Visible Light Photocatalytic Activities Of Ag₃PO₄ Composites

In recent years, the rapid development of industry leads to the growing salience of environmental concerns, especially from the organic contaminants. Since the semiconductor photocatalytic materials demonstrate the function in H2 generation from water splitting and degradation of organic dyes, there have been a lot of reports about improving photocatalytic properties of semiconductor complexes. However, the conversion efficiency of solar energy is still beyond to application, and thus developing novel visible light photocatalysts to improve the catalytic activity is the focus of material science.The discovery of Ag3PO4 demonstrating good visible light photocatalytic activity activates the systematic study on improving catalytic activity and chemical stability with Ag3PO4. At present, the research works of catalytic activity and chemical stability based on Ag3PO4 are mainly concentrated on the following fields: 1. The influence of morphology on catalytic activity, such as irregular sphericity, tetrahedral, cubic and rhombic dodecahedron Ag3PO4. 2. The surface-related effects of Ag3PO4 coupled with other materials, such as silver halides, graphene oxide, carbon nanotubes and silver. 3. The doped effects both inside and outside of Ag3PO4 combined with other materials, such as In(OH)3. The basic idea of mentioned-above strategies to improve catalytic activity Ag3PO4 is to increase the efficient separation time of photogenerated electron-hole pairs. Based on the research background of Ag3PO4 photocatalytic activity, this thesis will focus on two kinds of new catalytic composites combining Ag3PO4 with metal and carbon-based to improve the catalytic activity of Ag3PO4 and the involved photocatalytic mechanisms. The major results are summarized as following:(1) Ag3PO4/Ag nanowire composite system: Ag nanowires were firstly fabricated through a modified polyol process. Then Ag3PO4 and Ag3PO4/Ag nanowires composite were synthesized by the precipitation and in-situ precipitation method, respectively. The characterization results of XRD and SEM indicate little change of the composite morphology, but some differences on crystal phases. Together with results of UV-Vis, SEM and XRD, it can be confirmed the formation of Ag3PO4-Ag nanowire composite. The photocatalytic activities of as-prepared samples have been evaluated by eliminating Rhodamine B under visible light(>400 nm). The results demonstrate that Ag3PO4/Ag nanowire composite exhibits higher photocatalytic activities than that of individual Ag3PO4 and Ag nanowires, and the highest activity can be observed over the Ag3PO4/Ag with a molar ratio of 1:0.17. The mechanism analysis suggests that the improvement of photocatalytic performance arises from the more efficient separation of photogenerated electron-hole pairs.(2) Ag3PO4/Multiwalled carbon nanotubes(MWCNTs) composite: MWCNTs were acidified by concentrated nitric acid and sulfuric acid, and then Ag3PO4 and Ag3PO4/MWCNTs composite were synthesized by the precipitation and in-situ precipitation method, respectively. The photocatalytic activities of as-prepared samples were evaluated by eliminating Rhodamine B under visible light(>400 nm). The obtained results indicate that Ag3PO4/MWCNTs composite demonstrate a higher photocatalysts activity than that of individual Ag3PO4, although it has been found that the morphology, size, and crystal phase of Ag3PO4 and the composite are similar from the results of SEM, XRD and UV-vis DRS. The improved photocatalytic activity of composite can be attributed to the efficient reducing recombination of photogenerated electron-hole pairs.In a word, we have successfully obtained two kinds of visible light photocatalytic composites by combined Ag3PO4 with Ag nanowires and MWCNTs. The effective combination of Ag3PO4 with Ag and MWCNTs efficiently decreases the recombination of photogenerated electron-hole pairs, and thus improves the stability and photocatalytic activity of Ag3PO4. The results will be of significance in improving stability and photocatalytic activity of Ag3PO4-based or other semiconductor materials, and in developing new photocatalyst devices.