Green Synthesis Of Carbon Quantum Dots And The Study On Their Sensing Applications

Carbon quantum dots（CQDs）have been widely used in electronics,catalysis,bioimaging,sensing,and electricity because of their abundant raw materials,simple preparation,low toxicity,and unique optical properties.However,the quantum yield of CQDs is relatively low,which limits the application of CQDs.So,it is highly demanded to fabricate the CQDs with high fluorescence quantum yield.This paper mainly focuses on green synthesis of CQDs and their sensing aplications.Thiswork includes following content:Chapter 1:With acetylsalicylic acid as carbon source and ethylenediamine as nitrogen source,the nitrogen doped carbon quantum dots（N-CQDs）was synthesized by hydrothermal method,which emit blue fluorescence.It is clearly observed by Transmission Electron Microscope（TEM）that N-CQDs have a well-defined lattice structure.In this paper,the amount of ethylenediamine,external temperature,pH of diluter,concentration of NaCl and UV light was discussed on the influence of the fluorescence intensity of N-CQDs.The fluorescence emission of the N-CQDs was not depend on excitation and the fluorescence lifetime was 4.47 ns.The N-CQDs were applied to Co²⁺detection.The F/F₀ value show a good linear relationship with the concentration of cobalt ion in the range of 1²0μM,and the detection limit is 0.32μM.Chapter 2:Using Metal-Organic Frameworks（ZIF-8）as a host,a fluorescent composite that were encapsulated with CQDs and Curcumin（CCM）was fabricated by one-step synthesis method,whic-h was denoted as CCM&CQDs@ZIF-8 and can detect hypochlorite.Due to the spatial confinement effect,the distance between curcumin and carbon quantum dots is shortened,causing fluorescence resonance energy transfer（FRET）inside the CCM&CQDs@ZIF-8.To demonstrate the occurrence of FRET in CCM&CQDs@ZIF-8,the effects of CQDs and CCM on the emission behaviors and fluorescence lifetime of the CCM&CQDs@ZIF-8 were investigated..Hypochlorous acid can quench the fluorescence of curcumin,but it has no effect on the fluorescence intensity of CQDs within a certain concentration range,thus we construct a ratiometric fluorescence sensor for detecting hypochlorous acid.The ratio of F₄₁₂/F₅₈₅85 of CCM&CQDs@ZIF-8 show a good linearity with the hypochlorous acid ranged from 1 to 20μM.The detection limit was calculated to be0.25μM.Chapter 3:Fe-CQDs with peroxidase activity was synthesized by usingCQDs as a host and modified with ferric ions.The catalytic activity of Fe-CQDs was tested by 3,3’,5,5’-Tetramethylbenzidine（TMB）chromogenic reaction and the experimental conditions were optimized.It is found that free iron ions have weak catalytic activity,and the catalytic activity of Fe-CQDs obtained by combining with CQDs is greater than the free iron ions in the same concentration.CQDs not only act as a carrier,but also promote the catalytic activity.Adding different concentrations of glucose,concentration rang 20¹00μM of glucose can be detected with the detected limited of4.33μM,and the linear relationship between the absorbance of oxTMB at 652 nm and glucose concentration was good.