| Photocatalysis is an emerging, cross-disciplinary research field, which provides people with new solutions using solar energy to solve energy and environmental problems. There are many substances with optical activity, such as metal oxide semiconductors. particular types of dyes and heteropoly acid. as well as the compounds synthesized with those materials. Among those substances, layered double hydroxides (LDH) is a kind of anionic inorganic clay materials, whose application in the field of photocatalysis is arousing more and more attention from scientists. With its special layered structure, great adsorption capacity for anions, and its simple synthesis methods, LDH is quite suitable to act as a photocatalytic material, and its photocatalytic performance can be easily modified through additional substance loading or the change of the metal composition.Following this topic on the special structure of LDH and the easy modification of its photoactivity, this paper is focused on the study on the UV catalytic activity of Fe-contained ZnAl LDH and the visible light sensitization catalytic activity of the metal phthalocyanine loaded ZnAl LDH. This work is contained two parts:Part I:in this chapter, we added Fe onto the ZnAl LDH layered skeleton by co-precipitation method. The physical properties of the ZnAlFe LDH and their calcined products are characterized through a variety of analytical methods. Results showed that Fe dopped on the lattice is negative to the thermo stability of ZnAl LDH structure. After calcined in a lower temperature, Fe contained in the catalysts formed FexOy. As the activation temperature increased. Fe oxides reacted with the ZnO and formed into compositions of spinel structure. UV irradiated photocatalytic degradation experiments of phenol in aqueous solution were taken out to characterize the photocatalytic activities of the series of ZnAlFe LDH. We found that the Fe added decreased the UV irradiated photocatalytic activity. And combined with the catalyst structure analysis, we believe this is due to the impediment effect of the structured Fe to the growth of ZnO grains, and the poor photoactivity of the formed FexOy, which failed to perform a positive interaction with ZnO under our experimental conditions.PartⅡ:we modified ZnAl LDH with metal phthalocyanine by adsorption in the purpose to give ZnAl LDH visible-light activity by the dye-sensitization process, as well as to achieve the immobilization of the water-soluble zinc phthalocyanine (ZnPc) to avoid the secondary pollution of the dissolved dye species. Characterization of the samples before and after adsorption showed that ZnPc immobilization on the LDH was well realized. XRD data showed changes in the layerd structure, but with hardly any increase of the layer space distance after the MPc loaded, which indicated that the adsorption of the MPc molecular was only occurred on the LDH surface instead of inserting between the layered structures. Catalysts loaded with ZnPc performed a well absorbance to the visible light, and two markedly adsorption peaks were analyzed betweenλ400-800 nm. UV-vis DRS of ZnPc before and after immobilization were also determined. The spectra of absorption peaks were red shifted and became wider after loaded onto ZnAl LDH, but no obvious changes appeared in the spectral shape, indicating that interaction did occur between ZnPc and the carrier, but the phthalocyanine structure was not destroyed during the immobilzation. The photocatalytic degradation of 4-chlorophenol under visible light over ZnPc/LDH was studied and optimization experiments were carried out to investigate the influence of different reaction conditions. The best photocatalytic activity in this work was achieved using ZnPc/ZnAl-2-300(1%ppm) as the catalyst at pH 12 when the substrate was completely decomposed within 3h's visible light irradiation. |
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