Research On Redox Properties Of Carbon Dots In Initiating Polymerization And Enhancing Photoelectric Effect

Since carbon dots(CDs)were reported,several work has shown that they have redox properties.CDs act as both electron donors and electron acceptors,especially under the excitation of light or electricity,and thus becoming the active sites for redox properties.Passivated CDs show good potential in applications due to their surface modification with functional groups,so they are widely used in various fields.In this paper,a simple,mild and universal method for modifying CDs is proposed.The redox properties of CDs are applied to initiate polymerization and improve the electron transfer properties of optical or electrical materials.1.The CDs prepared by the top-down method were designed and modified by free radical polymerization.Taking the polymerization of acrylic acid,acrylic acid phosphate(phosphorus source)and sodium methacrylate(sulfur source)for example,the effect and mechanism of free radical polymerization of water-soluble monomers triggered by the redox properties of CDs,and the effect of regulating the passivation layer on the fluorescence were systematically study.When taking ammonium persulfate and CDs as a redox couple,the polymerization effect was evaluated from different feeding methods and reaction conditions.The results showed that terpolymer-modified CDs(T-CDs)can be obtained when CDs and ammonium persulfate were added dropwise together.The electron transfer between CDs and ammonium persulfate induced the generation of persulfate radicals that effectively initiate polymerization under mild conditions.In addition,The surface passivation of the CDs can be realized independent of their surface groups,and the passivation layer can also be tailored by the amount of monomers.The fluorescence quantum yield of the CDs was significantly increased up to 29.1%.2.The CDs prepared by the bottom-up method were designed and modified by free radical polymerization.Taking the polymerization of vinylcarbazoles for example,the mechanism and effect of the free radical polymerization,as well as the enhancement of the electron transfer properties of polyvinylcarbazole(PVK)were systematically studied.N,N-dimethylaniline and CDs were used as a redox couple,PVK and CDs composites(PVK-CDs)can be successfully prepared in the temperature range of 30-80^oC,indicating the feasibility of the redox couple for initiating the polymerization of vinylcarbazole.Besides,this work further proved the polymerization was independent of the surface groups of CDs and flexiblity of tailoring the passivation layer,in which CDs act as both initiators and fillers while PVK act as the matrix.The fluorescence quantum yield of PVK-CDs compared to pristine CDs is enhanced by 44.6%,reaching up to 28.75%.Moreover,PVK-CDs showed higher electron transfer efficiency because CDs as electron reservoirs in PVK show excellent electron-donating and electron-accepting properties,and also playing a vital role in initiating polymerization..3.The blue,green and red CDs prepared by bottom-up method are designed and modified by self-assembly method along with perylene diimide,respectively.The photoresponse behaviors of three types of CDs were compared and the photocatalytic production of hydrogen peroxide of their composites was evaluated.The green,blue,and red CDs with different band gaps were synthesized from o-,m-,and p-phenylenediamine,respectively.Moreover,they exhibited more electron separation,higher electron transfer effeciency and stronger redox properties under photoexcitation.The CDs and perylene diimide were uniformly dispersed in deionized water with a mass ratio of 1:10,and the composites were obtained after percipitation.By taking advantages of photoredox properties of CDs,the insufficient reducibility of perylene diimide got improved and the photocatalytic production of hydrogen peroxide was dramatically enhanced after modification.The blue CDs have the most suitable band gap along with perylene diimide,and their composites enhanced the efficiency of photocatalytic production of hydrogen peroxide by 7.6 times compared to perylene diimide.The thesis proposed a method to passivate CDs under mild conditions by free radical polymerization without relying on the surface groups of CDs,which can modify CDs and meanwhile broaden their application fields.Therefore,initiating the free radical polymerization of monomers and preparing CDs-modified composites by taking advantages of CDs provide theoretical guidance and possess practical application value.