Self-assembly Preparation Of Two-dimensional Materials/Metal Oxide Composites And Their Microwave Absorbing Properties

With the rapid advancement of electronic information technology,electromagnetic waves are widely used in various fields.However,electromagnetic pollution also poses a threat to human health and national defense security.Therefore,the development of highperformance electromagnetic wave absorbing materials that meet the requirements of "thin,light,wide,and strong" has received much attention.Traditional microwave absorbing materials have problems such as narrow effective absorption bandwidth and high density.In recent years,oxides and two-dimensional conductive materials have been proposed for designing microwave absorbing materials.However,single dielectric oxides have weak absorption,single magnetic oxides have narrow absorption bandwidth,and graphene and MXene have drawbacks such as high conductivity,easy stacking,and poor dispersion.This work is based on the multiscale design of composite microwave absorbing materials,using the electrostatic self-assembly theory at the molecular and microscopic levels.Three types of absorbing materials composed of oxides and twodimensional conductive materials were successfully designed and prepared through selfassembly.1.Aerogels with three-dimensional structure were prepared by adding graphene oxide as a precursor in the hydrothermal synthesis of manganese dioxide.The functional groups on the surface of graphene oxide anchor the precursors of manganese dioxide through electrostatic interaction,and the crystal growth process forms a self-curling onedimensional fiber core-shell structure.Adjusting the addition of graphene oxide gives a three-dimensional structure that is further self-assembled by van der Waals forces.The final obtained aerogel achieves an effective absorption bandwidth of 6.4 GHz at 2.2 mm at a filling level of 15 wt.%.At 17.36 GHz,the minimum reflection loss can reach-41.3d B.2.Hydroxy vanadium oxide(VOOH)with hollow structure was synthesized and modified by Poly(diallyldimethylammonium chloride)(PDDA)to have a positive surface charge.It is mixed with the MXene monolayer obtained by wet exfoliation.The two achieve layer-by-layer self-assembly between the particles and the sheets under the influence of positive and negative charges.Although The hollow structure prevents stacking between MXene sheet layers on a geometric level,as well as effectively controlling the density of the material.The resulting material achieves an effective absorption of 4.08 GHz at a loading of 30 wt.%.At 11.2 GHz,the minimum reflection loss is-34.9dB,corresponding to a matching thickness of 2.2 mm.3.Self-assembled spherical particles formed between graphene and ferric oxide particles are constructed by adding the precursor graphene oxide during the hydrothermal synthesis of ferric tetroxide.The PDDA modified magnetic tetroxide@graphene complex is then successfully employed to prepare a layer-by-layer self-assembled structure between magnetic particles and MXene by electrostatic self-assembly.The introduction of the magnetic phase expands the absorption efficiency of the material at low frequencies,while the conductive MXene broadens the absorption bandwidth at high frequencies.The final material achieves a maximum reflection loss of-5dB in the 8-12 GHz range,with an effective absorption of 5.04 GHz at high frequencies.The minimum reflection loss at a thickness of 3.6 mm is-48dB.