Enhanced degradation of tetracycline by gas-liquid discharge plasma coupled with g-C₃N₄/TiO₂

Plasma-catalysis is considered as one of the most promising technologies for antibiotic degradation in water. In the plasma-catalytic system, one of the factors affecting the degradation effect is the performance of the photocatalyst, which is usually restricted by the rapid recombination of electrons and holes as well as narrow light absorption range. In this research, a photocatalyst g-C₃N₄/TiO₂ was prepared and coupled with gas-liquid discharge (GLD) to degrade tetracycline (TC). The performance was examined, and the degradation pathways and mechanisms were studied. Results show that a 90% degradation rate is achieved in the GLD with g-C₃N₄/TiO₂ over a 10 min treatment. Increasing the pulse voltage is conducive to increasing the degradation rate, whereas the addition of excessive g-C₃N₄/TiO₂ tends to precipitate agglomerates, resulting in a poor degradation efficiency. The redox properties of the g-C₃N₄/TiO₂ surface promote the generation of oxidizing active species (H₂O₂, O₃) in solution. Radical quenching experiments showed that ·OH, hole (h ⁺), play important roles in the TC degradation by the discharge with g-C₃N₄/TiO₂. Two potential degradation pathways were proposed based on the intermediates. The toxicity of tetracycline was reduced by treatment in the system. Furthermore, the g-C₃N₄/TiO₂ composites exhibited excellent recoverability and stability.