Adsorption mechanism of Phosgene gas onto the pristine hBN and Cu-decorated hBN: A DFT study

The adsorption behavior of pristine hBN monolayer and Cu-decorated hBN monolayer towards the detection of toxic gas such as COCl₂ were explored using the first principle calculations based on Density Functional Theory (DFT). The calculated low adsorption energy for the A4 configurations indicates that the interaction of the COCl₂ gas with pristine hBN was weak, resulting in poor recovery time. Therefore, to enhance the adsorption affinity of hBN, the Cu atom was adsorbed onto the surface of hBN (Cu-hBN) and substitutionally doped (Cu-doped hBN). It was based on energy minimization, and B2 and C2 configurations were the most stable configurations among the different adsorption configurations. The adsorption study revealed that strong chemical interaction exists, and the adsorption of COCl₂ gas onto Cu-hBN and Cu-doped hBN was a chemisorption. Further, various calculations such as DOS, Hirshfeld atomic charge, charge density differences, ELF, and RDG were calculated for the most stable configurations. The resulting DOS plot revealed that the COCl₂ adsorption enhances the electrical conductivity due to the 72.25 % and 54.13 % reduction in the band gap. Hirshfeld and ELF analysis showed that substantial charge transfer occurs in the case of B2 and C2 compared to A4 configurations. ELF analysis revealed that the Cu atom loses electrons to the COCl₂, confirming the behavior of adsorbates as electron donors and COCl₂ as electron acceptors. Furthermore, RDG analysis revealed vdW interaction in the case of A4, whereas strong, attractive interaction exists in the case of B2 and C2 adsorption configurations. Finally, the calculated recovery time for B2 and C2 adsorption configurations at elevated temperatures under visible light suggests that Cu-doped hBN and Cu-hBN systems can be utilized as a sensing material in gas sensors to detect COCl₂ gas at high temperatures.