MXenes are at the forefront of 2D materials research

 2-D Materials Go Beyond Graphene

Research of 2D MXenes is prominently featured in an article in Chemical & Engineering News - bulletin of the American Chemical Society that goes in hard copy to more than 150,000 subscribers. No doubt, MXenes are at the forefront of 2D materials research.

Driven by the unique properties of ultrathin materials and their potential for new applications, researchers are crisscrossing the periodic table in search of new examples

This stack of separable Ti3C2 sheets (yellow micrograph, bottom) is one example of a MXene. Researchers have made a large variety of MXenes, which exhibit M2X, M3X2, and M4X3 stoichiometries, in which M is an early transition metal and X is carbon or nitrogen (models, top). Credit: Babak Ansori/Drexel U.

 Despite being just a single layer of carbon atoms, graphene sure can excite engineers and scientists. Unlike bulk graphite, the ultrathin material boasts flexibility, strength, and possibly enticing electronic properties for researchers to exploit in novel applications. Graphene mania crescendoed in 2010 when the material’s discovery was the subject of that year’s Nobel Prize in Physics. Since that time, researchers worldwide have been enthralled with vanishingly thin films and have succeeded in preparing a wide variety of so-called two-dimensional materials beyond graphene.

This story is about those other 2-D materials. They hail from across the periodic table and include an assortment of transition metals, carbon-group elements, chalcogenides, and others. Researchers are taking this trip through the periodic table in search of the ultrathin because, like graphene, some of the materials they’re making sport impressive properties that surpass those of their thicker counterparts.
These 2-D materials encompass electrical conductors, insulators, and semiconductors. They include chemically inert materials as well as ones that are readily modified through chemistry. And because these materials are ultrathin, they tend to be flexible and transparent, ideal features for new types of energy storage devices, high-speed and wearable electronics, and other applications.
So what exactly does it mean for a material to be 2-D?
The definition depends on whom you ask. The dozen or so scientists C&EN contacted for this story stipulate that to qualify as 2-D, the material needs to be well ordered, relatively expansive in two dimensions, and ultrathin in the third dimension—on the atomic or molecular scale. Beyond that there is little agreement.

In brief In the excitement after the isolation of graphene, materials chemists and other scientists began scrutinizing the periodic table for opportunities to make other molecularly thin materials. Driven by the chance to explore uncharted scientific territory and to discover technologically useful materials, these researchers quickly produced many examples of so-called two-dimensional materials beyond graphene.

The growing list now includes a large set of metal carbides (MXenes), a family of single-element graphene analogs (Xenes), a number of transition metal dichalcogenides, ultrathin organic crystals, and two-component nitrides.

For example, what passes as “ultrathin” can vary depending on the material and application. The graphene work that netted the Nobel Prize for Andre K. Geim and Konstantin S. (Kostya) Novoselov involved isolating one-atom-thin sheets of carbon from graphite. But researchers still consider a sample to be graphene—and a sample still exhibits some unique graphene properties—even when it is two, three, and more layers thick. In those cases, they’re just described as bilayer or few-layer graphene.

Interactive: The world of 2-D materials

Scientists have developed five groups of 2-D materials from elements across the periodic table. The key elements in each are color coded by family below. 

This graphic shows a periodic table, highlighting various elements that make up two dimensional materials; Also, there are cards explaining characteristics and applications for four 2-D materials, including MXenes, Xenes, transition metal dichalcogenides, 2-D organic materials, and nitrides.

So where do researchers draw the ultrathin line? How many atoms in thickness can a metal carbide or film of silicon be before it transitions from a 2-D material to a “thick” layered material or a coating? In general, scientists seem uninterested in assigning a strict limit to the thickness of these materials. But the thickness does matter when researchers are thinking about applications. “Mathematics is good at rigorous definitions, but this isn’t mathematics; it’s chemistry and physics,” says Boris I. Yakobson, a Rice University theoretician and materials scientist who studies 2-D materials. “It’s good to have definitions, but often, they’re not flexible enough to reflect reality.” The other gray area in defining 2-D is whether to require that these ultrathin films can be manipulated, picked up, and transferred. Two-dimensional materials can be grown via vapor deposition of precursor molecules or isolated from a multilayer crystal or flake. But a material doesn’t need to be freestanding or separable from the surface on which it was grown or derived to gain membership in the 2-D club.

