Non-uniform doping outperforms uniform doping for enhancing the photocatalytic efficiency of Au-doped TiO2 nanotubes in organic dye degradation

Uniform doping is usually recognized as an efficient method for enhancing photocatalysis of TiO2, while non-uniform doping is generally supposed to be inefficient because of the inhomogeneous dispersion of dopants. However, in this study, we present the first example of non-uniform doping (with Au)-better enhanced photocatalysis of TiO2 nanotubes, as compared to uniform doping, in terms of the photocatalytic organic dye degradation. The extent to which the non-uniform doping (achieved by liquid phase deposition (LPD)) can enhance photocatalysis is evaluated, along with a comparison with uniform doping. There exists an additional positive effect in the non-uniform doping system, that is, as generated interfaces between pure phase TiO2 and Au-doped TiO2, in contrast to the uniform doping system leading to a positive "platinum island" effect. Such double beneficial effects contribute to the highest performance in the photocatalytic organic dye degradation for the Au-non-uniformly doped TiO2 nanotubes as compared to other samples involved in this study. Both the "platinum island" and interfacial separation effects are helpful to isolate the photo-generated electrons and holes, resulting in enhanced photocatalytic activities.