DFT calculation on p-xylene sensing mechanism of (C₄H₉NH₃)₂PbI₄ single crystal based on physisorption

P-xylene (p-C₈H₁₀) is extremely harmful and dangerous to human health due to high toxicity and strong carcinogenicity. Exploring sensitive material to effectively detect p-xylene is of importance. In this paper, perovskite single crystal (C₄H₉NH₃)₂PbI₄ has been successfully synthesized via solution method. The obtained product was analyzed by single crystal X-ray diffraction. With the space group Pbca, orthorhombic (C₄H₉NH₃)₂PbI₄ layered perovskite structure consists of an extended two-dimensional network of corner-sharing PbI₆ octahedron. Single layer perovskite sheets of distorted PbI₆ octahedron alternated with protonated n-butylammonium cation bilayers, which offers many advantages and provides the possibility of forming a gas sensor device based on the change of resistances. Density functional theory (DFT) simulations regarding the adsorption energy revealed that this organic–inorganic hybrid perovskite compound has excellent selectivity toward p-xylene compared with other gases including C₂H₅OH, C₆H₆, CH₂Cl₂, HCHO, CH₃COCH₃ and C₇H₈. The calculation of electron density, density of states and electron density difference showed the sensing mechanism of p-C₈H₁₀ is mainly derived from physical adsorption–desorption in view of electron transfer.

For organic–inorganic hybrid perovskite (C₄H₉NH₃)₂PbI₄, single layer perovskite sheets of distorted PbI₆ octahedron alternated with protonated n-butylammonium cation bilayers (a), which offers many advantages and provides the possibility of forming a gas sensor device based on the change of resistances. Electron density difference calculation shows that adsorption of p-xylene molecule has an obvious effect on the electron distribution of (C₄H₉NH₃)₂PbI₄, results in electrically polarization as a local manner (b).