Publications by authors named "Babak Anasori"

62 Publications

Nacre-Mimetic, Mechanically Flexible, and Electrically Conductive Silk Fibroin-MXene Composite Foams as Piezoresistive Pressure Sensors.

ACS Appl Mater Interfaces 2021 Jul 14;13(29):34996-35007. Epub 2021 Jul 14.

Institute of Inorganic Chemistry, Department of Chemistry, University of Cologne, Greinstraße 6, 50939 Cologne, Germany.

The hierarchical nacre-like three-dimensional (3D) assembly of porous and lightweight materials is in high demand for applications such as sensors, flexible energy storage and harvesting devices, electromagnetic interference shielding, and biomedical applications. However, designing such a biomimetic hierarchical architecture is highly challenging due to the lack of experimental approaches to achieve the necessary control over the materials' microstructure on the multilength scale. Aerogels and foam-based materials have recently been developed as attractive candidates for pressure-sensing applications. However, despite recent progress, the bottleneck for these materials to achieve electrical conductivity combined with high mechanical flexibility and fast strain recovery remains. In this study, for the first time, inspired by the multiscale architecture of nacre, we fabricated a series of ultra-lightweight, flexible, electrically conductive, and relatively high-strength composite foams through hybridizing the cross-linked silk fibroin (SF) biopolymer, extracted from silkworm cocoon, reinforced with two-dimensional graphene oxide (GO) and TiC MXene nanosheets. Nacre is a naturally porous material with a lightweight, mechanically robust network structure, thanks to its 3D interconnected lamella-bridge micromorphology. Inspired by this material, we assemble a cross-linked SF fibrous solution with MXene and GO nanosheets into nacre-like architecture using a bidirectional freeze-casting technique. Subsequent freeze-drying and gas-phase hydrophobization resulted in composite foams with 3D hierarchical porous architectures with a unique combination of mechanical resilience, electrical conductance, and ultra-lightness. The developed composite presented excellent performances as piezoresistive pressure-sensing devices and sorbents for oil/water separation, which indicated great potential in mechanically switchable electronics.
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http://dx.doi.org/10.1021/acsami.1c09675DOI Listing
July 2021

High-Entropy 2D Carbide MXenes: TiVNbMoC and TiVCrMoC.

ACS Nano 2021 Jun 15. Epub 2021 Jun 15.

Department of Mechanical and Energy Engineering, Purdue School of Engineering and Technology, Indiana University-Purdue University Indianapolis, Indianapolis, Indiana 46202, United States.

Two-dimensional (2D) transition metal carbides and nitrides, known as MXenes, are a fast-growing family of 2D materials. MXenes 2D flakes have + 1 ( = 1-4) atomic layers of transition metals interleaved by carbon/nitrogen layers, but to-date remain limited in composition to one or two transition metals. In this study, by implementing four transition metals, we report the synthesis of multi-principal-element high-entropy MCT MXenes. Specifically, we introduce two high-entropy MXenes, TiVNbMoCT and TiVCrMoCT, as well as their precursor TiVNbMoAlC and TiVCrMoAlC high-entropy MAX phases. We used a combination of real and reciprocal space characterization (X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, and scanning transmission electron microscopy) to establish the structure, phase purity, and equimolar distribution of the four transition metals in high-entropy MAX and MXene phases. We use first-principles calculations to compute the formation energies and explore synthesizability of these high-entropy MAX phases. We also show that when three transition metals are used instead of four, under similar synthesis conditions to those of the four-transition-metal MAX phase, two different MAX phases can be formed (.., no pure single-phase forms). This finding indicates the importance of configurational entropy in stabilizing the desired single-phase high-entropy MAX over multiphases of MAX, which is essential for the synthesis of phase-pure high-entropy MXenes. The synthesis of high-entropy MXenes significantly expands the compositional variety of the MXene family to further tune their properties, including electronic, magnetic, electrochemical, catalytic, high temperature stability, and mechanical behavior.
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http://dx.doi.org/10.1021/acsnano.1c02775DOI Listing
June 2021

2D transition metal carbides (MXenes) in metal and ceramic matrix composites.

Nano Converg 2021 Jun 2;8(1):16. Epub 2021 Jun 2.

Department of Mechanical and Energy Engineering, Purdue School of Engineering and Technology, Indiana University-Purdue University Indianapolis, 46202, Indianapolis, IN, USA.

Two-dimensional transition metal carbides, nitrides, and carbonitrides (known as MXenes) have evolved as competitive materials and fillers for developing composites and hybrids for applications ranging from catalysis, energy storage, selective ion filtration, electromagnetic wave attenuation, and electronic/piezoelectric behavior. MXenes' incorporation into metal matrix and ceramic matrix composites is a growing field with significant potential due to their impressive mechanical, electrical, and chemical behavior. With about 50 synthesized MXene compositions, the degree of control over their composition and structure paired with their high-temperature stability is unique in the field of 2D materials. As a result, MXenes offer a new avenue for application driven design of functional and structural composites with tailorable mechanical, electrical, and thermochemical properties. In this article, we review recent developments for use of MXenes in metal and ceramic composites and provide an outlook for future research in this field.
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http://dx.doi.org/10.1186/s40580-021-00266-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8172761PMC
June 2021

Superior Wear-Resistance of TiCT Multilayer Coatings.

ACS Nano 2021 May 6;15(5):8216-8224. Epub 2021 Apr 6.

Department of Chemical Engineering, Biotechnology and Materials, FCFM, University of Chile, Santiago, 8370415, Chile.

