Pulsed discharge plasma on water surface coupled with CaFe2O4/Bi2O3 composites for synergistic degradation of aqueous tetracycline hydrochloride

Abstract

Due to the increasingly severe water contamination of antibiotics, high-efficient and green removal of antibiotics from aqueous solution is of great significance to environmental remediation and human health. The combined degradation of tetracycline hydrochloride (TCH) in water by pulsed discharge plasma on water surface (WSPDP) coupled with CaFe2O4/Bi2O3 composite was investigated. The basic properties of the prepared CaFe2O4/Bi2O3 composite were analyzed by XRD, SEM, TEM, PL and XPS, which indicated that the CaFe2O4/Bi2O3 sample was synthesized successfully. Degradation performance revealed that there existed a synergistic effect in the WSPDP + CaFe2O4/Bi2O3 system, and WSPDP could induce catalysis of CaFe2O4/Bi2O3 composite. After adding 0.4 g/L 7 wt% CaFe2O4/Bi2O3 sample to the WSPDP system, the degradation efficiency of TCH improved from 82.9% to 93.8%, and the kinetic constant enhanced from 0.0616 min−1 to 0.0953 min−1 after 30 min of discharge treatment. Furthermore, the effects of pulse peak voltage, pulse frequency, initial pH of solution and air flow rate on TCH degradation were evaluated. The highest TCH degradation efficiency of 97.8% could be obtained at the peak pulse voltage of 24.6 kV, pulse frequency of 50 Hz, initial pH of 3 and air flow rate of 2 L/min within 30 min. OH, h+ and O2− were the main reactive radicals for TCH degradation in the WSPDP + CaFe2O4/Bi2O3 system·H2O2 and O3 were also involved in TCH degradation of the synergistic system, and the addition of CaFe2O4/Bi2O3 could significantly improve the utilization of H2O2 and O3 in the solution. The intermediates of TCH degradation were identified by liquid chromatography-mass spectrometry (LC-MS). Finally, the possible degradation pathways and synergistic degradation mechanism of TCH in the WSPDP + CaFe2O4/Bi2O3 system were proposed.