First-principles study on adsorption of gas molecules by metal Sc modified Ti<sub>2</sub>CO<sub>2</sub>

Abstract

MXene materials have received increasing attention due to their unique properties and potential applications. Ti<sub>2</sub>CO<sub>2</sub>, as a typical MXene material that has been prepared, has been widely studied. The adsorption characteristics of two-dimensional materials for gas molecules can be significantly improved through transition metal modification. However, there are few studies on the use of transition metals to modify Ti<sub>2</sub>CO<sub>2</sub>. In this work, the adsorption processes of different harmful gases (CO, NH<sub>3</sub>, NO, SO<sub>2</sub>, CH<sub>4</sub>, H<sub>2</sub>S) on the surfaces of these two materials, i.e. Ti<sub>2</sub>CO<sub>2</sub> and metal Sc modified Ti<sub>2</sub>CO<sub>2,</sub> are studied and analyzed based on first-principles density functional theory and generalized gradient method. The geometric optimization calculation of the metal-modified adsorption harmful gas structure is carried out, and the kinetic energy cutoff energy of the plane wave basis set is taken as 450 eV. The calculation results show that the structure in which Sc atoms are located above the C atoms in the hollow position has a large binding energy, but it is smaller than the experimental value of the cohesive energy of solid Sc (3.90 eV). Sc atoms can effectively avoid clustering. Surface Sc metal provides active sites for gas adsorption. By analyzing the optimal adsorption points, adsorption energy and other parameters of different gases, the adsorption effects of metal Sc-modified Ti<sub>2</sub>CO<sub>2</sub> on these gases are analyzed. Among them, the adsorption effect of SO<sub>2</sub> is better, the adsorption energy is increased from –0.314 eV to –2.043 eV, and the adsorption effects of other gases are improved. Due to the introduction of new atoms on the surface of Ti<sub>2</sub>CO<sub>2</sub>, the carrier density and carrier mobility of the material are increased, thereby improving the charge transfer on the surface of the material, which is beneficial to its sensitivity to gas molecules. The results of density of states and work function further verify that the carrier density and carrier mobility of Sc-Ti<sub>2</sub>CO<sub>2</sub> are increased, which is beneficial to gas adsorption. It is expected that the metal Sc-modified Ti<sub>2</sub>CO<sub>2</sub> becomes an excellent gas-sensing material for the detection of CO, NH<sub>3</sub>, NO, SO<sub>2</sub>, CH<sub>4</sub> and H<sub>2</sub>S, and the present work can provide a reference for theoretically studying the gas-sensing performance of metal Sc-modified Ti<sub>2</sub>CO<sub>2</sub> materials.