Study On The Synthesis And Properties Of Graphene Nanoribbons And Their Composites

Electromagnetic wave absorption and shielding materials are mainly used to absorb or attenuate electromagnetic waves,which is an important means to prevent and control the increasingly serious electromagnetic radiation pollution.At present,the new electromagnetic wave absorption and shielding materials should meet the requirements of "strong","wide","light","thin" and resistant to high temperature,corrosion and other characteristics.Therefore,carbon materials,including carbon black,carbon fiber,graphene,carbon nanotubes,biomass,etc.,have attracted extensive attention in electromagnetic wave absorption and shielding fields due to their light weight,high temperature resistance,corrosion resistance and unique electrical properties.As a kind of derivative material of graphene,graphene nanoribbons?GNRs?have potential application value in many fields such as energy conversion and storage,catalysis,sensing,adsorption and electromagnetic wave absorption and shielding,due to their high specific surface area,excellent mechanical and electrical properties,high chemical reactivity and rich edge structure,as well as strong modifiable and controllable properties and structures.At present,the application research of graphene nanoribbons at home and abroad mainly focuses on energy conversion and storage,catalysis,sensing,adsorption and other fields,while the application research of graphene nanoribbons in electromagnetic wave absorption and shielding materials is rarely reported.In this paper,we used multi-walled carbon nanotubes?MWCNTs?as the raw materials,and prepared graphene oxide nanoribbons?GONRs?by longitudinal shear and stripping of MWCNTs using chemical oxidation method firstly.Then,we have fabricated graphene oxide nanoribbons with different reduction degree?r-GONRs?,graphene nanoribbons-Fe₃O₄?GNRs-Fe₃O₄?nanocomposites,and graphene nanoribbons-polyurethane?GNRs-PU?composite sponge by functionalizing and assembling the GONRs.In order to explore their potential application prospects,we have studied the absorption performance and mechanism of r-GONRs and GNRsFe₃O₄ nanocomposites,as well as the the properties of GNRs-PU composite sponge in strain sensing,electromagnetic shielding,organic solvent adsorption and electrochemistry.The research contents of this paper are mainly divided into the following three aspects:1.Firstly,we have prepared GONRs by longitudinal shear and stripping of MWCNTs using chemical oxidation method,and characterized the microstructure and chemical state of the prepared GONRs by TEM,SEM and XPS.The results showed that the MWCNTs have been cutting successfully into GONRs,and the prepared GONRs contained oxygen-containing functional groups such as epoxy,hydroxyl,carbonyl and carboxyl groups.Then,the graphene oxide nanoribbons with different reduction degree were prepared by freeze-drying and controlled reduction of hydrazine hydrate.The prepared GONRs have high EM wave absorption performance in the high frequency band,in the optimized reduction condition,the EM wave absorption value reaches the maximum value of-65 d B at 17 GHz with the thickness of 2.12 mm.Moreover,the efficient absorption bandwidth?reflection loss ?-10 d B?reaches 7.06 GHz?10.75-17.81 GHz?with the thickness of 2.5 mm.2.Based on the above research results on EM wave absorbing of graphene nanoribbons,in order to solve the problem of high EM wave absorbing performance moving to the lower frequency band,we have loaded Fe₃O₄ magnetic nanoparticles onto graphene nanoribbons.The GNRs-Fe₃O₄ nanocomposites with different Fe₃O₄ loads were prepared by in-situ coprecipitation method.The magnetic Fe₃O₄ nanoparticles prepared had a small particle size about 15-25 nm,which were superparamagnetic.Meanwhile,the interaction between Fe₃O₄ nanoparticles and GNRs is strong.The load of Fe₃O₄ nanoparticles plays a regulatory role in the electromagnetic parameters of GNRs-Fe₃O₄ nanocomposites,so as to adjust the impedance matching characteristics and loss capacity of the material.GNRs-Fe₃O₄ nanocomposites exhibit high EM absorption performance,and realize the movement of high absorption to the lower frequency band.For the composites of the weight ratio of GONRs and Fe₃O₄ nanoparticles is 1:4,the reflection loss is up to-67 d B at 11.9 GHz with the thickness of 2.25 mm and the effective absorption bandwidth is 4.57 GHz?11.52-16.09 GHz?with the thickness of 2 mm.3.Graphene nanoribbons are difficult to assemble into three-dimensional?3D?macroscopic materials.In this paper,with the aid of PU sponge as a template,we have introduced the GNRs into the 3D skeleton of PU sponge to prepare GNRs-PU composite sponges by electrophoretic deposition method.This kind of composite sponges improves the mechanical properties of GNRs 3D macroscopic materials.Because the composite sponge organically combines the good electrical conductivity of graphene nanoribbon with the excellent mechanical flexibility of polyurethane sponge,it has a good resistance response when used as the electrode of strain sensor.Due to the strong dielectric loss of GNRs and porous structure of the composite sponges,GNRs-PU composite sponges exhibit excellent electromagnetic shielding properties and can be used as electromagnetic shielding and absorbing materials.Due to the hydrophobicity of GNRs,the surface of composite sponges is hydrophobic and oleophilic,therefore,GNRs-PU composite sponges can be used in the adsorption field of organic solvents.Meanwhile,the GNRs-PU composite sponges with enhanced surface area and chemical functionality can serve as supercapacitor electrodes,showing a good cycling stability of 92% capacitance retention after 5000 cycles tested in a three-electrode electrochemical configuration.