KN-HCN exhibited enhanced photocatalytic ammonia production because of the presence of a large number of cyano groups and the loading mode of potassium and sodium ions.

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.