Photocatalytic Performance Analysis And Stability-Improvement For CsPbBr₃ Nanocrystals Of Nitrogen Doped Graphene Quantum Dots

Fluorescent graphene quantum dots（GQDs）,the zero-dimensional nano-carbon materials,are receiving much attentions due to their excellent fluorescence properties,good chemical stability,adjustable surface functional groups,high electrical and thermal conductivity,large specific surface area as well as low toxicity.GQDs has broad applications prospects in the field of lighting,bio-imaging and sensors,medical treatment,trace substance detection,and solar energy utilization,which show its broad application prospects.Due to these potentials,they are a hot option to replace traditional fluorescent materials.In this thesis,the relationships of fluorescence properties and chemical composition of graphene quantum dots after nitrogen doping were studied,and the photocatalytic performance improvement of nitrogen-doped graphene quantum dots（N-GQDs）combined with TiO₂ was analyzed.Besides that,N-GQDs was used as the surface ligand for controlling the growth of CsPbBr₃ nano crystals and the stability.The main research contents and progress made are as follows:（1）N-GQDs were prepared by direct heating using citric acid and urea as raw materials.The quantum dots with two-color fluorescence was prepared by adjusting the ratio of the two reactants.Through the chemical compositions,their own structures and electronic spectra of the N-GQDs,the effect of nitrogen doping on the luminescence properties of graphene quantum dots was studied.（2）Nitrogen-doped graphene quantum dots were combined with P25 TiO₂through stirring and hydrothermal steps,and the obtained composite product was applied to the degradation process of rhodamine B under visible light.The results show that the catalytic degradation rate of the composite catalyst is about 14 times that of pure TiO₂,showing a strong synergistic effect and a significant improvement in catalytic performance.（3）The N-GQDs were utilized as the surface ligand and stabilizer to replace the oliec acid and oleic ammonium in the synthesis of the CsPbBr₃ nanocrystals as well as controlling the growth of perovskite grains,and the nano crystals with the average size of 15.3 nm were obtained.（4）Poor stability of CsPbBr₃ nanocrystals is the bottleneck of the application in normal environment.Especially in water environment,the CsPbBr₃ crystals are dissolved easily.The nano-composite product prepared by combining N-GQDs with CsPbBr₃ can maintain stable dispersion in water,and the product exhibits strong blue fluorescence（under the irradiation of 365 nm）in water（its fluorescence quantum efficiency is 36%）.Besides,the composite product possesses a four times thermal stability than that of pure CsPbBr₃ nanocrystals.Stirring the composite product and P25 TiO₂ in water,and the obtained combined-catalyst showed 14 times the catalytic rate of pure TiO₂ in the test of visible light catalytic degradation to rhodamine B.