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Showing posts with label Chemistry. Show all posts
Showing posts with label Chemistry. Show all posts

Saturday, 25 January 2020

Researchers find way to harness the entire visible spectrum for energy production

For the very first time, scientists have demonstrated that it is possible to collect energy from the entire visible spectrum of sunlight and transform it quickly and efficiently into hydrogen. In fact, they have developed a single molecule that can efficiently absorb sunlight and also act as a catalyst to transform solar energy into hydrogen. A clean alternative to fossil fuels (for, in particular, motor vehicles).

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This new molecule collects energy from the entire visible spectrum and can harness more than 50% more solar energy than current solar cells. This discovery could well help humanity move from fossil fuels to energy sources that do not contribute to climate change.

“  The idea is to use the photons from the sun and transform them into hydrogen. Simply put, we collect energy from sunlight and store it in chemical bonds so it can be used later, "said Claudia Turro, professor of chemistry and director of the center at Ohio State University for chemical and biophysical dynamics (and who also directed this research). Namely, that photons are the elementary particles of light, and contain a certain amount of energy.

Thanks to this study, for the very first time, it has been demonstrated that it is possible to collect energy from the entire visible spectrum of sunlight, including low energy infrared ( part of the solar spectrum that had previously been difficult to collect) and transform it quickly and efficiently into hydrogen.

Hydrogen is a clean fuel, which means that it does not produce carbon or carbon dioxide as a by-product of its use. "  What makes it work is that the system is able to put the molecule in an excited state, where it absorbs the photon and is able to store two electrons to produce hydrogen. This storage of two electrons in a single molecule, as well as this use to produce hydrogen, is unprecedented,  ”said Turro.

Indeed, transforming the Sun's energy into fuel, for example to power a vehicle, first requires an energy collection mechanism. Then, this energy can be converted into fuel. The conversion requires a catalyst. In short: this is a device which accelerates a chemical reaction allowing the conversion of solar energy into a usable energy vector (in this case hydrogen).

Most of the previous attempts to collect solar energy and transform it into hydrogen have focused on higher energy wavelengths (like ultraviolet, for example). The latter have also relied on catalysts always involving two molecules (or more), which exchange electrons (energy) to produce fuel from solar energy. But a large part of this energy is lost in the exchange, which makes these multimolecular systems less efficient.

In addition, the few other attempts that relied on a single molecule catalyst were also ineffective "partly because they did not collect energy from the entire visible spectrum of the sun, and also because the catalysts themselves degraded quickly, "said Turro.

A system 25 times more efficient than current technologies

Now, Turro's research team has discovered how to make a catalyst from a single molecule, a form of rhodium (a chemical element), which means less energy is lost. The researchers also understood how to collect energy from the near infrared to the ultraviolet, more than the entire visible spectrum.

According to the researchers, the system they designed is nearly 25 times more efficient with low-energy near-infrared light than single-molecule systems operating with ultraviolet photons.

As part of this study, the researchers used LEDs to illuminate acid solutions containing the active molecule, and discovered that hydrogen was produced.

" I think the reason it works is because the molecule is difficult to oxidize,  " says Turro. "  And we have to have renewable energy. Just imagine, if we could use sunlight for our energy needs instead of coal, gas or oil, what we could do to fight climate change, ”added Turro.

But before the research team's results can be applied in the real world, "there is still a lot of work to do," admits Turro. Indeed, rhodium is a rare metal and the production of catalysts using it is expensive. The team is therefore working to improve this molecule to produce hydrogen over a longer period of time and to develop a catalyst exploiting less rare elements.


Article: Single-chromophore single-molecule photocatalyst for the production of dihydrogen using low-energy light

T. J. Whittemore, C. Xue, J. Huang, J. C. Gallucci & C. Turro

Nature Chemistry (2020)

Wednesday, 4 December 2019

Chemists trigger the coldest chemical reaction ever

Chemical reactions are extremely fast processes, involving complex and successive molecular interactions. Until now, researchers could only observe the beginning and end phases of a chemical reaction, without being able to observe the course of the reaction itself. Recently, however, chemists at Harvard University have been able to cool molecules to such a low temperature that they have been slowed down to the point where researchers have the opportunity to observe the chemical reaction in detail. A feat that could pave the way for new technologies, from civil engineering to quantum computing.

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It's 500 nanokelvins, a few millionths of a degree above absolute zero. The icy nature of this configuration is important because at these temperatures, molecules tend to slow down to the point of almost stopping. For a chemical reaction to occur, slow molecules are usually not indicated.