Owing to MXenes' tunable mechanical properties induced by their structural and chemical diversity, MXenes are believed to compete with state-of-the-art 2D nanomaterials such as graphene regarding their tribological performance. Their nanolaminate structure offers weak interlayer interactions and an easy-to-shear ability to render them excellent candidates for solid lubrication. However, the acting friction and wear mechanisms are yet to be explored. To elucidate these mechanisms, 100-nm-thick homogeneous multilayer TiCT coatings are deposited on technologically relevant stainless steel by electrospraying. Using ball-on-disk tribometry (SiN counterbody) with acting contact pressures of about 300 MPa, their long-term friction and wear performance under dry conditions are studied. MXene-coated specimens demonstrate a 6-fold friction reduction and an ultralow wear rate (4 × 10 mm N m) over 100 000 sliding cycles, outperforming state-of-the-art 2D nanomaterials by at least 200% regarding their wear life. High-resolution characterization verified the formation of a beneficial tribolayer consisting of thermally/mechanically degraded MXenes and amorphous/nanocrystalline iron oxides. The transfer of this tribolayer to the counterbody transforms the initial steel/SiN contact to tribolayer/tribolayer contact with low shear resistance. MXene pileups at the wear track's reversal points continuously supply the tribological contact with fresh, lubricious nanosheets, thus enabling an ultra-wear-resistant and low-friction performance.
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http://dx.doi.org/10.1021/acsnano.1c01555DOI Listing
May 2021

2D MXenes: Tunable Mechanical and Tribological Properties.

Adv Mater 2021 Apr 18;33(17):e2007973. Epub 2021 Mar 18.

Department of Mechanical and Energy Engineering, and Integrated Nanosystems Development Institute, Purdue School of Engineering and Technology, Indiana University-Purdue University Indianapolis, Indianapolis, IN, 46202, USA.

2D transition metal carbides, nitrides, and carbonitrides, known as MXenes, were discovered in 2011 and have grown to prominence in energy storage, catalysis, electromagnetic interference shielding, wireless communications, electronic, sensors, and environmental and biomedical applications. In addition to their high electrical conductivity and electrochemically active behavior, MXenes' mechanical properties, flexibility, and strong adhesion properties play crucial roles in almost all of these growing applications. Although these properties prove to be critical in MXenes' impressive performance, the mechanical and tribological understanding of MXenes, as well as their relation to the synthesis process, is yet to be fully explored. Here, a fundamental overview of MXenes' mechanical and tribological properties is provided and the effects of MXenes' compositions, synthesis, and processing steps on these properties are discussed. Additionally, a critical perspective of the compositional control of MXenes for innovative structural, low-friction, and low-wear performance in current and upcoming applications of MXenes is provided. It is established here that the fundamental understanding of MXenes' mechanical and tribological behavior is essential for their quickly growing applications.
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http://dx.doi.org/10.1002/adma.202007973DOI Listing
April 2021

High-temperature stability and phase transformations of titanium carbide (TiCT) MXene.

J Phys Condens Matter 2021 May 5;33(22). Epub 2021 May 5.

Department of Mechanical and Energy Engineering, Purdue School of Engineering and Technology, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202, United States of America.

Two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, known as MXenes, are under increasing pressure to meet technological demands in high-temperature applications, as MXenes can be considered to be one of the few ultra-high temperature 2D materials. Although there are studies on the stability of their surface functionalities, there is currently a gap in the fundamental understanding of their phase stability and transformation of MXenes' metal carbide core at high temperatures (>700 °C) in an inert environment. In this study, we conduct systematic annealing of TiCTMXene films in which we present the 2D MXene flake phase transformation to ordered vacancy superstructure of a bulk three-dimensional (3D) TiC and TiCcrystals at 700 °C ⩽⩽ 1000 °C with subsequent transformation to disordered carbon vacancy cubic TiCat higher temperatures (> 1000 °C). We annealed TiCTMXene films made from the delaminated MXene single-flakes as well as the multi-layer MXene clay in a controlled environment through the use ofhot stage x-ray diffraction (XRD) paired with a 2D detector (XRD) up to 1000 °C andannealing in a tube furnace and spark plasma sintering up to 1500 °C. Our XRDanalysis paired with cross-sectional scanning electron microscope imaging indicated the resulting nano-sized lamellar and micron-sized cubic grain morphology of the 3D crystals depend on the starting TiCTform. While annealing the multi-layer clay TiCTMXene creates TiCgrains with cubic and irregular morphology, the grains of 3D TiC and TiCformed by annealing TiCTMXene single-flake films keep MXenes' lamellar morphology. The ultrathin lamellar nature of the 3D grains formed at temperatures >1000 °C can pave way for applications of MXenes as a stable carbide material 2D additive for high-temperature applications.
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http://dx.doi.org/10.1088/1361-648X/abe793DOI Listing
May 2021

Electrocatalytic CO reduction on earth abundant 2D MoC and TiC MXenes.

Chem Commun (Camb) 2021 Feb 19;57(13):1675-1678. Epub 2021 Jan 19.

Department of Chemistry, Temple University, 1901 N. 13th Street, Philadelphia, PA 19122, USA.

MoC and TiC MXenes were investigated as earth-abundant electrocatalyts for the CO reduction reaction (CORR). MoC and TiC exhibited faradaic efficiencies of 90% (250 mV overpotential) and 65% (650 mV overpotential), respectively, for the reduction of CO to CO in acetonitrile using an ionic liquid electrolyte. The use of ionic liquid 1-ethyl-2-methylimidazolium tetrafluoroborate as an electrolyte in organic solvent suppressed the competing hydrogen evolution reaction. Density functional theory (DFT) calculations suggested that the catalytic active sites are oxygen vacancy sites on both MXene surfaces. Also, a spontaneous dissociation of adsorbed COOH species to a water molecule and adsorbed CO on MoC promote the CORR.
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http://dx.doi.org/10.1039/d0cc05822jDOI Listing
February 2021

Electrically conductive 3D printed TiCT MXene-PEG composite constructs for cardiac tissue engineering.

