The Design of Future Nano-Electronic  Circuits – Free Flowing Electrons in Graphene 



Electrons flowing like liquid in graphene start a new wave of physics – University of Manchester 

A new understanding of the physics of conductive materials has been uncovered by scientists observing the unusual movement of electrons in graphene.

Graphene is many times more conductive than copper thanks, in part, to its two-dimensional structure. In most metals, conductivity is limited by crystal imperfections which cause electrons to frequently scatter like billiard balls when they move through the material.


Now, observations in experiments at the National Graphene Institute have provided essential understanding as to the peculiar behaviour of electron flows in graphene, which need to be considered in the design of future nanoelectronic circuits.

In some high-quality materials, like graphene, electrons can travel micron distances without scattering, improving the conductivity by orders of magnitude. This so-called ballistic regime, imposes the maximum possible conductance for any normal metal, which is defined by the Landauer-Buttiker formalism.

Appearing today in Nature Physics (“Superballistic flow of viscous electron fluid through graphene constrictions”), researchers at The University of Manchester, in collaboration with theoretical physicists led by Professor Marco Polini and Professor Leonid Levitov, show that Landauer’s fundamental limit can be breached in graphene. Even more fascinating is the mechanism responsible for this.

Last year, a new field in solid-state physics termed ‘electron hydrodynamics’ generated huge scientific interest. Three different experiments, including one performed by The University of Manchester, demonstrated that at certain temperatures, electrons collide with each other so frequently they start to flow collectively like a viscous fluid.

The new research demonstrates that this viscous fluid is even more conductive than ballistic electrons. 

The result is rather counter-intuitive, since typically scattering events act to lower the conductivity of a material, because they inhibit movement within the crystal. However, when electrons collide with each other, they start working together and ease current flow.

This happens because some electrons remain near the crystal edges, where momentum dissipation is highest, and move rather slowly. At the same time, they protect neighbouring electrons from colliding with those regions. Consequently, some electrons become super-ballistic as they are guided through the channel by their friends.

Sir Andre Geim said: “We know from school that additional disorder always creates extra electrical resistance. In our case, disorder induced by electron scattering actually reduces rather than increase resistance. This is unique and quite counterintuitive: Electrons when make up a liquid start propagating faster than if they were free, like in vacuum”.

The researchers measured the resistance of graphene constrictions, and found it decreases upon increasing temperature, in contrast to the usual metallic behaviour expected for doped graphene.

By studying how the resistance across the constrictions changes with temperature, the scientists revealed a new physical quantity which they called the viscous conductance. The measurements allowed them to determine electron viscosity to such a high precision that the extracted values showed remarkable quantitative agreement with theory.


Source: University of Manchester

Army COE Creates New Energy Efficient ‘Graphene Oxide’ Water Filter at Commercial Scale



The Army Corps of Engineers have successfully created a usable prototype of a new type of water filter.

The membranes are made of a mixture of chitosan, a material commonly found in shrimp shells, and a new synthetic chemical known as “graphene oxide”. Graphene oxide is a highly researched chemical worldwide.

  According to the Army Corps, one problem encountered by scientists working with graphene oxide is not being able to synthesize the material on a scale that can be put to use.

“One of the major breakthroughs that we’ve had here is that with our casting process, we’re not limited by size,” explains Luke Gurtowski, a research chemical engineer working on the membranes.


These filters have been found to effectively remove a number of different contaminants commonly found in water.

Dr. Christopher Griggs is the research scientist in charge of overseeing development of the new membranes.

Dr. Griggs told us, “Anybody who’s experienced water shortages or has been concerned about their water quality, or any type of contaminants in the water, this type of technology certainly works to address that.”

Another challenged faced by conventional water filtering methods is maintaining high energy efficiency.

“It requires a lot of energy for the net driving pressure to force the water through the membrane,” Dr. Griggs explains. “…we’re going to have to look to new materials to try to get those efficiency gains, and so graphene oxide is a very promising candidate for that.”

The Engineer Research and Development Center currently has two patents associated with the new filters and hopes to apply them for both civil and military purposes in the near future. 

Flexible Batteries Power the Future of Wearable Technology: U of Manchester


flexiblebattCredit: University of Manchester

The rapid development of wearable technology has received another boost from a new development using graphene for printed electronic devices.

