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
By Michael Berger. Copyright © Nanowerk
(Nanowerk Spotlight) Within the field of nanofluidics, the manipulation of liquids typically deals with volumes of femtoliters (10-15 L). A femtoliter is one quadrillionth of a liter or 1 µm3. To put that in perspective: that is less than one percent of the volume of an average human cell.
Existing nanofluidic approaches to facilitate the manipulation of ultra-small amounts of liquids usually require their confinement within quasi-1D nanochannels or nanopores. In these devices, the movement of the liquid objects must follow pre-designed routes. Researchers have now demonstrated a new platform for digital nanofluidics where water nanodroplets are trapped between a mica surface and graphene.
Here, with the assistance of a graphene protection layer and ice-like lubricant monolayer, water nanodroplets can be moved, merged, separated, and patterned into regular arrays freely within a two-dimensional channel. “This is the first demonstration of manipulating individual water nanodroplets of such low volumes on surfaces,” Guangyu Zhang, a professor at the Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, in Beijing, tells Nanowerk. “While our strategy demonstrates the extension of the manipulation freedom from 1D to 2D, we were also able to move water nanodroplets one by one, which means this nanofluidic process is ‘digital’.”
The work, reported in the March 19, 2014 online edition of ACS Nano (“A Route toward Digital Manipulation of Water Nanodroplets on Surfaces”), also demonstrates the ability to manipulate water nanodroplets with a volume down to the yoctoliter scale (10-24 L). Such small amount of liquid is of great importance not only on study of fundamental physics or chemistry related to its size confinement effect but also for various functional applications.
Manipulation of water nanodroplets (WNs). (a) Schematic for the manipulation of a WN by an AFM tip. Inset shows the sandwich structure of graphene/WN/mica. (b and c) With a multistep translation, the disordered nanodroplets are rearranged into an ordered 3×3 array. The blue dotted arrow (the same below) represents the path of the tip we preset. (d and e) Two nanodroplets are moved to the same location and merged. (f) An ultrasmall nanodroplet with volume as small as 1.2 yoctoliter is separated from a big one in (e). Inset images of (c), (e), and (f) are the sketches for corresponding processes of the manipulation. (Reprinted with permission from American Chemical Society) (click image to enlarge)
Generally, water nanodroplets are hard to form stably on certain surfaces. They are likely to evaporate unless being frozen or under moisture. Thus it’s difficult to manipulate them. “Intrigued by the recent discovery of 2D ice formation between graphene and mica surface by James R. Health’s group at Caltech (“Graphene Visualizes the First Water Adlayers on Mica at Ambient Conditions”), we started to use this mica-water-graphene sandwich structure to realize the water nanodroplets manipulation,” Zhang explains the motivation for this work. Specifically, the researchers put water nanodroplets on a mica surface and covered them with graphene to stabilize them.
like 2D buffer layer formed between the water nanodroplets and the mica surface, acting as a lubricant for the droplets. This made them very mobile and allowed to move them around freely upon applying an external force. The researchers used an atomic force microscope (AFM) to facilitate this manipulation, including moving, merging and separating of these individual water nanodroplets. Zhang points out that the volume of the smallest manipulable water nanodroplet in their system is around yoctoliter scale, which is a more than 5 orders of magnitude improvement over the existing micro/nanofluidic manipulation limits.
Practically, the demonstrated nanofluidic platform provides a relatively simple solution for lab-on-a-chip applications on which one could carry out molecular analysis, chemical reactions, as well as microelectronic and bioengineering applications. “The inertia and impermeability of graphene makes it suitable for bearing many kinds of chemical solvent or biological molecules,” says Zhang. “And since the typical volume of liquid in our samples is ∼1-100×10-24 L, the synthesis and analysis processes could be low-cost, fast response and environmentally friendly.” Going forward, the team will extend the current, relatively simple platform to a more complex one with liquids other than water. They are also planning to carry out prototype demonstrations of certain functionalities of this platform.
Researchers have created a wearable device that is as thin as a temporary tattoo and can store and transmit data about a person’s movements, receive diagnostic information and release drugs into skin.
Similar efforts to develop ‘electronic skin’ abound, but the device is the first that can store information and also deliver medicine — combining patient treatment and monitoring. Its creators, who report their findings today in Nature Nanotechnology1, say that the technology could one day aid patients with movement disorders such as Parkinson’s disease or epilepsy.
