31 Jul 2015
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 new paper published this week in Nature Communications, researchers from MIT and the Federal University of Goiás 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 postdocs in the laboratory of Robert Langer, the David H. Koch Institute Professor at MIT’s Koch Institute for Integrative Cancer Research. (Eliana Martins Lima, of the Federal University of Goiás, 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.
Image: Nicolas Bertrand
Brandl had previously synthesized polymers that could be cleaved apart by exposure to UV light. But he and Bertrand came to question their suitability for drug delivery, since UV light can be damaging to tissue and cells, and doesn’t penetrate through the skin. When they learned that UV light was used to disinfect water in certain treatment plants, they began to ask a different question.
“We thought if they are already using UV light, maybe they could use our particles as well,” Brandl says. “Then 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.”
A trap for ‘water-fearing’ pollution
The researchers synthesized polymers from polyethylene glycol, a widely used compound found in laxatives, toothpaste, and eye drops and approved by the Food and Drug Administration as a food additive, and polylactic acid, a biodegradable plastic used in compostable cups and glassware.
Nanoparticles made from these polymers have a hydrophobic core and a hydrophilic shell. Due to molecular-scale forces, in a solution hydrophobic pollutant molecules move toward the hydrophobic nanoparticles, and adsorb onto their surface, where they effectively become “trapped.” This same phenomenon is at work when spaghetti sauce stains the surface of plastic containers, turning them red: In that case, both the plastic and the oil-based sauce are hydrophobic and interact together.
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, hormone-disrupting chemicals used to soften plastics, from wastewater; BPA, another endocrine-disrupting synthetic compound widely used in plastic bottles and other resinous consumer goods, from thermal printing paper samples; and polycyclic aromatic hydrocarbons, carcinogenic compounds formed from incomplete combustion of fuels, from contaminated soil.
The process is irreversible and the polymers are biodegradable, minimizing the risks of leaving toxic secondary products to persist in, say, a body of water. “Once they switch to this macro situation where they’re big clumps,” Bertrand says, “you won’t be able to bring them back to the nano state again.”
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 write in Nature Communications.
Even more exciting, they say, is the wide range of potential uses, from environmental remediation to medical analysis.
The polymers are synthesized at room temperature, and don’t need to be specially prepared to target specific compounds; they are broadly applicable to all kinds of hydrophobic chemicals and molecules.
“The interactions we exploit to remove the pollutants are non-specific,” Brandl says. “We can remove hormones, BPA, and pesticides that are all present in the same sample, and we can do this in one step.”
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.
“From the applied perspective, we showed in a system that the adsorption of small molecules on the surface of the nanoparticles can be used for extraction of any kind,” Bertrand says. “It opens the door for many other applications down the line.”
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. Bertrand cites DDT, banned for use as a pesticide in the U.S. since 1972 but still widely used in other parts of the world, as another example of a persistent pollutant that could potentially be remediated using these nanomaterials. “And for analytical applications where you don’t need as much volume to purify or concentrate, this might be interesting,” Bertrand says, 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.
“That we can apply some of the highly sophisticated, high-precision tools developed for the pharmaceutical industry, and now look at the use of these technologies in broader terms, is phenomenal,” says Frank Gu, an assistant professor of chemical engineering at the University of Waterloo in Canada, and an expert in nanoengineering for health care and medical applications.
“When you think about field deployment, that’s far down the road, but this paper offers a really exciting opportunity to crack a problem that is persistently present,” says Gu, who was not involved in the research. “If you take the normal conventional civil engineering or chemical engineering approach to treating it, it just won’t touch it. That’s where the most exciting part is.”
05 May 2015
California homes, farms and businesses depend on water that flows from the Sierra Nevada Mountains through the state’s main water distribution system to regions across the state, including the Bay Area, Central Valley, Central Coast and Southern California. But key portions of the system are outdated and crumbling, putting the security and reliability of our local water supplies at risk. Experts warn that the system could collapse in an earthquake, and is susceptible to salt water intrusion during major droughts or natural disasters.
The plan to fix California’s water system, known as the California Water Fix, will address the severe vulnerability in our water infrastructure and secure local water supplies. Outdated, dirt levees would be replaced with a modern water pipeline built to withstand Earthquakes and other natural disasters. Natural water flows would be restored to support the surrounding environs. The plan is critical for many California communities and our state’s economy. Learn more by scrolling down, and join our broad coalition.
