Though ZnO has a wide band gap of 3.37eV and TiO2 (Anatase) also has wide band gap of 3.2eV, ZnO still shows more photoluminescence and TiO2 shows more photocatalytic activity than photoluminescence.
Of course, better photoluminescence properties cause the less efficient photocatalytic activity of the material because the two processes depend on the photogeneration of electron-hole pairs. The increase of the lifetime of the photoinduced electron-hole pairs is the key factor for the improvement of the photoactivity. Besides, photoactivity also strongly depends on bulk and surface physicochemical properties of the photocatalysts.