Preparation Of Graphene Based Nanocomposites And Its Radiation Properties

Graphene,as a novel two-dimension carbon nanomaterial,has shown great potential applications in optoelectronics,biochemistry,aerospace and other fields owing to its outstanding thermodynamics,electromagnetism and other properties.Due to the high electron mobility and high thermal conductivity,the energy conversion of graphene can be accelerated by valence band transitions and lattice vibrations in order to adjust the target surface infrared emissivity to the ideal value.At the same time,electromagnetic losses and photoelectric conversion could achieve the microwave absorption.In addition,graphene can be modified through the surface group modification and in situ assembly methods to meet the different needs of composite nanomaterials.Quantum dots are conduction band electrons,valence band holes and excitons in three directions bound by the semiconductor nanostructures.Due to the unique quantum effects and surface effects,quantum dots have become the hot spots of photoelectric materials.The quantum dots with excellent optoelectronic properties has great potential applications in the field of absorption.In this paper,graphene was prepared by oxidation of natural graphite,and then rGO/Au was synthesized by in situ reduction method.Boron nitride quantum dots was fabricated by microwave reaction roution.Furthermore,3D-G/BNQDs was self-assembly prepared.The microstructure and composition of the products were characterized by Fourier transform infrared spectroscopy(FT-IR),ultraviolet visible absorption spectroscopy(UV-vis),fluorescence emission spectroscopy(PL),scanning electronic microscope(SEM),transmission electronic microscope(TEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and so on.Finally,the effects of different reaction conditions on microstructure,the infrared emissivity value in the wavelength ranged from 8 to 14 μm and the microwave absorption ranged from2 to 18 GHz of the products were investigated,and the following results were obtained.1.Synthesis and characterization of Graphene/Au(rGO/Au)Graphene oxide was prepared by oxidizing natural graphite powder,then added the chloroauric acid and sodium citrate,finally the rGO/Au was synthesized by in situ reduction.The influence of the reducing agent and reaction time on the size of gold particles and their distribution on the surface of graphene were investigated to regulate the infrared emissivity and microwave absorption.Graphene oxide has specific amount surface area,which contains a large number of active groups for gold nanoparticles to assemble and recombination.The research shown the infrared emissivity value(8~14 μm)of the nanocomposite were 0.618.As for microwave absorption,the product exhibited an optimal reflection loss of-19.2 dB with a broad effective absorption bandwidth of 8.1 GHz in the frequency range of 2~18 GHz,which is better than graphene.The results reveals the introduction of Au with highly reflective metallic could effectively reduce the infrared emissivity value of the composites.2.Synthesis and characterization of boron nitride quantum dots(BNQDs)Boron nitride quantum dots(BNQDs)were fabricated by a facile and high-efficiency microwave irradiation technique.Meanwhile,the particle size and QY of BNQDs can be well controlled by adjusting microwave reaction temperature as well as duration time.Boron nitride is a novel graphene-like two-dimensional nanomaterial with a wide band gap(6.4 eV),which has excellent optoelectronic properties,thus the boron nitride is a hot spot in the field of two-dimensional nanomaterials.Microwave irradiation strategy is identified as an advanced and beneficial method not only for high-efficiency energy inputting but also time-saving in comparison with the reported solvothermal process.The diameter of the as-prepared blue luminescent BNQDs were unique.The research shown the as-prepared BNQDs reveals low infrared emissivity value(8~14 μm).Furthermore,attributed to the unique nanostructure,quantum confinement effect,and high dielectric loss,the as-prepared BNQDs exhibits excellent microwave absorption in the frequency range of 2~18 GHz,demonstrating as potential microwave absorptionmaterial in electromagnetic interference field.3.Synthesis and characterization of 3D graphene/boron nitride quantum dots(3D-G/BNQDs)After the surface of graphene was modified,the 3D-G/BNQDs were prepared by self-assembly of layer-by-layer interface with the boron nitride quantum dots prepared by microwave irradiation.The layer spacing of the composition could be adjusted by the particle size of quantum dots.By adjusting the number of layers,layer spacing and other structural parameters,the radiation wave absorption or frequency shift process could be controllable,thus achieve the effectively coordination of the material,structure and function in multiple ways.Graphene owes a large specific surface area which provide access to quantum dots to assemble after surface modification.Furthermore,graphene has the similar structure to boron nitride,so the composite could enhance the synergistic effect of the two materials.The 3D structure has a huge specific surface area,which is easy to increase its interface polarization and increase Interlayer reflection loss,in order to achieve low infrared emission and microwave absorption requirements,demonstrating an ideal infrared and microwave compatible absorbing material.The infrared emissivity(8~14 μm)of 3D-G/BNQDs were as low as 0.608 and exhibited excellent microwave absorption performance in the 2~18GHz frequency range with a maximum reflection loss of-26.2 dB and an effective absorption bandwidth of 8.0 GHz.Compared with the traditional ferromagnetic microwave absorbing materials,3D-G/BNQDs have the advantages of large absorption bandwidth,small density,and environmentally friendly,which can meet the different needs in the field of electromagnetic interference.