Noul material se bazează pe fibrele din polimeri goi tratați pentru a-și păstra structura – și dimensiunile porilor – deoarece sunt transformate în carbon prin piroliză. Membranele de carbon sunt apoi utilizate într-un nou procedeu de „osmoză inversă cu solvent organic” (OSRO) în care se aplică presiune pentru a efectua separarea fără a necesita o schimbare de fază a amestecului chimic.Fibrele de carbon goale, grupate împreună în module, pot separa molecule ale căror dimensiuni diferă cu o fracțiune de nanometru, oferind în același timp rate de prelucrare superioare celor ale zeolitilor de sită moleculară existente.
Posted: Aug 19, 2016
Carbon molecular sieve membranes could cut energy in hydrocarbon separations (w/video)
(Nanowerk News) A research team from the Georgia Institute of Technology and ExxonMobil has demonstrated a new carbon-based molecular sieve membrane that could dramatically reduce the energy required to separate a class of hydrocarbon molecules known as alkyl aromatics. The new material is based on polymer hollow fibers treated to retain their structure – and pore sizes – as they are converted to carbon through pyrolysis. The carbon membranes are then used in a new „organic solvent reverse osmosis” (OSRO) process in which pressure is applied to effect the separation without requiring a phase change in the chemical mixture.
The hollow carbon fibers, bundled together into modules, can separate molecules whose sizes differ by a fraction of a nanometer while providing processing rates superior to those of existing molecular sieve zeolites. Because it uses a commercial polymer precursor, the researchers believe the new membrane has potential for commercialization and integration into industrial chemical separation processes. The research will be reported in the August 19 issue of the journal Science(„Reverse Osmosis Molecular Differentiation of Organic Liquids using Carbon Molecular Sieve Membranes „).
Separation is currently achieved through refining processes such as crystallization and adsorption with distillation, which are energy-intensive. Globally, the amount of energy used in conventional separation processes for alkyl aromatics is equal to that produced by about 20 average-sized power plants.
„We see this as a potentially disruptive technology in the way we separate xylenes and similar organic compounds,” said Benjamin McCool, one of the paper’s co-authors and an advanced research associate at ExxonMobil Corporate Strategic Research in Annandale, N.J. „If we can make this work on an industrial scale, it could dramatically reduce the energy required by these separation processes.”
A research team from the Georgia Institute of Technology and ExxonMobil has demonstrated a new carbon-based molecular sieve membrane that could dramatically reduce the energy required to separate a class of hydrocarbon molecules known as alkyl aromatics. The new material is based on polymer hollow fibers treated to retain their structure – and pore sizes – as they are converted to carbon through pyrolysis. The carbon membranes are then used in a new “organic solvent reverse osmosis” (OSRO) process in which pressure is applied to effect the separation without requiring a phase change in the chemical mixture.
Fabrication of the new membrane material begins with hollow polymer fibers approximately 200 microns in diameter, slightly thicker than the average human hair. The fibers have pore sizes of less than one nanometer, and are treated via cross-linking before they are converted to carbon through a pyrolysis process. The pore sizes of the fibers can be adjusted during the fabrication process.
„We take a scalable platform based on polymeric membranes and then turn those materials into inorganic molecular sieves,” explained Ryan Lively, an assistant professor in Georgia Tech’s School of Chemical & Biomolecular Engineering and the paper’s corresponding author. „Our membranes are mechanically robust and they can withstand the process conditions required by OSRO. They maintain advantageous mechanical properties and membrane performance as they are converted to carbon fiber.”
Lively and postdoctoral fellow Dong-Yeun Koh used the OSRO process in the laboratory to separate mixtures of para-xylene and ortho-xylene, molecules whose sizes differ by one-tenth of a nanometer. By applying pressure at room temperature, the membrane can convert the 50-50 mixture to an 85-15 mixture at a high flux relative to zeolite membranes.
Georgia Tech Assistant Professor Ryan Lively (left) and Postdoctoral Fellow Dong-Yeun Koh hold bundles of hollow polymer fibers that serve as precursors for the carbon membrane fiber used to separate alkyl aromatic chemicals.
