High tech metal nanoparticles may inadvertently take a toll on aquatic life

Interactions between fertilizers, animal waste and tiny substances called nanoparticles in farm runoff could intensify harmful algal blooms in wetlands, says a Duke-led study. Photo by Nara Souza, Florida Fish and Wildlife Commission

NANOMATERIALS COULD MEAN MORE ALGAE OUTBREAKS FOR WETLANDS, WATERWAYS

The last 10 years have seen a surge in the use of tiny substances called nanomaterials in agrochemicals like pesticides and fungicides. The idea is to provide more disease protection and better yields for crops, while decreasing the amount of toxins sprayed on agricultural fields.

But when combined with nutrient runoff from fertilized cropland and manure-filled pastures, these “nanopesticides” could also mean more toxic algae outbreaks for nearby streams, lakes and wetlands, a new study finds.

The results appear June 25 in the journal Ecological Applications.

Too small to see with all but the most powerful microscopes, engineered nanomaterials are substances manufactured to be less than 100 nanometers in diameter, many times smaller than a hair’s breadth.

Their nano-scale gives them different chemical and physical properties from their bulk counterparts, including more surface area for reactions and interactions.

Those interactions could intensify harmful algal blooms in wetlands, according to experiments led by Marie Simonin, a postdoctoral associate with biology professor Emily Bernhardt at Duke University.

Carbon nanotubes and teeny tiny particles of silver, titanium dioxide and other metals are already added to hundreds of commercial products to make everything from faster, lighter electronics, self-cleaning fabrics, and smarter food packaging that can monitor food for spoilage. They are also used on farms for slow- or controlled-release plant fertilizers and pesticides and more targeted delivery, and because they are effective at lower doses than conventional products.

These and other applications have generated tremendous interest and investment in nanomaterials. However the potential risks to human health or the environment aren’t fully understood, Simonin said.

Most of the 260,000 to 309,000 metric tons of nanomaterials produced worldwide each year are eventually disposed in landfills, according to a previous study. But of the remainder, up to 80,400 metric tons per year are released into soils, and up to 29,200 metric tons end up in natural bodies of water.

“And these emerging contaminants don’t end up in water bodies alone,” Simonin said. “They probably co-occur with nutrient runoff. There are likely multiple stressors interacting.”

Algae outbreaks already plague polluted waters worldwide, said Steven Anderson, a research analyst in the Bernhardt Lab at Duke and one of the authors of the research.

Nitrogen and phosphorous pollution makes its way into wetlands and waterways in the form of agricultural runoff and untreated wastewater. The excessive nutrients cause algae to grow out of control, creating a thick mat of green scum or slime on the surface of the water that blocks sunlight from reaching other plants.

These nutrient-fueled “blooms” eventually reduce oxygen levels to the point where fish and other organisms can’t survive, creating dead zones in the water. Some algal blooms also release toxins that can make pets and people who swallow them sick.

Simulated wetlands at the Center for the Environmental Implications of Nanotechnology (https://ceint.duke.edu/research/mesocosm). Photo by Steven Anderson, Duke University.
Simulated wetlands at the Center for the Environmental Implications of Nanotechnology (https://ceint.duke.edu/research/mesocosm). Photo by Steven Anderson, Duke University.

To find out how the combined effects of nutrient runoff and nanoparticle contamination would affect this process, called eutrophication, the researchers set up 18 separate 250-liter tanks with sandy sloped bottoms to mimic small wetlands.

Each open-air tank was filled with water, soil and a variety of wetland plants and animals such as waterweed and mosquitofish.

Over the course of the nine-month experiment, some tanks got a weekly dose of algae-promoting nitrates and phosphates like those found in fertilizers, some tanks got nanoparticles — either copper or gold — and some tanks got both.

Along the way the researchers monitored water chemistry, plant and algal growth and metabolism, and nanoparticle accumulation in plant tissues.

