Preparation And Properties Of Porous Oriented MXene Composite Aerogels Based On Modified Hyaluronic Acid

The rapid development of wireless electronic devices has brought great convenience to our society,and the increasingly serious electromagnetic radiation pollution has become a global problem.Therefore,it is significance to develop electromagnetic shielding materials to prevent electromagnetic radiation pollution.With the rapid development of aerospace field and wearable electronic devices,it is urgent need to develop lightweight,high-performance and multifunctional electromagnetic shielding materials.MXene,as an emerging two-dimensional nanomaterial,has excellent electrical conductivity,large specific surface area,good hydrophilicity,and unique layer structure,which makes it widely used in the field of electromagnetic shielding.However,the stacking problem caused by the lamellar structure of MXene nanosheets affects the formation of its active sites and charge conduction network,and the disadvantages of MXene such as weak self-assembly ability,poor mechanical properties and easy oxidation seriously affect the application of MXene in electromagnetic shielding field.Constructing two-dimensional MXene into three-dimensional structures is an effective way to solve the stacking problem and lightweighting,and can improve the ion conduction efficiency.Polymers are widely used to prepare functional MXene composites with three-dimensional skeletons because of their low cost,simple preparation,and tunable functions.However,combining lightweight,robust,high conductivity,self-healing,and environmental stability in a three-dimensional MXene macrostructure is still a very difficult challenge.In this thesis,we prepare multifunctional 3D porous composite aerogel with orientation by combining modified natural polysaccharide with 2D MXene not only to provide 3D skeleton structure for MXene,but also to better demonstrate the high electrical conductivity and high electromagnetic shielding properties of MXene.First,we constructed a three-dimensional ordered porous MXene/HAC composite aerogel by oriented freezing method using high conductivity two-dimensional Ti3C2Tx MXene nanosheets as conductive filler and dopamine-grafted hyaluronic acid（HAC）and sodium tetraborate（Borax）as aerogel backbone.The introduction of the three-dimensionally ordered porous structure drastically reduces the density of the material(up to 18.8 mg cm^-3),and the rich hydrogen bonding between HAC and MXene connects the MXene nanosheets to form an oriented porous aerogel,and such an oriented arrangement allows MXene to produce a continuous conductive network with a conductivity of 74 S m^-1.At the same time,the porous structure enhances the multiple scattering and attenuation of electromagnetic waves inside the composite material,which improves the absorption of electromagnetic waves and electromagnetic interference.At 90 wt%of MXene,the composite aerogel with 4mm thickness exhibited 54.2 d B of EMI shielding effectiveness（EMI SE）in the X-band（8.2-12.4 GHz）range,and its absolute shielding effectiveness SSE/t value could reach 7180d B cm²/g,with a shielding efficiency of 99.9996%.The introduction of modified natural polysaccharide HAC enhanced the mechanical properties of the three-dimensional porous backbone,and the composite aerogel with MXene content at 60 wt%could withstand a stress of 93 k Pa at 70%compressive strain.Meanwhile,the formation of dynamic catechol-borate bond between catechol moiety and sodium tetraborate makes it self-healing,and the conductivity and mechanical properties of the composite aerogel are improved after self-healing,and the composite aerogel can maintain 94%of the original shielding value after self-healing.In order to further impart its functionality,MXene/HA-DA/PG/PEI aerogel was prepared by introducing pyrogenic gallic acid（PG）and polyethyleneimine（PEI）into the aerogel structure on the basis of the above.The three-dimensionally ordered porous structure allows a minimum density of 31.9 mg cm^-3,and the addition of PG and PEI further enhances the mechanical properties of the three-dimensional porous skeleton with a maximum compressive stress of 96.7 k Pa at 70%compressive deformation.The MXene network provides up to 69.3 S m-1 conductivity,demonstrating 53 d B EMI shielding effectiveness at X-band and 4 mm thickness,and absolute shielding effectiveness SSE/t values up to 4154d B cm²/g,with shielding efficiency up to 99.9995%.While maintaining lightweight,robust and high conductivity,the catechol groups of dopamine and pyrogallic acid and polyethyleneimine can form catecholamine film to inhibit the diffusion of air into the three-dimensional skeleton,thus improving the easy oxidation of MXene.The aerogel without PG and PEI retained only 13.6%of its initial conductivity,while it retained 72%of its initial conductivity even after seven days in extreme environments.Meanwhile,the dynamic covalent bonds formed by the catechol groups and sodium tetraborate were repeatedly cross-linked by H₂O and O₂,and the compressive stress could reach 1 MPa after two weeks of placement in extreme environments,showing good self-growth properties.This lightweight,robust,stable and multifunctional electromagnetic shielding composite is expected to show potential applications in aerospace and portable communication electronic devices.