Study On The Synthesis Of Schiff Base And Carbon Dots And Its Detection Of Zinc And Chromium

Heavy metal ions harm the ecological environment and threaten human health.Effective,simple and rapid detection of heavy metal ions is a hot issue to be solved urgently.Fluorescence detection method has the advantages of simple detection,high sensitivity,high selectivity and fast response to the detection object,and it is one of the most effective methods for detecting heavy metal ions.Fluorescence probes detect heavy metals ions qualitatively and quantitatively by establishing the stoichiometry relationship between the fluorescent materials and the measured heavy metal ions.The development of fluorescence detection methods mainly depends on the exploitation of new fluorescent materials.Fluorescent materials are mainly divided into organic fluorescent materials and inorganic nano fluorescent materials.Among them,organic fluorescent materials have the advantages of simple synthesis steps,rapid response to ions,and low detection limits.Among the inorganic nano materials,carbon nanomaterials have green synthesis,a wide detection range and good selectivity.This research paper is devoted to preparing Schiff base fluorescent probes and biomass carbon dots fluorescent materials in a green,simple and gentle method,and exploring its potential applications in detecting heavy metal ions and phenolic compounds.The main work is as follows:1.At room temperature,o-phenylenediamine and salicylaldehyde are used as raw materials,and N,N’-Bis（salicylidene）-1,2-phenylenediamine Schiff base fluorescent material（L-probe）is prepared by amine-aldehyde condensation reaction.Its structure was characterized by hydrogen nuclear magnetic resonance spectrum,carbon nuclear magnetic resonance spectrum and infrared spectrum.Under the irradiation of 400 nm excitation wavelength,the fluorescence intensity of the ethanol solution of Zn²⁺at 516 nm is significantly enhanced.The ultraviolet absorption spectrum,fluorescence excitation and emission spectra,Job’s Plot curve and other means show that the complex ratio of the probe and Zn²⁺is 1:1.The ligand-metal charge transfer between the two components generates the chelation-enhanced fluorescence effect,realizing the specific recognition and detection of Zn²⁺in the ethanol solution,and the detection limit of Zn²⁺is 1.37μM.In addition,after adding kaempferol to L-probe alkaline solution,the fluorescence at520 nm was quenched at the excitation wavelength of 400 nm.The experiment confirmed the existence of the light-induced electron transfer effect,indicating that the fluorescent probe can be used in alkaline solution.The detection and identification of kaempferol has a detection limit of 9.41μM.2.Using pig’s toenail as a biomass carbon source,a two-step method is used to prepare toenail-derived carbon dots（PT-CDs）.The structure of PT-CDs was characterized by means of transmission electron microscopy,X-ray diffraction,Raman spectroscopy,infrared spectroscopy,etc.The results showed that the morphology of PT-CDs is approximately spherical,with an average particle size of2.11 nm,and high graphitization degree.Through UV-Vis spectroscopy and fluorescence spectroscopy,the influence of sodium chloride concentration,p H,temperature and other conditions on the fluorescence intensity of the product was explored.It was confirmed that the biomass carbon dots have excellent stability and optical properties.In addition,PT-CDs successfully realized the specific identification and detection of Cr³⁺with a detection limit of 0.92μM.PT-CDs’fluorescence response mechanism to Cr³⁺is also explored,confirming that its fluorescence quenching is caused by static quenching.In addition,the fluorescence intensity of the quenched system was recovered after adding citric acid.