Preparation Of Double Emission Carbon Quantum Dots And Application In Water Environment Detection

Carbon Quantum Dots(CQDs)is a kind of novel zero-dimensional carbon nanomaterials,with a diameter of less than 10 nm.Based on their numerous merits,including excellent biocompatibility,photostability,uniform particle size,and low-toxic,CQDs were widely used as fluorescent probes for analysis in recent years.However,most of the current CQDs-based fluorescent probes rely on the enhancement or quenching from a single wavelength,and such probes are susceptible to interference from background noise,instrument operation and local environment.All above problems can be solved through the ratiometric fluorescence probe.The quantification process of ratiometric fluorescence probe was based on fluorescence intensity at two peaks,which can effectively avoid interference from instrument operation,environmental change,and other factors.This method can improve the accuracy and sensitivity of the method and therefore obtain more reliable data.However,most of the CQDs-based ratiometric probes were constructed by coupling CQDs with other fluorescent probes.It is a tedious process.Through experimental design and material selection,if we can directly synthesis fluorescent CQDs with two emission peaks,furthermore,by the changing of the fluorescence signal of double emission peaks to constructe ratio probe,it will make the construction of probe more convenient,rapid and accurate.At present,various water pollutants are seriously threatening human health.The rapid and simple detection of pollutants in water is urgent.Therefore,the combination of the design synthesis of double-emission CQDs and the establishment of rapid and simple methods to detect pollutants in water shows particular importance.In this paper,by choosing glucose and p-phenylenediamine,boric acid and o-phenylenediamine,p-acetylaminophenol and ethylenediamine as raw materials,through water or solvothermal method,synthesis of double emission CQDs.Based on their specific response to sulfur ion(S2-),bismuth ion(Bi3+)and chromium ion(Cr(Ⅵ)),the "Single-Response-ON","Double-Response-Reverse" and "Double-Response-OFF"ratio fluorescence systems were constructed,which can provide novel fluorescent methods to analyze pollutants in the water environment.The main works of this thesis are listed here:1.Dual-emission fluorescence carbon quantum dots(GP-CQDs)were synthesized through a one-step hydrothermal method by using glucose and p-phenylenediamine as raw materials.The morphology and spectral properties of GP-CQDs were studied.The synthesized GP-CQDs have dual emission fluorescence signals at 348 nm and 452 nm under a single excitation wavelength at 300 nm.When MnO4-was added to the GP-CQDs solution,the fluorescence signal at 452 nm was significantly quenched;however,the signals at 348 nm keep stable.In the presence of S2-,a new fluorescence emission peak at 425 nm was generated.The fluorescence intensity at 425 nm was linearly enhanced with the S2-concentration.By using the fluorescence intensity at 425 nm as the responsive signal and 348 nm as the reference signal,a ratiometric fluorescent sensing probe for S2-was constructed.Under the optimal condition,this method shows a good linear relationship in the range of 3.1×10-8 mol/L～8.0×10-6 mol/L and the detection limit was calculated to be 9.4 × 10-9 mol/L(3σ/k).The basic mechanism of the proposed method was discussed.Moreover,this method can be applied to detect S2-in environmental water samples with satisfactory results.2.By using o-phenylenediamine and boric acid as raw materials,dual-emission fluorescence carbon quantum dots(OB-CQDs)were synthesized through a one-step hydrothermal method.The morphology and spectral properties of OB-CQDs were studied.As-synthesized OB-CQDs show dual emissions at 342 nm and 557 nm under a single excitation wavelength at 300 nm.When Bi3+was combined with OB-CQDs,the fluorescence signal at 342 nm was significantly enhanced,while the signal at 557 nm was gradually quenched.Therefore,based on the unique reaction between OB-CQDs and Bi3+,a ratio fluorescence sensing probe for Bi3+determination was constructed.Under the optimal experimental conditions,the ratio of fluorescence intensity(F342/F557)at 342 nm and 557 nm showed a good linear relationship with the concentration of Bi3+in the range of 2.0×10-7～1.0×10-5 mol/L,and the detection limit was calculated to be 6.7×10-8 mol/L(3σ/k).The method has high selectivity and can be used for the determination of Bi3+in environmental water samples.Moreover,the interaction mechanism between Bi3+and OB-CQDs was further discussed.3.Green double-emission carbon quantum dots(PE-CQDs)were synthesized through a one-step hydrothermal method by using p-acetamidophenol and ethanediamine as raw materials.The morphology and spectra properties of PE-CQDs were characterized by TEM,XRD,FT-IR,UV-vis,and FL.The PE-CQDs have two emission peaks at 371 nm and 510 nm under a single excitation at 285 nm.When Cr(Ⅵ)was added into the PE-CQDs system,the fluorescence intensity at the two emission peaks of PE-CQDs were both significantly quenched through electron transfer.A good linear relationship was found between the concentration of Cr(Ⅵ)and the ratio of fluorescence intensity of PE-CQDs in the range of 3.0 ×10-7～9.0×10-5 mol/L.Based on the above phenomenon,a new fluorescent method for Cr(Ⅵ)determination was proposed,and the detection limit of this method was calculated to be 4.2×10-8 mol/L(3 σ/k).At the same time,it was found that the changes from the single wavelength(Fb371-Fs371,Fb510-Fs510)also show a linear relationship with Cr(Ⅵ)concentration.The quenching mechanism of Cr(Ⅵ)was discussed.The fluorescence lifetime data and the changes in UV-vis absorption spectra showed that the quenching mechanism of the system was static quenching.This probe has high sensitivity and selectivity,and the method was further applied to the determination of Cr(Ⅵ)in environmental water samples with satisfactory results.