Preparation And Performances Of Chitosan-g-Poly N-[3-(Dimethylamino) Propyl Methacrylamide/ZIF-8 Composite Materials

The zeolitic imidazolate framework material（ZIFs）has the advantages of high porosity,high surface area,high thermal stability and frame adjustability.The properties of ZIF-8 can be regulated by adjusting its morphology,which makes it a potential candidate material for gas adsorption and separation.Chitosan possesses a typical amphiphilic structure.It can be constructed a surfactant-free emulsion system,and has good CO₂ responsiveness.Chitosan only dissolves in weak acidic environment,which is not conducive to the growth of ZIF-8.In the paper,a surfactant-free emulsion system is constructed by using hydroxyethyl cellulose（HEC）and chitosan as a composite surfactant-free emulsion and N-[3-（Dimethylamino）propyl]methylacrylamide（DMAPMA）modified chitosan.The morphology of ZIF-8 was investigated by two surfactant-free emulsions mentioned above to further prepare chitosan/ZIF-8 composite and study its properties.This paper consists of four parts.In Chapter 1,the progress on the controlled growth of MOFs in different emulsion systems was reviewed.Secondly,the controlled growth and product characteristics of ZIF-8 in different emulsion systems were summarized.Then,the structure and properties of chitosan were introduced,and the application of reversible addition fragmentation chain transfer polymerization（RAFT）in chitosan modification was summarized.Finally,the main research content and significance of this thesis are expounded.In Chapter 2,surfactant-free emulsion was constructed with chitosan/hydroxyethyl cellulose as emulsifier,and its morphology regulation on ZIF-8 was studied.The chitosan/hydroxyethyl cellulose/ZIF-8 composite（CHx Z）was prepared,and the carbon dioxide adsorption performance of the composite was also studied.The mass ratio of chitosan to hydroxyethyl cellulose was explored to control the morphology of ZIF-8.CHx Z was characterized by powder X-ray diffraction（PXRD）,Fourier transform infrared（FT-IR）,scanning electron microscopy（SEM-EDS）,transmission electron microscopy（TEM）,thermogravimetric characterization（TGA）,and specific surface area and aperture analysis（BET）.The results show that when m（CS）:m（HEC）increases from 0.2 to 5,the CHx Z lamellar thickness increases from 10 nm to 100 nm,and the crystallinity of CHx Z surface is higher.The CO₂adsorption capacity of CHx Z reached 1.48 mmol/g.The kinetic simulation showed that the morphology of ZIF-8 crystal in CHx Z had a significant effect on the adsorption mechanism of CO₂.When ZIF-8 crystal was a regular dodecahedron with uniform morphology,most of the adsorption behavior of ZIF-8 on CO₂ belonged to physical adsorption.When CHx Z has a fusiform lamellar structure,the adsorption behavior of CO₂ by CHx Z belongs to chemical adsorption.In Chapter 3,S-n-dodecyl-S’-（α,α’-dimethyl-α’-acetic acid）trithiocarbonate was used as chain transfer agent to synthesize poly N-（3-dimethylamino-propyl）methylacrylamide（PDMAPMA）by RAFT polymerization technique.Chitosan-g-poly(N-（3-dimethylaminopropyl）methyl acrylamide（CS-g-PDMAPMA）was prepared by‘grafting to’covalent combination of PDMAPMA and chitosan.The results were characterized by ¹H NMR and FT-IR.The actual molecular weight of PDMAPMA and the substitution degree of CS were calculated by nuclear magnetic resonance hydrogen spectrum.The critical micelle concentration（CMC）of CS-g-PDMAPMA was determined by ultraviolet method and fluorescence analysis pyrene probe method.The critical micelle concentration of CS-g-PDMAPMA was 0.3 mg/m L,and the critical micelle concentration of aggregation was 2mg/m L.SEM and TEM results showed that CS-g-PDMAPMA was self-assembled into spherical aggregates with a diameter of 100-150 nm in the aqueous phase.The chapter also studies the CO₂ responsiveness of CS-g-PDMAPMA in n-hexanol/water system.After CO₂ is introduced,a stable emulsion system is formed,and after N₂ is introduced,phase separation is realized.In Chapter 4,surfactant-free emulsion was constructed using CS-g-PDMAPMA to explore the morphological regulation of ZIF-8 by changing the composition factors of surfactant-free emulsion,and CS-g-PDMAPMA/ZIF-8 composite（ZIF-8@CS-g-PDMAPMAx）was prepared to further study its CO₂ adsorption performance.By means of PXRD and SEM,the crystal structure and morphology of the composites prepared by different molecular weight chitosan graft copolymer,CS-g-PDMAPMAx concentration,precursor addition sequence and reaction medium were investigated.When CS-g-PDMAPMAx of different molecular weight is added,ZIF-8@CS-g-PDMAPMAx nanoparticles were presented as dodecahedron,cube,sphere,etc.,and ZIF-8@CS-g-PDMAPMAx nanoparticles self-assemble into 3D hollow hierarchical pore structure.As the concentration of CS-g-PDMAPMA increases,excessive CS-g-PDMAPMA is loaded on the surface of ZIF-8,forming surface folded nanoparticles.When Zn²⁺is added first,ZIF-8@CS-g-PDMAPMA₃₀₀ is a dodecahedron with uneven particle size,and the nanoparticles self-assemble to form three-dimensional micro-mesoporous aggregates.When 2-MI is added first,the size of ZIF-8@CS-g-PDMAPMAx nanocomposite is uniform and the particle size is larger.After changing the reaction medium,ZIF-8@CS-g-PDMAPMAx showed a fusiform lamellar structure and a cross flower structure.Chitosan graft copolymer exhibits micellar state in water,and its rich structure regulates the morphology of ZIF-8@CS-g-PDMAPMAx composite materials.Moreover,chitosan graft copolymer can regulate the nucleation rate and morphology of ZIF-8 crystal through the coordination competition with 2-MI.ZIF-8@CS-g-PDMAPMA_X can adsorb 2.28 mmol/g of CO₂.The kinetic simulation shows that the CO₂adsorption kinetics of ZIF-8@CS-g-PDMAPMAx is more consistent with the PSO adsorption model,which belongs to chemical adsorption.The increasing concentration of CO₂in the atmosphere has caused many environmental problems,such as the greenhouse effect and snow melting.As a result,many efforts have been made to develop CO₂ capture technologies.ZIF-8 can adsorb CO₂ gas,and the adsorption efficiency and amount of CO₂ can be regulated by adjusting the morphology of ZIF-8.In this paper,by changing the structure of surfactant-free emulsion,different morphology of ZIF-8was obtained,such as ball,rod,cube,spindle sheet,cross flower,fold cube,etc.,which expanded the application of polymer/ZIF-8 composites in the field of CO₂ capture.