Enhanced photocatalytic degradation and CO₂ reduction activity of S-type ZnCdS/BiOBr heterojunction composites: mechanism insights and pathway analysis

S-type ZnCdS/BiOBr heterojunction photocatalysts were successfully created by the attachment of ZnCdS nanoparticles on the surface of BiOBr nanosheets. Upon simulated sunlight irradiation, the photocatalytic activity of ZnCdS/BiOBr composites for the removal of dyes (methyl orange (MO) and methylene blue (MB)) and an antibiotic (tetracycline (TC)) was systematically investigated. The findings suggested that the photodegradation performance of BiOBr was apparently improved after decoration with ZnCdS nanoparticles. The 4% ZnCdS/BiOBr sample manifested an optimal photocatalytic degradation activity, and compared with bare BiOBr, its removal rates for MB, MO and TC were improved by ∼2.8, ∼4.6 and ∼2.9 times, respectively. The probable degradation pathway of TC was studied in detail. On the other hand, the photocatalytic CO₂ reduction activity of the products was concurrently tested <i>via</i> excitation by simulated sunlight. The ZnCdS/BiOBr composites exhibited an enhanced catalytic performance for the reduction of CO₂ into CO compared with BiOBr. Among them, the 4% ZnCdS/BiOBr sample had the best CO yield rate of 2.61 μmol g^-1 h^-1 (4 h reaction), which is ∼1.68 times higher than that of bare BiOBr. The possible photocatalytic CO₂ reduction pathway was also predicted. The potential photocatalytic mechanism of the S-type ZnCdS/BiOBr heterojunction was proposed.