<p>With the advancement of the pharmaceutical industry and livestock farming, the increasing release of antibiotic-containing wastewater poses serious threats to both the natural environment and human health. Developing novel, efficient technologies to remove tetracycline from water is a critical priority. In this study, a ternary BiOBr/g-C₃N₄/EG composite was successfully synthesized via a one-step solvothermal method. Under optimal conditions, the composite achieved a tetracycline (TC) removal efficiency of 98.49% within 50 min of visible-light irradiation, with degradation rate constants 1.40 and 1.74 times higher than those of pristine BiOBr and g-C₃N₄, respectively. XPS analysis revealed that the introduction of EG effectively suppressed the photoreduction of Bi³⁺ to metallic Bi⁰, confirming that EG acts as an electron trap and establishes strong interfacial electronic interactions. BET analysis showed that the ternary composite possesses a specific surface area of 60.0 m²/g, which is significantly larger than that of BiOBr (28.9 m²/g) and g-C₃N₄ (37.1 m²/g), promoting active site exposure and pollutant adsorption. PL spectroscopy demonstrated a marked decrease in emission intensity for the ternary composite, indicating effective suppression of electron–hole recombination. Mechanistic studies, including radical trapping and EPR, identified ·O₂⁻and h⁺ as the primary reactive species governing TC degradation. The enhanced performance is attributed to the synergistic effects of EG: (i) its oxygen-containing functional groups anchor BiOBr and g-C₃N₄, preserving heterojunction integrity; (ii) it serves as an electron trap to accelerate charge separation; and (iii) it enlarges the specific surface area and provides a conductive network for rapid charge transfer. This work offers a feasible and innovative strategy for designing high-performance carbon-supported semiconductor heterojunctions for environmental remediation.</p>