The researchers constructed the device by layering a package of stretchable nanomaterials — sensors that detect temperature and motion, resistive RAM for data storage, microheaters and drugs — onto a material that mimics the softness and flexibility of the skin. The result was a sticky patch containing a device roughly 4 centimetres long, 2 cm wide and 0.003 millimetres thick, says study co-author Nanshu Lu, a mechanical engineer at the University of Texas in Austin.
“The novelty is really in the integration of the memory device,” says Stéphanie Lacour, an engineer at the Swiss Federal Institute of Technology in Lausanne, who was not involved in the work. No other device can store data locally, she adds.
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The trade-off for that memory milestone is that the device works only if it is connected to a power supply and data transmitter, both of which need to be made similarly compact and flexible before the prototype can be used routinely in patients. Although some commercially available components, such as lithium batteries and radio-frequency identification tags, can do this work, they are too rigid for the soft-as-skin brand of electronic device, Lu says.
Even if softer components were available, data transmitted wirelessly would need to be converted into a readable digital format, and the signal might need to be amplified. “It’s a pretty complicated system to integrate onto a piece of tattoo material,” she says. “It’s still pretty far away.”
Concern about the depletion of global water resources has grown rapidly in the past decade due to our increasing global population and growing demand for other diverse applications.
Since only 2.5% of the Earth’s water is fresh, it has been reported that almost half of the world’s population is at risk of a water crisis by the year 2025 . Accordingly, significant research efforts have been focused on the desalination of brackish/seawater and the remediation and reuse of wastewater to meet the agricultural, industrial, and domestic water demands. While much progress has been made, the advent of membrane desalination techniques over fifty years ago has given significant impetus to the advancement of water purification technology. However, the need for improved membrane performance and lower operating costs have been a barrier for both researchers and consumers alike. Current water treatment technology Water purification membranes are typically divided into four categories according to pore size:
- – microfiltration (MF, < few microns)
- – ultrafiltration (UF, < 100 nm)
- – nanofiltration (NF, < 10 nm)
- – reverse osmosis (RO, < 1 nm)
Feed water quality is an important consideration when selecting a suitable membrane. NF and RO membranes have typically been designed for use of brackish water (2-5 g/L of salt), seawater (35 g/L of salt), and waste water (from agriculture and industry) treatments due to their separation capacity of ions (mono-/di-valent) and organic materials (macromolecules, proteins, glucose, and amino acids) from the water.
Of the various candidate materials, conventional desalination membranes are mainly fabricated using aromatic polyamide (PA) thin film composites on a polysulfone support and Loeb-Sourirajan-type cellulose acetate (CA) membranes to create desired architecture.
CA membranes exhibit a specific water flux of 1-20 L/m2/day/bar with an average NaCl rejection of > 98%. The advantage of CA membranes is that they are easy-to-make, fairly well priced, and offer excellent stability against mechanical stress and chlorine. However, an inherent weakness of CA membranes is their performance decrease due to changes in pH, temperature, hydrolysis, and fouling.
PA membranes on the other hand exhibit a high flux (20-200 L/m2/day/bar) with a high salt rejection (> 99%) as well as increased stability against a wide range of pH and temperature. Unfortunately, despite having benefits, the extremely low resistance to chlorine and membrane fouling are construed as major obstacles for PA membranes. As a result, PA membranes are rendered uneconomical because of the high cost of pre-treatment steps prior to desalination membranes.
Most current desalination technologies on the market are based on energy-intensive processes such as multi-stage flash distillation (MSF; 35 kWh/m3) or a pressure-driven RO membranes (> 3 kWh/m3 for seawater and < 1 kWh/m3 for brackish water).
While membrane-based technology is more cost-effective than heat-based technology, the high cost for installation, operation, and maintenance are still major constraining factors for general use of membrane technologies in water treatment.
These costs (> 0.5 $/m3 for seawater and 0.2-0.3 $/m3 for brackish water ) are higher than the costs of obtaining fresh water from other sources. Furthermore, it has been predicted that current membrane technology is approaching the maximum performance achievable from CA and PA-based materials . Considering that water treatment costs are directly related to the membrane performance, there is an increasing demand for innovative solutions that move beyond the modification of conventional materials, in order to meet scientific and economic requirements.
Aquaporin-embedded biomimetic membrane At Ingenuity Lab in Edmonton, Alberta, Dr. Carlo Montemagno and a team of world-class researchers have been investigating plausible solutions to existing water purification challenges. They are building on Dr. Montemagno’s earlier patented discoveries by using a naturally-existing water channel protein as the functional unit in water purification membranes .