In a simulated wetland experiment at the Center for the Environmental Implications of Nanotechnology, nutrients together with nanoparticles turned clear water (left) murky (right). Photo by Steven Anderson, Duke University.
In a simulated wetland experiment at the Center for the Environmental Implications of Nanotechnology, nutrients together with nanoparticles turned clear water (left) murky (right). Photo by Steven Anderson, Duke University.

“The results were surprising,” Simonin said. The nanoparticles had tiny effects individually, but when added together with nutrients, even low concentrations of gold and copper nanoparticles used in fungicides and other products turned the once-clear water a murky pea soup color, its surface covered with bright green smelly mats of floating algae.

Over the course of the experiment, big algal blooms were more than three times more frequent and more persistent in tanks where nanoparticles and nutrients were added together than where nutrients were added alone. The algae overgrowths also reduced dissolved oxygen in the water.

It’s not clear yet how nanoparticle exposure shifts the delicate balance between plants and algae as they compete for nutrients and other resources. But the results suggest that nanoparticles and other “metal-based synthetic chemicals may be playing an under-appreciated role in the global trends of increasing eutrophication,” the researchers said.

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Nano-based manufacturing gets faster and cheaper

Spherical silver nanoparticles and nanowires after being fused by intense pulses of light.
Image: Rajiv Malhotra/Rutgers University-New Brunswick

Scalable and cost-effective manufacturing of thin film devices

Engineers at Rutgers University–New Brunswick and Oregon State University are developing a new method of processing nanomaterials that could lead to faster and cheaper manufacturing of flexible, thin film devices – from touch screens to window coatings, according to a new study.

The “intense pulsed light sintering” method uses high-energy light over an area nearly 7,000 times larger than a laser to fuse nanomaterials in seconds. Nanomaterials are materials characterized by their tiny size, measured in nanometers. A nanometer is one millionth of a millimeter, or about 100,000 times smaller than the diameter of a human hair.

The existing method of pulsed light fusion uses temperatures of around 250 degrees Celsius (482 degrees Fahrenheit) to fuse silver nanospheres into structures that conduct electricity. But the new study, published in RSC Advances and led by Rutgers School of Engineering doctoral student Michael Dexter, showed that fusion at 150 degrees Celsius (302 degrees Fahrenheit) works well while retaining the conductivity of the fused silver nanomaterials.

The engineers’ achievement started with silver nanomaterials of different shapes: long, thin rods called nanowires in addition to nanospheres. The sharp reduction in temperature needed for fusion makes it possible to use low-cost, temperature-sensitive plastic substrates like polyethylene terephthalate (PET) and polycarbonate in flexible devices, without damaging them.

“Pulsed light sintering of nanomaterials enables really fast manufacturing of flexible devices for economies of scale,” said Rajiv Malhotra, the study’s senior author and assistant professor in the Department of Mechanical and Aerospace Engineering at Rutgers–New Brunswick. “Our innovation extends this capability by allowing cheaper temperature-sensitive substrates to be used.”

Fusing, or sintering, nanoparticles by exposing them to pulses of intense light from a xenon lamp. Image: Rajiv Malhotra/Rutgers University-New Brunswick

Fused silver nanomaterials are used to conduct electricity in devices such as radio-frequency identification (RFID) tags, display devices and solar cells. Flexible forms of these products rely on fusion of conductive nanomaterials on flexible substrates, or platforms, such as plastics and other polymers.

“The next step is to see whether other nanomaterial shapes, including flat flakes and triangles, will drive fusion temperatures even lower,” Malhotra said.

In another study, published in Scientific Reports, the Rutgers and Oregon State engineers demonstrated pulsed light sintering of copper sulfide nanoparticles, a semiconductor, to make films less than 100 nanometers thick.

“We were able to perform this fusion in two to seven seconds compared with the minutes to hours it normally takes now,” said Malhotra, the study’s senior author. “We also showed how to use the pulsed light fusion process to control the electrical and optical properties of the film.”

