31 Jul 2015
Many human-made pollutants in the environment resist degradation through natural processes, and disrupt hormonal and other systems in mammals and other animals. Removing these toxic materials — which include pesticides and endocrine disruptors such as bisphenol A (BPA) — with existing methods is often expensive and time-consuming.
In a new paper published this week in Nature Communications, researchers from MIT and the Federal University of Goiás in Brazil demonstrate a novel method for using nanoparticles and ultraviolet (UV) light to quickly isolate and extract a variety of contaminants from soil and water.
Ferdinand Brandl and Nicolas Bertrand, the two lead authors, are former postdocs in the laboratory of Robert Langer, the David H. Koch Institute Professor at MIT’s Koch Institute for Integrative Cancer Research. (Eliana Martins Lima, of the Federal University of Goiás, is the other co-author.) Both Brandl and Bertrand are trained as pharmacists, and describe their discovery as a happy accident: They initially sought to develop nanoparticles that could be used to deliver drugs to cancer cells.
Image: Nicolas Bertrand
Brandl had previously synthesized polymers that could be cleaved apart by exposure to UV light. But he and Bertrand came to question their suitability for drug delivery, since UV light can be damaging to tissue and cells, and doesn’t penetrate through the skin. When they learned that UV light was used to disinfect water in certain treatment plants, they began to ask a different question.
“We thought if they are already using UV light, maybe they could use our particles as well,” Brandl says. “Then we came up with the idea to use our particles to remove toxic chemicals, pollutants, or hormones from water, because we saw that the particles aggregate once you irradiate them with UV light.”
A trap for ‘water-fearing’ pollution
The researchers synthesized polymers from polyethylene glycol, a widely used compound found in laxatives, toothpaste, and eye drops and approved by the Food and Drug Administration as a food additive, and polylactic acid, a biodegradable plastic used in compostable cups and glassware.
Nanoparticles made from these polymers have a hydrophobic core and a hydrophilic shell. Due to molecular-scale forces, in a solution hydrophobic pollutant molecules move toward the hydrophobic nanoparticles, and adsorb onto their surface, where they effectively become “trapped.” This same phenomenon is at work when spaghetti sauce stains the surface of plastic containers, turning them red: In that case, both the plastic and the oil-based sauce are hydrophobic and interact together.
If left alone, these nanomaterials would remain suspended and dispersed evenly in water. But when exposed to UV light, the stabilizing outer shell of the particles is shed, and — now “enriched” by the pollutants — they form larger aggregates that can then be removed through filtration, sedimentation, or other methods.
The researchers used the method to extract phthalates, hormone-disrupting chemicals used to soften plastics, from wastewater; BPA, another endocrine-disrupting synthetic compound widely used in plastic bottles and other resinous consumer goods, from thermal printing paper samples; and polycyclic aromatic hydrocarbons, carcinogenic compounds formed from incomplete combustion of fuels, from contaminated soil.
The process is irreversible and the polymers are biodegradable, minimizing the risks of leaving toxic secondary products to persist in, say, a body of water. “Once they switch to this macro situation where they’re big clumps,” Bertrand says, “you won’t be able to bring them back to the nano state again.”
The fundamental breakthrough, according to the researchers, was confirming that small molecules do indeed adsorb passively onto the surface of nanoparticles.
“To the best of our knowledge, it is the first time that the interactions of small molecules with pre-formed nanoparticles can be directly measured,” they write in Nature Communications.
Even more exciting, they say, is the wide range of potential uses, from environmental remediation to medical analysis.
The polymers are synthesized at room temperature, and don’t need to be specially prepared to target specific compounds; they are broadly applicable to all kinds of hydrophobic chemicals and molecules.
“The interactions we exploit to remove the pollutants are non-specific,” Brandl says. “We can remove hormones, BPA, and pesticides that are all present in the same sample, and we can do this in one step.”
And the nanoparticles’ high surface-area-to-volume ratio means that only a small amount is needed to remove a relatively large quantity of pollutants. The technique could thus offer potential for the cost-effective cleanup of contaminated water and soil on a wider scale.
“From the applied perspective, we showed in a system that the adsorption of small molecules on the surface of the nanoparticles can be used for extraction of any kind,” Bertrand says. “It opens the door for many other applications down the line.”
This approach could possibly be further developed, he speculates, to replace the widespread use of organic solvents for everything from decaffeinating coffee to making paint thinners. Bertrand cites DDT, banned for use as a pesticide in the U.S. since 1972 but still widely used in other parts of the world, as another example of a persistent pollutant that could potentially be remediated using these nanomaterials. “And for analytical applications where you don’t need as much volume to purify or concentrate, this might be interesting,” Bertrand says, offering the example of a cheap testing kit for urine analysis of medical patients.
The study also suggests the broader potential for adapting nanoscale drug-delivery techniques developed for use in environmental remediation.
“That we can apply some of the highly sophisticated, high-precision tools developed for the pharmaceutical industry, and now look at the use of these technologies in broader terms, is phenomenal,” says Frank Gu, an assistant professor of chemical engineering at the University of Waterloo in Canada, and an expert in nanoengineering for health care and medical applications.
“When you think about field deployment, that’s far down the road, but this paper offers a really exciting opportunity to crack a problem that is persistently present,” says Gu, who was not involved in the research. “If you take the normal conventional civil engineering or chemical engineering approach to treating it, it just won’t touch it. That’s where the most exciting part is.”
26 Mar 2015
To evaluate the prospects for sustaining such growth, the MIT researchers look at possible constraints on materials availability, and propose a system for evaluating the many competing approaches to improved solar-cell performance.
In a broad new assessment of the status and prospects of solar photovoltaic technology, Massachusetts Institute of Technology (MIT) researchers say that it is “one of the few renewable, low-carbon resources with both the scalability and the technological maturity to meet ever-growing global demand for electricity.”
The analysis is presented in Energy & Environmental Science; a broader analysis of solar technology, economics and policy will be incorporated in a forthcoming assessment of the future of solar energy by the MIT Energy Initiative.