But in this case, the reduction in temperature and speed gave the team led by Harvard University the opportunity to see something that had never been observed before: the moment when two molecules meet and form two new molecules. The results were published in the journal Science .

Slow down molecules to see their reaction in detail

The chemical reactions take only one picosecond, which makes it very difficult to observe what happens during this period of time. Even ultra-fast lasers acting as cameras can usually capture the beginning and the end of a reaction, but not what happens in the middle. Slowing the reaction through extremely cold temperatures obtained by the team was therefore the ideal solution.

The coldest temperature in the universe is absolute zero, a temperature that is experimentally impossible to reach. But it is possible to seriously approach it. Ultra-low temperatures mean very low energies, and therefore a much slower reaction: two rubidium potassium molecules chosen for their plasticity have been delayed during the reaction phase for a few microseconds.

Chemical reactions convert reagents into products via an intermediate state where bonds break and form. Often too short to be observed, this phase has so far escaped detailed observation. By "freezing" the rotation, the vibration and the movement of the reagents (here potassium-rubidium molecules) at a temperature of 500 nanokelvin (temperature barely higher than the temperature of absolute zero), the number of energetic states allowed for the products is limited. "Trapped" in the intermediate phase longer, researchers can then observe this phase directly with photoionization detection. Credits: Ming-Guang Hu

A technique known as photoionization detection was then used to observe what was happening between the two molecules, providing researchers with valuable real data to inform their models and assumptions. Being able to observe chemical reactions so closely and at such a fundamental level opens up the possibility of designing new reactions as well; an almost limitless number of combinations is imaginable, potentially useful in all areas, from material construction to quantum computing.


Direct observation of bimolecular reactions of ultracold KRb molecules

M.-G. Hu, Y. Liu, D. D. Grimes, Y.-W. Lin, A. H. Gheorghe2, R. Vexiau4, N. Bouloufa-Maafa4, O. Dulieu4, T. Rosenband2, K.-K. Ni,

Science  29 Nov 2019:
Vol. 366, Issue 6469, pp. 1111-1115
DOI: 10.1126/science.aay9531

Tuesday, 19 November 2019

New material breaks all records for thermoelectric power generation

More and more technologies are using thermoelectricity to supply energy. Thermoelectric energy comes from the conversion of heat into electricity through temperature differences. However, the usual thermoelectric materials generate a relatively small amount of energy. But recently, Austrian physicists have developed a brand new thermoelectric material breaking all records of the amount of energy generated. Such a material could equip the sensors and processors to self-power.

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Thermoelectric materials can convert heat into electrical energy. This is due to the Seebeck effect: if there is a temperature difference between the two ends of such a material, an electrical voltage can be generated and the current can begin to flow. The amount of electrical energy that can be generated at a given temperature difference is measured by the so-called ZT value: the higher the ZT value of a material, the better its thermoelectric properties.

The best thermoelectric materials to date have been measured at ZT values ​​of about 2.5 to 2.8. The physicists of the Technical University of Vienna have succeeded in developing a brand new material with a ZT value of 5 to 6. It is a thin layer of iron, vanadium, tungsten and aluminum applied on a silicon crystal.

The new material is so efficient that it could be used to provide power to sensors or even small computer processors. Instead of connecting small electrical devices to cables, they could generate their own electricity from temperature differences. The study was published in the journal Nature .

A combination of iron, vanadium, tungsten and aluminum

" A good thermoelectric material must have a strong Seebeck effect and must meet two important requirements, which are difficult to reconcile, " says physicist Ernst Bauer of the Institute of Solid Physics at TU Wien. " On the one hand, he must conduct electricity as well as possible; on the other hand, it must conduct the heat as little as possible. This is a challenge because electrical conductivity and thermal conductivity are usually closely related .

At the Christian Doppler laboratory for thermoelectricity, created by Ernst Bauer at TU Wien in 2013, various thermoelectric materials for different applications have been studied in recent years. This research has now revealed a particularly remarkable material: a combination of iron, vanadium, tungsten and aluminum.

Atomic structure of the new material. Credits: B. Hinterleitner et al. 2019

The atoms of this material are generally arranged in a strictly regular manner in a face-centered cubic lattice. The distance between two iron atoms is always the same, and the same goes for the other types of atoms. The whole crystal is therefore perfectly regular, "explains Bauer.

Weyl fermions and low thermal conductivity in crystalline structure

However, when a thin layer of material is applied to silicon, something amazing happens: the structure changes dramatically. Although atoms always form a cubic pattern, they are now arranged in a space-centered structure, and the distribution of different types of atoms becomes completely random.

