| Summary: | Photocatalytic degradation of an antibiotic by utilizing inexhaustible solar energy represents an ideal solution for tackling global environment issues. The target generation of active oxidative species is highly desirable for the photocatalytic pollutants degradation. Herein, aiming at the molecular structure of tetracycline hydrochloride (TC), we construct sunlight-activated high-efficient catalysts of TiO<sub>2</sub>-eggshell (TE). The composite ingeniously utilizes the photoactive function of TiO<sub>2</sub> and the composition of eggshell, which can produce oxidative ·CO<sub>3</sub><sup>−</sup> species that are especially active for the degradation of aromatic compounds containing phenol or aniline structures. Through the synergistic oxidation of the··CO<sub>3</sub><sup>−</sup> with the traditional holes (h<sup>+</sup>), superoxide radicals (·O<sup>2−</sup>) and hydroxyl radicals (·OH) involved in the photocatalytic process, the optimal TE photocatalyst degrades 92.0% TC in 30 min under solar light, which is higher than TiO<sub>2</sub> and eggshell. The photocatalytic degradation pathway of TC over TE has been proposed. The response surface methodology is processed by varying four independent parameters (TC concentration, pH, catalyst dosage and reaction time) on a Box–Behnken design (BBD) to optimize the experimental conditions. It is anticipated that the present work can facilitate the development of novel photocatalysts for selective oxidation based on ·CO<sub>3</sub><sup>−</sup>.
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