New research from The University of Manchester has demonstrated flexible battery-like devices printed directly on to textiles using a simple screen-printing technique.

The current hurdle with wearable technology is how to power devices without the need for cumbersome battery packs. Devices known as supercapacitors are one way to achieve this. A  acts similarly to a battery but allows for rapid charging which can fully charge devices in seconds.

Now a solid-state flexible supercapacitor device has been demonstrated by using conductive -oxide ink to print onto cotton fabric. As reported in the journal 2-D Materials the printed electrodes exhibited excellent mechanical stability due to the strong interaction between the ink and textile substrate. Graphene-Ribbon-Developing-Flexible-Li-Ion-Battery

Further development of graphene-oxide printed supercapacitors could turn the vast potential of  into the norm. High-performance sportswear that monitors performance, embedded health-monitoring devices, lightweight military gear, new classes of  and even wearable computers are just some of the applications that could become available following further research and development.

To power these new wearable devices, the energy storage system must have reasonable mechanical flexibility in addition to high energy and power density, good operational safety, long cycling life and be low cost.

 Credit: University of Manchester

Dr Nazmul Karim, Knowledge Exchange Fellow, the National Graphene Institute and co-author of the paper said: “The development of graphene-based flexible textile supercapacitor using a simple and scalable printing technique is a significant step towards realising multifunctional next generation wearable e-textiles.”

“It will open up possibilities of making an environmental friendly and cost-effective smart e-textile that can store energy and monitor human activity and physiological condition at the same time”.

Graphene-oxide is a form of graphene which can be produced relatively cheaply in an ink-like solution. This solution can be applied to textiles to create supercapacitors which become part of the fabric itself.

Kaust wearablebattery1Dr Amor Abdelkader, also co-author of the paper said: “Textiles are some of the most flexible substrates, and for the first time, we printed a stable device that can store energy and be as flexible as cotton.

“The  is also washable, which makes it practically possible to use it for the future smart clothes. We believe this work will open the door for printing other types of devices on  using 2-D-materials inks.”

The University of Manchester is currently completing the construction of its second major graphene facility to complement the National Graphene Institute (NGI). Set to be completed 2018, the £60m Graphene Engineering Innovation Centre (GEIC) will be an international research and technology facility.

The GEIC will offer the UK the unique opportunity to establish a leading role in graphene and related two-dimensional materials. The GEIC will be primarily industry-led and focus on pilot production and characterisation.

 Explore further: Researchers develop simple way to fabricate micro-supercapacitors with high energy density

 

 

MIT team creates flexible, transparent solar cells with graphene electrodes



Researchers at the Massachusetts Institute of Technology (MIT) have developed flexible and transparent graphene-based solar cells, which can be mounted on various surfaces ranging from glass to plastic to paper and tape. The graphene devices exhibited optical transmittance of 61% across the whole visible regime and up to 69% at 550 nanometers. The power conversion efficiency of the graphene solar cells ranged from 2.8% to 4.1%.

MIT team’s flexible, transparent solar cell with graphene electrodes image

A common challenge in making transparent solar cells with graphene is getting the two electrodes to stick together and to the substrate, as well as ensuring that electrons only flow out of one of the graphene layers. Using heat or glue can damage the material and reduce its conductivity, so the MIT team developed a new technique to tackle this issue. Rather than applying an adhesive between the graphene and the substrate, they sprayed a thin layer of ethylene-vinyl acetate (EVA) over the top, sticking them together like tape instead of glue.

The MIT team compared their graphene electrode solar cells against others made from standard materials like aluminum and indium tin oxide (ITO), built on rigid glass and flexible substrates. The power conversion efficiency (PCE) of the graphene solar cells was far lower than regular solar panels, but much better than previous transparent solar cells. This is a positive advancement, obviously.
Samples of solar cells using electrodes of different materials for testing image


Efficiency is often a trade-off from the graphene solar cells being flexible and transparent. In that regard the cells performed well, transmitting almost 70% of the light in the middle of the human range of vision. Hopefully the numbers will continue to improve. According to the researchers’ calculations, the efficiency of these graphene solar cells could be pushed as high as 10% without losing any transparency, and doing just that is the next step in the project. The researchers are also working on ways to scale up the system to cover windows and walls.
Source:  newatlas

EV Batteries: A $240 Billion Industry In the Making that China is Taking the Lead


BYD 960x0

Even those who consider themselves somewhat knowledgeable about the electric vehicle (EV) industry would be hard pressed to name more than a handful of EV battery suppliers.

