Fe-MFI zeolite-encapsulated copper oxide with excellent re-usability for efficient tetracycline degradation

Impregnation handlement can load highly dispersed CuO nanoparticles on the Fe-MFI zeolite and effectively enhances its catalytic activity in the tetracycline degradation reactions, but encounters serious re-usability problems. In this work, Fe-MFI zeolite-encapsulated copper oxide CuO@Fe-MFI was prepared via one-step hydrothermal synthesis and utilized as heterogeneous catalyst for the removal of tetracycline. The obtained 2CuO@1Fe-MFI zeolite presented a external surface area of 270 m2/g, which was almost 5.5 folds of 2CuO/1Fe-MFI zeolite obtained by impregnation handlement. In addition, there may be a near-neighbor effect between encapsulated CuO and framework iron evidenced by the shifts of UV–Vis absorption bands as well as binding energies for Fe 2p and Cu 2p. At pH = 7.0, 2CuO@1Fe-MFI zeolite attained the largest tetracycline removal rate of 99.6% within 20 min at experimental conditions: [TCE] = 50 mg/L, [Catalyst] = 0.5 g/L, [PMS] = 1.0 g/L, 323 K, and the biggest degradation rate constant of 2.42 min−1, which was almost 11.1 folds of that for 2CuO/1Fe-MFI zeolite. The large external surface area and near-neighbor effect together gave rise to the excellent tetracycline degradation performance for 2CuO@1Fe-MFI zeolite. On the same time, the obtained 2CuO@1Fe-MFI zeolite can be reused for more than five times. Quenching experiments and EPR characterizations demonstrated the reactive species for tetracycline removal over 2CuO@1Fe-MFI zeolite were •OH, SO4•−, •O2− and 1O2 species, and moreover 1O2 served as the major active species. Furthermore, possible tetracycline degradation pathways over 2CuO@1Fe-MFI zeolite were proposed.