Influence of the ferroelectric nature of lithium niobate to drive photocatalytic dye decolorization under artificial solar light

Photocatalytic decolorization of acid black 1 (a.k.a. amido black 10B) and rhodamine b was investigated over powders of lithium niobate or lithium niobate doped with iron to form n-type material doped or p-type magnesium doped lithium niobate. In all cases, photostimulation was performed using simulated solar illumination. The rate of decolorization of the dye solutions was found to be fastest over p-type material than with the undoped powder, with the n-type proving least effective. The change in rate was attributed to changes in the majority carrier, associated with the dopant altering the ratio of reactive species (holes and electrons). We also show that the surface depolarization field associated with a ferroelectric material alters the surface chemistry by changing the Stern and inner Helmholtz plane due to the interaction of catalyst surface charge and the polar nature of solvated species. The spatial separation of REDOX reactions in ferroelectric powders positively influences the proportion of reactions being driven to completion, enabling a high rate of decolorization despite the wide band gap (3.7 eV) of the catalyst. Finally, our results indicate that the band structure of lithium niobate enables single carrier oxidation of water to occur through an altered reaction mechanism when compared to a typical system such as titania, further enhancing the rate of decolorization. Our results give further evidence that ferroelectric materials provide an interesting alternative to nonferroelectric materials as photocatalysts.