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Line 2:   {{AFC comment|1=I have requested the assistance of ] to review this draft. ] (]) 20:25, 18 November 2014 (UTC)}} :{{afc comment|Problems: *1) Conflict of Interest almost certainly. The author should identify themselves. The writing should be more sober. *2) Overhyped, there are NO applications and predications of future breakthroughs based on DFT are too flimsy to be mentioned. DFT in general has little place here. Misplaced Pages is not a technical journal *3) the content might aim to rely on the one secondary source and minimize other sources. There is only one review in English. *4) The topic is worthwhile if it can be trimmed back. The area of research was launched in 2012, consists of about 40 publications, and is dominated by the Drexel group. *I took a stab at compressing this thing. Sorry about messing up the refs. It would not bother me to revert my work. }}------] (]) 01:17, 19 November 2014 (UTC)   In ], an '''MXene''' is a class of low-dimensional ]s. These materials consist of two-dimensional arrays of ] or carbonitride. First described in 2011, MXenes combine the metallic conductivity of transition metal carbides and hydrophilic nature because of their hydroxyl or oxygen terminated surfaces.<ref name=Adv>M. Naguib, V.N. Mochalin, M.W. Barsoum, Y. Gogotsi, 25th Anniversary Article: MXenes: A New Family of Two-Dimensional Materials, Advanced Materials, Volume 26, Issue 7, page 992-1005, 2014.</ref> ----   A MXene is a two-dimensional early transition metal carbide or carbonitride, produced by etching the A element from a ]. This family of materials was discovered at ] in 2011.<ref name=Adv2011>M. Naguib, M. Kurtoglu, V. Presser, J. Lu, J. Niu, M. Heon, L. Hultman, Y. Gogotsi, M. W. Barsoum, Adv. Mater. 2011, 23, 4248.</ref> MXenes combine the metallic conductivity of transition metal carbides and hydrophilic nature because of their hydroxyl or oxygen terminated surfaces.<ref name=NaguibNano>M. Naguib, O. Mashtalir, J. Carle, V. Presser, J. Lu, L. Hultman, Y. Gogotsi, M. W. Barsoum, ACS Nano 2012, 6, 1322.</ref><ref>M. Naguib, J. Halim, J. Lu, L. Hultman, Y. Gogotsi, M. W. Barsoum, J. Am. Chem. Soc. 2013,135, 15966.
</ref> The following MXenes have been synthesized: Ti<sub>3</sub>C<sub>2</sub>, Ti<sub>2</sub>C, V<sub>2</sub>C, Nb<sub>2</sub>C, (Ti<sub>0.5</sub>,Nb<sub>0.5</sub>)<sub>2</sub>C, Ta<sub>4</sub>C<sub>3</sub>, (V<sub>0.5</sub>,Cr<sub>0.5</sub>)<sub>3</sub>C<sub>2</sub>, Ti<sub>3</sub>CN, and many more are predicted and analyzed computationally.<ref name=Adv>M. Naguib, V.N. Mochalin, M.W. Barsoum, Y. Gogotsi, 25th Anniversary Article: MXenes: A New Family of Two-Dimensional Materials, Advanced Materials, Volume 26, Issue 7, page 992-1005, 2014.</ref>   ==SynthesisPreparation== MXenes are produced by selectively etching out the A element from a ], which has the general formula M<sub>n+1</sub>AX<sub>n</sub>, where M is an early transition metal, A is an element from group IIIA or IVA of the periodic table, X is C and/or N, and n = 1, 2, or 3. MAX phases have a layered hexagonal structure with P6<sub>3</sub>/mmc symmetry, where M layers are nearly closed packed and X atoms fill octahedral sites.<ref name=Adv /> Therefore, M<sub>n+1</sub>X<sub>n</sub> layers are interleaved with the A element, which is metallically bonded to the M element.<ref>Z. Sun, D. Music, R. Ahuja, S. Li, J. M. Schneider, Phys. Rev. B 2004, 70, 092102.
