Structure-activity correlation of Ti₂CT₂ MXenes for C–H activation

Abstract

As a bourgeoning class of 2D materials, MXenes have recently attracted significant attention within heterogeneous catalysis for promoting reactions such as hydrogen evolution and C-H activation. However, the catalytic activity of MXenes is highly dependent on the structural configuration including termination groups and their distribution. Therefore, understanding the relation between the structure and the activity is desired for the rational design of MXenes as high-efficient catalysts. Here, we present that the correlation between the structure and activity of Ti 2 CT 2 (T is a combination of O, OH and/or F) MXenes for C-H activation can be linked by a quantitative descriptor: the hydrogen affinity (E H ). A linear correlation is observed between the mean hydrogen affinity and the overall ratio of O terminations (x O ) in Ti 2 CT 2 MXenes, in which hydrogen affinity increases as the x O decreases, regardless to the species of termination groups. In addition, the hydrogen affinity is more sensitive to the presence of OH termination than F terminations. Moreover, the linear correlation between the hydrogen affinity and the activity of Ti 2 CT 2 MXenes for C-H activation of both -CH 3 and -CH 2 -groups can be extended to be valid for all three possible termination groups. Such a correlation provides fast prediction of the activity of general Ti 2 CT 2 MXenes, avoiding tedious activation energy calculations. We anticipate that the findings have the potential to accelerate the development of MXenes for heterogeneous catalysis applications.

Functionalizing MXenes by Tailoring Surface Terminations in Different Chemical Environments

“…Also, magnetic properties may be controlled as Cr 2 TiC 2 has been foreseen to be nonmagnetic when terminated with O and antiferromagnetic when terminated with OH or F . Finally, the catalytic activity of MXenes has been predicted to be highly sensitive to the composition of surface terminations. , …”

“…11 Also, magnetic properties may be controlled as Cr 2 TiC 2 has been foreseen to be nonmagnetic when terminated with O and antiferromagnetic when terminated with OH or F. 12 Finally, the catalytic activity of MXenes 13 has been predicted to be highly sensitive to the composition of surface terminations. 14,15 Conventionally, either HF or LiF + HCl is used as an etchant, resulting in MXenes terminated by combinations of O, OH, and F. Recent studies have shown that the realm of termination groups on MXenes may be expanded beyond the conventional mixture of O, OH, and F. Electrochemical etching in HCl, instead of HF, resulted in a mixture of O, OH, and Cl. 16 Furthermore, completely Cl-terminated Ti 2 C and Ti 3 C 2 MXenes were synthesized using molten salts.…”

Advances in two‐dimensional engineered nanomaterials applications for the agro‑ and food‐industries

“…It is easy to see that the nickname 'MXenes' comes from this particular chemical structure. 31 The interest in MXenes comes from their attractive chemical, electronic, and optical properties, which are being explored for advanced biosensors, 32 catalytic surfaces, 33 advanced electronic devices, 34 energy storage, 35 and so on, which is producing an increasing number of fundamental and applied research reports on a wide spectrum of possible uses. Nevertheless, as occurs for the other 2D nanomaterials, the synthesis methods require specialized chemical reactions involving strong acid reactions, which in principle could hinder the facile mass-production level for these kinds of structures.…”

Structure–Activity Relationships in Lewis Acid–Base Heterogeneous Catalysis

“…More explicitly, E H correlates linearly with the dehydrogenation energy barriers where low hydrogen affinity results in lower C–H activation barriers of both terminal methyl and middle methylene bridge groups of propane on Ti 2 CO 2– z (OH) z (0 ≤ z ≤ 2). The BEP scaling relationship was extended to include Ti 2 C MXenes terminated with a F group (i.e., Ti 2 CF 2 ) . The adsorption energy of pyridine molecule has also been used to probe the surface acidity and coordination geometry of Ga sites in β-Ga 2 O 3 nanoparticles .…”

“…The BEP scaling relationship was extended to include Ti 2 C MXenes terminated with a F group (i.e., Ti 2 CF 2 ). 148 The adsorption energy of pyridine molecule has also been used to probe the surface acidity and coordination geometry of Ga sites in β-Ga 2 O 3 nanoparticles. 149 It was shown that weak Lewis acid sites (attributed to tricoordinated Ga sites created upon vacancy formation on the (100) β-Ga 2 O 3 ) with lower pyridine adsorption energies, promote propylene production over cracking products in PDH reaction on the fully dehydroxylated oxygen-deficient β-Ga 2 O 3 surface.…”