Most would quickly name Japan’s Panasonic and South Korea’s Samsung and LG Chem, as well as reference the Gigafactoy that Panasonic and Tesla opened this past January in Nevada. A few of the more knowledgeable would also name BYD, a leading electric vehicle manufacturer in China that is also one of the world’s largest battery suppliers.

Other than those names, however, and perhaps one or two other lesser known players, the list would end there.

 

Nearly everyone would be surprised to learn that there are now more than 140 EV battery manufacturers in China, busily building capacity in order to claim a share of what will become a $240 billion global industry within the next 20 years. As in all things auto, EVs and the batteries that will power them promise to be big industries in China.

A $240 billion industry

The math is simple. Respected auto analysts like those at Bernstein, a Wall Street research and securities firm, are predicting that EVs will account for as much as 40% of global vehicle purchases in 20 years. Since almost 100 million vehicles are produced and sold globally, that means that the annual market for EVs will be 40 million, even if the total global vehicle build does not increase between now and then.

Assuming that battery prices reach parity with the $6,000 cost of an internal combustion engine, a $240 billion battery industry is now in the making. Due to its well-publicized problems combatting air pollution, China will lead the way in EVs, as well as in batteries.

Read more: Why China Is Leading The World’s Boom In Electric Vehicles

In order to meet projected demand, battery cell manufacturing capacity globally will need to increase dramatically, which is why China’s battery makers are aggressively expanding. When Tesla and Panasonic announced in 2014 their plans to build a “Gigafactory” capable of producing 35 Gigawatt hours (GWh) of battery cells every year, that was big news. (A GWh is equal to one million kilowatt hours.) After all, the entire battery capacity in the world at the time was less than 50 GWh.

A great deal has changed over the last three years, though. Led by China, battery cell manufacturing capacity has more than doubled to 125 GWh, and is projected to double again to over 250 GWh by 2020. Even that will not be nearly enough. Total cell production capacity will need to increase tenfold from 2020 to 2037, the equivalent of adding 60 new Gigafactories, during that period.

 

Shifting towards China

Battery technology originated in Japan; was then further developed by companies in Korea; and is now shifting strongly toward China. China’s cell production already has a larger share of global production than Japan’s, and China’s global market share is projected to rise to more than 70% by 2020.

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This photo taken on May 22, 2017 shows a car passing new electric vehicles parked in a parking lot under a viaduct in Wuhan, central China’s Hubei province. (STR/AFP/Getty Images)

Rapid market growth for EVs in China, as well as the tendency for Chinese auto assemblers to use homegrown products, augurs well for China’s continued leadership in battery cell manufacturing. According to Roland Berger’s E-mobility Index Q2 2017 report, locally made lithium-ion cells are used in more than 90% of the EVs produced by Chinese manufacturers.

Read more: The Electric Car Market Has A ‘Chicken Or Egg’ Problem — And China Is Solving It

With so many Chinese companies hoping to enter the battery sweepstakes, China’s government is considering policies that will set minimum production capacities for battery manufacturers as a way to further strengthen its position as a global leader. Although not yet official, Beijing would like Chinese manufacturers to have a production volume of at least 3 to 5 GWh per year. Separately, Beijing released draft guidelines at the end of 2016 stipulating that battery manufacturers would need to have at least 8 GWh of production capacity in order to qualify for subsidies. As a signal to the market, the government is planning to back the development of only those battery companies with annual production capacities of 40 GWh or more.img_0160

Who the government is championing

While Panasonic is the world’s largest supplier of electric vehicle batteries globally, Chinese companies are catching up.

Based in Shenzhen, BYD — which stands for “Build Your Dream” — is a Hong Kong listed, Chinese car company that in 2016 produced almost 500,000 cars and buses, approximately 100,000 of which were EVs or plug-in hybrids. Consistent with BYD’s strategy of vertical integration, it also has 20 GWh of battery cell capacity and is China’s largest battery maker.

In 2008, a subsidiary of Warren Buffet’s Berkshire Hathaway invested $230 million in BYD, which at the time represented a 10% stake in the company. BYD is now valued in the marketplace at $16.9 billion.

