On 7 April 2018, a suspected chemical attack on the Syrian town of Douma was reported to have killed at least 40 people and injured up to 500, including women and children. When Australian soldiers based in Mosul were exposed to a low-grade chemical attack by Islamic State in April 2017, the Department of Defence realised a 21st-century solution was needed.
“The current canisters in gas masks have been used by soldiers since World War I, and haven’t been improved since,” says Associate Professor Hill. “They offer virtually no protection from common chemicals like chlorine and ammonia, so we’ve been commissioned to make a new canister that can. We’ve already found an improvement up to a factor of 40 using metal-organic frameworks. ‘Once they’re on the market, they’ll be useful to anyone needing a safer gas mask, including our soldiers, but also firefighters, miners and construction workers.”
MOF are highly porous materials that make it possible to take-up, store, separate, release or protect gases or liquids from their pores. MOFs have the largest internal surface area of any known material that comes from their porous structure means that they can be used in a host of applications, from sensing to gas separation and storage and catalysis. They offer a real-world impact as vital as filtering toxic chemicals through a protective mask. Researchers at North Carolina State University have found that the MOF-treated fabric deactivated the chemical in minutes; this could form the basis for a thin, lightweight shield to degrade some chemical weapons which kill or injure on contact.
Metal–organic frameworks (MOFs) are periodic crystalline one-, two-, or three-dimensional structures composed of two major components: a metal ion or cluster of metal ions and an organic molecule called a linker. For this reason, the materials are often referred to as hybrid organic–inorganic materials. They are a subclass of coordination polymers, with the special feature that they are often porous. There are currently more than 60,000 known MOFs, and they are being investigated as promising materials for gas storage, including CO2 sequestration and hydrogen storage, and can even be used to harvest water in the desert.
However, MOF particles are usually difficult to be processed into application-specific devices because of their brittleness, insolubility, difficulty in molding, and low compatibility with other materials. It is an urgent need to shape MOF nanocrystals into various useful configurations by developing effective fabrication methods.
In a world-first breakthrough, researchers at Monash University, CSIRO, The University of Melbourne and The University of Texas at Austin have established an unprecedented new method to filter contaminants from groundwater and industrial wastewater, opening up new options to provide safe, clean drinking water in the developing world, and to protect the natural environment from industrial water pollution.
Although World Health Organisation guidelines determine fluoride to be safe for human consumption in levels up to 1.5 mg/litre, many developing countries have higher natural fluoridation levels in their groundwater, yet lack energy and cost-efficient methods to filter the water effectively. Also, the agriculture industry is increasingly searching for ways to clean up water pollution caused by fertiliser and pesticides, particularly in areas where contaminated run-off is at risk of entering rivers and the ocean.
Metal-organic frameworks (MOFs)
Metal-organic frameworks (MOFs) are made by linking inorganic and organic units by strong bonds (reticular synthesis). The flexibility with which the constituents’ geometry, size, and functionality can be varied has led to more than 20,000 different MOFs being reported and studied within the past decade. The organic units are ditopic or polytopic organic carboxylates (and other similar negatively charged molecules), which, when linked to metal-containing units, yield architecturally robust crystalline MOF structures with a typical porosity of greater than 50% of the MOF crystal volume.
Metal-organic frameworks exhibit the largest surface areas per gram known to man, thus exceeding those of traditional porous materials such as zeolites and carbons. Their surface area typically range from 1000 to 10,000 m2/g – one gram of MOF can have a surface area comparable to a FIFA soccer field. To date, MOFs with permanent porosity are more extensive in their variety and multiplicity than any other class of porous materials. These aspects have made MOFs ideal candidates for storage of fuels (hydrogen and methane), capture of carbon dioxide, and catalysis applications, to mention a few.
According to the pore sizes, porous materials can be categorized into three classes: microporous materials with pore sizes below 2 nm, mesoporous materials with pore sizes between 2 nm and 50 nm and macroporous materials with pore sizes larger than 50 nm. The majority of inorganic framework materials fall into the category of microporous materials.
The ability to vary the size and nature of MOF structures without changing their underlying topology gave rise to the isoreticular principle and its application in making MOFs with the largest pore aperture (98 Å) and lowest density (0.13 g/cm3). This has allowed for the selective inclusion of large molecules (e.g., vitamin B12) and proteins (e.g., green fluorescent protein) and the exploitation of the pores as reaction vessels.
