Syntheses And Properties Of CDs@ZIF-8 Composites

As a new type of zero-dimensional luminescent carbon nanomaterials,carbon dots(CDs)have received extensive attention from researchers due to their unique optical properties,excellent electron transport capabilities,good biocompatibility,low toxicity and chemical inertness.CDs plays an important role in sensing,biological imaging,drug transportation,catalysis,electrochemistry and many other fields.Combining CDs with other functional materials can utilize the advantages of them and make up for the shortcomings of single material.The synergy between them can make the composite material have enhanced optical/electrical properties.Metal-organic frameworks(MOFs)are porous crystalline materials constructed by organic ligands and inorganic metal ions or metal clusters,and have great potential in energy conversion,drug delivery,gas storage and separation,proton conduction,chemical sensing,catalysis,and many other fields.MOFs are ideal matrixes due to their ultra-high porosity,specific surface area,adjustable pore size and diversified structures.Such materials can effectively disperse CDs and limit the vibration and rotation of the surface functional groups of CDs,thereby stabilizing the physical and chemical properties of the CDs and enhancing their optical properties.On the other hand,CDs as guest materials can improve the chemical stability and thermal stability of MOFs.Furthermore,the synergy of the host-guest can promote the electron transfer ability between CDs and MOFs and futher enhance the interaction between the composite materials and the target molecule,which enables the composites to have improved electrical properties and new functions.This thesis focuses on the preparation and properties of CDs@MOF composites.We select a MOF material(e.g.ZIF-8)with simple synthesis and stable structure as host matrix,and use the organic ligands as the precursor materials of CDs to prepare CDs@ZIF-8 composites.On the one hand,we are committed to explore feasible and green synthesis strategies for constructing the composites,and on the other hand,the influence of synthesis conditions and structural compositions on the optical and catalytic properties of CDs@MOF have been studied.The main contents of this paper are as follows:1.In the first chapter,we first introduce the origin and development of metal-organic framework materials,the design and synthesis strategies based on their structure and properties,and their applications in various fields.Secondly,we present the various synthesis methods of carbon dots,and introduce the relationship between their optical/electrical properties and structures,and some related applications.Finally,we introduce the research status and significance of carbon dots-based composites from the aspects of preparation,classification and application,and further present the significance of the topic selection and research ideas of this thesis.2.In the second chapter,a new synthesis strategy of pyrolyzing organic ligands in MOFs to prepare CDs@MOF composite is proposed,and CNDs@ZIF-8 composites with adjustable luminescence are prepared by controlling the calcination time.CDs encapsulated in the MOFs matrixes usually block the pores of MOFs.This synthesis strategy allows CDs to grow in situ and embed in the interrupted cavities of MOFs,which makes the composites have better adsorption ability than the original MOFs.In addition,this synthesis strategy can make CDs and MOFs integrate closely,which may promote the interaction between host and guest,thus can further adjust the optical properties of CDs.CNDs@ZIF-8 exhibits approximate white light emission by combining the inherent blue emission of ZIF-8 and the yellow emission of CNDs.On the other hand,CNDs@ZIF-8 also shows temperature-responsive photoluminescence properties,so it can be used as a temperature sensor.This work paves a feasible way for the development of CNDs@MOF materials with both luminescence and adsorption properties.3.In order to further simplify the synthesis method and reduce environmental pollution,we propose a simple one-pot method to prepare CDs@ZIF-8 in a solvent-free system in the third chapter,and study the potential application of CDs@ZIF-8 as a nanoenzyme in biological analysis.In CDs@ZIF-8 composite,the ZIF-8 matrix can protect CDs from aggregation and quenching,which increases the participation of CDs for catalytic reactions.The embedding of CDs into ZIF-8 matrix is conducted to rapid electron transfer,and their synergetic effect promotes the composite materials to have superior peroxidase-like activity.Based on this,a sensitive and convenient colorimetric approach can be established to detect H2O2 and glutathione(GSH).This work provides a feasible strategy for the synthesis of CDs-based composite nanozyme with enhanced catalytic activity.4.In order to improve the catalytic performance of CDs@ZIF-8 nanoenzymes prepared in Chapter 3,cheap and easily available copper ions are introduced into non-active ZIF-8 nanocrystals to have good peroxidase-like activities in Chapter 4.Therefore,we design and synthesize the dual-catalyst CDs@Cu-ZIF-8 composite materials.The composites are synthesized by an one-pot method in solvent-free system as usual.The better catalytic performance can be obtained by adjusting the content of Cu ions in ZIF-8 matrix.CDs@Cu-ZIF-8 is more effective for glutathione than CDs@ZIF-8.In order to further verify the applicability of CDs@Cu-ZIF-8 as nanoenzymes,the composite is successfully used for the detection of glutathione in actual biological environment.This work expands the potential of CDs@MOF nanozymes in the fields of biochemical analysis and detection.5.Finally,in Chapter 5,we summarize the main research results of this thesis.Also,we put forward to accurately control the structures and performances of CDs@MOF and expanding their practical applications in the fields of biology,energy and environment.