Acta Biomater 2020 Dec 19. Epub 2020 Dec 19.

Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, United States; Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, United States. Electronic address:

Tissue engineered cardiac patches have great potential as a therapeutic treatment for myocardial infarction (MI). However, for successful integration with the native tissue and proper function of the cells comprising the patch, it is crucial for these patches to mimic the ordered structure of the native extracellular matrix and the electroconductivity of the human heart. In this study, a new composite construct that can provide both conductive and topographical cues for human induced pluripotent stem cell derived cardiomyocytes (iCMs) is developed for cardiac tissue engineering applications. The constructs are fabricated by 3D printing conductive titanium carbide (TiCT) MXene in pre-designed patterns on polyethylene glycol (PEG) hydrogels, using aerosol jet printing, at a cell-level resolution and then seeded with iCMs and cultured for one week with no signs of cytotoxicity. The results presented in this work illustrate the vital role of 3D-printed TiCT MXene on aligning iCMs with a significant increase in MYH7, SERCA2, and TNNT2 expressions, and with an improved synchronous beating as well as conduction velocity. This study demonstrates that 3D printed TiCT MXene can potentially be used to create physiologically relevant cardiac patches for the treatment of MI.
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http://dx.doi.org/10.1016/j.actbio.2020.12.033DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8213874PMC
December 2020

2H-MoS on MoCT MXene Nanohybrid for Efficient and Durable Electrocatalytic Hydrogen Evolution.

ACS Nano 2020 Nov 13;14(11):16140-16155. Epub 2020 Nov 13.

Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis, Singapore 138634, Singapore.

The development of highly efficient and durable earth-abundant hydrogen evolution reaction (HER) catalysts is crucial for the extensive implementation of the hydrogen economy. Members of the 2D MXenes family, particularly MoCT, have recently been identified as promising HER catalysts. However, their inherent oxidative instability in air and aqueous electrolyte solutions is hindering their widespread use. Herein, we present a simple and scalable method to circumvent adventitious oxidation in MoCT MXenes sulfidation to form a MoCT/2H-MoS nanohybrid. The intimate epitaxial coupling at the MoCT/2H-MoS nanohybrid interface afforded superior HER activities, requiring only 119 or 182 mV overpotential to yield -10 or -100 mA cm current densities, respectively. Density functional theory calculations reveal strongest interfacial adhesion was found within the nanohybrid structure as compared to the physisorbed nanohybrid, and the possibility to tune the HER overpotential through manipulating the extent of MXene sulfidation. Critically, the presence of 2H-MoS suppresses further oxidation of the MXene layer, enabling the nanohybrid to sustain industrially relevant current densities of over -450 mA cm with exceptional durability. Less than 30 mV overpotential degradation was observed after 10 continuous days of electrolysis at a fixed -10 mA cm current density or 100,000 successive cyclic voltammetry cycles. The exceptional HER durability of the MoCT/2H-MoS nanohybrid presents a major step forward to realize practical implementation of MXenes as noble metal free catalysts for broad-based applications in water splitting and energy conversion.
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http://dx.doi.org/10.1021/acsnano.0c08671DOI Listing
November 2020

Evidence of a magnetic transition in atomically thin CrTiCT MXene.

Nanoscale Horiz 2020 Dec 22;5(12):1557-1565. Epub 2020 Oct 22.

A.J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, PA 19104, USA.

Two-dimensional (2D) transition metal carbides and nitrides known as MXenes have shown attractive functionalities such as high electronic conductivity, a wide range of optical properties, versatile transition metal and surface chemistry, and solution processability. Although extensively studied computationally, the magnetic properties of this large family of 2D materials await experimental exploration. 2D magnetic materials have recently attracted significant interest as model systems to understand low-dimensional magnetism and for potential spintronic applications. Here, we report on synthesis of CrTiCT MXene and a detailed study of its magnetic as well as electronic properties. Using a combination of magnetometry, synchrotron X-ray linear dichroism, and field- and angular-dependent magnetoresistance measurements, we find clear evidence of a magnetic transition in CrTiCT at approximately 30 K, which is not present in its bulk layered carbide counterpart (CrTiAlC MAX phase). This work presents the first experimental evidence of a magnetic transition in a MXene material and provides an exciting opportunity to explore magnetism in this large family of 2D materials.
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http://dx.doi.org/10.1039/d0nh00343cDOI Listing
December 2020

Rational Design of Two-Dimensional Transition Metal Carbide/Nitride (MXene) Hybrids and Nanocomposites for Catalytic Energy Storage and Conversion.

ACS Nano 2020 Sep 31;14(9):10834-10864. Epub 2020 Aug 31.

Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis, Singapore 138634, Singapore.

