page_title: MXenes
section_title: Synthesis
hierarchical_section_title: MXenes / Synthesis
caption_attribution_description: This figure illustrates how from parental MAX phase compound transition can be made to MXenes. 3 structural types of MAX phases were shown as precursors. This illustration was made with help of the VESTA software.
context_page_description: In materials science, MXenes are a class of two-dimensional inorganic compounds. These materials consist of few-atoms-thick layers of transition metal carbides, nitrides, or carbonitrides. First described in 2011, MXenes combine metallic conductivity of transition metal carbides and hydrophilic nature because of their hydroxyl or oxygen terminated surfaces.
context_section_description: MXenes are typically synthesized by a top-down selective etching process. This synthetic route has been shown to be scalable, with no loss or change in properties as the batch size is increased. Producing a MXene by etching a MAX phase occurs mainly by using strong etching solutions that contain a fluoride ion (F⁻) such as hydrofluoric acid (HF), ammonium bifluoride (NH₄HF₂), and a mixture of hydrochloric acid (HCl) and lithium fluoride (LiF). For example, etching of Ti₃AlC₂ in aqueous HF at room temperature causes the A (Al) atoms to be selectively removed, and the surface of the carbide layers becomes terminated by O, OH, and/or F atoms. MXene can also be obtained in Lewis acid molten salts, such as ZnCl₂, and Cl terminal can be realized. The Cl-terminated MXene is structurally stable up to 750 °C. A general Lewis acid molten salt approach was proven viable to etch most of MAX phases members (such as MAX-phase precursors with A elements Si, Zn and Ga) by some other melts (CdCl₂, FeCl₂, CoCl₂, CuCl₂, AgCl, NiCl₂).
  The MXene Ti₄N₃ was the first nitride MXene reported, and is prepared by a different procedure than those used for carbide MXenes. To synthesize Ti₄N₃, the MAX phase Ti₄AlN₃ is mixed with a molten eutectic fluoride salt mixture of lithium fluoride, sodium fluoride, and potassium fluoride and treated at elevated temperatures. This procedure etches out Al, yielding multilayered Ti₄N₃, which can further be delaminated into single and few layers by immersing the MXene in tetrabutylammonium hydroxide, followed by sonication.
  The following MXenes have been synthesized to date:
  2-1 MXenes: Ti₂C, (Ti0.5,Nb0.5)₂C, V₂C, Nb₂C, Mo₂C 
  Mo₂N, (Ti0.5,Nb0.5)₂C, Ti₂N, W1.33C, Nb1.33C, Mo1.33C, Mo1.33Y0.67C 
  3-2 MXenes: Ti₃C₂ , Ti₃CN, Zr₃C₂ and Hf₃C₂
  4-3 MXenes: Ti₄N₃, Nb₄C₃ , Ta₄C₃ , V₄C₃, (Mo,V)₄C₃
  5-4 MXenes: Mo₄VC₄ 
  Double transition metal MXenes:
  2-1-2 MXenes: Mo₂TiC₂, Cr₂TiC₂, Mo₂ScC₂ 
  2-2-3 MXenes: Mo₂Ti₂C₃
caption: MXenes are produced by selective etching of the "A" element from the MAX phase structure
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