Alkali-mediated dissolution-recrystallization strategy for in situ construction of a BiVO4/Bi25VO40 heterojunction with promoted interfacial charge transfer: Formation mechanism and photocatalytic tetracycline degradation studies

Constructing a heterojunction between semiconductors with identical elements constitutes an intimate contact that can greatly accelerate the charge carrier transfer and separation. Herein, a novel BiVO4/Bi25VO40 heterojunction was designed by the in situ conversion of pre-prepared BiVO4 in alkaline conditions. We investigated the formation process of BiVO4/Bi25VO40 heterojunctions by XRD structural refinement, Raman spectra, morphology characterization, and density functional theory calculations, and found that heterojunction formation occurred through a dissolution–recrystallization process, in which monoclinic BiVO4 decahedrons were first etched by alkali solution on the preferential {0 1 0} face and then transformed into cubic Bi25VO40. By adjusting the alkali treatment conditions, the phase composition of the heterojunction can be precisely modulated with BiVO4 decreasing and Bi25VO40 increasing in content as the synthesis time was extended. Benefiting from the in situ conversion strategy and matched band structure, the intimate type II heterojunction with close interfacial contact was formed between BiVO4 and Bi25VO40, leading to facilitated charge transfer with spatial separation of carriers and significantly enhanced photocatalytic performance in the probe reaction of tetracycline (TC) degradation. The active species responsible for TC removal were explored by radical trapping tests and ESR spectra, and the photodegradation pathways were proposed on the basis of HPLC-MS. This work provides deeper insight on the rational design of highly efficient semiconductor photocatalysts by precise regulation of the crystal growth process for solar energy conversion.