Study On Preparation Of Heterojunction And Conjugated Polymer Materials And Their Catalytic Performance For Photoreduction Of CO₂

The photocatalytic reduction of carbon dioxide into value-added chemical fuels is a promising way to solve the greenhouse effect and energy crisis,which has received widespread attention from researchers all over the world.This thesis focuses on the design and synthesis of functional composite materials used in CO2 conversion,heterojunction-type and conjugated polymer-type photocatalysts have been prepared,and their photoreduction mechanism of CO2 has been studied.A series of two-dimensional nanocomposite materials（QA/n BiVO4,n is the mass ratio of BiVO4 to QA）were prepared by selecting organic dye molecule quinacridone（QA）and inorganic semiconductor bismuth vanadate（BiVO4）with hydrogen bond giving and accepting groups as raw materials.Under UV-visible light irradiation,with triethanolamine（TEOA）as a sacrificial reagent,QA/n BiVO4 can effectively reduce CO2 to CO and CH4.Among them,QA/10BiVO4 achieved the highest CO conversion activity of 407μmol·g^-1·h^-1,and the CO selectivity was 87%.Control reaction experiment and characterization results showed that QA/n BiVO4 are Z-type heterojunctions,in which QA is used as a photosensitizer and a catalytic site for photoreduction of CO2,and BiVO4 effectively promotes the transfer and separation of charges in the photoreaction,thereby enhancing the overall catalytic activity of QA/n BiVO4.Based on the self-polymerization and hydrolysis reaction of amino nitriles,new Amide-bridged conjugated organic polymers（COP,Amide-DAMN and Amide-DAEN）with vinylene as backbone and COP（Amide-34AB）with aromatic ring as backbone were prepared.Experiment information indicated that all three materials can simultaneously catalyze CO2 reduction and H2O oxidation under visible light without sacrificial reagents.Amide-DAMN,constructed with diaminomaleonitrile as monomer,achieved the best photocatalytic reduction of CO2.The CO generation rate is 20.6μmol·g^-1·h^-1,and the selectivity is 100%.Taking Amide-DAMN as the main research object,experimental tests and DFT calculations proved that the cyano/carbonyl groups are the active sites for photocatalytic reduction of CO2,the secondary amine groups are the active sites for H2O oxidation,and the adjacent redox sites may be the reason for the high selectivity of materials.