The team comprised MIT professors Vladimir Bulović, Tonio Buonassisi and Robert Jaffe, and graduate students Joel Jean and Patrick Brown. One useful factor in making meaningful comparisons among new photovoltaic technologies, they conclude, is the complexity of the light-absorbing material.
The report divides the many technologies under development into three broad classes: wafer-based cells, which include traditional crystalline silicon, as well as alternatives such as gallium arsenide; commercial thin-film cells, including cadmium telluride and amorphous silicon; and emerging thin-film technologies, which include perovskites, organic materials, dye-sensitized solar cells and quantum dots.
Illustration shows the MIT team’s proposed scheme for comparing different photovoltaic materials, based on the complexity of their basic molecular structure. The complexity increases from the simplest material, pure silicon (single atom, lower left), to the most complex material currently being studied for potential solar cells, quantum dots (molecular structure at top right). Materials shown in between include gallium aresenide, perovskite and dye-sensitized solar cells. Image courtesy of the researchers.
With the recent evolution of solar technology, says Jean, the paper’s lead author, it’s important to have a uniform framework for assessment. It may be time, he says, to re-examine the traditional classification of these technologies, generally into three areas: silicon wafer-based cells, thin-film cells and “exotic” technologies with high theoretical efficiencies.
“We’d like to build on the conventional framework,” says Jean, a doctoral student in MIT’s Dept. of Electrical Engineering and Computer Science. “We’re seeking a more consistent way to think about the wide range of current photovoltaic technologies and to evaluate them for potential applications. In this study, we chose to evaluate all relevant technologies based on their material complexity.”
Under this scheme, traditional silicon—a single-element crystalline material—is the simplest material. While crystalline silicon is a mature technology with advantages including high efficiency, proven reliability and no material scarcity constraints, it also has inherent limitations: Silicon is not especially efficient at absorbing light, and solar panels based on silicon cells tend to be rigid and heavy. At the other end of the spectrum are perovskites, organics and colloidal quantum dots, which are “highly complex materials, but can be much simpler to process,” Jean says.
The authors make clear that their definition of material complexity as a key parameter for comparison does not imply any equivalency with complexity of manufacturing. On the contrary, while silicon is the simplest solar-cell material, silicon wafer and cell production is complex and expensive, requiring extraordinary purity and high temperatures.
By contrast, while some complex nanomaterials involve intricate molecular structures, such materials can be deposited quickly and at low temperatures onto flexible substrates. Nanomaterial-based cells could even be transparent to visible light, which could open up new applications and enable seamless integration into windows and other surfaces. The authors caution, however, that the conversion efficiency and long-term stability of these complex emerging technologies is still relatively low. As they write in the paper: “The road to broad acceptance of these new technologies in conventional solar markets is inevitably long, although the unique qualities of these evolving solar technologies—lightweight, paper-thin, transparent—could open entirely new markets, accelerating their adoption.”
The study does caution that the large-scale deployment of some of today’s thin-film technologies, such as cadmium telluride and copper indium gallium diselenide, may be severely constrained by the amount of rare materials that they require. The study highlights the need for novel thin-film technologies that are based on Earth-abundant materials.
The study identifies three themes for future research and development. The first is increasing the power-conversion efficiency of emerging photovoltaic technologies and commercial modules.
A second research theme is reducing the amount of material needed per cell. Thinner, more flexible films and substrates could reduce cell weight and cost, potentially opening the door to new approaches to photovoltaic module design.
A third important research theme is reducing the complexity and cost of manufacturing. Here the researchers emphasize the importance of eliminating expensive, high-temperature processing, and encouraging the adoption of roll-to-roll coating processes for rapid, large-scale manufacturing of emerging thin-film technologies.
“We’ve looked at a number of key metrics for different applications,” Jean says. “We don’t want to rule out any of the technologies,” he says—but by providing a unified framework for comparison, he says, the researchers hope to make it easier for people to make decisions about the best technologies for a given application.
Source: Massachusetts Institute of
*** Note to Readers: With the installation of this first article (from the Financial Times) we will begin a series of articles addressing not only California’s “Water Disaster”, but the impact the lack of access to Clean, Abundant, Affordable WATER is having on our world – PLANET EARTH.
More importantly, we will address how we believe Nanotechnology with its ‘cross disciplines’ across many Scientific Fields “holds the KEY” to solving the World’s Water Crisis. We believe that Nanotechnology and the need for water will also create commercial opportunities and the “Opportunity to Do Well … by Doing Good”. – Team GNT
Next Week: “Nanotechnology and Desalinization – “An Answer to World’s Thirst for Water?”
(Story from the Financial Times: By Pilita Clark)
With his military fatigues and the holstered gun at his hip, Lieutenant John Nores Jr. is a slightly unnerving sight as he slips through the woody foothills overlooking the southern edge of California’s Silicon Valley. But what the 45-year-old game warden has come to look at is more alarming.
Here in the late summer heat, not far from the sleek headquarters of technology giants Apple and Google, he leads the way to a carefully hidden patch of terraced ground pockmarked with hundreds of shallow holes that until very recently contained towering marijuana plants.
California pioneered laws allowing marijuana use for medical reasons. But it has yet to follow states such as Colorado that permit recreational use and, in any case, this crop was on public land, making it illegal and dangerous to eliminate – Lt. Nores has witnessed several shoot-outs over the past decade.
He estimates that each of the state’s 2,000-odd cartel pot farms contains an average of 5,000 plants, and that each one sucks up between eight and 11 gallons of water a day, depending on the time of year. That means at least 80m gallons of water – enough for more than 120 Olympic-size swimming pools – is probably being stolen daily in a state that in some parts is running dry as a three-year-old drought shrinks reservoirs, leaves fields fallow and dries wells to the point that some 1,300 people have had no tap water in their homes for months.
Jerry Brown, California’s governor, declared a state of emergency in January after the driest year on record in 2013, but as the annual wet season beckons, the prospect of a complete drought recovery this winter is highly unlikely, government officials say.
“Marijuana cultivation is the biggest drought-related crime we’re facing right now,” says Lt Nores as he pokes at a heap of plastic piping the growers used to divert water from a dried-up creek near the plantation.
