"Smart rust" purifies water instead of polluting it

A new study suggests that pouring rust into water may not be as counterintuitive as it sounds. A team of researchers has come up with a unique type of iron oxide nanoparticles – called “smart rust” – that surprisingly purifies water instead of contaminating it.

Typically, adding rust to water would make it undrinkable. However, this new “smart rust” has the innate ability to attract a plethora of pollutants such as oil, nano and microplastics, and the herbicide glyphosate. 

Magnetic nanoparticles 

What’s even more interesting is how these pollutants are removed from the water. The magnetic nature of the nanoparticles ensures easy extraction using a mere magnet.

Recently, the scientists announced that they have further refined the particles to trap potentially harmful estrogen hormones, which are known to adversely affect aquatic life.

The groundbreaking research was recently presented at the fall meeting of the American Chemical Society (ACS) 2023.

Dramatically improving water treatment 

“Our ‘smart rust’ is cheap, nontoxic, and recyclable,” said Dr. Marcus Halik, the study’s principal investigator. “And we have demonstrated its use for all kinds of contaminants, showing the potential for this technique to improve water treatment dramatically.”

For years, Dr. Halik’s team at Friedrich-Alexander-Universität Erlangen-Nürnberg has been on a mission to find eco-friendly ways to purify water. 

Focus of the study

The core component of their research revolves around superparamagnetic iron oxide nanoparticles. These particles are unique due to their magnetic pull, attracting them to magnets without causing them to stick to one another.

Taking the research a step further, the scientists developed a technique to bind phosphonic acid molecules to these nanoparticles. 

Promising results 

“After we add a layer of the molecules to the iron oxide cores, they look like hairs sticking out of these particles’ surfaces,” said Dr. Halik. By manipulating the binding of the phosphonic acids, the team found they could alter the nanoparticles’ surfaces, enabling them to effectively absorb varied pollutants.

In their early experiments, the smart rust showed promising results in purifying water collected from the Mediterranean Sea of crude oil and pond water of glyphosate. In addition, the nanoparticles effectively removed nano and microplastics from various water samples.

Trace contaminants 

Lukas Müller, a graduate student on the team, took on the challenge to see if the nanoparticles could be altered further to draw in trace contaminants, specifically hormones. When these hormones, natural and synthetic estrogens, are disposed of, they seep into our waterways, causing potential harm to both plant and animal life.

Müller focused on the estrogen estradiol, and its four structurally similar derivatives. By coating the nanoparticles with two distinct compounds – one long and the other positively charged – he believed they could create countless “pockets” to effectively trap the estrogen. 

To verify their hypothesis, Müller has relied on sophisticated instruments, and while early results are promising, further experiments are in the pipeline.

Future research

Looking ahead, the research team plans to evaluate the efficiency of these nanoparticles on real-world water samples. They are optimistic that the high surface area of each nanoparticle, rich with trapping pockets, will offer multiple usages, making the purification process more cost-effective. 

“By repeatedly recycling these particles, the material impact from this water treatment method could become very small,” said Dr. Halik.

More about water purification 

Water purification is an essential process that ensures the availability of clean and safe drinking water for humans and animals. With rising concerns over water scarcity and the increasing contamination of available water sources, advancements in water purification techniques are becoming ever more vital.

Traditional methods

Boiling

One of the oldest methods, boiling kills many pathogens. However, it doesn’t remove chemical pollutants.

Solar disinfection (SODIS)

Placing water in transparent bottles and exposing them to sunlight for several hours can kill pathogens. This method harnesses UV radiation from the sun.

Filtration

Activated carbon filters

They are used to remove larger particles like sediment and silt from water. These filters also remove bad tastes and odors from the water.

Reverse osmosis

This involves forcing water through a semi-permeable membrane, which filters out contaminants and impurities.

Distillation

This process involves boiling water and then condensing the vapor back into liquid in a separate container, leaving many contaminants behind.

Chemical methods

Chlorination

Chlorine is added to water to kill bacteria and other pathogens. This is a common method used in municipal water treatment.

Iodine and chlorine dioxide

These are chemical tablets or drops that can purify water, often used by travelers and in emergency situations.

Modern innovations

Ultraviolet (UV) purification

UV light can destroy various bacteria and viruses. It’s a chemical-free method of purification.

Nanotechnology

This includes methods like the “smart rust” mentioned previously, using nanoparticles to trap and remove contaminants from water.

Biosand filters

A point-of-use decentralized water treatment system, it uses layers of sand, gravel, and sometimes crushed brick. The biofilm developed on the sand’s surface is the active layer that traps pathogens.

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