Synthesis of Three Families of Titanium Carbonitride MXenes

Layered MAX phases and two-dimensional (2D) MXenes derived from them are among the most studied materials due to their attractive properties and numerous potential applications. The tunability of their structure and composition allows for every property to be modulated over a wide range. Particularly, elemental replacement and formation of a solid solution without changing the structure allow fine-tuning of material properties. While solid solutions on the M (metal) site have received attention, the partial replacement of carbon with nitrogen (carbonitrides) has received little attention. By applying this concept, herein we report the synthesis of three families of titanium carbonitride Ti_<i>n</i>+1Al(C_1-<i>y</i>N_<i>y</i>)_<i>n</i> MAX phases and Ti_<i>n</i>+1(C_1-<i>y</i>N_<i>y</i>)_<i>n</i>T_<i>x</i> MXenes with one, two, and three C/N layers. This greatly expands the variety of known MAX phases and MXenes to encompass 16 titanium carbonitrides with tunable X-site chemistries and different 2D layer thicknesses, including MXenes in the Ti₄(C_1-<i>y</i>N_<i>y</i>)₃T_<i>x</i> system, which have not been previously reported. We further investigated the relationship among the composition, structure, stability, and synthesis conditions of the MXenes and their respective Al-based MAX phases. This range of materials will enable fundamental studies of the N/C ratio effect on optoelectronic, electromagnetic, and mechanical properties of MXenes, as well as tuning those properties for specific applications.