Insight into the activation of persulfate with ZrO2 modified S-doped g-C3N4 nanocomposite for degradation of tetracycline hydrochloride

Abstract

In this study, ZrO2 modified S-doped g-C3N4 (ZSCN) is synthesized as an innovative and efficient solar light-driven heterojunction nanocomposite. A sulfate radical based advanced oxidation process (SRAOP) coupled with as-prepared nanocomposite for solar degradation of tetracycline hydrochloride (TCH) is employed in the presence of persulfate ions (PS). The TCH degradation efficiency of the operational parameters comprising the initial TCH amount, pH, and photo-catalyst dosage on the TCH degradation process are investigated. The presence of the PS ions as an electron acceptor significantly enhanced the degradation of TCH under solar light irradiation. Surprisingly, the ZSCN + PS system exhibited excellent degradation of 93.4 % for the initial concentration (40 mg/L) of TCH solution within 150 min. Compared to pure ZSCN, the enhanced degradation efficiency results from higher solar light absorption and a larger surface area. Also, the heterojunction formation at the ZrO2/S-g-C3N4 interface effectively improves the electron-hole separation efficiency. Radical scavenging test and electron spin response (EPS) studies were used to identify the reactive oxygen species (ROS) generated in ZSCN + PS process. 1O2 was verified to be the major ROS responsible for TCH degradation. Scavenger tests and ESR analysis have shown that the •O2− as major radical, along with •OH and •SO4−, were essential free radicals that played a key part in the TCH degrading pathway. The re-usability and stability of heterojunction nanocomposite are evaluated through recycling experiments. It is supposed that the current work can provide a positive direction for the design and fabrication of various photo-catalysts for the treatment of water pollution effectively.