Research On The Application Of Quantum Dots In Photocatalytic Carbon Dioxide Reduction And Hydrogen Production Systems

Since the industrial revolution in the mid-18th century,mankind has been faced with a serious energy and environmental crisis.According to the current level of reserves and energy consumption,all available energy on the earth will not be enough to meet the demand in a century or two,and the continuous use of fossil energy will cause air pollution and greenhouse effect so people begin to look for new clean and sustainable energy.Solar energy is one of the most promising alternative energy sources to address these global challenges due to its sustainability,richness and environmental friendliness.Since Fujishima et al put forward the pioneering work in the field of photocatalytic water splitting in 1972,this field has been extensively studied in the past decades,and some remarkable progress has been made.Inspired by photosynthesis in nature,efforts has been made to convert water and carbon dioxide into chemical energy with solar energy as the only input energy.There mainly molecular catalysts and semiconductor catalysts which can be used as catalysts for water splitting and carbon dioxide reduction under illumination.There are many methods such as doping,grafting,constructing heterogeneous junction,constructing Z-scheme system and so on.Due its low cost,easy synthesis and unique optical properties,such as wide spectral absorption,large specific surface area and rich surface binding properties,quantum dots have been reported more and more.This paper mainly studies the following two contents:1.Three different chain length CdS quantum dots with doping modification of 3-mercaptopropionic acid,11-mercaptoundecanoic acid,3-mercaptopropionic acid and 11-mercaptoundecanoic acid were synthesized respectively.Triethanolamine was used as the electron donor,water as the solvent,then carbon dioxide was reduced to carbon monoxide,formic acid and microscale methane under visible light irradiation.By gas chromatography and nuclear magnetic resonance,the TON value of carbon monoxide and formic acid for the 3-mercaptopropionic acid modified cadmium sulphde quantum dots is 4.35 μmol/mg and 51.57 μmol/mg,the TON value of formic acid for the 11-mercaptoundecanoic acid modified cadmium sulphde quantum dots is 2.18 μmol/mg,and the TON value of carbon monoxide,methane and formic acid in the 3-mercaptopropionic acid and 11-mercaptoundecanoic acid modified cadmium sulphde quantum dots is TON（CO）=1.74 μmol/mg,TON（CH4）=0.2 μmol/mg,TON（COOH）=90 μmol/mg,respectively.The three kinds of quantum dots were characterized by transmission electron microscope,ultraviolet visible spectrum,fluorescence spectrum and carbon dioxide adsorption.2.CdSe quantum dots modified 11-mercaptoundecanoic acid as surface stabilizer were synthesized,which were self-assembled with water-insoluble nickel complexes using the hydrophlicity of carboxyl and the hydrophbicity of long chain alkyl to form a new water-soluble material.The assembly was proved to be successful by characterization methods such as energy dispersive X-ray spectrometer,ultraviolet visible absorption spectrum,fluorescence spectrum,transient emission spectrum,etc.Moreover,only ascorbic acid was added as the electron sacrificial agent show good hydrogen production performance.In an aqueous solution with a pH of 7,the TON and TOF based on nickel complex could be reached 15244 and 1684 h^-1 under visible light irradiation.