Development Of Plasmonic Photocatalyst By Site-selective Loading Of Bimetallic Nanoparticles Of Au And Ag On Titanium(?) Oxide

In the process of economic development and industrialization,facing the problems of energy consumption and environmental pollution,it is urgent for those countries to develop clean energy and control environmental pollution.Since the 1970s when Fujishima and Honda found that hydrogen could be produced by the electrocatalytic cracking of water with carbon dioxide(TiO2),researchers have conducted extensive research on TiO2 materials because of its excellent chemical stability,safety,non-toxic,low price and suitable redox ability.TiO2 material has been the research hotspot of researchers.At the same time,it has been widely used in solving the problems of energy consumption and environmental pollution.Before photocatalytic reaction,TiO2 materials need light with energy larger than the band gap width,and then produce electron hole pairs,which are transferred to the surface of TiO2.Finally,the electron hole reacts with substance adsorbed on the surface of TiO2.In the practical application process,TiO2 materials have two obvious limitations:(1)TiO2 has a large band gap and can only use the ultraviolet part of the sunlight,while the proportion of ultraviolet in the sunlight is very small.(2)TiO2 photo generated electron hole carrier has a large recombination rate.These two limitations greatly limit the photocatalytic activity.In order to overcome the influence of the limitation of TiO2 on the photocatalytic activity,the researchers tried to improve TiO2 from the following aspects:broadband narrow-band semiconductor composite,dye sensitization,metal/non-metal ion doping and metal nanoparticles modification,etc.Among them,the modification of metal particles extends the light response of TiO2 from ultraviolet to the visible light through the local plasmon resonance effect(LSPR).Because the method of preparing metal particles modified semiconductor is less difficult than the wide and narrow band semiconductor composite method,and it overcomes the problem of shorter photocatalytic reaction life caused by dye sensitization and the problem of easy recombination of electron hole pairs caused by metal ion doping,which causes the researchers to pay close attention.In this paper,rutile TiO2 and anatase TiO2 with morphology-controlled faces were prepared by hydrothermal synthesis,in which a proper amount of crystal forming agent was added or the hydrothermal temperature and time were adjusted appropriately.By comparing the ability of photocatalytic oxidation of 2-propanol of rutile TiO2 and anatase TiO2,the appropriate TiO2 was selected as the substrate for supporting metal nanoparticles.In this paper,Au or Ag metal nanoparticles with local plasma effect were loaded on the reduction sites(reduction face)of TiO2 by photo-deposition.TiO2 modified by Au or Ag nanoparticles has light absorption in the visible light region,and its light absorption intensity will not affect the photocatalytic reaction efficiency.In addition,the specific surface area of Au-TiO2 or Ag-TiO2 composite does not affect the photocatalytic reaction efficiency.The optimal loading amount of Au on rutile TiO2 and anatase TiO2 is 1 wt%and 0.25 wt%,respectively.In the three times of photocatalytic cycle endurance test,the photocatalytic activity of Au in the third time keeps at 96.5 wt%and 94.4 wt%of that in the first time,respectively.The optimal loading amount of Ag on rutile TiO2 and anatase TiO2 is 1 wt%and 0.25 wt%,respectively.In the three times of photocatalytic cycle endurance test,the photocatalytic activity of Ag in the third time keeps at 30.8 wt%and 28.1 wt%of that in the first week,respectively.The photocatalytic activity of Au modified photocatalyst is better than that of Ag modified photocatalyst.In this paper,AuAg-TiO2 composite material was also prepared by photo-deposition method.Through the analysis methods of XRD,SEM,TEM and EDS mapping,it was determined that AuAg bimetallic nanoparticles were successfully loaded on the reduction sites of rutile TiO2 and anatase TiO2.By testing the photocatalytic activity and photocatalytic cycle endurance test of the prepared samples under visible light,it was found that AuAg nanoparticles modified TiO2 had not only good photocatalytic activity,but also good photocatalytic cycle enduranceThe study found that for the enhancement of the photocatalytic ability by the plasma effect,the rutile TiO2 modified by Au or AuAg metal nanoparticles is stronger than the anatase TiO2 modified by Au or AuAg metal nanoparticles.In order to explain the cause of this phenomenon,we further tested its electron transfer method using double-beam photoacoustic spectroscopy,and found that the electrons on the valence band of rutile TiO2 modified by Au/AuAg metal nanoparticles were excited and transferred to the trap energy level,and then transferred from the trap level to the electron-deficient metal nanoparticles.And the electrons in the anatase TiO2 are generated by the metal nanoparticles and transferred to the trap energy level,and then transferred from the trap energy level to the conduction band.The oxidation reaction of the former occurs on the valence band,and the oxidation reaction of the latter occurs on the metal nanoparticles.Eventually,the rutile TiO2 modified by Au/AuAg metal nanoparticles has a strong photocatalytic ability to degrade organic matter.