Regulating spin polarization of Mn-doped ZnFe2O4 for boosting antibiotic degradation: Intermediate, toxicity assessment and mechanism

Restraining the fast recombination of electrons and holes is an essential method to enhance the photocatalytic reaction efficiency, which could be attempted by modulating the electron spin polarization except for energy band structures. Herein, we synthesized manganese zinc ferrite (MnxZFO) photocatalysts with spin polarization effect by doping Mn cation into ferromagnetic semiconductor ZnFe2O4 (ZFO). X-ray diffraction (XRD) characterization confirmed the successful preparation of ZFO and gradient Mn doping MnxZFO samples. In addition, the vibrating sample magnetometry (VSM) results of Mn0.6ZFO displayed a stronger magnetization property than ZFO, which was beneficial for the modulation via a magnet. In photodegradation experiments, Mn0.6ZFO exhibited a remarkable enhancement of about 30% for tetracycline (TC) removal with an external magnet. The improvement of TC photodegradation efficiency by Mn0.6ZFO and a magnetic field could be attributed to the spin polarization of materials. In detail, the opposite spin states of numerous light-induced electrons with the holes suppressed the rapid recombination of charge carriers, thus boosting the TC degradation performance. The DFT calculation indicated that Mn doping could realize the electron spin polarization of ZFO, while Mn0.6ZFO exhibited the most obvious spin polarization among the nearby compositions of MnxZFO and ZFO. Additionally, the antibacterial experiments of TC degradation products analyzed by LC-MS were carried out to determine the biotoxicity of TC intermediates. Specifically, the biotoxicity of the TC solution progressively declined as the reaction progressed. Moreover, the photocurrent implied Mn0.6ZFO with electron spin polarization behaved with a better charge separation ability than ZFO without spin polarization. This work would extend the strategy for tailoring the electron spin polarization in ferromagnetic photocatalysts by metal doping engineering.