Adsorption and Sensing of Cyanide Gases over Transition Metal (Mn and Fe)-Decorated CrS 2 Monolayers: Insights from DFT and AIMD Simulations

The present study proposes to comprehensively investigate the adsorption of toxic cyanide gases (HCN, CNF, CNCl, CNBr, and NCCN) on pristine and transition-metal (TM)-decorated CrS₂ monolayers using van der Waals-corrected density functional theory. The weak adsorption capability of pristine CrS₂ renders it unsuitable for use as a gas sensor; therefore, the monolayer was decorated with TMs, Mn, and Fe. Among the plausible decoration sites, TMs prefer to bind on the T_Cr site of the CrS₂. The energetic stability of the modified monolayers is ensured by high negative values of binding energies, i.e., -5.530 eV for Mn and -5.358 eV for Fe-CrS₂. The Mn and Fe decoration significantly improves the surface activity of the intrinsic CrS₂ by reducing the band gap (0.080 eV for Mn and 0.610 eV for Fe) and work function (4.945 eV for Mn and 5.173 eV for Fe). Compared with pristine CrS₂, the gas adsorption energy of the modified monolayers is greatly improved, and the adsorption distance is enormously reduced, indicating that modification of the monolayer with the TMs enhances the gas sensitivity of CrS₂ for toxic cyanide gases. The adsorption energy order is CNBr > CNF > NCCN > CNCl > HCN and NCCN > CNBr > CNF > CNCl > HCN for Mn and Fe-CrS₂ monolayers, respectively. The adsorption effects of the target gases were compared and analyzed from the perspectives of the change of band gap, charge density difference, energy band structures, and partial density of states plots. The efficacy of the decorated monolayers for gas sensing was assessed in terms of work function, recovery time, and sensitivity measurements. The comparative analysis revealed that the Mn-CrS₂ exhibits high adsorption strength and hence prolonged recovery times for the cyanide gases, signifying its potential as an effective adsorbent. On the contrary, the Fe-CrS₂ monolayer shows optimum adsorption strength and faster recovery behavior, emerging as a reusable gas sensor. Overall, this study provides a theoretical framework and opens up new avenues for the design and experimental investigation of high-performance CrS₂-based gas sensors to detect hazardous cyanide gases.