Adsorption and gas-sensitive properties of TM (Rh, Pd, Pt) modified Ti3C2F2 for SO2, NO2 and NH3 gas molecules: A DFT study

Abstract

In the present investigation, the adsorption and gas-sensitive properties of industrial toxic gases (SO₂, NO₂ and NH₃) on transition metal (Rh, Pd, Pt) modified Ti₃C₂F₂ monolayer was explored using density functional theory calculations. To gain insights into the change of adsorption and gas-sensitive properties of Ti₃C₂F₂ monolayer modified with metal atoms, the structures of metal modification and gas adsorption on Ti₃C₂F₂, charge transfer, adsorption energy, band structure, state density and molecular orbitals were analyzed. It is found that transition metal atoms' modification on the substrate improves the conductivity of Ti₃C₂F₂ monolayer. Moreover, the optimal structures for the modification of Ti₃C₂F₂ with Rh, Pd and Pt have been identified, with the binding energies of -2.614 eV, -0.819 eV and -1.411 eV guaranteeing the stability of the three structures during the adsorption process. The adsorption capacity of the original Ti₃C₂F₂ for SO₂, NO₂ and NH₃ is weak physical adsorption with adsorption energies in the range of -0.2 eV to -0.4 eV. Compared with the original Ti₃C₂F₂, the adsorption efficiency of Rh-Ti₃C₂F₂, Pd-Ti₃C₂F₂ and Pt-Ti₃C₂F₂ for SO₂, NO₂ and NH₃ is significantly improved: the adsorption energies of Rh-Ti₃C₂F₂ for the three gases are -1.2 eV to -1.6 eV, Pd-Ti₃C₂F₂ are -1.6 eV to -1.8 eV, and Pt-Ti₃C₂F₂ are -1.1 eV to -2.2 eV, all reaching the level of chemical adsorption. In addition, the Pd-Ti₃C₂F₂ monolayer exhibits high stability, and its structure remains unchanged after the adsorption of gases. Moreover, the analysis of the density of states indicates that Rh-Ti₃C₂F₂ exhibits the most pronounced interaction with NH₃ and the least significant interaction with NO₂, whereas both Pd-Ti₃C₂F₂ and Pt-Ti₃C₂F₂ display the greatest interaction with NO₂ and the weakest with NH₃. Investigations into molecular orbitals suggest that Rh-Ti₃C₂F₂'s electrical conductivity when exposed to gas molecules is as follows: NH₃ > SO₂ > NO₂, and the E_g(variation) values of the three gases are 2.96 %, 2.70 % and 2.16 % respectively. For Pd-Ti₃C₂F₂, the conductivity influenced by gases is NO₂ > NH₃ = SO₂ with the E_g(variation) values are 82.83 %, 1.26 % and 1.26 % respectively. Meanwhile, Pt-Ti₃C₂F₂ exhibits conductivity changes in the sequence of NO₂ > SO₂ > NH₃ when exposed to gas molecules where the E_g(variation) values are 24.54 %, 16.71 % and 8.62 % respectively. These findings offer a foundational theory for the fabrication of gas sensors utilizing Rh-Ti₃C₂F₂, Pd-Ti₃C₂F₂ and Pt-Ti₃C₂F₂ for the monitoring of hazardous industrial gases.