But California’s drought is exposing a series of problems in the US’s most populous state that are a reminder of an adage popularized by Michael Kinsley, the columnist: the scandal is often not what is illegal but what is legal.
The theft of 80m gallons of water a day by heavily armed marijuana cartels is undoubtedly a serious concern, not least when the entire state is affected by drought and 58 per cent is categorized as being in “exceptional drought”, as defined by the government-funded US Drought Monitor.
However, this is a tiny fraction of the water used legally every day in a state that, like so many other parts of the world, has a swelling population driving rising competition for more heavily regulated supplies that have long been taken for granted and may face added risks as the climate changes.
California has always been a dry state. For almost six months of the year many of its citizens get little rain. There have been at least nine statewide droughts since 1900, not counting the latest one.
The state’s history is littered with water wars, among them the conflicts surrounding Los Angeles’s move to siphon off most of the Owens river last century that inspired the classic 1974 film, Chinatown . That dispute was over just one part of a vast system of canals and reservoirs built in the last 100-odd years that are the reason California is sometimes called the most hydro-logically altered landmass on the planet.
The system channels water from wetter to drier spots, using rivers and streams that in a normal year fill with melted snow from mountain ranges ringing the state, supplying about a third of California’s farms and cities.
The crisis is more severe because a decline in snowfall has compounded problems caused by the lack of rain. The state’s mountain snowpack was just 18 per cent of its average earlier this year, a situation scientists say could be repeated as the climate warms.
As a result eight major reservoirs were last week holding less than half their average storage for this time of year. Reservoir levels sank worryingly when a bad drought hit California in 1976-77, but there were fewer than 22m people in the state then, compared with 38.3m now.
There were also fewer laws such as those protecting creatures such as the endangered Delta smelt, a finger-sized fish that can be affected by the management of the canal system, prompting restrictions on pumping the water used by a farming sector that accounts for nearly 80 per cent of the state’s human water use. Those laws regularly inflame debate between conservationists and farmers during droughts – and are doing so again today.
The farmer’s story
“I farm in a very environmentally conscious manner, but these regulations have made it much worse for the farmers,” says Barat Bisabri, a citrus and almond farmer whose property lies in the Central Valley, one of the regions worst hit by the drought.
This flat, fertile strip runs south for about 450 miles from the northern reaches of the Sacramento Valley through the heart of the state and grows a lot of what America eats. Nearly half the fruit and nuts grown in the US come from California, including 80 per cent of the world’s almonds.
An investigation into how businesses are having to adapt to rising water costs around the world
Much of that produce comes from the Central Valley, where farming is carried out on an industrial scale. Crops and orchards grow up to the edge of people’s houses. Driving down the valley’s long, straight roads, it is striking to see an orchard of dead, brown trees next to another with puddles of water around healthy ones.
This may partly be a symptom of a century-old water rights system that critics say is so weak and archaic it makes it hard for regulators to tell whose supplies should be cut during a drought.
Mr. Bisabri’s grim predicament shows why one study estimates the drought will cost the state $2.2bn in 2014.
From the windows of the roomy farmhouse that overlooks row upon row of the property’s citrus trees, Mr Bisabri points to two of California’s main waterways, the Delta-Mendota Canal and the California Aqueduct. Both run straight through his farm but because of the drought, authorities have sharply limited the amount of water many users can take from them.
“Unfortunately we cannot get water from either of them this year,” says Mr Bisabri, as he explains how, a few weeks earlier, he used bulldozers to rip out 85 acres of healthy mandarin, orange and grapefruit trees that would have used so much water it would have made the rest of the crop far less valuable.
“I had to make a decision to kill some so the other ones could survive,” he says, as he drives to the bare patch where the trees once stood. “Had I not made that decision and kept all the citrus that we had, then I would have run out of water in the middle of August.” It is a dilemma facing farmers across the Central Valley, many of whom have shifted from crops such as tomatoes or peppers to more valuable almonds or other trees that cannot be left unwatered in a dry year.
Perennial crops such as nuts and grapes accounted for 32 per cent of the state’s irrigated crop acreage in 2010, up from 27 per cent in 1998. The shift has been even more marked in the southern Central Valley, so when drought hits, farmers face difficult choices.
A few miles down the road from his farm, Mr Bisabri stops at a jaw-dropping sight by an almond orchard of withered trees: a huge earthmoving machine is scooping up several at a time and feeding them into another machine that grinds them with an ear-splitting roar into great mounds of woodchip.
“That is exactly the same machine that we used on my farm,” he says.
Mr Bisabri has had to bring in water from other sources this year, but he says the price was almost $1.2m, 10 times what it was the previous year.
That does not include the $250,000 he spent on digging new wells to try to get supplies from the one source farmers and communities have always turned to in times of drought: groundwater.
In a normal year, aquifers supply about a third of the state’s water. In a drought, that can rise to as much as 60 per cent. But one of the most alarming aspects of this drought is that groundwater levels are plummeting.
“Water levels are dropping at an incredibly rapid rate in some places, like 100ft a year,” says Michelle Sneed, a hydrologist with the US Geological Survey who monitors groundwater in the Central Valley. “It is very extreme. Ordinarily, talking with hydrologists, if you would talk about a well dropping 10ft a year that would really get somebody’s attention, like wow! Really? Ten feet? And now we’re 10 times that.”
The depletion of this vital resource is not just a concern because it is so difficult to refill some aquifers when drought eventually subsides. It is also creating extraordinary rates of subsidence because as the groundwater disappears the land above it can sink. In one part of the valley, land has been subsiding by almost a foot a year, which Ms Sneed says is among the fastest rates anywhere in the world.
This is damaging the very canal system California built to reduce reliance on groundwater, she says, because these waterways depend on gravity for a steady flow and when parts of a canal start sinking it creates a depression that needs more water to fill it before flows can resume.
‘We ran out of water in June’
Two hours’ drive south from Mr. Bisabri’s farm, the town of East Porterville has more pressing groundwater worries. At least 1,300 people in the town rely for drinking and bathing water on wells that have gone dry as the drought has deepened.
