Preparation Of Core-shell Carbon Dots-based Fluorescent Fibers And Its Application In Cr⁶⁺ Detection

Carbon dots have aroused great interest among researchers since it first discovered in 2004.As a new type of fluorescent nanoparticle,carbon dots are widely used in biological imaging,detection,drug tracking,photocatalysis,solar energy,battery,LED and other fields as carbon dots have the advantages of stable fluorescence,excellent anti-photobleaching,and simple synthesis process.In recent years,researchers have done a lot of work on the fluorescence mechanism and the application of carbon dots.Although great progress has been made,there are still many problems in limiting the application of carbon dots.As nanoparticles with high specific surface energy,carbon dots could easily aggregate in the liquid with high concentration or as solid state,triggering self-aggregation induced quenching,which limits the applications in related fields.As a kind of fluorescent material,carbon dots have fluorescent response to some metal ions and biomolecules,mainly manifested as fluorescence enhanced or weakened.However,the current application of carbon dots in the field of sensors is mostly as liquid state,which is not conducive to recycle and for practical operation,thus limiting its wide application.At present,doping carbon dots into starch,silica,and printing carbon dots on paper to achieve solid-state fluorescence materials have been reported.However,the one-step synthesis of solid-state fluorescence carbon dots and their application in fluorescent fibers have rarely been reported.According to above problems,carbon dots with solid-state fluorescence were prepared by one-step hydrothermal synthesis.Carbon dots-based fluorescent fibers were prepared by in-situ synthesis and electrospinning method.The fibers have high sensitivity and selectivity in Cr⁶⁺detection.The contents and results of this research are summarized as follows:A new type of high fluorescence quantum yield core-shell carbon dots was successfully prepared by one-step hydrothermal synthesis using citric acid as the carbon source and tris?2-aminoethyl?amine?TAEA?as nitrogen source.The size distribution of the core-shell structural carbon dots is uniform.The prepared carbon dots have excitation-wavelength-dependence property according to the test by fluorescence spectrometer.The fluorescence remained stable over a wide pH range from 4 to14.The fluorescence kept stable when exposed to ultraviolet light for a long time,showing excellent photobleaching resistance fluorescence.The carbon dots are resistant to self-aggregation-induced quenching in the solid state.The fluorescence quenching mechanism of the prepared carbon dots by several typical metal ions,such as Fe³⁺,Cu²⁺and Cr⁶⁺were analyzed.It was concluded that the quenching of the aminated carbon dots by these metals was due to the complexation of metal ions with the amino groups on the surface of the carbon dots.The metal ion layer has a shielding effect on the excitation and emission light of the carbon dots,which belongs to a physical quenching phenomenon.The quenching phenomenon of Fe²⁺/carbon dots by H₂O₂ was analyzed,and the result showed the hydroxyl radical had a strong destructive effect on the fluorescence center of the carbon dots.It is indicated that there is another fluorescence center which could be oxidized and destroyed by hydroxyl radicals.Then the fluorescent fractions of carbon dots were separated and purified by a high performance liquid chromatograph coupled with a fluorescence detector?FLD?and an UV-vis detector?DAD?.The result showed that it was a small fluorescent molecule with a molecular weight of 302.16 Da.Both the molecular-state and the carbon-core-state fluorescent centers contributed to the fluorescence of the carbon dots.Fluorescent cotton fibers were prepared by in-situ synthesis method in this study.The cotton fibers were immersed into the raw materials solution of the synthetic carbon dots,the precursor solution entered into the nanopores of cotton fiber with swelling by the method of padding and ultrasonication.The pores of cotton could be worked as reaction templates with excellent"microreactor"in which carbon dots could synthesized directly in the cotton fibers by hydrothermal synthesis.The fluorescent cotton fibers prepared by the method possessed stable fluorescence performance and exellent washing resistance,could be used as the anti-counterfeiting and identifiable field of the fiber and fabric;The amino-rich core-shell structure carbon dots prepared in this study possessed solid-state fluorescence property.Blending the carbon dots with hydrophobic PAN and hydrophilic PVA-co-PE fiber-forming polymers to prepare fluorescence nanofibers,indicating that the carbon dots could be dispersed uniformly in different polarities polymers without self-aggregation induced quenching.The above three kind of carbon dots-based fluorescence fibers were applied in the field of Cr⁶⁺detection,however the sensitivity needs to be improved.In order to improve the detection sensitivity of carbon dots to Cr⁶⁺,the carbon dots were grafted onto hydrophilic PVA-co-PE nanofibers with high specific surface area to prepare a fluorescence sensor,which realized the detection of trace Cr⁶⁺.This sensor possessed high selectivity and sensitivity to Cr⁶⁺,and could be recycled for many times without affecting its detection performance.