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(OC₃H ₇)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 N₂ 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 N₂/O₂/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 O_X-Ti-N_Y 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.