One key feature that MOFs possess is their responsiveness toward incoming guest molecules, resulting in changes in their physical and chemical properties. Such uniqueness generally arises owing to the influenceable ligands and/or metal units that govern the formation of these ordered architectures. The suitable host–guest interactions play an important role in determining the specific responses of these materials and thus find important applications in sensing, catalysis, separation, conduction, etc.
Along these lines, the thermal and chemical stability of many MOFs has made them amenable to postsynthetic covalent organic and metal-complex functionalization. These capabilities enable substantial enhancement of gas storage in MOFs and have led to their extensive study in the catalysis of organic reactions, activation of small molecules (hydrogen, methane, and water), gas separation, biomedical imaging, and proton, electron, and ion conduction. At present, methods are being developed for making nanocrystals and supercrystals of MOFs for their incorporation into devices.
The building blocks of the framework – metals and organic linkers – can be combined in almost infinite ways to create novel materials. Therefore, unique structural characteristics can be achieved by tuning the basic materials according to their specified application. As a rule of thumb, MOFs outperform other materials by a factor of 10.
Inorganic framework and metal-organic framework (MOF) materials are receiving tremendous attraction from chemists, physicists and materials scientists from all over the world because of their commercial interests on various applications from storing hydrogen gas and stripping carbon dioxide from air to sensing chemical weapons and catalysing reactions.
The storage of oxygen has applications for use by first responders and military personnel, as well as in the medical and aerospace industries.In these applications there is a need to increase the amount of oxygen stored per unit volume, or reduce the oxygen storage pressure due to safety concerns. Porous carbons such as MSC-7R and AX-21, as well as the zeolite NaX,have been tested for oxygen storage. The biggest drawback of activated carbons is the heterogeneity of the pore sizes which makes their design difficult.
However, the ability to tune the pore geometry and size of MOFs makes them excellent candidates for oxygen storage applications. Researchers have experimented with HKUST-1 (Cu-BTC) and NU-125, and found that compared to the zeolite NaX and Norit activated carbon, NU-125 has an increased excess capacity for oxygen of 237 % and 98 %, respectively. These materials could ultimately prove useful for oxygen storage in medical, military, and aerospace applications.
Breakthrough new research finds clean and green way to filter contaminants from water
In their study published in Nature Communications today (Thursday, 6 June 2019), the international research team outline their unprecedented control method through which to separate particular negatively-charged ions, termed anions, from water using Metal-Organic Frameworks (MOFs). The team developed a MOF with precisely tuned pores of a size and chemistry to be compatible with the selected anion.
In this instance, as outlined in the research paper entitled Fast and selective fluoride ion conduction in sub-1-nanometer metal-organic framework channels, the team demonstrated the success of this technique by identifying a MOF that showed high selectivity for fluoride anions over other anions.
When passing over the filter material, the selected anion was attracted to the pore, and easily passed through with little force or resistance, while other anions were largely unable to pass through the pores. This is an unprecedented breakthrough, as in other water filtering methods, all forms of anions need to be removed and filtered to extract the unwanted substance from the water, a costly and energy-intensive process that often requires some of the filtered anions to be added back into the water once the unwanted anions are removed.
“Based on our research, we now have the capability to produce simple and affordable water filters that can be used safely and effectively anywhere in the world,” said Professor Wang. “This is a significant outcome for people in developing countries who lack access to safe, clean drinking water, and for industries who are increasingly seeking ways to reduce the cost of their environmental impact. Our findings also prove we have the capability to determine the most effective filtering material and method to suit a specific material, or a particular industry need.”
“The ability to selectively remove targeted ions from water with such high levels of specificity provides new pathways to address fundamental challenges in energy-efficient production of fit-for-purpose water for a variety of water and energy applications,” said Professor Freeman.
Breakthrough technology purifies water using using metal-organic frameworks (MOFs) & sunlight
A global research team has been able to transform brackish water and seawater into safe, clean drinking water in less than 30 minutes using metal-organic frameworks (MOFs) and sunlight. Lead author Professor Huanting Wang from the Department of Chemical Engineering at Monash University in Australia, said this work opened up a new direction for designing stimuli-responsive materials for energy-efficient and sustainable desalination and water purification. The World Health Organization suggests good quality drinking water should have a total dissolved solid (TDS) of <600 parts per million (ppm). Researchers were able to achieve a TDS of <500 ppm in just 30 minutes and regenerate the MOF for reuse in four minutes under sunlight.
