Modification Of Chitin Nanocrystals And Their Application In Dye Adsorption And Amphiphobic Coating

Chitin originates from abundant marine resources.It is hard for chitin to dissolve in water and organic solvents,which directly restricts its development and research.Natural chitin can be converted into chitin nanocrystals?Ch NCs?through various mechanical techniques or chemical reactions.Ch NCs are a novel natural nanomaterial with a lot of advantages of high aspect ratio,high mechanical modulus,unique needlelike morphology,large specific surface area,good dispersibility in water,which is easy of functionalization and biodegradability.Based on these characteristics,it is of great significance to develop many applications of Ch NCs,which provides important theoretical and experimental basis for the realization of turning chitin into valuable chemicals.In this thesis,the surface modification of Ch NCs and their potential applications in dye adsorption and amphiphobic coating are discussed.?1?Ch NCs were prepared from crab shells by acid hydrolysis.Morphology,liquid crystal behavior,and rheological properties of Ch NC solution by the ultrasonic treatment were characterized.Ch NC aqueous solution shows a uniformly needlelike morphology in a stable colloidal state.When the concentration of Ch NCs was above10 wt.%,birefringence is observed under a polarized optical microscopy.Porous Ch NC scaffolds were prepared by freeze-drying the uniformly dispersed colloidal solution of Ch NCs.To improve the stability of the scaffolds,Ch NC scaffolds were chemically cross-linked with glutaraldehyde.The physical properties of cross-linked scaffolds?XCh NCs?were also tested.It was found that XCh NCs had high mechanical strength,ultra-light density,high porosity,and adjustable water absorption.?2?The hydrophilicity of Ch NCs is modified by dopamine.The modified Ch NCs?D-Ch NCs?acted as intercalation layers,were inserted into the stacked graphene oxide?GO?nanolayers to expand their interlayer spacing via the method of vacuum filtration.With the addition of D-Ch NCs,the hydrophilicity and pure water flux of D-Ch NCs/GO composite membranes are remarkably improved.Due to the synergistic effect of dopamine modification and unique channel structure,the pure water flux of the D-Ch NCs/GO composite membrane increases to 135.6 L·m^-2·h^-1,while that of the pure GO membrane was only 8.8 L·m^-2·h^-1.The composite membrane has a highly efficient rejection??97.5%?for various oil droplets and dyes.After 5 cycles,the rejection rate of wastewater on the composite membrane is still above 91.5%,exhibiting a good recyclability and reproducibility.Therefore,D-Ch NCs/GO composite membrane is an optional multifunctional nanoadsorbent for organic dye and separator for oil/water.?3?Si O₂ nanoparticles were deposited on the surface of Ch NCs to synthesize Ch NCs/Si O₂ composite particles through St?ber reaction.Then,Ch NCs/Si O₂ particles were modified with thiol-groups?-SH?and fluorinated long chains?-F?via thiol-ene click reaction.Finally,hierarchical micro/nanostructured Ch NCs-SH-F/Si O₂ particles were fabricated with low surface energy surface.The water/oil contact angles of Ch NCs-SH-F/Si O₂powders are both over 156.2°,and the sliding angles are both less than 9.3°.The prepared powder can even repel n-decane with ultra-low surface energy(surface energy 23.3 m N·m^-1),showing super hydrophobic and oleophobic properties.Meanwhile,Ch NCs-SH-F/Si O₂ coating has good abrasion resistance and temperature stability?-74?200°C?.After soaking in dye and oil solution repeatedly,the coated surface remains clean without wetting,illustrating the coating with good self-cleaning property.