(click image to enlarge)
Aquaporins are water-transport proteins that play an important osmoregulation role in living organisms . These proteins boast exceptionally high water permeability (~ 1010 water molecules/s), high selectivity for pure water molecules, and a low energy cost, which make aquaporin-embedded membrane well suited as an alternative to conventional RO membranes. Unlike synthetic polymeric membranes, which are driven by the high pressure-induced diffusion of water through size selective pores, this technology utilizes the biological osmosis mechanism to control the flow of water in cellular systems at low energy.
In nature, the direction of osmotic water flow is determined by the osmotic pressure difference between compartments, i.e. water flows toward higher osmotic pressure compartment (salty solution or contaminated water). This direction can however be reversed by applying a pressure to the salty solution (i.e., RO).
The principle of RO is based on the semipermeable characteristics of the separating membrane, which allows the transport of only water molecules depending on the direction of osmotic gradient. Therefore, as envisioned in the recent publication
the core of Ingenuity Lab’s approach is to control the direction of water flow through aquaporin channels with a minimum level of pressure and to use aquaporin-embedded biomimetic membranes as an alternative to conventional RO membranes.
Ingenuity Lab’s ongoing research efforts Although introduced a decade ago, only recently has the proof-of-concept for aquaporin-based water purification membranes been demonstrated. Their ultimate success depends on improved membrane performance and membrane functionality which is affected by:
1) Activity of aquaporin in the membrane (rate of water transport)
2) Design concept of the protein-incorporated membrane matrix
3) Membrane manufacturability.
Since aquaporin-incorporated membranes are the key component to attaining higher levels of salt rejection and water flux, Ingenuity Lab has two intense research efforts underway.
The first is to improve the quality and properties of the materials used to produce aquaporin-based membranes. Both the production yield and the stability of the aquaporin is being improved through genetic modification. Additionally, new materials are being developed for use as the matrix to house the aquaporin molecules and form stable, biocompatible membranes that provide structural support for the protein and eliminate leakage around the protein. Efficient production of functional aquaporin and biomimetic materials with optimal protein compatibility guarantees the highest level of water purification capacity, which adds maximum economic benefits to the invention.
Ingenuity Lab’s second major research effort focuses on the development of new methods for assembling and fabricating water purification membranes using novel design concepts. The goal of this task is to develop a platform which protects aquaporin from mechanical and chemical stresses, while maintaining functionality, enabling low cost, scalable production.
The work being done at Ingenuity Lab holds great promise for our generation and those to come. Ingenuity Lab’s water purification membranes will be applied to treat wastewater and seawater at a much lower pressure than current membranes. The low-energy requirement and high water flow rate of aquaporins are essential components to the realization of cost-effective water purification membranes. In addition to enhanced energy efficiency, unconventional manufacturability-driven membrane design contributes to cost-competitiveness, setting the membranes apart from traditional, more expensive, desalination processes.
In a unique approach, Ingenuity Lab is applying technology and expertise from a variety of disciplines to actively solve some of the world’s most pressing environmental challenges; including here in Alberta, where this technology could be used to reduce the environmental impact of withdrawing bitumen from the oil sands. By reducing the environmental impact of oil sands mining it will allow us to continue to utilize this valuable resource for years to come.
References  Kulshreshtha, S. N. A global outlook for water resources to the year 2025. Water Resour. Manag. 1998, 12(3), 167-184.  Fritzmann, C.; Löwenberg, J.; Wintgens, T.; Melin T. State-of-the-art of reverse osmosis desalination. Desalination. 2007, 216, 1-76.  Elimelech, M.; Phillip, W.A. The future of seawater desalination: energy, technology, and the environment. Science. 2011, 333(6043), 712-717.  Montemagno, C.D.; Schmidt, J.J.; Tozzi, S.P. Biomimetic Membranes. U.S. Patent 7,208,089 B2, 24 April 2007.  Borgnia, M.; Nielsen, S.; Engel, A.; Agre, P. Cellular and molecular biology of the aquaporin water channels. Annu. Rev. Biochem. 1999, 68, 425–458.
