Figure 3From: Self-organized vanadium and nitrogen co-doped titania nanotube arrays with enhanced photocatalytic reduction of CO2 into CH4High-resolution XPS spectra. Of the (a) Ti 2p, (b) O1s, (c) N 1 s, and (d) V 2p for N-TiO2, VN0, and VN3 samples.Back to article page