„These molecules have incredibly similar sizes and properties, but the membranes can tell them apart,” said Lively. „This bulk cut of the mixture greatly enhances the concentration with a very low energy input. This mixture could then be fed into a conventional thermal process for finishing, which would reduce the total energy input dramatically.”
In industrial use, the membranes would be bundled together in modules that would be used in chemical facilities. „In practice, you would get as many modules as you needed for a particular application, and if the need increased, you could simply add more modules,” Lively said. „It would be totally scalable.”
Reverse osmosis membranes are already widely used in desalination to produce drinking water from saltwater, consuming a fraction of the energy required by thermally-driven process. Carbon fiber membranes are being used for gas separations, but the new OSRO process is believed to be the first use of reverse osmosis with carbon membranes to separate liquid hydrocarbons.
Though the membrane has demonstrated promising results, it still faces a number of challenges. The membranes will have to be tested with more difficult separations before they can be considered for commercialization and scale-up. Industrial mixtures normally contain multiple different organic compounds, and they may include materials that can foul membrane systems. The researchers will also have to learn to make the material consistently and demonstrate that it can withstand long-term industrial use.
„Because we are starting with commercially-available polymers and we are using commercial-type equipment, we can see a clear line-of-sight to commercialization with this technology,” McCool said. „It’s a big advantage that the membranes are being spun on a hollow-fiber line similar to that currently used in the industry. The time horizon to make this happen and the cost of production could be highly advantaged over other inorganic systems or more exotic materials like graphene.”
Source: By John Toon, Georgia Institute of Technology
Acest lucru face ca noul studiu promitator pentru domeniul optic de calcul, a spus el, si un laser mic bazat pe biomateriale ar putea fi, de asemenea, implantat in corpul uman pentru aplicatii medicale
Un material nanocristalin care face rapid lumina alba din lumina albastra a fost dezvoltat de cercetatorii KAUST pentru iluminarea combinată și comunicarea de date.
A nanocrystal-based material converts blue laser emission to white light for combined illumination and data communication. (Image: KAUST)
While Wi-Fi and Bluetooth are now well established technologies, there are several advantages gained by shortening the wavelength of the electromagnetic waves used for transmitting information.
So-called visible-light communication (VLC) makes use of parts of the electromagnetic spectrum that are unregulated and is potentially more energy-efficient. VCL also offers a way to combine information transmission with illumination and display technologies–for example, using ceiling lights to provide internet connections to laptops.
Many such VLC applications require light-emitting diodes (LEDs) that produce white light. These are usually fabricated by combining a diode that emits blue light with phosphorous that turns some of this radiation into red and green light. However, this conversion process is not fast enough to match the speed at which the LED can be switched on and off.
„VLC using white light generated in this way is limited to about one hundred million bits per second,” said KAUST Professor of Electrical Engineering Boon Ooi.
Instead, Ooi, , Associate Professor Osman Bakr and their colleagues use a nanocrystal-based converter that enables much higher data rates.
The team created nanocrystals of cesium lead bromide that were roughly eight nanometers in size using a simple and cost-effective solution-based method that incorporated a conventional nitride phosphor. When illuminated by a blue laser light, the nanocrystals emitted green light while the nitride emitted red light. Together, these combined to create a warm white light.
The researchers characterized the optical properties of their material using a technique known as femtosecond transient spectroscopy. They were able to show that the optical processes in cesium lead bromide nanocrystals occur on a time-scale of roughly seven nanoseconds. This meant they could modulate the optical emission at a frequency of 491 Megahertz, 40 times faster than is possible using phosphorus, and transmit data at a rate of two billion bits per second.
„The rapid response is partly due to the size of the crystals,” said Bakr. „Spatial confinement makes it more likely that the electron will recombine with a hole and emit a photon.”
Importantly, the white light generated using their perovskite nanostructures was of a quality comparable to present LED technology.
„We believe that white light generated using semiconductor lasers will one day replace the LED white-light bulbs for energy-efficient lighting,” said Ooi.
