Construction Of Titanium Oxide-based Heterojunction Composites And Its Photothermal Catalytic Reduction Of Carbon Dioxide

With the rapid development of modern industry,the excessive emission of carbon dioxide caused by the use of a large number of fossil fuels has triggered the global greenhouse effect.In recent years,as a new artificial carbon cycle technology,CO₂conversion technology can achieve carbon emission reduction while producing high value-added hydrocarbon fuel,which is considered as one of the effective strategies to mitigate the greenhouse effect.However,the conversion efficiency of CO₂ is low at the present stage,which is far from meeting the requirements of industrial applications.Therefore,it is of great significance to develop efficient CO₂ conversion technology in order to further improve CO₂conversion efficiency.Photothermal catalysis is a new technology among the means of CO₂ reduction and conversion.Compared with conventional photocatalysis and thermal catalysis,photothermal catalysis has the following advantages:（1）it can reduce more energy costs and improve solar energy utilization;（2）the effective combination of photocatalysis and thermal catalysis can greatly exceed the effect achieved by a single mechanism;（3）photothermal catalysis can effectively avoid catalyst deactivation and improve product selectivity.Therefore,it is essential to develop new semiconductor photothermal catalysts with high efficiency.In order to solve the above problems,this dissertation has been developed by combining different semiconductor materials with TiO₂ grown in situ on metal titanium foil to form heterojunction structure.Graphene can provide certain photothermal effect,and g-C₃N₄/TiO_2-x with boron-doped and oxygen vacancies to achieve a"three-birds-in-one stone"strategy.Both of them provide the basis for the development of high efficiency semiconductor photothermal catalyst.The main contents of this article can be summarized as follows:（1）Construction of TiO₂/Ti foil GO（T-GO）composites and study on the performance of photothermal catalytic CO₂ reduction.The TiO₂/GO heterojunction was constructed by hydrothermal method by loading graphene oxide on TiO₂/Ti foil.The zero band gap of graphene provides the prerequisite for a perfect photoreceptor,and the photoinduced electrons can be excited on the Fermi layer of graphene under visible and infrared irradiation,and its high electron mobility is beneficial to improve the photocatalytic performance.The characterization demonstrates that the composite catalyst has high reduction activity in photothermal catalytic CO₂ reduction with a CO production rate of189.3μmol·g^-1·h^-1,which is 2.6 and 4.4 times higher than that of pure TiO₂ and GO,respectively.Moreover,due to its photothermal effect,the CO production rate can be increased to 234.0μmol·g^-1·h^-1 at 70℃.This work provides a useful exploration for the preparation of CO₂ photothermal materials.（2）Construction of g-C₃N₄/TiO_2-x Ti foil composite and its performance in photothermal catalytic CO2 reduction.Herein,a‘‘hitting three birds with one stone”strategy was reported to prepared boron-doped g-C₃N₄/TiO_2-x composite（BCT）by a one-step thermal reduction process,this strategy can integrate boron,oxygen defect and heterojunction into BCT composite catalyst simultaneously.A series of characterizations showed that the composite catalyst has extended full-spectrum absorption,rapid photogenerated charge separation,and outstanding CO₂ photoreduction performance(265.2μmol·g^-1·h^-1),which is 7.5 and 9.2 times higher than that of pure TiO₂ and g-C₃N₄,respectively.In addition,the CO₂ conversion rate can be further increased to 345.1μmol·g^-1·h^-1 at 70℃ due to its excellent photothermal conversion.Mechanistic studies reveal that synergistic effects alter the charge density distribution,thereby lowering the energy barrier for CO₂ conversion by adsorbing and activating CO₂ molecules.This work provides a novel three-in-one integrated strategy for fabricating high-efficiency catalysts.