N-Doped TiO₂ Photocatalyst Coatings Synthesized by a Cold Atmospheric Plasma

This work presents a simple, fast (20 min treatment), inexpensive, and highly efficient method for synthesizing nitrogen-doped titanium dioxide (N-TiO₂) as an enhanced visible light photocatalyst. In this study, N-TiO₂ coatings were fabricated by atmospheric pressure dielectric barrier discharge (DBD) at room temperature. The composition and the chemical bonds of the TiO₂ and N-TiO₂ coatings were characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The results indicate that the nitrogen element has doped the TiO₂ lattice, which was further confirmed by Raman spectroscopy and grazing incidence X-ray diffraction (GIXRD). The doping mechanism was investigated using OES to study the plasma properties under different conditions. It suggests that the NH radicals play a key role in doping TiO₂. The concentration of nitrogen in the N-TiO₂ coatings can be controlled by changing the concentration of NH₃ in the plasma or the applied power to adjust the concentration of NH radicals in the plasma. The band gap of N-TiO₂ was reduced after NH₃/Ar plasma treatment from 3.25 to 3.18 eV. Consequently, the N-TiO₂ coating showed enhanced photocatalytic activity under white-light-emitting-diode (LED) irradiation. The photocatalytic degradation rate for the N-TiO₂ coating was about 1.4 times higher than that of the undoped TiO₂ coating.