Abstract: In this paper, Bi19Br3S27 (BBS) catalyst powder with broad spectral response was prepared, and Alg/BBS gel microspheres were successfully fabricated by immobilizing the powder into calcium alginate gel beads (Alg) via physical embedding method. The morphology, crystal structure, and chemical composition of the catalyst were characterized by SEM, TEM, XRD, and XPS. Under outdoor natural sunlight, the photocatalytic degradation performance of Alg/BBS toward tetracycline was tested under weak light conditions, including cloudy and overcast days. The results showed that after 120 min of reaction, the tetracycline removal efficiency reached 80.21% on cloudy days and 76.63% on overcast days, demonstrating that the composite beads possess good catalytic activity under weak light conditions. In addition to favorable low-light responsiveness, Alg/BBS composite microspheres can be separated from the reaction solution via simple filtration, demonstrating promising recyclability potential.

Key words: Bi₁₉Br₃S₂₇; Calcium alginate microspheres, Tetracycline, Photocatalytic degradation; Outdoor weak light