Preparation Of Carbon Dots-Metal Organic Frameworks And The Applications In Detection Of Heavy Metal Ions

As a new type of fluorescent nanomaterial,carbon dots（CDs）show the low toxicity,high biocompatibility,environmental friendliness and good photo bleaching resistance compared with the traditional quantum dots and organic fluorescent molecules.The advantages of stable luminescent properties can be widely used in analytical detection,cell imaging,catalysis,biomedicine and other fields.The research on the synthesis methods,mechanism and luminescence properties of carbon dots have attracted the attention of many researchers and have carried out a lot of research around these aspects.With the further study of carbon dots,various synthetic methods have been developed and optimized,and the nature of carbon dots has been greatly improved.However,carbon dots still have certain defects,for example,the emission wavelength of carbon dots is relatively single and the emission wavelength is mostly located in the short-wave area.Therefore,in order to solve the problem,we designed a series of composite materials of carbon dots and metal organic frameworks（MOFs）.The composite material has the low toxicity,good biocompatibility,good stability and is a dual-emission fluorescent sensor and successfully applied to the analysis and detection of heavy metal ions.Therefore,this paper mainly carried out the following research.（1）Briefly introduce the preparation,properties and applications of carbon dots and MOFs materials,as well as the application of composite materials.（2）Preparation of CDs@Eu-MOFs material and its applications of Cr（Ⅵ）in actual samples by ratiometric fluorescence detectionCr（Ⅵ）is widely used in production and livings,but Cr（Ⅵ）is a serious threat to human health.Therefore,it is necessary to develop sensors with high sensitivity and selectivity for detecting trace amounts of Cr（Ⅵ）.Therefore,nitrogen and cobalt（II）co-doped blue carbon dots（CDs）encapsulated in the metal organic synthesis framework（CD@Eu-MOFs）to form a ratiometric fluorescence detection of Cr（Ⅵ）,and the morphology and properties were characterized.The results show that CD@Eu-MOFs not only has the characteristics of CDs and Eu-MOFs,but also produces double emission peaks,and also has the good stability.When Cr（Ⅵ）is present,the fluorescence intensity of CDs decreases and the fluorescence of Eu-MOFs remains unchanged.Under optimal conditions,the synthesized CD@Eu-MOFs have high sensitivity and high selectivity with a linear range of 2-100μM and a detection limit of 0.21μM.In addition,the method can be successfully used to detect Cr（Ⅵ）in natural water samples with good recovery.（3）Using synthetic jujube as raw material to synthesize fluorescent carbon dots-metal organic framework composites to detect Fe³⁺ions in samplesIf Fe³⁺ions is ingested excessively,it may cause diseases such as gastrointestinal damage and tissue damage.Therefore,the detection of Fe³⁺ions in water samples has received extensive attention.In this chapter,we use jujube as raw material to synthesize excited carbon-doped carbon dots and dope in metal-organic framework to synthesize composite materials（CD@Eu-MOFs）,and to characterize and study the surface and properties of the composites.The results show that the excitation peak of the composite at 465 nm is quenched by Fe³⁺ions,while the emission peak at 616 nm remains almost unchanged,thus forming a ratio fluorescent sensor to detect Fe³⁺ions.Under the optimal conditions,the prepared CDs@Eu-MOFs composite has high sensitivity,good selectivity and low detection limit for the detection of Fe³⁺ions.At the same time,the fluorescence sensor has a good recovery rate when detecting Fe³⁺in natural samples,which proves that it has a good application prospect.（4）Synthesis of Eu@MIL-101（Al）by post-treatment method and doping green synthetic carbon dots and detection of Cu²⁺ions in actual samplesCu²⁺is a very important and essential trace element in living organisms,but the concentration of Cu²⁺ions in human body must be kept within a certain range.If Cu²⁺ions is excessively consumed,it may cause damage to kidney or liver,gastrointestinal dysfunction,and neurodegenerative diseases that destroy cell metabolism.Therefore,it is essential to develop an environmentally friendly,simple,low cost,high selectivity and sensitivity method for quantitative determination of Cu²⁺ions.In this work,blue fluorescent carbon dots were prepared by hydrothermal synthesis using onion as raw materials,and doped into Eu@MIL-101（Al）for Cu²⁺ions detection.The Eu/CDs@MIL-101（Al）material produced has two emission peaks at 455 nm and 615nm at an excitation wavelength of 390 nm.When Cu²⁺ions is added,the emission peak at 455 nm decreases,and the emission peak at 615 nm remains substantially unchanged,thereby establishing a proportional fluorescence sensor to detect Cu²⁺ions.The study found that the ratiometric fluorescence sensor has good selectivity and sensitivity,and successfully applied the method to the detection of Cu²⁺ions in natural water samples.