</ref> MAX phases are etched mainly by using strong etchants such as ] (HF).<ref name=Adv /> Etching of Ti<sub>3</sub>AlC<sub>2</sub> in aqueous HF at room temperature causes the A (Al) atoms to be removed, and the surface of the carbide layers to be terminated by O, OH, and/or F atoms.<ref name=Adv /> It has been shown how the higher the value of n in the formula, the more stable the MXene.<ref name=NaguibNano />The following MXenes have been synthesized: Ti<sub>3</sub>C<sub>2</sub>, Ti<sub>2</sub>C, V<sub>2</sub>C, Nb<sub>2</sub>C, (Ti<sub>0.5</sub>,Nb<sub>0.5</sub>)<sub>2</sub>C, Ta<sub>4</sub>C<sub>3</sub>, (V<sub>0.5</sub>,Cr<sub>0.5</sub>)<sub>3</sub>C<sub>2</sub>, Ti<sub>3</sub>CN. Although theoretically possible, nitride-based MXenes have not yet been reported.<ref name=Adv /><ref name=Adv>   ==Structure==▼ One possible method of synthesizingMacroscopically, MXenes is etching a MAX phase in aqueous HF for a certain period of time that depends on the HF concentration and temperature at which the procedure is performed. After this, the mixture is centrifuged to separate the solid from the supernatant fluid, followed by washing the solid with deionized water until the pH of the suspension is between 4 and 6. This produceshave an accordion -like structure, which can be referred to as a multilayer MXene (ML-MXene), or a few-layer MXene (FL-MXene) when there are fewer than five layers. Because surface terminations by functional groups in MXenes can occur, the naming convention M<sub>n+1</sub>X<sub>n</sub>T<sub>x</sub> can be used, where T is a functional group.<ref name=Adv />   MXenes adopt three structures, as inherited from the parent MAX phases: M<sub>2</sub>C, M<sub>3</sub>C<sub>2</sub>, and M<sub>4</sub>C<sub>3</sub>. Although theoretically possible to produce them, attempts to produce nitride-based MXenes have not yet been successful.<ref name=Adv /> The lower cohesion energy of Ti<sub>n+1</sub>N<sub>n</sub> compared to Ti<sub>n+1</sub>C<sub>n</sub> implies that the nitride structure is less stable, while the higher formation energy of Ti<sub>n+1</sub>N<sub>n</sub> from Ti<sub>n+1</sub>AlN<sub>n</sub> relative to the formation energy of Ti<sub>n+1</sub>C<sub>n</sub> from Ti<sub>n+1</sub>AlC<sub>n</sub> implies that the Al-N bond is stronger than the Al-C bond in their respective MAX phases. It is also possible that less-stable nitride MXenes had been produced but were dissolved in the etchant.<ref name=Adv />   ▲==Structure== MXenes that have been produced have three structures inherited from MAX phases: M<sub>2</sub>C, M<sub>3</sub>C<sub>2</sub>, and M<sub>4</sub>C<sub>3</sub>. According to DFT (]) studies, there are two energetically favorable orientations for the terminating group (T) in Ti<sub>3</sub>C<sub>2</sub>T<sub>2</sub>: I and II.<ref>A. N. Enyashin, A. L. Ivanovskii, Comput. Theor. Chem. 2012, 989, 
27.</ref><ref name=Comput>Q. Tang, Z. Zhou, P. Shen, J. Am. Chem. Soc. 2012, 134, 16909.</ref> In configuration I, T is located above the hollow sites between three neighboring C atoms. In configuration II, T groups are located above C atoms on both sides of the MXene layers. A third stable configuration is possible, III, which occurs when one side of a MXene is terminated in configuration I, and the opposite in II. Relative DFT total energies suggest that the most stable configuration of these three is configuration I, and the least stable is configuration II.<ref name=Adv />   ==Intercalation== Intercalation in MXenes is possible because of the weak bonds between layers. Different species can intercalate MXenes, whether organic, inorganic, or ionic. AmongGuest molecules that have been intercalated into Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> areinclude ], ], and ].<ref name=Adv /> For example, N<sub>2</sub>H<sub>4</sub> (hydrazine) can be intercalated into Ti<sub>3</sub>C<sub>2</sub>(OH)<sub>2</sub> with the molecules parallel to the MXene basal planes to form a monolayer. Intercalaction increases the MXene c lattice parameter, which weakens the bondsbonding between MX layers.<ref name=Adv /> Ions, including Li<sup>+</sup>, Pb<sup>2+</sup>, and Al<sup>3+</sup>, can also be intercalaction into MXenes, either spontaneously or when a negative potential is applied to a MXene electrode.<ref>C. Eames, M. S. Islam, Ion Intercalation into Two-Dimensional Transition-Metal Carbides: Global Screening for New High-Capacity Battery Materials, Journal of the American Chemical Society Article ASAP, 13 Oct. 2014.</ref>   ==Properties== With a high electron density near the Fermi level, MXene monolayers are predicted to be metallic according to DFT studies.<ref name=Adv2011 /><ref name=Shein>I. R. Shein, A. L. Ivanovskii, Comput. Mater. Sci. 2012, 65, 104.</ref><ref name=Comput /><ref>M. Khazaei, M. Arai, T. Sasaki, C.-Y. Chung, N. S. Venkataramanan, 