Electro-, photo-, and photoelectrocatalysis play a critical role toward the realization of a sustainable energy economy. They facilitate numerous redox reactions in energy storage and conversion systems, enabling the production of chemical feedstock and clean fuels from abundant resources like water, carbon dioxide, and nitrogen. One major obstacle for their large-scale implementation is the scarcity of cost-effective, durable, and efficient catalysts. A family of two-dimensional transition metal carbides, nitrides, and carbonitrides (MXenes) has recently emerged as promising earth-abundant candidates for large-area catalytic energy storage and conversion due to their unique properties of hydrophilicity, high metallic conductivity, and ease of production by solution processing. To take full advantage of these desirable properties, MXenes have been combined with other materials to form MXene hybrids with significantly enhanced catalytic performances beyond the sum of their individual components. MXene hybridization tunes the electronic structure toward optimal binding of redox active species to improve intrinsic activity while increasing the density and accessibility of active sites. This review outlines recent strategies in the design of MXene hybrids for industrially relevant electrocatalytic, photocatalytic, and photoelectrocatalytic applications such as water splitting, metal-air/sulfur batteries, carbon dioxide reduction, and nitrogen reduction. By clarifying the roles of individual material components in the MXene hybrids, we provide design strategies to synergistically couple MXenes with associated materials for highly efficient and durable catalytic applications. We conclude by highlighting key gaps in the current understanding of MXene hybrids to guide future MXene hybrid designs in catalytic energy storage and conversion applications.
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http://dx.doi.org/10.1021/acsnano.0c05482DOI Listing
September 2020

Two-Dimensional Titanium and Molybdenum Carbide MXenes as Electrocatalysts for CO Reduction.

iScience 2020 Jun 18;23(6):101181. Epub 2020 May 18.

Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A∗STAR), 2 Fusionopolis Way, Innovis, Singapore 138634, Singapore. Electronic address:

Electrocatalytic CO reduction reaction (CORR) is an attractive way to produce renewable fuel and chemical feedstock, especially when coupled with efficient CO capture and clean energy sources. On the fundamental side, research on improving CORR activity still revolves around late transition metal-based catalysts, which are limited by unfavorable scaling relations despite intense investigation. Here, we report a combined experimental and theoretical investigation into electrocatalytic CORR on Ti- and Mo-based MXene catalysts. Formic acid is found as the main product on TiCT and MoCT MXenes, with peak Faradaic efficiency of over 56% on TiCT and partial current density of up to -2.5 mA cm on MoCT. Furthermore, simulations reveal the critical role of the T group: a smaller overpotential is found to occur at lower amounts of -F termination. This work represents an important step toward experimental demonstration of MXenes for more complex electrocatalytic reactions in the future.
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http://dx.doi.org/10.1016/j.isci.2020.101181DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7270606PMC
June 2020

Role of acid mixtures etching on the surface chemistry and sodium ion storage in TiCT MXene.

Chem Commun (Camb) 2020 Jun 30;56(45):6090-6093. Epub 2020 Apr 30.

A. J. Drexel Nanomaterials Institute, and Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104, USA.

Two-dimensional transition metal carbides and/or nitrides (MXenes) have shown promise in developing electrochemical storage of metal ions within conductive galleries due to redox reactions with transition metal atoms. Here, effect of surface chemistry on electrochemical storage of sodium ions within MXene interlayers is investigated by etching TiAlC MAX using different etchants - HF, HF/HCl, and HF/HSO.
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http://dx.doi.org/10.1039/d0cc01042aDOI Listing
June 2020

Enhanced Ionic Accessibility of Flexible MXene Electrodes Produced by Natural Sedimentation.

Nanomicro Lett 2020 Apr 11;12(1):89. Epub 2020 Apr 11.

State Key Laboratory of Organic-Inorganic Composites, Beijing Key Laboratory of Electrochemical Process and Technology for Materials, Beijing University of Chemical Technology, Beijing, 100029, People's Republic of China.

MXene nanosheets have been used for preparing highly flexible integrated electrodes due to their two-dimensional (2D) morphology, flexibility, high conductivity, and abundant functional groups. However, restacking of 2D nanosheets inhibits the ion transport in MXene electrodes, limiting their thickness, rate performance, and energy storage capacity. Here, we employed a natural sedimentation method instead of the conventional vacuum-assisted filtration to prepare flexible TiCT MXene films with enlarged interlayer spacing, which facilitates the access of the lithium ions to the interlayers and thus leads to a greatly enhanced electrochemical performance. The naturally sedimented flexible film shows a double lithium storage capacity compared to the conventional vacuum-filtered MXene film, along with improved rate performance and excellent cycle stability.
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http://dx.doi.org/10.1007/s40820-020-00426-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7770857PMC
April 2020

Beyond TiCT: MXenes for Electromagnetic Interference Shielding.

ACS Nano 2020 Apr 17;14(4):5008-5016. Epub 2020 Mar 17.

A. J. Drexel Nanomaterials Institute and Department of Materials Science and Engineering, Drexel University, Philadelphia 19104, Pennsylvania, United States.

New ultrathin and multifunctional electromagnetic interference (EMI) shielding materials are required for protecting electronics against electromagnetic pollution in the fifth-generation networks and Internet of Things era. Micrometer-thin TiCT MXene films have shown the best EMI shielding performance among synthetic materials so far. Yet, the effects of elemental composition, layer structure, and transition-metal arrangement on EMI shielding properties of MXenes have not been explored, despite the fact that more than 30 different MXenes have been reported, and many more are possible. Here, we report on a systematic study of EMI shielding properties of 16 different MXenes, which cover single-metal MXenes, ordered double-metal carbide MXenes, and random solid solution MXenes of M and X elements. This is the largest set of MXene compositions ever reported in a comparative study. Films with thicknesses ranging from nanometers to micrometers were produced by spin-casting, spray-coating, and vacuum-assisted filtration. All MXenes achieved effective EMI shielding (>20 dB) in micrometer-thick films. The EMI shielding effectiveness of sprayed TiCT film with a thickness of only ∼40 nm reaches 21 dB. Adjustable EMI shielding properties were achieved in solid solution MXenes with different ratios of elements. A transfer matrix model was shown to fit EMI shielding data for highly conductive MXenes but could not describe the behavior of materials with low conductivity. This work shows that many members of the large MXene family can be used for EMI shielding, contributing to designing ultrathin, flexible, and multifunctional EMI shielding films benefiting from specific characteristics of individual MXenes.
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http://dx.doi.org/10.1021/acsnano.0c01312DOI Listing
April 2020

Fabrication of Ti3C2 MXene Microelectrode Arrays for In Vivo Neural Recording.

