Non-radical degradation mechanism on ZnO quantum dots/hollow-sphere g-C3N4 S-scheme heterojunction photocatalysts for tetracycline degradation

Photocatalytic technology is currently one of the most effective methods for removing tetracycline (TC) from the environment; however, the underlying photocatalytic mechanism remains unclear. In this study, zinc oxide quantum dots (ZnO-QDs)/hollow-sphere g-C₃N₄ (CNHS) S-scheme heterojunction photocatalysts were synthesized for the photocatalytic degradation of tetracycline. Experimental results showed that the 7% ZnO-QDs/CNHS photocatalyst exhibited excellent TC degradation efficiency, with a removal rate of 80.2% within 15 min. Through free radical conversion pathway analysis, singlet oxygen (¹O₂) was identified as the primary active species responsible for tetracycline degradation. Further calculations indicated that the combination of holes (h⁺) and superoxide radicals (O₂ ^-) produces ¹O₂, accounting for 83.28% of the total contribution. These findings provide theoretical support for ¹O₂ as the primary active species in pollutant degradation.