“Desalination has been used to address escalating water shortages globally. Due to the availability of brackish water and seawater, and because desalination processes are reliable, treated water can be integrated within existing aquatic systems with minimal health risks,” Professor Wang said. “But, thermal desalination processes by evaporation are energy-intensive, and other technologies, such as reverse osmosis, has a number of drawbacks, including high energy consumption and chemical usage in membrane cleaning and dechlorination. “Sunlight is the most abundant and renewable source of energy on Earth. Our development of a new adsorbent-based desalination process through the use of sunlight for regeneration provides an energy-efficient and environmentally-sustainable solution for desalination.”
Metal-organic frameworks are a class of compounds consisting of metal ions that form a crystalline material with the largest surface area of any material known. In fact, MOFs are so porous that they can fit the entire surface of a football field in a teaspoon. The research team created a dedicated MOF called PSP-MIL-53. This was synthesised by introducing poly(spiropyran acrylate) (PSP) into the pores of MIL-53 – a specialised MOF well-known for its breathing effects and transitions upon the adsorption of molecules such as water and carbon dioxide. Researchers demonstrated that PSP-MIL-53 was able to yield 139.5L of fresh water per kilogram of MOF per day, with a low energy consumption. This was from desalinating 2,233 ppm water sourced from a river, lake or aquifer.
Professor Wang said this highlights the durability and sustainability of using this MOF for future clean water solutions. “This study has successfully demonstrated that the photoresponsive MOFs are a promising, energy-efficient, and sustainable adsorbent for desalination,” Professor Wang said. “Our work provides an exciting new route for the design of functional materials for using solar energy to reduce the energy demand and improve the sustainability of water desalination. “These sunlight-responsive MOFs can potentially be further functionalised for low-energy and environmentally-friendly means of extracting minerals for sustainable mining and other related applications.”
Chemical weapons could be neutralised by new coating for clothes
Researchers at North Carolina State University have developed a powdery coating which can be “grown” onto fabric and may be able to deactivate chemical weapons such as sarin. Scientists have, for several years, been exploring the properties of zirconium-based metal-organic framework (MOF) powders. These are tiny structures covered in pores, which can absorb a huge quantity of gases. The zirconium within the structure helps neutralise toxins.
Creating MOFs, however, is an expensive and time-consuming task, and keeping the powders stable enough to stick to protective clothing has proved a challenge. Taking an alternative approach, the researchers tried “growing” MOFs onto fabric at room temperature.
They exposed a treated synthetic fabric, polypropylene, to a mixture of zirconium-based MOF, solvent and binding agents. The MOF-covered fabric was then tested by exposure to a chemical with similar properties to sarin and other nerve agents. The researchers suggest that protective clothing coated with zirconium-based MOF could be helpful for soldiers and emergency workers at risk of chemical attack.
New SOFT e-textiles could offer advanced protection for soldiers and emergency personnel
In research published in the Journal of the American Chemical Society, the chemistry team of Katherine Mirica and Merry Smith describe the creation of new smart fabrics—named SOFT, for Self-Organized Framework on Textiles. The SOFT e-textile uses metal-organic frameworks (MOFs) to improve detection and protection from toxic chemicals
According to researchers, the SOFT devices featuring MOFs display reliable conductivity, enhanced porosity, flexibility and stability to washing. The fabrics are also stable in heat, have good shelf-lives and retain a full-range of utility under humid conditions.
Among other firsts described in the research are flexible, textile-supported electronic sensors based on materials known as metal-organic frameworks, or MOFs. In the study, the authors also describe a “simple” approach for integrating these conductive, porous materials into cotton and polyester fabrics to produce the e-textiles.
The research team also describes a one-step e-textile fabrication method based on MOFs through a process that Mirica describes as “similar to a building framework assembling itself.” Cotton and polyester textiles coated with conductive crystals at the fiber-level are created by direct self-assembly of molecules with organic molecular struts connected by metallic linkers from solution.
As part of the study, the Dartmouth team demonstrated that the new smart fabric can detect common toxic chemicals. Both the vehicle exhaust pollutant, nitric oxide, and the corrosive poison that reminds most of rotten eggs, hydrogen sulfide, were effectively identified by the SOFT system. In addition to sensing the chemicals, the electronic textiles are capable of capturing and filtering the dangerous toxins.
Wearable electronics are thought to have great potential in areas including homeland security, communication and healthcare. Soldiers, emergency personnel, factory workers and others that risk exposure to toxic chemicals could benefit from the new smart fabrics. The materials could also help medical patients that require monitoring of specific airborne chemicals that come from the environment or even from their own bodies.
Composites made from metal-organic frameworks can destroy nerve agents under relevant conditions.