J Vis Exp 2020 02 12(156). Epub 2020 Feb 12.

Department of Bioengineering, University of Pennsylvania; Center for Neuroengineering and Therapeutics, University of Pennsylvania; Corporal Michael J. Crescenz Veterans Affairs Medical Center; Department of Neurology, University of Pennsylvania; Department of Physical Medicine and Rehabilitation;

Implantable microelectrode technologies have been widely used to elucidate neural dynamics at the microscale to gain a deeper understanding of the neural underpinnings of brain disease and injury. As electrodes are miniaturized to the scale of individual cells, a corresponding rise in the interface impedance limits the quality of recorded signals. Additionally, conventional electrode materials are stiff, resulting in a significant mechanical mismatch between the electrode and the surrounding brain tissue, which elicits an inflammatory response that eventually leads to a degradation of the device performance. To address these challenges, we have developed a process to fabricate flexible microelectrodes based on Ti3C2 MXene, a recently discovered nanomaterial that possesses remarkably high volumetric capacitance, electrical conductivity, surface functionality, and processability in aqueous dispersions. Flexible arrays of Ti3C2 MXene microelectrodes have remarkably low impedance due to the high conductivity and high specific surface area of the Ti3C2 MXene films, and they have proven to be exquisitely sensitive for recording neuronal activity. In this protocol, we describe a novel method for micropatterning Ti3C2 MXene into microelectrode arrays on flexible polymeric substrates and outline their use for in vivo micro-electrocorticography recording. This method can easily be extended to create MXene electrode arrays of arbitrary size or geometry for a range of other applications in bioelectronics and it can also be adapted for use with other conductive inks besides Ti3C2 MXene. This protocol enables simple and scalable fabrication of microelectrodes from solution-based conductive inks, and specifically allows harnessing the unique properties of hydrophilic Ti3C2 MXene to overcome many of the barriers that have long hindered the widespread adoption of carbon-based nanomaterials for high-fidelity neural microelectrodes.
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http://dx.doi.org/10.3791/60741DOI Listing
February 2020

TiCT MXene-Reduced Graphene Oxide Composite Electrodes for Stretchable Supercapacitors.

ACS Nano 2020 Mar 19;14(3):3576-3586. Epub 2020 Feb 19.

Laboratory for Soft Machines & Electronics, School of Packaging, Michigan State University, East Lansing, Michigan 48824, United States.

The development of stretchable electronics requires the invention of compatible high-performance power sources, such as stretchable supercapacitors and batteries. In this work, two-dimensional (2D) titanium carbide (TiCT) MXene is being explored for flexible and printed energy storage devices by fabrication of a robust, stretchable high-performance supercapacitor with reduced graphene oxide (RGO) to create a composite electrode. The TiCT/RGO composite electrode combines the superior electrochemical and mechanical properties of TiCT and the mechanical robustness of RGO resulting from strong nanosheet interactions, larger nanoflake size, and mechanical flexibility. It is found that the TiCT/RGO composite electrodes with 50 wt % RGO incorporated prove to mitigate cracks generated under large strains. The composite electrodes exhibit a large capacitance of 49 mF/cm (∼490 F/cm and ∼140 F/g) and good electrochemical and mechanical stability when subjected to cyclic uniaxial (300%) or biaxial (200% × 200%) strains. The as-assembled symmetric supercapacitor demonstrates a specific capacitance of 18.6 mF/cm (∼90 F/cm and ∼29 F/g) and a stretchability of up to 300%. The developed approach offers an alternative strategy to fabricate stretchable MXene-based energy storage devices and can be extended to other members of the large MXene family.
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http://dx.doi.org/10.1021/acsnano.9b10066DOI Listing
March 2020

Temperature-dependent mechanical properties of TiCO (n = 1, 2) MXene monolayers: a first-principles study.

Phys Chem Chem Phys 2020 Feb 27;22(6):3414-3424. Epub 2020 Jan 27.

Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway.

Two-dimensional (2D) transition metal carbides, carbonitrides, and nitrides (named as MXenes) have become of the fastest growing family of 2D materials in terms of compositions and their applications in different areas. One of the least explored properties of MXenes is their mechanical properties. While the basic elastic properties of MXenes have been studied by first-principles, the effects of temperature on the elastic properties have never been explored. In this study, we investigate temperature-dependent structural and mechanical properties of the titanium-containing MXenes (TiCO (n = 1, 2)) based on the first-principles calculations combined with quasi-harmonic approximation. The effective Young's modulus of a single layer of TiCO and TiCO is calculated to be 565 and 482 GPa, respectively, at 0 K. By increasing temperature to 1000 K, Young's moduli of TiCO and TiCO decrease to 469 GPa and 442 GPa, respectively, which indicates a larger reduction in stiffness in thinner MXenes at higher temperatures. Our calculations of the temperature-dependent bond strengths within MXenes showed that titanium and carbon atoms in TiCO form stronger bonds than TiCO and atomic bonds in TiCO lose their stiffness more than TiCO with increasing temperatures. The Debye temperature of these monolayers is also calculated to provide a comparison of the thermal conductivity between these monolayers, in which the results show that the TiCO has a higher thermal conductivity than TiCO. Our calculated electronic properties results of the monolayers are also shown that the electrical conductivity of the monolayers would not change with temperature. Our study extends MXenes applications to high-temperature applications, such as structural composite components and aerospace coatings.
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http://dx.doi.org/10.1039/c9cp06721cDOI Listing
February 2020

In Situ N-Doped Graphene and Mo Nanoribbon Formation from Mo Ti C MXene Monolayers.

