Enhanced CO₂ Adsorption And Photocatalytic Conversion By Surface Oxygen Vacancies Of CeO₂

The capture and efficient conversion of CO2 are effective means to control environmental pollution and alleviate the energy crisis.Semiconductor photocatalysis technology is widely used in CO2 conversion due to its easy operation,low energy consumption and no secondary pollution.As a semiconductor,CeO2 is widely used in CO2 capture and photocatalytic conversion due to its high activity,wide use,and low cost,especially its unique surface characteristics.The construction of oxygen vacancies on the surface of CeO2 and its effect on CO2 adsorption and photocatalysis are still the main topics of current research.In this study,the surface oxygen vacancies are constructed via the processes of controlling the dispersion state of CeO2 and hydrogen reduction.Its effects on CO2 adsorption and photocatalytic conversion are investigated CeO2@HNbMoO6-NS(a composite of CeO2 and acidic HNbMoO6 nanosheets)and CeO2@MgAl-LDHs-NS(a composite of CeO2 and alkaline MgAl-LDHs nanosheets)are used as examples to verify the effect of the hydrogen reduction technology on the construction of oxygen vacancies and its photocatalytic reduction performance of CO2.The specific research contents are as follows:A series of CeO2@bio-C materials were prepared by dispersing CeO2 on bio-C materials by hydrothermal method.The dispersion behavior of CeO2 was characterized by XRD,SEM,EDS,etc.The interaction of CeO2 and the carrier bio-C,the analysis and calculation of the oxygen vacancies concentration were confirmed by Raman and XPS.CeO2 with different dispersion behaviors was applied to the adsorption of CO2,and the results showed that when the surface of bio-C was loaded with 5%CeO2(CeO2-5/bio-C),its dispersion and oxygen vacancy concentration are the highest,and its adsorption capacity for CO2 is also the largest(112.88 μmol·g-1CeO2).The photocatalytic reduction of CO2 experiment also showed that CeO25/bio-C showed the best CO reduction yield,which was 0.13 μmol·g-1·h-1.According to the spectroscopic analysis before and after CO2 adsorption,the adsorption of CO2 on the CeO2 surface with oxygen vacancies is a chemical adsorption,specifically bidentate carbonylate(δ2C,O)adsorption.After the hydrogen reduction at 300℃ for 3 h,the CO yield in the photocatalytic CO2 reduction reaction over the composite material increased to 0.45 μmol·g1·h-1.The CeO2@HNbMoO6-NS and CeO2@MgAl-LDHs-NS composite photocatalysts synthesized by the exfoliation-recombination method,were used as the examples to verify the effect of hydrogen reduction technology on the performance of photocatalytic CO2 reduction.XRD,SEM,and EDS proved the successful synthesis of the composite.And Raman and XPS revealed a significant interaction between CeO2 and the nanosheets.The photocatalytic CO2 reduction perfoemance of the composites were better than that of the single-component catalysts,but them were not obvious.After the reduction of the composite with H2 at 300℃ for 3 h,the photocatalytic CO2 reduction performances of the modified composite were twice that of the unmodified composite.It is proved that the surface hydrogenation reduction of CeO2 contributes to the photocatalytic reduction of CO2 due to the increase of oxygen vacancy concentration on its surface.It is found that both the modification of dispersion behavior and hydrogen reduction can effectively change the oxygen vacancy concentration on the CeO2 surface,thus modifying the adsorption and photocatalytic conversion of CO2.In addition,over the three compounds(CeO2@bio-C,CeO2@HNbMoO6-NS and CeO2@MgAl-LDHs-NS)without hydrogen reduction modification,a certain amount of CH4 was produced during the photocatalytic CO2 reduction,and the more alkaline the carrier was,the more CH4 content was.The selectivity of CO was improved by hydrogen reduction modification.Figure[40]Table[6]Reference[105]...