Technology developed by researchers at Ben-Gurion University of the Negev in partnership with Rice University in Houston, Texas is being commercialized by LIGC Application Ltd. to develop and manufacture products for filtration systems, including those that filter COVID-19 airborne particles.
LIGC is a company at the forefront of laser-induced graphene (LIG) commercialization. Hubei Forbon Technology Co. Ltd. (300387.SZ) in Wuhan, China provided $3 million in funding.
“For the past five years, our lab at BGU's Zuckerberg Institute for Water Research has focused on the development of LIG, specifically in antimicrobial filtration and environmental applications,” says Dr. Chris Arnusch. “We are excited to be commercializing our technology in a number of air filtration products for COVID-19 and other specialized filtration applications.”
LIGC Co-founder and Chief Executive Officer Yehuda Borenstein says, “In the absence of better filtration technology, the indoor spaces where we used to spend most of our ‘normal’ life—schools, stores and workplaces— due to COVID-19 present a real risk. This technology will provide cleaner and more breathable air with lower energy and maintenance costs and virtually silent sound levels.”
Active air filters made with LIG are designed to damage and destroy organic particles including bacteria, mold spores and viruses at the micron and sub-micron levels when passed through a microscopic network of porous graphene.
This cost-effective and scalable approach is produced using commercially available CO2 lasers to create a conductive graphene mesh. The graphene mesh heats, electrocutes and neutralizes organic particles and pathogens with revolutionary efficiency compared to active carbon filters, UV-C and fiber HEPA filters that are used widely in schools, offices, homes, ships, and other facilities. Aircraft are already equipped with HEPA filters that remove viruses and bacteria from the circulated cabin air, but at high energy and maintenance costs.
Since the LIGC filter uses low voltage electricity to eliminate bacteria and viruses, lower density filtration media can be used, resulting in significantly less energy consumption. In addition, LIGC active filters require lower maintenance than other filters and are safe for the operator during maintenance and replacement.
“To understand the technology, imagine the porous graphene is an electric fence that functions like a mosquito zapper at the submicron level,” Bornstein says. “When an airborne bacteria or virus touches the graphene surface, it is shocked at a low voltage and currents that are safe for use. While 2020 has highlighted the importance of protecting against airborne viruses, the post-pandemic world will likely show us how important it is to do so without increasing energy costs past the point of affordability.”
Israeli startup LIGC announced a $3M USD Series A round from public listed Wuhan-based Hubei Forbon Technology Co. Ltd (300387.SZ). The funding will be used to scale and manufacture LIGC's Laser-Induced Graphene filters (LIG).
The technology was developed by Houston's Rice University in partnership with Ben-Gurion University (BGU) of the Negev in Israel and was licensed from BGN technologies, the technology transfer company of BGU. It utilizes graphene's conductivity to run an electric current through the filter.
"For a simplified analogy, one can see the graphene as an electric fence to the micron and submicron level with similar functionality as a mosquito zapper," said LIGC Co-founder & CEO Yehuda Borenstein. "When an airborne bacteria or virus touches the graphene surface, it's electrified and damaged, and only low voltages and currents that are safe for use are needed."
Since the LIGC filter uses active means to eliminate bacteria and viruses, lower density filtration media can be used, resulting in significantly less energy consumption. In addition, LIGC active filters require lower maintenance than other filters and are safe to the operator during maintenance and replacement.
Air filters are all around us in airplanes, ships, schools, offices, and homes. In some cases, like airplanes, they already have HEPA filters that remove viruses and bacteria from the air circulated but at high energy and maintenance costs.
While 2020 has underlined the importance of protecting against airborne viruses, the post-pandemic world will likely show us how important it is to do so without increasing energy costs past the point of affordability.
"There's still much to learn about COVID-19, but it's now established that airborne transmission is possible," said Borenstein. "In the absence of better filtration technology, the indoor spaces where we used to spend most of our 'normal' life--schools, stores, offices-- present a real risk."
A shield of graphene helps particles destroy antibiotic-resistant bacteria and free-floating antibiotic resistance genes in wastewater treatment plants.
Think of the new strategy developed at Rice University as “wrap, trap and zap.”
The labs of Rice environmental scientist Pedro Alvarez and Yalei Zhang, a professor of environmental engineering at Tongji University, Shanghai, introduced microspheres wrapped in graphene oxide in the Elsevier journal Water Research.
Alvarez and his partners in the Rice-based Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment (NEWT) have worked toward quenching antibiotic-resistant “superbugs” since first finding them in wastewater treatment plants in 2013.
