The role of Cs dopants for improved activation of molecular oxygen and degradation of tetracycline over carbon nitride

Molecular oxygen (O₂) is activated to reactive oxygen species (ROS) by transferring energy and carriers in the photocatalytic process, which plays an important role in environmental remediation. Herein, Cs-doped carbon nitride (CN-xCs, x = 0.2, 0.8, 1) was prepared by CsCl directly inducing the structural reconstruction of carbon nitride (CN), which had obvious molecular oxygen activation ability to promote tetracycline (TC) degradation. Besides, we explored the influence of Cs doping concentration. As a consequence, the doping concentration of Cs was an important factor affecting the activation of O₂, which could cause changes in the physical and chemical structure of CN, make O enter the CN structure, form N vacancy defects and cyano groups. In addition, a proper amount of Cs doping could reduce the band gap value, increase the light absorption range, have better charge separation and transfer performance, which could remarkably promote the activation of O₂. Benefiting from these advantages, CN-0.8Cs could generate a higher concentration of superoxide radicals (^?O₂^?, 179.30 µmol/L), which was much higher than CN (6.22 µmol/L). Therefore, it exhibited excellent TC degradation photocatalytic performance, and the rate constant k of TC degradation was 0.020 min^?1, which was 6.7 times the degradation rate of CN (k = 0.0030 min^?1). Furthermore, the possible degradation pathways of TC were proposed based on the results of HPLC-MS.