Preparation Of Imprinted Sensor Embedded CQDs And Research On Selective Detection For Li~+

In recent years,with the rapid development of lithium batteries and other industries,the problem of lithium pollution is becoming increasingly severe.Though the toxicity of lithium is low,excessive lithium could also cause serious harm to human health.Therefore,it is of great significance for human health and environmental protection to develop a highly efficient and sensitive detection technology of Li⁺.Carbon quantum dots?CQDs?are a kind of carbon nanofluorescence material with unique photoelectric properties.It is widely used in detecting some molecules and ions.However,this detection method is vulnerable to external environment and interfering ions,and the ability of selective recognition is weak,so it is difficult to achieve accurate quantitative detection of target substances.Ion imprinting technology can achieve specific selection of target ions through specific recognition sites.Therefore,it is very important to combine CQDs with Ion imprinting technology to prepare a fluorescent imprinting sensor with both fluorescence detection ability of CQDs and specific identification and selective adsorption capacity of Ion imprinting technology for Li⁺.In this paper,nitrogen doped carbon quantum dots?N-CQDs?were prepared and three CQDs lithium-ion imprinting sensors were prepared by different methods.With the aid of SEM,TEM,FT-IR and fluorescence testing,the morphology,structure,thermal stability,fluorescence characteristics and detection parameters were analyzed,and the selection recognition and quantitative detection ability were further discussed.The following main conclusions are obtained:?1?The optimum process for preparing N-CQDs by one-step hydrothermal method:the hydrothermal temperature is 150 degrees,the hydrothermal time is 5 h,the amount of citric acid?CA?is 0.5256 g,the amount of ethylenediamine?EDA?is435?L,and the pH of water solution is 7.The N-CQDs prepared by the optimal process parameters has good dispersion and fluorescence stability,and its fluorescence quantum yield?QY?is 65%.?2?The fluorescence sensor,CQD/IIP,was prepared by precipitation polymerization,and its size is about 20 nm.Its fluorescence intensity varies linearly with the concentration of Li⁺ion in the range 1-70?mol L^-1 and the detection limit is0.36 mol L^-1.Imprinting factor IF is 3 and the imprinting effect is very significant.Compared with other interfering ions,CQD/IIP has high selectivity for Li⁺and it can detect Li⁺quantitatively in aqueous solution.?3?The CQDs were wrapped by st?ber method and then CQD@SiO₂ was synthesized.Ulteriorly,silicon-based fluorescent imprinting sensor,CQD@SiO₂@IIP,was prepared by surface imprinting polymerization.The particle size of the sensor was about 50-60 nm and the imprinting layer was about 5 nm.The linear detection range is 0.5-50?mol L^-1 and the detection limit is 0.16 mol L^-1.The imprinting factor IF is 4.53 and the imprinting effect is good.Selective recognition experiments and quantitative detection experiments show that CQD@SiO₂@IIP has the ability of specific selection and recognition for Li⁺,and the results of quantitative detection are accurate and reliable.?4?Fe₃O₄ was prepared by hydrothermal method,and then Fe₃O₄@SiO₂@CQD was obtained by st?ber method.Furhermore.Fe₃O₄@SiO₂@CQD@IIP was synthesized by surface imprinting polymerization based on Fe₃O₄@SiO₂@CQD.The results show that the particle size of Fe₃O₄@SiO₂@CQD@IIP is about 350 nm,and the thickness of imprinted layer is about 25 nm.It has good paramagnetic property and good separation can be achieved.The linear detection range is 0.5-40?mol L^-1and the detection limit is 0.12?mol L^-1.The imprinting factor IF is 2.39,and the imprinting effect is obvious.The selectivity recognition performance for Li⁺of Fe₃O₄@SiO₂@CQD@IIP is stronger,and its quantitative detection function of the Li⁺is accurate.