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Kathleen Maleski1 Chang Evelyn Ren1 Mengqiang Zhao1 2 Babak Anasori1 Yury Gogotsi1

1, Drexel University, Philadelphia, Pennsylvania, United States
2, Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania, United States

Two-dimensional (2D) transition metal carbides and/or carbonitrides (MXenes) have been developed as promising materials for a wide variety of applications due to their advantageous mechanical, electrochemical, electrical, and optical properties.1 MXenes exhibit a general formula of Mn+1XnTx, where M represents a transition metal (Ti, Mo, Nb, V, Cr, etc.), X is either carbon and/or nitrogen, and Tx represents surface terminations.1 Along with the high electronic conductivities (8,000-10,000 S/cm), the materials are hydrophilic and can be synthesized in large quantities (~100 g per batch) and high concentrations (>50 mg/mL), making them fundamentally feasible for solution processing.2,3 However, the as-produced colloidal solutions contain flakes with widespread lateral sizes (ranging from 0.1 to ~5 µm), presenting a challenge for maintaining precise control over properties and performance.

Here, we will discuss recent progress on developing size selection methods to control and sort 2D MXene flake sizes after synthesis based on sonication and density gradient centrifugation, respectively.4 Furthermore, characterization of size-dependent properties will be discussed, including tuning the conductivity of free-standing films, changes in optical absorption, and differences in electrochemical behaviors. This size selection methodology allows for control of a diverse family of materials, optimizing the performance in applications for MXenes beyond energy storage, including but not limited to, gas sensors, conductive inks, coatings, fibers, and electronic, optic and biomedical devices.

References
1. Anasori, B.; Lukatskaya, M. R.; Gogotsi, Y., Nature Reviews Materials 2017, 2, 16098.
2. Alhabeb, M.; Maleski, K.; Anasori, B.; Lelyukh, P.; Clark, L.; Sin, S.; Gogotsi, Y., Chemistry of Materials 2017, 29, 7633-7644.
3. Akuzum, B.; Maleski, K.; Anasori, B.; Lelyukh, P.; Alvarez, N. J.; Kumbur, E. C.; Gogotsi, Y., ACS Nano 2018, 12, 2685-2694.
4. Maleski, K.; Ren, C.E.; Zhao, M.-Q.; Anasori, B.; Gogotsi, Y.; ACS Applied Materials and Interfaces 2018, in press

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