<p>This study presented a simple heat treatment process to synthesize graphitic carbon nitride (g-C₃N₄)/carbon black (CB) composites for applications in photocatalytic and sonocatalytic antibiotic degradation. The chemical and crystal structure, morphology, surface chemical composition and surface structure, and optical properties of g-C₃N₄/CB composites were studied using FTIR, XRD, FESEM, XPS, N₂ adsorption/desorption analyses, and UV–Vis absorption spectroscopy. The antibiotic degradation ability of g-C₃N₄/CB composites was evaluated separately under visible light irradiation and ultrasonic irradiation. The degradation experiments revealed that both the photocatalytic and sonocatalytic performance were affected by the carbon black concentration of the samples. Although no significant change was observed in the adsorption capacity of g-C₃N₄/CB, the photocatalytic and sonocatalytic performance of g-C₃N₄/CB showed a significant improvement compared to pure g-C₃N₄. The best photocatalytic and sonocatalytic performance was obtained with the composite containing 1 wt% of carbon black. The specified composite sample could remove 54.7% of tetracycline after 120&#xa0;min of visible light irradiation and 53.4% of tetracycline after 120&#xa0;min of ultrasonic irradiation. Radical trapping experiments revealed that superoxide radicals played a major role in the photocatalytic tetracycline degradation. Both superoxide and hydroxyl radicals played important roles in the sonocatalytic removal of tetracycline. g-C₃N₄/CB composites demonstrated reusability for tetracycline degradation over five consecutive cycles, maintaining a removal efficiency of 43.9% and 43.0% by photocatalytic and sonocatalytic process, respectively.</p> Graphical Abstract <p></p>