Anisotropic CO adsorption and enhanced O₂ activation on defective TiS₂ monolayer: A DFT study

This study employs density functional theory (DFT) calculations to investigate the adsorption behaviour of CO and O₂ on a defective TiS₂ monolayer. The primary objective is to evaluate the potential of TiS₂ for gas sensing and catalytic applications. By exploring the adsorption of CO and O₂ on a monolayer with a sulfur vacancy, this study provides significant new insights into their interaction mechanisms and energetics. The DFT simulations showed that the adsorption of the CO molecule is anisotropic (i.e., orientation dependent) with higher adsorption energy for the carbon end (Ti-CO) -0.63 eV than the oxygen end (Ti-OC) -0.16 eV. In both scenarios, the CO molecule bond length does not change significantly. In contrast, the adsorption of O₂ molecule is the strongest with the highest adsorption energy of -3.25 eV. The defective TiS₂ monolayer exhibits notable catalytic properties through the elongation of the O-O bond from 1.21 Å to 1.47 Å, comparable to the O-O bond length in peroxides (∼ 1.45 Å). Additionally, the adsorption mechanism is explained in variation observed in Density of States (DOS), Partial Density of States (PDOS), and Mulliken charges, thus establishing its potential for gas sensing and catalytic applications.