Research On The Rapid Detection Of Heavy Metal Ions In Water By Nitrogen And Sulfur Co-doped Fluorescent Carbon Quantum Dots

In recent years,pollution induced by various heavy metal ions has become a critical worldwide issue threatening the health of human beings and the eco-system.The fluorescent sensor has attracted extensive attention in recent years due to its merits including simplicity,cost effectiveness,high sensitivity,intuitiveness,and fast response.Among them,carbon quantum dots,as a new type of fluorescent carbon nanomaterials,have attracted wide attention due to their good water-solubility and excellent photochemical properties,and have a certain development prospect.First of all,NS-CQDs were prepared by hydrothermal method by using furfural as carbon source and L-cysteine as nitrogen and sulfur source,so as to achieve the purpose on detecting Hg²⁺in environmental water samples;And then,to achieve the purpose on detecting Cr⁶⁺in environmental water samples,we prepared PEG/NS-CQDs by PEG₄₀₀passivated NS-CQDs;On the basis of this,fluorescence sensing equipment for Cr⁶⁺detection was constructed with a continuous light source of 370 nm,and PEG/NS-CQDs was taken as the detection solution,so as to achieve the rapid field detection of Cr⁶⁺.The results are as follows:（1）In this work,we have developed a one step hydrothermal method strategy for synthesis of nitrogen and sulfur co-doped fluorescent carbon dots（NS-CQDs）using furfurals as the carbon source,L-cysteine as N and S dopants,respectively.The PL spectrum of NS-CQDs showed a strong peak at 540 nm when the excitation wavelength is 360 nm.TEM、FT-IR and XPS image was showed that the NS-CQDs are nearly spherical.NS-CQDs presented a size distribution range of 2.0-5.5 nm with an average diameter of 3.7 nm.Meanwhile,the surface of PEG/NS-CQDs contains amino group and hydroxyl group,which has good water solubility.Through fluorescence detection of13 metal ions,it can be determined that NS-CQDs has specific selectivity to Hg²⁺and is not interfered by other metal ions,of which the detection range is 0-200μM,the detection limit is as low as 0.1μM.In this experiment,the effects of different p H and storage time on the fluorescence intensity of NS-CQDs were also investigated.The results showed that NS-CQDs had good fluorescence stability.Furthermore,the detection was applied in Songhua river and Tongken river samples with the standard recovery rate is 98%-102.5%.（2）PEG/NS-CQDs was obtained by PEG₄₀₀passivated NS-CQDs.The best excitation wavelength was 370 nm and emission wavelength was 480 nm,with blue fluorescence.It can be seen from the characterization results that PEG/NS-CQDs shows good dispersion,with an average particle size of about 4.1 nm.Meanwhile,the surface of PEG/NS-CQDs contains amino group and carboxyl group,which has good water solubility.Through fluorescence detection of 13 kinds of metal ions,it can be determined that PEG/NS-CQDs has specific selectivity to Cr⁶⁺and is not interfered by other metal ions,of which the detection range is 0-150μM and the detection limit is as low as 0.09μM.In this experiment,the effects of different p H and storage time on the fluorescence intensity of PEG/NS-CQDs were also investigated.The results showed that PEG/NS-CQDs had good fluorescence stability.Meanwhile,standard recovery experiments were carried out in water from Songhua river and Tongken river,with the standard recovery rate of 98%-108%,which proved that PEG/NS-CQDs can be used to detect Cr⁶⁺in actual water samples.（3）To achieve the purpose of the on-site rapid detection of Cr⁶⁺,this study established a fluorescence detection equipment by PEG/NS-CQDs solution for detection,the light is 370 nm super continuous light,and in the Songhua river water and Tongken river standard addition recovery experiment was carried out,the standard addition recovery was 90%-110%,experiment proved that the fluorescence detection equipment can be applied in actual water samples of Cr⁶⁺detection.It has certain using value.