Detection Of Different Ions By Sulfur-doped Carbon Quantum Dots

Water resources are one of the most important natural resources for human beings.The environment of water resources and the quality of water are directly related to the future of our live.At present,water pollution detection is one of the main means to deal with the increasingly problem of water pollution.As a kind of contaminant in water,heavy metal ions will accumulate through the food chain and eventually affect human health.Therefore,it is of great significance to develop a low cost,fast detection and accurate method to detect heavy metal ions.Fluorescence analysis to detect heavy metal ions has got the attention of researchers because of the advantages of the lower cost,faster detection and more convenient operation.Among them,the carbon quantum dots(CQDs)as a unique optical properties of the material,used to detect various harmful metal ions in water sample is of great significance to human health and the environment,Adjust the structure of CQDs by doping sulfur,nitrogen or other elements and other ways can make it have different structure and lead to the variation of its performance,showing more application prospects.In this experiment,two kinds of nitrogen,sulfur doped CQDs(N,S-CQDs)were synthesized and response of the two kinds of N,S-CQDs to different ions was studied,and the practical application of the second kind of sulfur doped carbon quantum dots in environmental water samples was also studied.The first N,S-CQDs was synthesized with L-cysteine as the carbon source,using graphene oxide to assist synthesis.By optimizing the synthesis conditions,the N,S-CQDs was synthesized with the reaction temperature of 120°C and the reaction time of 2 hours.The characterization of its performance and structure of the N,S-CQDs were synthesis by transmission electron microscopy(TEM),infrared spectrum,UV-Vis absorption spectrum,fluorescence spectrum and X-ray photoelectron spectroscopy(XPS).According to the fluorescence spectrum,the maximum excitation wavelength was 405nm and the maximum emission wavelength was 510nm.Under ultraviolet light,the N,S-CQDs showed green fluorescence.The TEM images show that the prepared N,S-CQDs was well separated and have a near spherical morphology with an average particle size of 12.25±2.80 nm.The obvious lattice spacing was 0.286 nm.XPS spectrum shows that sulfur and nitrogen elements have been successfully doped into the carbon quantum dots.The response of the first N,S-CQDs to different ions was evaluated.As the result,the N,S-CQDs showed the responsed to Fe³⁺,Cu²⁺,Pb²⁺,Ag⁺,Cr³⁺and Cu²⁺.The second CQDs were synthesized with L-cysteine and graphene oxide as carbon source.Compared with the method of synthesizing the first CQDs,the reaction temperature and time were changed to 180°C and 3 hours.The characterization of its performance and structure of the sulfur and nitrogen doped CQDs were synthesis by transmission electron microscopy(TEM),infrared spectrum,UV-Vis absorption spectrum,fluorescence spectrum and X-ray photoelectron spectroscopy(XPS).According to the fluorescence spectrum,the maximum excitation wavelength is 330 nm and the maximum emission wavelength is 400 nm.Under ultraviolet light,the N,S-CQDs showed blue fluorescence..The TEM images show that the prepared N,S-CQDs are well separated and have a near spherical morphology with an average particle size of 7.07±1.47 nm.The obvious lattice spacing was 0.192 nm.XPS spectrum shows that sulfur and nitrogen elements have been also successfully doped into the carbon quantum dots.The response of the second N,S-CQDs to different ions and different p H values was evaluated,and it shows different response to Fe³⁺,Cu²⁺,Pb²⁺,Hg²⁺,Ni²⁺,Ag⁺,Cr³⁺,Cu²⁺and Se O₃^2-.Further research found that the N,S-CQDs shows different linear response to Fe³⁺,Hg²⁺,Ni²⁺,Pb²⁺and Cu²⁺in the range of different concentration,and the fluorescence was relatively stable at p H 4-10.Finally,the synthesized N,S-CQDs with blue fluorescence was applied to the quantitative analysis of tap water and Zhujiang River water,and the results showed that it had been successfully applied to the analysis of actual water samples containing tap water and Zhujiang River water,showed a good application prospect on detecting water quality as the platform.