“Superbugs are known to breed in wastewater treatment plants and release extracellular antibiotic resistance genes (ARGs) when they are killed as the effluent is disinfected,” Alvarez said. “These ARGs are then discharged and may transform indigenous bacteria in the receiving environment, which become resistome reservoirs.
“Our innovation would minimize the discharge of extracellular ARGs, and thus mitigate dissemination of antibiotic resistance from wastewater treatment plants,” he said.
The Rice lab showed its spheres — cores of bismuth, oxygen and carbon wrapped with nitrogen-doped graphene oxide — inactivated multidrug-resistant Escherichia coli bacteria and degraded plasmid-encoded antibiotic-resistant genes in secondary wastewater effluent.
The graphene-wrapped spheres kill nasties in effluent by producing three times the amount of reactive oxygen species (ROS) as compared to the spheres alone.
The spheres themselves are photocatalysts that produce ROS when exposed to light. Lab tests showed that wrapping the spheres minimized the ability of ROS scavengers to curtail their ability to disinfect the solution.
The researchers said nitrogen-doping the shells increases their ability to capture bacteria, giving the catalytic spheres more time to kill them. The enhanced particles then immediately capture and degrade the resistant genes released by the dead bacteria before they contaminate the effluent.
“Wrapping improved bacterial affinity for the microspheres through enhanced hydrophobic interaction between the bacterial surface and the shell,” said co-lead author Pingfeng Yu, a postdoctoral research associate at Rice’s Brown School of Engineering. “This mitigated ROS dilution and scavenging by background constituents and facilitated immediate capture and degradation of the released ARGs.”
Because the wrapped spheres are large enough to be filtered out of the disinfected effluent, they can be reused, Yu said. Tests showed the photocatalytic activity of the spheres was relatively stable, with no significant decrease in activity after 10 cycles. That was significantly better than the cycle lifetime of the same spheres minus the wrap.
Deyi Li of Tongji University, Shanghai, is co-lead author of the paper. Co-authors are Xuefei Zhou and Zhang of Tongji and Jae-Hong Kim, the Henry P. Becton Sr. Professor and Chair of Chemical and Environmental Engineering at Yale University. Alvarez is the George R. Brown Professor of Civil and Environmental Engineering, a professor of chemistry, of materials science and nanoengineering, and of chemical and biomolecular engineering and director of NEWT.
The National Science Foundation, the National Natural Science Foundation of China and the National Key R&D Program of China supported the research.
Project lead Ayrat Dimiev has been working on this topic since 2012, when he was a part of Professor James Tour's group at Rice University. First results saw light in 2014. That paper, which has amassed 490 citations at this moment, dealt with the mechanism of turning graphite into graphene oxide (GO). Dr. Dimiev later transferred to the private sector and resumed his inquiries in 2017, after returning to Kazan Federal University and opening the Advanced Carbon Nanomaterials Lab. The experimental part of this new publication was conducted by Dr. Ksenia Shukhina and Dr. Artur Khannanov.
Natural graphite, used as the precursor for graphene oxide production, is a highly ordered crystalline inorganic material, which is believed to be formed by decay of organic matter. It is extremely thermodynamically stable and resistant to be converted to the organic-like metastable graphite oxide. On this route, it goes through several transformations, resulting in respective intermediate products. The first intermediate product is graphite intercalation compound (GIC). GICs have been intensively studied in the second half of the 20th century. In recent years they gained renewed interest due to the discovery of graphene and related materials. The second step of the complex reaction, i.e. the conversion of GIC to pristine graphite oxide, remained mysterious. The most interesting question was about the nature of species attacking carbon atoms to form covalent C-O bonds. For many years, it was conventionally assumed that the attacking species are the manganese derivatives like Mn2O7 or MnO3+. In this study, the authors unambiguously demonstrated that the manganese derivatives do not even penetrate graphite galleries; they only withdraw electron density from graphene, but the actual species attacking carbon atoms are water molecules. Thus, reaction cannot proceed in fully anhydrous conditions, and speeds up in presence of small quantities of water.
