Photocatalytic Reduction Of CO₂ By Non-Noble Metal Manganese（Ⅱ）-Based And Iron（Ⅲ）-Based Bipyridine Complexes

For the conversion of carbon dioxide into high value-added chemicals,the development of catalysts with having high catalytic properties and high selectivity has always been a hot topic for researchers.In this thesis,the catalytic reduction of CO₂ with two systems driven by visible light were studied.In this thesis,the catalytic reduction of CO₂ under visible light was studied,with the complexes formed by the reaction of non-noble metal manganese and iron with bipyridine ligands as molecular catalysts.Specifically,the application of seven catalysts in photocatalytic reduction of CO₂ were involved.In the process of research,it was divided into two systems by different metal centers:four manganese（Ⅱ）molecular catalyst systems and three iron（Ⅲ）molecular catalyst systems.Mn-OH-BPY,Mn-F-BPY,Mn-Cl-BPY,Mn-BrBPY were synthesized by the reaction of Mn（ClO₄）₂·6H₂O with 6-hydroxy-2,2’bipyridine,6-fluoro-2,2’-bipyridine,6-chloro-2,2’-bipyridine and 6-bromo-2,2’bipyridine,respectively.Fe-OH-BPY Fe-Cl-BPY and Fe-Br-BPY were synthesized by the reaction of Fe（ClO₄）₂·6H₂O with 6-hydroxy-2,2’-bipyridine,6-chloro-2,2’bipyridine and 6-bromo-2,2’-bipyridine,respectively.1.The single crystal test of the synthesized complex was carried out,and the results were analyzed and the structure was characterized.The single crystal test results were detected by the CCDC（Cambridge Crystallographic Data Centre）database and all of them were new crystals,which had never been reported before.The specific characterizations are as follows:nuclear magnetic resonance spectroscopy,powder Xray diffraction,mass spectrometry,thermogravimetry,infrared spectroscopy,ultraviolet-visible Absorption.2.Study on the photocatalytic reduction of CO₂ by manganese complexes.Through the screening of the conditions of photocatalytic reduction of CO₂ by four manganese complexes and the exploration of blank control experiments,the optimal conditions were obtained:1 μM catalyst,0.45 mM photosensitizer[Ru][Ru（bpy）₃·6H₂O)],0.029 mM sacrificial agent BIH.The mixed system with PC/TEOA=7:1（v/v total volume of 6 mL）as solvent in saturated CO₂ atmosphere was irradiated with LED white light lamp（450 nm）for 12 h.Among them,the catalytic effect of Mn complex is better than that of its metal salt,and the best catalytic effect among the four manganese catalysts was Mn-OH-BPY.It produced 37.8 μmol CO.The TON,selectivity and TOF were 7124.5,55.4%and 593.7 h^-1,respectively.3.Study on the photocatalytic reduction of CO₂ by iron complexes.Through the screening of photocatalytic reduction of CO₂ by three iron complexes and the exploration of blank control experiments,the optimal conditions were obtained:1 μM catalyst,0.56 mM photosensitizer[Ru],0.029 mM sacrificial agent BIH.The mixed system with MeCN/H₂O=2:1（v/v,1 mL TEOA,total volume of 6 mL）as solvent in saturated CO₂ atmosphere was irradiated with LED white light lamp（450 nm）for 12 h.Among them,the catalytic effect of Fe complexes was better than that of the metal salts used for synthesis,and the best catalytic effect among the three iron catalysts is Fe-BrBPY,which produces 15.6 μmol CO selectivity,TON and TOF of 76.9%,4715.3 and 392.9 h^-1,respectively.4.Combined with high resolution mass spectrometry,Density functional theory（DFT）calculation,Ultraviolet-Visible absorption spectrum test and electrochemical test,the catalytic mechanism was explored,and a reasonable mechanism of photocatalytic reduction of CO₂ by manganese complexes and iron complexes was obtained.