“We ran out of water in June,” says Donna Johnson, a 72-year-old retired counsellor who delivers water to dozens of dry households from the back of her pick-up truck. Ms Johnson depends on a hose running to her home from a neighbor whose well is still working.
Until now, California has been notable among dry, western states for a pump-as-you-please approach to groundwater. A powerful agricultural lobby resisted repeated attempts at reform.
But the severity of this drought finally led to a package of measures signed into law in September requiring local agencies to monitor and manage wells, or face state intervention. Some critics say it is too little too late: many local agencies will have five to seven years to come up with plans, and until 2040 to implement them. Still, it is a lot better than nothing, say others.
“It’s a giant step for California,” says Robert Glennon, a law professor at the University of Arizona and the author of Unquenchable: America’s Water Crisis and What To Do About It . “You cannot manage what you don’t measure, full stop.”
The crisis may also encourage approval of another measure to be voted on in November allowing billions of dollars to be borrowed for new reservoirs and other steps to strengthen drought resilience.
None of this will help farmers such as Mr. Bisabri or the residents of East Porterville this year. Still, it is one more example of how the state often responds to a serious drought, says Jay Lund, a water expert at the University of California, Davis.
“Every drought brings a new innovation where we say, ‘Oh, here’s something we haven’t been doing that would really be helpful’,” says Prof Lund, pointing to irrigation systems, reservoirs and water markets rolled out after past dry spells.
“In this drought, it’s groundwater regulation so far,” he says. And will it eventually work? “It opens the door.”
That is small comfort when the latest outlook from the US Climate Prediction Center suggests the drought “will likely persist or intensify in large parts of the state” this winter.
“If there’s no water for people to live, and you don’t have the basic necessities of life, your population is going to leave,” says Andrew Lockman, the emergency services manager responsible for East Porterville. “Our primary economic driver is agriculture. If there’s no water to water crops, we’re not going to have any agriculture business, so you could see the economy of this area just decimated.”
Next Week: “Nanotechnology and Desalinization – “An Answer to World’s Thirst for Water?”
20 Aug 2014
IBM Researchers build solar concentrator that generates electricity and enough heat for desalination or cooling.
Researchers envision giant concentrators, built with low-cost materials, that produce electricity and heat for use in desalination or cooling. Credit: IBM Research.
Cooling a supercomputer can provide clues on how to make solar power cheap, says IBM.
IBM Research today detailed a prototype solar dish that uses a water-cooling technology it developed for its high-end computers (see “Hot Water Helps Super-Efficient Supercomputer Keep Its Cool”). The solar concentrator uses low-cost components and produces both electricity and heat, which could be used for desalination or to run an air conditioner.
The work, funded by $2.4 million grant from the Swiss Commission for Technology and Innovation, is being done by IBM Research, the Swiss company Airlight Energy, and Swiss researchers. Since this is outside IBM’s main business, it’s not clear how the technology would be commercialized. But the high-concentration photovoltaic thermal (HCPVT) system promises to be cost-effective, according to IBM, and the design offers some insights into how to use concentrating solar power for both heat and electricity.
Typically, parabolic dishes concentrate sunlight to produce heat, which can be transfered to another machine or used to drive a Stirling engine that makes electricity (see “Running a Marine Unit on Solar and Diesel”). With this device, IBM and its partners used a solar concentrator dish to shine light on a thin array of highly efficient triple-junction solar cells, which produce electricity from sunlight. By concentrating the light 2,000 times onto hundreds of one-centimeter-square cells, IBM projects, a full-scale concentrator could provide 25 kilowatts of power.
In this design, the engineers hope to both boost the output of the solar cells and make use of the heat produced by the concentrator. Borrowing its liquid-cooling technology for servers, IBM built a cooling system with pipes only a few microns off the photovoltaic cells to circulate water and carry away the heat. More than 50 percent of the waste heat is recovered. “Instead of just throwing away the heat, we’re using the waste heat for processes such as desalination or absorption cooling,” says Bruno Michel, manager, advanced thermal packaging at IBM Research.
Researchers expect they can keep the cost down with a tracking system made out of concrete rather than metal. Instead of mirrored glass on the concentrator dish, they plan to use metal foils. They project the cost to be 10 cents per kilowatt-hour in desert regions that have the appropriate sunlight, such as the Sahara in northern Africa.
One of the primary challenges of such a device, apart from keeping costs down and optimizing efficiency, is finding a suitable application. The combined power and thermal generator only makes sense in places where the waste heat can be used at least during part of the day. The researchers envision it could be used in sunny locations without adequate fresh water reserves or, potentially, in remote tourist resorts on islands. In those cases, the system would need to be easy to operate and reliable.
What is Nanotechnology?
A basic definition: Nanotechnology is the engineering of functional systems at the molecular scale. This covers both current work and concepts that are more advanced.
In its original sense, ‘nanotechnology’ refers to the projected ability to construct items from the bottom up, using techniques and tools being developed today to make complete, high performance products.
Nanotechnology (sometimes shortened to “nanotech”) is the manipulation of matter on an atomic and molecular scale. The earliest, widespread description of nanotechnology referred to the particular technological goal of precisely manipulating atoms and molecules for fabrication of macroscale products, also now referred to as molecular nanotechnology.
A more generalized description of nanotechnology was subsequently established by the National Nanotechnology Initiative, which defines nanotechnology as the manipulation of matter with at least one dimension sized from 1 to 100 nanometers. This definition reflects the fact that quantum mechanical effects are important at this quantum-realm scale, and so the definition shifted from a particular technological goal to a research category inclusive of all types of research and technologies that deal with the special properties of matter that occur below the given size threshold.
It is therefore common to see the plural form “nanotechnologies” as well as “nanoscale technologies” to refer to the broad range of research and applications whose common trait is size. Because of the variety of potential applications (including industrial and military), governments have invested billions of dollars in nanotechnology research.
