Two Novel Bi-Based Borate Photocatalysts: Crystal Structure, Electronic Structure, Photoelectrochemical Properties, and Photocatalytic Activity under Simulated Solar Light Irradiation

Through the combination of Bi3+ and a large negative charge ion (BO3)3–, two novel Bi-based borate photocatalysts Bi4B2O9 and Bi2O2[BO2(OH)] with layered structure have been successfully developed. For the first time, the borates were investigated as photocatalysts. They were synthesized by solid-state reaction and hydrothermal method, respectively, and further characterized by XRD, SEM, TEM, HRTEM, and DRS. Bi4B2O9 and Bi2O2[BO2(OH)] possess direct and indirect transition optical band gaps of 3.02 and 2.85 eV, respectively. Density functional calculations revealed that the valence band (VB) and conduction band (CB) of both borates were composed of hybridized states of the O 2p and Bi 6p or 6s orbitals, and a large dispersion was observed in the energy band of Bi2O2[BO2(OH)]. The photodecomposition experiments demonstrated that Bi4B2O9 and Bi2O2[BO2(OH)] can be used as effective photocatalysts under simulated solar irradiation, and Bi2O2[BO2(OH)] exhibits the high photocatalytic activity, which is 2.5 and 3.2 times compared with that of P25 and Bi2O2CO3, respectively. Moreover, the photocurrent conversion further confirmed that Bi4B2O9 and Bi2O2[BO2(OH)] were potential photofunctional materials. The layered structure with (Bi2O2)2+ layer, hybridized and dispersion energy band, and large negative charge of (BO3)3– ion should be responsible for the high photocatalytic activity of Bi2O2[BO2(OH)].