Table 5. Band Gaps of Metal-Doped Titanate Nanotubes.

samples	band gap (eV)
Mg-TNT	2.26
Ca-TNT	2.26
Zn-TNT	2.3
K-TNT	2.8
Cr-TNT	2.12
Ce(IV)-TNT	2.02
Ce(III)-TNT	2.46
Mo(V)-TNT	2.36
La-TNT	2.51