Photoelectric Properties Of Fe₂O₃ Modified By Mn/CDs And Its Catalytic Reduction Of CO₂

The burning of fossil fuels leads to excessive emissions of carbon dioxide,Excessive emission of carbon dioxide will cause a series of environmental problems such as the greenhouse effect and the hole in the ozone layer.Nowadays,the two major problems facing mankind are energy shortage and environmental pollution crisis.As an important carbon source,carbon dioxide can be chemically converted into methane,formic acid,methanol and other high value-added fuels.Efficient utilization of solar energy is one of the effective ways to achieve green and sustainable development of energy.Take solar energy and electric energy as energy input.The conversion of CO₂into artificial fuel without environmental pollution by photocatalytic reduction has a promising prospect.The selection of efficient catalyst is the key in this process.In the process of catalyst selection.Efficient use of solar energy is an important indicator.In the last few years of research,Hematite（α-Fe₂O₃）is considered to be an excellent visible light catalyst,Due to its narrow band gap,the theoretical band gap is 2.20e V,and it can absorb light with wavelengths up to 563 nm,accounting for about 40%of the sunlight.However,it also has some defects,such as serious electron-hole recombination and poor carrier mobility,which hinder its application in photocatalysis.The photoelectric properties of Fe₂O₃can be optimized by metal nanomaterials and carbon nanomaterials.In this paper,Fe₂O₃material was modified with carbon points and Mn metal nanoparticles to improve its photoelectric performance and catalytic reduction performance of CO₂.Carbon points were synthesized by one step hydrothermal method using silkworm sand as carbon source.The particle size of the prepared carbon point is 1-5 nm,and it is spherical.Soluble in ethanol.CDs/Fe₂O₃materials were prepared by surface coating.Evaluate its photoelectric properties and apply it to catalytic reduction of CO₂.CDs can act as a conductive channel for electrons,Enhance the electron transport rate of the electrode material,Block electron-hole recombination,Infrared results show that CDs surface functional groups are abundant,and the more functional groups there are,the more surface defects there are.These defects can provide reaction sites,The band gap of CDs/Fe₂O₃prepared under the optimal conditions is 0.72 e V lower than that of Fe₂O₃,and the material with narrow band gap is easier to be excited by visible light,Because CDs contains amino functional groups,which can promote its adsorption of CO₂,it is calculated that the electrochemical adsorption capacity of CDs/Fe₂O₃for CO₂is 2.64 times that of Fe₂O₃,Under-1.10 V voltage,After 7 h photocatalytic CO₂reduction experiment,the methanol yield of catalytic CO₂reduction product is 0.62 mmol·L^-1·cm^-2,1.51 times that of Fe₂O₃(0.41 mmol·L^-1·cm^-2).On the basis of CDs/Fe₂O₃material,Mn/CDs/Fe₂O₃was prepared by pulsed electrodeposition,XRD and XPS results showed that Mn was introduced into the electrode material,SEM results showed that Mn was modified on CDs/Fe₂O₃surface in the form of metal nanoparticles,The size is 10～20 nm,As a cocatalyst,Mn metal nanoparticles can improve the catalytic performance of electrode materials,In addition,when the metal nanoparticles are placed in a semiconductor-electrolyte interface,can improve the electron transfer rate of the semiconductor,thereby impede electron hole composite,The absorbance of Mn/CDs/Fe₂O₃prepared under the best preparation conditions is further improved in the visible light absorption range compared with CDs/Fe₂O₃,The light response is more obvious than that of single CDs modification,Moreover,the instantaneous photocurrent density was higher.The introduction of Mn metal nanoparticles reduced the electrochemical AC impedance of the electrode material by 5.20Ω,and the reduction starting potential of catalytic reduction of CO₂decreased by 0.09 V,which reduced the energy consumption required by the reaction and increased the photoelectric conversion efficiency by 6.54%,further enhancing the photoelectric performance.In the photocatalytic reduction of CO₂for 7 h,the methanol yield of CO₂product catalyzed by Mn/CDs/Fe₂O₃is 0.80 mmol·L^-1·cm^-2,which is higher than that of CDs/Fe₂O₃.