Preparation Of Double-layer Cerium Oxide Hollow Structure Heterojunction Material And Its Application In Photocatalytic Degradation Of Pollutants

Semiconductor photocatalysis technology,which can be used to treat a variety of toxic and hazardous substances in wastewater,is considered to be the most promising way to use solar energy at the moment.Among many semiconductor materials,CeO2 has high oxygen storage capacity and relatively easy shuttle between Ce3+ and Ce4+,which makes CeO2 widely used in photocatalytic degradation of pollutants.However,it is inevitable that in practical applications,CeO2 has a wide internal band gap,leading to its low light utilization efficiency,short photo-generated carrier life and easy recombination,which limit its practical effect in sewage treatment.Therefore,based on CeO2,it is of great significance to design a new photocatalyst with broad absorption of visible light and near-infrared light and high charge separation rate,and to apply it to wastewater treatment.Aiming at the shortcomings in the application of CeO2 semiconductor photocatalysts,this article is based on double-layer cerium oxide hollow semiconductor materials.By constructing a heterojunction and loading carbon quantum dots(CQDs)on the interface,a series of new semiconductor photocatalysts have been synthesized.Using RhB,Cr(VI)and tetracycline(TC)as simulated pollutants,evaluate the treatment effect of the materials on organic pollutants,inorganic toxic substances and antibiotic wastewater,and explain the possible mechanism of action of the composite materials.The main contents are as follows:(1)Preparation of CeO2@TiO2 heterojunction modified by CQDs and application of photocatalytic degradation of pollutants.The double-layer CeO2 hollow material(D-CeO2)was synthesized by the original method of this research group,and the D-CeO2:CQDs@TiO2 nanocomposite hollow material was prepared by the sol-gel and calcination method after loading CQDs.After a detailed analysis of the morphology and optical and electrochemical properties of the material,the photodegradation performance of the material on RhB and Cr(VI)is emphasized.And proposed the possible mechanism of D-CeO2:CQDs@TiO2 nanocomposite hollow material in the photocatalytic degradation experiment.Experiments have shown that D-CeO2:CQDs@TiO2 nanocomposite hollow materials have higher photocatalytic activity than pure materials.Under visible light irradiation,compared with D-CeO2 and TiO2,the degradation rate of D-CeO2:CQDs@TiO2 nanocomposite hollow material to RhB is 22.76 times and 3.55 times that of the two pure substances,respectively The degradation rate of composite materials to Cr(VI)is 8.56 times that of D-CeO2 and 22.25 times that of TiO2.According to the experimental results and energy band theory,we speculate that the D-CeO2 double-layer hollow material with surface-modified CQDs and TiO2 successfully constructed a type II heterojunction.It effectively improves the separation efficiency of photogenerated carriers,and further improves the ability of the composite material to degrade pollutants(2)Preparation of CQDs modified CeO2/BiOCl heterojunction with oxygen-rich vacancies and application research on photocatalytic degradation of pollutants.The prepared D-CeO2 is calcined in an argon-hydrogen mixed atmosphere and loaded with CQDs.Then use this as the base and continue to use hydrothermal technology to construct a D-CeO2:CQDs/BiOCl nanocomposite hollow material rich in oxygen vacancies.By exploring the effects of CeO2 shell,BiOCl concentration and CQDs concentration on the visible light degradation performance of organic dyes RhB and metal ion Cr,we found that when the BiOCl concentration is 5%,the D-CeO2:CQDs/BiOCl nanocomposite hollow material possess strong photodegradation activity.At the same time,we found that the concentration of CQDs has little effect on the photodegradation activity of D-CeO2:CQDs/BiOCl nanocomposite hollow materials.There are a large number of oxygen vacancies(OVs)inside the generated D-CeO2:CQDs/BiOCl heterojunction.The synergistic effect of OVs and CQDs enhances the visible light absorption of the composite material and realizes effective carrier separation,thereby increasing the visible light of the material active.(3)The preparation of CQDs modified oxygen-rich CeO2@WO3 heterojunction and its application in photocatalytic degradation of pollutants.Taking D-CeO2 loaded with CQDs as the substrate,using the method of first hydrothermal and then calcination in argon-hydrogen mixed gas,the D-CeO2:CQDs@WO3 nanocomposite hollow material rich in oxygen vacancies was synthesized.Under visible light,RhB,Cr(VI)and TC are used as simulated pollutants to evaluate the material’s ability to deal with pollutants and determine the optimal doping ratio of WO3 in the material.Studies have shown that,compared with D-CeO2 and WO3,the synthesized D-CeO2:CQDs@WO3 nanocomposite hollow material exhibits better photocatalytic activity.And when reacting with RhB,Cr(VI)and TC,the optimal doping ratio of WO3 in the material is 1:1,1:1 and 3:2,respectively.WO3 and D-CeO2 have matching energy levels,which is conducive to the formation of heterojunctions,enhances the absorption and utilization of visible light,and at the same time promotes the effective separation of light-induced charge carriers under the combined action of OVs and CQDs.The synergistic promotion of several substances gave D-CeO2:CQDs@WO3 nanocomposite hollow materials with better photocatalytic activity.In summary,the three double-layer cerium oxide hollow structure heterojunction materials prepared in this article have improved to a certain extent the defects of a single material such as low light utilization efficiency and easy recombination of photo-generated carriers.It provides a new idea for the use of photocatalytic technology to treat many types of pollutants in wastewater.