Preparation And Properties Of Two-dimensional Transition Metal Carbides/nitrides(MXenes)-based Aerogels

Transition metal carbides/nitrides(MXenes)are emerging group of two-dimensional(2D)materials with outstanding electrical properties and versatile chemical properties derived from surface terminations.By now,the studies and applications of MXenes are mainly based on their composite films and powder-like hybrid nanomaterials.However,the stacks of MXenes can trigger some problems,including the reduction of specific surface area and the increased contact electrical resistance between the sheets,which will restrict the performance of MXene-based materials.Construction of three-dimensional(3D)porous architectures can solve these problems in micro-scale.Nevertheless,the limited surface terminations and weak interactions between MXene sheets make it difficult to assemble MXene nanosheets into 3D macroscale structure.Herein,we need to investigate accessible methods to realize the assembly of MXene sheets so that we can manipulate the micro-structure of nano-materials.To realize the assembly of 2D MXene into 3D structure,we develop various assembly strategies,including assembly of MXene in mono-liquid phase and at the interface between different liquid phases.As a result,we successfully prepare MXene aerogels with tunable micro-structure,which can overcome the problems derived from the stacks of MXene sheets.We also study the applications of as-synthesized MXene-based aerogels such as employing the aerogels as conductive fillers to prepare conductive nanocomposites for electromagnetic interference shielding.The main works are as follows:(1)Preparation of MXene-based conductive aerogels via reduced graphene oxide(RGO)assisted assembly in liquid phase,and the applications of MXene aerogels filled nanocomposites for electromagnetic interference shielding:because of the assembly capacity of RGO during the liquid phase reduction process of graphene oxide,RGO,which is obtained by hydrothermal and chemical reduction,is employed to induce the assembly of MXene in liquid phase.After the assembly,we obtain a MXene-based 3D architecture.In addition,ethanol assisted directional-freezing and subsequent freeze-drying are used to obtain MXene/RGO conductive hybrid aerogels with uniform pores.When the aerogels are employed as conductive fillers in epoxy conductive nanocomposite,the nanocomposite shows electrical conductivity as high as 695.9 S m-1 with only 0.74 vol%MXene content,in addition,its electromagnetic interference shielding efficiency exceeds 50 dB with maximum value of 56.4 dB over the whole X band.(2)Preparation of Janus MXene by selective modification,and the investigation of its amphiphilicity.Amphiphilicity assisted assembly of Janus MXene at the oil/water interface for MXene aerogels preparation:a single face of MXene is modified to be oleophilic via one-step transferring of positively charged polystyrene chains onto one surface of MXene sheets,while another face remains hydrophilic.Consequently,amphiphilic Janus MXene is prepared,which enriches the species of Janus particles and strategies for preparation of Janus particles.Herein,the amphiphilicity of Janus MXene endows it with ability to assemble at the oil/water interface and reduce the interfacial tension so that it can stabilize the emulsion.Inspired by such phenomena,we assemble Janus MXene at the interface of emulsion and subsequently remove the liquid phase to obtain MXene-based aerogels.The micro-structure of MXene aerogels are tunable,so this attempt opens a new avenue for applications of MXene.