Theoretical Study of a Transition Metal-Modified B₁₂N₁₂ Nanocage for COCl₂ Detection: Advances toward High-Sensitivity Materials for Phosgene Sensing

Phosgene gas (COCl₂) is highly toxic and poses severe risks to human health and the environment. Its release can contaminate soil and water, disrupt ecosystems, and contribute to air pollution. This study employs density functional theory and time-dependent density functional theory calculations to explore the potential of pure and B₁₂N₁₂ nanocages modified with transition metals for phosgene detection. First-row transition metals (TM = Sc-Zn) were incorporated into the nanocages via five configurations: doped (TMB₁₁N₁₂ and B₁₂N₁₁TM), decorated (TM@b₆₄ and TM@b₆₆), and encapsulated (TM@B₁₂N₁₂). Geometric, electronic, and optical properties, charges, and adsorption energies were analyzed to understand the gas sensing properties. The results showed that phosgene weakly adsorbs on isolated B₁₂N₁₂ but preferentially binds via oxygen to the TM or boron atoms of the modified nanocages, undergoing dissociation in some interactions, such as in B₁₂N₁₁Sc and B₁₂N₁₁Ti, suggesting distinct adsorption mechanisms. TM modifications reduced the HOMO-LUMO gap, enhancing the conductivity and reactivity. Quantum descriptors identified Mn@b₆₄ (TM decorated on a bond between four- and six-membered rings) as the most stable in the series, with Mn@b₆₄ standing out for its high electronic sensitivity to phosgene, moderate adsorption energy (<i>E</i>_ads = -0.48 eV), and short recovery time (1.29 μs), which can be improved with an increase in temperature. The doped configuration B₁₂N₁₁Mn exhibited a stronger work function response (ΔΦ = 65%) than Mn@b₆₄ (25%). Mn@b₆₄ also demonstrated optical activity for COCl₂ detection in UV-vis spectra and high selectivity against gases like H₂, CH₄, CO₂, NH₃, and H₂S and water. Molecular dynamics (MD) confirmed the stability of the Mn@b₆₄ system before and after phosgene adsorption. Compared with other systems in the literature, Mn@b₆₄ exhibits better sensitivity and selectivity, even under high humidity or extreme temperatures. These results highlight its potential for developing high-performance, selective, and cyclic phosgene sensors.