A textile coated with metal-organic frameworks (MOFs) could make an efficient anti-nerve agent material, according to experiments by researchers at Northwestern University in the US. The MOFs, which are based on zirconium, could act as catalysts to degrade chemical warfare agents such as VX and soman (GD) much faster than existing technologies, which are based on activated carbon and metal-oxide blends. The composite material, which might be used in protective suits and face masks for soldiers on the battlefield, does not require liquid water to work either, as previously thought.
Although the chemical degradation reaction requires water, the researchers say the nanopores in the MOFs can supply the needed water by absorbing it from ambient humidity. This will make it easier to deploy filters and other anti-nerve agent equipment based on this material in the field, Farha explains.
In their experiments, the team studied a Zr-based MOF with the chemical formula [Zr6O4(μ3-OH)4(OH)6(H2O)6(BTC)2]·nH2O (more commonly known as MOF-808). They began by applying a solution containing this material and polyethylenimine (PEI) to strips of cotton fabric. After allowing the fabric to dry overnight, they exposed it to DMNP, a nerve agent simulant commonly used in academic research labs. These tests showed that the MOF/PEI composite degraded DMNP even in the absence of water.
Farha and colleagues also tested the material’s durability. They found that the MOF remains securely adhered to the cotton and retains its crystallinity even when immersed in water and agitated for 24 hours. The composite’s catalytic activity also remains high after being exposed to ambient air for 100 days. In a final series of tests, they found the material retains its catalytic activity when exposed to sweat, atmospheric carbon dioxide and pollutants such as octane – environmental and physiological conditions similar to what a soldier might face on the battlefield.
The researchers, who report their work in the Journal of the American Chemical Society (JACS), hope their material will one day replace existing anti-CWA technology – namely activated carbon and metal-oxide blends, which react more slowly to nerve agents. Ultimately, they would like to create an improved MOF composite that instantly detoxifies these agents. “We are also interested in designing fabrics that can degrade multiple agents at the same time,” Farha tells Physics World.
US Army contracts NuMat Technologies to develop nanoporous materials
US-based NuMat Technologies has received a contract to develop next-generation materials to protect and sustain the modern combatant. The contract will enable NuMat Technologies to use its nanoporous materials called metal organic frameworks (MOF) in the creation of new filtration technology tools to better combat emerging threats from unknown toxic agents. The company will explore the use of MOFs in reinventing gas masks, breathing apparatus, and other equipment intended to provide new protection for the modern soldier. NuMat Technologies founder and CEO Benjamin Hernandez said: “We are excited to bring our state-of-the-art technology to the warfighter, including advanced toxic industrial chemical filtration, purification, and abatement.
MOFs, which are highly programmable nanomaterials with higher surface areas to absorb toxic chemicals, have already been deployed in the electronics and speciality gas sectors. NuMat noted that the contract amount will be used to construct a commercial-scale manufacturing site for MOFs and an advanced application development lab for next-generation filtration and purification technologies.
RDECOM C&B Center Chemical Engineering Research Greg Peterson said: “We have already demonstrated that particular MOFs are highly effective at reacting with toxic gases such as nerve agents and toxic industrial chemicals at the lab scale. “Now our goal is to integrate these materials into a variety of fielded items across the chemical and biological defence commodity area.”
New Technique to Find Latent Prints at Crime Scenes
Latent prints are left by chance on a surface when someone touches an item, and represent a partial impression of the unique ridge pattern located on an individual’s fingers and palms. Latent prints on nonporous surfaces such as weapons, vehicles, glass bottles, and plastic bags can pose a challenge for investigators because they are very fragile. They consist of 99% water and approximately 1% amino acids, lipids, and other compounds that can easily be wiped away if the evidence is not handled carefully.
According to policeone.com, a new time-saving technology has recently been developed by Dr. Kang Liang of the Commonwealth Scientific and Industrial Research Organization (CSIRO). The method involves identifying an item of evidence that may contain latent print residue and adding a small amount of metal-organic framework (MOF) crystals. The crystals bond with the fingerprint residue much like superglue fuming creating an outline of the ridge detail. The reaction happens within 30 seconds and the prints can immediately be viewed with ultraviolet light and digitally photographed.
This new technology has the potential to save crime scene investigators an enormous amount of time. Furthermore, the technique is not limited to a crime laboratory setting but can be utilized at the crime scene. Rather than collecting multiple items and having to transport the evidence to the crime laboratory for processing, the crystals can be applied to surfaces such as windows, door knobs, and electronics at the actual scene.
References and resources also include