Study On The Preparation And Functionalization Of MXene-based Conductive Hydrogel

Hydrogels are a kind of soft and flexible polymer materials with a three-dimensional（3D）network structure.Due to the good flexibility and water retention capacity,various hydrogels have been developed to meet the application requirements in different fields.However,traditional hydrogels still have shortcomings,such as low electrical conductivity,poor mechanical properties and biocompatibility,and single response to external stimuli,which limit their practical application range.A variety of methods have been implemented to improve the properties of hydrogels and expand their application range.Among them,the method of introducing functionalized nano-materials into the hydrogel network has attracted wide attention from researchers.Appropriate introduction of functionalized nanomaterials not only can improve the conductivity of the hydrogel,enhance the mechanical properties and biocompatibility,but also provide new functional responsiveness,which greatly breaks through the limitations of traditional hydrogels.Recently,a new class of two-dimensional（2D）transition metal carbide/nitride materials,called MXenes,exhibits unique metal conductivity,hydrophilicity,and good processability.Therefore,the two-dimensional MXenes nanosheets Gelation can not only maintain the performance of the original hydrogel to a certain extent,but also introduce new properties,so as to realize the multi-functionalization of MXenes-based hydrogel materials.To solve the above problems,this study adopted the research idea of gelatinizing two-dimensional MXene nanosheets,and then successfully prepared functionalized MXene hydrogels inspired by biomineralization methods.The MXene-based hydrogels not only maintain good physical properties,but also achieve excellent strain sensing performance,and can be further assembled into novel hydrogel-type microwave absorbers and electromagnetic shielding materials.（1）In the experiment,Ti₃C₂T_xMXene is prepared by the HCl-Li F etching method,then MXene nanosheets,polyacrylic acid（PAA）and amorphous calcium carbonate（ACC）are efficiently assembled into MXene-PAA-ACC composite hydrogels combined with the biomineralization process.Furthermore,the optimum MXene-PAA-ACC composite hydrogels are obtained by adjusting the experimental parameters（such as stirring speed,reaction time,reaction temperature and so on）.Then,a series of characterizations proved the successful formation of the hydrogel and showed a typical porous structure.（2）The MXene-PAA-ACC composite hydrogels prepared via a biomineralization method show good physical properties.MXene-PAA-ACC composite hydrogels exhibit good stretchability（～1500%）and self-healing capability.Moreover,the MXene-PAA-ACC composite hydrogels have excellent processability,and can conformally adhere to objects with complex shapes,which are different from MXene films.In addition,due to the existence of MXene nanosheets,the MXene-PAA-ACC composite hydrogels exhibit solid-like behavior,which is different from PAA-ACC hydrogels with liquid-like characteristics.More importantly,the MXene-PAA-ACC composite hydrogels with different MXene content maintained moderate electrical conductivity(0.1～0.8 S m^-1)and dry-swelling recyclability,making them flexible and reliable in applications.（3）In this paper,the MXene-PAA-ACC composite hydrogel-based strain sensors are successfully prepared by self-assembly,and the sensitivity（GF）of sensors is positively correlated with MXene content,while the sensing range is negatively correlated with MXene content.For instance,the maximum GF of 8.5 wt%MXene-PAA-ACC composite hydrogel-based strain sensor is 1.8,and the test sensing range is about 280%.What’s more,it can detect small deformation at a strain as low as 1%,and maintain stable resistance response even at a high tensile rate of 500 mm min^-1,which indicates that the hydrogel-based strain sensor has good reliability.Finally,the MXene-PAA-ACC composite hydrogel-based strain sensor can be used as a wearable device to recognize human motion.It can not only identify some large-scale and small-scale human activities,but also is suitable for some advanced sensing applications.（4）The microwave absorption and the absorption-dominated terahertz shielding performance of MXene-PAA-ACC composite hydrogels are systematically studied in this part.The MXene-PAA-ACC composite hydrogels with different MXene content are assembled into hydrogel-type microwave absorbers.Thanks to the high conductivity of MXene nanosheets,in the frequency of 16.4 GHz,the reflection loss of 8.5 wt%MXene-PAA-ACC composite hydrogel can reach-38.024 d B,and the effective absorption bandwidth is 2.32 GHz,achieving a good microwave absorption performance.Similarly,the MXene-PAA-ACC composite hydrogel-type terahertz shielding materials in this experiment are further prepared.The results show that:the EMI SE of the only 0.13 mm thickness of 8.5 wt%MXene-PAA-ACC composite hydrogel can reach 45.3 d B and the RL_maxvalue is 23.2 d B in the test frequency range of 0.2-2.0 THz.Moreover,the effective absorption bandwidth covers the whole band,which is better than previous reported terahertz shielding and absorption materials so far.In summary,the MXene-PAA-ACC composite hydrogel synthesized by the biomineralization-inspired process in this paper shows outstanding stretchability and processability,excellent shape adaptability and adhesion,rapid self-healing ability and recyclability,which demonstrate the flexibility and reliability in a variety of application areas.In addition,the MXene-PAA-ACC composite hydrogels exhibit sensitive deformation response and can be used as a sensor on the skin.Due to the combination of porous structure,moderate electrical conductivity and internal water-rich environment,the MXene-PAA-ACC composite hydrogels achieve good microwave absorption performance,and theterahertz shielding performance of the composite hydrogels show absorption-dominated characteristics.In short,this work not only provides an alternative strategy for the design of next-generation microwave absorbing materials and EMI shielding materials,but also provides an efficient and convenient method for the fabrication of MXene composite materials on a macro scale.