Preparation Of CeO₂ Semiconductor Composites And Study On Photocatalytic Degradation Of Organic Polluants

With the acceleration of urban development and population growth,water quality has deteriorated significantly.Various industrial processes discharge a large amount of toxic wastewater into the environment.Organic pollutants in wastewater,including dyes and antibiotics,have complex structures and are not easy to degrade,posing a great threat to human health.Semiconductor photocatalytic technology has the advantages of high efficiency,low cost,green and safe,and has been widely used in the degradation of organic pollutants.As the catalytic activity of semiconductor photocatalysts is affected by many factors such as photoelectron-hole separation efficiency,photo absorption capacity and redox capacity,it is still an important challenge to design novel and efficient photocatalysts.CeO₂ has attracted wide attention due to its rich oxygen vacancies,high stability,reversible Ce³⁺/Ce⁴⁺pairs and light corrosion resistance.However,as a broadband gap n-type semiconductor,CeO₂ only absorbs ultraviolet light and a small amount of visible light,and its low utilization of solar energy limits its practical application.Modification methods such as morphology regulation,metal doping,nonmetallic doping,precious metal deposition and heterojunction construction are often used to improve the catalytic activity of CeO₂.In this paper,three different types of heterojunction were constructed by combining CeO₂ with BiOIO₃,Bi₂MoO₆ and Ag₃PO₄.The details are as follows:1.By using hydrothermal synthesis method,CeO₂ nanorods were uniformly covered on the surface of BiOIO₃ nanosheets,and Type II CeO₂/BiOIO₃ heterojunction was constructed.It is tested that the visible light absorption edge of the prepared composite was significantly red-shifted,and the separation efficiency of the electron-hole pair was significantly improved.According to the test results of photocatalytic activity,the degradation efficiency of composite materials for Rhodamine B（Rh B）was higher than that of single CeO₂ and BiOIO₃.When the mass ratio of CeO₂ and BiOIO₃ was 1:4,the degradation efficiency was the highest.The results of free radical capture experiment showed that the main active species produced by CeO₂/BiOIO₃ during Rh B degradation was h⁺.The possible degradation pathway of Rh B was analyzed by mass spectrometry.After three cycles,the composite still maintained excellent catalytic activity.2.By solvothermal method,CeO₂ nanorods were covered on the surface of Bi₂MoO₆microspheres to construct Z-type CeO₂/Bi₂MoO₆ heterojunction.The effect of CeO₂ content on the catalytic activity of CeO₂/Bi₂MoO₆ composite under visible light irradiation was studied.The results showed that the degradation efficiency of Rh B was the highest when the mass ratio of CeO₂ to Bi₂MoO₆ was 2:5,and the degradation rate constant was 38.2 times and 33.1 times of that of CeO₂ and Bi₂MoO₆,respectively.The effects of the amount of photocatalyst and the concentration of Rh B on the degradation efficiency were analyzed.The high stability of CeO₂/Bi₂MoO₆ composite was proved by three cycles.The construction of Z-type heterojunction maintained strong redox potential,good visible light response and enhanced electron-hole pair separation efficiency.3.CeO₂/Bi₂MoO₆/Ag₃PO₄ternary composite was prepared by simple coprecipitation method,which can effectively degrade methyl orange（MO）and tetracycline（TC）in water.CeO₂ nanorods and Bi₂MoO₆ nanoflakes were dispersed on the surface of Ag₃PO₄ with spherical structure.The sufficient interfacial contact between the three promoted the charge transfer,prolonged the corrosion time,and played a protective role in the photo corrosion of Ag₃PO₄.The results of free radical capture experiment and electron spin resonance test showed that the main active species of CeO₂/Bi₂MoO₆/Ag₃PO₄ during photocatalysis were·O₂^-and·OH.Combined with the semiconductor band structure,a double Z-type charge transfer mechanism was proposed.The intermediates and possible degradation paths in the process of photocatalytic degradation of TC were analyzed by mass spectrometry.The construction of double Z-type CeO₂/Bi₂MoO₆/Ag₃PO₄ heterojunction provided more transfer paths for photogenerated electrons and holes,improved the visible light absorption capacity and enhanced the photocorrosion resistance and cycle stability of the composites.