Learn more: Rutgers-Led Innovation Could Spur Faster, Cheaper Nano-Based Manufacturing

 

 

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New process makes it easier to build nanomaterials into transistors, solar cells and other devices


Postdoctoral researcher Yuanyuan Wang holds a ‘mask’ used in a new process that makes it easier to build nanomaterials into transistors, solar cells and other devices.
Photo byJean Lachat

UChicago, Argonne scientists create technique to build nanomaterials into electronic devices

Scientists at the University of Chicago and Argonne National Laboratory have discovered a new way to precisely pattern nanomaterials that could open a new path to the next generation of everyday electronic devices.

The new research, published in Science, is expected to make such materials easily available for eventual use in everything from LED displays to cellular phones to photodetectors and solar cells. Though nanomaterials are promising for future devices, ways to build them into complex structures have been limited and small-scale.

“This is a step needed to move quantum dots and many other nanomaterials from proof-of-concept experiments to real technology we can use,” said co-author Dmitri Talapin, professor of chemistry at UChicago and a scientist with the Center for Nanoscale Materials at Argonne. “It really expands our horizons.”

But the method has its limitations. Only a few materials can be patterned this way; it was originally developed for silicon, and as silicon’s half-century reign over electronics reaches its end, scientists are looking ahead to the next materials.

One such avenue of interest is nanomaterials—tiny crystals of metals or semiconductors. At this scale, they can have unique and useful properties, but manufacturing devices out of them has been difficult.

The new technique, called DOLFIN, makes different nanomaterials directly into “ink” in a process that bypasses the need to lay down a polymer stencil. Talapin and his team carefully designed chemical coatings for individual particles. These coatings react with light, so if you shine light through a patterned mask, the light will transfer the pattern directly into the layer of nanoparticles below—wiring them into useful devices.

“We found the quality of the patterns was comparable to those made with state-of-the-art techniques,” said lead author Yuanyuan Wang, postdoctoral researcher at UChicago. “It can be used with a wide range of materials, including semiconductors, metals, oxides or magnetic materials—all commonly used in electronics manufacturing.”

Learn more: New method promises easier nanoscale manufacturing

 

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New material promises transparent window coatings and the tripling of solar cell efficiencies

Near-perfect broadband absorber that’s thin, flexible and transparent in visible light

Transparent window coatings that keep buildings and cars cool on sunny days. Devices that could more than triple solar cell efficiencies. Thin, lightweight shields that block thermal detection. These are potential applications for a thin, flexible, light-absorbing material developed by engineers at the University of California San Diego.

The material, called a near-perfect broadband absorber, absorbs more than 87 percent of near-infrared light (1,200 to 2,200 nanometer wavelengths), with 98 percent absorption at 1,550 nanometers, the wavelength for fiber optic communication. The material is capable of absorbing light from every angle. It also can theoretically be customized to absorb certain wavelengths of light while letting others pass through.

Materials that “perfectly” absorb light already exist, but they are bulky and can break when bent. They also cannot be controlled to absorb only a selected range of wavelengths, which is a disadvantage for certain applications. Imagine if a window coating used for cooling not only blocked infrared radiation, but also normal light and radio waves that transmit television and radio programs.

By developing a novel nanoparticle-based design, a team led by professors Zhaowei Liu and Donald Sirbuly at the UC San Diego Jacobs School of Engineering has created a broadband absorber that’s thin, flexible and tunable. The work was published online on Jan. 24 in Proceedings of the National Academy of Sciences.

“This material offers broadband, yet selective absorption that could be tuned to distinct parts of the electromagnetic spectrum,” Liu said.

The absorber relies on optical phenomena known as surface plasmon resonances, which are collective movements of free electrons that occur on the surface of metal nanoparticles upon interaction with certain wavelengths of light. Metal nanoparticles can carry a lot of free electrons, so they exhibit strong surface plasmon resonance — but mainly in visible light, not in the infrared.

UC San Diego engineers reasoned that if they could change the number of free electron carriers, they could tune the material’s surface plasmon resonance to different wavelengths of light. “Make this number lower, and we can push the plasmon resonance to the infrared. Make the number higher, with more electrons, and we can push the plasmon resonance to the ultraviolet region,” Sirbuly said. The problem with this approach is that it is difficult to do in metals.

