Nature Nanotechnology

Scientists Discover Hundreds of 2D Materials That Could Be The Next Graphene

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This is so amazing!

Part of what makes graphene so fantastically useful is its amazing thinness – it’s just one atom thick.

Scientists have now found hundreds of other materials that are equally thin, providing a wide selection of new materials with perhaps as much potential as graphene.

The team analysed data in open resources including the Crystallography Open Database, looking for materials with structural similarities to graphene with the help of a custom computer program.

They were looking for materials with strong chemical bonds along one plane – the 2D atom layer – and relatively weak non-chemical action along the perpendicular plane. It’s this combination that lets us peel sheets of graphene from graphite.

Starting off with a pool of over 100,000 crystal structures, the team from the École Polytechnique Fédérale de Lausanne in Switzerland was able to narrow down the selection to 1,825 compounds with the potential to form sheets just a single atom thick.

“Two-dimensional materials provide opportunities to venture into largely unexplored regions of the materials space,” the researchers explain in their study.

“On the one hand, their ultimate thinness makes them extremely promising for applications in electronics. On the other, the physical properties of monolayers often change dramatically from those of their parent 3D materials, providing a new degree of freedom for applications while also unveiling novel physics.”

In the case of graphene and graphite, graphite is held together by a relatively weak electrostatic interaction known as a van der Waals force. Usually this is strong enough to keep the material together, but it does allow graphene to be extracted.

Whether or not that will also be true for the 1,825 materials identified here remains to be seen, but they have been shown to be structurally similar in terms of atom locations and their chemical bonds. A few of the structures have never been seen before.

Based on calculations run on 258 of the less complex chemicals in the final list, the researchers found that 166 turned out to be semiconductors with a variety of voltages. Meanwhile, 92 materials were identified as metallic, with another 56 likely to have unusual magnetic properties.

Even if just a small subsection of these new materials end up functioning like graphene does, that gives us a lot more options for creating materials for specific purposes in electronics and other areas. The next step is to test how these compounds work in both sheet form and in tightly packed layers.

What we do know thanks to this advanced database search is that these materials might just be exfoliable – able to be peeled into super-thin layers just like graphene. It’s going to be exciting to see what happens next with the materials on this list.

“The materials identified are classified into groups of easily or potentially exfoliable compounds, showing that only a very small fraction of possible 2D materials has been considered up to now,” conclude the researchers.

The research has been published in Nature Nanotechnology.

Scientists have invented a graphene-based sieve that turns seawater into drinking water.

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Researchers have achieved a major turning point in the quest for efficient desalination by announcing the invention of a graphene-oxide membrane that sieves salt right out of seawater.

At this stage, the technique is still limited to the lab, but it’s a demonstration of how we could one day quickly and easily turn one of our most abundant resources, seawater, into one of our most scarce – clean drinking water.

 

The team, led by Rahul Nair from the University of Manchester in the UK, has shown that the sieve can efficiently filter out salts, and now the next step is to test this against existing desalination membranes.

“Realisation of scalable membranes with uniform pore size down to atomic scale is a significant step forward and will open new possibilities for improving the efficiency of desalination technology,” says Nair.

“This is the first clear-cut experiment in this regime. We also demonstrate that there are realistic possibilities to scale up the described approach and mass produce graphene-based membranes with required sieve sizes.”

Graphene-oxide membranes have long been considered a promising candidate for filtration and desalination, but although many teams have developed membranes that could sieve large particles out of water, getting rid of salt requires even smaller sieves that scientists have struggled to create.

One big issue is that, when graphene-oxide membranes are immersed in water, they swell up, allowing salt particles to flow through the engorged pores.

The Manchester team overcame this by building walls of epoxy resin on either side of the graphene oxide membrane, stopping it from swelling up in water.

 This allowed them to precisely control the pore size in the membrane, creating holes tiny enough to filter out all common salts from seawater.

The key to this is the fact that when common salts are dissolved in water, they form a ‘shell’ of water molecules around themselves.

“Water molecules can go through individually, but sodium chloride cannot. It always needs the help of the water molecules,” Nair told Paul Rincon from the BBC.

