Building at the nanoscale is not like building a house. Scientists often start with two-dimensional molecular layers and combine them to form complex three-dimensional architectures.
And instead of nails and screws, these structures are joined together by the attractive van der Waals forces that exist between objects at the nanoscale.
Van der Waals forces are critical in constructing materials for energy storage, biochemical sensors and electronics, although they are weak when compared to chemical bonds. They also play a crucial role in drug delivery systems, determining which drugs bind to the active sites in proteins.
In new research that could help inform development of new materials, Cornell chemists have found that the empty space (“pores”) present in two-dimensional molecular building blocks fundamentally changes the strength of these van der Waals forces, and can potentially alter the assembly of sophisticated nanostructures.
The findings represent an unexplored avenue toward governing the self-assembly of complex nanostructures from porous two-dimensional building blocks.
“We hope that a more complete understanding of these forces will aid in the discovery and development of novel materials with diverse functionalities, targeted properties, and potentially novel applications,” said Robert A. DiStasio Jr., assistant professor of chemistry in the College of Arts and Sciences.
In a paper titled “Influence of Pore Size on the van der Waals Interaction in Two-Dimensional Molecules and Materials,” published Jan. 14 in Physical Review Letters, DiStasio, graduate student Yan Yang and postdoctoral associate Ka Un Lao describe a series of mathematical models that address the question of how void space fundamentally affects the attractive physical forces which occur over nanoscale distances.
In three prototypical model systems, the researchers found that particular pore sizes lead to unexpected behavior in the physical laws that govern van der Waals forces.
Further, they write, this behavior “can be tuned by varying the relative size and shape of these void spaces … [providing] new insight into the self-assembly and design of complex nanostructures.”
While strong covalent bonds are responsible for the formation of two-dimensional molecular layers, van der Waals interactions provide the main attractive force between the layers. As such, van der Waals forces are largely responsible for the self-assembly of the complex three-dimensional nanostructures that make up many of the advanced materials in use today.
The researchers demonstrated their findings with numerous two-dimensional systems, including covalent organic frameworks, which are endowed with adjustable and potentially very large pores.
“I am surprised that the complicated relationship between void space and van der Waals forces could be rationalized through such simple models,” said Yang. “In the same breath, I am really excited about our findings, as even small changes in the van der Waals forces can markedly impact the properties of molecules and materials.”
Explore further: Researchers refute textbook knowledge in molecular interactions
More information: Yan Yang et al, Influence of Pore Size on the van der Waals Interaction in Two-Dimensional Molecules and Materials, Physical Review Letters (2019). DOI: 10.1103/PhysRevLett.122.026001
University of Alberta chemists have taken a critical step toward creating a new generation of silicon-based lithium ion batteries with 10 times the charge capacity of current cells.
“We wanted to test how different sizes of silicon nanoparticles could affect fracturing inside these batteries,” said Jillian Buriak, a U of A chemist and Canada Research Chair in Nanomaterials for Energy.
Silicon shows promise for building much higher-capacity batteries because it’s abundant and can absorb much more lithium than the graphite used in current lithium ion batteries. The problem is that silicon is prone to fracturing and breaking after numerous charge-and-discharge cycles, because it expands and contracts as it absorbs and releases lithium ions.
Existing research shows that shaping silicon into nano-scale particles, wires or tubes helps prevent it from breaking. What Buriak, fellow U of A chemist Jonathan Veinot and their team wanted to know was what size these structures needed to be to maximize the benefits of silicon while minimizing the drawbacks.
The researchers examined silicon nanoparticles of four different sizes, evenly dispersed within highly conductive graphene aerogels, made of carbon with nanoscopic pores, to compensate for silicon’s low conductivity. They found that the smallest particles—just three billionths of a metre in diameter—showed the best long-term stability after many charging and discharging cycles.
“As the particles get smaller, we found they are better able to manage the strain that occurs as the silicon ‘breathes’ upon alloying and dealloying with lithium, upon cycling,” explained Buriak.
The research has potential applications in “anything that relies upon energy storage using a battery,” said Veinot, who is the director of the ATUMS graduate student training program that partially supported the research.
“Imagine a car having the same size battery as a Tesla that could travel 10 times farther or you charge 10 times less frequently, or the battery is 10 times lighter.”
Veinot said the next steps are to develop a faster, less expensive way to create silicon nanoparticles to make them more accessible for industry and technology developers.
The study, “Size and Surface Effects of Silicon Nanocrystals in Graphene Aerogel Composite Anodes for Lithium Ion Batteries,” was published in Chemistry of Materials.
