The Preparation Of Fluorescent Carbon Quantum Dots And Its Research In Detection

Carbon dots（CDs）,also known as carbon nanodots or carbon quantum dots,are new spherical carbon nanomaterials with a size less than 10 nm.Carbon quantum dots have attracted wide attention due to their advantages such as good chemical stability and light stability,no light flicker,low toxicity,good biocompatibility and adjustable excitation and emission spectra.Carbon dots have been used in many research area including biosensing,chemical analysis and environmental monitoring,which possessed potential practical prospect.The purpose of this paper is to design and synthesize fluorescent carbon quantum dots by a one-step hydrothermal method（choosing celery,sodium ethylenediamine tetraacetate and melamine as precursors respectively）.Enriching their surface by all kinds of functional groups such as amino group and carboxyl group,the synthesized carbon quantum dots can be combined with nitroaromatic compounds or heavy metals ions caused quenching the fluorescence.The performance of detection of CDs was investigated and the corresponding paper sensor was also exploited based the fluorescent detection probe.Firstly,natural celery leaves and glutathione was used as precursors to prepare carbon dots（CDs）,as a novel fluorescent and paper sensor CDs exhibited high sensitivity and selective detection for explosive nitrophenol（including 2-nitrophenol（2-NP）,3-nitrophenol（3-NP）and 4-nitrophenol（4-NP））.The prepared CDs featured blue fluorescence emission under irradiation of an UV lamp and the fluorescence quantum yield was as high as 53%.As a fluorescent probe,the CDs possessed particular response to 2-NP,3-NP and 4-NP,the detection limit of 2-NP,3-NP and 4-NP was determined at 39 nM,43 nM and 26 nM,respectively.Getting multiple advantages including good water solubility,low toxicity and excellent stability,the CDs are expected to be widely used.Meanwhile,CDs based test paper was exploited and displayed distinctive quenching response when exposed to the 3-NP and 4-NP,the visual detection limits of 0.5μM and 0.1μM,respectively.Furthermore,the low toxicity and biocompatibility of CDs were also demonstrated by evaluating in cell culturing experiments,and the CDs showed good potential application in imaging.The prepared CDs were promising for fluorescent,paper sensors and bioimaging.Secondly,the fluorescent carbon dots（CDs）have been synthesized by hydrothermal method by using edetate disodium（EDTA·2Na）as a raw materials.The prepared CDs exhibited bright blue fluorescence emission excited by 340 nm with the quantum yield as high as 52%.The CDs possess special fluorescence responses to 2-nitrophenol（2-NP）and 4-nitrophenol（4-NP）,and the slump of emission was demonstrated by CDs in the existence of 2-nitrophenol and4-nitrophenol.The detection limit of 2-NP and 4-NP was determined at 77 nM and 60 nM,respectively.Meanwhile,the color response to 2-NP and 4-NP can be observed from achromatic solution to yellow by naked eye,which allowed the dual signal detection of CDs.The CDs can be applied as fluorescent and colorimetric dual-mode probe in detection of 2-NP and 4-NP.Thirdly,a novel,simple and low-cost carbon dot-magnetic nanocomposites（Fe₃O₄/CDs）was prepared by one-step hydrothermal method for sensitive detection of Hg²⁺.The prepared Fe₃O₄/CDs exhibited excellent fluorescence（FL）characteristics and good stability.The obtained Fe₃O₄/CDs serve as fluorescent probes with higher sensitivity and selectivity for Hg²⁺,with the lowest detection line of 2.01 nM.The cyclic utilization of the Fe₃O₄/CDs was realized by restoring their fluorescence after the addition of saturated ethylene diamine tetraacetic acid（EDTA）solution.And the magnetic particles can be used to remove Hg²⁺from the water.In addition,it has been successfully applied to the determination of Hg²⁺in actual environmental water samples.Fe₃O₄/CDs have a very good application prospect as a fluorescent probe for detecting Hg²⁺.