Effect of substrate on evaluation of the photocatalytic activity of TiO2 nanocrystals with exposed {0 0 1} facets

There are increasing debates on the high photocatalytic activity of TiO2 nanocrystals with exposed high-energy facets. In this paper, the effect of substrate on evaluation of the photocatalytic activity of anatase TiO2 nanocrystals with exposed {0 0 1} facets was studied. Surface-clean anatase TiO2 nanocrystals with exposed {0 0 1} facets were prepared by a microwave-assisted hydrothermal route in a Ti(OC4H9)4-HF-H2O mixed solution (both the amount of Ti(OC4H9)4 and HF were 60 mmol). It was found that the percentage of exposed {0 0 1} facets is negatively correlated with the molar ratio of water to titanium/or fluoride (x). With increasing x from 0 to 21, the percentage of exposed {0 0 1} facets steadily decreases from 81% to 36%. Anionic dye Brilliant Red X-3B (X3B) and cationic dye Methylene Blue (MB) were used as probes to evaluate the relative photocatalytic activity of the prepared TiO2 samples. TiO2 nanocrystals with exposed 40% {0 0 1} facets at x = 15 shows the highest photocatalytic activity in degradation of MB. However, an overwhelmingly better performance of TiO2 sample with exposed 49% {0 0 1} facets at x = 9 was found among all the photocatalysts in photocatalytic degradation of X3B, reflecting the importance of substrate on evaluation the photocatalytic activity of high-energy TiO2 nanocrystals.