Some of the materials in this story are freestanding; others are not. Not being freestanding, though, can hinder a material’s use in applications. Eventually, researchers may come up with ways to separate 2-D materials that currently cannot be freed. That kind of advance will likely open the door to developing new applications, and ultimately, new applications will continue driving this field.
One reason so many research groups focus on 2-D materials is because of the unique collection of properties the materials exhibit. For example, 2-D versions of silicon (silicene), phosphorus (phosphorene), and some of carbon’s other neighbors in the periodic table are semiconductors with band gaps and other electronic properties that, in principle, can be tuned more easily than they can in the bulk materials. That’s because those properties depend greatly on layer thickness and doping.
Adding one layer to a single-layer material significantly alters its thickness. Not so for the bulk counterpart. And because all the atoms in a single-layer film are exposed, they are all accessible for chemical modification, which can further modify electronic properties. In a bulk material, most of the atoms are buried under the surface and are inaccessible for chemical modification.
The thinness of 2-D materials also allows electric fields to leak through them and interact with other materials below them. This feature could allow researchers to control the electronic properties of those underlying layers, according to Mark C. Hersam of Northwestern University, a specialist in semiconductor devices. Scientists can use that unique electrostatic penetration to make new types of diodes, memory circuits, and other devices that would be impossible to make with bulk semiconductors, he says.

Grown via vapor deposition of boron, atomically thin borophene adopts a buckled structure, as seen in this atomic-resolution scanning tunneling micrograph. Credit: Andy Mannix and Nathan Guisinger/Argonne National Laboratory/Mark Hersam/Northwestern U

“These unique properties may lead to new and useful applications, and that is part of their appeal, but I think that’s secondary,” says Yury Gogotsi, who leads a nanomaterials research group at Drexel University. “More importantly, we’re learning to use 2-D materials as building blocks to custom make modern materials.” Gogotsi and others envision developing methods for combining, either by stacking or by juxtaposing laterally, various types of 2-D materials with distinct sets of properties to build materials with truly novel features on demand.

Regardless of whether researchers uncover truly unique properties in 2-D materials, the work is providing scientists with an exciting opportunity to trek through unexplored territory, Yakobson says.

Gogotsi agrees: “Whether you’re a five-year-old child playing with a new toy at home or a 50-year-old child playing with a new toy in the lab, it’s fun. When people see new toys, they get excited.”

These new toys can be divided into five major groups: MXenes, Xenes, organic materials, transition metal dichalcogenides, and nitrides. Some groups have many members; others few. Some have already been used in demonstration devices, while others are still laboratory curiosities. But they have all taken researchers into the ultrathin world. The rest of the story provides brief glimpses of four of these groups. To explore all the groups and take a 2-D trip across the periodic table, go to cenm.ag/2dmaterials.

MXenes: A 2-D surprise

About six years ago, Gogotsi and Michel W. Barsoum, a materials scientist at Drexel University, were searching for ways to make high-performance lithium-ion battery anodes. The team had experience with a promising family of electrically conducting carbides and nitrides known as the MAX phases. M refers to early transition metals, A symbolizes main-group elements such as aluminum and silicon, and X represents carbon or nitrogen.

The team wanted to boost the efficiency with which Li ions reversibly insert themselves in the anodes during charging and discharging. So they tried to make room for the ions by using concentrated hydrofluoric acid to selectively remove aluminum atoms from Ti3AlC2 and other MAX phases. The process improved the materials’ performance in batteries. It also completely removed the Al layers and exfoliated the crystals into ultrathin, 2-D, graphenelike sheets of Ti3C2.

The team showed that this exfoliation process can also produce Ti2C, Ta4C3, (Ti0.5Nb0.5)2C, (V0.5Cr0.5)3C2, Ti3CN, and other materials. They named the family of materials MXenes, which is pronounced “maxenes” to deliberately rhyme with graphene. The researchers have now prepared nearly 30 MXenes, and many more have been predicted (Nat. Rev. Mater. 2017, DOI: 10.1038/natrevmats.2016.98).

