question: Herein, we describe the hydrothermal immobilization of BiVO4 on activated carbon fibers (ACFs) and characterize the obtained composite by several instrumental techniques, using Reactive Black KN-B (RB5) as a model pollutant for photocatalytic performance evaluation and establishing the experimental conditions yielding maximal photocatalytic activity. The photocatalytic degradation of RB5 is well fitted by a first-order kinetic model, and the good cycling stability and durability of BiVO4@ACFs highlight the potential applicability of the proposed composite. The enhanced photocatalytic activity of BiVO4@ACFs compared to those of BiVO4 and ACFs individually was mechanistically rationalized, and the suggested mechanism was verified by ultraviolet-visible spectroscopy, attenuated total reflectance Fourier-transform infrared spectroscopy, and RB5 degradation experiments. Thus, this work contributes to the development of BiVO4@ACF composites as effective photocatalysts for environmental remediation applications.