Read more: China And The U.S. Supercharge The Growing Global Electric Vehicle Industry

CATL is another leading Chinese battery company. Founded in 2011 and headquartered in Ningde, Fujian province, CATL focuses on the production of lithium-ion batteries and the development of energy storage systems. With manufacturing bases in Qinghai, Jiangsu, and Guangdong provinces, CATL has 7.7 GWh of battery capacity and plans to have battery production capacity of 50 GWh by 2020. Like BYD, CATL is the type of company that the Chinese government wants to support and promote as a national champion.

Companies to watch

Other companies to watch are Tianjin based Lishen Battery and Hangzhou’s Wanxiang Group.

BYD 3960x0

State Grid Corp. of China (SGCC) battery packs sit on display in the showroom of Wanxiang Group Corp. in Hangzhou, China in September 2016. (Photographer: Qilai Shen/Bloomberg)

Lishen has production bases in Bejing, Qingdao, Suzhou, Wuhan, Ningbo, Shenzhen and Mianyang, and plans to have 20 GWh of battery cell capacity by 2020. And Wanxiang is one of China’s largest private companies and one of the country’s leading automotive components suppliers. In 1994, Wanxiang established a U.S. company in Elgin, Illinois. Since then, Wanxiang has made over two dozen acquisitions in the United States, including A123, a battery maker that had gone into bankruptcy, in 2013, and Fisker Automotive in 2014.

The flip side to the coming Electric Revolution, of course, is that for every battery pack that is put into a vehicle, one less internal combustion engine is needed. While the growth of EVs will give rise to a large global battery industry, it will also make obsolete the substantial investments that have been made in global engine and engine component capacity.

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Chasing the ‘Holey’ Grail of Batteries ~ Will Porous Graphene Provide the Next ‘Quantum Leap’?


Holy Grail Battery sk-2017_04_article_main_desktop

A porous form of graphene, the world’s thinnest and lightest nanomaterial, could help bring about the quantum leap in battery efficiency that’s needed to better harness renewable energy

The future, we’re told, will run on batteries. Fully electric vehicles will become the industry standard, running fast and far on a single charge. Our phone and laptop batteries will last for days and recharge in minutes. Our homes may even power themselves, storing energy from rooftop solar panels in lightweight and long-lasting battery packs.

One thing’s clear, though: If this battery-powered future is going to happen, we need a quantum leap in battery technology. Current lithium-ion batteries have hit a wall. For the past decade, researchers have been experimenting with new materials and novel designs to build batteries that are more powerful, last longer, and charge faster. energy_storage_2013 042216 _11-13-1 LARGE

This week, a team of researchers from the United States, China, and Saudi Arabia unveiled a new type of battery electrode made with “holey” graphene. In a paper published in Science, the researchers describe a porous form of graphene — the world’s thinnest and lightest nanomaterial — that overcomes some key challenges in creating next-generation batteries.

To understand how the porous graphene helps, first you need to know how today’s lithium-ion batteries work. Like all batteries, lithium-ion cells contain a positive electrode (cathode) and a negative electrode (anode) separated by a chemical medium called an electrolyte and a semi-permeable barrier called a separator.

RELATED: Fern-Like Sheets of Graphene Could Boost Solar Panel Efficiency

When the battery is charged, lithium ions flow to the anode, which is made of graphite. The lithium ions stick to the surface of the graphite and also bury themselves deep in its layers, which is how the energy is stored. When the battery goes to work powering a device, the ions flow from the anode to the cathode, passing through the separator at a steady rate. At the same time, electrons are released at the anode, flow out into the external circuit, and eventually return to the cathode.

To recap, there are two processes that make batteries work, the transport and storage of ions between electrodes, and the release of electrons into the external circuit. To build a battery that stores more energy and recharges faster, you need to optimize the flow of both ions and electrons.

That’s where nanomaterials come in.

Graphene Anodes 1 id35611Nanomaterials are named for their impossibly small dimensions, measured in nanometers (one millionth of a millimeter). A number of nanoscale materials have been explored as potential electrode materials that could promise far higher performance than today’s batteries. However, those extraordinary results have only been achieved in the lab using research devices with ultrathin electrodes, not the thicker electrodes required for real-world devices.