To address this challenge, engineers designed and built an absorber from materials that could be modified, or doped, to carry a different amount of free electrons: semiconductors. Researchers used a semiconductor called zinc oxide, which has a moderate number of free electrons, and combined it with its metallic version, aluminum-doped zinc oxide, which houses a high number of free electrons — not as much as an actual metal, but enough to give it plasmonic properties in the infrared.

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Schematic of the nanotube array

The materials were combined and structured in a precise fashion using advanced nanofabrication technologies in the Nano3 cleanroom facility at the Qualcomm Institute at UC San Diego. The materials were deposited one atomic layer at a time on a silicon substrate to create an array of standing nanotubes, each made of alternating concentric rings of zinc oxide and aluminum-doped zinc oxide. The tubes are 1,730 nanometers tall, 650 to 770 nanometers in diameter, and spaced less than a hundred nanometers apart. The nanotube array was then transferred from the silicon substrate to a thin, elastic polymer. The result is a material that is thin, flexible and transparent in the visible.

“There are different parameters that we can alter in this design to tailor the material’s absorption band: the gap size between tubes, the ratio of the materials, the types of materials, and the electron carrier concentration. Our simulations show that this is possible,” said Conor Riley, a recent nanoengineering Ph.D. graduate from UC San Diego and the first author of this work. Riley is currently a postdoctoral researcher in Sirbuly’s group.

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SEM images of a nanotube array: side view (left) and top view (right)

Those are just a few exciting features of this particle-based design, researchers said. It’s also potentially transferrable to any type of substrate and can be scaled up to make large surface area devices, like broadband absorbers for large windows. “Nanomaterials normally aren’t fabricated at scales larger than a couple centimeters, so this would be a big step in that direction,” Sirbuly said.

Learn more: Thin, flexible, light-absorbent material could be used in energy and stealth applications

 

 

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Never seen before self-assembled materials with unprecedented complexity

Study co-authors Pawel Majewski and Kevin Yager preparing nanoscale films of self-assembling materials.

New technique leverages controlled interactions across surfaces to create self-assembled materials with unprecedented complexity

Building nanomaterials with features spanning just billionths of a meter requires extraordinary precision. Scaling up that construction while increasing complexity presents a significant hurdle to the widespread use of such nano-engineered materials.

Now, scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have developed a way to efficiently create scalable, multilayer, multi-patterned nanoscale structures with unprecedented complexity.

The Brookhaven team exploited self-assembly, where materials spontaneous snap together to form the desired structure. But they introduced a significant leap in material intelligence, because each self-assembled layer now guides the configuration of additional layers.

Building nanomaterials with features spanning just billionths of a meter requires extraordinary precision. Scaling up that construction while increasing complexity presents a significant hurdle to the widespread use of such nano-engineered materials.

Now, scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have developed a way to efficiently create scalable, multilayer, multi-patterned nanoscale structures with unprecedented complexity.

The Brookhaven team exploited self-assembly, where materials spontaneous snap together to form the desired structure. But they introduced a significant leap in material intelligence, because each self-assembled layer now guides the configuration of additional layers.

The results, published in the journal Nature Communications, offer a new paradigm for nanoscale self-assembly, potentially advancing nanotechnology used for medicine, energy generation, and other applications.

“There’s something amazing and rewarding about creating structures no one has ever seen before,” said study coauthor Kevin Yager, a scientist at Brookhaven Lab’s Center for Functional Nanomaterials (CFN). “We’re calling this responsive layering—like building a tower, but where each brick is intelligent and contains instructions for subsequent bricks.”

The technique was pioneered entirely at the CFN, a DOE Office of Science User Facility.

“The trick was chemically ‘sealing’ each layer to make it robust enough that the additional layers don’t disrupt it,” said lead author Atikur Rahman, a Brookhaven Lab postdoc during the study and now an assistant professor at the Indian Institute of Science Education and Research, Pune. “This granted us unprecedented control. We can now stack any sequence of self-organized layers to create increasingly intricate 3D structures.”

