Sonophotocatalytic degradation of 17β-estradiol by Er3+-CdS/MoS2: The role and transformation of reactive oxygen species

Reactive oxygen species (ROS) play a considerable role in the catalytic reaction for removing organic pollutants, however, the generation and transformation mechanism by catalyst with light and ultrasonic irradiation still requires intensive investigation. In this study, a novel Er3+-CdS/MoS2 (ECMS) composite was synthesized, and the synergetic degradation effects for 17β-estradiol (17β-E2) during the sonophotocatalytic (SPC) process were investigated. The contribution of ROSs for eliminating 17β-E2 during the SPC process through quenching experiments was generally ranked in the following order: superoxide radical (•O2−) ≈ hole (h+) > hydroxyl radical (•OH) > H2O2 > singlet oxygen (1O2). •OH plays a crucial role in 17β-E2 removal by ECMS under sonocatalysis and photocatalysis conditions. The transformation process among ROSs was further analyzed and elucidated in the light of the probe measurement results with positive or negative correlation among ROSs. Besides, we observed a phenomenon that the generated concentration of •O2− rises first and then falls during the SPC process, which might be attributed to the formation of 1O2 via the oxidation of h+ or recombination with •OH. This work clarifies the underlying mechanisms of sonophotocatalytic generation and transformation of ROSs in depth.