Effects of bulk and surface defects on the photocatalytic performance of size-controlled TiO2 nanoparticles.

Defects are one of the crucial factors influencing the photocatalytic activities of TiO2 nanoparticles (NPs), as they directly affect the charge separation efficiencies. However, we found that the effect of bulk or surface defects on the photocatalytic performance of TiO2 is totally different. Here, we controllably synthesized four kinds of uniform TiO2 NPs, which were used to investigate how the bulk and surface defects influenced the photoactivities of samples with different particle sizes. Through XPS and EPR analysis, bulk and surface defects were observed in all the TiO2 samples and their amounts had been reduced after the calcination process. The reduction of bulk and surface defects enhanced the photoactivities of TiO2 NPs with diameters >10 nm, but the situation was inverse for those samples with diameters <10 nm. Therefore, we demonstrated that bulk defects play a dominate role in the change in photoactivity in particles larger than 10 nm, while surface defects are more important than bulk defects for particles less than 10 nm.