High photocatalytic efficiency of a ZnO nanoplate/Fe₂O₃ nanospindle hybrid using visible light for methylene blue degradation

Abstract

In this work, ZnO nanoplates and Fe₂O₃ nanospindles were successfully fabricated <i>via</i> a simple hydrothermal method using inorganic salts as precursors. The ZnO/Fe₂O₃ hybrid was fabricated using a mechanical mixture of two different ZnO : Fe₂O₃ weight ratios to investigate the effect of weight ratio on catalytic properties. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that ZnO nanoplates (NPls) are about 20 nm thick with lateral dimensions of 100 × 200 nm, and Fe₂O₃ nanospindles (NSs) are about 500 nm long and 50 nm wide. X-ray diffraction (XRD) patterns revealed the successful formation of the ZnO, Fe₂O₃, and ZnO/Fe₂O₃ samples and indicated that their crystallite sizes varied from 20 to 29 nm depending on the ZnO : Fe₂O₃ weight ratio. Ultraviolet-visible (UV-vis) spectra showed that the bandgap energies of ZnO and Fe₂O₃ were 3.15 eV and 2.1 eV, respectively. Energy dispersive X-ray spectroscopy (EDS) results revealed the successful combination of ZnO and Fe₂O₃. Photocatalytic activity of the materials was evaluated through the degradation of methylene blue (MB) in aqueous solution under green light-emitting diode (GLED) irradiation. The results indicated that the ZnO/Fe₂O₃ composite showed a remarkable enhanced degradation capacity compared to bare ZnO NPls and Fe₂O₃ NSs. The ZnO : Fe₂O₃ = 3 : 2 sample demonstrated the best performance among all samples under identical conditions with a degradation efficiency of 99.3% for MB after 85 min. The optimum photocatalytic activity of the sample with ZnO : Fe₂O₃ = 3 : 2 was nearly 3.6% higher than that of the pure ZnO sample and 1.12 times more than that of the pristine Fe₂O₃ sample. Moreover, the highest photo-degradation was obtained at a photocatalyst dosage of 0.25 g l^-1 in dye solution.