A Two-Dimensional Zirconium Carbide by Selective Etching of Al 3 C 3 from Nanolaminated Zr 3 Al 3 C 5

We report the room temperature synthesis of a new two-dimensional (2D) zirconium-containing carbide, Zr3C2Tz MXene. In contrast to traditional preparation of MXene, the layered ternary Zr3Al3C5 material instead of MAX phases is used as source under hydrofluoric acid treatment. The structural, mechanical and electronic properties of the synthesized 2D carbide are investigated combined with firstprinciples density functional calculations. A comparative study on the structrual stability of our obtained 2D Zr3C2Tz and Ti3C2Tz MXenes at elevated temperatures is performed. The obtained 2D Zr3C2Tz exhibits relatively better ability to maintain 2D nature and strucural integrity compared to Tibased Mxene. The difference in structural stability under high temperature condition is explained by theoretical investigation on binding energy. During the past decade, two-dimensional (2D) materials have attracted extensive attention due to their high surface area to volume ratio, unique electronic structures and physiochemical properties derived from their low dimensionality. Graphene, the most studied 2D material with ultrahigh mechanical strength, excellent electronic and thermal conductivities, 10-11] exhibits potential applications in electrochemical energy storage, transparent electrodes, and nano-composites. However, due to its intrinsic zero bandgap and simple chemistry, applications of graphene are restricted in some aspects, such as field effect transistors. Thus, investigations on other 2D materials are performed, especially for those 2D materials with two or more composition elements, such as metal oxide, layered metal chalcogenides (LMDCs), hexagonal boron nitride(BN), hydroxides, etc. 13] In recent years, a new class of 2D materials called MXenes, have emerged Members in this family are described by the general formula of Mn+1XnTz (wherein M is an early transition metal, X is C and/or N, n is 1, 2, 3, and Tz denotes surface terminated functional groups). Generally, MXenes are produced by the selective etching of Al layers from their parental layered ternary MAX phases, a large group which comprises more than 70 members. Through selective etching of aluminium layers, experimental investigations have successfully identified about 10 different MXenes, Ti3C2Tz, Ti2CTz, Ta4C3Tz, TiNbCTz, (V0.5,Cr0.5)3C2Tz, Ti3CNTz, Nb2CTz, V2CTz, and Nb4C3Tz. 17] Most of the synthesized MXenes are metallic, hydrophilic, and predicted to have high elastic moduli, implying potential application as reinforcement of polymer. The existance of Dirac electrons in some MXenes has also been theoretically predicted . Moreover, similar to graphene, MXenes are promising candidate electrode materials for lithium-ion batteries and supercapacitors by facile intercalation of Li ions into the MXene layers. Recently, considerable efforts have been made to further expand the family of 2D carbides. On the basis of a substitutional solid solution method, Gogotsi and Barsoum et al. successfully synthesized Mo2TiC2Tz, Mo2Ti2C3Tz, and Cr2TiC2Tz MXenes, and surface dependent electrochemical behaviors in the case of Mo2TiC2Tz have been revealed. Moreover, Mo2CTz MXene [29] has been synthesized through selective etching of gallium (Ga) from a thin film of the new ternary nanolaminated Mo2Ga2C. Besides, large-area high-quality 2D αMo2C, WC, and TaC crystals have been fabricated by a chemical vapour deposition (CVD) process. However, potential MXene compounds in materials systems where Al-containing MAX phases are not established, such as Hf2C and Zr2C, are yet to be produced. Herein, for the first time, we report the preparation of Zr-containing 2D carbide based on selective extraction of Al-C units from an alternative layered ternary Zr3Al3C5, benefiting from the relatively weakly bonded and hydrolysis-prone Al-C layers in the Zr3Al3C5 crystal structure. Zr3Al3C5 is a typical member of the layered ternary and quaternary transition-metal carbides beyond MAX phases; holding a common formula of MnAl3C2 and Mn[Al(Si)]4C3 (where M= Zr or Hf, n = 1-3). The crystal structure of these carbides can be described as an intergrowth structure of layers with hexagonal MC and Al4C3-like Al3C2/[Al(Si)]4C3 sharing a carbon monolayer at their coupling boundaries. We prepared Zr3Al3C5 by an in situ reactive pulsed electric current sintering (PECS) process (see the Supporting Information, SI, Section 1, S1) similar to our previous study. The exfoliation process of Zr3Al3C5 was implemented by using concentrated hydrofloric (HF) acid. The structural, electronic and elastic properties of the as-exfoliated nanosheets were investigated combined with first-principles density functional calculations. Moreover, the structural stability of the as-prepared nanosheets at elevated temperatures were studied and compared with that of Ti3C2Tz MXenes. [*] J. Zhou, [+] X. H. Zha, [+] ,Fan Y. Chen, Q. Ye, Prof. S. Y. Du, Prof. Q. Huang Engineering Laboratory of Specialty Fibers and Nuclear Energy Materials (FiNE), Ningbo Institute of Materials Engineering and Technology, Chinese Academy of Sciences, Ningbo,Zhejiang 315201, China E-mail: huangqing@nimte.ac. cn, dushiyu@nimte.ac. cn Prof. P. Eklund Thin Film Physics Division, Linköping University, IFM, 581 83 Linköping, Sweden [] These authors contributed equally to this work. Supporting information for this article is given via a link at the end of the document.