“The size of the shell of water around the salt is larger than the channel size, so it cannot go through.”

Not only did this leave seawater fresh to drink, it also made the water molecules flow way faster through the membrane barrier, which is perfect for use in desalination.

“When the capillary size is around one nanometre, which is very close to the size of the water molecule, those molecules form a nice interconnected arrangement like a train,” Nair explained to Rincon.

“That makes the movement of water faster: if you push harder on one side, the molecules all move on the other side because of the hydrogen bonds between them. You can only get that situation if the channel size is very small.”

There are already several major desalination plants around the world using polymer-based membranes to filter out salt, but the process is still largely inefficient and expensive, so finding a way to make it quicker, cheaper, and easier is a huge goal for researchers.

Thanks to climate change, seawater is something we’re going to have plenty of in the future – Greenland’s coastal ice caps which have already passed the point of no return are predicted to increase sea levels by around 3.8 cm (1.5 inches) by 2100, and if the entire Greenland Ice Sheet melts, future generations will be facing oceans up to 7.3 metres (24 feet) higher.

But at the same time, clean drinking water is still incredibly hard to come by in many parts of the world – the UN predicts that by 2025, 14 percent of the world’s population will encounter water scarcity. And many of those countries won’t be able to afford large-scale desalination plants.

The researchers are now hoping that the graphene-based sieve might be as effective as large plants on the small scale, so it’s easier to roll out.

Graphene oxide is also a lot easier and cheaper to make in the lab than single-layers of graphene, which means the technology will be affordable and easy to produce.

“The selective separation of water molecules from ions by physical restriction of interlayer spacing opens the door to the synthesis of inexpensive membranes for desalination,” Ram Devanathan from the Pacific Northwest National Laboratory, who wasn’t involved in the research, wrote in an accompanyingNature News and Views article.

“The ultimate goal is to create a filtration device that will produce potable water from seawater or wastewater with minimal energy input.”

He added that the next step will be to test how durable the membranes are when used over long periods of time, and how often they need to be replaced.

Source: Nature Nanotechnology.

Scientists develop nanoscale ‘train set’ controlled by DNA

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A nanoscale ‘train set’ powered by microscopic motors and controlled by DNA has been developed by scientists.

The system can construct its own network of tracks spanning tens of micrometres in length, and use them to transport cargo.

DNA

Researchers were inspired by the melanophore, a living system used by fish to change colour. It uses motor proteins to transport pigment along tracks that come to a central point, like spokes on a wheel. Bringing pigment to the centre makes cells lighter because the surrounding space is left empty and transparent.

Scientists at Oxford University built a similar system from DNA and a motor protein called kinesin. The kinesin molecules move along micro-tracks made from short strands of DNA. The kinesin molecules are used either as “assemblers” that move elements of track around, or “shuttles” that carry cargo molecules along the tracks. A natural fuel source called ATP, which drives cell metabolism, is used to power the system.

“DNA is an excellent building block for constructing synthetic molecular systems, as we can programme it to do whatever we need,” said Adam Wollman, who led the Oxford University team. “We design the chemical structures of the DNA strands to control how they interact with each other. The shuttles can be used to either carry cargo or deliver signals to tell other shuttles what to do.

“We first use assemblers to arrange the track into ‘spokes’, triggered by the introduction of ATP. We then send in shuttles with fluorescent green cargo which spread out across the track, covering it evenly.

“When we add more ATP, the shuttles all cluster in the centre of the track where the spokes meet. Next, we send signal shuttles along the tracks to tell the cargo-carrying shuttles to release the fluorescent cargo into the environment, where it disperses. We can also send shuttles programmed with ‘dismantle’ signals to the central hub, telling the tracks to break up.”

The experiment used green dye as a cargo, but the same technique could be used to transport other molecules. Spoke-like track systems could be used to speed up chemical reactions by concentrating necessary compounds at the central hub, said the scientists.

Using DNA to control motor proteins could aid the development of sophisticated self-assembling systems for a wide variety of applications.

Mixing nanoparticles to make multifunctional materials.

