Upcycling sediment wastes into S-scheme heterojunctions for efficient photocatalytic tetracycline degradation: Performance, DFT calculations and toxicity assessment

In this study, a green and economical ZnO/sediments (ZNS) S-scheme heterojunction photocatalyst was constructed using SM-550 (calcination temperature was 550 °C) as the raw material, which effectively removes tetracycline (TC) from water under the 300 W xenon lamp irradiation. The experimental results showed that the optimal ZNS7:3 composite photocatalytic system exhibited significantly better TC degradation activity than ZnO (11.36 %) and SM-550 (16.00 %), with the TC degradation rate of 73.58 % in 90 min and the first-order kinetic constant of 0.0117 min −1 . After six reaction cycles, the TC degradation rate was only reduced by 7.57 %. Research ranging from a series of characterizations such as XPS and electrochemical testing to DFT calculations revealed that the S-scheme heterostructure of ZnO to SM-550 and synergistic effects endowed the system with high-energy carrier transfer kinetics and strong oxygen reduction ability. Additionally, the attack sites of individual atoms in TC were predicted by calculating its electron density, electrostatic potential, and Fukui index, which elucidated the control of the S-scheme ZNS heterojunction by electrophilic, nucleophilic, and general radical during the photocatalytic degradation of TC. Meanwhile, the lower ecological risk of TC degradation products was further verified based on the Ecological Structure Activity Relationships (ECOSAR) models and the bean sprout cultivation experiments. In summary, ZNS was the novel low-cost photocatalyst with good stability and environmental safety, strong adaptability, and wide application prospects. This study not only provided an effective solution for sediments resource utilization, but also offered an economical and green alternative catalytic material for the sustainable purification of antibiotic-contaminated water.