions. Fluorinated contaminants in water want to separate themselves from the water and find other fluorine-rich matter.” 

 

Blue fluorine. Photo by Géry PARENT Wikimedia Commons

 

After discovering this phenomenon and the compound’s capacity to switch between a film state and the bead shape, the researchers were instantly interested in concocting a possible pollutant catcher. 

There are artificial chemicals containing fluorine commonly used in manufacturing of water- or grease-repellent products. They’re called Per- and polyfluoroalkyl substances (PFAS). 

It may sound harmless, but their molecular structure allows them to accumulate in environments and the human body permanently. 

“Nature hasn’t evolved ways to break down fluorine-containing molecules efficiently, so these compounds stick around for a long time.  

“They enter wastewater and soil, make their way into drinking water and food, and we consume them—and our bodies don’t degrade them very well, either,” said Medina. 

New material film vs polluted water 

To test the new compound’s potential for PFAS capture, the researchers added contaminated water to a plastic container coated with their fluorinated amino acid film.  

The film captured PFAS substances within two hours and was able to hold them for up to 24 hours. From this stage, the researchers could agitate the film containing PFAS so that it could reform itself cohesive bead that could be easily collected from the now-purified water. 

Although the experiment result was satisfactory, the researchers wanted to explore more about the capabilities of the pollutant extraction. They wanted to investigate whether they can apply it not only for ater purification but also the potential to harvest compounds from air. 

With further research into its applications, the fluorinated compound could become a multi-use contaminant removal tool for use in a variety of settings. 

Medina said, “There’s a lot of effort being placed into investigating the toxicology of PFAS and how to regulate them. This material could be implemented to remove PFAS from drinking water—and we think it could have a lot of utility in other areas as well.” 

If you want to read more about this discovery, you can find it in journal library Advanced Functional Materials. 

 

Sources

https://www.sciencedaily.com/releases/2021/08/210811113139.htm 

https://www.sciencedaily.com/releases/2021/07/210727171639.htm 

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