Graphene is a nanomaterial with some very unique properties. A single sheet of graphene is only one atom thick and consists of a 2D lattice of tightly bonded carbon atoms. Its structure makes it one of the best conductors of electricity on the planet. So if you incorporate graphene into a battery, you can greatly speed up the flow of electrons.

The problem with graphene is that while it’s terrific at moving electrons, it’s impenetrable to ions. If you tried to make an electrode purely out of graphene, the charge/discharge rate of the battery would be slowed by ions having to take detours around the broken edges of the graphene. That’s why researchers decided to punch holes straight through the graphene. Graphene Anodes 2images

Xiangfeng Duan from the UCLA, one of the authors of the Science paper, explained that the “holey” graphene is used as a conductive scaffold to speed the flow of electrons and direct the transport of ions with maximum efficiency. The graphene scaffold has a three-dimensional “hierarchical” structure with large holes feeding into smaller holes, ensuring that ions are funneled to every available nanometer of the electrode.

“It’s like a transportation network in a city,” said Duan. “You start with wide highways and then you move to narrow local roads to access every home. In the battery, the scaffold allows for the efficient transport of ions across a porous network to directly deliver charge to all of the electrode material.”

RELATED: Seaweed Could Provide a Powerful Boost to Next-Gen Batteries

In their experiments, Duan and his team placed the graphene as a conductive scaffold on niobia (Nb2O5) nanoparticles, a material known for its fast charge/discharge rate. Other labs have experimented with building electrodes solely from materials like niobia in super-thin sheets weighing almost nothing. But Duan said that the performance of the active material in such tiny amounts is canceled out by the bulkier inactive components of an electrode, like the current collectors. In other words, what works in the lab won’t cut it in real-world devices.

By loading the niobia on a graphene scaffold, Duan and his team achieved performance results that were several times greater than with a thin nanomaterial alone. Duan pointed out that the same porous scaffold design they used with niobia could be used with other active materials like silicon or tin oxide, which boast high energy density, the ability to store lots of ions for longer-lasting batteries.

It will still be a while before we see “holey” graphene batteries in real-world devices, said Duan, who calls this paper “a critical step, but just a starting point toward commercialization.” Looking ahead, he could easily see niobia-based batteries that charge up to five or 10 times faster than today’s lithium-ion cells. And batteries made with energy-dense materials like silicon could power laptops for 20 or 30 hours on a single charge, and triple the driving range of an electric vehicle.

“I think this really gives us a pathway toward using these high-performance materials in real-world devices,” Duan said.

U of Pennsylvania: Large Scale Production of Graphene + Graphene Updates and Videos


Graphene Mem 050815 3-anewapproach
Draw a line with a pencil and it’s likely that somewhere along that black smudge is a material that earned two scientists the 2010 Nobel Prize in Physics. The graphite of that pencil tip is simply multiple layers of carbon atoms; where those layers are only one atom thick, it is known as graphene.

The properties of a material change at the nanoscopic scale, making graphene the strongest and most conductive substance known. Instead of marking mini-golf scores on paper, this form of carbon is suited for making faster and smaller electronic circuitry, flexible touchscreens, chemical sensors, diagnostic devices, and applications yet to be imagined.

Graphene is not yet as ubiquitous as plastic or silicon, however, and producing the material in bulk remains a challenge. Because graphene’s properties rely on it being only one atom thick, until recently, it was only possible to make it in small patches or flakes.

Physicists at Penn have discovered a way around these limitations, and have spun out their research into a company called Graphene Frontiers. Graphene Frontiers

 


More About Graphene

Turning saltwater into clean drinking water is an expensive, energy-intensive process, but could the wonder material graphene make it more accessible?

New Discovery Could Unlock Graphene’s Full Potential – 


Read More:

3D GrapheneFollow this direct link to Seeker.com for more information and Videos about the ‘Wonder Material’ of Graphene.

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Graphene sieve turns seawater into drinking water

“Graphene-oxide membranes have attracted considerable attention as promising candidates for new filtration technologies. Now the much sought-after development of making membranes capable of sieving common salts has been achieved. New research demonstrates the real-world potential of providing clean drinking water for millions of people who struggle to access adequate clean water sources.
The new findings from a group of scientists at The University of Manchester were published today in the journal Nature Nanotechnology. Previously graphene-oxide membranes have shown exciting potential for gas separation and water filtration.”

