Preparation And Catalytic Activity Of α-Fe₂O₃

With the accelerating industrialization in the world and the rapid population growth,the demand for energy is also rapidly increasing.At present,the vast majority of global energy consumption comes from fossil fuels,and the massive consumption of these fossil fuels has brought about two major problems of energy crisis and environmental pollution.Developing and utilizing clean,renewable energy is an effective way to solve both these problems.Photoelectrochemical decomposition of water to hydrogen technology can convert a steady stream of solar energy into clean,storable hydrogen energy,it has received great attention.Photocatalytic technology is the use of solar energy to organic pollutants into inorganic small molecules,can be used to deal with sewage,is a cheap and environmentally friendly method.The problem of energy crisis and environmental pollution can be solved perfectly by photoelectrochemical decomposition of water to hydrogen production and photocatalysis.As a kind of narrow bandgap n-type semiconductor,α-Fe2O3 is a kind of ideal photoanode material and photocatalyst,which has an increasingly suitable forbidden band width and absorbs most of the visible light.It is stable and inexpensive,non-toxic and non-polluting Aroused people’s attention.However,α-Fe2O3 itself has some defects,such as:easy to compound photo-generated carriers,surface oxygen production kinetics is slow,poor conductivity,weak light absorption and other shortcomings seriously hampered its application.In this thesis,α-Fe2O3 thin films and powders were prepared by magnetron sputtering and hydrothermal method,respectively,and then a series of surface modification treatments such as cationic doping and heterojunction fabrication were carried out to improve their photoelectrochemical properties and light Catalytic activity,and studied the modification mechanism,the conclusions obtained are as follows:(1)DC magnetron sputtering method was used to deposit Fe and Pt films with good crystallinity on the FTO glass substrate,and the best sputtering process was explored.On this basis,the sample was placed in a thermal oxidation furnace for oxidation,thus preparing a Pt-doped α-Fe2O3 thin film.After the optimization of the thermal oxidation process,the samples incubated at 600℃/2 h show the best photoelectrochemical properties.By changing the substrate heating temperature(300,400,500 and 600℃)during magnetron sputtering,different thin film samples were prepared.The prepared samples were tested for their structures and photoelectrochemical properties.X-ray diffraction patterns show that the two peaks of the prepared Pt-doped α-Fe2O3 films corresponding to(104)and(110)respectively.The results of X-ray photoelectron spectroscopy show that Pt in the fabricated film oxide as PtO2.Ultraviolet-visible spectroscopy showed that the best absorbance of the sample was obtained when the substrate was heated at 500℃.(2)Research on photoelectric conversion mechanism.The study found,the photo current density of Pt-doped α-Fe2O3 thin films increased by one order of magnitude compared with that of pure α-Fe2O3 thin films at 1.23 V vs RHE,which indicated that Pt could significantly improve the photoelectrochemical properties of the samples.There are two main reasons for this enhancement.First,Pt is a precious metal.The work function is different from that of a semiconductor,which is ΦM>ΦS.In this way,photogenerated electrons are transferred from the semiconductor to the metal surface.So the photo-induced charge can be effectively separated.The second reason is that after the thermal oxidation,Pt finally changes from the Pt to PtO2,that is,the valence of Pt changes from Pt(0)to Pt(Ⅳ)and the electron transfer takes place,indicating that separation of electron-hole pairs occurs in this process,thereby increasing the lifetime of photogenerated holes.(3)α-Fe2O3 nanoparticles were successfully prepared by a hydrothermal method.The results of photocatalytic decomposition of methylene blue show that α-Fe2O3 can catalyze the degradation of methylene blue.When the reaction time is 90 min,the photocatalytic degradation rate of α-Fe2O3 to methylene blue reaches 25%.(4)SnO2/α-Fe2O3 heterostructures were successfully prepared by two-step hydrothermal method.The SEM results showed that SnO2 was embedded in the surface of α-Fe2O3 nanospheres in the form of small spheres.The heterojunction can catalyze the degradation of methylene blue.When the reaction time is 90 min,the degradation efficiency of methylene blue by SnO2/α-Fe2O3 heterostructures reaches 44%.Compared with pure α-Fe2O3 powder photocatalytic decomposition of methylene blue efficiency doubled.This shows SnO2/α-Fe2O3 heterojunction can significantly improve the photocatalytic activity,thereby enhancing the photocatalytic efficiency.The SnO2/α-Fe2O3 heterojunction increases both the electron-hole separation efficiency and the carrier mobility.