Preparation And Photoelectrochemical Performance Of Iron-zinc Oxide Microspheres Based On Zinc-containing Dust

The high value-added utilization of metallurgical zinc-containing dust and sludge based on wet chemical method can simultaneously materialize multiple valuable elements and significantly improve the added value of this resource utilization,which is of positive significance for building sustainable industry ecology of resources and environment.The results of our previous study showed that cauliflower-likeα-Fe₂O₃@Zn Fe₂O₄heterojunction microspheres with good photocatalytic activity could be obtained through homoiothermic reflux homogeneous precipitation（HRHP）process by using the acidolysis solution of zinc-containing dust as starting reactant.The composition and morphology evolution of the product are closely related to the wet chemical reaction conditions,but the structure-activity relationship and related mechanism of the products at the initial stage of the reaction are still unclear.In this work,using acidolysis solution with Fe/Zn molar ratio of 4:1 from the mixture of zinc-containing blast furnace dust and steel rolling sludge as the starting reactant,the precursors were prepared under relatively mild conditions by HRHP process in water-glycol double solvent system,and iron-zinc oxide microspheres were obtained by roasting the precursors.The effect of process conditions for wet chemical reactions（p H value,homoiothermic reaction time,dosage of ethylene glycol,etc.）on the composition,morphology and photocatalytic performance of iron-zinc oxide microspheres obtained within 1 h of homoiothermic reflux were systematically studied by using XRD,XRF,FESEM,particle size analysis,photoelectrochemistry and photocatalytic characterization,and the structure-activity relationship between product composition and morphology evolution was also studied.By changing the adding method and amount of urea,the effect of the p H value of the wet chemical reaction of the binary solvent system on the product was systematically investigated when refluxing at homoiothermic for 1 h.Two kinds of urea adding methods were set:"adding before reflux reaction"and"adding when reflux system reaches a constant temperature of 110°C".The experimental results show that the final products obtained by the two urea addition methods areα-Fe₂O₃/Zn Fe₂O₄composite microspheres with good photocatalytic activity,but the different urea addition methods will lead to differences in the p H of the reaction system,thereby affecting the structure and performance of the product.Compared with the product prepared by adding urea when the reflux system reaches a constant temperature of 110°C,the product obtained by adding urea before the reflux reaction exhibits microsphere with better morphology,larger particle size,rough surface,more mesopores,larger specific surface area,higher zinc content and lower iron content（higher Zn Fe₂O₄content）;At the same time,the photocurrent density of the product increases and interfacial impedance decreases,which has better photocatalytic activity and the photocatalytic degradation rate of MB is increased by about 5%.The dosage of urea was set as 0.05 mol,0.075 mol,0.1 mol,0.125 mol and 0.15mol respectively.The experimental results show that the final products obtained with different dosage of urea are allα-Fe₂O₃/Zn Fe₂O₄composite microspheres,but the dosage of urea also affect the structure and performance of the product by adjusting the p H value.Compared with other different amounts of urea,the product with 0.1mol of urea has a higher content of Zn Fe₂O₄,best microspherical appearance,medium particle size,largest specific surface area,larger photocurrent density and the fast photogenerated carrier transport rate,which gives the best photocatalytic performance(D_MB>90%).By changing the homoiothermic reaction time,the effect of different isothermal reaction times on the product in the wet chemical reaction of the binary solvent system was preliminarily explored.The homoiothermic reaction time is set as 10 min,20 min,30 min,40 min,50 min and 60 min respectively.The experimental results show that the products obtained at the homoiothermic reaction time of 20 min and above are allα-Fe₂O₃/Zn Fe₂O₄composite microspheres,while the products obtained at the homoiothermic reaction time of 10 min are Zn-doped single-phaseα-Fe₂O₃microspheres.It can be seen that the homoiothermic reflux reaction time has a significant impact on the composition and photoelectrochemical performance of the product.Compared with 20,30,40 and 50 min,the composite materialα-Fe₂O₃/Zn Fe₂O₄obtained with a homoiothermic reaction time of 60 min has a higher proportion of Zn Fe₂O₄,the best microsphere appearance,larger particle size,larger specific surface area,larger photocurrent density,lower transport resistance of photogenerated carriers and recombination ratio of photogenerated electron-hole pairs,which shows the best photocatalytic performance(D_MB=90.97%).The product obtained from homoiothermic reaction time of 10 min is single-phase Zn-dopedα-Fe₂O₃,which has smaller particle size,larger specific surface area,and more mesopores on the surface,and its photocatalytic performance(D_MB=85.28%)is better than the product obtained by reflux for 20-40 min and less than that of 50-60 min.The effect of the adding amount of ethylene glycol on the product during the wet chemical reaction of the binary solvent system was investigated.The adding amount of ethylene glycol was set as 100,90,80,70,60,50,40 and 30 ml respectively.The experimental results show that the final products obtained with different adding amounts of ethylene glycol are allα-Fe₂O₃/Zn Fe₂O₄composite microspheres.The adding amount of ethylene glycol has little effect on the proportion ofα-Fe₂O₃and Zn Fe₂O₄in the obtained composite microspheres,but it will lead to the evolution of the product morphology,thereby affecting the photoelectrochemical performance of the product.When the adding amount of ethylene glycol is 100 ml,the obtained product has the best microspherical appearance dispersibility and separation and transport performances of photogenerated carriers.At the same time,the kinetic rate constant of MB photodegradation is 96%higher than that of the product obtained by adding 30 ml of ethylene glycol.In view of the fact that the Zn-doped single-phaseα-Fe₂O₃microspheres obtained in the experiment show good photoelectrochemical performance,the homoiothermic reaction time of the wet chemical process is further refined to 10,5and 0 min.Under the optimized experimental conditions obtained by the above research work,the influence of the homoiothermic reaction time on the composition,morphology and performance of the obtained Zn-dopedα-Fe₂O₃microspheres was systematically investigated.The experimental results show that:Zn-doped single-phaseα-Fe₂O₃microspheres with good photocatalytic activity can be obtained within 10 min of homoiothermic reaction time.However,due to the short homoiothermic reaction time,the microspherical appearance of each product is poor.Among all products,the product obtained with a homoiothermic reaction time of 0min has a smaller particle size,larger specific surface area,higher photocurrent density,lower interfacial resistance in the process of photogenerated carrier separation and transfer,and the best photocatalytic performance(D_MB=90.14%).