Collaborative Construction And Properties Of Cellulose Nanofibers/MXene Functional Composites

Cellulose nanofibers(CNFs)are a new kind of one-dimensional nanomaterials derived from natural plants.With characteristics of extensive sources,environmental protection,high aspect ratio,excellent mechanical properties,and adjustable physical and chemical properties,CNFs have important potentials for the applications of wearable and flexible electronics.Although CNFs can endow flexible electronic products with excellent mechanical properties,it will also bring challenges such as low conductivity to electronic products as CNFs are electronic insulating materials.As a new two-dimensional nanomaterial,MXenes with characteristics such as excellent electrical conductivity,thermal conductivity,photothermal properties,and antibacterial property,have aroused the wide concern of researchers all over the world.It has been reported to be applied in many fields such as energy,environment,biomedicine,and so on.However,the poor interactions of two-dimensional MXene nanosheets lead to low mechanical strength and poor flexibility of the MXene based materials.Therefore,based on the excellent physicochemical properties of one-dimensional CNFs and two-dimensional MXene,this paper develops a series of construction strategies and methods of CNFs/MXene functional composites with different structural forms,reveals the synergistic mechanism between one-dimensional CNFs and two-dimensional MXene nanosheets,and improves the comprehensive properties of CNFs/MXene composites through component regulation and structural design.We also explore the applications of CNFs/MXene functional composites in a variety of flexible electronic scenes(such as electromagnetic shielding,electronic fibers and textiles,nanogenerators,etc.).It can provide theoretical support and technical guidance for the realization of functionalization,high value,and diversified utilization of cellulose nanofibers based materials.It mainly includes the following aspects:1.Based on the problems of traditional shielding materials with large thickness,poor mechanical properties,and poor shielding performance,an ultrathin and flexible CNFs/d-Ti₃C₂T_x MXene composite electromagnetic shielding paper was prepared by combining one-dimensional CNFs with two-dimensional d-Ti₃C₂T_x MXene via a vacuum-filtration-induced self-assembly process.Under the synergistic action of two-dimensional d-Ti₃C₂T_x nanosheets and one-dimensional CNFs,the tensile strength,fracture strain,and the folding endurance of the composite paper can reach 135.4 MPa,16.7%,and?14260 times,respectively.Based on its excellent conductivity(739.4 S m^-1),the electromagnetic shielding value of CNFs/d-Ti₃C₂T_x composite paper is?25.8 d B at 12.4 GHz,which can shield more than99.7%of electromagnetic waves.Therefore,the CNFs/d-Ti₃C₂T_x composite paper has broad application prospects in the fields of flexible wearable equipments,weapon equipments,and robot joints.2.In the above work,the direct mixing of CNFs and MXene will decrease the conductivity of the composite paper.Therefore,we have prepared the ultrathin and flexible carbon nanotubes(CNTs)/d-Ti₃C₂T_x/CNFs CNFs(CMC GS)composite paper with gradient and"sandwich"structure.In this study,the introduction of CNFs into the composite paper in the form of interlayer improves the mechanical properties of the composite paper(tensile strength is about 97.9 MPa),and also eliminates the problem that the conductivity of the composite paper decreases due to the direct mixing of CNFs as an insulating material(the conductivity of CMC GS is about 2506.6 S m^-1).The undulating layered structure and slit?shaped micropores of composite layer are of great significance for increasing the reflection and absorption of electromagnetic waves and further enhancing its electromagnetic interference(EMI)shielding performance(EMI SE>43 d B).Through the analysis of the shielding performance of the composite paper,we conclude that the design of the sandwich structure can significantly improve the total electromagnetic shielding value of the composite paper,while the gradient structure has little effect on the total electromagnetic shielding value of the composite paper,but affecting the absorption coefficient,SE_R and SE_A value.Therefore,this work has important guiding significance for the preparation of composite materials with adjustable shielding performance.3.Inspired by natural materials,for the first time,flexible smart fibres and textiles are fabricated using a 3D printing process with hybrid inks of TEMPO-mediated oxidized cellulose nanofibrils(TOCNFs)and d-Ti₃C₂T_x MXene.The hybrid inks display good rheological properties,which allow them to achieve accurate structures and be rapidly printed.TOCNFs/d-Ti₃C₂T_x in hybrid inks self-assemble to fibres with an aligned structure in ethanol,mimicking the features of the natural structures of plant fibres.In contrast to conventional synthetic fibres with limited functions,smart TOCNFs/d-Ti₃C₂T_x fibres and textiles exhibit significant responsiveness to multiple external stimuli(electrical/photonic/mechanical).TOCNFs/d-Ti₃C₂T_x textiles with electromechanical performance can be processed into sensitive strain sensors.Such multifunctional smart fibres and textiles will be promising in diverse applications,including wearable heating textiles,human health monitoring,and human-machine interfaces.4.To overcome the problem that traditional TENGs are hard to achieve both extensibility and high electrical output performance simultaneously,a novel nanogenerator(CM-TENG)with shape adaptive and high electrical output performance was proposed by using TOCNFs/MXene mixture as liquid electrode and elastic silicone rubber as both packaging material and triboelectrification layer.The open-circuit voltage of CM-TENG can reach?300 V.The excellent fluidity and high electronegativity of MXene liquid electrode,rendered the TENG generates stable electrical output regardless of diverse extreme deformations.With harvesting mechanical energy from hand tapping motion,the TENG in a self-charging system can charge up capacitors to drive wearable electronics.Moreover,the TENG can be attached to both human skin and clothes as a human motion monitoring sensor,which can inspect the frequency and amplitude of various physiological movements.This work provides a new methodology for the construction of stretchable power sources and self-powered sensors,which have potential applications in diverse fields such as robotics,kinesiology,and biomechanics.