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 (E ads = -0.48 eV), and short recovery time (1.29 mu s), which can be improved with an increase in temperature. The doped configuration B12N11Mn exhibited a stronger work function response (Delta Phi = 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.