Source: King Abdullah University of Science & Technology
au descoperit un nou tip de semimetal Weyl, un material care deschide calea pentru studiul în continuare a fermiunilor Weyl, un tip de particule elementare fără masa, ipotezat de teoria particulelor de energie înaltă și potențial util pentru crearea de circuite electronice de mare viteză și computere cuantice.Cercetătorii au creat un cristal de molibden și telur, unul dintre puținele compuși care se presupune că găzduiesc un tip nou de Weyl, postulat, în care benzile electronice și electronice se separă în mod normal printr-o atingere indirectă la câteva puncte Weyl. Aceste puncte sunt echivalente cu monopolurile magnetice din spațiul de impuls și sunt conectate prin arce Fermi.
Posted: Aug 15, 2016
New material discovery allows study of elusive Weyl fermion
(Nanowerk News) Researchers at the U.S. Department of Energy’s Ames Laboratory have discovered a new type of Weyl semimetal, a material that opens the way for further study of Weyl fermions, a type of massless elementary particle hypothesized by high-energy particle theory and potentially useful for creating high-speed electronic circuits and quantum computers (Nature Materials, „Spectroscopic evidence for a type II Weyl semimetallic state in MoTe2„).
Researchers created a crystal of molybdenum and tellurium, one of only a few compounds that had been predicted to host a new and recently postulated type of Weyl state, where the hole and electron bands normally separated by an indirect gap touch at a few Weyl points. Those points are equivalent to magnetic monopoles in the momentum space and are connected by Fermi arcs.
A combination of angle resolved photoemission spectroscopy (ARPES), modelling, density functional theory and careful calculations were used to confirm the existence of this new type of Weyl semimetal.
This material provides an exciting new platform to study the properties of Weyl fermions, and may lead the way to more new materials with unusual transport properties.
„This an important, interdisciplinary discovery because it allows us to study many aspects of these exotic particles predicted by high energy physics theory in solid state, without need for extremely expensive particle accelerators,” said Adam Kaminsky, Ames Laboratory scientist and professor in the Department of Physics and Astronomy at Iowa State University. „From my perspective as solid state physicist it is absolutely extraordinary to observe two bands touching each other at certain points and being connected by Fermi arcs – objects that are prohibited to exist in „ordinary” materials.”
au descoperit că forma bi-dimensională a carbonului, cunoscută sub numele de grafen, ar putea fi materialul ideal pentru fabricarea dispozitivelor plasmonice capabile să detecteze materiale explozive, substanțe chimice toxice alți compuși organici bazați pe o singură moleculă, afirmă un articol publicat în Physical Review B ( „Descrierea de sine strictă a amplificatorului cuantic al grafeinei” ).Dispozitivul de spargere de grafen poate fi utilizat pentru a proiecta dispozitive compacte de măsurare spectrală capabile să detecteze chiar și o singură moleculă dintr-o substanță, care este esențială pentru multe aplicații potențiale. Astfel de senzori ar putea detecta moleculele organice pe baza tranzițiilor lor vibraționale caracteristice („amprentele digitale”), deoarece lumina emisă / absorbită cade în regiunea infraroșie medie, care este exact în cazul în care funcționează spaserul bazat pe grafeni
Posted: Aug 15, 2016
‘Sniffer plasmons’ could detect a single molecule of explosives
(Nanowerk News) Physicists from the Moscow Institute of Physics and Technology (MIPT) have found that the two-dimensional form of carbon, known as graphene, might be the ideal material for manufacturing plasmonic devices capable of detecting explosive materials, toxic chemicals, and other organic compounds based on a single molecule, says an article published in Physical Review B („Self-consistent description of graphene quantum amplifier”).
Design of the spaser with the graphene layer shown as a honeycomb lattice above the dielectric layer (blue). The spaser is optically pumped through the active (gain) medium shown in orange.
Plasmons in constructing high-accuracy electronics and optics
Scientists have long been fascinated by the potential applications of a quasiparticle called the plasmon, a quantum of plasma oscillations. In the case of a solid body, plasmons are the oscillations of free electrons. Of special interest are the effects arising from the surface interactions of electromagnetic waves with plasmons—usually in the context of metals or semimetals, as they have a higher free electron density. Harnessing these effects could bring about a breakthrough in high-accuracy electronics and optics. One possibility opened up by plasmonic effects is the subwavelength light focusing, which increases the sensitivity of plasmonic devices to a point where they can distinguish a single molecule. Such measurements are beyond what any conventional (classical) optical devices can achieve. Unfortunately, plasmons in metals tend to lose energy quickly due to resistance, and for this reason they are not self-sustained, i.e. they need continuous excitation. Scientists are trying to tackle this issue by using composite materials with predefined microstructure, including graphene.