Many research groups are studying these 2-D materials, but the Drexel scientists remain at the forefront. They have devised a method for making MXene-polymer composites that are electrically conductive, strong, flexible, and durable—ideal properties for electrodes in energy storage and wearable technology (Proc. Natl. Acad. Sci. USA 2014, DOI: 10.1073/pnas.1414215111). The Drexel team has also demonstrated that MXenes can serve as lightweight, inexpensive shielding materials to protect cell phones and other devices from electromagnetic interference (Science 2016, DOI: 10.1126/science.aag2421). They’ve also recently started making 100-g batches of MXenes with a custom-made reactor.

Xenes: Elements go solo

Carbon isn’t the only element that can form ultrathin, monoatomic sheets. In the past few years, elements that are clustered in the periodic table near carbon (B, Si, P, Ge, and Sn) have jumped onto the 2-D stage. Scientists refer to this family collectively as Xenes, where X represents the name of the element and “ene” comes from graphene. These materials, which include borophene, silicene, phosphorene, germanene, and stanene, all share a buckled or corrugated shape—unlike graphene’s flat sheets—and sport atoms arranged in a honeycomb lattice. Silicene, phosphorene, and borophene are the most studied of the family.

“Whether you’re a five-year- old child playing with a new toy at home or a 50-year- old child playing with a new toy in the lab, it’s fun.” —Yury Gogotsi, Drexel University

Silicon is used in bulk throughout the electronics industry. But researchers in the U.S. and Italy showed that the element can also be useful in its 2-D form. The team grew a 2-D silicene layer on silver and capped it with a protective layer of alumina. The researchers used the single layer of silicon atoms as the channel in a field-effect transistor, which shuttles charge from the source to the drain electrodes (Nat. Nanotechnol. 2015, DOI: 10.1038/nnano.2014.325).

Phosphorene could also be useful for making fast electronics because of its high charge mobility. But the material degrades upon exposure to air, thwarting efforts to use it. Northwestern’s Hersam came up with one way around the problem. His group protects the material by treating flakes of black phosphorus, the starting material from which researchers isolate ultrathin phosphorene sheets, with a solution of a benzenediazonium derivative that passivates and protects the material (Nat. Chem. 2016, DOI: 10.1038/nchem.2505).

 This artist’s rendition of 2-D materials in water depicts a research trend to develop inexpensive, solution-based processing methods for these materials. Shown here are (from top) graphene (black); hexagonal boron nitride (B is green, N is pink); molybdenum disulfide (Mo is blue, S is yellow), and tungsten diselenide (W is purple, Se is red). Credit: Joohoon Kang and Mark Hersam/Northwestern UUnlike other materials in this group, borophene has metallic character, making it potentially useful for connecting elements in circuits and acting as a transparent conductor. This Xene made its debut when two research teams used vapor deposition methods to grow one-atom-thick boron films on metals (Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201509285; Science 2015, DOI: 10.1126/science.aad1080). But to use borophene in applications will require separating the material intact from its support, something that has yet to be demonstrated.

Organic materials: Carbon moves beyond grapheneIt’s not just single elements, or combinations of a few elements, that can enter the 2-D world. Multielement organic molecules also form ultrathin materials.

The richness of organic chemistry offers a unique opportunity to customize the properties of these organic 2-D materials to make chemical and biological sensors, chemically selective membranes, and electronic devices. But forming these 2-D crystals is challenging because of covalent bonding between layers.

One solution has been to exfoliate covalent organic frameworks (COFs), which are crystalline porous polymers. Sonicating COFs thins them, but how thin they get depends on the strength of the bonding within a single layer versus the strength of the bonding between adjacent layers. If the interlayer bonding is stronger, the COFs resist thinning. Common boronate-linked COFs tend to do this. But as Northwestern’s William R. Dichtel showed, sonicating hydrazone-linked COFs in dioxane and other common solvents yields bulk quantities of few-layer 2-D crystals (J. Am. Chem. Soc. 2013, DOI: 10.1021/ja408243n).

A. Dieter Schlüter of the Swiss Federal Institute of Technology (ETH), Zurich, demonstrated a different approach and applied it to a related material—metal organic frameworks (MOFs), which are porous crystalline materials composed of metal ions joined by organic linkers. His team prepared a series of ultrathin crystals made of tri- and hexa-functionalized terpyridine-based groups joined by Zn2+ ions. The researchers then selectively exchanged the zinc ions with Fe2+, Pb2+, and Co2+, thereby making a new set of 2-D MOFs (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja501849y).