Another new finding, registered by Ksenia Shukhina for the first time, was the imaginary reversibility of the C-O bond formation, as long as the graphite sample remains intercalated with sulfuric acid. The as-formed C-O bonds can be easily cleaved by the laser irradiation, converting GO back to stage-1 GIC in the irradiated areas of the graphite flake. After careful analysis, this "reversibility" was interpreted by the authors as the mobility of the C-O bonds, i.e. the bonds do not cleave, but freely migrate along the graphene plane for micron-scale distances. The discovered phenomena and proposed reaction mechanism provide rationale for a range of the well-known but yet poorly understood experimental observations in the graphene chemistry. Among them is the existence of the oxidized and graphenic domains in the GO structure.
The results of this fundamental study give a comprehensive view on the driving forces of the complex processes occurring during the transformation of graphite into graphene oxide. This is the first time such a multifaceted description of a dynamic system has been made, and this is the result not only of newly obtained experimental data, but also of many years of reflection on the issue by the project lead. Understanding these processes will finally let one to control this reaction and get products with desired properties. This applies not only to the final product of graphene oxide, but also to the entire family of materials obtained by exposing graphite to acidic oxidizing mixtures: expanded graphite, graphene nano-platelets containing from 3 to 50 graphene sheets, graphite intercalates, and doped graphene. As for graphene oxide itself, its successful use has already been repeatedly demonstrated in such areas as composite materials, selective membranes, catalysis, lithium-ion batteries, etc. However, the use of graphene oxide is hampered by the high cost of its production and the lack of control over the properties of the synthesized product. The published research addresses both of these problems.
Currently, work is ongoing to study the interaction of graphene oxide with metals. The researchers are firmly convinced that this process is based not just on electrostatic attraction, or on non-specific adsorption, as it is commonly believed, but on a chemical interaction with bond formation through the coordination mechanism. The objective now is to describe the complex reaction mechanism of the rearrangements, leading to the metal bonding in the dynamic structure of graphene oxide.
Rice University chemist James Tour has won a Royal Society of Chemistry Centenary Prize. The award, given annually to up to three scientists from outside Great Britain, recognizes researchers for their contributions to the chemical sciences industry or education and for successful collaborations. Tour was named for innovations in materials chemistry with applications in medicine and nanotechnology.
The prestigious award, established in 1947, comes with a 5,000-pound (about $6,260) cash prize and a medal. Winners are invited to undertake a lecture tour of the United Kingdom, but the COVID-19 pandemic has delayed that until 2021.
Additional winners this year are Teri Odom, the chair and Charles E. and Emma H. Morrison Professor of Chemistry at Northwestern University, and Eric Anslyn, the Welch Regents Chair and University Distinguished Teaching Professor at the University of Texas at Austin. Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer science and of materials science and nanoengineering at Rice.
“Receiving the Royal Society of Chemistry 2020 Centenary Prize is an enormous honor,” Tour said. “The award recognizes the accomplishments of my research group over a period of 32 years. I am greatly indebted to a host of students, postdocs and collaborators that have carried the weight of this research endeavor.
“We have sought to use chemistry to extend the boundaries of new materials development for use in medicine, electronic devices, nano-enhanced structures and renewable energy platforms,” he said. “It is a joy to realize the work done by this array of people in and with my laboratory has afforded such advances that are being recognized by this Centenary Prize.”
Work by Tour and his group in recent years includes the development of versatile laser-induced graphene, flash graphene from waste material, light-activated nanodrills that destroy cancer cells and “superbug” bacteria, silicon-oxide memory circuits that have flown on the International Space Station, the development of graphene quantum dots from coal, asphalt-based materials to capture carbon dioxide from gas wells, and the use of nanoparticles to quench damaging superoxides after an injury or stroke.
“We live in an era of tremendous global challenges, with the need for science recognized now more so than ever — so it is important to recognize those behind the scenes who are making significant contributions towards improving the world we live in,” said acting Royal Society of Chemistry chief executive Helen Pain. “In recognizing the work of Professor Tour, we are also recognizing the important contribution this incredible network of scientists makes to improve our lives every day.”
These are scary times, aren't they? First and foremost, my thoughts and prayers go out to anyone who is directly affected by the current global crisis caused by the SARS-CoV-2 coronavirus. It's an extremely serious issue that will require worldwide cooperation to overcome.
I have very clear and distinct memories of the previous SARS epidemic. In March 2003, while working at Rice University, I was helping to lead a group of ~50 science and engineering students on an overseas study trip to Hong Kong and Singapore with my former Rice colleague, Dr. Cheryl Matherly (who is now at Lehigh University). We were caught in the middle of the rapidly developing crisis and our travel itinerary had us departing Singapore for Hong Kong on the day the Singapore government warned its own citizens not to travel to Hong Kong!
