Engineering an intimate BiOBr/g-C3N4 heterojunction with expanded graphite for enhanced photocatalytic antibiotic degradation

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-C 3 N 4 /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-C 3 N 4 , respectively. XPS analysis revealed that the introduction of EG effectively suppressed the photoreduction of Bi 3+ to metallic Bi 0 , 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 m 2 /g, which is significantly larger than that of BiOBr (28.9 m 2 /g) and g-C 3 N 4 (37.1 m 2 /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 ·O 2 − 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-C 3 N 4 , 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.