Preparation Of Nitrogen-doped Fluorescent Carbon Dots And Their Application In Metal Ion Detection

Chromium and iron,as common metal elements,exist widely in production and living water and ecological environment water,and are closely related to human life.Some recent research results show that excessive intake of Fe³⁺will lead to diseases such as liver cancer or kidney cancer,and excessive intake of Cr⁶⁺will significantly increase the incidence of skin diseases,respiratory diseases and other diseases.Therefore,there is an urgent need for a more rapid and sensitive method to detect Fe³⁺and Cr⁶⁺,which is of great significance in protecting environmental safety and human health.In recent years,fluorescent probes have been successfully used in various fields due to their high sensitivity and unique photoluminescence properties.Currently,there are mainly two kinds of fluorescent probes for detecting Fe³⁺and Cr⁶⁺,organic fluorescent molecular probes and chemically modified quantum dots.However,both of them have shortcomings,such as high toxicity,serious environmental pollution,and difficulty in modification,which limit their further application in detection.Carbon dots(CDs)have been widely concerned by researchers because of their small size,excellent water solubility,stable optical property,low toxicity,high biocompatibility,and simple preparation process.Based on this,the main research work of this paper is as follows:Using L-glutamic acid and polyacrylamide as carbon and nitrogen sources,blue-emitting carbon dots(N-CDs)were successfully prepared by a convenient one-step hydrothermal method.The experimental results showed that the N-CDs were carbon nanoparticles with approximately spherical shape and uniform particle size distribution,and the surface contained abundant functional groups such as amino groups,carboxyl groups and hydroxyl groups.The N-CDs had outstanding fluorescence intensity,excellent water dispersibility and stability,and excitation wave-dependent property,and their fluorescence quantum yield(QY)reached 18%.The fluorescent probe based on N-CDs showed high selectivity and accuracy for the detection of Cr⁶⁺in aqueous solution with a limit of detection(LOD)of 22.7 nM.In addition,the mechanism of Cr⁶⁺quenching the fluorescence of N-CDs was analyzed according to the UV absorption spectrum and fluorescence lifetime spectrum.Finally,the probe successfully realized the detection of Cr⁶⁺in real samples,indicating its great application potential in environmental detection.High-sensitivity green-emitting carbon dots(G-CDs)were successfully prepared by a one-step hydrothermal method using L-glutamic acid and dopamine hydrochloride as precursors.The G-CDs showed high fluorescence intensity and excellent photostability,and exhibited typical excitation-independent property.The fluorescent probe based on G-CDs,whose fluorescence was rapidly quenched after recognizing Fe³⁺,could detect Fe³⁺in aqueous solution with a detection limit of 12.9nM.Through the analysis of the experimental results,the fluorescence quenching of G-CDs was mainly caused by static quenching.In addition,the fluorescent probe prepared based on this method had also been successfully applied to the determination of Fe³⁺in real samples(tap water and lake water),reflecting that it had a better development prospect in environmental detection.