Fortunately, everyone in our student group made it through that experience safely, and as unsettling as it was, the current situation is much much worse, with as yet unknown - but sure to be significant - social, economic and political ramifications that will most definitely impact future generations around the world.
I am currently based in Bangkok, Thailand, which is a global tourist destination. While we were fortunately to escape the first wave of of the SARS-CoV-2 virus that emanated from China, we're now faced with a second wave imported from Europe. We're not quite under total lockdown here, but things appear to be headed in that direction. It is clear to me form observation that the several governments in the region (Singapore, Hong Kong, and Taiwan, to be specific) are applying the lessons they learned from the previous SARS epidemic to help control the current pandemic. This give me hope, and the circumstances in general have given me plenty of time to think and reflect about what - if anything - I and my company, planarTECH, can do to improve this situation.
Graphene: The "Wonder Material"
I was lucky to fall into the world of graphene and 2D materials by accident through acquaintance with another former Rice University colleague, Dr. James Tour, and conversations I had with him 8 years ago. I will not spend a lot of time here talking about the specific properties of graphene as such information is widely available. The European Union's Graphene Flagship project, for example, has an excellent overview. The University of Manchester - where graphene was first isolated and where planarTECH's Chairman, Ray Gibbs, currently serves as the Director of Commercialization for the Graphene Engineering and Innovation Centre - also has a fantastic YouTube channel with many instructive videos about graphene and its properties.
With all of the amazing properties of graphene, the question is, can it offer any kind of solution to the current pandemic and global crisis?
Academic Work: Graphene's Antiviral Properties
The short answer to the question above is "possibly," but with some caveats. In particular, it would appear that graphene oxide (GO) may play a role in providing a solution.
I should say that I am not a doctor, an epidemiologist or someone with formal training in the biological sciences. I am an engineer by trade, and for the last 8 years, an entrepreneur in the field of graphene. However, since entering the graphene industry, I have grown accustomed to reading academic papers in order to understand the potential applications for graphene.
A paper published in 2015 by researchers at the Huazhong Agricultural University (ironically located in Wuhan, China, where the current pandemic originated) explored the antiviral properties of graphene oxide, and the authors of the paper concluded "that GO and rGO exhibit broad-spectrum antiviral activity toward both DNA virus (PRV) and RNA virus (PEDV) at a noncytotoxic concentration," and that "the broad-spectrum antiviral activity of GO and rGO may shed some light on novel virucide development." While encouraging, it should be noted that the researchers looked specifically at pseudorabies virus (PRV) and porcine epidemic diarrhea virus (PEDV), not the SARS-CoV-2 virus responsible for the current global pandemic.
Another paper published in 2017 by researchers at Southwest University in China looked at cyclodextrin functionalized graphene oxide and it's possible role in combatting respiratory syncytial virus (RSV), concluding that "the curcumin loaded functional GO was confirmed with highly efficient inhibition for RSV infection and great biocompatibility to the host cells." Likewise, a third paper published in 2019 by researchers at Sichuan Agricultural University in China demonstrated that "GO/HY [graphene oxide/hypericin] has antiviral activity against NDRV [novel duck reovirus] both in vitro and in vivo."
The conclusion we can draw from these works is that graphene oxide may offer a platform to fight a variety of viral infections (such as the SARS-CoV-2 coronavirus), possibly as some form of coating, though certainly more work needs to be done.
(Note that my good friends over at The Graphene Council had a recent and excellent blog post covering the same 3 articles in a little more detail. And kudos to them for shining light on the topic before me!)
Productization: From Lab to Market
If there's one thing I've learned from the past 8 years being involved with graphene commercialization (and the past 14 years working directly in the Asian supply chain) is that it is one matter to write an excellent academic paper as a proof-of-concept, but it is an entirely different matter to take work from an academic lab and turn it into a real product.
With respect to graphene in general, what we are seeing today is definite movement on the Gartner hype cycle from the Trough of Disillusionment to the Slope of Enlightenment. Real products using graphene are now on the market. One such example is the recent announcement of of a collaboration between UK-based Haydale Graphene Industries plc and Korea-based ICRAFT Co., Ltd. that results in the release of a graphene cosmetic face mask. And I am pleased to be able to say that - in connection with my previous responsibilities for Haydale's Asia-Pacific operations - I had some role (together with my colleague Yong-jae "James" Ji) in getting this product off the ground and into the marketplace.
