Preparation Of Dual Z-scheme NiO/NiFe₂O₄/Fe₂O₃ Photocatalyst And Study On Treatment Of Dye Wastewater And Hydrogen Production

Environment pollution and energy shortage are two worldwide problems those have always perplexed the development of human society.Therefore,it is essential to develop efficient environmental treatment technologies and renewable energy sources.As an advanced oxidation technology,photocatalytic technology has obvious advantages such as high efficiency and no secondary pollution,which shows potential application value in the fields of sewage purification and clean energy production.In the photocatalytic hydrogen evolution reaction,the organic pollution in the dye wastewater can act as electron donors（sacrifice agents）to accelerate the reaction.In the meantime,the organic pollution is degraded into carbon dioxide,water and some inorganic ions,which makes it possible to treat organic pollution in the dye wastewater while producing clean energy.However,some semiconductor photocatalysts that can be used for both photocatalytic degradation and hydrogen production often have wide band gap.Therefore,there are some obvious defects in the photocatalytic reaction.Such as low utilization rate of sunlight and high recombination rate of photo-induced carriers.Hence,it is necessary to modify them（wide band gap semiconductor photocatalysts）to improve their photocatalytic activity.A large number of researches have shown that,compared with a single semiconductor photocatalyst,the Z-scheme photocatalyst composed of two different semiconductors with appropriate band gaps has the advantages of lower photo-induced carriers recombination rate,wider solar spectrum utilization range and stronger redox capacity.However,in some traditional Z-scheme photocatalytic systems,the relatively high photo-induced carriers recombination rate is still a thorny problem.This is because the existence of inherent interfaces between different contacting particles in the traditional Z-scheme photocatalytic system,which leads to the obstruction of charge carriers in the process of interface transportation.Therefore,it is crucial to reduce or even eliminate the adverse effects between the interfaces.In this study,a dual Z-scheme photocatalytic system is constructed via partial solid phase chemical reaction method.The construction of this system reduces the transport impedance of photo-induced carriers and provides more paths for their transportation.As a result,the recombination of photo-induced carriers in each monomer photocatalyst is further inhibited.In addition,the dual Z-scheme photocatalytic system not only retains the strong oxidation and reduction ability,but also improves the utilization rate of sunlight,and realizes the photocatalytic hydrogen production while effectively degrading a large number of organic pollutants.In conclusion,the dual Z-scheme NiO/NiFe₂O₄/Fe₂O₃ composite photocatalyst was designed and successfully prepared via partial solid phase chemical reaction method.The crystal structure,elemental composition and microstructure of the prepared samples were analyzed via X-ray powder diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,energy dispersive X-ray spectroscopy（EDX）,X-ray photoelectron spectroscopy（XPS）,ultraviolet visible diffuse reflectance spectroscopy（UV-vis DRS）,and X-ray photoelectron spectroscopy（XPS）.In addition,photoluminescence spectroscopy（PL）,the transient photocurrent response（TPR）and electrochemical impedance spectroscopy（EIS）were used to investigate the recombination of photo-induced carriers in the sample after the photoexcitation.In order to evaluate the activities of the prepared photocatalysts,the experiments of photocatalytic degradation of target organic pollutants and hydrogen evolution was carried out under simulated sunlight.The experimental results show that the dual Z-scheme NiO/NiFe₂O₄/Fe₂O₃ composite photocatalyst has a high photocatalytic activity.The four cycle experiments show that it has good reusable ability and structural stability.Finally,the existence of active species in the photocatalytic reaction process is confirmed via active species capture experiments and the possible reaction mechanism is explored.