“Smart rust” pulls pollutants out of the water

Illustration of the scavenging of estrogen molecules by an iron oxide nanoparticle with a “hairy” coating. © dr Dustin Vivod and Prof. Dr. Dirk Zahn, Computer Chemistry Center (CCC), Friedrich-Alexander-University Erlangen-Nuremberg

Environment

A versatile possibility for water treatment is emerging: German researchers have developed ingeniously coated iron oxide nanoparticles that can now also bind estrogen hormones in addition to crude oil, glyphosate and microplastics. The scientists report that the "smart grate" and its catch can then be removed from the water by magnetic force.

As is well known, humans threaten the water quality and thus the aquatic organisms in a variety of ways: various pollutants are constantly entering the water bodies via municipal sewage and agriculture, or they can be released in large quantities as a result of accidents. A team of researchers from the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) has been working for some time on the development of a sophisticated technology to free water from the contamination.

The scientists used a substance that is not very popular in metal objects as the basic material: iron oxide – also known as rust. However, they use this material in a special way. They are nanoparticles with supermagnetic properties. This means the tiny beads are attracted to magnets but not to each other, so they don't clump together. In order to turn them into cleaning units, the researchers have developed a method to equip the iron oxide nanoparticles with certain molecules on the surface that can act as tentacles.

Used attraction twice

"After we have applied a layer of the molecules to the iron oxide cores, they look like hairs protruding from the surface of these particles," says team leader Marcus Halik from FAU. The scientists explain that various compounds can then dock onto these structures, which can have an attraction for certain substances. Attraction also plays a decisive role in the concept a second time: Since the nanoparticles are magnetic, they can be removed from the water by magnets together with the collected pollutants and then cleaned.

So far, the team has already developed versions of the smart grate that can remove crude oil and the crop protection agent glyphosate from water. Special adjustments to the system also made it possible to remove nano- and microplastics from the water using the power of the iron nanoparticles. With their latest development, the researchers are now illustrating the all-round potential of their concept: Even problematic trace impurities can be removed from water, they reported at the 2023 fall conference of the American Chemical Society in San Francisco. Specifically, they demonstrated this potential in the case of estrogen hormones. In natural or synthetic form, these substances enter bodies of water via waste water and have so far been difficult to remove. Studies show that even in very low concentrations, these hormone substances can have problematic effects on many organisms.

captured estrogen substances

As the scientists report, they were able to use a special coating to design the iron oxide particles in such a way that estrogens adhere to them. As they explain, this is based on two different molecules: Short positively charged ones interacting with the slightly negative charges of the estrogen hormones. Longer molecules, on the other hand, capture their "bodies". "I started with the most common estrogen, estradiol, and then examined four other derivatives with similar molecular structures," reports team member Lukas Müller from FAU.

Preliminary results already confirm efficient extraction of the hormones from laboratory samples, the researchers report. Modeling suggests that its efficiency is based on the formation of many tiny pockets from the combined action of the two molecules, which strongly bind estrogen. However, this effect must first be confirmed by further analyses. "We are trying to use different pieces of the puzzle to understand how the molecules actually arrange themselves on the surface of the nanoparticles," says Müller.

In the future, the team will now test the concept further and also determine how often the particles can be reused. Because they likely have high binding capacity, the researchers say they should be able to remove estrogens over multiple uses, thus reducing the cost per purification. A new and practicable way of treating water is therefore becoming more and more apparent. "By repeatedly recycling these particles, the material impact of this water treatment method could become very small," concludes Halik.

Source: American Chemical SocietyAlexander University Erlangen-Nuremberg

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