Ag/Fe₃O₄/CuO/ZnO incorporated NGP materials: Visible light driven photocatalysts for the degradation of water pollutants

Ag/Fe₃O₄/CuO/ZnO/nanographene platelets (NGP) composites with different NGP loadings were synthesized in the present study using a simple hydrothermal method. The photocatalytic activities of the prepared Ag/ Fe₃O₄/CuO/ZnO/NGP composites were then studied for their ability to degrade different kinds of dyes in aqueous solutions under visible light irradiation. The X-ray diffraction (XRD) results indicate a face-centered cubic structure for Ag, a cubical spinel structure for Fe₃O₄, a monoclinic structure for CuO, and a hexagonal wurtzite structure for ZnO. Furthermore, a graphite-like structure could be detected for NGP. The thermal stability of the samples was evaluated by TGA; the results further confirm the good agreement between the actual and theoretical (5, 10, and 15 wt.%) weight loadings of NGP in the samples. Ultraviolet-visible (UV-Vis) absorbance spectroscopy was used to analyze the optical properties of the prepared samples; a surface plasmon resonance (SPR) phenomenon could be detected around ~ 440 nm and after the addition of NGP, the absorption band shifted to the visible light region. The ternary Ag/ Fe₃O₄/CuO/ZnO/NGP composites exhibit a significantly enhanced photocatalytic activity than either Ag/ Fe₃O₄/CuO/ZnO or Fe₃O₄/CuO/ZnO in degrading a methylene blue (MB) dye in an aqueous solution. When the NGP loading was 10 wt.%, the composites displayed the highest photocatalytic activity. The Ag/ Fe₃O₄/CuO/ZnO/NGP could efficiently degrade a variety of organic dyes, such as MB, Congo red (CR), and methyl orange (MO) under visible light irradiation. The species active in the degradation process were found to be the holes. More importantly, Ag/ Fe₃O₄/CuO/ZnO/NGP composites demonstrated good stability and reusability in repetitive photocatalytic activity processes.