" Two iron atoms can be assembled next to each other, adjacent sites can be filled with vanadium or aluminum, and there is no longer a rule dictating the location of the next iron atom in the crystal ".

This mixture of regularity and irregularity of the atomic arrangement also modifies the electronic structure, which determines the way in which the electrons move in the solid. " The electric charge moves in a particular way in the material in order to protect it from diffusion processes .  The charges passing through the material are called Weyl Fermions . In this way, a very low electrical resistance is obtained.

Graphics showing the thermoelectric properties of the material. Credits: B. Hinterleitner et al. 2019

On the other hand, the vibrations of the network, which carry the heat from the high temperature zones to the low temperature zones, are inhibited by the irregularities of the crystalline structure. As a result, the thermal conductivity decreases. This is important if the electrical energy has to be generated permanently from a temperature difference - because if the temperature differences could be balanced very quickly and all the material had the same temperature everywhere, the thermoelectric effect 'stop.

Equip interconnected technologies with standalone power

Of course, such a thin layer can not generate a particularly large amount of energy, but it has the advantage of being extremely compact and adaptable. We want to use it to provide energy for sensors and small electronic applications . "

The demand for such small-scale generators is growing rapidly: in the "Internet of Things", more and more devices are connected together online, so they automatically coordinate their behavior with each other. This is particularly promising for future production plants, where one machine must react dynamically to another.

" If you need a lot of sensors in a plant, you can not connect them together. It's much smarter for the sensors to be able to generate their own power using a small thermoelectric device, "concludes Bauer.


Article: Thermoelectric performance of a metastable thin-film Heusler alloy

Authors: B. Hinterleitner, I. Knapp, E. Bauer

Nature (2019)


Tuesday, 12 November 2019

Two daily cleaning products have generated toxic fumes in a restaurant, killing an employee

The manager of a Buffalo Wild Wings restaurant died after being exposed to toxic fumes generated by blending two common cleaning products. Other employees (more than a dozen) were also affected by the toxic releases.

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On Thursday, November 7th, an employee of a Buffalo Wild Wings in Burlington, Mass., Began cleaning the back of the restaurant with a common cleaner called "Super 8". The incident occurred shortly thereafter.

The solution of Super 8 is based on sodium hypochlorite, a disinfectant and bleaching agent (used especially in the form of bleach). Its unique use does not represent a danger. However, unbeknownst to the employee, another acid-based cleaner, the Scale Kleen, had been spilled on the floor shortly before, according to NBC News .

A deadly mixture

Blending the two chemicals produced a substance that "turned green and started to bubble," said Michael Patterson, Burlington Fire Chief.

The first exposed employee quickly developed eye burns and began to experience breathing difficulties. He then left the premises. The restaurant manager then took over, trying to scrape the mixture, but he too developed severe symptoms, making him unable to continue.

The manager, Ryan Baldera, 32, died shortly after at the hospital, according to the local newspaper NBC Boston . Thirteen other people, also exposed to toxic fumes, were taken care of.

The chemical accident occurred at a Buffalo Wild Wings in Burlington, Massachusetts (United States). Credits: Google Street View

Common cleaning products can be dangerous or even deadly when mixed incorrectly. For example, bleach can react with ammonia, acids and other cleaners. The resulting reactions can give rise to potentially life-threatening toxic fumes.

Responsible potential: chlorine gas

When bleach is mixed with acid (such as vinegar or chemicals found in some window cleaners, drains and toilet bowls), chlorine gas is produced. Exposure to chlorine usually causes irritation of the eyes, throat and nose, causing coughing and breathing problems. Moreover, it should be known that due to its toxicity, the dichlore was one of the first combat gases used during the First World War.

At high concentrations, chlorine gas can cause severe breathing difficulties and fluid production in the lungs. At very high concentrations, a deep emanation can cause death.

A team specialized in dangerous substances was convened to treat the premises of the restaurant, which was temporarily closed by the city. Occupational Safety and Health Administration (OSHA) is also investigating the accident.

Source1 Source 2

Sunday, 3 November 2019

Polymers that degrade in the body and the environment

Researchers have succeeded in developing polymers that are more easily degradable in the body as well as in the environment by simply adding an additional monomer to the basic formulation. These polymers may be as useful for administering drugs or carrying medical imaging agents as for replacing certain industrial plastics.

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The polymerization by ring opening metathesis (ROMP) is the name the experts give a chemical reaction that enables the production of polymers for various uses. Most often from norbornene (C 7 H 10 ), a bridged hydrocarbon to which it is easy, before the polymerization reaction , to add drugs or medical imaging agents. The problem is that the polymers thus produced do not degrade easily.