More information: Maryam Aghajamali et al. Size and Surface Effects of Silicon Nanocrystals in Graphene Aerogel Composite Anodes for Lithium Ion Batteries, Chemistry of Materials (2018). DOI: 10.1021/acs.chemmater.8b03198
Watch a YouTube Video about an Energy Storage Company Tenka Energy, Inc., that has developed and prototyped the NextGen of silicon-lithium-ion batteries for EV’s, Drones, Medical Sensors ….
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** See More About Graphene (YouTube Video) and Desalination at the end of this article **
Researchers at The University of Manchester’s National Graphene Institute in the UK have succeeded in making artificial channels just one atom in size for the first time. The new capillaries, which are very much like natural protein channels such as aquaporins, are small enough to block the flow of smallest ions like Na+ and Cl- but allow water to flow through freely. As well as improving our fundamental understanding of molecular transport at the atomic scale, and especially in biological systems, the structures could be ideal in desalination and filtration technologies.
“Obviously, it is impossible to make capillaries smaller than one atom in size,” explains team leader Sir Andre Geim. “Our feat seemed nigh on impossible, even in hindsight, and it was difficult to imagine such tiny capillaries just a couple of years ago.”
Naturally occurring protein channels, such as aquaporins, allow water to quickly permeate through them but block hydrated ions larger than around 7 A in size thanks to mechanisms like steric (size) exclusion and electrostatic repulsion. Researchers have been trying to make artificial capillaries that work just like their natural counterparts, but despite much progress in creating nanoscale pores and nanotubes, all such structures to date have still been much bigger than biological channels.
Geim and colleagues have now fabricated channels that are around just 3.4 A in height. This is about half the size of the smallest hydrated ions, such as K+ and Cl-, which have a diameter of 6.6 A. These channels behave just like protein channels in that they are small enough to block these ions but are sufficiently big to allow water molecules (with a diameter of around 2.8 A) to freely flow through.
The structures could, importantly, help in the development of cost-effective, high-flux filters for water desalination and related technologies – a holy grail for researchers in the field.
Publishing their findings in Science the researchers made their structures using a van der Waals assembly technique, also known as “atomic-scale Lego”, which was invented thanks to research on graphene. “We cleave atomically flat nanocrystals just 50 and 200 nanometre in thickness from bulk graphite and then place strips of monolayer graphene onto the surface of these nanocrystals,” explains Dr. Radha Boya, a co-author of the research paper. “These strips serve as spacers between the two crystals when a similar atomically-flat crystal is subsequently placed on top. The resulting trilayer assembly can be viewed as a pair of edge dislocations connected with a flat void in between. This space can accommodate only one atomic layer of water.”
Using the graphene monolayers as spacers is a first and this is what makes the new channels different from any previous structures, she says.
Until now, researchers had only been able to measure water flowing though capillaries that had much thicker spacers (around 6.7 A high). And while some of their molecular dynamics simulations indicated that smaller 2-D cavities should collapse because of van der Waals attraction between the opposite walls, other calculations pointed to the fact that water molecules inside the slits could actually act as a support and prevent even one-atom-high slits (just 3.4 A tall) from falling down. This is indeed what the Manchester team has now found in its experiments.
Measuring water and ion flow
“We measured water permeation through our channels using a technique known as gravimetry,” says Radha. “Here, we allow water in a small sealed container to evaporate exclusively through the capillaries and we then accurately measure (to microgram precision) how much weight the container loses over a period of several hours.”
To do this, the researchers say they built a large number of channels (over a hundred) in parallel to increase the sensitivity of their measurements. They also used thicker top crystals to prevent sagging, and clipped the top opening of the capillaries (using plasma etching) to remove any potential blockages by thin edges present here.
To measure ion flow, they forced ions to move through the capillaries by applying an electric field and then measured the resulting currents. “If our capillaries were two atoms high, we found that small ions can move freely though them, just like what happens in bulk water,” says Radha. “In contrast, no ions could pass through our ultimately-small one-atom-high channels.
“The exception was protons, which are known to move through water as true subatomic particles, rather than ions dressed up in relatively large hydration shells several angstroms in diameter. Our channels thus block all hydrated ions but allow protons to pass.”
Since these capillaries behave in the same way as protein channels, they will be important for better understanding how water and ions behave on the molecular scale – as in angstrom-scale biological filters. “Our work (both present and previous) shows that atomically-confined water has very different properties from those of bulk water,” explains Geim. “For example, it becomes strongly layered, has a different structure, and exhibits radically dissimilar dielectric properties.”
Explore further: Devices made from 2-D materials separate salts in seawater
Want to Read More About Cutting Edge Desalination, Energy Storage and Carbon Nanotubes?
