Study On The Preparation Of Fluorescent Carbon Dots And The Detection And Adsorption Of Heavy Metal Ions

Fluorescent carbon dots?CDs?is a novel carbon nanomaterial with the diameter less than 10 nm,which have advantages of low toxicity and good biocompatibility,and can be used as a new type of fluorescent probe.However,CDs did not show obvious advantages in terms of fluorescence quantum yield,selectivity,fluorescence activity and sensitivity.Therefore,the development and application of functionalized fluorescent CDs probes with high fluorescence quantum yields have become very important.Three CDs were prepared by different amino passivators.CDs are prone to fluorescence quenching in the aggregate state,and its strong water solubility,which is not conducive to industrial application.To overcome these difficulties,the CDs with the highest fluorescence quantum yield are polymerized into the microgel,and the gel material with dual function of detection and adsorption of heavy metal ions was prepared.The fluorescence nonwoven material was prepared by grafting CDs with sensitive and selective detection to Hg²⁺ on PET nonwoven.Firstly,three kinds of fluorescent CDs-1,CDs-2 and CDs-3 were synthesized by hydrothermal method using ethylenediamine,melamine and polyamidoamine as passivating agents and citric acid as carbon source.The composition,structure and fluorescence properties were characterized.The results showed that CDs-1,CDs-2 and CDs-3 mainly contained a large number of functional groups such as-NH2,-COOH,-OH.They were spherical,with the average size distributions around 7-8 nm,and had typical wavelength-dependent PL behavior.CDs-1 has the highest fluorescence intensity and the maximum fluorescence quantum yield among three kinds of fluorescent CDs.Furthermore,we investigated the fluorescence quenching effect of various metal ions on CDs.Hg²⁺ Cu²⁺ and Fe³⁺ had quenching effect on CDs-1.CD-2 exhibited high sensitivity and selectivity toward Hg²⁺.Hg²⁺ and Cu²⁺has a significant quenching effect on CDs-3.Then the further functionalization of CDs-1 was carried out with GMA to produce PCD,P?Am-CD-AMPS?microgel was prepared by inverse emulsion polymerization using PCD as a fluorescent probe,Am and AMPS.The results showed that microgel remained the wavelength-dependent PL property and metal ion responses.The limit of detection?LOD?for Hg²⁺,Fe³⁺ and Cu²⁺ were respectively calculated to be 2.3 nM,3.2?M and 1.3 ?M,which were lower than the World Health Organization's Maximum contaminant limits in drinking water.Microgel had certain adsorption to Fe³⁺ and Cu²⁺.The kinetic mechanism study showed that the adsorption of Fe³⁺ and Cu²⁺ conformed to the Lagergren second-order kinetic model,that is,the tendency to chemisorption.Through desorption experiment,the fluorescence regeneration performance and adsorption regeneration performance of the microgel reached more than 80%of initial.The P?Am-CD-AMPS?microgel can simultaneously detect and remove heavy metal ions.In addition,PET-DAMP-CDs were prepared by grafting CDs-2 onto the surface of PET nonwoven modified by 2-methyl-1,5-diaminopentane?DAMP?through glutaraldehyde?G A?.The results showed that CDs-2 can sensitively and selectively detect Hg²⁺,and had a good linear relationship in the range of Hg²⁺ concentration of 5×10^-8?25 ×10^-8 mol/L with a detection limit as low as 2 nM.PET-DAMP-CDs nonwoven retained the fluorescence properties of CDs,emitting strong blue fluorescence under ultraviolet light,and can be quenched by Hg²⁺.PET-DAMP-CDs nonwoven had advantages of stability,environmental protection,convenience,low cost for the detection of heavy metal ions,and avoided the losing of CDs in water,which was a very promising fluorescent detection material.