Small 2020 Feb 14;16(5):e1907115. Epub 2020 Jan 14.

Soochow Institute for Energy and Materials Innovations, College of Physics, Optoelectronics and Energy, Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou, 215006, China.

Since the advent of monolayered 2D transition metal carbide and nitrides (MXenes) in 2011, the number of different monolayer systems and the study thereof have been on the rise. Mo Ti C is one of the least studied MXenes and new insights to this material are of value to the field. Here, the stability of Mo Ti C under electron irradiation is investigated. A transmission electron microscope (TEM) is used to study the structural and elemental changes in situ. It is found that Mo Ti C is reasonably stable for the first 2 min of irradiation. However, structural changes occur thereafter, which trigger increasingly rapid and significant rearrangement. This results in the formation of pores and two new nanomaterials, namely, N-doped graphene membranes and Mo nanoribbons. The study provides insight into the stability of Mo Ti C monolayers against electron irradiation, which will allow for reliable future study of the material using TEM. Furthermore, these findings will facilitate further research in the rapidly growing field of electron beam driven chemistry and engineering of nanomaterials.
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http://dx.doi.org/10.1002/smll.201907115DOI Listing
February 2020

Synthesis of MoVAlC MAX Phase and Two-Dimensional MoVC MXene with Five Atomic Layers of Transition Metals.

ACS Nano 2020 Jan 17;14(1):204-217. Epub 2019 Dec 17.

Department of Materials Science and Engineering, and A.J. Drexel Nanomaterials Institute , Drexel University , Philadelphia , Pennsylvania 19104 , United States.

MXenes are a family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides with a general formula of MXT, in which two, three, or four atomic layers of a transition metal (M: Ti, Nb, V, Cr, Mo, Ta, etc.) are interleaved with layers of C and/or N (shown as X), and T represents surface termination groups such as -OH, ═O, and -F. Here, we report the scalable synthesis and characterization of a MXene with five atomic layers of transition metals (MoVCT), by synthesizing its MoVAlC MAX phase precursor that contains no other MAX phase impurities. These phases display twinning at their central M layers which is not present in any other known MAX phases or MXenes. Transmission electron microscopy and X-ray diffraction were used to examine the structure of both phases. Energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and high-resolution scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy were used to study the composition of these materials. Density functional theory calculations indicate that other five transition metal-layer MAX phases (M'M″AlC) may be possible, where M' and M″ are two different transition metals. The predicted existence of additional Al-containing MAX phases suggests that more MCT MXenes can be synthesized. Additionally, we characterized the optical, electronic, and thermal properties of MoVCT. This study demonstrates the existence of an additional subfamily of MXT MXenes as well as a twinned structure, allowing for a wider range of 2D structures and compositions for more control over properties, which could lead to many different applications.
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http://dx.doi.org/10.1021/acsnano.9b07708DOI Listing
January 2020

Sculpting Liquids with Two-Dimensional Materials: The Assembly of TiCT MXene Sheets at Liquid-Liquid Interfaces.

ACS Nano 2019 Nov 11;13(11):12385-12392. Epub 2019 Oct 11.

Department of Physics , University of California at Berkeley , Berkeley , California 94720 , United States.

The self-assembly of nanoscale materials at the liquid-liquid interface allows for fabrication of three-dimensionally structured liquids with nearly arbitrary geometries and tailored electronic, optical, and magnetic properties. Two-dimensional (2D) materials are highly anisotropic, with thicknesses on the order of a nanometer and lateral dimensions upward of hundreds of nanometers to micrometers. Controlling the assembly of these materials has direct implications for their properties and performance. We here describe the interfacial assembly and jamming of TiCT MXene nanosheets at the oil-water interface. Planar, as well as complex, programmed three-dimensional all-liquid objects are realized. Our approach presents potential for the creation of all-liquid 3D-printed devices for possible applications in all-liquid electrochemical and energy storage devices and electrically active, all-liquid fluidics that exploits the versatile structure, functionality, and reconfigurability of liquids.
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http://dx.doi.org/10.1021/acsnano.9b05088DOI Listing
November 2019

Colloidal Gelation in Liquid Metals Enables Functional Nanocomposites of 2D Metal Carbides (MXenes) and Lightweight Metals.

ACS Nano 2019 Nov 14;13(11):12415-12424. Epub 2019 Oct 14.

Department of Chemistry and James Franck Institute , University of Chicago , Chicago , Illinois 60637 , United States.

Nanomaterials dispersed in different media, such as liquids or polymers, generate a variety of functional composites with synergistic properties. In this work, we discuss liquid metals as the nanomaterials' dispersion media. For example, 2D transition-metal carbides and nitrides (MXenes) can be efficiently dispersed in liquid Ga and lightweight alloys of Al, Mg, and Li. We show that the Lifshitz theory predicts strong van der Waals attraction between nanoscale objects interacting through liquid metals. However, a uniform distribution of MXenes in liquid metals can be achieved through colloidal gelation, where particles form self-supporting networks stable against macroscopic phase segregation. This network acts as a reinforcement boosting mechanical properties of the resulting metal-matrix composite. By choosing Mg-Li alloy as an example of ultralightweight metal matrix and TiCT MXene as a nanoscale reinforcement, we apply a liquid metal gelation technique to fabricate functional nanocomposites with an up to 57% increase in the specific yield strength without compromising the matrix alloy's plasticity. MXenes largely retain their phase and 2D morphology after processing in liquid Mg-Li alloy at 700 °C. The 2D morphology enables formation of a strong semicoherent interface between MXene and metal matrix, manifested by biaxial strain of the MXene lattice inside the metal matrix. This work expands applications for MXenes and shows the potential for developing MXene-reinforced metal matrix composites for structural alloys and other emerging applications with metal-MXene interfaces, such as batteries and supercapacitors.
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http://dx.doi.org/10.1021/acsnano.9b06207DOI Listing
November 2019

The Rise of MXenes.

