Fabrication of double-shell CuOx@Fe3O4 hollow spheres for efficient adsorption removal of tetracycline and oxytetracycline from water

Double-shell CuOx@Fe3O4 hollow spheres (DCFHS) were synthesized by a three-step method to enhance the adsorption of tetracycline (TTC) and oxytetracycline (OTC) from water. The XRD and SEM analysis indicated that DCFHS had a fine crystal structure and exhibited a hollow sphere morphological structure with a diameter of 1- 2 mu m. In addition, XPS analysis demonstrated that there were rich hydroxyl groups on the surface of DCFHS. The Temkin model and the pseudo-second-order kinetic model were more suitable to depicting the adsorption behaviors, and the maximum adsorption capacities of DCFHS for TTC and OTC were 1600.9 mg/g and 1398.7 mg/ g, respectively. Moreover, DCFHS was highly regenerable, and the removal efficiency could still reach about 75 % after five sorption-desorption cycles. Furthermore, after sorption of TTC and OTC, the leached iron and copper ions would not cause new pollution under neutral pH conditions. The FTIR and XPS analysis combined with DFT calculations revealed the intrinsic adsorption mechanisms for TTC and OTC, which are mainly controlled by hydrogen bonds, pi-pi, cation-pi interaction, and surface complexation.