| Nowadays,with the improvement of people's living standards,people's expectation for a better life is becoming more and more pressing.However,environmental pollution and energy shortage are two main problems that impede the sustainable development of human society.Since the Japanese scientist Fujishima found nano-TiO2 can decompose water under illumination in 1972,semiconductor photocatalytic technology has developed rapidly in the next few decades due to its environmental protection and direct use of solar light.It has become a very potential technology to govern environmental pollution and to produce clean energy.At present,the major research directions of photocatalyst include decomposition of water,degradation of organic or inorganic pollutants,reduction of carbon dioxide,etc.In the field of life,photocatalytic technology involves air and water purification,fruit and vegetable preservation,new energy vehicles and household appliances,which have broad application prospects.However,the low photocatalytic efficiency affects the large-scale industrial application of photocatalytic technology seriously.The factors affecting photocatalytic efficiency include light absorption,carrier separation efficiency,crystal structure,specific surface area and grain size of semiconductor.At present,the light absorption,crystal structure,specific surface area and grain size of semiconductors can be solved by improving experimental conditions and methods,so carrier separation efficiency becomes a major factor which limits photocatalytic efficiency.How to use effective ways to improve the separation efficiency of carriers has great significance for improving the efficiency to degrade of ethylene and to produce hydrogen.Here,three effective methods are used to promote the efficient separation of carriers,which are loading precious metals,doping,and constructing heterojunctions.The main contents are listed as follows:In the first chapter,we briefly introduced the basic principles,research background and current main research directions of photocatalysis technology,and then introduced the main application fields of photocatalysis technology,including gas phase degradation and hydrogen production.We also summarized several effective ways to improve carrier separation efficiency and construct high-efficiency photocatalyst.Then the significance and research content of this paper are presented.In the second chapter,we mainly introduced the method of loading noble metals to improve the efficiency of carrier separation.Pure ZnO has very low ethylene degradation efficiency.After photo-reduction and annealing methods,Au or Ag supported ZnO are synthesized(Au/ZnO and Ag/ZnO).The experimental data explain the degradation efficiencies of single metal-supported Au/ZnO and Ag/ZnO are 17.5 and 26.8 times than that of pure ZnO,indicating that the load of noble metals can effectively improve the photocatalytic efficiency.Then we modified the noble metal and synthesized the bimetallic alloy AuAg supported ZnO(AuAg/ZnO),and we found AuAg/ZnO has good cycle stability,and the degradation efficiency is 94.8 times than that of pure ZnO,indicating the plasmon resonance effect and the synergistic effect of Au and Ag can jointly promote electron transfer and enhance separation efficiency of carriers,thereby greatly improving the efficiency of ethylene degradation.This work has obtained a high activity and high stability photocatalytic material,and proposed a new idea of bimetallic alloy for photocatalytic degradation of ethylene.In the third chapter,we mainly introduced a method of semiconductor doping to improve the carrier separation efficiency.Firstly,Fe-doped WO3 was prepared.And the effect of Fe doping concentration on degradation of ethylene was studied.It was found that doping Fe has better degradation of ethylene activity than WO3.This was because pure WO3 products are easily reduced by electrons under illumination,which affects photocatalytic activity.When Fe3+ was incorporated into the lattice of WO3,due to the reduction potential of Fe3+/Fe2+ is more positive than W6+/W5+,Fe3+preferentially obtained electrons than W6+ under illumination conditions,which increasing the separation of electrons and holes in WO3 and avoiding the WO3 being reduced by itself.On this basis,we loaded Pt on Fe-doped WO3 to make electrons transfer to Pt,which further increases the effective separation of electrons and holes.The efficiency of Pt@Fe-WO3 to degraded ethylene is 3.3 times higher than that of pure WO3 under visible light,More importantly,the stability of the catalyst Pt@Fe-WO3 is very good,that is,the activity can still be completely maintained after 9 tests of photocatalytic cycle.In the fourth chapter,we mainly introduced the method of constructing heterojunction to improve the efficiency of carrier separation.Firstly,the Z-type g-C3N4/WO2.72 heterojunction was obtained by hydrothermal method.It was found that the hydrogen production activity of the g-C3N4/WO2.72 heterojunction is about 4 times that of pure g-C3N4,because the carrier separation efficiency was increased due to the special electron transfer way of the Z-type heterojunction.After that,we placed three kinds of electronic wires in the heterojunction:that are,carbon quantum dots(CQDs),graphene oxide(RGO)and indium tin oxide nanoparticles(ITO NPs).The hydrogen production activities of obtained g-C3N4/ITO/WO2.72,g-C3N4/RGO/WO2.72,g-C3N4/CQDs/WO2.72 were 10 times,14 times,and 24 times than that of pure g-C3N4,respectively.So it is an effective mean to improve photocatalytic activity by constructing a heterojunction and placing an electron wires to promote efficient separation and separation of electron holes.In the fifth chapter,we summarize the paper,analyze and discuss the innovations and deficiencies of this paper,and looks forward to the next step. |
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