Preparation Of Carbon Quantum Dot Fluorescent Probe And Its Application In Detection Of Cr(?) And HCHO

In recent years,the detection of molecules or ions which harm human health and pollute the environment has attracted the close attention of environmental protection departments and researchers.However,traditional analytical methods,such as chromatography,spectroscopy and electrochemistry,have the issues of high analysis cost and complex sample pretreatment,which limits their application in analytical detection field.Fluorescent probes have become a research hotspot in the field of analysis and detection because of their simplicity,rapidity,high sensitivity and selectivity.Compared with traditional semiconductor quantum dots and organic dyes,fluorescent carbon quantum dots?CQDs?have better water solubility,fluorescence stability,photobleaching resistance,biocompatibility,low toxicity,excitation and emission wavelength adjustability,which have been widely used in the fields of analysis and detection.In addition,it is widely used in bioimaging,chemical sensing and other fields.In this paper,two kinds of fluorescent carbon quantum dots were prepared.Based on the"turn off"principle,high sensitive and selective fluorescent probe detection methods for Cr???and HCHO were established respectively.The specific contents include the following aspects:?1?Nitrogen-doped carbon quantum dots?N-CQDs?with strong blue fluorescence emission were synthesized by hydrothermal method using gelatin as carbon source.The optimum preparation conditions were optimized by single factor and orthogonal experiments with fluorescence intensity as the index,when the hydrothermal reaction temperature is 200oC,time is 6 h,and gelatin dosage is 6.0 g,the prepared N-CQDs have the best properties;the structure and fluorescence properties of N-CQDs were characterized by Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy,X-ray diffraction,ultraviolet spectrophotometer and fluorescence spectrometer,and the results showed that N-CQDs were uniformly dispersed spherical with an average particle size of 1.82 nm,and had abundant oxygen-containing functional groups and good water solubility.The maximum excitation wavelength and the maximum emission wavelength of N-CQDs with a certain wavelength dependence is 375 nm and 451 nm respectively.In addition,the effects of pH,ionic strength,solvent type,concentration of N-CQDs and irradiation time of xenon lamp on fluorescence intensity of N-CQDs were investigated.The results showed that N-CQDs had good photobleaching resistance,fluorescence stability and water solubility.?2?Based on the principle of fluorescence quenching of N-CQDs by Cr???,a"turn off"fluorescence probe for detecting Cr???was designed and applied to the quantitative detection of Cr???in leather.Taking F₀-F as an index,the suitable conditions for N-CQDs to detect Cr???were selected by single factor experiments are as follows:the concentration of N-CQDs was 10 ug/mL,the pH was about 9,and the reaction time was 20 min at room temperature.The results showed that the fluorescence intensity of N-CQDs decreases with the increase of the concentration of Cr???.The fluorescence quenching degree of N-CQDs fluorescent probe had a good linear relationship with the concentration of Cr???intherangeof10⁶0?mol/L.Thelinearequationis?F₀-F?/F₀=0.00986C+0.03857,R²=0.995,the detection limit is 28.36?mol/L,the recovery is 99.4%¹00.7%,RSD is 0.50%;Compared with diphenylcarbazide method,this method has higher sensitivity,more convenient operation,and is not affected by non-fluorescent dyes and other metal ions.It has good application prospects in the detection of Cr???.?3?Amino-functionalized carbon quantum dots?NH₂-CQDs?with strong blue fluorescence were synthesized from citric acid and urea in one step by hydrothermal method.The optimum preparation conditions were optimized by single factor and orthogonal experiments with relative fluorescence intensity as the evaluation index,when the hydrothermal reaction temperature is 160oC,time is 5 h,citric acid to urea ratio is 1:1,the prepared of NH₂-CQDs had the best properties;The structure and fluorescence properties of NH₂-CQDs were characterized by Fourier transform infrared spectroscopy,X-ray photoelectricity.sub-energy spectroscopy,X-ray diffraction,ultraviolet spectrophotometer and fluorescence spectrometer.The results showed that NH₂-CQDs were uniformly dispersed sphere with an average particle size of 1.90 nm,and were rich in oxygen-containing functional groups and good water solubility.The maximum excitation wavelength and the maximum emission wavelength of NH₂-CQDs with no wavelength dependence is 370 nm and 442 nm respectively.In addition,the effects of pH,ionic strength,solvent type,concentration of NH₂-CQDs and irradiation time of xenon lamp on the fluorescence intensity of NH₂-CQDs were investigated.The results showed that NH₂-CQDs had good photobleaching resistance,fluorescence stability and water solubility.?4?Based on the principle of fluorescence quenching of NH₂-CQDs by HCHO,a"turn off"fluorescent probe for detecting HCHO was designed and applied to the quantitative detection of HCHO in leather products and tannery wastewater.With F₀-F as the index,the suitable conditions for detecting HCHO by NH₂-CQDs were selected through single factor experiments:the concentration of NH₂-CQDs was 0.10 mg/mL,the pH was neutral,and the reaction temperature was 25oC for 20 min.The results showed that the fluorescence intensity of NH₂-CQDs decreases with the increase of HCHO concentration,The fluorescence quenching degree of NH₂-CQDs fluorescence probe has a good linear relationship with HCHO concentration in the range of0.10¹.5 ug/mL.The linear equation is?F₀-F?/F₀=0.46221C-0.01819,R²=0.991,and the detection limit is 0.18 ug/mL.The RSD was 1.21%and the recovery was96%¹20%.More importantly,NH₂-CQDs are not affected by non-fluorescent dyes and other interfering ions.It has higher sensitivity and easier operation,The N-CQDs had good application prospects in HCHO testing.