Preparation Of Titanate Catalyst And Study On Photocatalytic CO₂ Reduction Under "Magnetic-Optical-Thermal" Three-field Coupling

Solar-driven photocatalytic reduction of CO₂ into economically valuable chemical fuels is an effective way to deal with the greenhouse effect and energy crisis,and it has very important scientific and practical significance.Strontium titanate（SrTiO₃）is a photocatalyst material that has attracted much attention due to its high chemical stability,low cost,low toxicity,and easy synthesis.However,its limited light absorption range,easilly recombined photogenerated electrons and holes,etc have limited its photocatalytic performance.To solve the above problems,this paper used two methods to modify SrTiO₃,namely,loading metal oxides and constructing heterojunction,which effectively improved the performance of photocatalytic CO₂reduction,and to further improve the catalytic performance,the reaction conditions of"magnetic-optical-thermal"three-field coupling was introduced,the exploration of titanate photocatalysts and catalytic systems with high CO₂ reduction activity have been made.1.SrTiO₃（m）catalyst loaded with Ni₂O₃ of different proportions was prepared by hydrothermal method using TiO₂ microspheres as the raw material.The effect of Ni₂O₃ loading on the photocatalytic CO₂reduction of SrTiO₃（m）was explored,and the mechanism of the enhanced photocatalytic activity was proposed.By PL,UV-vis DRS,EIS and transient photocurrent characterizations,it is found that Ni₂O₃loading not only significantly reduces the recombination rate of photogenerated electrons and holes in the catalyst,but also extends its light absorption,the sample with 5.4 wt%Ni₂O₃ loading exhibited the best photocatalytic activity in the 3 h photocatalytic CO₂ reduction reaction.The yield of CO and CH₄ reached11.57μmol/g,and 1.51μmol/g,respectively,which are 3.15 times and 14.84 times the corresponding yield on pure STO（m）.2.Bi₄Ti₃O₁₂/SrTiO₃ heterojunction catalysts with different ratios were prepared by one-step hydrothermal method using TiO₂ P25 as raw material.By UV-vis DRS,Mott-Schottky,XPS and UPS tests,the energy band structure of the heterojunction catalyst was obtained,and it was proved that a built-in electric field was formed on the interface between the two phases of SrTiO₃ and Bi₄Ti₃O₁₂ due to their intimate contact.Electrons and holes transfer to form a Z-type charge transport path because of the electric field force,which effectively separates electrons and holes.In addition,after 3 h of photocatalytic CO₂reduction reaction,CH₄ was not produced on pure SrTiO₃ and Bi₄Ti₃O₁₂,while it was produced on all heterojunction catalysts and the yield of CO was greatly improved.The CO and CH₄ yield on the Sr_0.5Bi_0.5TO catalyst reached 13.37μmol/g and 1.55μmol/g,respectively,the CO yield was 5.74 times that of pure SrTiO₃.3.A magnetic field generator was used to generate～50 m T alternating magnetic field and a magnetic material nickel foam was used as catalyst carrier to introduce the thermal field through magnetocaloric effect to construct a"magnetic-optical-thermal"three-field coupling reaction system.LSV,Mott-Schottky and reaction temperature measurements have proved that coupling magnetic field promotes the separation of photogenerated carriers on the catalyst under illumination,inhibits the recombination of electrons and holes,increases the charge transfer rate,and generates magnetocaloric effect on the magnetic carrier nickel foam to transfer thermal energy to the reaction system.The catalytic reduction of CO₂ was tested on all of the synthesized catalysts under the three-field cross-control reaction conditions,the best catalytic performance was under the"magnetic-optical-thermal"three-field coupling condition,After 3 h reaction,the yield of CO（50.53μmol/g）and CH₄（9.15μmol/g）on the N_5.4STO（m）catalyst is 4.37 times and 6.06times the yield under sole photocatalysis,and the CO（70.16μmol/g）and CH₄（11.74μmol/g）on Sr_0.5Bi_0.5TO are 5.25 times and 7.56 times that of pure photocatalysis.Under the synergistic effect of the three fields of magnetic,optical and thermal,the catalytic efficiency has been greatly improved.