Preparation And Photocatalytic CO₂ Reduction Properties Of Cobalt Metal Coordination Polymer And Ligand Modified CdS Quantum Dots

The photocatalytic conversion of CO₂ into CO or other organic substances(CH₃OH,CH₃COOH,C₄H₄,etc.)is one of the most ideal methods to solve energy shortage and climate problems.Over the past few decades,scientists have dedicated many efforts to develop efficient,stable and low-cost catalysts.However,there still exists some problems in the photocatalytic CO₂ reduction system.First,the diversity of catalytic products leads to low selectivity of a single product.Second,the heavy using of precious metals makes it difficult to realize large-scale industrial application.Aiming at these two problems,we have designed and constructed two photocatalytic systems for CO₂ reduction.The main research contents and conclusions are as follows:1.In order to improve the photocatalytic CO₂ reduction activity,selectivity and reduce the catalyst cost,we selected polyethylene imine,which has primary,secondary and tertiary amine functional groups,as the polymer ligand.After cross linking with non-noble metal cobalt ion,the heterogeneous coordination polymer PEI₆-Co with multiple cobalt active centers was obtained.The CO₂ adsorption and infrared spectrum characterization showed that the coordination polymer has enrichment effect to CO₂and synergistic catalytic effect in CO₂ reduction process.Further photocatalytic CO₂reduction experiments showed that PEI₆-Co is an excellent heterogeneous catalyst with CO conversion rate of 1170 mmol?g^-1 and selectivity of 95%in water containing system.The catalytic performance is 2.8 times higher than that of the mononuclear cobalt catalyst(Co L¹),and the catalytic activity is comparable to that of the binuclear cobalt catalyst(Co₂L).2.Taking CdS quantum dots as the model,we investigated the relationship between the ligand number of CdS-MPAx and the photocatalytic performance of CO₂reduction.For CdS-MPAx,the average number of ligands on the surface of each CdS-MPAx was calculated by UV-vis and NMR measurements.Further photocatalytic CO₂reduction experiments showed that with the increase of the surface ligands,the selectivity of CO in CdS-MPA/Co₂L'assembly system changed in a parabolic pattern,and when the number of mercaptopropionic acid ligand was 200,the best catalytic performance was obtained..