Study On Mechanisms Of Photocatalytic Performance For CO₂ Reduction And Preparation Of Titanium-based Catalysts

With the development of economic globalization,the extensive use of fossil fuels has inevitably caused global ecological and environmental problems.The most obvious consequence is the massive emission of carbon dioxide（CO₂）,which causes global warming,rising sea levels and energy shortages that should be solved urgently.Photocatalytic technology has the advantages of using solar energy,cleanliness,and low cost.It has been paid attention to by researchers around the world and is expected to alleviate environmental pollution and energy shortages.The key to the current photocatalytic reduction of carbon dioxide technology lies in the development of high-efficiency green visible light-responsive photocatalysts.Constructing a semiconductor heterojunction is the most commonly used effective measure to improve photocatalytic efficiency,which is conducive to broadening the visible light response range,improving the separation and transmission of photogenerated carriers,and thereby improving the catalytic performance of the catalyst.In this paper,NH₂-MIL-125（Ti）and amorphous titanium dioxide（Am-TiO₂）composite,Ti₃C₂ and porous graphite phase carbon nitride（g-C₃N₄）composite to construct a high-efficiency heterojunction catalyst to improve the performance of photocatalytic reduction of CO₂.Firstly,MIL-125（Ti）and NH₂-MIL-125（Ti）were prepared by changing the precursor materials and simple hydrothermal synthesis.Under visible light irradiation,the ability of to catalytically reduce CO₂ to produce methane（CH₄）of MIL-125（Ti）and NH₂-MIL-125（Ti）was investigated.The results showed that NH₂-MIL-125（Ti）had stronger catalytic activity.The characterization results of X-ray diffraction,solid ultraviolet and Fourier infrared showed that NH₂-MIL-125（Ti）not only had a stronger visible light absorption capacity,but also had a stronger ability to absorb CO₂ and water compared with MIL-125（Ti）,which effectively improved the performance of the catalyst for catalytic reduction of CO₂ under visible light.Secondly,in order to further improve the photocatalytic performance,Am-TiO₂/NH₂-MIL-125（Ti）catalysts loaded with different Am-TiO₂ content were obtained with water-bath reflux method.Under visible light irradiation,the photocatalytic reduction of CO₂ was studied on the above catalysts.The results showed that when the loading of Am-TiO₂ is 25 wt%,the catalytic efficiency of this system was the highest,reaching 1.18μmol·h^-1·g^-1_catalyst.X-ray diffraction,Raman,X-ray photoelectron spectroscopy and other characterization analysis showed that Am-TiO₂and NH₂-MIL-125（Ti）had a strong interaction,and the addition of Am-TiO₂ effectively improved the absorption capacity and the separation and transport efficiency of carriers,further enhanced the ability of the composite catalyst to catalytically reduce CO₂.At the same time,the reaction type and reaction path were clarified through in-situ FTIR technology.Finally,in order to carry out the research on the photocatalytic reduction of CO₂ by titanium-based catalyst Ti₃C₂,Ti₃C₂ and porous g-C₃N₄ were combined by simple electrostatic adsorption and self-assembly,and the research on the catalytic reduction of CO₂ under visible light and water conditions was carried out.The results showed that when the loading of Ti₃C₂is 2 wt%,the catalytic activity of the catalyst is the highest,reaching 0.99μmol·h^-1·g^-1_catalyst.Characterization and analysis of the composite material like X-ray diffraction,solid ultraviolet,and high-power electron microscopy showed that Ti₃C₂ and PCN were connected through-NHx-Ti and had a strong interface interaction.At the same time,the addition of Ti₃C₂significantly improved the separation and transport capacity of photogenerated carriers,thereby greatly improving the photocatalytic performance.On this basis,through in-situ FTIR,the basic reaction pathway in the reaction process was clarified.