Chemical effect of silver (Ag) and yttrium (Y) co-doping on silicon-based fullerene (Ag@Si₅₉Y) sensor nanostructures: a computational adsorption study of cyanogenic halide gases

Cyanogenic gases, such as hydrogen cyanide and cyanogen, are highly toxic and pose serious risks to both human health and the environment. Effective adsorption strategies are essential to mitigate these hazards. In this study, the adsorption potential of a silver-decorated and yttrium-doped silicon nanocluster (Ag@Si₅₉Y) toward cyanogenic gases-BrCN, ClCN, and FCN-was investigated using density functional theory (DFT) at the ωB97XD/GenECP/LanL2DZ/Def2SVP level of theory. Adsorption was explored in two orientations for each gas molecule. The computed adsorption energies indicated favorable interaction, particularly for BrCN, with values of -30.121, -17.571, -17.571, -16.943, -16.316, and -16.316 kcal mol^-1 for BrCN-Br-, BrCN-N-, ClCN-Cl-, ClCN-N-, FCN-F-, and FCN-N-Ag@Si₅₉Y complexes, respectively. BrCN showed the strongest affinity, suggesting preferential adsorption on the Ag@Si₅₉Y surface. Noncovalent interaction (NCI) analysis and recovery time calculations confirmed the presence of strong chemisorptive interactions, especially for BrCN, characterized by significant charge transfer and bonding stability. The frontier molecular orbital (FMO) analysis revealed a notable reduction in the energy gap upon gas adsorption, highlighting the enhanced reactivity of the surface. High dipole moment values across all adsorbed complexes indicate substantial charge separation, which is advantageous for sensor-based applications. Furthermore, the Electron Localization Function (ELF) analysis provided visual insight into the nature of bonding interactions. ELF maps exhibited moderate to high localization around the adsorption regions, particularly in BrCN-Br-Ag@Si₅₉Y and FCN-N-Ag@Si₅₉Y, suggesting mixed covalent and noncovalent bonding characteristics. These observations corroborate findings from QTAIM and NBO analyses, validating the interaction types and reinforcing the reliability of the proposed adsorption mechanisms. Thus, Ag@Si₅₉Y demonstrates strong and selective adsorption properties toward cyanogenic gases, making it a promising candidate for use in gas sensing and environmental detoxification technologies.