In this paper, first-principle calculations were performed to investigate the effects of oxygen (O) vacancies (Ovac) on the crystal structure, electronic distribution, adsorption energies of O₂ and H₂O and the density of states (DOS) of monoclinic bismuth vanadate (m-BiVO₄). Ovac were stable when incorporated into m-BiVO₄(001) and increased the adsorption energy of O₂. Ovac changed the V3d orbitals of m-BiVO₄(001) by adding a new band gap level, causing the redundant electrons of V atoms to become carriers and promoting the separation efficiency of electrons and holes. To verify the first-principle calculations, m-BiVO₄ with different Ovac levels was prepared via hydrothermal synthesis. X-ray diffraction (XRD) patterns confirmed the existence of the (001) crystal surface of m-BiVO₄. In addition, X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) spectroscopy of m-BiVO₄ confirmed the presence of Ovac and demonstrated that, as the Ovac level increased, the number of superoxide radicals ( O 2 - · ) and hydroxyl radicals (·OH) produced increased. In addition, m-BiVO₄ with a higher Ovac level possessed superior photocatalytic properties to and degraded rhodamine B (RhB) dye nearly 2-fold faster than m-BiVO₄ with a lower Ovac level. Finally, the removal rate of RhB increased from 23 to 44%. All experimental results were in good agreement with the first-principle calculated results.

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