Source: Ingenuity Lab
Read more: Novel water treatment technology surfaces at Ingenuity Lab http://www.nanowerk.com/spotlight/spotid=34964.php#ixzz2xB4hRpTp Follow us: @nanowerk on Twitter
22 Mar 2014
Presented at a meeting of the American Chemical Society. March 16, 2014
DALLAS, March 16, 2014 — Sunlight plus a common titanium pigment might be the secret recipe for ridding pharmaceuticals, pesticides and other potentially harmful pollutants from drinking water. Scientists combined several high-tech components to make an easy-to-use water purifier that could
work with the world’s most basic form of energy, sunlight, in a boon for water purification in rural areas or developing countries.
The talk was one of more than 10,000 presentations at the 247th National Meeting & Exposition of the American Chemical Society (ACS), the world’s largest scientific society, taking place here through Thursday.
Anne Morrissey, Ph.D., explained that the new technology could someday be incorporated into an easy-to-use consumer product that would remove these stubborn pollutants from drinking water as a final step after it has already been treated with conventional methods.
Her group at Dublin City University in Ireland started with a compound called titanium dioxide (TiO2), a powder used to whiten paints, paper, toothpaste, food and other products. With the right energy, TiO2 can also act as a catalyst — a molecule that encourages chemical reactions — breaking down unwanted compounds in drinking water like pesticides and pharmaceuticals. Morrissey explained that modifying current water treatment methods to get rid of these potentially harmful species can be costly and energy-intensive, and often, these modifications don’t completely eliminate the pollutants.
But Morrissey said TiO2 is usually only activated by ultraviolet light, which is produced by special bulbs. To access titanium dioxide’s properties with the sun’s light, Morrissey and her group experimented with different shapes of TiO2 that would better absorb visible light. She found that nanotubes about 1,000 times thinner than a human hair were best, but they couldn’t do it on their own.
That’s why she turned to graphene, a material made of sheets of carbon just one atom thick. “Graphene is the magic material, but its use for water treatment hasn’t been fully developed,” she said. “It has great potential.” Morrissey put the TiO2 nanotubes on these graphene sheets. Pollutants stuck to the surface of the graphene as they passed by, allowing TiO2 to get close enough to break them down.
Her research group successfully tested the system on diclofenac, an anti-inflammatory drug notorious for wiping out nearly an entire vulture population in India.
“We’re looking at using the graphene composite in a cartridge for one-step drinking water treatment,” said Morrissey. “You could just buy a cartridge off the shelf and plop it into the pipe where the drinking water comes into your house.” The cartridge system would also ensure that the graphene stays immobilized and does its job without contaminating the clean water.
Morrissey noted, however, that the technology will never be strong enough to completely clean drinking water on its own. Rather, she sees it as a polishing step after traditional water treatment processes to mop up the most insidious pollutants.
That could be especially useful in her home country, where she said many rural communities use small water treatment systems that only supply a few dozen homes. Because they don’t have the infrastructure that large-scale urban treatment plants do, she thinks that a cartridge that could clean with only the sun’s energy could help make their water safer.
Ultimately, Morrissey said there are still many questions to answer before declaring her TiO2-graphene system a success. One of the biggest is making sure that when it breaks down pollutants, it is producing harmless byproducts. She also wants to make sure that the energy required for the system compares favorably to simply using TiO2 with ultraviolet light. But so far, she reported, her design seems to be easier to make and dispose of than other visible-light activated TiO2 purifiers.
The authors wish to acknowledge the financial support of the Marie Curie Initial Training Network funded by the EC FP7 People Programme; ATWARM (Advanced Technologies for Water Resource Management); Tyndall National Institute, Ireland, for their support through the SFI-funded National Access Programme (NAP407); and the Environmental Protection Agency STRIVE program.
The American Chemical Society is a nonprofit organization chartered by the U.S. Congress. With more than 161,000 members, ACS is the world’s largest scientific society and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences. Its main offices are in Washington, D.C., and Columbus, Ohio.
20 Mar 2014
The Ni3S2/CNT nanocomposite can be easily synthesized using hydrothermal method.
The HER performance of Ni3S2/CNT nanocomposite is activated by base treatment.
The HER activity of nanocomposite is correlated to Ni3S2 morphology on CNTs.
Ni3S2 and conductive CNTs impart high HER activity and stability to the catalyst.
The composite electrode exhibits high catalytic activity toward glucose oxidation.
In this study, the nanocomposite of Ni3S2 and multi-walled carbon nanotubes (MWCNTs) with the high catalytic activities toward hydrogen evolution reaction (HER) and glucose oxidation was synthesized using glucose-assisted hydrothermal method. Ni3S2 nanoparticles with the diameters ranging from 10 to 80 nm were highly dispersed over conductive MWCNT surface.
