Separating gases using flexible molecular sieves

Separating gases using flexible molecular sieves
The dynamic nature and flexibility of molecular sieves is crucial in understanding their performance for transport of small molecules. Credit: University of Liverpool

Researchers at the University of Liverpool and the King Abdullah University of Science and Technology have made reported some exciting findings relating to metal-organic frameworks (MOFs), a class of porous materials, which could benefit a wide range of important gas separation processes.


The findings are reported in two research papers published this month.

Metal-organic frameworks (MOFs) are a relatively new class of porous, crystalline materials with a broad range of applications.

Some MOFs can act as a molecular sieve, allowing one type of gas molecule from a mixture to pass through while blocking the others. For example, it is known that some MOFs separate propylene from propane, an important process in the manufacture of polypropylene plastics for which high purity propylene is required.

In a first paper published in Nature Communications, researchers demonstrate that unlike a kitchen sieve, these three dimensional molecular sieves can change their pore shape and their flexibility is vital for this performance.

The computational modelling supported by experimental X-ray data indicate that for one such high-performing MOF, called KAUST-7, the structural changes in the MOF triggered by the presence of the propylene and propane gas molecules are qualitatively different and result in stronger adsorption and faster transport of propylene thus essentially sieving propane molecules out.

However, it is hard to predict which other kinds of MOFs possess this functional flexibility and therefore might also be good for a given gas separation because the performance is controlled by specific molecular interactions that are hard to anticipate or identify experimentally.

In a second paper published in Physical Chemistry Chemical Physics, researchers focus on this challenge.

They developed a computational screening approach to assess over four thousand previously reported MOFs for their flexibility when acting like a molecular sieve. Using this approach, they identified the top four MOFs which show the potential to separate propylene from propane—two of them have been already known to have a good performance while the other two have not yet been tested for this application experimentally.

Dr. Matthew Dyer, a lecturer in Chemistry and part of the University’s Leverhulme Research Centre for Functional Materials Design, said: “MOFs have attracted considerable interest in recent years and there are great hopes for technical applications especially for flexible MOFs.

“Our research adds to our knowledge of MOFs, why some are able to act as sieves and which ones show flexibility.

“Using a computational approach, we are able to identify flexible MOFs and these findings have the potential to make the process of purifying gases more energy efficient. This is important in terms for the manufacture of high-quality plastics which need pure starting compounds that are commonly extracted from gaseous by-products in petrochemical processing. “

“Such high throughput screening approaches can be applied to many different materials with varying potential applications. They have the potential to change the way that we find materials

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Graphene balloons to identify noble gases

Graphene balloons to identify noble gases
Credit: TU Delft/Makars Šiškins

New research by scientists from Delft University of Technology and the University of Duisburg-Essen uses the motion of atomically thin graphene to identify noble gasses. These gasses are chemically passive and do not react with other materials, which makes it challenging to detect them. The findings are reported in the journal Nature Communications.


Graphene is an ultimately thin material consisting of only one layer of carbon atoms. Its atomic thickness makes it a perfect filter material for gasses and liquids: graphene by itself it is not permeable, but small perforations make it very permeable. Moreover, the material is among the strongest known and withstands high stresses. Together, these two traits provide the perfect basis for new types of gas sensors.

Nano balloons

The scientists use microscopic balloons made of bilayer graphene (with a thickness of 0.7 nm), with very small nanopore perforations with diameters down to 25 nm, to detect gasses. They use a laser to heat the gas inside the balloon and make it expand. The pressurized gas then escapes through the perforation. “Picture a balloon that deflates when you let the air run out,” says TU Delft researcher Irek Rosłoń, “We measure the time it takes the balloon to deflate. At such a small scale, this happens very quickly—within around 1/100.000th of a second—and interestingly, the length of time depends strongly on the type of gas and the size of the pores. For example helium, a light gas with high molecular velocity, escapes five times faster than krypton, a heavy and slowly moving gas.” The method allows to distinguish gasses based on their mass and molecular velocity, which normally requires big mass spectrometers.

