The Design Of Fluorescence Sensing Systems Based Carbon Dots And Cu-MOFs For The Detection Of Heavy Metal Ions

Heavy metals are widely used in agriculture,manufacture,military and medicine industry,which have brought serious environmental pollution problems.For example,the pollution of Cr⁶⁺,Fe³⁺and Hg²⁺is a great threat to human health and environment.Therefore,establishment and development of a simple,accurate and highly sensitive detection method of heavy metals is particularly important to protect the environment and human health.Presently,the traditional detection methods of heavy metals mainly rely on large-scale instruments.Despite these detection methods have excellent accuracy,they also have some unavoidable defects such as complicated sample pretreatment,high cost and professional operation,which limit their real-time field detection.In view of the above problems,nanosensors provide an effective method for metal ions detection.Fluorescence spectrometry based on nanomaterials exhibits the advantages of simple operation,high sensitivity,good selectivity and rapid response.Therefore,it has been widely used in heavy metals detection.In this study,we constructed three kinds of fluorescent sensors and investigated their responses to three metal ions Cr⁶⁺,Fe³⁺and Hg²⁺.Firstly,nitrogen-doped carbon dots?N-CDs?and Cu?II?-based metal-organic frameworks?Cu-MOFs?were synthezied via a simple hydrothermal/solvent thermal method.Then,three fluorescence detection systems were constructed based on N-CDs,Cu-MOFs and CND/Cu-MOFs composite.The prepared materials were characterized by SEM,TEM,XPS,XRD and FT-IR.The optical performances of as-constructed sensors were investigated by UV-Vis absorption spectrum and fluorescence analysis.Finally,the fluorescent sensors were used for the detection of Cr⁶⁺,Fe³⁺and Hg²⁺.The main research contents are as follows:?1?N-CDs with excellent dispersion,high fluorescence intensity and high quantum yield were prepared by one-step hydrothermal method with thymidine as carbon source and ethylenediamine as nitrogen source.N-CDs based fluorescent sensor was constructed based on inner filter effect?IFE?and used for sensitive detection of Cr⁶⁺.Under optimal conditions,a good logarithmic relationshipwas obtained in Cr⁶⁺range of 0.1-430?M?R²=0.9921?,and the theoretical detection limit was 1.26 nM?S/N=3?.In addition,the N-CDs fluorescent sensor had excellent anti-interference ability and good reproducibility.A satisfactory recovery in real water samples?89.51%-111.27%?was obtained and the results of the sensor were close to the inductively coupled plasma mass spectrometry?ICP-MS?results,which provided an excellent platform for the detection of Cr⁶⁺in environmental water samples.?2?A luminescent amino-functionalized metal-organic framework?Cu-MOFs?was synthesized from 2-aminoterephthalic acid and Cu?II?ions by a solvothermal method.Then,the related characterization and optical properties were studied.A fluorescent sensor based on Cu-MOFs nanoparticles was constructed and applied to sensitive detection of Fe³⁺in real water samples.The obtained detection range for Fe³⁺was 2-35?M?R²=0.9927?and the theoretical detection limit was 0.50?M?S/N=3?.Additionally,a good logarithmic relationship between relative fluorescence intensity and Fe³⁺concentration ranging from 2-180?M was obtained with detection limit of 1.56?M?R²=0.9975?.In addition,the Cu-MOFs fluorescent sensor had acceptable recoveries for the detection of Fe³⁺in real water samples?92.66%-110.65%?,and the detection results were consistent with the ICP-MS results,providing an effective mean for the application of MOFs in environmental protection or monitoring.?3?A new ratio fluorescent sensor based on fluorescence resonance energy transfer?FRET?was constructed by encapsulating green fluorescent coumarin derivative?CND?in Cu-MOFs nanoparticles.The constructed CND/Cu-MOFs ratio fluorescent sensor was used for sensitive detection of Hg²⁺.Its optical performances were analyzed by UV-Vis spectrophotometer and fluorescence spectrophotometer.The influence of alcohol-water ratio,temperature and reaction time on the performances of sensor were investigated.Under optimal conditions,between the range of 2×10^-8-0.001 nM,the concentration of Hg²⁺and the ratio of fluorescence emission intensity of the system(F₄₃₀/F₅₀₅)showed a good logarithmic relationship?R²=0.9901?.In addition,the sensor had excellent anti-interference ability and good stability,and it showed good recoveries for the detection of Hg²⁺in real water samples.