DFT Study on the Sensing of Industrial Toxic Gases (XO2, X = N, S) by TiS2 TMD Monolayer

Two-dimensional transition metal dichalcogenides (TMDs) have shown substantial gas sensing properties due to their impressive surface area to volume ratio and tunable electronic and chemical properties. This study investigates the gas sensing characteristics of one of the dichalcogenide $\text{TiS}_{2}$ monolayers for NO2 and SO2 gases. We have used the CASTEP program for optimizing adsorption structures and analyzing several gas sensing properties such as adsorption properties, charge transfer, electronic band diagrams, density of states, and conductivity. The $\text{TiS}_{2}$ monolayer structure is thermodynamically stable. NO2 and SO2 both show physisorption-type adsorption with -0.204 eV and -0.235 eV adsorption energies. After adsorption, more charge transfer is found for NO2 compared to SO2. The band gap change is also more pronounced for NO2 adsorption than for SO2 adsorption. NO2 reduces the band gap of $\text{TiS}_{2}$ from 0.098 eV to 0 eV, which leads to increased conductivity and sensitivity for NO2. SO2 increases the band gap slightly (0.098 eV to 0.099 eV). These findings illustrate that both compounds show significant interactions with the $\text{TiS}_{2}$ monolayer; however, NO2 shows more changes than SO2. These computational results can be useful in further real-life gas sensor demonstrations.