A series of linear polarization measurements suggested that the HER activity of nanocomposite of Ni3S2 and MWCNTs was increased with decreasing the loading amount of Ni3S2 on MWCNTs and the optimal Ni3S2 loading on MWCNTs was 55 wt%. Furthermore, the immersion of the composite catalyst in a concentrated KOH solution induced the morphological change of the Ni3S2 nanoparticles on MWCNTs, which increases the active surface area of the composite electrode.
As a result, the KOH-treated composite electrode showed a higher HER activity than other electrodes. For example, the value of exchange current density of the KOH-treated composite electrode was ca. 395 times and 1.6 times larger than that of Ni3S2 electrode and as-synthesized composite, respectively. Furthermore, the impedance measurements showed the KOH-treated composite electrode had the smaller charge transfer resistance of the HER than Ni3S2 electrode.
Based on the slopes obtained from Arrhenius curves of the electrodes, the estimated HER activation energy (71.8 kJ/mol) of KOH-treated composite electrode was only one-third of that of the pure Ni3S2 electrode. The high catalytic activity of the KOH-treated composite electrode was stemmed from the synergistic effect of the large active surface area of Ni3S2 nanoparticles and the excellent electrical coupling to the conductive MWCNT network.
More importantly, the current density of KOH-treated composite electrode showed no sign of degradation after the continuous 1000 cycling in a 1 M KOH solution at the temperature of 323 K. On the other hand, the nanocomposite of Ni3S2 and MWCNTs was proposed for the first time as an enzyme-free sensor for glucose.
The Ni3S2 nanoparticles on MWCNTs exhibited high electrocatalytic activity toward glucose oxidation and were insensitive to uric acid and ascorbic acid. Furthermore, the composite electrode exhibited that its catalytic current was linearly dependent on the concentration of glucose in the range from 30 to 500 μM and its sensitivity was as high as 3345 μA/mM.
The present work suggested that the nanocomposite of Ni3S2 and MWCNTs not only served as an inexpensive, highly active and stable electrode material for alkaline water electrolysis, but also showed a great potential application as a highly sensitive and selective biosensor for glucose.
- Nickel sulfide;
- Carbon nanotubes;
- Hydrogen evolution
One of the most promising technologies for the treatment of various cancers is nanotechnology, creating drugs that directly attack the cancer cells without damaging other tissues’ development. The Laboratory of Cellular Oncology at the Research Unit in Cell Differentiation and Cancer, of the Faculty of Higher Studies (FES) Zaragoza UNAM (National Autonomous University of Mexico) developed a therapy to attack cervical cancer tumors.
According to the researcher Rosalva Rangel Corona, head of the project, the antitumor effect of interleukin in cervical cancer is because their cells express receptors for interleukin-2 that “fit together ” like puzzle pieces with the protein to activate an antitumor response .
The scientist explains that the nanoparticle works as a bridge of antitumor activation between tumor cells and T lymphocytes. The nanoparticle has interleukin 2 on its surface, so when the protein is around it acts as a switch, a contact with the cancer cell to bind to the receptor and to carry out its biological action.
Furthermore, the nanoparticle concentrates interleukin 2 in the tumor site, which allows its accumulation near the tumor growth. It is not circulating in the blood stream, is “out there” in action.
The administration of IL-2 using the nanovector reduces the side effects caused by this protein if administered in large amounts to the body. These effects can be fever, low blood pressure, fluid retention and attack to the central nervous system, among others.
It is known that interleukin -2 is a protein (a cytokine, a product of the cell) generated by active T cells. The nanoparticle, the vector for IL-2, carries the substance to the receptors in cancer cells, then saturates them and kills them, besides generating an immune T cells bridge (in charge of activating the immune response of the organism). This is like a guided missile acting within tumor cells and activating the immune system cells that kill them.
A woman immunosuppressed by disease produces even less interleukin. For this reason, the use of the nanoparticle would be very beneficial for female patients. The researcher emphasized that his group must meet the pharmaceutical regulations to carry their research beyond published studies and thus benefit the population.
Knowing this bouncing probability would give scientists an essential understanding of a variety of applications that involve water flow: the movement of water through soil, the formation of clouds and fog, and the efficiency of water-filtration devices.
