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In this study, we investigated sulfate-modified BiVO₄ with the high photocatalytic activity synthesized by a sol-gel method in the presence of thiourea, followed by the annealing process at different temperatures. Its structure was characterized by thermal gravimetric analysis (TGA), powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). The BiVO₄ synthesized in the presence of thiourea and calcined at 600 &#176;C (T-BVO-600) exhibited the highest photocatalytic degradation efficiency of methylene blue (MB) in water; 98.53% MB removal was achieved within 240 min. The reaction mechanisms that affect MB photocatalytic degradation on the T-BVO-600 were investigated via an indirect chemical probe method, using chemical agents to capture the active species produced during the early stages of photocatalysis, including 1,4-benzoquinone (scavenger for O₂^&#8722;), ethylenediaminetetraacetic acid disodium salt (scavenger for h⁺), and <i>tert</i>-butanol (scavenger for HO^&#8226;). The results show that holes (h⁺) and hydroxyl radicals (HO^&#8226;) are the dominant species of MB decomposition. Photoluminescence (PL) measurement results of terephthalic acid solutions in the presence of BiVO₄ samples and BiVO₄ powders confirm the involvement of hydroxyl radicals and the separation efficiency of electron-hole pairs in MB photocatalytic degradation. Besides, the T-BVO-600 exhibits good recyclability for MB removal, achieving a removal rate of above 83% after five cycles. The T-BVO-600 has the features of high efficiency and good recyclability for MB photocatalytic degradation. These results provide new insight into the purpose of improving the photocatalytic activity of BiVO₄ catalyst.