Liquid-Phase Pulsed Plasma Preparation Of Carbon Quantum Dots And Their Optical Properties

Carbon quantum dots(CDs)are very popular new nanomaterials in recent years.They have unique luminescent properties,good water solubility,low toxicity,light stability,and good biocompatibility.Existing carbon quantum dot preparation methods require conditions such as high temperature and long-term reaction.Therefore,it is one of the current primary tasks to find a simple,rapid and environmentally friendly method for preparing carbon quantum dots.In this thesis,carbon quantum dots were successfully prepared by the pulsed liquid plasma method.Plasma occurs in the aqueous solution of citric acid and urea(or melamine),triggering a series of reactions,prompting the citric acid and urea(or melamine)to break and repolymerize the chemical bond,generating carbon quantum dots.The main research findings of the paper are as follows:(1)Carbon quantum dots were prepared with citric acid as the carbon source and melamine as the nitrogen source under the action of pulsed liquid plasma.It was found that citric acid and melamine can quickly form carbon quantum dots under the condition of corona discharge,and the emission wavelength of carbon quantum dots is in the blue-violet light band.As the amount of melamine increases,the emission peak wavelength shifts blue and the fluorescence intensity increases;as the amount of citric acid increases,the fluorescence intensity increases first and then decreases.When the nitrogen and carbon source materials are 1.2×10-2 mol/L and 0.39 mol/L,respectively,the generated carbon quantum dots have the highest fluorescence emission peak loudness.(2)Carbon quantum dots were prepared with citric acid as the carbon source and urea as the nitrogen source under the action of liquid-phase pulsed plasma.When the mass ratio of urea and citric acid ranges from 2:1 to 6:1,the fluorescence intensity of the generated carbon quantum dots increases with the amount of urea added.When the mass ratio of urea and citric acid is From 6:1 to 10:1,the fluorescence intensity of carbon quantum dots will decrease as the amount of urea increases.The fluorescence intensity of carbon quantum dots is also related to the generation method of liquid phase plasma.The quantum dots generated by pulse corona discharge are stronger than the pulse spark discharge,but the emission peak wavelength of the quantum dots generated by pulse spark discharge is greater than that of pulse corona discharge.The emission peak wavelength of the generated carbon quantum dots;the fluorescence of the carbon quantum dots will increase with the increase of the discharge time at the beginning,and after 10 minutes of discharge,the fluorescence of the quantum dots will decrease with the increase of time.Using transmission electron microscopy to characterize the quantum dots,it was found that the produced carbon quantum dots were concentrated at 3-6 nm,and the particle size was relatively uniform.The fluorescence quantum yield of carbon quantum dots is 14.6%.Fe3+will cause the fluorescence quenching reaction of this quantum dot,resulting in a decrease in fluorescence intensity,which can be used to detect Fe3+content in the concentration range below 50 mg/L.This paper uses pulsed liquid plasma to act on citric acid and urea(or melamine)to quickly prepare carbon quantum dots at room temperature and pressure.It has easy experimental conditions,simple reaction equipment,high production efficiency,and strong fluorescence.Features.It provides a new and efficient method for the preparation of carbon quantum dots.