Graphene for Water Desalination
Water, one of the world’s most abundant and highly demanded resources for sustaining life, agriculture, and industry, is being contaminated globally or is unsafe for drinking, creating a need for new and better desalination methods. Current desalination methods have high financial, energy, construction, and operating costs, resulting in them contributing to less than 1% of the world’s reserve water supplies. Advances in nanoscale science and engineering suggest that more cost effective and environmentally friendly desalination process using graphene is possible …
A chemical reaction pathway central to plant biology have been adapted to form the backbone of a new process that converts water into hydrogen fuel using energy from the sun.
In a recent study from the U.S. Department of Energy’s (DOE) Argonne National Laboratory, scientists have combined two membrane-bound protein complexes to perform a complete conversion of water molecules to hydrogen and oxygen.
The work builds on an earlier study that examined one of these protein complexes, called Photosystem I, a membrane protein that can use energy from light to feed electrons to an inorganic catalyst that makes hydrogen. This part of the reaction, however, represents only half of the overall process needed for hydrogen generation.
By using a second protein complex that uses energy from light to split water and take electrons from it, called Photosystem II, Argonne chemist Lisa Utschig and her colleagues were able to take electrons from water and feed them to Photosystem I.
“The beauty of this design is in its simplicity—you can self-assemble the catalyst with the natural membrane to do the chemistry you want”—Lisa Utschig, Argonne chemist
In an earlier experiment, the researchers provided Photosystem I with electrons from a sacrificial electron donor. “The trick was how to get two electrons to the catalyst in fast succession,” Utschig said.
The two protein complexes are embedded in thylakoid membranes, like those found inside the oxygen-creating chloroplasts in higher plants. “The membrane, which we have taken directly from nature, is essential for pairing the two photosystems,” Utschig said. “It structurally supports both of them simultaneously and provides a direct pathway for inter-protein electron transfer, but doesn’t impede catalyst binding to Photosystem I.”
According to Utschig, the Z-scheme—which is the technical name for the light-triggered electron transport chain of natural photosynthesis that occurs in the thylakoid membrane—and the synthetic catalyst come together quite elegantly. “The beauty of this design is in its simplicity—you can self-assemble the catalyst with the natural membrane to do the chemistry you want,” she said.
One additional improvement involved the substitution of cobalt or nickel-containing catalysts for the expensive platinum catalyst that had been used in the earlier study. The new cobalt or nickel catalysts could dramatically reduce potential costs.
The next step for the research, according to Utschig, involves incorporating the membrane-bound Z-scheme into a living system. “Once we have an in vivo system—one in which the process is happening in a living organism—we will really be able to see the rubber hitting the road in terms of hydrogen production,” she said.
More information: Lisa M. Utschig et al, Z-scheme solar water splitting via self-assembly of photosystem I-catalyst hybrids in thylakoid membranes, Chemical Science (2018). DOI: 10.1039/c8sc02841a
” The new colloidal processing techniques allow for preparation of virtually ideal quantum-dot emitters with nearly 100 percent emission quantum yields shown for a wide range of visible, infrared and ultraviolet wavelengths. These advances have been exploited in a variety of light-emission technologies, resulting in successful commercialization of quantum-dot displays and TV sets … “
Intentionally “squashing” colloidal quantum dots during chemical synthesis creates dots capable of stable, “blink-free” light emission that is fully comparable with the light produced by dots made with more complex processes. The squashed dots emit spectrally narrow light with a highly stable intensity and a non-fluctuating emission energy. New research at Los Alamos National Laboratory suggests that the strained colloidal quantum dots represent a viable alternative to presently employed nanoscale light sources, and they deserve exploration as single-particle, nanoscale light sources for optical “quantum” circuits, ultrasensitive sensors, and medical diagnostics.
“In addition to exhibiting greatly improved performance over traditional produced quantum dots, these new strained dots could offer unprecedented flexibility in manipulating their emission color, in combination with the unusually narrow, ‘subthermal’ linewidth,” said Victor Klimov, lead Los Alamos researcher on the project. “The squashed dots also show compatibility with virtually any substrate or embedding medium as well as various chemical and biological environments.”
The new colloidal processing techniques allow for preparation of virtually ideal quantum-dot emitters with nearly 100 percent emission quantum yields shown for a wide range of visible, infrared and ultraviolet wavelengths. These advances have been exploited in a variety of light-emission technologies, resulting in successful commercialization of quantum-dot displays and TV sets.
