Oxycarbide MXenes and MAX phases identification using monoatomic layer-by-layer analysis with ultralow-energy secondary-ion mass spectrometry

MXenes: trends, growth, and future directions

“…1). With the recent discovery of oxygen substitution in carbide MXenes [4] and formation of oxycarbides, X can include oxygen as well (at least in solid-solution MXenes). MXenes can have different numbers of M-X-M layers, which is shown by n, and ranges from 1 to 4, and x in T x is ≤ 2 [5].…”

“…In 2022, it was shown that the Ti 3 C 2 T x precursor, Ti 3 AlC 2 , can contain substitutional oxygen in its structure. For example, up to 30 at.% of oxygen in the carbon layer was found in Ti 3 AlC 2 made via the conventional method of synthesis form elemental precursors using a stoichiometric ratio mix of 2TiC:1Al:1Ti, while no oxygen was detected in Ti 3 AlC 2 using the modified non-stoichiometric mix of 2TiC:2Al:1.25Ti powders [4]. The resulting MXene has shown greatly improved oxidation resistance and conductivity compared to the oxygen-containing Ti 3 C 2 T x [18].…”

“…Apparently, oxygen substitution may enable new MAX and MXene structures which are not stable in the pure M-X system. Beyond the X sites, a better understanding of M sites in ordered double-metal and high-entropy MAX and MXenes is needed to characterize ordering, intermixing, and in-plane segregation of elements in M layers [4,19]. Defect engineering is another frontier in controlling properties of MXenes.…”

“…However, many more challenges listed in Refs. 4 and 20 (which we will not repeat here) remain and addressing them will require joint efforts of the MXene community and collaborators. In return, one can expect exciting new fundamental science related to quantum confinement in 2D MXene sheets with an unprecedented level of control over their structure, composition and properties, novel chemistry in confinement between MXene sheets, as well as solutions to practical problems in energy, electronics, environmental and healthcare fields.…”

Delamination of Ti3C2Tx Nanosheets with NaCl and KCl for Improved Environmental Stability of MXene Films

“…While the MAX phase used in this work and another commercial MAX phase (Carbon-Ukraine) allowed for delamination with NaCl and KCl, the stoichiometric MAX phase prepared with an excess of Al during the sintering process did not delaminate when 10.8 M HCl was used during the etching process. One potential reason might be the difference in the ratio of surface terminations and concentration of defects in MXenes fabricated from different MAX phases …”