Effect of plasma processing gas composition on the nitrogen-doping status and visible light photocatalysis of TiO2

The atmospheric pressure plasma enhanced nanoparticle synthesis (APPENS) process is applied to produce nitrogen (N) doped titania (TiO2) photocatalysts. With TTIP (titanium tetraisopropoxide; Ti(OC3H7)(4)) and water vapors as precursors, the effect of plasma and annealing gas composition on the N-doping status is identified by a cross comparison of the chemical shift of N atoms with those of Ti and O atoms. The activities of various types of N-doped photocatalysts are evaluated via the conversion of isopropyl alcohol (IPA). The results show that the N-doped TiO2 particles with O-x-Ti-N-y and -(NO) dopants are produced via N-2 plasma gas followed by air or N2 annealing gases. They have better visible and UV photocatalytic activities compared to the pure TiO2 photocatalysts prepared under O-2/Ar plasma and annealing gases. On the other hand, the N-doped TiO2 photocatalyst produced under N-2/O-2/Ar plasma gas and then annealed with pure N2 gas tends to have an additional dopant of -(NO2), but its photocatalytic activity is even worse than those of the pure TiO2 photocatalysts. The results reveal that the Ox-Ti-Ny and -(NO) dopants may have positive effects on the visible light photocatalytic activity while the -(NO2) dopant tends to have a negative effect on the visible light photocatalytic activity.