Preparation And Properties Of Precious Metal Supported TiO 2 Submicron Photocatalyst

In recent years, along with the rapid development of social economy, the excessive consumption of fossil fuels, like fossil oil, produce heavy emissions of pollutants and exacerbate the environmental pollution, which brings a great threat to the health of human beings. Water pollution is one of the biggest problems that need to be solved in the world. Photocatalytic technology is a kind of advanced oxidation technology for treatment and purification of the polluted water. It is developping so rapidly in recent years that the research and application of photocatalytic technology is becoming a new area. Photocatalytic technology shows its unique advantages on treatment of many poisonous and harmful organic pollutants. And it fully exhibits a broad prospect of application in the field of environmental protection. Environmental pollution and energy shortage is the two problems that urgently need to be solved for the development of the human society. Hydrogen with high energy density is clean to environment and easy to use which is considered to be an ideal energy carrier. Photocatalytic hydrogen production with solar is a kind of low cost, integrating light energy transformation and storage. However, the key to the use of photocatalytic technology is to research and develop efficient photocatalytic materials.One of the key issues for photocatalytic materials is to promote the separation of charge carrier. Noble metals decorated on the surface of TiO₂ can form Schottky barrier which will become the electron trap and prevent the electrons transfer back to TiO₂. Thus, it takes advantages for electrons transfer and restrains the separation of charge carrier which prolong the life of charge carriers. Aim at this issue, we synthesize a series of Pt/TiO₂ and Au-Pt/TiO₂ photocatalysts. And we analyze the structure and morphology of the photocatalysts through characterizations of XRD, BET, TEM, XPS, DRS and so on. We also test the degradation of organic pollutants and the activity of hydrogen production. The work mainly divided into the following three parts.（1） Among the numerous methods of synthesizing Pt/TiO₂, photodeposition is widely used due to its simple operation. Firstly, we modulate the Pt loading amount and the type of sacrificial agent to synthesize a series of Pt/TiO₂ photocatalysts. Here, we choose five sacrificial agents including methanol, ethanol, ethylene glycol, glycerin, isopropyl alcohol. Through the test of phenol photodegradation, we find that TiO₂ decorated with Pt reduce the photodegradation rate. According to the UV-Vis adsorption spectrum of phenol during the photodegradation, Pt/TiO₂ change the phenol degradation route comparing to the bare TiO₂. However, comparing with the bare TiO₂, Pt/TiO₂ enhance the photocatalytic activity of methyl orange photodegradation and hydrogen production.（2） The mainly used methods in published papers of synthesizing Pt/TiO₂ may be photodeposition, H2 reduction, Na BH4 reduction, HCHO reduction and deposition precipitation. Comparing different methods, Pt/TiO₂ synthesized by H2 reduction exhibits highest photocatalytic activity of hydrogen production. Pt/TiO₂ synthesized by Na BH4 reduction in the second place. The Pt state in Pt/TiO₂（synthesized by H2 reduction） is mostly Pt0 through the investigation of Pt4 f XPS spectrum.（3） Synthesizing bimetal Au and Pt decorating on TiO₂ by photodeposition. We change the photodeposition order to obtain a series of Au-Pt/TiO₂ photocatalysts and then investigate their photocatalytic activity of hydrogen production. What we find is that the photocatalyst 1.0 wt% Au-1.0 wt% Pt/TiO₂ that photodeposition Au firstly then Pt secondly shows better photocatalytic activity of hydrogen production than other photocatalysts. Since the sacrificial agent is excessive during the two step photodeposition, we investigate whether the existence of sacrificial agent influence the second step photodeposition of Pt. We find that if there is no sacrificial agent during the second step photodeposition of Pt, the photocatalytic activity of hydrogen production of the sample will has an enhancement. Through analyzing the TEM images, the Pt nanoparticles that come from second step photodeposition overlap on the Au nanoparticles and deposite on the surface of TiO₂ which deposited Au nanoparticles. Meanwhile, according the analyzation of TEM, EDX and XPS results, the Au nanoparticles from 1.0 wt% Pt-1.0 wt% Au/TiO₂ which photodeposition Au firstly then Pt secondly display different particle size and loading amount compared to the Au nanoparticles from 1.0 wt% Au-1.0 wt% Pt/TiO₂.