Graphene is an allotrope of carbon in the form of a two-dimensional crystal. It can be visualised as a one-atom-thick honeycomb lattice made of carbon atoms. Two MIPT graduates, Andre Geim and Konstantin Novoselov, were the first to isolate graphene, which won them a Nobel Prize in Physics. Graphene is a semiconductor with extremely high charge carrier mobility. Its electrical conductivity is also exceptionally high, which makes graphene-based transistors possible.
Theoretical physicists give the okay
Although, plasmonic devices have seemed an exciting prospect to pursue from the start, to take advantage of them, it was first necessary to find out whether the technology behind them was feasible. To do this, scientists had to find a numerical solution to the relevant quantum-mechanical equations. This was accomplished by a team of researchers at the Laboratory of Nanostructure Spectroscopy headed by Prof. Yurii Lozovik: they formulated and solved the necessary equation. Their research has led them to develop a quantum model that predicts plasmonic behaviour in graphene. As a result, the scientists described the operation of a surface-plasmon-emitting diode (SPED) and the nanoplasmonic counterpart of the laser—known as the spaser—whose construction involves a graphene layer.
A spaser could be described as a device similar to a laser and operating on the same basic principle. However, to produce radiation, it relies on optical transitions in the gain medium, and the particles emitted are surface plasmons, as opposed to photons produced by a laser. An SPED is different from a spaser in that it is an incoherent source of surface plasmons. It also requires considerably lower pump power. Both devices would operate within the infrared region of the spectrum, which is useful for studying biological molecules.
‘The graphene spaser could be used to design compact spectral measurement devices capable of detecting even a single molecule of a substance, which is essential for many potential applications. Such sensors could detect organic molecules based on their characteristic vibrational transitions (‘fingerprints’), as the light emitted/absorbed falls into the medium infrared region, which is exactly where the graphene-based spaser operates,’ says Alexander Dorofeenko, one of the authors of the study.
Source: Moscow Institute of Physics and Technology
au creat un dispozitiv nanostructurat, aproximativ jumătate din dimensiunea unei ștampile poștale, care dezinfecteaza apa cu mult mai rapid decât metoda UV, folosind de asemenea partea vizibilă a spectrului solar , care conține 50% din energia soarelui
Posted: Aug 15, 2016
Nanostructured device grabs more solar energy to disinfect water faster
(Nanowerk News) In many parts of the world, the only way to make germy water safe is by boiling, which consumes precious fuel, or by putting it out in the sun in a plastic bottle so ultraviolet rays will kill the microbes. But because UV rays carry only 4 percent of the sun’s total energy, the UV method takes six to 48 hours, limiting the amount of water people can disinfect this way.
Now researchers at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have created a nanostructured device, about half the size of a postage stamp, that disinfects water much faster than the UV method by also making use of the visible part of the solar spectrum, which contains 50 percent of the sun’s energy.
This nanostructured device, about half the size of a postage stamp, uses sunlight to quickly disinfect water. It consists of thin flakes of molybdenum disulfide arranged like walls on a glass surface and topped with a thin layer of copper. Light falling on the walls triggers formation of hydrogen peroxide (H2O2) and other “reactive oxygen species” that kill bacteria. (Image: C. Liu et al., Nature Nanotechnology)
In experiments reported today in Nature Nanotechnology („Rapid water disinfection using vertically aligned MoS2 nanofilms and visible light”), sunlight falling on the little device triggered the formation of hydrogen peroxide and other disinfecting chemicals that killed more than 99.999 percent of bacteria in just 20 minutes. When their work was done the killer chemicals quickly dissipated, leaving pure water behind.
“Our device looks like a little rectangle of black glass. We just dropped it into the water and put everything under the sun, and the sun did all the work,” said Chong Liu, lead author of the report. She is a postdoctoral researcher in the laboratory of Yi Cui, a SLAC/Stanford associate professor and investigator with SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC.