The next frontier is exploration of colloidal quantum dots as single-particle, nanoscale light sources. Such future “single-dot” technologies would require particles with highly stable, nonfluctuating spectral characteristics. Recently, there has been considerable progress in eliminating random variations in emission intensity by protecting a small emitting core with an especially thick outer layer. However, these thick-shell structures still exhibit strong fluctuations in emission spectra.
In a new publication in the journal Nature Materials, Los Alamos researchers demonstrated that spectral fluctuations in single-dot emission can be nearly completely suppressed by applying a new method of “strain engineering.” The key in this approach is to combine in a core/shell motif two semiconductors with directionally asymmetric lattice mismatch, which results in anisotropic compression of the emitting core.
This modifies the structures of electronic states of a quantum dot and thereby its light emitting properties. One implication of these changes is the realization of the regime of local charge neutrality of the emitting “exciton” state, which greatly reduces its coupling to lattice vibrations and fluctuating electrostatic environment, key to suppressing fluctuations in the emitted spectrum. An additional benefit of the modified electronic structures is dramatic narrowing of the emission linewidth, which becomes smaller than the room-temperature thermal energy.
Explore further: Sandwich structure of nanocrystals as quantum light source
More information: Young-Shin Park et al, Asymmetrically strained quantum dots with non-fluctuating single-dot emission spectra and subthermal room-temperature linewidths, Nature Materials (2018). DOI: 10.1038/s41563-018-0254-7
Washington State University researchers have developed a novel way to deliver drugs and therapies into cells at the nanoscale without causing toxic effects that have stymied other such efforts.
The work could someday lead to more effective therapies and diagnostics for cancer and other illnesses.
Led by Yuehe Lin, professor in WSU’s School of Mechanical and Materials Engineering, and Chunlong Chen, senior scientist at the Department of Energy’s Pacific Northwest National Laboratory (PNNL), the research team developed biologically inspired materials at the nanoscale that were able to effectively deliver model therapeutic genes into tumor cells. They published their results in the journal, Small.
Researchers have been working to develop nanomaterials that can effectively carry therapeutic genes directly into the cells for the treatment of diseases such as cancer. The key issues for gene delivery using nanomaterials are their low delivery efficiency of medicine and potential toxicity.
“To develop nanotechnology for medical purposes, the first thing to consider is toxicity — That is the first concern for doctors,” said Lin.
The flower-like particle the WSU and PNNL team developed is about 150 nanometers in size, or about one thousand times smaller than the width of a piece of paper. It is made of sheets of peptoids, which are similar to natural peptides that make up proteins. The peptoids make for a good drug delivery particle because they’re fairly easy to synthesize and, because they’re similar to natural biological materials, work well in biological systems.
The researchers added fluorescent probes in their peptoid nanoflowers, so they could trace them as they made their way through cells, and they added the element fluorine, which helped the nanoflowers more easily escape from tricky cellular traps that often impede drug delivery.
The flower-like particles loaded with therapeutic genes were able to make their way smoothly out of the predicted cellular trap, enter the heart of the cell, and release their drug there.
“The nanoflowers successfully and rapidly escaped (the cell trap) and exhibited minimal cytotoxicity,” said Lin.
After their initial testing with model drug molecules, the researchers hope to conduct further studies using real medicines.
“This paves a new way for us to develop nanocargoes that can efficiently deliver drug molecules into the cell and offers new opportunities for targeted gene therapies,” he said.
The WSU and PNNL team have filed a patent application for the new technology, and they are seeking industrial partners for further development.
- Yang Song, Mingming Wang, Suiqiong Li, Haibao Jin, Xiaoli Cai, Dan Du, He Li, Chun-Long Chen, Yuehe Lin. Efficient Cytosolic Delivery Using Crystalline Nanoflowers Assembled from Fluorinated Peptoids. Small, 2018; 14 (52): 1803544 DOI: 10.1002/smll.201803544
Your knees and your smartphone battery have some surprisingly similar needs, a University of Michigan professor has discovered, and that new insight has led to a “structural battery” prototype that incorporates a cartilage-like material to make the batteries highly durable and easy to shape.
The idea behind structural batteries is to store energy in structural components — the wing of a drone or the bumper of an electric vehicle, for example. They’ve been a long-term goal for researchers and industry because they could reduce weight and extend range. But structural batteries have so far been heavy, short-lived or unsafe.
In a study published in ACS Nano, the researchers describe how they made a damage-resistant rechargeable zinc battery with a cartilage-like solid electrolyte. They showed that the batteries can replace the top casings of several commercial drones. The prototype cells can run for more than 100 cycles at 90 percent capacity, and withstand hard impacts and even stabbing without losing voltage or starting a fire.