While this may seem like a trivial accomplishment given the context and seriousness of the current global pandemic, I offer this example as proof that graphene can be utilized in an everyday, cost-sensitive product, and it is not such a great conceptual leap to go from a cosmetic face mask to a protective face mask, which as we all know are in great demand these days (especially here in Asia). I would invite iCRAFT (or anyone else) to consider collaboration with planarTECH to develop such a product. (Above photo courtesy of Macau Photo Agency on Unsplash.)
Productization: Existing Products?
Very much related to this topic and very curious is a recent public announcement by LIGC Applications of its Guardian G-Volt face mask with a graphene-based filtration system. However, my understanding is that LIGC is not employing graphene specifically for it's potential antiviral properties but rather for its potential to enhance a filtration system, including (due to graphene's electrical conductivity) the ability to pass an electrical charge through the mask that "would repel any particles trapped in the graphene mask."
What I find very curious about this case is that subsequent to this announcement, LIGC's Indiegogo crowdfunding campaign, which was live, has now been placed under review, and the company's pitch video on YouTube has likewise been made private. I do not know what has happened here - perhaps is was perceived as poor timing? - but as a fellow entrepreneur who is conducting my own crowdfunding campaign, I wish LIGC the best of luck with its product development and ultimate launch. I definitely want to see more viable graphene products in the marketplace.
The Graphene Supply Chain: planarTECH's Role
One of the challenges the graphene industry faces overall is scalability. Very few graphene companies today (if any at all) can produce graphene at the scale, at the right cost, and with the consistent quality such that it can be used for truly high-volume applications. Over the past 8 years, I have met numerous customers, mostly in Asia, who want to use graphene in their products but cannot find a secure and stable supply that meets their expectations on specification, volume, and price.
At planarTECH we're interested in not only the end applications, but also in solving this problem of production scalability. While we have in the past mainly been focused on production systems for graphene and other 2D materials by Chemical Vapor Deposition (CVD), we also recently started offering continuous flow production systems for graphene oxide, which we believe can take graphene oxide production from lab-scale, high-cost (grams per week) to production-scale, low-cost (kilograms per hour). We're actively seeking partners to work with us on setting up production and exploration of the application space for graphene oxide, and we're currently conducting a crowdfunding campaign on Seedrs to help us expand our business and make graphene a commercial reality. As seen above, we think graphene oxide's antiviral properties can be exploited to make new and useful products.
I should clarify and caution that planarTECH is not in the position today to offer a graphene-based product that can immediately help alleviate current crisis and prevent widespread infection. Unfortunately, such a product is realistically 1-2 years away. But what we can offer is market expertise specific to graphene, production technologies, and experience in taking products from the idea phase to a reality in the marketplace.
Conclusion: Graphene is a Possible Solution
To conclude, I would like to reiterate a few broad points.
• Graphene (graphene oxide in particular) and coatings made from graphene would appear to have antiviral properties as reported in several published academic papers.
• Real commercial products exist that use graphene, but the industry as a whole still faces challenges around scalability, cost and quality.
• An immediate graphene-based solution to alleviate the effects of the global SARS-CoV-2 coronavirus pandemic is likely unrealistic, but could be possible in the future.
• planarTECH has a role in the supply chain and is seeking partners, as well as investors via its crowdfunding campaign, to expand its business and help end customers develop useful products.
Graphene is a paradox: it is the thinnest material known to science, yet also one of the strongest. Now, research from U of T Engineering shows that graphene is also highly resistant to fatigue — able to withstand more than a billion cycles of high stress before it breaks.
Graphene resembles a sheet of interlocking hexagonal rings, similar to the pattern you might see in bathroom flooring tiles. At each corner is a single carbon atom bonded to its three nearest neighbours. While the sheet could extend laterally over any area, it is only one atom thick.
The intrinsic strength of graphene has been measured at more than 100 gigapascals, among the highest values recorded for any material. But materials don’t always fail because the load exceeds their maximum strength. Small repetitive stresses can weaken materials by causing microscopic dislocations and fractures that slowly accumulate over time, a process known as fatigue.
“To understand fatigue, imagine bending a metal spoon,” says Professor Tobin Filleter (MIE), one of the senior authors of the study, which was recently published in Nature Materials. “The first time you bend it, it just deforms. But if you keep working it back and forth, eventually it’s going to break in two.”
The research team — consisting of Filleter, fellow U of T Engineering professors Chandra Veer Singh (MSE) and Yu Sun (MIE), their students, and collaborators at Rice University — wanted to know how graphene would stand up to repeated stresses. Their approach included both physical experiments and computer simulations.