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Scientists at the U.S. Department of Energy‘s Brookhaven National Laboratory have developed a general approach for combining different types of nanoparticles to produce large-scale composite materials. The technique, described in a paper published online by Nature Nanotechnology on October 20, 2013, opens many opportunities for mixing and matching particles with different magnetic, optical, or chemical properties to form new, multifunctional materials or materials with enhanced performance for a wide range of potential applications.

Mixing nanoparticles to make multifunctional materials

The approach takes advantage of the attractive pairing of complementary strands of synthetic DNA-based on the molecule that carries the genetic code in its sequence of matched bases known by the letters A, T, G, and C. After coating the  with a chemically standardized “construction platform” and adding extender molecules to which DNA can easily bind, the scientists attach complementary lab-designed DNA strands to the two different kinds of nanoparticles they want to link up. The natural pairing of the matching strands then “self-assembles” the particles into a three-dimensional array consisting of billions of particles. Varying the length of the DNA linkers, their surface density on particles, and other factors gives scientists the ability to control and optimize different types of newly formed  and their properties.

“Our study demonstrates that DNA-driven assembly methods enable the by-design creation of large-scale ‘superlattice’ nanocomposites from a broad range of nanocomponents now available-including magnetic, catalytic, and fluorescent nanoparticles,” said Brookhaven physicist Oleg Gang, who led the research at the Lab’s Center for Functional Nanomaterials (CFN). “This advance builds on our previous work with simpler systems, where we demonstrated that pairing nanoparticles with different functions can affect the individual particles’ performance, and it offers routes for the fabrication of new materials with combined, enhanced, or even brand new functions.”

Future applications could include quantum dots whose glowing fluorescence can be controlled by an external magnetic field for new kinds of switches or sensors; gold nanoparticles that synergistically enhance the brightness of quantum dots’ fluorescent glow; or catalytic nanomaterials that absorb the “poisons” that normally degrade their performance, Gang said.

“Modern nano-synthesis methods provide scientists with diverse types of nanoparticles from a wide range of atomic elements,” said Yugang Zhang, first author of the paper. “With our approach, scientists can explore pairings of these particles in a rational way.”

Pairing up dissimilar particles presents many challenges the scientists investigated in the work leading to this paper. To understand the fundamental aspects of various newly formed materials they used a wide range of techniques, including x-ray scattering studies at Brookhaven’s National Synchrotron Light Source (NSLS) and spectroscopy and electron microcopy at the CFN.

For example, the scientists explored the effect of particle shape. “In principle, differently shaped particles don’t want to coexist in one lattice,” said Gang. “They either tend to separate into different phases like oil and water refusing to mix or form disordered structures.” The scientists discovered that DNA not only helps the particles mix, but it can also improve order for such systems when a thicker DNA shell around the particles is used.

They also investigated how the DNA-pairing mechanism and other intrinsic physical forces, such as magnetic attraction among particles, might compete during the assembly process. For example, magnetic particles tend to clump to form aggregates that can hinder the binding of DNA from another type of particle. “We show that shorter DNA strands are more effective at competing against magnetic attraction,” Gang said.

For the particular composite of gold and magnetic nanoparticles they created, the scientists discovered that applying an  could “switch” the material’s phase and affect the ordering of the particles. “This was just a demonstration that it can be done, but it could have an application-perhaps magnetic switches, or materials that might be able to change shape on demand,” said Zhang.

The third fundamental factor the scientists explored was how the particles were ordered in the superlattice arrays: Does one type of particle always occupy the same position relative to the other type-like boys and girls sitting in alternating seats in a movie theater-or are they interspersed more randomly? “This is what we call a compositional order, which is important for example for  because their optical properties-e.g., their ability to glow-depend on how many  are in the surrounding environment,” said Gang. “If you have compositional disorder, the optical properties would be different.” In the experiments, increasing the thickness of the soft DNA shells around the particles increased compositional disorder.

These fundamental principles give scientists a framework for designing . The specific conditions required for a particular application will be dependent on the particles being used, Zhang emphasized, but the general assembly approach would be the same.