Through its National Nanotechnology Initiative, the USA has invested 3.7 billion dollars. The European Union has invested 1.2 billion and Japan 750 million dollars
Houston, TX | Posted on July 10th, 2014
Rice University’s breakthrough silicon oxide technology for high-density, next-generation computer memory is one step closer to mass production, thanks to a refinement that will allow manufacturers to fabricate devices at room temperature with conventional production methods.
First discovered five years ago, Rice’s silicon oxide memories are a type of two-terminal, “resistive random-access memory” (RRAM) technology. In a new paper available online in the American Chemical Society journal Nano Letters, a Rice team led by chemist James Tour compared its RRAM technology to more than a dozen competing versions.
“This memory is superior to all other two-terminal unipolar resistive memories by almost every metric,” Tour said. “And because our devices use silicon oxide — the most studied material on Earth — the underlying physics are both well-understood and easy to implement in existing fabrication facilities.” Tour is Rice’s T.T. and W.F. Chao Chair in Chemistry and professor of mechanical engineering and nanoengineering and of computer science.
Tour and colleagues began work on their breakthrough RRAM technology more than five years ago. The basic concept behind resistive memory devices is the insertion of a dielectric material — one that won’t normally conduct electricity — between two wires. When a sufficiently high voltage is applied across the wires, a narrow conduction path can be formed through the dielectric material.
The presence or absence of these conduction pathways can be used to represent the binary 1s and 0s of digital data. Research with a number of dielectric materials over the past decade has shown that such conduction pathways can be formed, broken and reformed thousands of times, which means RRAM can be used as the basis of rewritable random-access memory.
RRAM is under development worldwide and expected to supplant flash memory technology in the marketplace within a few years because it is faster than flash and can pack far more information into less space. For example, manufacturers have announced plans for RRAM prototype chips that will be capable of storing about one terabyte of data on a device the size of a postage stamp — more than 50 times the data density of current flash memory technology.
The key ingredient of Rice’s RRAM is its dielectric component, silicon oxide. Silicon is the most abundant element on Earth and the basic ingredient in conventional microchips. Microelectronics fabrication technologies based on silicon are widespread and easily understood, but until the 2010 discovery of conductive filament pathways in silicon oxide in Tour’s lab, the material wasn’t considered an option for RRAM.
Since then, Tour’s team has raced to further develop its RRAM and even used it for exotic new devices like transparent flexible memory chips. At the same time, the researchers also conducted countless tests to compare the performance of silicon oxide memories with competing dielectric RRAM technologies.
“Our technology is the only one that satisfies every market requirement, both from a production and a performance standpoint, for nonvolatile memory,” Tour said. “It can be manufactured at room temperature, has an extremely low forming voltage, high on-off ratio, low power consumption, nine-bit capacity per cell, exceptional switching speeds and excellent cycling endurance.”
This scanning electron microscope image and schematic show the design and composition of new RRAM memory devices based on porous silicon oxide that were created at Rice University.
Credit: Tour Group/Rice University
In the latest study, a team headed by lead author and Rice postdoctoral researcher Gunuk Wang showed that using a porous version of silicon oxide could dramatically improve Rice’s RRAM in several ways. First, the porous material reduced the forming voltage — the power needed to form conduction pathways — to less than two volts, a 13-fold improvement over the team’s previous best and a number that stacks up against competing RRAM technologies. In addition, the porous silicon oxide also allowed Tour’s team to eliminate the need for a “device edge structure.”
“That means we can take a sheet of porous silicon oxide and just drop down electrodes without having to fabricate edges,” Tour said. “When we made our initial announcement about silicon oxide in 2010, one of the first questions I got from industry was whether we could do this without fabricating edges. At the time we could not, but the change to porous silicon oxide finally allows us to do that.”
Wang said, “We also demonstrated that the porous silicon oxide material increased the endurance cycles more than 100 times as compared with previous nonporous silicon oxide memories. Finally, the porous silicon oxide material has a capacity of up to nine bits per cell that is highest number among oxide-based memories, and the multiple capacity is unaffected by high temperatures.”
Tour said the latest developments with porous silicon oxide — reduced forming voltage, elimination of need for edge fabrication, excellent endurance cycling and multi-bit capacity — are extremely appealing to memory companies.
“This is a major accomplishment, and we’ve already been approached by companies interested in licensing this new technology,” he said.
Study co-authors — all from Rice — include postdoctoral researcher Yang Yang; research scientist Jae-Hwang Lee; graduate students Vera Abramova, Huilong Fei and Gedeng Ruan; and Edwin Thomas, the William and Stephanie Sick Dean of Rice’s George R. Brown School of Engineering, professor in mechanical engineering and materials science and in chemical and biomolecular engineering.
Despite the recently reported battery-flaming problem of lithium-ion batteries (LIBs) in Boeing’s 787 Dreamliners and laptops (in 2006), LIBs are now successfully being used in many sectors. Consumer gadgets, electric cars, medical devices, space and military sectors use LIBs as portable power sources and in the future, spacecraft like James Webb Space Telescope are expected to use LIBs.
The main reason for this rapid domination of LIB technology in various sectors is that it has the highest electrical storage capacity with respect to its weight (one unit of LIB can replace two nickel-hydrogen battery units). Also, LIBs are suitable for applications where both high energy density and power density are required, and in this respect, they are superior to other types of rechargeable batteries such as lead-acid, nickel-cadmium, nickel-metal hydride, nickel-metal batteries, etc.
However, LIBs are required to improve in the following aspects: (i) store more energy and deliver higher power for longer duration of time, (ii) get charged in shorter period of time, (iii) have a longer life-time and (iv) be resistant to fire hazards. Figure 1 depicts the basic LIB Characteristics required for different applications and the respective properties that need to be improved.
Basic LIB characteristics required for different applications 1,2 (DOD: Depth of Discharge, SOC: State of Charge). (click on image to enlarge)
At present, there is a great deal of interest to upgrade the existing LIBs with improved properties and arrive at a battery technology that would permit smart-storage of electric energy. Futuristic smart electric grids that can provide an uninterruptible power supply to a household for 24 hours can replace the currently used lead acid battery systems by performing better in terms of longer back up time and reduced space requirements.
