| The cerium dioxide(CeO2)has potential application in many fields,especially the outstanding contribution to photocatalytic oxidation.Thus,it was the first time to solve current global air pollution by developing the ability of photocatalytic oxidation for NOx removal.Traditional CeO2 is a green and friendly photocatalyst with high photocatalytic activity and high oxygen storage capacity.Moreover,the low-cost semiconductor photocatalyst shows strong redox avility.Undoubtedly,it is a good choice for environmental purification due to abundant reserves of rare earth Ce.A huge number of studies have found that the CeO2 cannot make good use of solar energy due to the large bandgap energy,greatly limiting its potential value.In this paper,the CeO2 photocatalyst with three-dimensional(3D)structure was prepared by combining hydrothermal and heat treatment method based on previous studies,and the NO removal ability was further evaluated.In addition,a heterogeneous system of CeO2 was designed to improve its photocatalytic NO removal ability,which firstlty developed the application prospect of CeO2 in NO removal field.The specific work and research results can be summarized into the following three aspects:(1)The structure of 3D CeOHCO3 was constructed with the template agent,and the Bi3+ was reduced to Bi0 by using reductant glucose,which further randomly dispersed on CeOHCO3.The heterojunction photocatalysts ?-Bi2O3/CeO2 were finally obtained after in situ heat treatment.The NO removal rate of 4%?-Bi2O3/CeO2 achieved to 42.9%,which surpassed ?-Bi2O3 and CeO2 about 25.9%and 15.9%,respectively,exhibiting excellent stability under visible light.More importantly,the production of NO2 decreased from 47.8 and 12.2 ppb to 8.9 ppb in sequence.The visible light utilization rate of CeO2 was improved due to the synergistic effect of?-Bi2O3 and OVs.The separation and migration rate of charge carriers were accelerated under the built-in electric field,which promoted the quantum efficiency of CeO2.More active groups were generated in the ?-Bi2O3/CeO2 system with stronger redox ability,accelerating the photocatalytic reaction of NO removal.Furthermore,the constructed process of p-n heterojunction ?-Bi2O3/CeO2 was elucidated according to the calculation of first principles.The mechanism of photocatalytic NO removal was ultimately proposed based on the trapping experiment and in situ FTIR spectra investigation.(2)The Bi0 was deposited on the surface of flower-like spheres CeO2 by using solvent-heat method,and the successful preparation of Bi0/CeO2 photocatalysts was proved by XRD and HRTEM.The characterization of SEM,TEM,and BET showed that Bi0 was tightly combined with CeO2 nanoplates and the loose 3D structure of CeO2 was filled with Bi0 particles.Besides,the decent photocatalytic activity was benefited from a large specific surface area.The UV-vis absorption spectra displayed that the visible light absorption capacity of Ce02 was significantly enhanced owing to the presence of Bi0.The NO removal rate of 10%Bi0/CeO2 photocatalyst achieved to 43.7%,and the production of NO2 was reduced to 2.96 ppb5 demonstrating remarkable selective catalytic abilities in comparation with CeO2.The stability was slightly weakened due to the surface of photocatalyst was wrapped by reaction products.The photocatalytic path and mechanism of NO removal were proposed according to the capture experiment and in situ FTIR spectra.Moreover,the 10%Bi0/CeO2 was treated by H2O2 to fill the OVs,the NO removal rate and NO2 yield were obtained subsequently.It revealed that the OVs in photocatalyst played a significant role on selective catalysis of NO.The photocatalyst 10%Bi0/CeO2 showed prominent carrer separation efficiency and higher NO removal activity,which may be associated to the synergistic effect of Bi0 and CeO2 based on electrochemical tests and other analyses.(3)The combination of BiOI and CeO2 were carried using water bath method,and the XRD and HRTEM further demonstrated the successful fabrication of p-n heterojunction photocatalyst BiOI/CeO2 photocatalysts.It was proved that the 2D/3D structure endowed the catalysts with a large specific surface area and thereby with sufficient active sites based on SEM,TEM,and BET.The UV-vis absorption spectra illustrated that the absorption band edge of CeO2 was obviously shifted by BiOI from 460 nm to 660 nm,increasing its visible light absorption capacity.The photocatalytic activity of 9%BiOI/CeO2 was significantly enhanced,and the NO removal rate was up to 48%.Cycling experiments showed that the photocatalyst had good stability and was suitable for the photocatalytic oxidation of NO removal.Whereafter,the possible photocatalytic process and mechanism of NO removal were proposed according to the capture experiment and M-S plots.The analysis and summary of electrochemical test results indicated that an intimate connection was established between BiOI and CeO2,which in depth formed a built-in electric field facilitating the rapid separation and transfer of e-/h+.Therefore,more reactive groups were generated to participate in the process of NO removal,the p-n heterojunction photocatalyst ultimately displayed higher NO removal efficiency. |
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