| dc.description.abstract | The purpose of this study was to develop a catalyst with high photocatalytic activity and had core/shell structure. It could be applied to the decomposition of organic pollutants under UV light illumination. The literature shows that doping precious metal on the surface of titanium dioxide can enhance the photocatalytic activity because noble metal can form active sites to promote the electronic charge transfer in the interface of metal and titanium dioxide. Although the activity of this kind of structure is high, the exposed metal is easy to dissolve or corrosive, leading to catalyst decay. Core/shell structure can be used to overcome this shortcoming, noble metals located in the core, while titanium dioxide is in the shell.
In this study, Au@TiO2 and Ag@TiO2 catalysts with core/shell structure were synthesized by sol-gel method with hydrothermal treatment. Different preparation parameters lead to different sizes of metal core, different crystal size of TiO2 and different crystallinity of TiO2. These catalysts were characterized by UV-vis spectroscopy (UV-vis), Dynamic light scattering analyzer (DLS), inductively-coupled plasma-mass spectrometry (ICP-MS), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS).
TEM micrographs, UV-vis spectra and DLS results showed the Au core size of Au@TiO2 could effectively be controlled between 6.6 and 32.37 nm by different CTAB concentration. However, the Ag core size of Ag@TiO2 could just be controlled between 6.82 and 15.35 nm by different ratio of hydrazine to silver nitrate. XRD patterns exhibited the crystallinity of TiO2 increased with increasing the temperature of hydrothermal process.
The photoreaction was carried out in a 10 ppm methylene blue solution with two 8w 254 nm UV light as the light source. The concentration of MB in the degradation samples were measured by UV-vis spectrometer (UV-vis). The effect of various metal core sizes, various noble metals loading amount and the hydrothermal temperature were investigated. The results showed the small metal core size had slightly higher activity than the larger ones, and the optimal amounts of Au and Ag loading were 1wt. % and 0.5 wt. %, respectively. Furthermore, the sample with the highest hydrothermal temperature had the highest activity due to the highest crystallinity.
From these results, the photocatalytic activity of Metal@TiO2 catalyst mainly depended on the crystallinity of TiO2, the amount of noble metal loading and the kinds of cocatalyst rather than the size of noble metal core.
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