Stepwise adsorption-oxidation removal of oxytetracycline by Zn0-CNTs-Fe3O4 from aqueous solution

A novel strategy to remove oxytetracycline (OTC) from aqueous solution was proposed by two-step process of adsorption followed by oxidation degradation: OTC was firstly concentrated on the surface of the Zn-0-CNTsFe3O4 composite by adsorption process under neutral condition. Then, the concentrated OTC on the surface of Zn-0-CNTs-Fe3O4 was oxidized by Zn-0-CNTs-Fe3O4/O-2 Fenton-like process at pH of 3 with high solid-water ratio, which can reduce the amount of acid used for adjusting pH for Fenton reaction. Approximately 98.6% of OTC was oxidized at initial OTC concentration of 100 mg/L by the two-step process, which was higher than that by the one-step process of adsorption-oxidation at pH 3 or pH 6. The used Zn-0-CNTs-Fe3O4 in two-step process could be reused after Zn-0 was reloaded. The removal efficiency of OTC decreased only 6.7% after four-recycle use of the Zn-0-CNTs-Fe3O4. The possible adsorption mechanism of OTC onto the Zn-0-CNTs-Fe3O4 surface and the oxidation mechanism of the concentrated OTC by the Zn-0-CNTs-Fe3O4/O-2 process were proposed.