“A battery that is also a structural component has to be light, strong, safe and have high capacity. Unfortunately, these requirements are often mutually exclusive,” said Nicholas Kotov, the Joseph B. and Florence V. Cejka Professor of Engineering, who led the research.
Harnessing the properties of cartilage
To sidestep these trade-offs, the researchers used zinc — a legitimate structural material — and branched nanofibers that resemble the collagen fibers of cartilage.
“Nature does not have zinc batteries, but it had to solve a similar problem,” Kotov said. “Cartilage turned out to be a perfect prototype for an ion-transporting material in batteries. It has amazing mechanics, and it serves us for a very long time compared to how thin it is. The same qualities are needed from solid electrolytes separating cathodes and anodes in batteries.”
In our bodies, cartilage combines mechanical strength and durability with the ability to let water, nutrients and other materials move through it. These qualities are nearly identical to those of a good solid electrolyte, which has to resist damage from dendrites while also letting ions flow from one electrode to the other.
Dendrites are tendrils of metal that pierce the separator between the electrodes and create a fast lane for electrons, shorting the circuit and potentially causing a fire. Zinc has previously been overlooked for rechargeable batteries because it tends to short out after just a few charge/discharge cycles.
Not only can the membranes made by Kotov’s team ferry zinc ions between the electrodes, they can also stop zinc’s piercing dendrites. Like cartilage, the membranes are composed of ultrastrong nanofibers interwoven with a softer ion-friendly material.
In the batteries, aramid nanofibers — the stuff in bulletproof vests — stand in for collagen, with polyethylene oxide (a chain-like, carbon-based molecule) and a zinc salt replacing soft components of cartilage.
Demonstrating safety and utility
To make working cells, the team paired the zinc electrodes with manganese oxide — the combination found in standard alkaline batteries. But in the rechargeable batteries, the cartilage-like membrane replaces the standard separator and alkaline electrolyte. As secondary batteries on drones, the zinc cells can extend the flight time by 5 to 25 percent — depending on the battery size, mass of the drone and flight conditions.
Safety is critical to structural batteries, so the team deliberately damaged their cells by stabbing them with a knife. In spite of multiple “wounds,” the battery continued to discharge close to its design voltage. This is possible because there is no liquid to leak out.
For now, the zinc batteries are best as secondary power sources because they can’t charge and discharge as quickly as their lithium ion brethren. But Kotov’s team intends to explore whether there is a better partner electrode that could improve the speed and longevity of zinc rechargeable batteries.
The research was supported by the Air Force Office of Scientific Research and National Science Foundation. Kotov teaches in the Department of Chemical Engineering. He is also a professor of materials science and engineering, and macromolecular science and engineering.
- Mingqiang Wang, Ahmet Emre, Siu On Tung, Alycia Gerber, Dandan Wang, Yudong Huang, Volkan Cecen, Nicholas A. Kotov. Biomimetic Solid-State Zn2 Electrolyte for Corrugated Structural Batteries. ACS Nano, 2019; DOI: 10.1021/acsnano.8b05068
Elon Musk’s Tesla Inc. arguably has one of the most affordable lines of electric vehicle, but that all could change as a Chinese company just unveiled what is now dubbed as the “World’s Cheapest Electric Car.”
Great Wall Motors, an automotive company based in Baoding, China, pulled the veil on its cheapest electric vehicle called the ORA R1, which is being marketed with a price of $8,680 according to the company, Express reported.
“As a new market entrant, ORA R1 delivers an unprecedented experience to drivers,” general manager of the Ora line and vice president of Great Wall Motors, Ning Shuyong, said in a statement.
“ORA replaces the traditional sales, service, spare parts and surveys (4S) dealership-centered model that is common in China with a network consisting of ORA Home, experience centers and smart outlets in the central business districts of Chinese cities.”
“In addition, the big data cloud that is created as the result of the information collected from the ORA app, the ORA shopping site and the Tmall e-shop opens the way to the development of multiple scenarios for offline sales and services as well as new transportation services for both drivers and passengers.”
Waking up the vehicle is as easy as a simple greeting of “Hello, ORA” thanks to its artificial intelligence system, Mashable said. Its body is also said to be made out of 60% high-strength steel.
The car will come with a three-year or 120,000 kilometer (74,564 mile) guarantee for the entire vehicle while its components have an eight-year (93,205 miles) guarantee. So far Great Wall Motor is only selling the ORA R1 in China, but they’ve shown interest in bringing the cheapest electric car to other countries as well, Electrek reported.
Images screenshot via YouTube / MOTOTREND