Degradation of tetracycline hydrochloride through g-C3N4/TiO2 nanotube arrays for photoelectrocatalytic activation of PMS system: Performance and mechanistic analysis

To enhance the pollutant degradation ability of TiO 2 nanotube arrays (TNAs) in a photoelectrocatalytic system (PEC), g-C 3 N 4 /TNAs photoanode was synthesized using anodic oxidation-slow evaporation method. Then, peroxymonosulfate (PMS) was incorporated and the resulting PEC-PMS system was applied to degrade tetracycline hydrochloride (TCH). The results from SEM , XRD and UV–vis DRS analyses indicated that g-C 3 N 4 was successfully loaded onto the surface of TNAs, reducing the forbidden bandwidth from 3.10 eV to 2.89 eV. I-t and EIS curves demonstrated that the loading of g-C 3 N 4 increased the electron transfer rate of TNAs. The photoanode prepared with a g-C 3 N 4 solution (concentration of 100 mg L −1 ) exhibited the best degradation performance for TCH. The degradation rate of TCH by the PEC-PMS system reached 95.69 % at a TCH concentration of 10 mg L −1 , pH of 9, PMS dosage of 2 mM, and voltage of 2 V, significantly higher than that of the PEC system without PMS (35.14 %). The contribution of active radicals to the system was in the order of SO 4 ·- > h + > ·O 2 - > ·OH. Three possible pathways for TCH degradation were proposed based on the experimental results. In conclusion, this work provides a theoretical basis for the preparation of photoelectrodes responsive to visible light and their application in the degradation of pollutants by the PEC-PMS system. In this study, a photoelectrocatalytic activation of PMS for the degradation of tetracycline hydrochloride using g-C 3 N 4 /TNAs as anode was constructed, and three pathways for the emergence of free radicals were proposed based on the experiments and XPS valence band spectra. A new theoretical basis was provided for the removal of difficult-to-degrade pollutants in water. • The g-C 3 N 4 /TiO 2 nanotube arrays were proposed for the degradation of TCH in a combined PEC-PMS system. • The radicals that produce degradation in this system are SO 4 ·- 、h + 、·O 2 - 、·OH. • A mechanism for the generation of reactive radicals in g-C 3 N 4 /TiO 2 nanotube arrays in the PEC-PMS system is proposed. • Three possible pathways for the degradation of tetracycline hydrochloride are proposed.