Controllable Synthesis Of Iron-based Two-dimensional Semiconductor Materials With Enhanced Photocatalysis Activity

Coal,oil,natural gas and other fossil energy support the rapid development of human society,but the non-renewable characteristics and human over-exploitation lead to the gradual exhaustion of these fossil energy.Moreover,the greenhouse gases（CO,CO₂,etc.）released by burning these energy also lead to global warming,glacier melting and abnormal weather.Therefore,it is extremely urgent to research and explore green renewable energy.Up to now,the researchers have made various explorations in solving the problem.Solar energy is considered as the ideal energy to solve the problem of fossil energy shortage and reduce environmental pollution because of its inexhaustible and renewable characteristics as well as the advantages of cleanness and no pollution.By simulating plant photosynthesis,it is a good solution to convert solar energy into hydrogen energy by utilizing the characteristics of semiconductor materials that can be simulated by solar energy.In recent years,photocatalytic technology has been widely used in environmental protection fields such as pollutant degradation,and has also achieved significant economic benefits.In addition,the researchers find that solar energy has considerable application prospects faced with energy crisis.Converting solar energy into pollution-free,highly efficient and storable hydrogen,hydrocarbon fuel and other fossil energy?the use of photocatalytic technology has become an important research direction of future energy development.Hydrogen energy has the characteristics of clean,high calorific value,good combustion stability,and can be preserved in the form of gaseous,liquid or solid metal hydrides,which can adapt to different requirements of various application environments.At the same time,the by-product of hydrogen energy is water,which is environmentally friendly and an ideal renewable secondary energy.The optimal photocatalytic water splitting can directly generate hydrogen and oxygen.However,due to the complex process of four-electron transfer,H-O bond breaking and O-O bond formation and other chemical kinetics problems,oxygen generation reaction has become the rate-determining step of the photocatalytic water splitting.In order to further understand the reaction mechanism,the oxygen generation reaction was isolated and studied.Among those materials,Fe-based semiconductor materials have drawn much attention due to their low cost,simple synthesis,stable structure and excellent photocatalytic water decomposition performance.The synthesis and optimization of related materials are also worthy of our further research and development.This thesis mainly focuses on the controllable synthesis of iron-based two-dimensional semiconductor photocatalytic materials and explores their photocatalytic oxygen generation performance,which is mainly discussed from three aspects:1.One-step solvothermal formation of Pt nanoparticles decorated Pt²⁺-dopedα-Fe₂O₃ nanoplates with enhanced photocatalytic O₂ evolutionIn this chapter,Pt nanoparticles decorated Pt²⁺-dopedα-Fe₂O₃ nanoplates have been synthesized by a one-step solvothermal method,which exhibit the highest photoactivity and photostablity for water oxidation.The introduction of the Pt into theα-Fe2O3 by the means of elemental doping and nanoparticle decoration accounts for the enhanced performance.The doping of Pt²⁺intoα-Fe₂O₃ lowers the differences between the short and long bonds to O atoms,which boosts the state of hybridization and thus improves the charge transport thus remarkably increase the lifetime of hole carriers.And the adherence of metal Pt nanoparticles to the surface ofα-Fe2O3 leads to formation of the schottky barrier at the interface which effectively impedes the combination of photogenerated electrons and holes.Therefore,Pt/Pt-Fe₂O₃ NPs show better photocatalytic water oxidation performance.2.One-step solvothermal formation of metal nanoparticles decorated metal ion dopedα-Fe2O3 nanoplates with enhanced photocatalytic O2 evolutionIn this chapter,we synthesized different metal particles loaded metal ions dopedα-Fe₂O₃ nanoplates by one-step solvothermal method,respectively.We found that theα-Fe₂O₃ NPs have the"self-purification"ability by doping different ions,which cannot be fully doped regardless of whether the doped ions have the same radius with Fe³⁺.With the increase of ion radius,the concentration of doped ions decreases gradually.Ethanol,as a solvent,has a weak reducibility.When the ions with positive redox pairs that do not enter the lattice are reduced to metal particles in the solution under high temperature and pressure,they can be attached to the material surface.This internally doped iron oxide supported by surface metal particles exhibits better photocatalytic water oxidation ability.3.Hydrothermal synthesis of Bi₂Fe₄O₉ nanoplates with tunable thickness to enhance photocatalytic oxygenHerein Bi₂Fe₄O₉ nanoplates with tunable thickness were successfully synthesized by an hydrothermal method with different contents of sodium dodecyl benzene sulfonate（SDBS）ranging from 0 g to 2 g.Reducing thickness can improve the separation efficiency of electrons and holes and reduce the charge transfer resistance,greatly.Therefore,the photocatalytic activity of the material can be improved significantly.The BFO-2 shows excellent photocatalytic H₂O oxidization performance under visible light irradiation with O₂ evolution rate of 461.084μmol g^-1 h^-1,which is about 7.87 times higher than primitive Bi₂Fe₄O₉(BFO,58.55μmol g^-1 h^-1).