Nanoparticles clean up environmental pollutants

Nanoparticles can clean up environmental pollutants

9:03 AM, 22nd July 2015
Nanoparticles can clean up environmental pollutants
The new nanoparticles have been designed to extract endocrine disruptors, pesticides, and other contaminants from water and soils. The system exploits the large surface-to-volume ratio of nanoparticles, while the photo induced precipitation ensures nanomaterials are not released in the environment.

CAMBRIDGE, US: Many human-made pollutants in the environment resist degradation through natural processes, and disrupt hormonal and other systems in mammals and other animals. Removing these toxic materials- which include pesticides and endocrine disruptors such as bisphenol A (BPA) — with existing methods is often expensive and time-consuming.

In a news paper published in Nature Communications, researchers from MIT and the Federal University of Goias in Brazil demonstrate a novel method for using nanoparticles and ultraviolet (UV) light to quickly isolate and extract a variety of contaminants from soil and water.

Ferdinand Brandl and Nicolas Bertrand, the two lead authors, are former post docs in the laboratory of Robert Langer, the David Koch Institute professor at MIT’s Koch Institute for integrative cancer research. Eliana Martins Lima, of the Federal University of Goias, is the other co-author. Both Brandl and Bertrand are trained as pharmacists, and describe their discovery as a happy accident: They initially sought to develop nanoparticles that could be used to deliver drugs to cancer cells.

“We came up with the idea to use our particles to remove toxic chemicals, pollutants, or hormones from water, because we saw that the particles aggregate once you irradiate them with UV light,” Brandl said.

The researchers synthesized polymers from polyethylene glycol, a widely used compound, approved by the US FDA as a food additive and polylactic acid, a biodegradable plastic. Nanoparticles made from these polymers have a hydrophobic core and a hydrophilic shell.

If left alone, these nanomaterials would remain suspended and dispersed evenly in water. But when exposed to UV light, the stabilizing outer shell of the particles is shed, and - now “enriched” by the pollutants - they form larger aggregates that can then be removed through filtration, sedimentation, or other methods. The researchers used the method to extract phthalates from wastewater and BPA, a synthetic compound widely used in plastic bottles, from contaminated soil.

The process is irreversible and the polymers are biodegradable, minimizing the risks of leaving behind toxic secondary products. “Once they switch to this macro situation where they’re big clumps, you won’t be able to bring them back to the nano state again,” Bertrand said.

The fundamental breakthrough, according to the researchers, was confirming that small molecules do indeed adsorb passively onto the surface of nanoparticles. “To the best of our knowledge, it is the first time that the interactions of small molecules with pre-formed nanoparticles can be directly measured,” they wrote.

Even more exciting, they say, is the wide range of potential uses, from environmental remediation to medical analysis.

And the nanoparticles’ high surface-area-to-volume ratio means that only a small amount is needed to remove a relatively large quantity of pollutants. The technique could thus offer potential for the cost-effective cleanup of contaminated water and soil on a wider scale.

This approach could possibly be further developed, he speculates, to replace the widespread use of organic solvents for everything from decaffeinating coffee to making paint thinners. “And for analytical applications where you don’t need as much volume to purify or concentrate, this might be interesting,” Bertrand said, offering the example of a cheap testing kit for urine analysis of medical patients.

The study also suggests the broader potential for adapting nanoscale drug-delivery techniques developed for use in environmental remediation.

© Massachusetts Institute of Technology News

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