Guiding nanoscale conversations

4D Overhead

The added color in this scanning electron microscope (SEM) image showcases the discrete, self-assembled layers within these novel nanostructures. The pale blue bars are each roughly 4,000 times thinner than a single human hair.

Other nano-fabrication methods—such as lithography—can create precise nano-structures, but the spontaneous ordering of self-assembly makes it faster and easier. Further, responsive layering pushes that efficiency in new directions, enabling, for example, structures with internal channels or pockets that would be exceedingly difficult to make by any other means.

“Self-assembly is inexpensive and scalable because it’s driven by intrinsic interactions,” said study coauthor and CFN scientist Gregory Doerk. “We avoid the complex tools that are traditionally used to carve precise nano-structures.”

The CFN collaboration used thin films of block copolymers (BCP)—chains of two distinct molecules linked together. Through well-established techniques, the scientists spread BCP films across a substrate, applied heat, and watched the material self-assemble into a prescribed configuration. Imagine spreading LEGOs over a baking sheet, sticking it in the oven, and then seeing it emerge with each piece elegantly snapped together in perfect order.

However, these materials are conventionally two-dimensional, and simply stacking them would yield a disordered mess. So the Brookhaven Lab scientists developed a way to have self-assembled layers discretely “talk” to one another.

The team infused each layer with a vapor of inorganic molecules to seal the structure—a bit like applying nanoscale shellac to preserve a just-assembled puzzle.

“We tuned the vapor infiltration step so that each layer’s structure exhibits controlled surface contours,” Rahman said. “Subsequent layers then feel and respond to this subtle topography.”

Coauthor Pawel Majewski added,  “Essentially, we open up a ‘conversation’ between layers. The surface patterns drive a kind of topographic crosstalk, and each layer acts as a template for the next one.”

Exotic configurations

4D Overhead

An aerial view of a complete, self-assembled, multilayer nanostructure. In this instance, parallel bars of block copolymers with varying thickness were criss-crossed.

As often occurs in fundamental research, this crosstalk was an unexpected phenomenon.

“We were amazed when we first saw templated ordering from one layer to the next, Rahman said. “We knew immediately that we had to exhaustively test all the possible combinations of film layers and explore the technique’s potential.”

The collaboration demonstrated the formation of a broad range of nano-structures—including many configurations never before observed. Some contained hollow chambers, round pegs, rods, and winding shapes.

“This was really a Herculean effort on the part of Atikur,” Yager said. “The multi-layer samples covered a staggering range of combinations.”

Mapping never-before-seen structures

3D Assemblies

This image shows the range of multilayer morphologies achieved through this new technique. The first column shows a cross section of the novel 3D nanostructures as captured by scanning electron microscopy (SEM). The computer renderings in the second column highlight the integrity and diversity of each distinct layer, while the overhead SEM view of the third column reveals the complex patterns achieved through the “intelligent” layering.

The scientists used scanning electron microscopy (SEM) to probe the nanoscale features, getting cross-sectional details of the emergent structures. A focused electron beam bombarded the sample, bouncing off surface features before being detected to enable reconstruction of an image depicting the exact configuration.

They complemented this with x-ray scattering at Brookhaven’s National Synchrotron Light Source II—another DOE Office of Science User Facility. The penetrative scattering technique allowed the researchers to probe the internal structure.

“CFN brings together a unique concentration of skills, interests, and technology,” said CFN Director and coauthor Charles Black. “In one facility, we have people interested in creating, converting, and measuring structures—that’s how we can have these kinds of unanticipated and highly collaborative breakthroughs.”

This fundamental breakthrough substantially broadens the diversity and complexity of structures that can be made with self-assembly, and correspondingly broadens the range of potential applications. For example, intricate three-dimensional nanostructures could yield transformative improvements in nano-porous membranes for water purification, bio-sensing, or catalysis.

Learn more: Nanoscale ‘Conversations’ Create Complex, Multi-Layered Structures

 

 

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