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

Highlights: • A new 2D Bi-layered oxyhalogenide NaBi₃O₄Cl_1.5Br_0.5 was prepared via Sol-Gel method. • There is an isolated Eu-4f impurity energy level intersecting in the middle of the band gap of NaBi₃O₄Cl_1.5Br_0.5. • Eu doping makes the variation of band gap and band width become more outstanding than the other RE ions. • Optical active Eu³⁺ ion shows significant improvement of photodegradation of dye solutions. • Eu³⁺-doped NaBi₃O₄Cl_1.5Br_0.5 is not favorable for the photoluminescence application but is favorable for photocatalysis. 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 NaBi₃O₄Cl_1.5Br_0.5 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 NaBi₃O₄Cl_1.5Br_0.5. La³⁺ and Gd³⁺ doping slightly narrowed the band gap (several nanometers) of NaBi₃O₄Cl_1.5Br_0.5, 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 NaBi₃O₄Cl_1.5Br_0.5, which was suggested to enhance photodegradation and delay the recombination of light-generated electrons and holes. Eu³⁺-doped NaBi₃O₄Cl_1.5Br_0.5 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.