ACS Nano 2019 08;13(8):8491-8494

Indiana University-Purdue University Indianapolis.

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http://dx.doi.org/10.1021/acsnano.9b06394DOI Listing
August 2019

Additive-free MXene inks and direct printing of micro-supercapacitors.

Nat Commun 2019 04 17;10(1):1795. Epub 2019 Apr 17.

CRANN and AMBER Research Centers, Trinity College Dublin, Dublin 2, Ireland.

Direct printing of functional inks is critical for applications in diverse areas including electrochemical energy storage, smart electronics and healthcare. However, the available printable ink formulations are far from ideal. Either surfactants/additives are typically involved or the ink concentration is low, which add complexity to the manufacturing and compromises the printing resolution. Here, we demonstrate two types of two-dimensional titanium carbide (TiCT) MXene inks, aqueous and organic in the absence of any additive or binary-solvent systems, for extrusion printing and inkjet printing, respectively. We show examples of all-MXene-printed structures, such as micro-supercapacitors, conductive tracks and ohmic resistors on untreated plastic and paper substrates, with high printing resolution and spatial uniformity. The volumetric capacitance and energy density of the all-MXene-printed micro-supercapacitors are orders of magnitude greater than existing inkjet/extrusion-printed active materials. The versatile direct-ink-printing technique highlights the promise of additive-free MXene inks for scalable fabrication of easy-to-integrate components of printable electronics.
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http://dx.doi.org/10.1038/s41467-019-09398-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6470171PMC
April 2019

Prediction of Synthesis of 2D Metal Carbides and Nitrides (MXenes) and Their Precursors with Positive and Unlabeled Machine Learning.

ACS Nano 2019 Mar 7;13(3):3031-3041. Epub 2019 Mar 7.

Department of Materials Science and Engineering , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States.

Growing interest in the potential applications of two-dimensional (2D) materials has fueled advancement in the identification of 2D systems with exotic properties. Increasingly, the bottleneck in this field is the synthesis of these materials. Although theoretical calculations have predicted a myriad of promising 2D materials, only a few dozen have been experimentally realized since the initial discovery of graphene. Here, we adapt the state-of-the-art positive and unlabeled (PU) machine learning framework to predict which theoretically proposed 2D materials have the highest likelihood of being successfully synthesized. Using elemental information and data from high-throughput density functional theory calculations, we apply the PU learning method to the MXene family of 2D transition metal carbides, carbonitrides, and nitrides, and their layered precursor MAX phases, and identify 18 MXene compounds that are highly promising candidates for synthesis. By considering both the MXenes and their precursors, we further propose 20 synthesizable MAX phases that can be chemically exfoliated to produce MXenes.
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http://dx.doi.org/10.1021/acsnano.8b08014DOI Listing
March 2019

Control of MXenes' electronic properties through termination and intercalation.

Nat Commun 2019 01 31;10(1):522. Epub 2019 Jan 31.

Department of Materials Science & Engineering, Drexel University, Philadelphia, PA, 19104, USA.

MXenes are an emerging family of highly-conductive 2D materials which have demonstrated state-of-the-art performance in electromagnetic interference shielding, chemical sensing, and energy storage. To further improve performance, there is a need to increase MXenes' electronic conductivity. Tailoring the MXene surface chemistry could achieve this goal, as density functional theory predicts that surface terminations strongly influence MXenes' Fermi level density of states and thereby MXenes' electronic conductivity. Here, we directly correlate MXene surface de-functionalization with increased electronic conductivity through in situ vacuum annealing, electrical biasing, and spectroscopic analysis within the transmission electron microscope. Furthermore, we show that intercalation can induce transitions between metallic and semiconductor-like transport (transitions from a positive to negative temperature-dependence of resistance) through inter-flake effects. These findings lay the groundwork for intercalation- and termination-engineered MXenes, which promise improved electronic conductivity and could lead to the realization of semiconducting, magnetic, and topologically insulating MXenes.
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http://dx.doi.org/10.1038/s41467-018-08169-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6355901PMC
January 2019

Surface-Engineered MXenes: Electric Field Control of Magnetism and Enhanced Magnetic Anisotropy.

ACS Nano 2019 Mar 23;13(3):2831-2839. Epub 2019 Jan 23.

Department of Materials Science and Engineering , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States.

