Preparation And Photoelectrocatalytic Properties Of ?-Fe₂O₃ Composite Nanorod Array Materials

The rapid development of human society is facing the problem of increasing energy shortage.Photoelectric catalytic water splitting technology is expected to solve this problem.For decades,people have been devoted to research on photoelectrocatalytic water splitting photoelectrode materials.Hematite(?-Fe₂O₃)has received extensive attention due to its suitable forbidden band width,abundant reserves,non-toxicity and low price.However,the disadvantages of small light absorption coefficient,slow water oxidation rate,low carrier mobility,and short hole diffusion distance lead to low photocatalytic performance,and the photocurrent density is much lower than the theoretical value.Therefore,the research on the modification of ?-Fe₂O₃ to improve its photocatalytic performance possesses high research value and practical significance.In this dissertation,one-dimensional ?-Fe₂O₃ nanorod array materials perpendicular to the FTO conductive substrate were prepared by a hydrothermal-annealing method.Graphene coupled on the surface of ?-Fe₂O₃ by spin-coating thermal reduction method,nano-Au particles modified on ?-Fe₂O₃ by electrochemical deposition and Sn doped on ?-Fe₂O₃ by high temperature thermal diffusion method improve the ?-Fe₂O₃ carrier migration rate,separation of photogenerated electron-hole pairs,absorption of visible light and the photoelectric conversion efficiency to enhance ?-Fe₂O₃ photoelectric catalytic performance.The main research contents and results are as follows:1.One-dimensional ?-Fe₂O₃ nanorod array materials perpendicular to the FTO conductive substrate were prepared by a hydrothermal-annealing method.Graphite oxide is synthesized from graphite powder,concentrated sulfuric acid and potassium permanganate.?-Fe₂O₃/r GO nanorod array was prepared by spin-coating thermal reduction method.The effect of r GO on the photocatalytic performance of ?-Fe₂O₃ nanorod arrays was studied,and the effect of the loading of r GO on the photocatalytic performance of ?-Fe₂O₃/r GO nanorod arrays was investigated.The results show that the ?-Fe₂O₃ nanorod array synthesized by hydrothermal treatment at 90 ? and annealing at 550 ? are evenly distributed without obvious agglomeration.The length of the nanorods is about 500 nm;the diameter is about 70 nm,and the aspect ratio is about 7.The maximum photocurrent density is 0.053 m A/cm2.The photocatalytic performance of ?-Fe₂O₃/r GO nanorod arrays obtained by spin coating 1 mg/m L graphene oxide solution 3 times with 10 ?l each time was best.The photocurrent density of ?-Fe₂O₃/r GO at 1.23 V reached 0.28 m A/cm2,which was 5.3 times higher than the maximum photocurrent density of ?-Fe₂O₃.Electrochemical impedance spectroscopy showed that r GO increased the carrier migration rate of the nanorod array,thereby reducing the Faraday resistance at the interface between anode material and electrolyte and improving the photocatalytic performance.2.Using tetrachloroauric acid as a gold source,nano-Au particles were modified on ?-Fe₂O₃/r GO by electrochemical deposition to prepare ?-Fe₂O₃/r GO/Au.The effects of nano-Au on the photocatalytic performance of ?-Fe₂O₃/r GO nanorod arrays were studied.The experimental parameters of electrochemical deposition were investigated and the influence of different deposition parameters were studied on the morphology and properties of ?-Fe₂O₃/r GO/Au.The results show that under the parameters of the electrochemical deposition of nano-Au particles: the nucleation voltage-1.4 V,the growth voltage-1.2 V,and the growth time 20 s,the photocatalytic performance of the ?-Fe₂O₃/r GO/Au nanorod array is best.The photocurrent density of ?-Fe₂O₃/r GO/Au at 1.23 V reached 0.44 m A/cm2,which was 1.6 times higher than that of ?-Fe₂O₃/r GO.Ultraviolet-visible light absorption spectroscopy shows that nano-Au particles improve the absorption of visible light,and electrochemical impedance spectroscopy shows that Au accelerates the reaction process between the anode material and the electrolyte interface,thereby improving the photocatalytic performance.3.(Sn)-?-Fe₂O₃ was obtained by Sn-doping ?-Fe₂O₃ nanorod arrays at 800 ?,and(Sn)-?-Fe₂O₃/r GO nanoparticles were prepared by spin coating-high temperature thermal reduction two-step method.Nano-Au particles were modified on(Sn)-?-Fe₂O₃/r GO by electrochemical deposition to prepared(Sn)-?-Fe₂O₃/r GO/Au.The photoelectrocatalytic performance of(Sn)-?-Fe₂O₃/r GO/Au nanorod array was studied.The results show that the ?-Fe₂O₃ photocurrent density after reaches 0.43 m A/cm2 Sn-doping with thermal diffusion at a high temperature of 800 ?,which is nearly 8 times higher than that of pure ?-Fe₂O₃.The photocurrent density of(Sn)-?-Fe₂O₃/r GO after coupled graphene by spin coating-thermal reduction method reached 0.77 m A/cm2,which was 1.8 times higher than that of(Sn)-?-Fe₂O₃.Photoluminescence spectroscopy and transient fluorescence spectroscopy indicate that r GO improves the separation of photo-generated electron-hole pairs,and electrochemical impedance spectroscopy shows that r GO improves the carrier migration rate of the nanorod array and thus reduces the Faraday resistance at the interface between the anode material and the electrolyte The photoelectric conversion efficiency also shows the excellent conductivity of r GO,which accelerates the migration of carriers and converts more photons into electric currents,thereby improving the photoelectric catalytic performance.The photocurrent density of(Sn)-?-Fe₂O₃/r GO/Au reached 1.15 m A/cm2,which was increased by 1.5 times compared to(Sn)-?-Fe₂O₃/r GO.Ultravioletvisible absorption spectrum shows that nano-Au particles improve the absorption of visible light,photoluminescence spectrum and transient fluorescence spectrum show that nano-Au particles improve the separation of photo-generated electron hole pairs,and electrochemical impedance spectroscopy shows that Au accelerates the reaction on the interface between anode material and the liquid,thus improving the photoelectric catalytic performance.