With the advent of next generation LIBs, electric vehicles are expected to cover longer distances with shorter charging times; mobile phones and laptops are expected to be charged within minutes and last longer.
What Nanotechnology can do to Improve the Performance of LIBs Nanotechnology has the potential to deliver the next generation LIBs with improved performance, durability and safety at an acceptable cost. A typical LIB consists of three main components: an anode (generally made of graphite and other conductive additives), a cathode (generally, a layered transition metal oxide) and electrolyte through which lithium ions shuttles between the cathode and anode during charging and discharging cycles.
On electrodes: The electrodes of LIB, both anode and cathode are made of materials that have the ability to be easily intercalated with lithium ions. The electrodes also should have high electrical conductivity so that the LIB can have high charging rates. Faster intercalation of Li ions can be facilitated by using nanosized materials for electrodes, which offer high surface areas and short diffusion paths, and hence faster storage and delivery of energy. One prominent example is the cathode material of A123 LIBs that use nanosized lithium iron phosphate cathode. Researchers have been trying to increase the electrical conductivity of lithium iron phosphate by doping it with metals.
However, without the need for doping, the conductivity and hence the performance of the cathode material could be improved significantly by using nano-sized lithium iron phosphate. One dimensional vanadium oxide materials, LiCoO2 nanofibers, nanostructured spinels (LiMn2O4) and phosphor-olivines (LiFePO4), etc., are being explored as cathode materials for the next generation LIBs. Similarly, nanosizing the anode materials can make the anode to have short mass and charge pathways (i.e allow easier transport of both lithium ions and electrons) resulting in high reverse capacity and deliver at a faster rate.
Nanostructured materials like silicon nanowires, silicon thin films, carbon nanotubes, graphene, tin-filled carbon nanotubes, tin, germanium, etc., are currently being explored as anode materials for the next generation LIBs.
On electrolyte: Electrolytes in LIB conduct lithium ions to and fro between two electrodes. Using solid electrolytes could render high-energy battery chemistries and better safety (avoids fire hazards) when compared to the conventionally used liquid electrolytes. However, achieving the optimal combination of high lithium-ion conductivity and a broad electrochemical window is a challenge. Also, reduction of interfacial resistance between the solid electrolyte and lithium based anodes also poses a formidable challenge3.
Nanostructuring of solid electrolytes has proven to improve the lithium ion conductivity, for example, when the conventional bulk lithium thiophosphate electrolyte was made nanoporous, it could conduct lithium ions 1000 times faster4. Another example is the nanostructured polymer electrolyte (NPE), which ensures safety. Main advantage of using this benign electrolyte is that it allows the use of lithium metal as anodes (instead of carbon based anodes) and contribute to the increase of energy density of the battery5.
On improving the performance of LIBs: The performance of the LIB is typically measured by its power and energy stored per unit mass or unit volume. The power density of the LIBs can be increased but often at an expense of energy density5. In order to achieve high power density as well as energy density, researchers are using nanotechnology to design electrodes with high surface area and short diffusion paths for ionic transport.
The high surface area provides more sites for lithium ions to make contact allowing greater power density and faster discharging and recharging. Another important parameter known as rate capability, indicates the maximum current output the LIB can provide and it plays an important role in deciding life-cycle of the LIB. In general, higher the rate capability, greater is the power density and longer the cycle-life.
The demand for the LIBs with increased power/energy density (P/E) ratio is accompanied by the greater safety risk of the battery. Preferably, a P/E ratio of roughly 0.5 along with uncomplicated heat management is proposed for the next generation LIBs. In order to avoid fire hazards, heat generated during the charging and discharging of the battery should be dissipated quickly and non-combustible materials should be used in LIBs.
In case of the LIBs with lithium metal as anodes, the so-called dendrite problem (growth of microscopic fibers of lithium across the electrolyte that leads to short circuits and overheating) remains to be solved. Separators with nanoporous structures can prevent the spreading of dendtrites by acting as a mechanical barrier without hindering the ion-transport during charging and discharging cycles.
Recently, a nanoporous polymer-ceramic composite separator that could prevent the spreading of dendrites has been reported. This novel separator consist of a laminated nanoporous gamma alumina sheet (pore size of 100 nm) sandwiched between macroporous polymer membranes. The nanoporous alumina in this layered composite could effectively impede the proliferation of dendrites and prevent cell failure that are caused by short circuits13. Thermally stable electrolytes, for example, nanoarchitectured plastic crystal polymer electrolytes (N-PCPE) can facilitate the development of safe LIBs.
Owing to its nanoarchitectural structure, N-PCPE is flexible while maintaining high ionic conductance and thermal stability. This makes the material to perform well with high electrochemical stability even in a wrinkled state. As it suffers no internal short-circuit problems even under severely deformed state, N-PCPE can be used in place of currently used flammable carbonate-based liquid electrolytes and polyolefin separator membranes to improve the safety of the LIBs14. In another context, it can be said that nanotechnology, in a way helps to use thermally stable advanced new materials as electrodes.
For example, Li4Ti5O12 spinel, which is a state-of-the-art anode material for LIBs has excellent safety and structural stability during cycling, but suffer from low ionic and electronic conductivities (in bulk form) that hampers the wide-spread use of this material. By making anodes with nanosized Li4Ti5O12 spinel and Li4Ti5O12/carbon nanocomposites, the safety as well as the electrochemical performance of the battery can be improved15. Also, nano-enabled separators with improved stability and low shrinkage properties at high temperatures have proved to improve the safety aspects as well as the performance of the LIBs16.
Cambridge, MA | Posted on May 8th, 2014
MIT researchers have devised a novel cancer treatment that destroys tumor cells by first disarming their defenses, then hitting them with a lethal dose of DNA damage.
In studies with mice, the research team showed that this one-two punch, which relies on a nanoparticle that carries two drugs and releases them at different times, dramatically shrinks lung and breast tumors. The MIT team, led by Michael Yaffe, the David H. Koch Professor in Science, and Paula Hammond, the David H. Koch Professor in Engineering, describe the findings in the May 8 online edition of Science Signaling.
