Theoretical investigations of adsorption and sensing properties of M2Pc (M=Cr, Mo) monolayers towards volatile organic compounds

Abstract

The continuous expansion of industrial production has led to significant emissions of volatile organic compounds (VOCs), posing a serious threat to the ecological environment. Consequently, developing advanced gas sensors for the efficient detection of VOCs is critically important. In this work, first-principles methods based on density functional theory (DFT) are employed to investigate the stability, electronic structure, and gas-sensing properties of Cr₂Pc and Mo₂Pc monolayers upon adsorption of five representative VOCs (C₂H₄, CH₃Cl, C₆H₆, H₂CO, and CH₃OH). The results reveal that Cr₂Pc monolayer exhibits weak adsorption for C₂H₄, CH₃Cl, and C₆H₆, while demonstrating moderate adsorption strength for H₂CO and CH₃OH. In contrast, Mo₂Pc monolayer shows strong chemisorption for all five VOCs, with adsorption energies ranging from −0.92 eV to −2.34 eV. The mechanisms underlying these interactions are elucidated through detailed analyses of electronic properties, including charge transfer, charge density difference, density of states, and work function changes for each adsorption system. Furthermore, a comprehensive evaluation of sensitivity and recovery time suggests that two-dimensional Cr₂Pc is a promising reusable CH₃OH gas sensor at room temperature, featuring an ultrafast recovery time of 0.14 s and resistance to interference from common gases such as H₂O, N₂, CO₂ and CH₄. In contrast, 2D Mo₂Pc demonstrates potential as a reusable CH₃Cl gas sensor at high temperature, though its performance is susceptible to interference from H₂O and N₂ in ambient air. Overall, this study provides theoretical insights to guide the development and fabrication of novel, efficient two-dimensional bimetallic phthalocyanine-based gas sensors.