Nanoflake Walls and Eager Electrons
Under an electron microscope the surface of the device looks like a fingerprint, with many closely spaced lines. Those lines are very thin films – the researchers call them “nanoflakes” – of molybdenum disulfide that are stacked on edge, like the walls of a labyrinth, atop a rectangle of glass.
In ordinary life, molybdenum disulfide is an industrial lubricant. But like many materials, it takes on entirely different properties when made in layers just a few atoms thick. In this case it becomes a photocatalyst: When hit by incoming light, many of its electrons leave their usual places, and both the electrons and the “holes” they leave behind are eager to take part in chemical reactions.
By making their molybdenum disulfide walls in just the right thickness, the scientists got them to absorb the full range of visible sunlight. And by topping each tiny wall with a thin layer of copper, which also acts as a catalyst, they were able to use that sunlight to trigger exactly the reactions they wanted – reactions that produce “reactive oxygen species” like hydrogen peroxide, a commonly used disinfectant, which kill bacteria in the surrounding water.
Molybdenum disulfide is cheap and easy to make – an important consideration when making devices for widespread use in developing countries, Cui said. It also absorbs a much broader range of solar wavelengths than traditional photocatalysts.
Solving Pollution Problems
The method is not a cure-all; for instance, it doesn’t remove chemical pollutants from water. So far it’s been tested on only three strains of bacteria, although there’s no reason to think it would not kill other bacterial strains and other types of microbes, such as viruses. And it’s only been tested on specific concentrations of bacteria mixed with less than an ounce of water in the lab, not on the complex stews of contaminants found in the real world.
Still, “It’s very exciting to see that by just designing a material you can achieve a good performance. It really works,” said Liu, who has gone on to work on a project in Cui’s lab that is developing air filters for combating smog. “Our intention is to solve environmental pollution problems so people can live better.”
capabilitățile îmbunătățite ale senzorilor ar însemna că un „vertue” ar putea colecta datele jurnalului doar ca răspuns la anumite activități suspecte, în loc să colecteze date despre fiecare eveniment
au dezvoltat un nou metamaterial care schimba forma folosind Kirigami, arta antica japoneza de taiere si pliere a hartiei pentru a obtine forme 3D.Metamaterialele sunt o clasă de materiale proiectate pentru a produce proprietăți care nu apar în mod natural. În prezent, metamaterialele sunt folosite pentru a face absorbanți artificiali și vibrații artificiali și senzori de înaltă performanță. Kirigami poate fi aplicat pentru a transforma materialele din tablă bidimensională în forme tridimensionale complexe cu o gamă mai largă de geometrii decât origami „clasice”.
Posted: Aug 05, 2016
Shape-changing metamaterial developed using Kirigami technique
(Nanowerk News) Engineers from the University of Bristol have developed a new shape-changing metamaterial using Kirigami, which is the ancient Japanese art of cutting and folding paper to obtain 3D shapes.
This image shows an open honeycomb at each stage during the manufacturing process. (Image: University of Bristol)
Metamaterials are a class of material engineered to produce properties that don’t occur naturally. Currently metamaterials are used to make artificial electromagnetic and vibration absorbers and high-performance sensors. Kirigami can be applied to transform two-dimensional sheet materials into complex three-dimensional shapes with a broader choice of geometries than ‘classical’ origami.
The research, developed within a PhD programme run by the University’s EPSRC Centre for Doctoral Training in Advanced Composites for Innovation and Science (ACCIS CDT), is published in Scientific Reports („Shape morphing Kirigami mechanical metamaterials”).
The type of mechanical metamaterials using the Kirigami technique, developed by PhD student Robin Neville, changes shape seamlessly, exhibits large variations in mechanical performance with small geometry changes, and can be adapted to modify its configuration by using mainstream actuation mechanisms.
This image shows bending behavior. (a) Synclastic curvature in the closed configuation; (b) cylindrical curvature in the open rec configurations; (c) an open rec specimen folder double. (Image: University of Bristol) (click on image to enlarge)
The Kirigami metamaterial can also be produced using off-the-shelf thermoplastic or thermoset composite materials, and different sensing and electronics systems can be embedded to obtain a fully integrated smart shape-changing structure.