Researchers develop blue-, yellow-, and red-emitting Graphene Quantum Dots


Graphene QD's China id47457_1

PL spectra of GQDs (a), PEI1800 GQDs (b), and PEI600 GQDs (c) at different excitation wavelengths. Inset: photograph of aqueous solution of these three GQDs under room light (left) and 365 nm UV irradiation lamp (right). UV-vis absorption spectra (d) of GQDs, PEI1800 GQDs, and PEI600 GQDs dispersed in water. (© ACS) 

Graphene quantum dots (GQDs) show great potential in the fields of photoelectronics, photovoltaics, biosensing, and bioimaging owing to their unique photoluminescence (PL) properties, including excellent biocompatibility, low toxicity, and high stability against photobleaching and photoblinking.

However, further development of GQDs is limited by their synthetic methodology and unclear PL mechanism. Therefore, it is urgent to find efficient and universal methods for the synthesis of GQDs with high stability, controllable surface properties, and tunable PL emission wavelength.In new work reported in ACS Applied Materials & Interfaces (“Red, Yellow, and Blue Luminescence by Graphene Quantum Dots: Syntheses, Mechanism, and Cellular Imaging”), researchers in China have synthesized PL-tunable GQDs with blue, yellow, and red emission colors by coating with polyethyleneimine (PEI) of different molecular weights.

photoluminescence spectra of graphene quantum dotsPL spectra of GQDs (a), PEI1800 GQDs (b), and PEI600 GQDs (c) at different excitation wavelengths. Inset: photograph of aqueous solution of these three GQDs under room light (left) and 365 nm UV irradiation lamp (right). UV-vis absorption spectra (d) of GQDs, PEI1800 GQDs, and PEI600 GQDs dispersed in water. (© ACS) (click on image to enlarge)

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(continued from above)

The team employed TEM, AFM, XRD, FTIR, XPS, DLS, and zeta potential to characterize the structures of the as-prepared GQDs and they stufied the PL mechanism by theoretical calculations.The average sizes of uncoated yellow-emitting GQDs, blue-emitting PEI1800 GQDs, and red-emitting PEI600 GQDs were 2.37, 6.05, and 57.31 nm, respectively. The yellow-emitting and blue-emitting GQDs were monolayer structures, whereas the red-emitting GQDs were multilayer structures. The red-emitting GQDs possessed a big PEI cage with multiple GQDs inside, whereas the blue-emitting PEI-coated GQDs had a single GQD core.The scientists found that carboxyl groups were changed to amide groups on the surface of GQDs and that this amidation reaction was crucial for PL change. By analyzing the molecular orbital and charge density, it was found that amide bonds decreased the conjugation and increased the energy gap thus inducing the blue shift of the PL.For the red-emitting GQDs, the conjugation area was enlarged by the interaction of GQDs in the PEI cage; thus, the PL peak exhibited a red shift.Remarkably, as the team points out, all GQDs exhibited good stability at high ionic strength and resisted photobleaching. Cell viability after treatment with the as-prepared GQDs indicated that GQDs had quite low cytotoxicity.”The GQDs could be used for bioimaging and are expected to be widely applied in multicolor imaging and bioanalysis applications,” the authors cocnlude their report. “We hope that this work will inspire the design of even better GQDs with tunable PL properties.”

Primary Story Contributed by Micheal Berger Nanowerk

MIT: Dialysis membrane made from Graphene filters more quickly


MIT Dialysis 170629131958_1_540x360
1) Graphene, grown on copper foil, is pressed against a supporting sheet of polycarbonate. 2) The polycarbonate acts to peel the graphene from the copper. 3) Using interfacial polymerization, researchers seal large tears and defects in graphene. 4) Next, they use oxygen plasma to etch pores of specific sizes in graphene.
Credit: Courtesy of the researchers (edited by MIT News)

Material can filter nanometer-sized molecules at 10 to 100 times the rate of commercial membranes

Source: Massachusetts Institute of Technology

Summary: A functional dialysis membrane has been fabricated from a sheet of graphene — a single layer of carbon atoms, linked end to end in hexagonal configuration like that of chicken wire. The graphene membrane, about the size of a fingernail, is less than 1 nanometer thick.