“I think it’s a harbinger of what nanomedicine can do for us in the future,” says Hammond, who is a member of MIT’s Koch Institute for Integrative Cancer Research. “We’re moving from the simplest model of the nanoparticle — just getting the drug in there and targeting it — to having smart nanoparticles that deliver drug combinations in the way that you need to really attack the tumor.”
Doctors routinely give cancer patients two or more different chemotherapy drugs in hopes that a multipronged attack will be more successful than a single drug. While many studies have identified drugs that work well together, a 2012 paper from Yaffe’s lab was the first to show that the timing of drug administration can dramatically influence the outcome.
In that study, Yaffe and former MIT postdoc Michael Lee found they could weaken cancer cells by administering the drug erlotinib, which shuts down one of the pathways that promote uncontrolled tumor growth. These pretreated tumor cells were much more susceptible to treatment with a DNA-damaging drug called doxorubicin than cells given the two drugs simultaneously.
“It’s like rewiring a circuit,” says Yaffe, who is also a member of the Koch Institute. “When you give the first drug, the wires’ connections get switched around so that the second drug works in a much more effective way.”
Erlotinib, which targets a protein called the epidermal growth factor (EGF) receptor, found on tumor cell surfaces, has been approved by the Food and Drug Administration to treat pancreatic cancer and some types of lung cancer. Doxorubicin is used to treat many cancers, including leukemia, lymphoma, and bladder, breast, lung, and ovarian tumors.
Staggering these drugs proved particularly powerful against a type of breast cancer cell known as triple-negative, which doesn’t have overactive estrogen, progesterone, or HER2 receptors. Triple-negative tumors, which account for about 16 percent of breast cancer cases, are much more aggressive than other types and tend to strike younger women.
That was an exciting finding, Yaffe says. “The problem was,” he adds, “how do you translate that into something you can actually give a cancer patient?”
From lab result to drug delivery
To approach this problem, Yaffe teamed up with Hammond, a chemical engineer who has previously designed several types of nanoparticles that can carry two drugs at once. For this project, Hammond and her graduate student, Stephen Morton, devised dozens of candidate particles. The most effective were a type of particle called liposomes — spherical droplets surrounded by a fatty outer shell.
The MIT team designed their liposomes to carry doxorubicin inside the particle’s core, with erlotinib embedded in the outer layer. The particles are coated with a polymer called PEG, which protects them from being broken down in the body or filtered out by the liver and kidneys. Another tag, folate, helps direct the particles to tumor cells, which express high quantities of folate receptors.
Once the particles reach a tumor and are taken up by cells, the particles start to break down. Erlotinib, carried in the outer shell, is released first, but doxorubicin release is delayed and takes more time to seep into cells, giving erlotinib time to weaken the cells’ defenses. “There’s a lag of somewhere between four and 24 hours between when erlotinib peaks in its effectiveness and the doxorubicin peaks in its effectiveness,” Yaffe says.
The researchers tested the particles in mice implanted with two types of human tumors: triple-negative breast tumors and non-small-cell lung tumors. Both types shrank significantly. Furthermore, packaging the two drugs in liposome nanoparticles made them much more effective than the traditional forms of the drugs, even when those drugs were given in a time-staggered order.
As a next step before possible clinical trials in human patients, the researchers are now testing the particles in mice that are genetically programmed to develop tumors on their own, instead of having human tumor cells implanted in them.
The researchers believe that time-staggered delivery could also improve other types of chemotherapy. They have devised several combinations involving cisplatin, a commonly used DNA-damaging drug, and are working on other combinations to treat prostate, head and neck, and ovarian cancers. At the same time, Hammond’s lab is working on more complex nanoparticles that would allow for more precise loading of the drugs and fine-tuning of their staggered release.
“With a nanoparticle delivery platform that allows us to control the relative rates of release and the relative amounts of loading, we can put these systems together in a smart way that allows them to be as effective as possible,” Hammond says.
Morton and Lee are the lead authors of the Science Signaling paper. Postdocs Zhou Deng, Erik Dreaden, and Kevin Shopsowitz, visiting student Elise Siouve, and graduate student Nisarg Shah also contributed to the research. The work was funded by the National Institutes of Health, the Center for Cancer Nanotechnology Excellence, and a Breast Cancer Alliance Exceptional Project Grant.
Written by Anne Trafton, MIT News Office
Copyright © Massachusetts Institute of Technology
Battery graphite demand could double in 6 years with no growth elsewhere US automotive giant, Tesla, has revealed plans to build a new $5bn lithium-ion battery (Li-ion battery) ‘gigafactory’ which could potentially increase natural graphite demand by up to 37% by 2020. The factory, which is forecast to start production by 2017, is expecting to have an output of 35 gWh/year by as early as 2020, which would over double the size of the current market.
In IM Dataor synthetic materials remains unclear. Nonetheless, expansion of the battery market for electric vehicles (EVs) on this scale presents a valuable opportunity to graphite suppliers.
Seizing an opportunity
In 2012, consumption from the battery sector constituted 8% of global natural graphite demand. For the natural graphite market to supply the type of market growth Tesla are forecasting, large flake graphite output will need to increase significantly over the coming years.
IM Data estimates that large flake grades (+80 mesh and larger) only made up just over 20% of total flake graphite output of 375,000 tonnes in 2013, and with competition for these grades from other traditional markets (i.e. the refractories sector), new projects are likely to be required to meet the battery market demand.
A number of junior projects are aiming to reach production over the coming 2-3 years, many boasting large flake reserves capable of supplying new hi-tech markets. With China’s large flake reserves depleting, and the efficiency of the country’s spherodization process under question, these projects have an opportunity to play a major role in supplying emerging markets. Tesla’s rapid EV expansion plans are, however, centered around lowering Li-ion battery costs by over 30% per kWh, which will allow the company to bring a more price competitive product to market.
Raw material costs are therefore likely to be under close scrutiny as the company gears up for production, meaning any potential graphite suppliers will have to be competitive not only with other producers but also alternative carbon anode companies. The FOB price of Chinese uncoated spherical graphite, 99.95% C, 15 microns stands at $3,400/tonne today, while prices of coated spherical graphite – the final material used in battery anodes – is valued at around three times this level.