M. Estili, Y. Sakka, Y. Kawazoe, Adv. Funct. Mater. 2012, 23, 2185.</ref><ref>Y. Xie, P. R. C. Kent, Phys. Rev. B 2013, 87, 235441.</ref> In MAX phases, N(E<sub>F</sub>) is mostly M 3d orbitals, and the valence states below E<sub>F</sub> are composed of two sub-bands. One, sub-band A, made of hybridized Ti 3d-Al 3p orbitals, is near E<sub>F</sub>, and another, sub-band B, -10 to -3 eV below E<sub>F</sub> which is due to hybridized Ti 3d-C 2p and Ti 3d-Al 3s orbitals. Said differently, sub-band A is the source of Ti-Al bonds, while sub-band B is the source of Ti-C bond. Removing A layers causes the Ti 3d states to be redistributed from missing Ti-Al bonds to delocalized Ti-Ti metallic bond states near the Fermi energy in Ti<sub>2</sub>, therefore N(E<sub>F</sub>) is 2.5-4.5 times higher for MXenes than MAX phases.<ref name=Shein />   Only bare-surface MXenes exhibitare magnetic properties;. Cr<sub>2</sub>C, Cr<sub>2</sub>N, and Ta<sub>3</sub>C<sub>2</sub> are ferromagnetic, Ti<sub>3</sub>C<sub>2</sub> and Ti<sub>3</sub>N<sub>2</sub> are antiferromagnetic. Electronic properties of MXenes are also dependent on surface groups. While Ti<sub>3</sub>C<sub>2</sub> is a metallic conductor, addition of surface groups give rise to small band gaps, 0.05 eV for Ti<sub>3</sub>C<sub>2</sub>(OH)<sub>2</sub> and 0.1 eV for Ti<sub>3</sub>C<sub>2</sub>F<sub>2</sub>.<ref name=Adv />   Another interesting trait of MXenes is their mechanical properties. Their M-C and M-N bonds are some of the strongest known.<ref name=Adv /> High elastic moduli for MXenes have been predicted.<ref name=Adv2011 />   ==Applications== Because of spontaneous intercalation in aqueous salt solutions of cations between Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> layers, MXenes can be used to produce outstanding ].<ref>M. R. Lukatskaya, O. Mashtalir, C. E. Ren, Y. Dall’Agnese, P. Rozier, P. L. Taberna, M. Naguib, P. Simon, M. W. Barsoum, Y. Gogotsi, Science 2013, 341, 1502.</ref> MXenes’ chemistries, morphologies, and electrical conductivities make them ideal candidates for applications including sensors, catalysts, conductive reinforcement additives to polymers, and energy storage.<ref name=Adv /> Although MXenes' gravimetric capacities may not be as high as that of Si anodes in lithium-ion batteries, their advantage is offering a high cycling rate with good capacity.<ref>J. R. Szczech, S. Jin, Energy Environ. Sci. 2011, 4, 56.
</ref> Because MXenes exhibit high cycling rates, they are good candidates for hybrid cells, which combine high energy densities characteristic of lithium ion batteries and high power densities of electrical double layer capacitors.<ref name=Adv /> MXenes have also shown high volumetric capacitance on aqueous electrolytes.<ref>M. Heon, S. Lofland, J. Applegate, R. Nolte, E. Cortes, J. D. Hettinger, P.-L. Taberna, P. Simon, P. Huang, M. Brunet, Y. Gogotsi, Energy Environ. Sci. 2011, 4, 135.</ref>   Intercalation of MXenes by Na<sup>+</sup>, Mg<sup>2+</sup>, and Al<sup>3+</sup> suggests that they can be used in multivalent ion batteries other than lithium ion batteries.<ref name=Adv />   It is expected that MXenes used as additives in polymers can provide excellent mechanical properties and good electrical conductivity.<ref name=Adv />   ==References== Line 42 ⟶ 36: * *   == External links == * http://max.materials.drexel.edu * http://nano.materials.drexel.edu

