Boosting photodegradation of dye solutions based on Eu3+ doping in Bismuth-layered oxyhalogenide semiconductor NaBi3O4Cl1.5Br0.5

Abstract Two-dimensional bismuth layered oxyhalogenides have excellent photoelectric applications for energy conversion and storage due to its unique crystal structures, narrow band gaps. In this work, we reported an indirect semiconductor NaBi3O4Cl1.5Br0.5 prepared via sol–gel synthesis with the subsequent solid-state reaction. This is a typical bismuth layered framework characterized by [Bi2O2]2+ slab intercalated with [Cl/Br]− layers. There are distinct influences of rare ions (La3+, Gd3+, Eu3+) doping on the optical properties of NaBi3O4Cl1.5Br0.5. La3+ and Gd3+ doping slightly narrowed the band gap (several nanometers) of NaBi3O4Cl1.5Br0.5, while the band energy was greatly decreased from 2.37 eV to 2.18 eV via the Eu3+ doping in the lattice. As far as photochemical properties are concerned, La3+/Gd3+ doping didn’t show an obvious contribution, while, Eu3+-doping gave an improvement to photodegradation. A comparison with DFT calculations revealed that Eu-4f could bring about the isolated energy band intersecting the forbidden band of NaBi3O4Cl1.5Br0.5, which was suggested to enhance photodegradation and delay the recombination of light-generated electrons and holes. Eu3+-doped NaBi3O4Cl1.5Br0.5 is favorable for photocatalysis, but is not favorable for photoluminescence application. This bismuth layered semiconductor can be expected to have possible applications in developing advanced energy conversion or energy storage materials such as photocatalyst, optoelectronics, and batteries.