Controlling magnetism in two-dimensional (2D) materials via electric fields and doping enables robust long-range order by providing an external mechanism to modulate magnetic exchange interactions and anisotropy. In this report, we predict that transition metal carbide and nitride MXenes are promising candidates for controllable magnetic 2D materials. The surface terminations introduced during synthesis act as chemical dopants that influence the electronic structure, enabling controllable magnetic order. We show ground-state magnetic ordering in Janus MXO F (M is an early transition metal, X is carbon or nitrogen, and x = 0.5, 1, or 1.5) with asymmetric surface functionalization, where local structural and chemical disorder induces magnetic ordering in some systems that are nonmagnetic or weakly magnetic in their pristine form. The resulting magnetic states of these noncentrosymmetric structures can be robustly switched and stabilized by tuning the interlayer exchange couplings with small applied electric fields. Furthermore, bond directionality is enhanced by Janus functionalization, resulting in improved magnetic anisotropy, which is essential to stable 2D magnetic ordering. The mixed termination-induced anisotropy leads to robust Ising ferromagnetism with an out-of-plane easy axis over the full range of relevant termination compositions for Janus MnN. Janus CrC, VC, and TiC were found to be robustly antiferromagnetic. Our results provide a strategy for exploiting asymmetric surface functionalization to achieve room-temperature nanoscale magnetism under ambient conditions in MXenes with currently available synthesis techniques.
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http://dx.doi.org/10.1021/acsnano.8b09201DOI Listing
March 2019

A Tungsten-Based Nanolaminated Ternary Carbide: (W,Ti)C.

Inorg Chem 2019 Jan 4;58(2):1100-1106. Epub 2019 Jan 4.

Department of Materials Science and Engineering , Drexel University , Philadelphia , Pennsylvania 19104 , United States.

Nanolamellar transition metal carbides are gaining increasing interests because of the recent developments of their two-dimensional (2D) derivatives and promising performance for a variety of applications from energy storage, catalysis to transparent conductive coatings, and medicine. To develop more novel 2D materials, new nanolaminated structures are needed. Here we report on a tungsten-based nanolaminated ternary phase, (W,Ti)C, synthesized by an Al-catalyzed reaction of W, Ti, and C powders at 1600 °C for 4 h, under flowing argon. X-ray and neutron diffraction, along with Z-contrast scanning transmission electron microscopy, were used to determine the atomic structure, ordering, and occupancies. This phase has a layered hexagonal structure ( P6 /mmc) with lattice parameters, a = 3.00880(7) Å, and c = 19.5633(6) Å and a nominal chemistry of (W,Ti)C (actual chemistry, WTiC). The structure is comprised of layers of pure W that are also twin planes with two adjacent atomic layers of mixed W and Ti, on either side. The use of Al as a catalyst for synthesizing otherwise difficult to make phases, could in turn lead to the discovery of a large family of nonstoichiometric ternary transition metal carbides, synthesized at relatively low temperatures and shorter times.
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http://dx.doi.org/10.1021/acs.inorgchem.8b02226DOI Listing
January 2019

van der Waals epitaxy of highly (111)-oriented BaTiO on MXene.

Nanoscale 2019 Jan;11(2):622-630

Department of Materials Science & Engineering, Drexel University, Philadelphia, PA 19104, USA.

We report on the high temperature thin film growth of BaTiO3 on Ti3C2Tx MXene flakes using van der Waals epitaxy on a degradable template layer. MXene was deposited on amorphous and crystalline substrates by spray- and dip-coating techniques, while the growth of BaTiO3 at 700 °C was accomplished using pulsed laser deposition in an oxygen rich environment. We demonstrate that the MXene flakes act as a temporary seed layer, which promotes highly oriented BaTiO3 growth along the (111) direction independent of the underlying substrate. The lattice parameters of the BaTiO3 films are close to the bulk value suggesting that the BaTiO3 films remains unstrained, as expected for van der Waals epitaxy. The initial size of the MXene flakes has an impact on the orientation of the BaTiO3 films with larger flake sizes promoting a higher fraction of the polycrystalline film to grow along the (111) direction. The deposited BaTiO3 film adopts the same morphology as the original flakes and piezoresponse force microscopy shows a robust ferroelectric behavior for individual grains. Transmission electron microscopy results indicate that the Ti3C2Tx MXene fully decomposes during the BaTiO3 deposition and the surplus Ti atoms are readily incorporated into the BaTiO3 film. Electrical measurements show a similar dielectric constant as a BaTiO3 film grown without the MXene seed layer. The demonstrated process has the potential to overcome the longstanding issue of integrating highly oriented complex oxide thin films directly on any desired substrate.
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http://dx.doi.org/10.1039/c8nr07140cDOI Listing
January 2019

MXene Sorbents for Removal of Urea from Dialysate: A Step toward the Wearable Artificial Kidney.

ACS Nano 2018 10 1;12(10):10518-10528. Epub 2018 Oct 1.

A.J. Drexel Nanomaterials Institute, and Materials Science and Engineering Department , Drexel University , 3141 Chestnut Street , Philadelphia , Pennsylvania 19104 , United States.

The wearable artificial kidney can deliver continuous ambulatory dialysis for more than 3 million patients with end-stage renal disease. However, the efficient removal of urea is a key challenge in miniaturizing the device and making it light and small enough for practical use. Here, we show that two-dimensional titanium carbide (MXene) with the composition of TiCT , where T represents surface termination groups such as -OH, -O-, and -F, can adsorb urea, reaching 99% removal efficiency from aqueous solution and 94% from dialysate at the initial urea concentration of 30 mg/dL, with the maximum urea adsorption capacity of 10.4 mg/g at room temperature. When tested at 37 °C, we achieved a 2-fold increase in urea removal efficiency from dialysate, with the maximum urea adsorption capacity of 21.7 mg/g. TiCT showed good hemocompatibility; it did not induce cell apoptosis or reduce the metabolizing cell fraction, indicating no impact on cell viability at concentrations of up to 200 μg/mL. The biocompatibility of TiCT and its selectivity for urea adsorption from dialysate open a new opportunity in designing a miniaturized dialysate regeneration system for a wearable artificial kidney.
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http://dx.doi.org/10.1021/acsnano.8b06494DOI Listing
October 2018
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