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

Through the combination of Bi 3+ and a large negative charge ion (BO 3 ) 3–, two novel Bi-based borate photocatalysts Bi 4 B 2 O 9 and Bi 2 O 2 [BO 2 (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. Bi 4 B 2 O 9 and Bi 2 O 2 [BO 2 (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 Bi 2 O 2 [BO 2 (OH)]. The photodecomposition experiments demonstrated that Bi 4 B 2 O 9 and Bi 2 O 2 [BO 2 (OH)] can be used as effective photocatalysts under simulated solar irradiation, and Bi 2 O 2 [BO 2 (OH)] exhibits the high photocatalytic activity, which is 2.5 and 3.2 times compared with that of P25 and Bi 2 O 2 CO 3, respectively. Moreover, the photocurrent conversion further confirmed that Bi 4 B 2 O 9 and Bi 2 O 2 [BO 2 (OH)] were potential photofunctional materials. The layered structure with (Bi 2 O 2 ) 2+ layer, hybridized and dispersion energy band, and large negative charge of (BO 3 ) 3– ion should be responsible for the high photocatalytic activity of Bi 2 O 2 [BO 2 (OH)].