Transition metal dichalcogenides: Scaling up

Numerous research groups have demonstrated that ultrathin layers of transition metal dichalcogenides such as MoS2 and WS2 can serve as key circuit components in fast electronics. But methods to make the thin films tend to be laborious and yield just tiny quantities of material.

To sidestep the slow production, Cornell University’s Jiwoong Park used Mo(CO)6 or W(CO)6 as precursors in a chemical vapor deposition process to form films of MoS2 and WS2, respectively, that were only three atoms thick but covered an area of about 65 cm2 (Nature 2015, DOI: 10.1038/nature14417). The films were high enough in quality to be used in field-effect transistors.

And last year, Northwestern’s Hersam and coworkers reported a low-cost method for separating single- and bilayer ReS2 through liquid-phase exfoliation based on ultrasonication followed by ultracentrifugation (NanoLett. 2016, DOI: 10.1021/acs.nanolett.6b03584).

Source: http://cen.acs.org/articles/95/i22/2-D-materials-beyond-graphene.html

 

News from MRC.ORG.UA

Twenty Third Annual Conference - YUCOMAT 2022 Twelfth World Round Table Conference on Sintering - XII WRTCS 2022 Herceg Novi, August 29 – September 2, 2022

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Our collaborators and partners  presented our joint research at the Yucomat conference - at Symposium on Biomaterials and two collaborative posters at Conference Poster Session.

 
MRC team visited 2nd international MXene conference "MXenes: Addressing Global Challenges with Innovation"at Drexel University, USA on Aug. 1-3, 2022

second MXene COnference 2022, Drexel University, USA

MRC team members Dr. Oleksiy Gogotsi, Veronika Zahorodna, Dr. Iryna Roslyk visited MXene Confrence 2022.  This 2nd international MXene conference at Drexel University, August 1-3, 2022, put major MXene discoveries, including their record-breaking electrical conductivity, electromagnetic interference shielding capability, electrochemical capacitance, light-to-heat conversion, and other properties, into perspective.

 
Launching HORIZON-MSCA-2021-SE-01 MX-MAP Project: Towards MXenes biomedical applications by high-dimensional immune MAPping

MX-MAP project Meeting during the MXene international conference held in Drexel University on Aug. 3,  2022, and discussing the roadmap for launching MX-MAP research project on MXenes for medical applications.

 
H2020-MSCA-RISE NANO2DAY research project, last updates

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Researchers from University of Latvia and Materials Research Center, Ukraine are visiting Drexel University due to Horizon-2020-MSCA-RISE NANO2DAY research project.

 
MXene-Assisted Ablation of Cells with a Pulsed Near-Infrared Laser

Development of tailored MXene PTT treatment targeting tumor cells. We demonstrate both low toxicity and good biocompatibility of this MXene in vitro, as well as a favorable safety profile based on the experiments in vivo.Presenting our recent collaborative research paper on  MXene use for PPT anticancer therapy, the biocompatibility of MXenes in vitro and in vivo studies:

Sergiy Kyrylenko, Oleksiy Gogotsi, Ivan Baginskiy, Vitalii Balitskyi, Veronika Zahorodna, Yevheniia Husak, Ilya Yanko, Mykolay Pernakov, Anton Roshchupkin, Mykola Lyndin, Bernhard B. Singer, Volodymyr Buranych, Alexander Pogrebnjak, Oksana Sulaieva, Oleksandr Solodovnyk, Yury Gogotsi, Maksym Pogorielov, MXene-Assisted Ablation of Cells with a Pulsed Near-Infrared Laser. ACS Appl. Mater. Interfaces 2022, 14, 25, 28683–28696, https://doi.org/10.1021/acsami.2c08678

 
MXenes—A New Class of Two-Dimensional Materials: Structure, Properties and Potential Applications

Presenting our collaborative paper on recen advances in MXene research and their potential applications:

Pogorielov M, Smyrnova K, Kyrylenko S, Gogotsi O, Zahorodna V, Pogrebnjak A. MXenes—A New Class of Two-Dimensional Materials: Structure, Properties and Potential Applications. Nanomaterials. 2021; 11(12):3412. https://doi.org/10.3390/nano11123412

