The Synthesis Of ZnO/ZnFe₂O₄ Composite Photocatalyst With Magnetic Research Of Recycling

The environmental pollution caused by the development of industrialization has seriously jeopardized the health and safety of human beings,thus causing human attention to environmental governance.Photocatalytic technology can effectively control water pollution.Compared with traditional physical methods such as adsorption,filtration and sedimentation,it is easy to operate with low-cost.Currently,photocatalysis is mainly based on semiconductor materials.Zinc oxide is a new type of wide band gap II-VI semiconductor material with a band gap of about 3.2 eV at room temperature,high exciton binding energy（60 meV）,high reactivity,environmental friendliness and low cost.It has become a promising photocatalytic material,but it can only absorb a small amount of ultraviolet light due to its band gap limitation,and it is difficult to quickly separate it from the liquid due to its small particle size.Zinc ferrite（ZnFe₂O₄）has a narrow band gap（1.9 eV）and absorbs visible light and is magnetic.By constructing a ZnO/ZnFe₂O₄ heterojunction,broadened the absorption of visible light and enhanced photocatalytic activity of ZnO.In addition,magnetic ZnFe₂O₄ is used as a carrier to assist in catalyst recovery.The combination of the two is just to supplement the shortcomings of the other side,and take advantage of both sides.In this paper,this paper intends to develop high performance ZnO and ZnO/ZnFe₂O₄ photocatalytic materials for the catalytic degradation of organic pollutants.Mainly from the following aspects of research.Firstly,nano-ZnO photocatalysts with different characteristics were prepared by homogeneous precipitation method by adjusting Zn²⁺concentration and selecting zinc source.The morphological and photocatalytic properties of ZnO prepared by different Zn²⁺concentrations were studied by adjusting the concentration of Zn²⁺in the precursor solution.The results show that ZnO prepared with Zn²⁺concentration of 0.3mol/L has excellent photocatalytic activity.Then the effects of different types of zinc salts（zinc nitrate,zinc sulfate,zinc acetate and zinc chloride）on the morphology and photocatalytic properties of ZnO photocatalysts were studied with the Zn²⁺concentration equal to 0.3 mol/L.Experiments show that zinc nitrate is the most ideal zinc source.By studying the effects of different Zn²⁺concentrations and zinc sources on ZnO,the experimental results show that Zn²⁺concentration is 0.3 mol/L,and ZnO prepared by using zinc nitrate as zinc source has excellent UV photocatalytic performance and cycle stability.Secondly,ZnO/ZnFe₂O₄ catalysts were prepared by coprecipitation combined with heat treatment.On the basis of co-precipitation method,ZnO/ZnFe₂O₄nanocomposites calcined at different temperatures were successfully prepared,which had good photocatalytic activity under ultraviolet light irradiation.The photocatalytic activity of ZnO/ZnFe₂O₄ particles in the degradation of methyl orange（MO）under ultraviolet light irradiation was investigated.The results show that the ZnO/ZnFe₂O₄catalyst calcined at 500°C shows the highest degradation efficiency.This result can be attributed to the combined effect of crystallinity and specific surface area.Thirdly,through simple solvent hot method of the synthesis of pure ZnO,ZnFe₂O₄ and ZnO/ZnFe₂O₄ composite photocatalyst,through regulating the Zn²⁺/Fe³⁺mole ratio for different phase content and appearance characterisitics of ZnO/ZnFe₂O₄ composite photocatalyst,with methylene blue as a target the pollutant,at under 500 W Xenon-lamp irradation photocatalyst for the degradation of methylene blue solution performance,the results show that the ZnO/ZnFe₂O₄ composite photocatalst has certain visible light catalytic degradation activity,including Zn²⁺/Fe³⁺mole ratio of 5:2,the degradation activity of ZnO/ZnFe₂O₄ composite photocatalyst was better than pure ZnO and ZnFe₂O₄,and the degradation rate of methylene blue reached 36%after 210 min.At the same time,the hysteresis loop and separation and recovery performance of ZnO/ZnFe₂O₄ composite photocatalyst were studied by means of magnetometer and external magnetic field.It can be known that when the molar ratio of Zn²⁺/Fe³⁺is 5:2,the saturation magnetization is 27.6 emu/g,and it has strong ferromagnetism.Under the action of external magnetic field,it can be quickly separated from the euspended solution.