Preparation Of Novel Carbon Quantum Dots@ZIF-8 Optical Composites And Study Of Their Fluorescence Sensing Propertie

Metal-organic framework（MOFs）,also known as porous coordination polymers（PCPs）,is a class of coordinated compounds composed of metal ions and organic ligands.It has the advantages of high crystallinity,adjustable pore size,clear structure and high functional degree and is a new type of inorganic-organic hybrid material.MOFs have attracted attention for the development of excellent luminescent materials due to their own luminescence centers of inorganic and organic molecules.The pores inside the MOFs can also be used to encapsulate a large number of luminescent objects,which provides a wider range of luminescent properties for MOFs materials.In this work,we introduced different luminescence groups into the classical ZIF-8 skeleton to obtain composite hybrid materials,and used it as a fluorescent probe for a series of luminescence detection.Powder diffraction,infrared spectrum,ultraviolet spectrum and transmission electron microscopy were used to test the properties and applications of the products,and to explore the applications of chiral substances,biological small molecules and amines.This work is summarized as follows:1、In this work,ZIF-8 framework was synthesized by one-pot method,and oil-soluble carbon nanoclusters（CNCs）were successfully introduced into ZIF-8framework to produce a stable hybrid materials CNCs@ZIF-8（1）.The PXRD pattern of the hybrid material was confirmed to be consistent with the simulation results by powder diffraction characterization,and the structural stability and solvent stability of1 were verified,and 1 could stably exist in a variety of solvents.Fluorescence characteristics and transmission electron microscopy（TEM）results showed that CNCs were successfully encapsulated in ZIF-8 skeleton and pores.In addition,fluorescence detection also showed that 1 could identify nitrofurazone(NFZ,K_BH:1.99×10⁶M^-1)and lysine(Lys,K_SV:2.26×10⁵M^-1)with high sensitivity and selectivity with“on”and“off”fluorescence switches,respectively,with a lower detection limit（NFZ:0.0229μM.Lys:0.0096μM）,and has a good repetition efficiency.According to the fluorescence enhancement effect of 1 before and after adding lysine,1 can be used as a fluorescent ink for anti-counterfeiting.2、In this part,ZIF-8 was also used as the basic framework,and the chiral hybrid material CCQDs@ZIF-8（2）was obtained by adding the chiral carbon quantum dots（CCQDs）in the process of preparing the ZIF-8 skeleton.Powder diffraction characterization（PXRD）not only confirmed the successful synthesis of 2skeleton,but also confirmed its purity.2 has good stability,whether in different solutions or in the presence of folic acid,2 can maintain structural stability.Transmission electron microscopy（TEM）was used to observe the morphology changes of 2 before and after the adsorption of carbon CCQDs,which proved that CCQDs could adsorb in the ZIF-8 skeleton without affecting the structure of ZIF-8.Photoluminescence results showed that 2 could selectively distinguish the presence of folic acid in a series of chiral substances,especially for D-folic acid(FA,K_BH（D-FA）:9.82×10⁴M^-1.K_BH（L-FA）:2.99×10⁴M^-1),and the discrimination K_D/K_Lof the two configurations was 3.28.In addition,2 was also effective in distinguishing nitrofurazone(NFZ,K_BH:3.29×10⁴M^-1)from other substances among antibiotics.2has the advantages of high selectivity,low detection limit（D-FA:0.31μM.L-FA:4.36μM.NFZ:3.06μM）and high sample reusability in the detection of FA and NFZ.Due to the fluorescence enhancement effect caused by the addition of FA and NFZ,2can be used as fluorescent ink and mixed matrix membranes for anti-counterfeiting materials.In practice,2 can detect the FA content of different brands and compare the advantages and disadvantages by NFZ content in different brands of milk.3、In this work,the previous work was extended by adding fluorescein in 2 and using the“one-pot”method to synthesize the hybrid material fluorescein/CCQDs@ZIF-8（3）.The results of powder diffraction characterization（PXRD）of 3 were consistent with the theoretical fitting results,which proved the successful synthesis and confirmed the purity of 3.In addition,the structural stability of 3 was verified.In a variety of organic solvents,3 could keep its skeleton unchanged,and the target would not destroy the structure of 3.Transmission electron microscopy（TEM）showed that the chiral carbon quantum dots（CCQDs）were attached to the ZIF-8 skeleton.The results of photoluminescence showed that CCQDs and fluorescein could be used as a variety of fluorescent probes due to their characteristic luminescence and different luminescence intensity.3 can effectively identify p-phenylenediamine in the isomer of phenylenediamine and distinguish the oxidized o-,m-,and p-phenylenediamine.The performance of this result is slightly different in different solvents.When ethanol is used to prepare the target solution,3can be used as ratiomeric fluorescent probe to detect the newly prepared PPD(K_BH:1.85×10³M^-1and detection limit:8.51μM);as a ratiomeric fluorescent probe,the K_SVof oxidized PPD was 6.82×10²M^-1,and the detection limit was 0.112 mM;for oxidized MPD as ratiomeric fluorescent probe,the K_BHwas 1.65×10³M^-1and the detection limit was 35.03μM;for oxidized OPD as ratiomeric fluorescent probe,the K_BHwas 2.40×10⁶M^-1,and the detection limit was 0.105μM.3 can also be made into fluorescent ink for anti-counterfeiting applications,and make mixed matrix membranes to achieve the rapid and easy detection of p-phenylenediamine.