TiO2 nanotube (T_NT) surface treatment revisited: Implications of ZnO, TiCI4, and H2O2 treatment on the photoelectrochemical properties of T_NT and T_NT-CdSe

摘要

The surface treatment of an anodized TiO2 nanotube (T_NT) is very desirable for enhancing its photoelectrochemical properties and often is a prerequisite to deposition of any overlying layer for photoactivity efficiency improvement. This study provides a comparative analysis of the effects of such surface treatments and the mechanistic insights behind the observed improvements in the performance of the treated T_NTs. T_NT surface treatment using three approaches, viz., TiCI4, Zn(IMH3)4~(2+), and H2O2 is examined. TiCI4 and Zn(NH3)4~(2+) treatment results in the formation of discontinuous islands of the respective oxides with 5-10 nm and 15-20 nm diameter particles. TiCI4 treatment demonstrates an increase of 7.4% in photovoltage and is the most effective of the three approaches. Zn(NH3)4~(2+) treatment also results in an ~2% increase in photovoltage. However, a surface treatment of T_NT using H2O2 results only in a favourable shift in flatband potential (80 mV). The TJMTs are rendered ineffective as H2O2 treatment causes the destabilization of the T_NT at the base. Finally, the activity of an overlying chalcogenide layer is improved with the TiCI4 and Zn(NH3)4~(2+) treatment (and not with H2O2) as evident from the photoelectrochemical responses: (J_(T_NT-TiO2-CdSe) > J_(T_NT-ZnO-CdSe) > J_(T_NT-CdSe) > J_(T_NT-H2O2-CdSe)).