Read About the Plan Here:
30 Apr 2015
Abstract: Adam Alonzi
The approaching water crisis will be solved by devices made possible by nanotechnology.
Since its conception concerns have been raised about nanotechnology’s potentially deleterious impact on the environment, but at this point it looks as though it will do more good than harm. From water remediation to solar cells to pollutant monitoring, nanotechnology, as I wrote in a recent blog entry, presents humanity with a “bevy of Black Swans.” The world’s fresh water supply is dwindling. Nanotech devices can empower governments and individuals around the world to use otherwise untapped sources through desalination and reclamation.
Zhang calls the scale of groundwater pollution “enormous” and the complexity “seemingly intractable.” Of the hundreds of thousands of sites in the United States identified by environmental agencies over the last three decades less than one third have been restored. Old mining areas, factories, landfills and dumping grounds continue to increase. As well as obvious undesirables like pathogens and heavy metals, more modern toxins, like endocrine disruptors and pharmaceuticals, must also be removed. While infrastructure improvements are necessary and inevitable in many places, nanotech research will accelerate, and be expedited by, the decentralization of water treatment.
Nanofiltration involves using membranes with tiny pores (1-10 NM across) to remove specific molecules from a solution. Among other applications they are used to separate whey from the other constituents of milk and antibiotics from salty waste products. The major advantage they have over their competitors is the amount of pressure needed to pass liquid through them. Carbon nanotube membranes can remove an assortment of contaminants and aluminum based nanostructures are good at dismantling negatively charged baddies like viruses and bacteria, as well as some organic and inorganic compounds. Biomagnetite removes chlorinated organic molecules, silver slays bacteria and titanium dioxide, which is already used in a variety of consumer and industrial products, can break down organic compounds.
Dr. Sujoy Das assembled a silica-silver nanocomposite via biosynthesis. In other words, its production is cheap and green. The proteins covering the nanoparticles prevent them from leaching into the water. They also function as both reducing and protective agents for the silver nanoparticles. The nanocomposite removes dyes and microorganisms quickly. Moreover, the material can be reused several times.The LifeSaver bottle, invented shortly after hurricane Katrina, removes objects larger than 15 nanometers and works well for up to 1,500 gallons. It does not take out salt or some metals, however. This is unfortunate as in many regions the ocean is the only option.
Yet desalination is costly. It requires approximately 12 times the electricity needed to prepare fresh water for consumption. There is also the large initial investment of 200 million dollars or more to build a plant. Although for a glass of water 3 kilowatt hours is not bad at all, desalination is unfeasible on a large scale. Perforene, a graphene nanomembrane developed by Lockheed-Martin, was originally touted as being 100 times more efficient than other methods, but this estimate was later lowered to 20%. Thus, the enthusiasm was massively excessive and woefully premature. Yet this should not discourage. Every boom, or potential boom industry, has its share of exaggerated but stock boosting announcements, and does not mitigate the promise held by the technology in question.
Graphene, a hydrophobic material almost synonymous with nanotech, creates ultrafine capillaries through which water can pass. The pores can be extremely selective and the water can pass through them as easily as through a coffee filter, thus eliminating the need for energy-intensive high pressure systems. However, as Dr. Cohen cautions, a membrane that is five hundred times more permeable than its predecessor will not translate into proportional savings. Dr. Nair, one of the researchers working with this material says it “is as fast and as precise as one could possibly hope for such narrow capillaries. Now we want to control the graphene mesh size and reduce it below nine Angstroms to filter out even the smallest salts like in seawater. Our work shows that it is possible.”
Baines, Lawrence. “The Fight for Water.” Project-Based Writing in Science. SensePublishers, 2014. 81-89.
Cohen-Tanugi, David, and Jeffrey C. Grossman. “Water desalination across nanoporous graphene.” Nano letters 12.7 (2012): 3602-3608.
Inderscience Publishers. “Nanotechnology for water purification.” ScienceDaily. ScienceDaily, 28 July 2010. .
R. K. Joshi, P. Carbone, F. C. Wang, V. G. Kravets, Y. Su, I. V. Grigorieva, H. A. Wu, A. K. “Precise and Ultrafast Molecular Sieving through Graphene Oxide Membranes” Geim and R. R. Nair, Science, 2014.
Qu, Xiaolei, Pedro JJ Alvarez, and Qilin Li. “Applications of nanotechnology in water and wastewater treatment.” water research 47.12 (2013): 3931-3946.