“In our atomistic simulations, we found that cyclic loading can lead to irreversible bond reconfigurations in the graphene lattice, causing catastrophic failure on subsequent loading,” says Singh, who along with postdoctoral fellow Sankha Mukherjee (MSE) led the modelling portion of the study. “This is unusual behaviour in that while the bonds change, there are no obvious cracks or dislocations, which would usually form in metals, until the moment of failure.”
PhD candidate Teng Cui, who is co-supervised by Filleter and Sun, used the Toronto Nanofabrication Centre to build a physical device for the experiments. The design consisted of a silicon chip etched with half a million tiny holes only a few micrometres in diameter. The graphene sheet was stretched over these holes, like the head of a tiny drum.
Using an atomic force microscope, Cui then lowered a diamond-tipped probe into the hole to push on the graphene sheet, applying anywhere from 20 to 85 per cent of the force that he knew would break the material.
“We ran the cycles at a rate of 100,000 times per second,” says Cui. “Even at 70 per cent of the maximum stress, the graphene didn’t break for more than three hours, which works out to over a billion cycles. At lower stress levels, some of our trials ran for more than 17 hours.”
As with the simulations, the graphene didn’t accumulate cracks or other tell-tale signs of stress — it either broke or it didn’t.
“Unlike metals, there is no progressive damage during fatigue loading of graphene,” says Sun. “Its failure is global and catastrophic, confirming simulation results.”
The team also tested a related material, graphene oxide, which has small groups of atoms such as oxygen and hydrogen bonded to both the top and bottom of the sheet. Its fatigue behaviour was more like traditional materials, in that the failure was more progressive and localized. This suggests that the simple, regular structure of graphene is a major contributor to its unique properties.
“There are no other materials that have been studied under fatigue conditions that behave the way graphene does,” says Filleter. “We’re still working on some new theories to try and understand this.”
In terms of commercial applications, Filleter says that graphene-containing composites — mixtures of conventional plastic and graphene — are already being produced and used in sports equipment such as tennis rackets and skis.
In the future, such materials may begin to be used in cars or in aircraft, where the emphasis on light and strong materials is driven by the need to reduce weight, improve fuel efficiency and enhance environmental performance.
“There have been some studies to suggest that graphene-containing composites offer improved resistance to fatigue, but until now, nobody had measured the fatigue behaviour of the underlying material,” he says. “Our goal in doing this was to get at that fundamental understanding so that in the future, we’ll be able to design composites that work even better.”
Two-dimensional materials are atomically thin, the most well-known being graphene, a single-atom-thick layer of carbon atoms. "People have struggled to make these 2D materials without defects," said Mauricio Terrones, Verne M. Willaman Professor of Physics, Penn State. "That's the ultimate goal. We want to have a 2D material on a four-inch wafer with at least an acceptable number of defects, but you want to evaluate it in a quick way."
The researchers' -- who represent Penn State, Northeastern University, Rice University and Universidade Federal de Minas Gerais in Brazil -- solution is to use laser light combined with second harmonic generation, a phenomenon in which the frequency of the light shone on the material reflects at double the original frequency. They add dark field imaging, a technique in which extraneous light is filtered out so that defects shine through. According to the researchers, this is the first instance in which dark field imaging was used, and it provides three times the brightness of the standard bright field imaging method, making it possible to see types of defects previously invisible.
"The localization and identification of defects with the commonly used bright field second harmonic generation is limited because of interference effects between different grains of 2D materials," said Leandro Mallard, a senior author on a recent paper in Nano Letters and a professor at Universidade Federal de Minas Gerais. "In this work we have shown that by the use of dark field SHG we remove the interference effects and reveal the grain boundaries and edges of semiconducting 2D materials. Such a novel technique has good spatial resolution and can image large area samples that could be used to monitor the quality of the material produced in industrial scales."
Vincent H. Crespi, Distinguished Professor of Physics, Materials Science and Engineering, and Chemistry, Penn State, added, "Crystals are made of atoms, and so the defects within crystals -- where atoms are misplaced -- are also of atomic size.
"Usually, powerful, expensive and slow experimental probes that do microscopy using beams of electrons are needed to discern such fine details in a material," said Crespi. "Here, we use a fast and accessible optical method that pulls out just the signal that originates from the defect itself to rapidly and reliably find out how 2D materials are stitched together out of grains oriented in different ways."
