The effect of hetero-structure material MoS$_{2}$-TiO$_{2}$(110) on CO and NO adsorption: insights from \textit{ab-initio} calculations

Using first-principles simulation based on the density functional theory, we show the effect of substrate on the adsorption of small gas molecules (CO and NO) on molybdenum disulfide (MoS$_{2})$ by investigating the adsorption on bare MoS$_{2}$ and on MoS$_{2}$-TiO$_{2}$(110) systems. First, our results show that MoS$_{2}$ binds to the rutile TiO$_{2}$ surface by forming bonds between unsaturated edge sulfur atoms of MoS$_{2}$ with both bridge oxygen atoms and five-fold titanium atoms of TiO$_{2}$. Second, results from structural optimizations show that CO prefers to adsorb on ($\bar{1}$010) edge (S-edge) of bare MoS$_{2}$ but on (10$\bar{1}$0) edge (Mo-edge) of MoS$_{2}$ when coupled to the TiO$_{2}$(110) surface. Third, results from Bader analysis indicate a very small difference in charge transfer (i.e. 0.01e) to CO molecule from these two systems. We also present detailed analysis of the electronic density of states and the charge density of adsorbate-substrate systems to explain the effect of substrates on the adsorption of CO. We compare and contrast the adsorption characteristics of NO with those of CO on these surfaces.