Said Gang, “We can vary the lengths of the DNA strands to change the distance between  from about 10 nanometers to under 100 nanometers-which is important for applications because many optical, magnetic, and other properties of nanoparticles depend on the positioning at this scale. We are excited by the avenues this research opens up in terms of future directions for engineering novel classes of materials that exploit collective effects and multifunctionality.”




Microscopic ‘Tuning Forks’ Could Make the Difference Between Life and Death in the Hospital.

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A patient admitted to a hospital with a serious bacterial infection may have only a few hours to live. Figuring out which antibiotic to administer, however, can take days. Doctors must grow the microbes in the presence of the drugs and see whether they reproduce. Rush the process, and they risk prescribing ineffective antibiotics, exposing the patient to unnecessary side effects, and spreading antibiotic resistance. Now, researchers have developed a microscopic “tuning fork” that detects tiny vibrations in bacteria. The device might one day allow physicians to tell the difference between live and dead microbes—and enable them to recognize effective and ineffective antibiotics within minutes.

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“It’s a brilliant method,” provided subsequent investigations confirm the researchers’ interpretation of their data, says Martin Hegner, a biophysicist at Trinity College Dublin who was not involved in the work.

The research involves tiny, flexible bars called cantilevers that vibrate up and down like the prongs of a tuning fork when they receive an input of energy. Cantilevers are an important part of atomic force microscopy, which is useful for making atomic scale resolutions of surfaces for use in nanotechnology or atomic physics research. In this technique, a minute needle attached to a cantilever moves across a surface, and the deflection of the cantilever gives information about how atoms are arranged on the surface. It can even be used to shunt atoms around. More recently, however, they have been used without the needle as tiny oscillators, allowing scientists to investigate matter directly attached to the cantilever.

Biophysicist Giovanni Longo and colleagues at the Swiss Federal Institute of Technology in Lausanne and the University of Lausanne in Switzerland immersed these cantilevers in a liquid bacterial growth medium and monitored their movement using a laser. They found that the bare cantilever moved very slightly as a result of the thermal movement of the liquid molecules in the medium. They then covered both sides of the cantilever withEscherichia coli bacteria, which can cause food poisoning, and immediately found that the oscillations became much more pronounced. The researchers believe that chemical processes that occur inside the bacteria as they metabolize energy are driving the oscillation. “What we see is that if you have some sort of a moving system on the cantilever, you are going to induce a movement on the cantilever itself,” Longo explains. “Exactly what kind of metabolic movement we see is something that we are still studying.”

To determine if the cantilevers could detect the impact of drugs, the team added ampicillin, an antibiotic that the cultured bacteria were sensitive to. The size of the cantilever’s oscillations decreased almost 20-fold within 5 minutes, the researchers report online today in Nature Nanotechnology. Fifteen minutes later, the scientists flushed the antibiotic out with fresh growth medium, but the movement of the cantilever did not increase again. This, the researchers say, suggests that the antibiotic had killed the bacteria. When they used an ampicillin-resistant strain of E. coli, however, they found that the oscillations initially decreased but returned to normal within about 15 minutes, indicating that the microbes had recovered.

Hegner cautions that the research is still “basic science. … It’s not yet an applied tool which is robust enough to be used in an ER or something.” That, he says, might take another 5 or 10 years.

Before that happens, Hegner says, researchers need to determine what the sensors are picking up and whether that signal can be conclusively linked to the bacteria and their antibiotic resistance. They also need to find out if properties of the medium affect the results, he says. “If you inject a bacterium into a medium with different viscosity and different density, this also might affect the vibration of the sensor.”

The Swiss researchers are continuing to investigate clinical applications of their system. They have recently obtained access to a more secure lab licensed to handle highly pathogenic bacteria and are working on confirming their results in these microbes. They are also thinking beyond the clinic. “Our dream is to send something like this to Mars to see if there is life,” Longo says. “It’s much faster than any other technique one can imagine—you just put some of the martian dirt inside the liquid and whatever attaches to the cantilever, if it moves it’s alive.”

Source: sciencemag.org