Construction And Application Of Nitrogen Doped Graphene Quantum Dots Sensor

Graphene Quantum Dots?GQDs?are carbon nanomaterials with a unique 2D structure that have unique optical and electrical properties due to quantum confinement effects and edge effects.The inherent inertness of carbon atoms is only the stability of the chemical and physical properties of GQDs.GQDs have the characteristics of easy surface modification,which can be doped into a quantum dot to synthesize nitrogen-doped graphene quantum dots?N-GQDs?.Compared with GQDs,N-GQDs not only have photoluminescence stability,large specific surface area,adjustable band gap,etc.,but also have richer functional groups and higher fluorescence quantum efficiency on the surface.Therefore,N-GQDs can be used in the fields of batteries,sensors and biological imaging,and are a new type of quantum dots with broad prospects.In this paper,N-GQDs were prepared by hydrothermal synthesis using citric acid and urea as raw materials,and their properties were characterized.A series of sensors based on N-GQDs were constructed for the determination of actual samples of nitrite?NO₂^-?,ascorbic acid?AA?,silver ions?Ag⁺?and iodide ions?I^-?.1.A new fluorescence sensor based on N-GQDs detection of NO₂^-was developed.N-GQDs were prepared by hydrothermal synthesis by selecting citric acid as the carbon source and urea as the carbon source.A series of characterizations of N-GQDs,including Transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?,X-ray diffractometry?XRD?,Fourier transform infrared spectroscopy?FRIR?,Raman spectroscopy,UV-visible absorption spectrometer and other instruments.N-GQDs have a uniform distribution and having a group such as hydroxyl group,carboxyl group,and amino group on the surface were obtained,and fluorescence in the range of 380 to 630 nm was emitted under excitation light of 445 nm.By adding NO₂^-to the N-GQDs solution,the system fluorescence is effectively quenched due to electron transfer.The fluorescence intensity ratio?F₀-F?/F₀ of N-GQDs was positively correlated with the concentration of NO₂^-,ranging from 0-800 nM,and the detection limit was 2.7 nM.The recoveries of the spiked samples in actual sample analysis ranged from 102.27%to 116.66.%.The fluorescence method we developed is simple,sensitive and repeatable and can be used to determine the content of NO₂^-in water samples.2.We have developed a new fluorescent"off-on"sensor based on N-GQDs.Since Ce⁴⁺can bind to carboxyl,amino and hydroxyl groups on N-GQDs,the fluorescence intensity is quenched by the formation of N-GQDs/Ce⁴⁺complexes.In the fluorescent"on"step,redox occurs between AA and Ce⁴⁺to increased fluorescence intensity.The corresponding influencing factors and mechanisms in the"off"and"on"processes of fluorescence are discussed.Therefore,high sensitivity and high selectivity fluorescent"off"and"on"platforms for the determination of AA and LOD were designed.Under the optimal conditions,AA showed a good linear relationship in the range of 0.2-20?M.The detection limit LOD is 15nM.This method has been successfully applied to the determination of AA in actual samples3.We have successfully designed an“off-on”fluorescent sensor based on N-GQDs system to detect silver ions in water and iodide ions in milk.The fluorescence intensity of N-GQDs was significantly quenched by Ag⁺through forming N-GQDs/Ag⁺complexes due to the binding between Ag⁺and functional groups on the surface of N-GQDs.However,with the addition of I^-to the N-GQDs/Ag⁺system,the fluorescence intensity was significantly restored because of the formation of AgI complexes by"hard and soft acids and bases principle"?HSAB?between Ag⁺and I^-.Under the optimal conditions,Ag⁺had a good linear relationship in the range of 0.01 to 0.6?M with a detection limit?LOD?by counted 3?/K as 3nM.The fluorescence intensity of N-GQDs/Ag⁺linearly increased with the increasing of I^-concentrations in the range of 0.0125 to 4.0?M,and the detection limit?LOD?by counted3?/K as 5.6 nM.The proposed method has been successfully applied to the detection of water and milk powder,which is a detection system with good development prospects owing to convenient,rapid and low toxicity.