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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> In ], a '''MXene''' is a class of low-dimensional ]s. These materials consist of two-dimensional arrays of ] or carbonitrides. 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>




==Preparation== ==Preparation==
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> 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>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. Although theoretically possible, nitride-based MXenes have not yet been reported.<ref name=Adv />


==Structure== ==Structure==
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==Properties== ==Properties==
With a high electron density near the Fermi level, MXene monolayers are predicted to be metallic.<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 /> With a high electron density near the Fermi level, MXene monolayers are predicted to be metallic.<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><ref name=Shein>I. R. Shein, A. L. Ivanovskii, Comput. Mater. Sci. 2012, 65, 104.</ref><ref name=Comput>Q. Tang, Z. Zhou, P. Shen, J. Am. Chem. Soc. 2012, 134, 16909.</ref><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 are magnetic . 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. Only bare-surface MXenes are magnetic. 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.


==References== ==References==

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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, a MXene is a class of low-dimensional inorganic compounds. These materials consist of two-dimensional arrays of transition metal carbide or carbonitrides. 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.

Structure

Macroscopically, MXenes have 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 Mn+1XnTx can be used, where T is a functional group.

MXenes adopt three structures, as inherited from the parent MAX phases: M2C, M3C2, and M4C3.

Intercalation

Intercalation in MXenes is possible because of the weak bonds between layers. Guest molecules include dimethyl sulfoxide (DMSO), hydrazine, and urea. For example, N2H4 (hydrazine) can be intercalated into Ti3C2(OH)2 with the molecules parallel to the MXene basal planes to form a monolayer. Intercalaction increases the MXene c lattice parameter, which weakens the bonding between MX layers. Ions, including Li, Pb, and Al, can also be intercalaction into MXenes, either spontaneously or when a negative potential is applied to a MXene electrode.

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. M. Naguib, O. Mashtalir, J. Carle, V. Presser, J. Lu, L. Hultman, Y. Gogotsi, M. W. Barsoum, ACS Nano 2012, 6, 1322.
  4. M. Naguib, J. Halim, J. Lu, L. Hultman, Y. Gogotsi, M. W. Barsoum, J. Am. Chem. Soc. 2013,135, 15966.
  5. 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.
  6. M. Naguib, M. Kurtoglu, V. Presser, J. Lu, J. Niu, M. Heon, L. Hultman, Y. Gogotsi, M. W. Barsoum, Adv. Mater. 2011, 23, 4248.
  7. ^ I. R. Shein, A. L. Ivanovskii, Comput. Mater. Sci. 2012, 65, 104.
  8. Q. Tang, Z. Zhou, P. Shen, J. Am. Chem. Soc. 2012, 134, 16909.
  9. M. Khazaei, M. Arai, T. Sasaki, C.-Y. Chung, N. S. Venkataramanan, 
M. Estili, Y. Sakka, Y. Kawazoe, Adv. Funct. Mater. 2012, 23, 2185.
  10. Y. Xie, P. R. C. Kent, Phys. Rev. B 2013, 87, 235441.
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