Abstract
Zinc oxide (ZnO) has been shown as a potential photocatalyst under ultraviolet (UV) light but its catalytic activity has a limitation under visible (Vis) light due to the wide bandgap energy and the rapid recombination of electrons and holes. Thus, hierarchical structure Au/ZnO composites were fabricated by the hydrothermal method and chemical reduction method for enhanced photocatalytic performance under visible light. As-prepared composites were characterized by UV-vis diffuse reflectance spectra (DR/UV-Vis), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and electron paramagnetic resonance (EPR). The Au/ZnO-5 composite showed the highest adsorption among as-prepared samples in the range of 250-550 nm, having bandgap energy of 0.13 eV. Au nanoparticles of about 3-5 nm were well dispersed on hierarchical flower ZnO with approximately 10-15 μm. The EPR signal at [Formula: see text] on both ZnO and Au/ZnO samples was attributed to oxygen vacancy Vo•, but the presence of Au led to a decrease in signal strength of Au/ZnO composite, showing the degradation efficiency (DE) and reaction rate of 99.2% and 0.109 min-1, respectively; these were larger than those of other samples. The effects of reaction parameters and oxidizing agents on photocatalytic performance were investigated and showed that the presence of H2O2 and O2 could improve the reaction of composite. In addition, the kinetic and photocatalytic mechanism of tartrazine (TA) on catalysts were studied by the first-order kinetic model and characterized analyses.
Highlights
With the development of science and technology techniques, nanomaterials are being widely studied for many potential applications in medicine, environment, and industrialization
Hierarchical structure Au/Zinc oxide (ZnO) composite was successfully synthesized by the hydrothermal method and chemical reduction by sodium citrate
The Au particles of 3-5 nm in size were well dispersed on the ZnO structure, which was observed in energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and electron paramagnetic resonance (EPR) results
Summary
With the development of science and technology techniques, nanomaterials are being widely studied for many potential applications in medicine, environment, and industrialization. Gold nanoparticles have attracted the attention of researchers for the reasons of nontoxic, high chemical and physical stability, perform surface functions with organic molecules, and countless optical properties associated with surface plasmon resonance [2]. The condition for resonance phenomenon is the frequency of the exciting light up to the oscillation frequency of the free electronic system on the metal surface. Au nanoparticles have resonance frequencies within the visible radiation area. They will strongly absorb visible light including solar light and causing the color effect [3]. Since the high interaction ability on the surface of other materials, the Au nanoparticles are commonly used as an agent to get the mutagenic properties within the catalysis, polymer, semiconductor, and medicine fields [4,5,6,7]
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