| In the past few decades,due to the excessive use of fossil energy,a large amount of carbon dioxide(CO2)has been produced and entered the atmosphere,resulting in a sharp rise in the concentration of greenhouse gases in the atmosphere,which has caused a series of global climate and environmental problems such as the greenhouse effect In this case,scientists envision a carbon-neutral cycle of artificial photosynthesis(artificial leaves)that can turn waste into treasure by harnessing the planet's abundant and renewable solar energy to efficiently photocatalytic reduce CO 2to valuable chemicals or fuels,along with corresponding oxidation reactions such as water oxidation reducing CO2 emissions can also reduce human dependence on fossil fuels,which is of great significance for alleviating the dual pressure of energy and environment In the whole transformation process,the artificial photosynthetic system usually consists of two half reactions,the oxidation of water to produce oxygen(or other oxidation reactions)and the reduction of carbon dioxide(or other reduction reactions,such as the reduction of water to produce hydrogen).The coupling reaction system is driven by light energy However,the realization of photochemically driven CO2 conversion is still a huge challenge,especially for large-scale applications in the future.Therefore,among many photocatalysts,molecular(homogeneous)catalysts with tunable structure,high selectivity,excellent activity and clear catalytic mechanism have attracted the focus of researchers In this paper,taking CO2 reduction reaction as the target system,a series of non-noble metal cobalt complexes were designed and synthesized,and their selective photocatalytic CO2 reduction performance was studied and improved.The specific research contents are as follows:1.Based on the ligand abpt(abpt=3,5-di(2-pyridyl)-4-amino-1,2,4-triazole,as shown in figure below),dinuclear cobalt complexe[Co2(abpt)2(H2O)2(NO3)2]·2NO3(CoCo-abpt)andmononuclearcobalt(II)complexe[Co(abpt)2(CH3OH)2](C16SO3)2·H2O(Co-abpt)are synthesized respectively,perform as highly efficient and selective catalyst for photocatalytic reduction of CO2 to CO.The results show that CoCo-abpt shows excellent photocatalytic activity under visible light irradiation.The selectivity of CO is 95%,TON and TOF values are 14360 and0.40 s-1,respectively.The catalytic performance is more than 4 times compare with Co-abpt catalyst.Electrochemical investigations and DFT calculations have revealed that when CoCo-abpt is used as a catalyst,one CoII acts as a catalytic center,while the other CoII serves as an assistant catalytic site to prompt the cleavage of C-OH bond in O=C-OH intermediate(?G=4.77 kcal/mol).This catalytic mechanism makes the catalyst CoCo-abpt have higher selectivity and catalytic activity.2.We report a dinuclear cobalt cryptate,[Co2(Hbpt)2(CH3OH)2(NO3)2](CoCo-Hbpt,Hbpt=3,5-di(2-Pyridyl)-1H-1,2,4-triazole)as a catalyst for the visible light catalytic reduction of CO2 to CO.According to the results,in aqueous system(CH3CN:DMF:H2O=3:1:1(v/v/v)),CoCo-Hbpt exhibit good photocatalytic performance,with CO selectivity of 92%,TON and TOF values of 1230 and 0.032 s-1,respectively.However,the photocatalytic activity of CoCo-Hbpt is worse than that of CoCo-abpt,which may be caused by the stronger force between NH 2 and CO2 on the ligand of CoCo-abpt,indicating that the local regulation of the ligand will affect the photocatalytic activity of the complex. |
PDF Full Text Request