Degradation of tetracycline in water by gas-liquid plasma in conjunction with rGO-TiO₂ nanocomposite

Tetracycline (TC) is an antibiotic mainly used in livestock production and respiratory infection. Traditional methods are not effective in removing TC from solution. In this study, TC was degraded by gas-liquid plasma in the presence of rGO-TiO₂ in solution. The rGO-TiO₂ was prepared by modified hummers and hydrothermal method. The electrical and optical properties of the gas-liquid discharge plasma were studied and the produced long-lived reactive species were analyzed by spectrophotometer. The degradation efficiency of TC was improved by 41.4% after plasma treatment for 12 min in presence of 30 mg l^-1 rGO-TiO₂ compared to that with plasma alone. The degradation efficiency increased with increasing discharge power, but as the initial concentration was increased from 20 to 80 mg l^-1, the degradation efficiency of TC decreased. The initial pH had no significant effect on the degradation of TC. The intermediate products were determined by UV-vis spectrophotometry and ESI (+)-MS, and the degradation mechanism was analyzed. The reactive species, including O₃, •OH, and H₂O₂, etc., produced in the plasma/catalyst system attracted electron-rich functional groups (amino group, aromatic ring, and double bond). Therefore, the gas-liquid plasma/catalyst system could be an effective and promising method for pharmaceutical wastewater treatment in future.