Preparation Of Biomass Carbon Quantum Dots And The Fluorescent Color(Blue/Red) Tuning Based On Epipremnum Aureum

Recently,carbon quantum dots（CQDs）,as a kind of fluorescent nanomaterials,had been widely used in various fields due to their excellent physical and chemical properties.Compared with the preparation process of CQDs involving organic reagents and low yield,the preparation of CQDs from biomass carbon sources had great advantages such as green,environmental protection,abundant and easy to be obtained.At present,blue-green biomass CQDs had the characteristics of high quantum yield,high stability and good fluorescence response,but red biomass CQDs were still faced with low fluorescence intensity,low quantum yield,complex preparation technology and other problems.And the fluorescence quenching mechanism of the detection of relevant substances and ions was still unclear.In order to obtain color-tunable biomass CQDs,this paper used epipremnum aureum as carbon source,explored different preparation routes,obtained blue and red biomass CQDs,and tried to carry out gradual"color tuning"of CQDs fluorescence color.The specific research content and relevant results of this paper were as follows:（1）Blue fluorescent biomass CQDs（B-CQDs）synthesized by hydrothermal method using the biomass carbon source from the powder of epipremnum aureum.CQDs were prepared by controlling the concentration of raw material and the temperature of water.By studying the influence of concentration on the fluorescence intensity of CQDs,the optimal process conditions were finally established:when the powder of Greenwood leaves was 0.1g,the deionized water was30 ml,the hydrothermal temperature was 260℃,and the reaction time was 4 h,the CQDs fluorescence emission peak position was 434 nm,and the fluorescence intensity was the highest.At the same time,the effects of NaCl ion concentration,UV light irradiation time and pH of aqueous solution on the fluorescence intensity of CQDs were explored.It was found that CQDs had good salt and light stability,but a certain dependence on pH.FT-IR and XPS spectrogram analysis showed that B-CQDs surface contains hydroxyl,carboxyl and other functional groups,which had good solubility in water.Fe³⁺had a significant quenching effect on the fluorescence of B-CQDs,and other metal ions had little interference on its detection.Based on the linear relationship between the fluorescence intensity and the concentration of Fe³⁺ions,CQDs prepared by Greenwood can rapidly detect the concentration of Fe³⁺in aqueous solution,and the detection limit（3σ/k）is 0.77μM.B-CQDs was successfully synthesized by hydrothermal method.The whole preparation process was simple and green,environmentally friendly and non-toxic.（2）Study on the preparation and application of red fluorescent biomass CQDs（R-CQDs）:the powder of epipremnum aureum was still used as carbon source,and R-CQDs with red fluorescence color were successfully obtained by adding ethanol solvent and regulating solvothermal temperature and time.The optimum preparation conditions were as follows:when the powder was 0.5g,ethanol was 6 ml,solvothermal temperature was 150℃ and reaction time was 4 h,the fluorescence intensity of CQDs in red band（676 nm）was the highest,the absolute quantum yield of R-CQDs reached14.1%,and the half-peak width at 676 nm was 27 nm.By FT-IR and XPS analysis,R-CQDs were found to contain carbon oxygen groups and a small amount of impurity nitrogen.The absorbance,fluorescence intensity and fluorescence color of R-CQDs powder were significantly affected by water content when different volume ratios of H2O and organic reagent（DMF,ethanol）were controlled as solvents.An interesting phenomenon was that the R-CQDs fluorescent color gradually changed from red to blue under UV light as the water content increased.Therefore,when detecting the water content in ethanol,the absorbance had a linear relationship with the water content,and the lowest detection limit was 0.45%.When detecting the water content in DMF,the fluorescence intensity of red band had a linear relationship with the water content between 40%-95%,and its detection limit was 1.1%.（3）The preparation and color tuning mechanism of the asymptotic fluorescent CQDs:the powder of the epipremnum aureum as the carbon source,by controlling different proportions of ethanol and water as solvents,under the condition of 150℃,4 h to prepare the multicolor fluorescent CQDs.By controlling the amount of water in the solvent,CQDs presents different fluorescent colors under ultraviolet light:red,pink,thistle,mediumslateblue and blue.By comparison of fluorescence spectra,it was found that the emission fluorescence intensity of blue band gradually increased,while that of red band gradually decreased.By comparing and analyzing the surface functional groups and element contents of CQDs,it was found that with the increase of water content,the solution polarity and O/C element content increased,and blue fluorescence emission was more easily formed.The reduction of sp²/sp³ hybridization factor lead to the increase of band gap and the blue shift of emission peak position based on the change of element content and conjugate domain ratio.In this study,the fluorescence color of CQDs could be tuned effectively by simple change of solvent ratio concentration.CQDs with different fluorescent colors were prepared by hydrothermal method and solvothermal method using the powder of green leaves as the carbon source of biomass,and the purpose of regulating the gradual color of CQDs was achieved simply by changing the solvent ratio concentration.These studies provided some new ideas for the green preparation and application of biomass CQDs.