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  • Comment: Problems: *1) Conflict of Interest almost certainly. The author should identify themselves. The writing should be more sober.*2) Overhyped, there are NO applications and predications of future breakthroughs based on DFT are too flimsy to be mentioned. DFT in general has little place here. Misplaced Pages is not a technical journal*3) the content might aim to rely on the one secondary source and minimize other sources. There is only one review in English.*4) The topic is worthwhile if it can be trimmed back. The area of research was launched in 2012, consists of about 40 publications, and is dominated by the Drexel group.*I took a stab at compressing this thing. Sorry about messing up the refs. It would not bother me to revert my work.------Smokefoot (talk) 01:17, 19 November 2014 (UTC)

In materials science, an MXene is a class of low-dimensional inorganic compounds. These materials consist of two-dimensional arrays of transition metal carbide or carbonitride. First described in 2011, MXenes combine the metallic conductivity of transition metal carbides and hydrophilic nature because of their hydroxyl or oxygen terminated surfaces.


Preparation

MXenes are produced by selectively etching out the A element from a MAX phase, which has the general formula Mn+1AXn, where M is an early transition metal, A is an element from group IIIA or IVA of the periodic table, X is C and/or N, and n = 1, 2, or 3. MAX phases have a layered hexagonal structure with P63/mmc symmetry, where M layers are nearly closed packed and X atoms fill octahedral sites. Therefore, Mn+1Xn layers are interleaved with the A element, which is metallically bonded to the M element. MAX phases are etched mainly by using strong etchants such as hydrofluoric acid (HF). Etching of Ti3AlC2 in aqueous HF at room temperature causes the A (Al) atoms to be removed, and the surface of the carbide layers to be terminated by O, OH, and/or F atoms. It has been shown how the higher the value of n in the formula, the more stable the MXene.The following MXenes have been synthesized: Ti3C2, Ti2C, V2C, Nb2C, (Ti0.5,Nb0.5)2C, Ta4C3, (V0.5,Cr0.5)3C2, Ti3CN. Although theoretically possible, nitride-based MXenes have not yet been reported.Cite error: A <ref> tag is missing the closing </ref> (see the help page).

Properties

With a high electron density near the Fermi level, MXene monolayers are predicted to be metallic. In MAX phases, N(EF) is mostly M 3d orbitals, and the valence states below EF are composed of two sub-bands. One, sub-band A, made of hybridized Ti 3d-Al 3p orbitals, is near EF, and another, sub-band B, -10 to -3 eV below EF which is due to hybridized Ti 3d-C 2p and Ti 3d-Al 3s orbitals. Said differently, sub-band A is the source of Ti-Al bonds, while sub-band B is the source of Ti-C bond. Removing A layers causes the Ti 3d states to be redistributed from missing Ti-Al bonds to delocalized Ti-Ti metallic bond states near the Fermi energy in Ti2, therefore N(EF) is 2.5-4.5 times higher for MXenes than MAX phases.

Only bare-surface MXenes are magnetic . Cr2C, Cr2N, and Ta3C2 are ferromagnetic, Ti3C2 and Ti3N2 are antiferromagnetic.

References

  1. ^ M. Naguib, V.N. Mochalin, M.W. Barsoum, Y. Gogotsi, 25th Anniversary Article: MXenes: A New Family of Two-Dimensional Materials, Advanced Materials, Volume 26, Issue 7, page 992-1005, 2014.
  2. Z. Sun, D. Music, R. Ahuja, S. Li, J. M. Schneider, Phys. Rev. B 2004, 70, 092102.

  3. Cite error: The named reference NaguibNano was invoked but never defined (see the help page).
  4. Cite error: The named reference Adv2011 was invoked but never defined (see the help page).
  5. ^ I. R. Shein, A. L. Ivanovskii, Comput. Mater. Sci. 2012, 65, 104.
  6. Cite error: The named reference Comput was invoked but never defined (see the help page).
  7. M. Khazaei, M. Arai, T. Sasaki, C.-Y. Chung, N. S. Venkataramanan, 
M. Estili, Y. Sakka, Y. Kawazoe, Adv. Funct. Mater. 2012, 23, 2185.
  8. Y. Xie, P. R. C. Kent, Phys. Rev. B 2013, 87, 235441.
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