From Ford to Tesla?
In 1913, Henry Ford introduced the use of an assembly line in the production of the Ford Model T motor car, which revolutionized the automobile industry and brought an affordable product to market in the US. Over a century on and Tesla’s plans to internalise its Li-ion battery production could prove just as pivotal in the emergence of the EV market, unlocking a lucrative new layer of demand for natural graphite producers.
Although the use of graphite in Li-ion battery technologies is not a new concept, the quantities used in more developed portable device markets, such as phones or tablets, are not substantial enough to be a major source of demand for flake graphite.
As much as 56kg of graphite is, however, used per EV, making the market an exciting new prospect for the graphite community which has fueled a wave of interest in recent years. While the market has failed to expand at the rate many had forecast –both the US and China have fallen short of government growth targets – EVs present the most feasible opportunity for graphite producers to diversify from traditional industrial markets.
If Tesla manages to meet its expansion plans over the coming six years, the company is likely to further the cause of not only the EV industry, but also the graphite market in its path.
Should Tesla choose to use spherical graphite sourced from natural flake as its raw material of choice, at capacity the plant will need substantial volumes.
Spherical graphite demand = 28,000 tpa
A new study from Los Alamos National Laboratory and the University of Milano-Bicocca demonstrates that superior light-emitting properties of quantum dots can be applied in solar energy, boosting the output of solar cells and allowing for the integration of photovoltaic-active architectural elements into buildings.
A house window that doubles as a solar panel could be on the horizon, thanks to recent quantum-dot work by Los Alamos National Laboratory researchers in collaboration with scientists from University of Milano-Bicocca (UNIMIB), Italy. Their project demonstrates that superior light-emitting properties of quantum dots can be applied in solar energy by helping more efficiently harvest sunlight.
This schematic shows how the quantum dots are embedded in the plastic matrix and capture sunlight to improve solar panel efficiency.
“The key accomplishment is the demonstration of large-area luminescent solar concentrators that use a new generation of specially engineered quantum dots,” said lead researcher Victor Klimov of the Center for Advanced Solar Photophysics (CASP) at Los Alamos.
Quantum dots are ultra-small bits of semiconductor matter that can be synthesized with nearly atomic precision via modern methods of colloidal chemistry. Their emission color can be tuned by simply varying their dimensions. Color tunability is combined with high emission efficiencies approaching 100 percent. These properties have recently become the basis of a new technology – quantum dot displays – employed, for example, in the newest generation of the Kindle Fire e-reader.
A luminescent solar concentrator (LSC) is a photon management device, representing a slab of transparent material that contains highly efficient emitters such as dye molecules or quantum dots. Sunlight absorbed in the slab is re-radiated at longer wavelengths and guided towards the slab edge equipped with a solar cell.
Klimov explained, “The LSC serves as a light-harvesting antenna which concentrates solar radiation collected from a large area onto a much smaller solar cell, and this increases its power output.”
“LSCs are especially attractive because in addition to gains in efficiency, they can enable new interesting concepts such as photovoltaic windows that can transform house facades into large-area energy generation units,” said Sergio Brovelli, who worked at Los Alamos until 2012 and is now a faculty member at UNIMIB.
Because of highly efficient, color-tunable emission and solution processability, quantum dots are attractive materials for use in inexpensive, large-area LSCs. One challenge, however, is an overlap between emission and absorption bands in the dots, which leads to significant light losses due to the dots re-absorbing some of the light they produce.
“Giant” but still tiny, engineered dots
To overcome this problem the Los Alamos and UNIMIB researchers have developed LSCs based on quantum dots with artificially induced large separation between emission and absorption bands (called a large Stokes shift).
These “Stokes-shift” engineered quantum dots represent cadmium selenide/cadmium sulfide (CdSe/CdS) structures in which light absorption is dominated by an ultra-thick outer shell of CdS, while emission occurs from the inner core of a narrower-gap CdSe. The separation of light-absorption and light-emission functions between the two different parts of the nanostructure results in a large spectral shift of emission with respect to absorption, which greatly reduces losses to re-absorption.
To implement this concept, Los Alamos researchers created a series of thick-shell (so-called “giant”) CdSe/CdS quantum dots, which were incorporated by their Italian partners into large slabs (sized in tens of centimeters) of polymethylmethacrylate (PMMA). While being large by quantum dot standards, the active particles are still tiny – only about hundred angstroms across. For comparison, a human hair is about 500,000 angstroms wide.
“A key to the success of this project was the use of a modified industrial method of cell-casting, we developed at UNIMIB Materials Science Department” said Francesco Meinardi, professor of Physics at UNIMIB.
Spectroscopic measurements indicated virtually no losses to re-absorption on distances of tens of centimeters. Further, tests using simulated solar radiation demonstrated high photon harvesting efficiencies of approximately 10% per absorbed photon achievable in nearly transparent samples, perfectly suited for utilization as photovoltaic windows.
Despite their high transparency, the fabricated structures showed significant enhancement of solar flux with the concentration factor of more than four. These exciting results indicate that “Stokes-shift-engineered” quantum dots represent a promising materials platform. It may enable the creation of solution processable large-area LSCs with independently tunable emission and absorption spectra.
Funding: The Center for Advanced Solar Photophyscis (CASP) is an Energy Frontier Research Center funded by the Office of Science of the US Department of Energy.
The work of the UNIMIB team was conducted within the UNIMIB Department of Materials Science and funded by Fondazione Cariplo (2012-0844) and the European Community’s Seventh Framework Programme (FP7/2007-2013; grant agreement no. 324603).
Publication: Francesco Meinardi, et al., “Large-area luminescent solar concentrators based on ‘Stokes-shift-engineered’ nanocrystals in a mass-polymerized PMMA matrix,” Nature Photonics (2014); doi:10.1038/nphoton.2014.54
Source: Los Alamos National Laboratory
Image: Los Alamos National Laboratory