Research On Synthesis And Photoluminescence Mechanism Of Coal-based Carbon Quantum Dots Based On Chemical Oxidation

Recently,carbon quantum dots have drawn extensive attention due to their unique optical properties,low environmental impacts and significant biocompatibility.Coal is a suitable raw material for large-scale CDs production,thus in-depth research on the synthesis and photoluminescence mechanism of coal-based CDs is of great significance.In this subject,coal-based CDs were prepared by chemical oxidation,the influence of experimental conditions and coal structure were discussed,and finally the photoluminescence and synthesis mechanism were put forward to provide a theoretical basis and technical ideas for the controllable preparation of coal-based CDs.The main research contents of the subject are as follows:Firstly,a chemical oxidation method was used to synthesize coal-based CDs under a typical condition.The morphology,chemical structures and luminescent properties of CDs were characterized.It's found that the CDs has a diameter of about 1.59 nm and height between 0.7-3.0 nm,contains rich functional groups and defect structures.It's obviously photoluminescent as yellow-green fluorescence is emitted under 320 nm excitation.The mass yield can reach 19.96%and the relative quantum yield is about 0.75%.Secondly,the effects of preparation and application environment conditions on the optical properties of coal-based CDs were studied to obtain the optical conditions.It's found that when increasing the reaction temperature or time,the PL intensity of coal-based CDs increases first and then decreases.As the coal rank increases,the mass production of CDs increases first and then decreases while the PL intensity continues to increase.Under the preparation conditions of sulfuric acid and nitric acid ratio of 60 ml/20 ml,coal mass of 0.3g,V_daf between 20-30%,100?and 18 h can obtain the CDs with the best property.As for the application environment conditions,the maximum PL intensity can be obtained with the excitation wavelength of 320 nm,solution concentration of 1 mg/8 ml and p H of 7.Finally,the structural evolution was analyzed to investigate the synthesis and photoluminescence mechanism.It's found that when coal contains fewer defects,the resulting CDs contain more defects and the optical performance is better.During the reaction,the unsaturated C=C,C=O bonds and the aliphatic chains in coal are reacted first,then the dehydrocyclization between carbon crystallites forms aromatic clusters with the size grows,and finally oxygen-containing functional groups especially C-O are introduced to form coal-based CDs.The photoluminescence mechanism of coal-based CDs is complex.The emission peak near 435 nm is related to the confined sp² domains as well as the emission peak near 500 nm is related to the defect structure.