The C/N ratio as a lever for infrared properties tuning in carbonitride MXenes

MXenes have demonstrated a broad range of properties in the infrared (IR) range being either efficient thermal emitters of IR light, or highly reflective, similar to polished metals. A combination of tunable IR reflectivity with the unique physical and chemical properties of MXenes, such as low thermal conductivity and efficient light-to-heat conversion, offer opportunities for a range of applications. However, one needs to know the effect of elemental composition, particularly carbon and nitrogen content, to obtain IR properties meeting the needs of specific applications. This work investigates the tunability of properties in titanium carbonitride MXenes by varying their carbon-to-nitrogen ratio across four distinct compositions (2C:0N, 1.75C:0.25N, 1.5C:0.5N, and 1C:1N). Multiple experimental characterization techniques, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermal emissivity measurements, were combined with density functional theory (DFT) calculations to understand the influence of C/N ratio on infrared properties. The study reveals that the C/N ratio significantly affects the IR response of MXenes in the 1-$25\mu m$ range. Higher carbon content enhances IR reflectance, supporting superior thermal management and IR stealth, while increased nitrogen content elevates the emissivity and alters the phonon absorption bands. These findings demonstrate that C/N ratio modulations enable precise tuning of IR properties in titanium carbonitride MXenes, making them promising materials for thermal management, sensing, and multispectral electromagnetic shielding applications.