 
MXene nanoflakes decorating ZnO tetrapods for enhanced performance of skin-attachable stretchable enzymatic electrochemical glucose sensor

Presenting our joint research paper supported by CANBIOSE research project: and published in Biosensors and Bioelectronics: MXene nanoflakes decorating ZnO tetrapods for enhanced performance of skin-attachable stretchable enzymatic electrochemical glucose sensor

 
If you want to help and support the purchase of aid consignments, shipping cost to Ukraine and delivery within Ukraine to the places in nee, please donate

Our volunteersBig thanks to all our friends, partners, volunteers for help and their tireless work! We continue to help our defenders and deliver military equipment, humanitarian aid, tactical medicine and special medical supplies to units of Ukrainian Army, territorial defense and hospitals on the front line!

 
Delivering help to Ukraine from the USA, Europe, and the rest of the world!

3.jpg - 197.81 KbOur organization in Kyiv, Materials Research Center, is well aware of the needs in Ukraine now. Together with our partners, fellow Ukrainian scientists, we have organized a warehouse in Lviv, where we collect cargos and distribute them throughout Ukraine, with detailed reports confirming the delivery to the final destination, including photos of the transfer. We have transportation that can pick cargo in Poland and deliver it through a green corridor for humanitarian cargos at the Polish-Ukrainian border. 
We are ready to respond promptly, as required by the situation in Ukraine. If there are individuals, foundations or volunteer organizations willing to send help to Ukraine from Europe or the United States, we are ready to accept it in our warehouses, make collection or individual parties according to your request and pass them on to those in need. All humanitarian aid, first aid, and protective gear will be delivered to the final destination.
Please contact Dr. Oleksiy Gogotsi, MRC Director: Tel / Viber / WhatsApp / Telegram / Signal: + 380 63 233 2443, Cell phone in the USA: +1 808 203 8092, e-mail: helpukraine@mrc.org.ua
Being currently on a business trip in Philadelphia, the United States, we can meet with you in person, if needed.

 
MRC Ukraine Foundation. Providing of military first aid medicine for the Special Operations Forces of the Armed Forces of Ukraine

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MRC Ukraine Foundation. Providing of military first aid medicine for the Special Operations Forces of the Armed Forces of Ukraine via volunteers. Specialized military first aid medical supplies were provided by the Special Forces Foundation, Green Berets Humanitarian Fund, USA

 
Delivering military first aid medicine from the Special Forces Foundation Green Beret Humanitarian Fund (GBHF) from the USA to territorial defences, army unit and 2 hospitals

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Delivering military first aid medicine from the Special Forces Foundation Green Beret Humanitarian Fund (GBHF) from the USA via the Kernel Volunteer Group for the Territorial Defense of Kyiv, Poltava, Vinnytsia, Voznesensk, as well as some military unit in Kyiv and Ternopil. Also part of medical supplies is transferred to hospitals in Krasnopillia in Sumy region and Voznesensk in Mykolaiv region

 

 
MRC Ukraine Foundation. Transfer of military first aid medicine at our hub in Lviv

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MRC Ukraine Foundation. Transfer of military first aid medicine at our hub in Lviv from the American Green Beret Humanitarian Fund for some military units.

 
BSU and LU parthers secondment visits to MRC an seminar discussion of ongoing research works under the NANO2DAY project at Materials Research Center, February 2022

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During the secondment visits of project partners from BSU and LU to MRC research works were performed and a seminar discussion of ongoing research works and obtained results was held under the NANO2DAY project.

 
Registration is now open for the upcoming MXene Certificate Course, February 7-11, 2022 from Professor Yury Gogotsi and his team, Drexel University, USA

altRegistration is now open for the upcoming MXene Certificate Course, February 7-11, 2022! This virtual certificate course will teach best practices for the synthesis (2 days), characterization (2 days), and electrochemical measurements of MXenes with a new lecture in the biomedical applications of MXenes (you may choose electrochemical measurements OR biomedical applications - 1 day).

 
Visiting resracher S. Stankevich performed secondment to MRC due to NANO2DAY project

altStanislav Stankevich, research assistant from Latvias University, Riga, Latvia, performed secondment visit to Materials Research Center, Kyiv, Ukraine, due to the MSCA RISE research project NANO2DAY working on project tasks related to MXene based composites. Dates of performed secondment visit November 17-December 16, 2021.