But researchers at the Massachusetts Institute of Technology (MIT, USA) have developed a method that makes them more degradable by simply adding a monomer . A silyl ether which forms chemical bonds that weak acids or bases as well as fluoride ions are able to decompose.

A new type of polymer designed by chemists from the  Massachusetts Institute of Technology (MIT, USA) incorporates a special monomer - here in yellow - that helps polymers break down more easily under certain conditions. © Demin Liu, MIT 

A single monomer in addition

Employed in a 1: 1 ratio with norbornene, silyl ether - evenly distributed over the entire molecular structure of the polymer - aids in degrading polymeric structures similar to those prepared by the ROMP method.

Tests on mice have shown that these new polymers remain as present in the body as the old ones during the two weeks following the injection. But after six weeks, the concentrations were between three and ten times lower. So what to rid the body much faster of these polymers used as drug carriers , for example.

MIT researchers also believe that the process could also be economically profitable for the plastics and adhesives industry, among others. What make these products also more degradable.


Monday, 28 October 2019

Researchers have designed an "artificial sheet" producing clean gas by photosynthesis

In recent years, progress in sustainable development and renewable energy has been encouraging, but there is still much work to be done to build a less uncertain climate future. In this effort, researchers at the University of Cambridge have developed an "artificial sheet" to produce "clean" synthetic fuel.

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The advantage of the proposed solution is the sustainable production of syngas (or synthesis gas), a mixture of hydrogen and carbon monoxide. Currently, syngas is widely used in the production of various fuels, drugs, plastics and fertilizers.

It can be made in different ways, but usually involves the remains of products derived from coal or petroleum-based materials. Thus, the final product is not always carbon neutral. To overcome this problem, the researchers wanted to find a clean and sustainable solution.

A gas production without release of carbon dioxide

The new device, acting like a leaf, is immersed in water and is powered by sunlight. However, it can also work in cloudy weather. It makes it possible to produce a sustainable synthesis gas without releasing carbon dioxide into the air. The study was published in the journal Nature Materials.

" You may not have heard of the synthesis gas itself, but every day you consume products created with this gas, " says chemist Erwin Reisner , lead author of the study, from the University of Cambridge in the United Kingdom.

" Being able to produce it in a sustainable way would be a crucial step in closing the global carbon cycle and establishing a sustainable industry for chemicals and fuels, " he adds.

The new device in full operation. Credits: Virgil Andrei

The artificial leaf imitates plant photosynthesis, combining incoming light, water and carbon dioxide with a catalyst. Operation is provided by two light absorbers (similar to plant molecules that harvest sunlight), combined with a catalyst made from cobalt. At the other end, hydrogen and carbon monoxide are produced, which can then themselves be used to produce syngas.

The selected, state-of-the-art perovskite light absorbers are ultra-efficient: they provide high voltage and high electrical current to fuel the chemical reaction by which carbon dioxide is reduced to carbon monoxide . Compared with light absorbers composed of silicon or dye-sensitive materials, this system is much more efficient.

The researchers also used molecular cobalt catalysts instead of platinum or silver. Cobalt is not only less expensive (because it is more abundant on Earth), but it is also more efficient at producing carbon monoxide than other catalysts.

Although the performance of the system is rather low at the moment, it should be possible to improve it with further research. Scientists announce that it is the unique combination of materials and catalysts that makes their system much more interesting than similar devices in terms of environmental impact and usage framework.

" You are not limited to using this technology only in hot countries, or to keep the process running only during the summer months ," says chemist Virgil Andrei from Cambridge University. " You can use it from dawn to dusk, anywhere in the world ."

Virgil Andrei, holding the artificial leaf that he developed with his team. Credits: Chanon Pornrungrog / Cambridge University / PA Wire

This is of course important in areas of the world where a stable power supply (solar panels or other) is not always guaranteed. And although renewable energy vectors such as wind turbines and photovoltaic panels are becoming more efficient, global energy demand goes far beyond domestic electricity.

Indeed, Reisner says that synthetic fuel production is vital because electricity can currently only supply about 25% of our total global energy demand. In particular, there is a strong demand for liquid fuels for heavy transport, including freight transport (sea and air), all of which require cleaner fuels. This artificial leaf could allow to produce a certain amount.

With respect to this new study, team members reported having confidence in their catalysts and the combination of materials chosen. Over time, synthesis gas may not even be needed as an intermediate step: fuel production could be done directly from carbon dioxide and water.

" What we would like to do next, instead of producing synthesis gas first and then converting it to liquid fuel, is to make the liquid fuel in one step, from carbon dioxide and water, " Reisner concludes.