Study On The External-Field-Assisted Semiconductor Photocatalytic Performance

Semiconductor photocatalysis technology is a kind of advanced oxidation process(AOPs),which can convert solar energy into chemical energy,that is often uesd to degrade organic pollutants,produce hydrogen and oxygen,and reduce CO2,etc.However,low photocatalytic efficiency caused by high photoinduced carrier recombination rate is a bottleneck restricting the development of photocatalytic technology and the application in practical industrial production.Therefore,how to improve the efficiency of photocatalysis has become the main task in the field of energy research.In recent years,the use of different non-contact fields to assist semiconductor photocatalysis has attracted the attention of researchers.According to the characteristics of different catalysts,introducing an appropriate external field in the process of photocatalysis can effectively accelerate the carrier separation rate and improve the degradation performance of organic pollutants.For example,the cavitation effect of ultrasonic field can be used to assist photocatalysis.The magnetic catalyst can use the magnetic field to regulate the spin polarization,so as to promote the photocatalytic reaction.The effect of external field synergistic photocatalytic reaction can be analyzed accroding to the synergistic index SI(taking ultrasonic synergistic photocatalysis as an example,SI=k(US+UV)/(kUS+kUV)),and the synergistic effect of external field can be explained.The specific content of this thesis is divided into the following five chapters:Chapter 1:The development history,the principle and the restrictive factors of photocatalysis technology were introduced.Two kinds of modification methods were proposed to solve the above technical bottleneck,respectively from the improvement of the photocatalyst and the external field assist.Chapter 2:The chemical reagents required,the methods for sample preparation,and the instruments for characterization of samples were introduced.Chapter 3:TiO2 samples of two crystalline phases,namely nanorod-like rutile phase and nano-flake anatase phase,were grown on carbon fiber paper by hydrothermal method.The crystal phase and microstructure of the samples were characterized,the spectrum and band structure were analyzed,the carrier migration rate of the two samples was characterized by PEC photoelectric performance test,the photocatalytic performance of the samples under different light sources was tested,the ultrasonic assisted photocatalytic reaction was studied,and the total reaction oxygen generation in the reaction process was tested.The quantities of ·O2-and ·OH were measured quantitatively.Finally,combined with free radical capture experiments,the unique two-step formation pathway of OH in the ultrasonic assisted photocatalytic reaction was analyzed.Chapter 4:Using rutile phase TiO2 nanorods in Chapter 3 as catalyst.The samples were immersed in different concentrations of H2O2 to adjust the oxygen vacancy content of the samples.XRD and SEM were used to characterize the crystal phase and microstructure of the samples.XPS and EPR were used to analyzed the concentration of oxygen vacancy in the samples.On one hand,increasing the oxygen vacancy content appropriately can improve the samples’ absorbance and band gap.On the other hand,the photocatalytic performance was also improved.The catalytic efficiency is found to be enhanced remarkably under the case of visible light assisted with ultrasonic wave,.in comparison with the case of light or ultrasonic wave,which indicates there exist a positive ultrasonic synergy effect.In addition,PEC photoelectric performance test indicated that carrier mobility was closely related to the concentration of oxygen vacancy.Chapter 5:Firstly,single-phase BaTiO3(BTO)was prepared by hydrothermal method.XRD and Raman indicate a tetragonal distortion of BTO.Secondly,BaTiO3-CoFe2O4(BTO-CFO)was prepared by hydrothermal method and molten salt method.The lattice morphology and element distribution of heterojunction were characterized.The SI value of BTO-0.2CFO is the highest coupled with the magnetic field,and the magnetic field synergy effect is the best.In addition,VSM test shows that has magnetic properties and can be used for magnetic recovery,effectively avoiding the problem of secondary pollution.Summary:The research of the external field assist semiconductor photocatalysis was summarized,and the future work was prospected.