N-doped TiO2 anatase nanoparticles as a highly sensitive gas sensor for NO2 detection: insights from DFT computations

Abstract

Density functional theory calculations were carried out to investigate the adsorption behavior of the NO₂ molecule on pristine and N-doped TiO₂ anatase nanoparticles in order to completely exploit the potential applicability of N-doped nanoparticles for the removal and sensing of NO₂ molecules. van der Waals (vdW) interactions were included to obtain the most stable geometrical structures of NO₂–TiO₂ complexes and the possible orientations of the NO₂ molecules towards the N-doped nanoparticles. The NO₂ molecule can be adsorbed on the surface of the nanoparticles through its oxygen and nitrogen atoms. The results indicate that the adsorption of the NO₂ molecule on the N-doped nanoparticles is energetically more favorable than the adsorption on the undoped ones, suggesting that the N-doped nanoparticles have stronger adsorption ability than the pristine ones in the adsorption process. The detachment of the dangling oxygen atom by the NO₂ molecule suggests that the NO₂ can be oxidized to NO₃ after the adsorption process. The fivefold coordinated titanium site was also demonstrated to be an active adsorption site with an increased affinity for the two oxygen atoms of the NO₂ molecule. The obtained results indicate that the adsorption on the N-doped nanoparticles provides the most stable configurations and consequently the most efficient adsorption complexes. The results presented include structural and electronic analyses such as bond lengths/angles, adsorption energies, density of states, Mulliken charge analysis and molecular orbitals. Our theoretical study thus suggests that the N-doped nanoparticles are greatly sensitive compared to the undoped ones for applications such as in gas removers or sensors for NO₂ detection in the environment.