Synthesis And Functionalization Of Fluorescent Carbon Dots

Carbon dots,a kind of spherical fluorescence particles less than 10 nm and composed by intermediate carbon nucleus and surface containing N/O functional groups,have become a rising star in the carbon material family due to their unique optical and physicochemical properties and potential market application value.This thesis has made research and exploration on the rapid synthesis and functional application of carbon dots.The details are as follows:1.A novel ratiometric fluorescent nanosensor?RbH-CD?for Hg²⁺sensing based on carbon dots has been synthesized via bonding rhodamine B hydrazide to the carbon dots surface by an amide reaction,where the CD_CA is prepared by carbonizing citric acid at a high temperature.The obtained RbH-CD composite showed high selectivity and sensitivity toward Hg²⁺over other common metal ions.In addition,this rhodamine hydrazide-functionalized ratiometric nanosensor can be sensitive to the qualitative and semi-quantitative detection of target ions by the naked eye compared to single fluorescent probes and most"turn-off"sensors.2.Two kinds of solid composite luminescent materials were synthesized by directly adding carbon dots(CD_saw and CD_PPDA)with special surface functional groups during the process of preparing the silica gel and metal organic framework?MOF?to avoid fluorescence quenching caused by aggregation of carbon dots.Firstly,based on the fact that the surface of CD_saw contains abundant hydroxyl groups that can accelerate the gel formation of tetraethyl orthosilicate,the strongly luminescent CD-silica aerogel material with CD_saw as gel center and high quantum yield?43.4%?has been prepared by sol-gel method.The obtained CD-silica was used for the sensing of aniline vapor,and the fluorescence quenching efficiency of aniline gas could reach76.4%under the optimal conditions.Secondly,CD@MOF and CMOF composite luminescent materials were synthesized by two different strategies for assembling CD_PPDA and MOF carrier.Interestingly,different strategies led to red-shift or blue-shift in the fluorescence of CD_PPDA,respectively.The red shift of CD@MOF can be attributed to the continuous reabsorption and re-emission process.For CMOF,dehydration reaction causes the amino group to be substituted by amide,and the defect state of the CD_PPDA surface changes.In addition,both the steric hindrance effect and the introduction of the electron-withdrawing functional group can impair the conjugation effect,causing blue-shift of the fluorescence of CD_PPDA.Phosphor with bright white light can be obtained by mixing the samples prepared by above two strategies,which can be applied to white light emitting devices.3.Blue carbon dots?b-CD?and red carbon dots?r-CD?were synthesized with p-phenylenediamine and oxalic acid used as precursors through controlleing the solvent type of solvothermal reaction.And obtained carbon dots were successfully applied to HeLa cells imaging,showing excellent dyeing results.Moreover,the prepared r-CD exhibited good solvent and pH responses.When the r-CD was dispersed in different solvents,they exhibited fluorescent emission of each color from red to green,the tunable photoluminescence mechanism of r-CD for solvent response can be attributed to changes of surface state.In addition,due to the change in surface charge caused by protonation and deprotonation,the color of the r-CD solution under visible light shows a transition from reddish brown to lavender as the pH decreases,indicating its potential for visual detection of pH.In summary,the fluorescence tuning of the carbon dots and the multi-color carbon dots are obtained by the solvent-controlled and solvent-responsed strategies.