Enhanced Visible Light Photocatalytic Activity for TiO₂ Nanotube Array Films by Codoping with Tungsten and Nitrogen

Figure 3

High resolution XPS spectra of (a) N 1s, (b) W 4d, (c) Ti 2p, and (d) O 1s for N-TiO₂ and W-N-TiO₂-1 samples.

(a)

(b)

(c)

(d)