Interlayer Incorporation of A‑Elements into MXenes Via Selective Etching of A′ from M n+1A′1–x A″ x C n MAX Phases

• Published in: ACS nano 2023-10, Vol.17 (19), p.18747-18757
• Main Authors: Bagheri, Saman, Lipatov, Alexey, Vorobeva, Nataliia S., Sinitskii, Alexander
• Format: Article
• Language: English
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.3c02198

MXenes are a large family of two-dimensional materials with a general formula M n+1X n T z , where M is a transition metal, X = C and/or N, and T z represents surface functional groups. MXenes are synthesized by etching A-elements from layered MAX phases with a composition of M n+1AX n . As over 20 different chemical elements were shown to form A-layers in various MAX phases, we propose that they can provide an abundant source of very diverse MXene-based materials. The general strategy for A-modified MXenes relies on the synthesis of M n+1A′1–x A″ x X n MAX phase, in which the higher reactivity of the A′-element compared to that of A″ enables its selective etching, resulting in A″-modified M n+1X n T z . In general, the A″-element could modify the interlayer spaces of MXene flakes in a form of metallic or oxide species, depending on its chemical identity and synthetic conditions. We demonstrate this strategy by synthesizing Sn-modified Ti3C2T z MXene from the Ti3Al0.75Sn0.25C2 MAX phase, which was used as a model system. Although the incorporation of Sn in the A-layer of Ti3AlC2 decreases the MAX phase reactivity, we developed an etching procedure to completely remove Al and produce Sn-modified Ti3C2T z MXene. The resulting MXene sheets were of very high quality and exhibited improved environmental stability, which we attribute to the effect of a uniform Sn modification. Finally, we demonstrate a peculiar electrostatic expansion of Sn-modified Ti3C2T z accordions, which may find interesting applications in MXene-based nano-electromechanical systems. Overall, these results demonstrate that in addition to different combinations of M and X elements in MAX phases, an A-layer also provides opportunities for the synthesis of MXene-based materials.