Another coauthor compared the technique to finding a particular zero on a page full of zeroes. "In the dark field, all the zeroes are made invisible so that only the defective zero stands out," said Yuanxi Wang, assistant research professor at Penn State's Materials Research Institute.
The semiconductor industry wants to have the ability to check for defects on the production line, but 2D materials will likely be used in sensors before they are used in electronics, according to Terrones. Because 2D materials are flexible and can be incorporated into very small spaces, they are good candidates for multiple sensors in a smartwatch or smartphone and the myriad of other places where small, flexible sensors are required.
"The next step would be an improvement of the experimental setup to map zero dimension defects -- atomic vacancies for instance -- and also extend it to other 2D materials that host different electronic and structural properties," said lead author Bruno Carvalho, a former visiting scholar in Terrones' group.
A new process introduced by the Rice University lab of chemist James Tour can turn bulk quantities of just about any carbon source into valuable graphene flakes. The process is quick and cheap; Tour said the “flash graphene” technique can convert a ton of coal, waste food or plastic into graphene for a fraction of the cost used by other bulk graphene-producing methods.
“This is a big deal,” Tour said. “The world throws out 30% to 40% of all food, because it goes bad, and plastic waste is of worldwide concern. We’ve already proven that any solid carbon-based matter, including mixed plastic waste and rubber tires, can be turned into graphene.”
As reported in Nature, flash graphene is made in 10 milliseconds by heating carbon-containing materials to 3,000 Kelvin (about 5,000 degrees Fahrenheit). The source material can be nearly anything with carbon content. Waste food, plastic waste, petroleum coke, coal, wood clippings and biochar are prime candidates, Tour said. “With the present commercial price of graphene being $67,000 to $200,000 per ton, the prospects for this process look superb,” he said.
Tour said a concentration of as little as 0.1% of flash graphene in the cement used to bind concrete could lessen its massive environmental impact by a third. Production of cement reportedly emits as much as 8% of human-made carbon dioxide every year.
“By strengthening concrete with graphene, we could use less concrete for building, and it would cost less to manufacture and less to transport,” he said. “Essentially, we’re trapping greenhouse gases like carbon dioxide and methane that waste food would have emitted in landfills. We are converting those carbons into graphene and adding that graphene to concrete, thereby lowering the amount of carbon dioxide generated in concrete manufacture. It’s a win-win environmental scenario using graphene.”
“Turning trash to treasure is key to the circular economy,” said co-corresponding author Rouzbeh Shahsavari, an adjunct assistant professor of civil and environmental engineering and of materials science and nanoengineering at Rice and president of C-Crete Technologies. “Here, graphene acts both as a 2D template and a reinforcing agent that controls cement hydration and subsequent strength development.”
In the past, Tour said, “graphene has been too expensive to use in these applications. The flash process will greatly lessen the price while it helps us better manage waste.”
“With our method, that carbon becomes fixed,” he said. “It will not enter the air again.”
The process aligns nicely with Rice’s recently announced Carbon Hub initiative to create a zero-emissions future that repurposes hydrocarbons from oil and gas to generate hydrogen gas and solid carbon with zero emission of carbon dioxide. The flash graphene process can convert that solid carbon into graphene for concrete, asphalt, buildings, cars, clothing and more, Tour said.
Flash Joule heating for bulk graphene, developed in the Tour lab by Rice graduate student and lead author Duy Luong, improves upon techniques like exfoliation from graphite and chemical vapor deposition on a metal foil that require much more effort and cost to produce just a little graphene.
Even better, the process produces “turbostratic” graphene, with misaligned layers that are easy to separate. “A-B stacked graphene from other processes, like exfoliation of graphite, is very hard to pull apart,” Tour said. “The layers adhere strongly together. But turbostratic graphene is much easier to work with because the adhesion between layers is much lower. They just come apart in solution or upon blending in composites.
“That’s important, because now we can get each of these single-atomic layers to interact with a host composite,” he said.
The lab noted that used coffee grounds transformed into pristine single-layer sheets of graphene.
Bulk composites of graphene with plastic, metals, plywood, concrete and other building materials would be a major market for flash graphene, according to the researchers, who are already testing graphene-enhanced concrete and plastic.
The flash process happens in a custom-designed reactor that heats material quickly and emits all noncarbon elements as gas. “When this process is industrialized, elements like oxygen and nitrogen that exit the flash reactor can all be trapped as small molecules because they have value,” Tour said.
