Photocatalytic degradation of tetracycline from aqueous solution with graphene oxide and hydroxyapatite composites

The increasing presence of antibiotics such as tetracycline (TC) in aquatic environments has become a critical issue due to their persistence and contribution to antibiotic resistance. In this study, a graphene oxide and hydroxyapatite (GO-HAp) composite was synthesized as photocatalyst, and its performance for visible-light-induced degradation of TC from aqueous solution was evaluated. The incorporation of GO reduced the band gap of HAp from 3.5 eV to 2.8 eV, thereby enhancing the photocatalytic efficiency. The evaluation and optimization of the process parameters including pH, initial TC concentration, and catalyst dosage were carried out using Box-Behnken Design (BBD). Under the optimum conditions (pH 11, 50 mg L^-1 TC, 15 mg catalyst), a degradation efficiency of 86.65% was obtained after 120 min of irradiation. Kinetic analysis showed that the degradation followed a pseudo-first-order model with an R² value of 0.95. Additionally, the photocatalyst synthesized in the study exhibited good reusability and showed an efficiency of 83% after three cycles. These results indicate that the GO-HAp composite is a promising and reusable material for the efficient photodegradation of tetracycline under visible light.