Gas pumping

The graphene balloons are continuously driven by an optothermal force at high-frequencies of 100 kHz, causing gas to be pumped in and out through the nano-pores very rapidly. The permeation of the gas can be studied by looking at the mechanical motion of the graphene. At low pumping frequencies, the gas has plenty of time to escape and does not affect the motion of the graphene significantly. However, the membrane experiences a large amount of drag at increased pumping frequencies, in particular when the period of pumping corresponds to the typical time it takes for the gas to leave the balloon. “By measuring at various frequencies, we can find that peak in the drag. The frequency at which a peak is observed corresponds to the permeation speed of the gas.”

The researchers extended this idea to study gas flow through nano-channels. Connecting the balloon to a long channel makes it much harder for the gas to escape. The increase in the deflation time gives experimental insight into the gas flow mechanics within the nano-channels. Altogether, this work shows how the extraordinary properties of graphene can be used to study gas dynamics at the nanoscale, as well as to engineer new types of sensors and devices. In the future, this can enable small, low-cost and versatile sensor devices to

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Surge in Greenhouse Gases Sustained Despite COVID Lockdowns: U.N. | World News

GENEVA (Reuters) – Greenhouse gas concentrations climbed to a new record in 2019 and rose again this year despite an expected drop in emissions due to COVID-19 lockdowns, the World Meteorological Organization said on Monday, warning against complacency.

Many scientists expect the biggest annual fall in carbon emissions in generations this year as measures to contain coronavirus have grounded planes, docked ships and kept commuters at home.

However, the WMO described the projected 2020 drop as a “tiny blip” and said the resulting impact on the carbon dioxide concentrations that contribute to global warming would be no bigger than normal annual fluctuations.

“…In the short-term the impact of the COVID-19 confinements cannot be distinguished from natural variability,” the WMO’s Greenhouse Gas Bulletin said.

The annual report released by the Geneva-based U.N. agency measures the atmospheric concentration of the gases – carbon dioxide, methane and nitrous oxide – that are warming our planet and triggering extreme weather events.

Levels of carbon dioxide, a product of burning fossil fuels that is the biggest contributor to global warming, touched a new record of 410.5 parts per million (ppm) in 2019, it said.

The annual increase is larger than the previous year and beats the average over the last decade.

“Such a rate of increase has never been seen in the history of our records,” WMO Secretary-General Professor Petteri Taalas said, referring to a rise of 10 ppm since 2015, calling for a “sustained flattening of the (emissions) curve”.

WMO’s head of atmospheric environment research Dr. Oksana Tarasova said the magnitude of the increase in carbon dioxide levels over the past four years was comparable to changes seen during the shift from ice age to more temperate periods but, back then, the transition happened over a much longer timeframe.

“We humans did it without anything, with just with our emissions, and we did it within four years.” .

Global data is not yet available for 2020 but the trend of rising concentrations appears to be intact, the WMO said, citing initial readings from its Tasmania and Hawaii stations.

Like other scientific bodies, the WMO said it expects annual global carbon emissions to fall this year due to COVID measures, and ventured a preliminary estimate of between 4.2-7.5%.

Such a drop would not cause atmospheric carbon dioxide to go down, but would slow the rate of increase temporarily on a scale that falls within normal variations, it said.

“Our whole economy and our consumption patterns wire us to extremely high emissions even if we all sit in lockdown,” said Tarasova.

Irrespective of what we do to curb emissions today, much of the carbon dioxide already emitted decades ago remains in the atmosphere and contributes to global warming, climate scientists say.

Over the 2018-2019 period, concentrations of the more potent heat-trapping gas methane increased by 8 parts per billion, the report said – slightly lower than the previous year-on-year change but still above-average over the last 10-year period.

Methane concentrations data is closely watched by scientists

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Surge in greenhouse gases sustained despite Covid-19 lockdowns, U.N. says

GENEVA — Greenhouse gas concentrations climbed to a new record in 2019 and rose again this year despite an expected drop in emissions due to Covid-19 lockdowns, the World Meteorological Organization (WMO) said on Monday, warning against complacency.