This last application spurred Karnik and his colleagues — Jongho Lee, an MIT graduate student in mechanical engineering, and Tahar Laoui, a professor at the King Fahd University of Petroleum and Minerals (KFUPM) in Saudi Arabia — to study water’s probability of bouncing. The group is developing membranes for water desalination; this technology’s success depends, in part, on the ability of water vapor to flow through the membrane and condense on the other side as purified water.
By observing water transport through membranes with pores of various sizes, the group has measured a water molecule’s probability of condensing or bouncing off a liquid surface at the nanoscale. The results, published in Nature Nanotechnology, could help in designing more efficient desalination membranes, and may also expand scientists’ understanding of the flow of water at the nanoscale.
“Wherever you have a liquid-vapor surface, there is going to be evaporation and condensation,” Karnik says. “So this probability is pretty universal, as it defines what water molecules do at all such surfaces.”
Getting in the way of flow
One of the simplest ways to remove salt from water is by boiling and evaporating the water — separating it from salts, then condensing it as purified water. But this method is energy-intensive, requiring a great deal of heat.
Karnik’s group developed a desalination membrane that mimics the boiling process, but without the need for heat. The razor-thin membrane contains nanoscale pores that, seen from the side, resemble tiny tubes. Half of each tube is hydrophilic, or water-attracting, while the other half is hydrophobic, or water-repellant.
As water flows from the hydrophilic to the hydrophobic side, it turns from liquid to vapor at the liquid-vapor interface, simulating water’s transition during the boiling process. Vapor molecules that travel to the liquid solution on the other end of the nanopore can either condense into it or bounce off of it. The membrane allows higher water-flow rates if more molecules condense, rather than bounce.
Designing an efficient desalination membrane requires an understanding of what might keep water from flowing through it. In the case of the researchers’ membrane, they found that resistance to water flow came from two factors: the length of the nanopores in the membrane and the probability that a molecule would bounce, rather than condense.
In experiments with membranes whose nanopores varied in length, the team observed that greater pore length was the main factor impeding water flow — that is, the greater the distance a molecule has to travel, the less likely it is to traverse the membrane. As pores get shorter, bringing the two liquid solutions closer together, this effect subsides, and water molecules stand a better chance of getting through.
But at a certain length, the researchers found that resistance to water flow comes primarily from a molecule’s probability of bouncing. In other words, in very short pores, the flow of water is constrained by the chance of water molecules bouncing off the liquid surface, rather than their traveling across the nanopores. When the researchers quantified this effect, they found that only 20 to 30 percent of water vapor molecules hitting the liquid surface actually condense, with the majority bouncing away.
A no-bounce design
They also found that a molecule’s bouncing probability depends on temperature: 64 percent of molecules will bounce at 90 degrees Fahrenheit, while 82 percent of molecules will bounce at 140 degrees. The group charted water’s probability of bouncing in relation to temperature, producing a graph that Karnik says researchers can refer to in computing nanoscale flows in many systems.
“This probability tells us how different pore structures will perform in terms of flux,” Karnik says. “How short do we have to make the pore and what flow rates will we get? This parameter directly impacts the design considerations of our filtration membrane.”
Jan Eijkel, a professor of microfluidics and nanofluidics at the University of Twente in the Netherlands, says the group’s work may be useful in understanding a wide range of phenomena, including the microphysics and chemistry of clouds, fluids, aerosols, and the atmosphere.
“Their main contribution is the introduction of an entirely new method, which has the very nice flexibility of being able to adjust the distance between water surfaces down to very short distances,” says Eijkel, who did not contribute to the work. “Also, the innovation of changing the composition of the two solutions independently is elegant.”
Lee says that knowing the bouncing probability of water may also help control moisture levels in fuel cells.
“One of the problems with proton exchange membrane fuel cells is, after hydrogen and oxygen react, water is generated. But if you have poor control of the flow of water, you’ll flood the fuel cell itself,” Lee says. “That kind of fuel cell involves nanoscale membranes and structures. If you understand the correct behavior of water condensation or evaporation at the nanoscale, you can control the humidity of the fuel cell and maintain good performance all the time.”
The research was funded by the Center for Clean Water and Clean Energy at MIT and KFUPM.
- Jongho Lee, Tahar Laoui, Rohit Karnik. Nanofluidic transport governed by the liquid/vapour interface. Nature Nanotechnology, 2014; DOI: 10.1038/nnano.2014.28
|Source: NanoHybrids (press release)|