Dialysis, in the most general sense, is the process by which molecules filter out of one solution, by diffusing through a membrane, into a more dilute solution. Outside of hemodialysis, which removes waste from blood, scientists use dialysis to purify drugs, remove residue from chemical solutions, and isolate molecules for medical diagnosis, typically by allowing the materials to pass through a porous membrane.

Today’s commercial dialysis membranes separate molecules slowly, in part due to their makeup: They are relatively thick, and the pores that tunnel through such dense membranes do so in winding paths, making it difficult for target molecules to quickly pass through.

Now MIT engineers have fabricated a functional dialysis membrane from a sheet of graphene — a single layer of carbon atoms, linked end to end in hexagonal configuration like that of chicken wire. The graphene membrane, about the size of a fingernail, is less than 1 nanometer thick. (The thinnest existing membranes are about 20 nanometers thick.) The team’s membrane is able to filter out nanometer-sized molecules from aqueous solutions up to 10 times faster than state-of-the-art membranes, with the graphene itself being up to 100 times faster.

While graphene has largely been explored for applications in electronics, Piran Kidambi, a postdoc in MIT’s Department of Mechanical Engineering, says the team’s findings demonstrate that graphene may improve membrane technology, particularly for lab-scale separation processes and potentially for hemodialysis.

MIT Dialysis 170629131958_1_540x360“Because graphene is so thin, diffusion across it will be extremely fast,” Kidambi says. “A molecule doesn’t have to do this tedious job of going through all these tortuous pores in a thick membrane before exiting the other side. Moving graphene into this regime of biological separation is very exciting.”

Kidambi is a lead author of a study reporting the technology, published in Advanced Materials. Six co-authors are from MIT, including Rohit Karnik, associate professor of mechanical engineering, and Jing Kong, associate professor of electrical engineering.

Plugging graphene

To make the graphene membrane, the researchers first used a common technique called chemical vapor deposition to grow graphene on copper foil. They then carefully etched away the copper and transferred the graphene to a supporting sheet of polycarbonate, studded throughout with pores large enough to let through any molecules that have passed through the graphene. The polycarbonate acts as a scaffold, keeping the ultrathin graphene from curling up on itself.

The researchers looked to turn graphene into a molecularly selective sieve, letting through only molecules of a certain size. To do so, they created tiny pores in the material by exposing the structure to oxygen plasma, a process by which oxygen, pumped into a plasma chamber, can etch away at materials.

“By tuning the oxygen plasma conditions, we can control the density and size of pores we make, in the areas where the graphene is pristine,” Kidambi says. “What happens is, an oxygen radical comes to a carbon atom [in graphene] and rapidly reacts, and they both fly out as carbon dioxide.”

What is left is a tiny hole in the graphene, where a carbon atom once sat. Kidambi and his colleagues found that the longer graphene is exposed to oxygen plasma, the larger and more dense the pores will be. Relatively short exposure times, of about 45 to 60 seconds, generate very small pores.

Desirable defects

The researchers tested multiple graphene membranes with pores of varying sizes and distributions, placing each membrane in the middle of a diffusion chamber. They filled the chamber’s feed side with a solution containing various mixtures of molecules of different sizes, ranging from potassium chloride (0.66 nanometers wide) to vitamin B12 (1 to 1.5 nanometers) and lysozyme (4 nanometers), a protein found in egg white. The other side of the chamber was filled with a dilute solution.

The team then measured the flow of molecules as they diffused through each graphene membrane.

Membranes with very small pores let through potassium chloride but not larger molecules such as L-tryptophan, which measures only 0.2 nanometers wider. Membranes with larger pores let through correspondingly larger molecules.

The team carried out similar experiments with commercial dialysis membranes and found that, in comparison, the graphene membranes performed with higher “permeance,” filtering out the desired molecules up to 10 times faster.

Kidambi points out that the polycarbonate support is etched with pores that only take up 10 percent of its surface area, which limits the amount of desired molecules that ultimately pass through both layers.

“Only 10 percent of the membrane’s area is accessible, but even with that 10 percent, we’re able to do better than state-of-the-art,” Kidambi says.

To make the graphene membrane even better, the team plans to improve the polycarbonate support by etching more pores into the material to increase the membrane’s overall permeance. They are also working to further scale up the dimensions of the membrane, which currently measures 1 square centimeter. Further tuning the oxygen plasma process to create tailored pores will also improve a membrane’s performance — something that Kidambi points out would have vastly different consequences for graphene in electronics applications.

