Visible light photochemical activity of heterostructured PbTiO3-TiO2 core-shell particles

Heterostructured powders composed of microcrystalline PbTiO3 cores coated with nanostructured TiO2 shells were prepared by a sol-gel method. When exposed to visible light (lambda > 420 nm), the heterostructured powder degrades methylene blue at a rate 4.8 times greater than PbTiO3, TiO2, or mechanical mixtures of the phases. The rate at which the heterostructured powder degrades methylene blue depends on the processing temperature; samples annealed at 500 degrees C are the most reactive, even though they do not have the highest surface area. Enhanced degradation rates were not observed for Pb-doped TiO2, indicating that it is the core-shell architecture and not contamination by lead that increases the reactivity. The improved reactivity of microcrystalline-PbTiO3/nanostructured-TiO2 heterostructures in visible light is attributed to visible light absorption in the PbTiO3 core, charge separation at the buried interface between the ferroelectric PbTiO3 and the dielectric TiO2, and dye degradation on the nanostructured TiO2 shell.