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