Synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid, HF

Michael Naguib, Olha Mashtalir, Joshua Carle, Volker Presser, Jun Lu, Lars Hultman, Yury Gogotsi, and Michel W. Barsoum, “Two-Dimensional Transition Metal Carbides”, ACS Nano, Vol 6, No. 2, 1322-1331, 2012

ACerS' Ross Coffin Purdy Award will recognize the article, which was the first to describe a facile method to produce a large family of two-dimensional layered, early transition metal carbides and nitrides, labeled MXenes. The latter are so-called because they are produced by selective etching of the A-group element — aluminum in this case — from an even larger family of layered solids labeled the MAX phases. The MAX phases were in turn discovered by Michel Barsoum, Ph.D., and co-workers roughly 15 years ago at Drexel University. synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid

Barsoum, A.W. Grosvenor and Distinguished Professor at Drexel University, and Distinguished University Professor and Trustee Chair Yury Gogotsi, Ph.D., also from Drexel Materials, were co-authors of the award-winning paper, along with students Michael Naguib, Olha Mashtalir and Joshua Carle, together with collaborators from Linkoping University in Sweden.

The annual Ross Coffin Purdy Award recognizes researchers "judged to have made the most valuable contribution to ceramic technical literature." The ACerS board unanimously agreed to grant the honor to the Barsoum and Gogotsi team's work. The award will be presented in October during the Materials Science and Technology Conference in Montréal, Canada.

MXenes have potential uses in a broad range of energy and electronics applications, including lithium-ion batteries and supercapacitors. The materials' layered structure resembles that of graphene — hence the suffix ene — a two-dimensional sheet of carbon, but its chemistry is more complex and more versatile.

"The research reported in this paper is an exciting advance in this new family of materials for which the applications are just beginning to be envisioned," said Dawn Bonnell, Ph.D., Trustee Chair Professor in the Materials Science Department of the University of Pennsylvania and director of the Nano/Bio Interface Center. Bonnell nominated Barsoum's group for the honor. The SEM image captured by Babak Anasori shows MXene particles

In their ACS Nano paper "Two-Dimensional Transition Metal Carbides," the authors acknowledge funding from the Assistant Secretary for Energy Efficiency and Renewable Energy Office of Vehicle Technologies of the U.S. Department of Energy, the Commonwealth of Pennsylvania's Ben Franklin Technology Development Authority and the Alexander von Humboldt Foundation.

Ross Coffin Purdy, in whose honor this award is given, served The American Ceramic Society for 24 years as General Secretary and Editor of its publications. He was the recipient of many awards, a Fellow and Honorary Life Member, and President of the Society.

The American Chemical Society is a nonprofit organization chartered by the U.S. Congress. With more than 163,000 members, ACS is the world’s largest scientific society and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences.

Abstract

Secondary electron SEM micrographs for (A) Ti3AlC2 particle before treatment, which is typical of unreacted MAX phases, (B) Ti3AlC2 after HF treatment, (C) Ti2AlC after HF treatment, (D) Ta4AlC3 after HF treatment, (E) TiNbAlC after HF treatment, and (F) Ti3AlCN after HF treatment. In (B–F), the exfoliation is obvious. Herein we report on the synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid, HF. The MAX phases represent a large (>60 members) family of ternary, layered, machinable transition metal carbides, nitrides, and carbonitrides. Herein we present evidence for the exfoliation of the following MAX phases: Ti₂AlC, Ta₄AlC₃, (Ti_0.5,Nb_0.5)₂AlC, (V_0.5,Cr_0.5)₃AlC₂, and Ti₃AlCN by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication. The removal of the “A” group layer from the MAX phases results in 2-D layers that we are labeling MXenes to denote the loss of the A element and emphasize their structural similarities with graphene. The sheet resistances of the MXenes were found to be comparable to multilayer graphene. Contact angle measurements with water on pressed MXene surfaces showed hydrophilic behavior.

Keywords: MXene; two-dimensional materials; carbides; carbonitrides; exfoliation

Two-dimensional (2-D) materials, such as graphene, are known to have unique properties that, in turn, can potentially lead to some promising applications. Over the years, other 2-D materials with different chemistries have been synthesized by exfoliation of layered 3-D precursors such as boron nitride, metal chalcogenides (e.g., MoS₂, WS₂, oxides, and hydroxides). In most, if not all, of these cases, the initial bonding between the layers was relatively weak, making the structure amenable to exfoliation.

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