Preparation Of Sm³⁺/Tm³⁺ Doped Metal Oxide Photocatalysts And Their CO₂ Reduction Performance Study

The level of CO₂ in the atmosphere continues to rise and is becoming a serious global environmental problem.The photocatalytic conversion of CO₂ into fuel chemicals could offer a promising solution to the problem of the greenhouse effect caused by CO₂ emissions.Rare earth ions have a special outermost electron structure and can enhance the adsorption capacity of semiconductor materials to a certain extent.In addition,rare earth ions can act as electron traps and prevent the compounding of electron-hole pairs,which has gradually become a hot research topic.The structure and properties of different metal oxides doped with rare earth elements also vary to a certain extent.The main research of this thesis is as follows:1.Sm³⁺/Tm³⁺co-doped FeVO₄ nanorods photocatalysts were synthesized by hydrothermal method,and their structural and physicochemical properties were characterized by XRD,SEM and TEM.Among them,FeVO₄ doped with 10 wt%Sm and 10 wt%Tm showed the best photocatalytic activity with a CO generation rate of 1.94μmol/g/h,which was 2.15 times higher than that of pure FeVO₄.The original FeVO₄ sample consisted of many nanorods,and a large number of nanoparticles were attached to the nanorod surface of the sample,and this structure might prevent the migration of photogenerated carriers and was not conducive to the separation of photogenerated carriers.In contrast,the optimized FeVO₄ semiconductor performance was improved because the Sm³⁺/Tm³⁺co-doping caused the disappearance of a large number of nanoparticles on the surface of the sample nanorods and the nanorods became smooth,which may have reduced the migration resistance of photogenerated carriers,thus enhancing the separation of photogenerated electron-hole pairs and allowing more carrier ions to participate in the reaction.In addition,the 4f leap of Sm³⁺/Tm³⁺can facilitate the transfer of photogenerated electrons,slowing down the chance of photogenerated carrier complexation.Ultimately,the photocatalytic performance is improved.2.Sm³⁺/Tm³⁺co-doped BiVO₄ photocatalysts were synthesized by hydrothermal combined calcination.The prepared samples were characterized by SEM and TEM,and it was found that the doping of rare earth ions changed the morphology of BiVO₄ semiconductors.The activity was evaluated by the CO₂ reduction ability,and the best photocatalytic activity was found for the BiVO₄doped with 10 at%Sm and 10 at%Tm,with CO and CH₄ generation rates of 5.082μmol/g/h and1.257μmol/g/h,respectively,and CO and CH₄ selectivities of 80.17%and 19.83%,respectively.Sm³⁺/Tm³⁺co-doping increases the band gap of the semiconductor,resulting in a more negative conduction band of the BiVO₄ semiconductor,which is more reductive and can provide higher energy for the photocatalytic reaction.Moreover,the 4f transitions of Sm³⁺/Tm³⁺can promote the transfer of photogenerated electrons and slow down the chance of photogenerated carrier complexation.3.A series of Sn₃O₄ co-doped with different mass ratios of Sm³⁺/Tm³⁺rare-earth ions were obtained by hydrothermal doping of Sn₃O₄ semiconductors.The samples showed excellent performance in CO₂ reduction under full-spectrum irradiation,with CO and CH₄ production rates of8.31μmol/g/h and 0.83μmol/g/h for the 10 wt%Sm/10 wt%Tm/Sn₃O₄ samples,which were 2.25and 1.63 times higher than those of the pure Sn₃O₄ samples,respectively.The excellent photocatalytic performance was attributed to the large pore size of the nanoflake structure of the material itself,and the rare earth ion doping further increased the specific surface area and pore size of the sample,which significantly enhanced the light trapping ability of the sample and enabled the sample to generate more electron-hole pairs.On the other hand,the Sm³⁺/Tm³⁺co-doping of the Sn₃O₄ semiconductor facilitates the separation of photo-induced electron-hole pairs and allows for a higher reduction of photo-generated electrons.