Simultaneous enhancement of the optical absorption, ferroelectric polarization, and photocatalytic activity by designing the Ti/Fe ratio for Bi5Ti3FeO15

Bismuth-contained Aurivillius compounds are potentially low-cost and eco-friendly photocatalysts for organic pollutant degradation because of their unique layered crystal structure. Bi5Ti3-xFe1+xO15 (BTF-x, x = 0–1) photocatalysts were synthesized through the molten salt method. The crystal structure was determined by XRD Rietveld refinements. The phase constitution was found to change from a single 4-layered Aurivillius phase for x = 0 to mixed Aurivillius phases with different layer numbers as x increases. BTF-0.8 and BTF-1 exhibit better frequency stability of dielectric properties. The decrease in the Ti/Fe ratio leads to a monotonic reduction of the bandgap, ascribed to the increase in the octahedral distortion rather than the oxygen vacancy concentration. Surprisingly, the ferroelectric polarization is also improved by decreasing the Ti/Fe ratio and the best ferroelectricity was obtained in BTF-1. The photocatalytic activity of BTF-x catalysts was examined by RhB degradation under visible-light irradiation. The decrease in the Ti/Fe ratio also enhances the photocatalytic activity of BTF-x catalysts. The fastest photodegradation rate was obtained in BTF-1, about 9 times higher than that of BTF-0. Scavenger test studies confirmed that the level of contribution to RhB photodegradation was h+, O2•−, and •OH radicals in descending order. Furthermore, the excellent stability and reusability of BTF-x catalysts were demonstrated by the photocatalytic cycle tests. All the results suggested without introducing hetero elements, adjusting the Ti/Fe ratio was an effective means to narrow the bandgap, improve the ferroelectricity and enhance the photocatalytic activity simultaneously. We hope the present study can be generalized to other Aurivillius phases to acquire much better performance and broader application.