“What’s exciting is, what’s not great for the electronics field is actually perfect in this [membrane dialysis] field,” Kidambi says. “In electronics, you want to minimize defects. Here you want to make defects of the right size. It goes to show the end use of the technology dictates what you want in the technology. That’s the key.”


Story Source:

Materials provided by Massachusetts Institute of Technology. Original written by Jennifer Chu. Note: Content may be edited for style and length.


Journal Reference:

  1. Piran R. Kidambi, Doojoon Jang, Juan-Carlos Idrobo, Michael S. H. Boutilier, Luda Wang, Jing Kong, Rohit Karnik. Nanoporous Atomically Thin Graphene Membranes for Desalting and Dialysis ApplicationsAdvanced Materials, 2017; 1700277 DOI: 10.1002/adma.201700277

Graphene Oxide Membrane (Sieve) Turns Seawater into Drinking Water: University of Manchester


Graphene Seives 58e264acaef12

Newsfacts:

New research shows graphene can filter common salts from water to make it safe to drink Findings could lead to affordable desalination technology

 Graphene membrane

Graphene-oxide membranes have attracted considerable attention as promising candidates for new filtration technologies. Now the much sought-after development of making membranes capable of sieving common salts has been achieved.

New research demonstrates the real-world potential of providing clean drinking water for millions of people who struggle to access adequate clean water sources.
The new findings from a group of scientists at The University of Manchester were published today in the journal Nature Nanotechnology.
Previously graphene-oxide membranes have shown exciting potential for gas separation and water filtration.

Graphene-oxide membranes developed at the National Graphene Institute have already demonstrated the potential of filtering out small nanoparticles, organic molecules, and even large salts. Until now, however, they couldn’t be used for sieving common salts used in desalination technologies, which require even smaller sieves.

Previous research at The University of Manchester found that if immersed in water, graphene-oxide membranes become slightly swollen and smaller salts flow through the membrane along with water, but larger ions or molecules are blocked.

The Manchester-based group have now further developed these graphene membranes and found a strategy to avoid the swelling of the membrane when exposed to water.
The pore size in the membrane can be precisely controlled which can sieve common salts out of salty water and make it safe to drink.
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.

Professor Rahul Raveendran Nair

As the effects of climate change continue to reduce modern city’s water supplies, wealthy modern countries are also investing in desalination technologies. Following the severe floods in California major wealthy cities are also looking increasingly to alternative water solutions.

When the common salts are dissolved in water, they always form a ‘shell’ of water molecules around the salts molecules. This allows the tiny capillaries of the graphene-oxide membranes to block the salt from flowing along with the water. Water molecules are able to pass through the membrane barrier and flow anomalously fast which is ideal for application of these membranes for desalination.

Professor Rahul Nair, at The University of Manchester said: “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.

“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.”

Mr. Jijo Abraham and Dr. Vasu Siddeswara Kalangi were the joint-lead authors on the research paper: “The developed membranes are not only useful for desalination, but the atomic scale tunability of the pore size also opens new opportunity to fabricate membranes with on-demand filtration capable of filtering out ions according to their sizes.” said Mr. Abraham.

By 2025 the UN expects that 14% of the world’s population will encounter water scarcity. This technology has the potential to revolutionise water filtration across the world, in particular in countries which cannot afford large scale desalination plants.

It is hoped that graphene-oxide membrane systems can be built on smaller scales making this technology accessible to countries which do not have the financial infrastructure to fund large plants without compromising the yield of fresh water produced.

Advanced materials

A UK-based team of researchers has created a graphene-based sieve capable of removing salt from seawater.
The sought-after development could aid the millions of people without ready access to clean drinking water. The promising graphene oxide sieve could be highly efficient at filtering salts, and will now be tested against existing desalination membranes.
It has previously been difficult to manufacture graphene-based barriers on an industrial scale. Reporting their results in the journal Nature Nanotechnology, scientists from the University of Manchester, led by Dr Rahul Nair, shows how they solved some of the challenges by using a chemical derivative called graphene oxide.
Advanced materials is one of The University of Manchester’s research beacons – examples of pioneering discoveries, interdisciplinary collaboration and cross-sector partnerships that are tackling some of the biggest questions facing the planet. #ResearchBeacons