Comparative DFT investigation of 1T and 2H phase Janus TaSSe monolayers as potential sensors for toxic gas molecules

In this study, Density functional theory (DFT) calculations were employed to investigate a comparative analysis of the gas-sensing performance of 2D Janus TaSSe monolayers in both 1T and 2H structural phases. The adsorption characteristics of several toxic gases, including AsH 3 , H 2 S, NH 3 , COCl 2 , O 3 , and PH 3 , were analyzed. Our results indicate that the 1T phase is thermodynamically more stable and exhibits stronger gas–surface interactions compared to the 2H phase. Among the studied gases, AsH 3 shows the highest adsorption energy (E ads ), reaching − 2.4 eV on the Se-site of 1T-TaSSe and − 2.125 eV on the S-site of 2H-TaSSe. For the remaining toxic gases, the E ads range from − 0.542 eV to -1.970 eV in the 1T phase, and from − 0.187 eV to -1.706 eV in the 2H phase. Notably, PH 3 demonstrates the second-highest adsorption affinity, while H 2 S exhibits the weakest interaction. Despite these relatively strong interactions, analyses based on charge density difference (CDD), electron localization function (ELF), and reduced density gradient (RDG) confirm that the adsorption mechanism is governed by strong physisorption through van der Waals interactions, without the formation of chemical bonds. Recovery time ( \(\:τ\:\) ) analysis indicates efficient regeneration behavior. At 500 K, the \(\:τ\:\) for AsH 3 adsorption on the S-site are 1.52 \(\:×\:\) 10 6 s for 1T-TaSSe and 2.63 \(\:×\:\) 10 3 s for 2H-TaSSe. In contrast, for NH 3 at 300 K, significantly faster recovery times are observed, with values of 0.591 s for 1T (S-site) and 0.41 ms for 2H (S-site). These findings suggest that 1T phase is comparatively more sensitive for the selected gases, while the 2H phase is advantageous for rapid recovery in the case of weakly interacting gases such as H 2 S, NH 3 , and COCl 2 .