Many scientists expect the biggest annual fall in carbon emissions in generations this year as measures to contain coronavirus have grounded planes, docked ships and kept commuters at home.

However, the WMO described the projected 2020 drop as a “tiny blip” and said the resulting impact on the carbon dioxide concentrations that contribute to global warming would be no bigger than normal annual fluctuations.

“…In the short-term the impact of the Covid-19 confinements cannot be distinguished from natural variability,” the WMO’s Greenhouse Gas Bulletin said.

The annual report released by the Geneva-based U.N. agency measures the atmospheric concentration of the gases — carbon dioxide, methane and nitrous oxide — that are warming our planet and triggering extreme weather events.

Levels of carbon dioxide, a product of burning fossil fuels that is the biggest contributor to global warming, touched a new record of 410.5 parts per million in 2019, it said.

The annual increase is larger than the previous year and beats the average over the last decade.

“Such a rate of increase has never been seen in the history of our records,” WMO Secretary-General Professor Petteri Taalas said, referring to rises since 2015, calling for a “sustained flattening of the (emissions) curve.”

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Global data is not yet available for 2020, but the trend of rising concentrations appears to be intact, the WMO said, citing initial readings from its Tasmania and Hawaii stations.

Like other scientific bodies, the WMO said it expects annual global carbon emissions to fall this year due to Covid measures, and ventured a preliminary estimate of between 4.2-7.5 percent.

Such a drop would not cause atmospheric carbon dioxide to go down, but would slow the rate of increase temporarily on a scale that falls within normal variations, it said.

Irrespective of what we do to curb emissions today, much of the carbon dioxide already emitted decades ago remains in the atmosphere and contributes to global warming, climate scientists say.

Over the 2018-2019 period, concentrations of the more potent heat-trapping gas methane increased by 8 parts per billion, the report said, slightly lower than the previous year-on-year change but still above-average over the last 10-year period.

Methane concentrations data is closely watched by scientists as the gas is prone to unexpected leaks such as those from the fossil fuel industry. That can make its atmospheric levels harder to predict than carbon dioxide.

Levels of nitrous oxide, which erodes the atmosphere’s ozone layer and expose humans to harmful ultraviolet rays, also increased in 2019 but at a lower rate than the previous year and on par with the average growth over the last decade.

Source Article

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Surge in greenhouse gases sustained despite COVID lockdowns: UN

By Emma Farge



a crowded beach on a sunny day: FILE PHOTO: People enjoy Bournemouth Beach during an unusual heat wave in Bournemouth, England


© Reuters/TOBY MELVILLE
FILE PHOTO: People enjoy Bournemouth Beach during an unusual heat wave in Bournemouth, England

GENEVA (Reuters) – Greenhouse gas concentrations climbed to a new record in 2019 and rose again this year despite an expected drop in emissions due to COVID-19 lockdowns, the World Meteorological Organization said on Monday, warning against complacency.



a map of a canyon: FILE PHOTO: Dried-up rivers and creeks can be seen in the Queensland outback near the town of Mount Isa, Australia


© Reuters/David Gray
FILE PHOTO: Dried-up rivers and creeks can be seen in the Queensland outback near the town of Mount Isa, Australia

Many scientists expect the biggest annual fall in carbon emissions in generations this year as measures to contain coronavirus have grounded planes, docked ships and kept commuters at home.

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However, the WMO described the projected 2020 drop as a “tiny blip” and said the resulting impact on the carbon dioxide concentrations that contribute to global warming would be no bigger than normal annual fluctuations.

“…In the short-term the impact of the COVID-19 confinements cannot be distinguished from natural variability,” the WMO’s Greenhouse Gas Bulletin said.

The annual report released by the Geneva-based U.N. agency measures the atmospheric concentration of the gases – carbon dioxide, methane and nitrous oxide – that are warming our planet and triggering extreme weather events.

