Synthesis And Photocatalytic Application Of Carbon Dots With High Quantum Yield

At present,the problem of water pollution is becoming more and more serious and has become an urgent global crisis.Photocatalytic technology has been regarded as the most effective method for purifying wastewater.The key to the successful application of photocatalytic technology lies in the design and development of high performance photocatalytic materials.Carbon dots?CDs?as co-catalyst have been successfully applied in the field of photocatalysis due to their outstanding light absorption,unique photoluminescence and fast photo-generated electron transfer properties.In recent years,CDs-based composite photocatalytic materials are active in this field.However,most of CDs used for photocatalysis suffer from some disadvantages,such as narrow photo-response range and limited electron mobility,which lead to CDs unable to effectively improve the photocatalytic efficiency of semiconductor materials.Therefore,designing and developing high-performance CDs for constructing new high-efficiency CDs-based composite photocatalyst has important practical significance.In this basis,from the perspective of optimizing the characteristics of CDs,this thesis is committed to the development of high-performance CDs for the creation of outstanding CDs-based composite materials for efficient photocatalytic degradation applications.Firstly,CDs were synthesized by a new solvothermal method using1,2-dicyanobenzene as carbon source and nitrogen source?denoted as LNCDs?.The samples were well characterized by various techniques,showing that uniform CDs consisting of carbon and nitrogen with an average size of².3 nm were obtained.Subsequently,the optical properties of the LNCDs were investigated.The results showed that the LNCDs had superior light absorption and long-wavelength emission properties with high fluorescence quantum yields up to 63%,which made the LNCDs have high photo-generated electron migration ability.Graphite carbon nitride?CN?synthesized by direct condensation of melamine at high temperature was used to fabricate CN/LNCDs composite by a hydrothermal method.The successful loading of the LNCDs was confirmed by a series of characterization methods.The effect of LNCDs on the properties of the CN/LNCDs composite was explored,indicating that the addition of LNCDs effectively improved the specific surface area,photo-response ability and photo-generated charge separation of the CN/LNCDs sample.The photocatalytic effect of the CN/LNCDs under simulated sunlight was evaluated.The CN/LNCDs with a LNCDs loading content of 0.5 wt%?CN/LNCDs-0.5?presented the highest photocatalytic performance,resulting in methyl orange?MO?degrading efficiency of 98%within60 min.The related rate constant(k=0.06497 min^-1)was about 8.3 times that of pure CN.Finally,the stability,recyclability of the CN/LNCDs-0.5 and the effect of pH value on the degradation of MO were investigated.The results showed that the catalytic efficiency of CN/LNCDs-0.5 could still reach 85%after 4 cycles.At the same time,the high removal efficiency of MO can be maintained over a wide pH range of 5¹1,indicating a significant vision of the CN/LNCDs-0.5 in practical applications of photocatalysis.