Oxygen vacancy-mediated sandwich-structural TiO2−x /ultrathin g-C3N4/TiO2−x direct Z-scheme heterojunction visible-light-driven photocatalyst for efficient removal of high toxic tetracycline antibiotics

A surface defect sandwich-structural TiO2−x/ultrathin g-C3N4/TiO2−x direct Z-scheme heterojunction photocatalyst is successfully constructed. The results manifest the existence of oxygen vacancies, sandwich structure and direct Z-scheme heterojunction. Noticeably, TiO2−x/ultrathin g-C3N4/TiO2−x efficiently eliminates high toxic tetracycline hydrochloride by means of·O2−, h+ and·OH, whose removal rate is 87.7% during 90 min and the pseudo-first-order rate constant reaches up to 31.7 min−1 × 10−3. The extraordinary performance can be attributed to the special 3D structure, Z-scheme heterojunction expediting charge transfer and promoting the generation of active species, meanwhile the oxygen vacancies enhancing the spatial separation of photo-induced carriers. Moreover, various environmental factors are systematically explored by statistics. SO42−, NH3-N and pH exhibit an obvious impact on removal rate. Meanwhile, TiO2−x/ultrathin g-C3N4/TiO2−x could also effectually remove tetracycline hydrochloride from complex actual-wastewater and exhibit high stability. Besides, the photocatalytic mechanism and degradation path of tetracycline hydrochloride are also elucidated.