Type-II surface heterojunction of bismuth-rich Bi4O5Br2 on nitrogen-rich g-C3N5 nanosheets for efficient photocatalytic degradation of antibiotics

A novel g-C 3 N 5 /Bi 4 O 5 Br 2 surface heterojunction was developed via in-situ growth of Bi-rich Bi 4 O 5 Br 2 on g-C 3 N 5 nanosheets. The optimal composite achieved 3.6- and 16.0- times of sulfathiazole (STZ) degradation activity when compared with pristine Bi 4 O 5 Br 2 and g-C 3 N 5 . The interlayer stacking morphology and extra nitrogen in triazine units significantly narrowed the conduction band of g-C 3 N 5 , which greatly promoted its visible utilization; while the bismuth-rich property of Bi 4 O 5 Br 2 prolonged the excited charge carrier lifetime. Both photoluminescence and electrochemical impedance spectroscopy analysis demonstrated that the type-II surface heterojunction (g-C 3 N 5 /Bi 4 O 5 Br 2 ) offered remarkable charge transfer and separation due to the matched energy band structure. The STZ degradation mechanism and pathways were proposed based on experiments and density functional theory calculation, and the contribution of reactive species for STZ degradation followed the order of O 2 ∙ - $O_2^{\bullet -}$  > h + > OH. Moreover, the toxicity evolution of STZ was evaluated, suggesting that sufficient mineralization is required to ensure safe discharge. The Box-Behnken experimental design methodology study revealed that g-C 3 N 5 /Bi 4 O 5 Br 2 exhibited high reactivity for antibiotics degradation under different water matrix. This study suggested that g-C 3 N 5 /Bi 4 O 5 Br 2 has great application potential for cost-effective remediation of persistent organic contaminants by using solar light.