Cyclic performance and photo-induced crystalline growth of nanostructured AgI/TiO ₂ visible light photocatalyst

Nanostructured AgI/TiO ₂ visible light photocatalyst was prepared with AgNO ₃, KI, and Ti(OBu) ₄ as precursors. The photocatalyst was used repeatedly to degrade methylene blue and methyl orange in water with visible light irradiation. Though a high photocatalytic efficiency was observed for the photocatalyst in the first cycle, the photocatalytic efficiency was found to decrease dramatically in subsequent cycles. X-ray diffraction and SEM analyses revealed an obvious crystalline growth of AgI in AgI/TiO ₂ nanocomposite after photocatalysis or visible light irradiation. It was proposed that photo-induced crystalline growth had occurred to AgI in the course of photocatalysis and resulted in dramatic decrease in the photocatalytic efficiency of the photocatalyst. Photo-induced crystalline growth may be a limiting factor for the lifetime of photocatalysts and should be examined as an important aspect of photostability when new photocatalysts are developed.