Preparation Of Cerium Oxide-based Nanocomposites And Study On Their Photocatalytic Performance

CeO₂ is a widely studied semiconductor photocatalyst,which can be used for photocatalytic decomposition of water to produce hydrogen and photocatalytic degradation of organic pollutants,but due to its wide band gap,narrow light response range,and solar energy utilization low,which greatly limits its application in the field of environment and energy.Therefore,it is of great research significance to develop a highly efficient CeO2 photocatalyst with visible light response.In this paper,two kinds of CeO₂,nanobelts and nanoparticles with different morphologies were successfully synthesized by hydrothermal method and high temperature calcination method,and both of them have visible light response.In order to further improve their photocatalytic performance,the prepared CeO₂ photocatalyst was modified,and Bi₂O₃/CeO₂ and COF/CeO2 nanocomposite photocatalysts were prepared.The prepared samples were characterized by XRD,SEM,TEM,DRS,XPS,BET,PL,OTCS,EIS,etc.The morphology,crystal structure,conductivity,and light absorption of the samples were analyzed.The photocatalytic activity of the synthesized photocatalyst to decompose water to produce hydrogen and the cycle stability were tested as described below.In addition,the photocatalytic hydrogen production mechanism of Bi₂O₃/CeO₂ and COF/CeO2 nanocomposites was also discussed.The main work includes the following three aspects:?1?The Ce?OH?CO₃ precursor was synthesized by the condensing reflux method.The precursor was then used to prepare CeO2 nanobelts by hydrothermal method.The effects of reaction conditions on the structure and morphology of the prepared CeO2were studied.The results show that the CeO₂ nanobelts prepared under different temperature conditions are cubic phases,but their morphology is different.When the temperature is low,the agglomeration phenomenon between the bands is obvious,and the nanobelts are broken when the temperature is high.Among them,the sample has a uniform nanobelts structure at 150?,which can provide reaction sites for other particles loaded on the surface of the CeO2 nanobelts.In addition,CeO2 nanoparticles were successfully synthesized through a two-step hydrothermal calcination method.SEM results showed that the particles were uniform in size and small in diameter,about10-30 nm.The effects of different types of sacrificial agents on the performance of photocatalytic reactions were studied,and it was found that the rate of photocatalytic hydrogen production was highest when methanol was used as a sacrificial agent.?2?In order to improve the photocatalytic performance of CeO₂ nanobelts,Bi₂O₃nanoparticle and CeO₂ nanobelts were coupled by a simple stirring method,and a Bi₂O₃/CeO₂ nano-composite photocatalyst was successfully synthesized.SEM and TEM analysis showed that Bi₂O₃ nanoparticles were uniformly supported on the surface of Ce O₂ nanobelts and the edges of the nanobelts.XPS analysis shows that the elemental valence in CeO₂ is mainly+4,indicating that its oxidation is not complete.Moreover,the effects of different loadings on photocatalytic performance were studied,and the results showed that there was an optimal loading,9%Bi₂O₃/CeO₂ had the highest hydrogen-producing activity and its hydrogen-producing rate was 90.8?mol/g/h.This indicates that Bi₂O₃ nanoparticles supported on CeO₂ surface can improve their photocatalytic hydrogen production.In addition,the mechanism of photocatalytic decomposition of water to generate hydrogen by Bi₂O₃/CeO₂ composites is also discussed.According to the positional relationship between the conduction band and valence band,the mechanism of photocatalytic hydrogen production is the Z-Scheme electron transfer mechanism.?3?COF/CeO₂ composites with different COF loadings were synthesized by hydrothermal method in order to improve the photocatalytic performance of CeO₂nanoparticles.SEM,TEM and HRTEM analysis results show that COF and CeO₂nanoparticles can be well combined by hydrothermal.DRS analysis shows that the CeO₂ nanoparticles have a band gap of 2.44 eV and a narrower band gap,and a wider range of COF response to visible light.The combination of the two is more conducive to absorption of visible light.Photocatalytic tests show that the photocatalytic activity of CeO₂ to decompose water to generate hydrogen under visible light is enhanced by loading COF materials.Among them,5%COF/CeO₂ has the best performance,and its hydrogen production rate is 35?mol/g/h,which is the result of CeO₂ nanoparticles.It is also 5 times larger than CeO₂ nanoparticles.