Levels of carbon dioxide, a product of burning fossil fuels that is the biggest contributor to global warming, touched a new record of 410.5 parts per million (ppm) in 2019, it said.

The annual increase is larger than the previous year and beats the average over the last decade.

“Such a rate of increase has never been seen in the history of our records,” WMO Secretary-General Professor Petteri Taalas said, referring to a rise of 10 ppm since 2015, calling for a “sustained flattening of the (emissions) curve”.

WMO’s head of atmospheric environment research Dr. Oksana Tarasova said the magnitude of the increase in carbon dioxide levels over the past four years was comparable to changes seen during the shift from ice age to more temperate periods but, back then, the transition happened over a much longer timeframe.

“We humans did it without anything, with just with our emissions, and we did it within four years.” .

Global data is not yet available for 2020 but the trend of rising concentrations appears to be intact, the WMO said, citing initial readings from its Tasmania and Hawaii stations.

Like other scientific bodies, the WMO said it expects annual global carbon emissions to fall this year due to COVID measures, and ventured a preliminary estimate of between 4.2-7.5%.

Such a drop would not cause atmospheric carbon dioxide to go down, but would slow the rate of increase temporarily on a scale that falls within normal variations, it said.

“Our whole economy and our consumption patterns wire us to extremely high emissions even if we all sit in lockdown,” said Tarasova.

Irrespective of what we do to curb emissions today, much of the carbon dioxide already emitted decades ago remains in the atmosphere and contributes to global warming, climate scientists say.

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Chemists develop new material for the separation of carbon dioxide from industrial waste gases

Chemists develop new material for the separation of CO₂ from industrial waste gases
Electron microscopic cross-sectional image of the new hybrid material. It was possible to produce the glass platelets very precisely and, interrupted by spacers, to layer them on top of each other. Credit: Martin Rieß

Chemists at the University of Bayreuth have developed a material that could well make an important contribution to climate protection and sustainable industrial production. With this material, the greenhouse gas carbon dioxide (CO₂) can be specifically separated from industrial waste gases, natural gas, or biogas, and thereby made available for recycling. The separation process is both energy efficient and cost-effective. In the journal Cell Reports Physical Science the researchers present the structure and function of the material.


The Green Deal presented by the European Commission in 2019 calls for the net emissions of greenhouse gases within the EU to be reduced to zero by 2050. This requires innovative processes that can separate and retain CO2from waste gases and other gas mixtures so that it is not released into the atmosphere. The material developed in Bayreuth has one fundamental advantage over previous separation processes: It is capable of completely removing CO2from gas mixtures without chemically binding CO2.

These gas mixtures can be waste gases from industrial plants, but also natural gas or biogas. In all these cases, CO2accumulates in the cavities of the material solely due to physical interaction. From there, it can be released without great expenditure of energy, to be made available again as a resource for industrial production. Hence, the separation process works, chemically speaking, according to the principle of physical adsorption. Like a spacious storage tank, the new material can be filled with and emptied of carbon dioxide in an energy-efficient way. In Bayreuth laboratories, it was designed in such a way as to only separate out CO2and no other gas from the most varied gas mixtures.

“Our research team has succeeded in designing a material that fulfils two tasks at the same time. On the one hand, the physical interactions with CO2are strong enough to free and retain this greenhouse gas from a gas mixture. On the other hand, however, they are weak enough to allow the release of CO2from the material with only a small amount of energy,” says Martin Rieß M.Sc., first author of the new publication and doctoral researcher at the Inorganic Chemistry I research group at the University of Bayreuth.

The new material is an inorganic-organic hybrid. The chemical basis is clay minerals consisting of hundreds of individual glass platelets. These are only one nanometre thick each, and arranged precisely one above the other. Between the individual glass plates there are organic molecules that act as spacers. Their shape and chemical properties have been selected so that the pore spaces created are optimally tailored to accumulate CO2. Only carbon dioxide molecules can penetrate into the pore system of the material and be retained there. In contrast, methane, nitrogen, and other exhaust gas

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