Characterization of MXenes at every step, from their precursors to single flakes and assembled films

Shekhirev, Mikhail; Shuck, Christopher E.; Sarycheva, Asia; Gogotsi, Yury

doi:10.1016/j.pmatsci.2020.100757

Cited by 443 publications

(319 citation statements)

References 340 publications

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“…18 The etching conditions used here, 50% HF for 96 h at 55 ºC, are among the harshest conditions used for the synthesis of MXenes. 57 Additionally, while our results indicate favorable entropy stabilization, we cannot rule out the tendency of Mo and Cr to prefer the outer transition metal atomic layers in a MXene 2D flake, as was observed in ordered double transition metal MAX and MXene phases. 12,[58][59][60][61][62][63] The possible preferred atomic positions of Mo and Cr can expose them directly to HF during etching, which leads to their relatively higher removal rates while creating their transition metal vacancies in the outer M layers.…”

Section: Resultscontrasting

confidence: 67%

High-Entropy 2D Carbide MXenes

Nemani¹,

ZHANG²,

Wyatt³

et al. 2021

Preprint

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Two-dimensional (2D) transition metal carbides and nitrides, known as MXenes, are a fast-growing family of 2D materials. MXenes 2D flakes have n + 1 (n = 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, through the use of four transition metals, we report the synthesis of multi-principal element high-entropy M4C3Tx MXenes. Specifically, we introduce two high-entropy MXenes, TiVNbMoC3Tx and TiVCrMoC3Tx, as well as their precursor TiVNbMoAlC3 and TiVCrMoAlC3 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-element MAX phase, two different MAX phases can be formed (i.e. 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 expand the compositional variety of the MXene family to further tune their properties, including electronic, magnetic, electrochemical, catalytic, high temperature stability, and mechanical properties.

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Section: Resultscontrasting

confidence: 67%

High-Entropy 2D Carbide MXenes

Nemani¹,

ZHANG²,

Wyatt³

et al. 2021

Preprint

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“…Similar trends are observed for the other MAX to MXene conversions, indicating successful removal of the Al layers for all MXenes studied here. In the MXene XRD patterns, only the (00 l ) peaks remain, indicating successful etching and delamination, with no impurities remaining in the MXene colloid [62] . Dynamic light scattering (DLS; Fig.…”

Section: Resultsmentioning

confidence: 99%

“…From the representative image, the flakes used in this study are confirmed to be single layers (about 1 nm in thickness), with sizes commensurate with DLS. They have O, OH and F on the surface, which affect their chemical properties and biological activity [62] , [63] , [64] .…”

Section: Resultsmentioning

confidence: 99%

2D MXenes with antiviral and immunomodulatory properties: A pilot study against SARS-CoV-2

et al. 2021

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Two-dimensional transition metal carbides/carbonitrides known as MXenes are rapidly growing as multimodal nanoplatforms in biomedicine. Here, taking SARS-CoV-2 as a model, we explored the antiviral properties and immune-profile of a large panel of four highly stable and well-characterized MXenes - Ti 3 C 2 T x , Ta 4 C 3 T x , Mo 2 Ti 2 C 3 T x and Nb 4 C 3 T x . To start with antiviral assessment, we first selected and deeply analyzed four different SARS-CoV-2 genotypes, common in most countries and carrying the wild type or mutated spike protein. When inhibition of the viral infection was tested in vitro with four viral clades, Ti 3 C 2 T x in particular, was able to significantly reduce infection only in SARS-CoV-2/clade GR infected Vero E6 cells. This difference in the antiviral activity, among the four viral particles tested, highlights the importance of considering the viral genotypes and mutations while testing antiviral activity of potential drugs and nanomaterials. Among the other MXenes tested, Mo 2 Ti 2 C 3 T x also showed antiviral properties. Proteomic, functional annotation analysis and comparison to the already published SARS-CoV-2 protein interaction map revealed that MXene-treatment exerts specific inhibitory mechanisms. Envisaging future antiviral MXene-based drug nano-formulations and considering the central importance of the immune response to viral infections, the immune impact of MXenes was evaluated on human primary immune cells by flow cytometry and single-cell mass cytometry on 17 distinct immune subpopulations. Moreover, 40 secreted cytokines were analyzed by Luminex technology. MXene immune profiling revealed i) the excellent bio and immune compatibility of the material, as well as the ability of MXene ii) to inhibit monocytes and iii) to reduce the release of pro-inflammatory cytokines, suggesting an anti-inflammatory effect elicited by MXene. We here report a selection of MXenes and viral SARS-CoV-2 genotypes/mutations, a series of the computational, structural and molecular data depicting deeply the SARS-CoV-2 mechanism of inhibition, as well as high dimensional single-cell immune-MXene profiling. Taken together, our results provide a compendium of knowledge for new developments of MXene-based multi-functioning nanosystems as antivirals and immune-modulators.

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“…Every step in the synthesis of MXenes affects their final structure, physiochemical properties, and the oxidation stability [ 54 ]. MXenes are topochemically derived from their parent MAX phases; therefore, the structure and properties of MXenes are highly affected by the quality of the MAX phase.…”

Section: Methods For Improving the Oxidation Stability Of Mxenesmentioning

confidence: 99%

Improving oxidation stability of 2D MXenes: synthesis, storage media, and conditions

et al. 2021

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Understanding and preventing oxidative degradation of MXene suspensions is essential for fostering fundamental academic studies and facilitating widespread industrial applications. Owing to their outstanding electrical, electrochemical, optoelectronic, and mechanical properties, MXenes, an emerging class of two-dimensional (2D) nanomaterials, show promising state-of-the-art performances in various applications including electromagnetic interference (EMI) shielding, terahertz shielding, electrochemical energy storage, triboelectric nanogenerators, thermal heaters, light-emitting diodes (LEDs), optoelectronics, and sensors. However, MXene synthesis using harsh chemical etching causes many defects or vacancies on the surface of the synthesized MXene flakes. Defective sites are vulnerable to oxidative degradation reactions with water and/or oxygen, which deteriorate the intrinsic properties of MXenes. In this review, we demonstrate the nature of oxidative degradation of MXenes and highlight the recent advancements in controlling the oxidation kinetics of MXenes with several promising strategic approaches, including careful control of the quality of the parent MAX phase, chemical etching conditions, defect passivation, dispersion medium, storage conditions, and polymer composites.

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Characterization of MXenes at every step, from their precursors to single flakes and assembled films

Cited by 443 publications

References 340 publications

High-Entropy 2D Carbide MXenes

High-Entropy 2D Carbide MXenes

2D MXenes with antiviral and immunomodulatory properties: A pilot study against SARS-CoV-2

Improving oxidation stability of 2D MXenes: synthesis, storage media, and conditions

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