| Since the second industrial revolution,along with the rapid development of human society and the increasing demand for people’s lives,environmental pollution and energy shortage have become two major global problems that threaten human survival and affect social progress.Because of its abundant reserves,cleanliness and pollution-free characteristics,solar energy has become a new renewable energy with development prospects,which has important potential applications in solving future human social energy and environmental problems.Photocatalytic technology is a new technology that can effectively utilize solar energy and can convert low-density solar energy into high-density chemical energy,which is considered to be one of the most promising solutions to future energy shortages and environmental pollution problems.Since 1972,Fujishima successfully realized photocatalytic decomposition of water to produce hydrogen and oxygen on titanium dioxide photoelectrodes,photocatalytic technology has received extensive attention from scientists all over the world.However,the current low photocatalytic efficiency is a bottleneck restricting the further development and wide application.Therefore,it is of great significance to further improve the photocatalytic efficiency and design new high-efficiency photocatalytic materials.Among the many factors that restrict the photocatalytic efficiency,the separation efficiency of photogenerated carriers is one of the most important factors.To deposition of a metal cocatalyst on a semiconductor photocatalyst has been considered to be an effective method for promoting photo-generated carrier separation,thereby improving photocatalytic activity.At present,the research of metal cocatalyst is mainly concentrated on precious metal materials,which is lack of research on the control and mechanism of the load process.Therefore,from the perspective to promote carrier separation,the surface modification of metal cocatalyst on photocatalytic materials is carried out,and then the loading process and mechanism of metal nanoparticles are explored.Simultaneously,the alternative materials for precious metal promoters are investigated.In the first chapter,the research background,basic principles,applications and research status of semiconductor photocatalysis technology are briefly described.Then,the constraints of semiconductor photocatalysis technology are analyzed.Aiming at the two problems of narrow photo-response range and low photon efficiency which restrict the development of photocatalytic materials,the common methods for synthesizing high-efficiency photocatalytic materials are summarized.The mechanism and research status of metal promoter strengthen composites are mainly analyzed based on Ag/TiO2 composites and Pt/g-C3N4 composites.Finally,the significance and research content of this paper are introduced.In the second chapter,we studied the preparation,characterization and photocatalytic properties of Agn+/TiO2 composites.We synthesize TiO2 with high exposure(001)active surface with hydrothermal way.And the Ag clusters were supported on the(001)oxidation surface of the TiO2 by in-situ photodeposition.Ag clusters on the high active oxidation surface become oxide and assembled into Agn+clusters.Agn+ clusters could play a role of transferring photogenerated holes.Compared with pure TiO2,Agn+/TiO2 composites have better photocatalytic activity of CO2 reduction.In Agn+ clusters,Ag0 can capture holes and be oxidized by holes to convert to Ag+.Subsequently,Ag+ can be irradiated under visible light and turns into Ag0,which forms a cycle of Ag0 and Ag+ in the aqueous phase.The test results show that the ratio of Ag0 and Ag+ can be adjusted by changing the processing temperature.And the proper ratio of Ago and Ag+ is one of the key factors affecting the catalytic efficiency.In the third chapter,we studied the preparation,characterization and photocatalytic properties of Pt/Bi/g-C3N4 composites.In this work,we adopted a method of loading metal Bi first and then loading metal Pt on Bi/g-C3N4,so that the metal Bi could partially replace the noble metal Pt to enhance the photocatalytic hydrogen production of carbonitride.The experimental results show that the Pt and Bi co-loaded on g-C3N4 can greatly reduce the amount of Pt(over 60%),and can further improve the photocatalytic hydrogen production activity of g-C3N4.The increase in photocatalytic activity is attributed to the synergistic action of the bimetals(Bi and Pt)and the core-shell structure of the Pt-coated Bi.On the one hand,the Bi replaces a part of action to collect electrons of Pt,which also ensures that the H+ reaction occurs on the surface of the metal Pt,thereby improving the utilization rate of the metal Pt.On the other hand,the synergistic action of the bimetal further enhances the separation efficiency of the photogenerated carriers.In the fourth chapter,we first summarize the main research contents and conclusions of this thesis,then enumerate the main innovations of this paper,and finally analyze and put forward the shortcomings of this paper.At the same time,the next step research plans were elaborated.In summary,the process of loading the metal promoter and the control of the load position have a special effect on improving the photocatalytic activity;the core-shell structure of the bimetal is an effective method to improve the utilization of precious metals;the synergy of the bimetals help further improve the photo-generated carrier separation efficiency of the photocatalytic material. |
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