Figure 9.

a and b XPS spectra of OH-signified titanium oxide nanoparticles (sample 2 in Table 1) and microtubes (sample 4 in Table 1), respectively, showing O 1 s and Ti 2p3/2 signals with Gaussian fits showing a predominant Ti3+ as opposed to Ti4+ and Ti2+ in the presence of OH species (cf. text). Note the Ti2+ content is significantly higher in sample 2 than sample 4 in accord with a lower minimum band gap for the former

Huang et al. Nanoscale Research Letters 2010 5:972-985   doi:10.1007/s11671-010-9591-4