He said the flash process produces very little excess heat, channeling almost all of its energy into the target. “You can put your finger right on the container a few seconds afterwards,” Tour said. “And keep in mind this is almost three times hotter than the chemical vapor deposition furnaces we formerly used to make graphene, but in the flash process the heat is concentrated in the carbon material and none in a surrounding reactor.
“All the excess energy comes out as light, in a very bright flash, and because there aren’t any solvents, it’s a super clean process,” he said.
Luong did not expect to find graphene when he fired up the first small-scale device to find new phases of material, beginning with a sample of carbon black. “This started when I took a look at a Science paper talking about flash Joule heating to make phase-changing nanoparticles of metals,” he said. But Luong quickly realized the process produced nothing but high-quality graphene.
Atom-level simulations by Rice researcher and co-author Ksenia Bets confirmed that temperature is key to the material’s rapid formation. “We essentially speed up the slow geological process by which carbon evolves into its ground state, graphite,” she said. “Greatly accelerated by a heat spike, it is also stopped at the right instant, at the graphene stage.
“It is amazing how state-of-the-art computer simulations, notoriously slow for observing such kinetics, reveal the details of high temperature-modulated atomic movements and transformation,” Bets said.
Tour hopes to produce a kilogram (2.2 pounds) a day of flash graphene within two years, starting with a project recently funded by the Department of Energy to convert U.S.-sourced coal. “This could provide an outlet for coal in large scale by converting it inexpensively into a much-higher-value building material,” he said.
Tour has a grant from the Department of Energy to scale up the flash graphene process, which will be co-funded by the start-up company, Universal Matter Ltd.
Co-authors of the paper include Rice graduate students Wala Ali Algozeeb, Weiyin Chen, Paul Advincula, Emily McHugh, Muqing Ren and Zhe Wang; postdoctoral researcher Michael Stanford; academic visitors Rodrigo Salvatierra and Vladimir Mancevski; Mahesh Bhatt of C-Crete Technologies, Stafford, Texas; and Rice assistant research professor Hua Guo. Boris Yakobson, the Karl F. Hasselmann Chair of Engineering and a professor of materials science and nanoengineering and of chemistry, is co-corresponding author.
Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer science and of materials science and nanoengineering at Rice.
A new method of producing carbon nanotubes - tiny molecules with incredible physical properties used in touchscreen displays, 5G networks and flexible electronics - has been given the green light by researchers, meaning work in this crucial field can continue.
Single-walled carbon nanotubes are among the most attractive nanomaterials for a wide range of applications ranging from nanoelectronics to medical sensors. They can be imagined as the result of rolling a single graphene sheet into a tube.
Their properties vary widely with their diameter, what chemists call chirality - how symmetrical they are - and by how the graphene sheet is rolled.
The problem faced by researchers is that it is no longer possible to make high quality research samples of single-walled carbon nanotubes using the standard method. This was associated with the Carbon Center at Rice University, which used the high-pressure carbon monoxide (HiPco) gas-phase process developed by Nobel Laureate, the late Rick Smalley.
The demise of the Carbon Center in the mid-2010s, the divesting of the remaining HiPco samples to a third-party entity with no definite plans of further production, and the expiration of the core patents for the HiPco process, meant that this existing source of nanotubes was no longer an option.
Now however, a collaboration between scientists at Swansea University (Wales, UK), Rice University (USA), Lamar University (USA), and NoPo Nanotechnologies (India) has demonstrated that the latter's process and material design is a suitable replacement for the the Rice method.
Analysis of the Rice "standard" and new commercial-scale samples show that back-to-back comparisons are possible between prior research and future applications, with the newer HiPco nanotubes from NoPo Nanotechnologies comparing very favourably to the older ones from Rice.
These findings will go some way to reassure researchers who might have been concerned that their work could not continue as high-quality nanotubes would no longer be readily available.
Professor Andrew Barron of Swansea University's Energy Safety Research Institute, the project lead, said:
"Variability in carbon nanotube sources is known to be a significant issue when trying to compare research results from various groups. What is worse is that being able to correlate high quality literature results with scaled processes is still difficult".
Erstwhile members of the Smalley group at Rice University, which developed the original HiPco process, helped start NoPo Nanotechnologies with the aim of updating the HiPco process, and produce what they call NoPo HiPCO® SWCNTs.
Lead author Dr. Varun Shenoy Gangoli stated:
"It is in the interest of all researchers to understand how the presently available product compares to historically available Rice materials that have been the subject of a great range of academic studies, and also to those searching for a commercial replacement to continue research and development in this field."