Preparation Of Defective Titanium Oxide Via Laser For Photo/Photothermal CO₂ Reduction

With the development of global industrialization,the environmental pollution and resource shortage caused by fossil energy consumption have become one of the biggest obstacles in society development.Among them,the greenhouse effect caused by excessive carbon dioxide（CO₂）emissions has a significant impact on climate,environment and economy.Therefore,scientists focus on the resource utilization of CO₂,and photocatalysis and photothermal catalytic CO₂ reduction based on solar energy have also become one of the research hotspots.Among many catalysts,titanium dioxide（TiO₂）has become one of the most promising catalysts due to its low cost,safety and non-toxicity advantages.However,due to its large band gap（3.2e V）,low light absorption capacity,and rapid recombination of photogenerated carriers,the application and development of this catalyst in the field of catalytic CO₂reduction have been hindered.It is an effective method to improve the catalytic efficiency of the material by regulating the energy band structure of TiO₂ through constructing oxygen vacancies to enhancing the light absorption and carrier separation ability.However,how to precisely control the oxygen vacancies concentration of materials is worth exploring.In this paper,the regulation method of oxygen vacancies concentration for TiO₂ is explored,and metal ions are supported on TiO_x on oxygen-rich vacancies by means of adsorption of metal ions and photothermal reduction,and its performance in photocatalysis and photothermal catalytic CO₂ reduction is also studied.The specific research contents are as follows:（1）Laser construction of oxygen-rich vacancies TiO_x nanoparticles and regulation of oxygen vacancies concentration:TiO_xnanoparticles with oxygen-rich defects were successfully obtained by laser bombardment of titanium metal target under anoxic conditions with narrow pulse width and high peak power.By adjusting the oxygen concentration in the closed container during the laser preparation process,the oxygen vacancy concentration could be controlled precisely.It was confirmed in the subsequent test and characterization that the oxygen-rich TiO_xsample prepared by laser bombardment had ultra-small particle size and high specific surface area,and the band gap was significantly reduced（0.5 e V）,and enhanced the optical absorption ability of the material.In the test of photocatalytic CO₂ reduction,the CO yield of 0.7%O₂-TiO_x sample is 154.53μmol g^-1 h^-1,which is 3.4 times of the defect-free TiO₂ sample prepared under oxygen-rich conditions and 3.75 times of commercial TiO₂（P25）.（2）Preparation of Pt-TiO_x nanoparticles for photocatalytic CO₂reduction:Pt-TiO_xnanoparticles were successfully prepared by loading Pt particles on TiO_x nanoparticles through stirring adsorption and laser thermal reduction on the basis of oxygen-rich TiO_x samples.In the test of photocatalytic CO₂reduction,the selectivity of Pt-TiO_xsample products changed to methane（CH₄）with more economic value compared with the substrate TiO_x nanoparticles,and the yield reached at 305.35μmol g^-1 h^-1.It proved that Pt can be used as a co-catalyst and hydrogenation active site in the photocatalytic system to improve the photocatalytic activity of the material.（3）Preparation of Ru-TiO_x nanoparticles for photothermal catalytic reduction of CO₂:Due to the limited photocatalytic performance of CO₂ reduction,the combination of photocatalytic and thermal catalysis has more advantages.In this work,Ru-TiO_xnanoparticles were successfully prepared by stirring adsorption and photothermal reduction.In the photothermal catalytic CO₂ reduction test,the material has excellent CO₂ reduction performance and CH₄selectivity（99.99%）,and the methane yield reach at 15.8 mmol g^-1 h^-1 under 1 W·cm^-2 xenon lamp irradiation.In order to expand the practical application in the field of photothermal catalysis of materials,the photothermal catalytic CO₂ reduction performance was tested for seven consecutive days（11:00–12:00 daily）with real sunlight as the light source and heat source of the catalytic reaction.The material still has excellent catalytic performance(about 1mmol g^-1 h^-1 in cloudless weather)and stability.It is confirmed that the Ru-TiO_x system synthesized by laser bombardment has potential practical application value in the photothermal catalysis of CO₂ hydrogenation.