Preparation And Photocatalytic Application Of Novel Polychromtic Luminescent Carbon Dot

Carbon dots,as a new type of 0-dimensional carbon nanomaterials,have attracted extensive attention of researchers once they were discovered.A series of advantages such as good biocompatibility,low toxicity,convenient preparation,and outstanding fluorescence properties make it have great application prospects in the fields of catalysis,pharmaceutical medicine,disease treatment,and bioimaging.However,most of the carbon dots reported so far only have short-wavelength emission of blue-green light.The short emission wavelength means that the light absorption range of carbon dots is narrow,which reduces the utilization efficiency of solar energy by carbon dots,and greatly limits the application research of carbon dots in photocatalysis.Hence synthesis of new long-wavelength emitting carbon dots is an effective strategy to solve the above problems.At present,there are few reports on the long-wavelength emitting carbon dots,and the fluorescence mechanism and the reasons for the long-wavelength emission have not been determined.Therefore,there is an urgent need to not only study the synthesis of new long-wavelength emitting CDs,but also to explore the mechanism of their long-wavelength fluorescence emission,in order to summarize the effective methods of CDs fluorescence regulation to better guide the long-wavelength emission carbon dot synthetic applications.Based on the above content,this thesis actively explores and studies the multicolor carbon dot system containing long wavelength emission and its application in the field of photocatalysis.The main contents are as follows:First,a series of multicolor fluorescent carbon dots were prepared by in-situ solvent-free carbonization method using dihydroxybenzoic acid system as precursor.Its maximum emission wavelength is from 410 nm to 610 nm,covering the visible light region from blue to red.Through physical property characterization,we revealed that the luminescence mechanism is that the difference in the position of the hydroxyl group of the precursor leads to the difference in the degree of decarboxylation in the reaction.The precursor of red CDs is easier to decarboxylate to form a large sp² conjugated system,which greatly improves the overall conjugation of CDs.The degree of conjugate,as well as the crystallinity,lead to a red shift of its luminescence.The related results provide a new idea for the synthesis and preparation of long-wavelength emitting carbon dots.Afterwards,we applied the polychromatic carbon dots to the photocatalytic water splitting of modified carbon nitride for hydrogen production applications.The red carbon dots and g-C₃N₄ were combined to form a composite material by calcination.Experiments show that carbon dot modification can effectively improve the light absorption capacity of the composite material in the visible light region,and promote the charge separation on the surface of the material,which makes up for the shortcomings of pure g-C₃N₄ in these two aspects,thereby improving the photocatalytic efficiency.The experimental results show that the photocatalytic hydrogen production capacity of the composites loaded with 1%Pt can reach 3669μmol·g^-1·h^-1,which is 3.6times that of pure g-C₃N₄ without carbon dot modification.The experimental conclusion has certain research significance and value for the improvement of carbon dot modification g-C₃N₄ modification technology.