Preparation And Photocatalytic Performance Of Metal-modified CdMoO₄

Cadmium molybdate is a kind of luminescence substrate materials with good chemical stability which is reported to be a photocatalyst under UV irradiation. So far, cadmium molybdate has been successfully prepared via various methods. And the way to improving the photocatalytic reactivity was also studied, while, most of the studies focused on changing the preparation methods to adjust the morphology, The other modification methods such as doping to improve the photocatalytic activity are few. Therefore modification of the cadmium molybdate to improve the photocatalytic activity is worth researching.In the thesis, ⅢA metal elements (Al, Ga, In) and noble metal (Ag, Au) modified cadmium molybdate were successfully prepared by hydrothermal method and Sodium borohydride reduction method, respectively. The composition and structure of the catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), Raman spectroscopy and Fourier-transform infrared spectroscopy (FT-IR) techniques. The photo-response and surface state of the catalysts were detailedly investigated by UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic degradation of rhodamine B (RhB) was used as the model reaction to evaluate the ultraviolet photocatalytic performance and the selective oxidation of benzyl alcohol was used to evaluate the photocatalytic activity under visible light irradiation. Meanwhile the mechanism of the degradation was also studied.The main results and conclusions obtained from the present research are as follows:(1) The ⅢA metal elements were introduced into cadmium molybdate successfully and the valence of the meal elements are all+3. It was found that Al3+and Ga3+ have been introduced into the interstitial void of cadmium molybdate crystal, while, due to the larger atomic radius of In3+, only part of them was introduced into the interstitial void of cadmium molybdate crystal, and another part of them existed on the surface of the crystal. The introduced metal ion to the interstitial void of cadmium molybdate can cause lattice distortion, and thus can improve the photocatalytic activity of cadmium molybdate greatly. Instead, the introduction of In3+ showed a lower phototocatalytic activity compared to cadmium molybdate owing to the existence on the surface of cadmium molybdate crystal as the recombination center of photon-generated carriers,. The degradation mechanism of rhodamine B (RhB) over cadmium molybdate under UV light stayed unchanged after the moditication of the ⅢA metal elements (Al, Ga and In), but the ratio of the effective active radical have changed.2. Noble metal particles reduced by sodium borohydride existed on the surface of the crystal with zero valent state. The photocatalytic activity of cadmium molybdate under UV light increased greatly because of the larger ability of the transfer of the electronafter the deposition of the noble metal (Ag, Au). With the increasing amount of noble metal particles, the photocatalytic activity decreased, due to some noble metal particles became the recombination center of electrons and holes. Due to the local surface plasmon effects of noble metals, cadmium molybdate have photocatalytic activity under visible light after depositing noble metal for the selective oxidation benzyl alcohol to benzaldehyde and the selectivity is 100%. It was found that deposition of the nobel metal did not change the photocatalytic mechanism of cadmium molybdate through the comparison of the photocatalytic activity beween cadmium molybdate and cadmium molybdate deposited the noble metal, under UV light, while, the ratio of the effective active radical has been changed.