Visible light-driven dye degradation by magnetic cobalt-doped zinc oxide/iron oxide photocatalyst

Abstract

Zinc oxide (ZnO) serves as a photocatalyst, but it faces challenges due to its high band gap energy, limiting photoactivation to ultraviolet irradiation and rendering it scarcely recoverable after degradation. This work focuses on enhancing the photocatalytic efficiency of ZnO through cobalt doping and immobilization onto magnetic iron oxide (Fe3O4) via co-precipitation. The concentration of the cobalt precursor (0–10 mol %) and the molar ratio between Co–ZnO and Fe3O4 (5:1–15:1) were varied to achieve the optimal degradation efficiency and magnetic properties. Characterization tools such as the scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), attenuated total reflectance – Fourier-transform infrared spectroscopy (ATR-FTIR), and X-ray diffraction analysis (XRD) were utilized to evaluate the effect of cobalt doping on the physicochemical properties of the developed photocatalyst. Tauc plots indicated that 5 mol % Co–ZnO (Co5–ZnO) had the smallest band gap energy (2.79 eV), resulting in the highest photodegradation of methylene blue (88.72 %), compared to pristine ZnO (74.88 %) with a band gap energy of 3.39 eV. Co–ZnO/Fe3O4 showed a slight degradation efficiency decline, reaching a minimum of 84.53 % for the 5:1 molar ratio. These photocatalysts exhibited magnetic properties, with recovery efficiency ranging between 69.8 % and 72 %. Active radicals trapping experiments confirmed the involvement of holes, hydroxyl, and superoxide radicals in the degradation process, with superoxide radicals playing the most significant roles. In summary, this study successfully demonstrated that the synthesized Co–ZnO photocatalysts gained visible light sensitivity, and the incorporation of Fe3O4 imparted magnetic separability to the composite, thereby facilitating photocatalyst recovery.