Homogeneous V incorporation via single-step anodization : structural doping or heterostructure formation?

Two distinct-phenomena were reported for anodic elemental-incorporation; structural-doping/heterostructure formation. Herein, by adding V for the first time in TiO2-nanotubes via anodization; the foreign elemental incorporation is peered. The bandgap (3.2 eV), flat band (0.07 VRHE) and valence band (VB) positions of V incorporated anatase-TiO2 nanotubes remained invariant which ruled out structural doping of TiO2. The first step in anodization is Ti-oxidation that occurs momentarily; thereby, the oxidation/dissolution dominancy of anodization in later stages impeded V-structural doping even for varying times (1–24 h) and voltages (6–60 V) and thus a small fraction of V2O5 was observed in surface and microscopic studies. Density functional theory realistic simulations revealed TiO2/V2O5 forms commensurate-heterostructure at common lattice constants with charge transfer from TiO2 to V2O5 at the heterostructure interface; exhibiting type-II band-alignment having CB from V2O5 and VB from TiO2 with decreasing bandgap. In photoelectrochemical-setup, the photogenerated electron transfer from V2O5 to the heterostructure interface was suppressed due to barrier-height which decreased photocurrent for TiO2/V2O5 (52 µA/cm2 ) as compared to pure-TiO2 (140 µA/cm2 ) at ~1.0 VRHE. Contrarily, in photolysis, improved light absorption and facile carrier migration from TiO2/V2O5 resulted in better photodegradation activity of methylene-blue. We unlocked anodization is ineffective for structural-doping, indeed it results in uniform low-content elemental incorporation forming oxides heterostructure