Fabrizio Scarpa, Professor of Smart Materials and Structures in the Department of Aerospace Engineering and ACCIS, said: „Mechanical metamaterials exhibit unusual properties through the shape and deformation of their engineered subunits. Our research presents a new investigation of the kinematics of a family of cellular metamaterials based on Kirigami design principles. This technique allows us to create cellular structures with engineered cuts and folds that produce large shape and volume changes, and with extremely directional, tuneable mechanical properties.”
This is a demonstrator honeycomb changing shape in response to cable tension. The arrows indicate which cable is being pulled. (Image: University of Bristol)
Robin Neville, PhD student, added: „By combining analytical models and numerical simulations we have demonstrated how these Kirigami cellular metamaterials can change their deformation characteristics. We have also shown the potential of using these classes of mechanical metamaterials for shape change applications like morphing structures.”
In the future, this Kirigami metamaterial could be used in robotics, morphing structures for airframe and space applications, microwave and smart antennas.
Din analiza detaliata a suprafetei, s-au gasit grupuri hidroxil hidrofile grupate de-a lungul suprafetei exterioare a corpului de nanopot de carbon”, a spus Associate Prof. Yokoi. „Grapena este de obicei hidrofobă, totuși, dacă grupările hidroxil sunt împachetate dens pe suprafața exterioară a corpului, zona respectivă va fi hidrofilă. Cu alte cuvinte, nanopotul de carbon ar putea fi un nanomaterial unic, cu caracteristici hidrofobe și hidrofile. Procesul de realizare a unei analize de suprafață mai sofisticate pentru a obține acea asigura
Posted: Aug 05, 2016
Development of a novel carbon nanomaterial ‘pot’
(Nanowerk News) A novel, pot-shaped, carbon nanomaterial developed by researchers from Kumamoto University, Japan is several times deeper than any hollow carbon nanostructure previously produced. This unique characteristic enables the material to gradually release substances contained within and is expected to be beneficial in applications such as drug delivery systems.
Carbon is an element that is light, abundant, has a strong binding force, and eco-friendly. The range of carbon-based materials is expected to become more widespread in the eco-friendly society of the future. Recently, nanosized (one-billionth of a meter) carbon materials have been developed with lengths, widths, or heights below 100 nm. These materials take extreme forms such as tiny grained substances, thin sheet-like substances, and slim fibrous substances. Example of these new materials are fullerenes, which are hollow cage-like carbon molecules; carbon nanotubes, cylindrical nanostructures of carbon molecules; and graphene, one-atom thick sheets of carbon molecules.
Why are these tiny substances needed? One reason is that reactions with other materials can be much larger if a substance has an increased surface area. When using nanomaterials in place of existing materials, it is possible to significantly change surface area without changing weight and volume, thereby improving both size and performance. The development of carbon nanomaterials has provided novel nanostructured materials with shapes and characteristics that surpass existing materials.
To create the new material, researchers used their own, newly developed method of material synthesis. The container-shaped nanomaterial has a complex form consisting of varied layers of stacked graphene at the bottom, the body, and the neck areas of the container, and the graphene edges along the outer surface of the body were found to be very dense. Due to these innovate features, Associate Prof. Yokoi and colleagues named the material the „carbon nanopot.”
The carbon nanopot has an outer diameter of 20 ~ 40 nm, an inner diameter of 5 ~ 30 nm, and a length of 100 ~ 200 nm. During its creation, the carbon nanopot is linked to a carbon nanofiber with a length of 20 ~ 100 µm meaning that the carbon nanopot is also available as a carbon nanofiber. At the junction between nanopots, the bottom of one pot simply sits on the opening of the next without sharing a graphene sheet connection. Consequently, separating nanopots is very easy.
„From a detailed surface analysis, hydrophilic hydroxyl groups were found clustered along the outer surface of the carbon nanopot body,” said Associate Prof. Yokoi. „Graphene is usually hydrophobic however, if hydroxyl groups are densely packed on the outer surface of the body, that area will be hydrophilic. In other words, carbon nanopots could be a unique nanomaterial with both hydrophobic and hydrophilic characteristics. We are currently in the process of performing a more sophisticated surface analysis in order to get that assurance.”
Since this new carbon nanopot has a relatively deep orifice, one of its expected uses is to improve drug delivery systems by acting as a new foundation for medicine to be carried into and be absorbed by the body.
