Controllable Preparation,Electromagnetic Excitation Mechanism And Microwave Absorption Of Cu-Based Core-Shell Heterostructures

Copper nanowires?NWs?are an excellent electromagnetic shielding material with low percolation threshold,low cost,high conductivity,high thermal conductivity,and high abundance.According to the principle of impedance matching,high conductivity is conducive to the reflection of electromagnetic waves but against the absorption of electromagnetic waves.The reflected electromagnetic wave forms secondary pollution,at the same time the pure copper is easily oxidized when exposed to air.In this paper,a hydrothermal method was developed to synthesize Cu₂O/PPy core-shell nanowires?Cu₂O/PPy CSNWs?,which worked as the precursor for the controllable synthesis of a series of copper-based CSNWs via carbon thermal reduction,vapor deposition,Ostwald maturation and liquid phase reduction.The formation mechanism of CSNWs and the regulation methods of their size,composition,structure and surface-interface were systematically studied,and the effects of size,composition,structure and surface-interface on their static magnetic properties and microwave absorption properties?MAPs?were investigated.Specific research contents are as follows:1.Controlled preparation and characterization of Cu₂O/PPy CSNW precursorsHigh purity cuprous Cu₂O/PPy core-shell nanowires?Cu₂O/PPy CSNWs?were synthesized by a hydrothermal method for mass production of high purity copper-based core-shell nanowires.Meanwhile,peapod-like Cu₂O/PPy CSNWs were formed via an Ostwald maturation process.The phase structure,C shell thickness and diameter?d?of Cu₂O/PPy CSNWs were adjusted by controlling the ratio???of copper acetate to pyrrole,reaction temperature?T?and reaction time?t?.With the increase of???=2?12?,the diameter of Cu₂O/PPy CSNWs with a length of 100?m decreased from 240±20 nm to 70±20 nm,the shell thickness ranged from 5 to 40 nm.The peapod-like Cu₂O/PPy CSNWs with controllable morphology could be obtain by further adjustment of curing time?t_a?.The results provide a simple,low-cost,controllable and high yield method for the preparation of1D heterogeneous core-shell nanomaterials.2.Controlled preparation and microwave absorbing performances?MAPs?of Cu/CCSNWsUsing Cu₂O/PPy CSNWs as the precursors,copper/carbon core-shell nanowires?Cu/C CSNWs?with diameters ranging from 70 to 190 nm and shells ranging from 5 to 40 nm were prepared through a carbothermal reduction method.The phase structure,C shell thickness and core diameter of Cu/C CSNWs can handily be tuned via changing sintering temperate?T_s?,acetone volume?V_a?,the molar ratios of Cu?Ac?₂ to pyrrole???and sintering temperature and time.The optimal MAP was exhibited by Cu/C CSNWs with the diameter of 110±20 nm,C shell thickness of 5–8 nm and C/Cu mass ratio of 0.051 to 0.61 produced at T_s=600°C,?=6 and V=0?1 mL.The effective bandwidth?R_L?–10 dB?showed the maximal value of 6.28 GHz,corresponding to a sample thickness of 2.4 mm.The minimum R_L value of-46.6 dB was reached at 17.3 GHz with a sample thickness of 2.0 mm.The superior MAP is ascribed to the synergy of Plasmon resonance enhanced permittivity,dual dielectric relaxation,high attenuation and good impedance matching.Therefore,our findings provide a new strategy for Plasmon resonance enhanced permittivity and MAPs to solve electromagnetic?EM?pollution problems.3.Controllable synthesis and microwave absorption properties of Cu/Fe/C andCu/Fe₃O₄/C CSNWsAccording to the impedance matching principle,the enhancement of the permeability is an effective way to improve the absorbing performance.We reported the synthesis of Cu/Fe/C and hollow Cu/Fe₃O₄/C CSNWs chemically converted from Cu₂O/PPy CSNWs via an in-situ carbothermic reduction-CVD process.Temperature?T_s?,Fe?CO?₅ volume?V_b?and N₂ purity are the key factors to modulate the surface and interface,composition,size and phase of the products.Changing T_s and V_b could also handily modulate the surface morphology and composition of the products;Controlling N₂ purity could selectively synthesize hollow Cu/Fe₃O₄/C CSNWs and Cu/Fe/C CSNWs with strawberry-like surface based on the surface diffusion mechanism.The Cu/Fe/C CSNWs and hollow Cu/Fe₃O₄/C CSNWs exhibited high soft magnetic and MAPs.In view of the synergistic effect of the enhanced permittivity and permeability,dual dielectric relaxations,dual magnetic resonances,high attenuation and good impedance matching,Cu/Fe/C CSNWs formed at T_c=600°C and V_b=4 mL were excellent absorbers that feature strong absorption,broad bandwidth and light weight.An optimal reflection loss?RL?of-43.09 is achieved at 13.07 GHz with a matching thickness of 1.8 mm,and RL values less than–20 dB can be gained over 3.3?4.5 GHz and5.11?15.9 GHz.This work may provide a general method for modulating surface and interface of carbon-based magnetic composites for lightweight and broad bandwidth microwave absorbing materials.4.Controlled preparation and characterization of Cu₂O/PPy/Ag CSNWsIn order to enhance the MACs of Cu₂O/PPy CSNWs,a low temperature chemical reduction method was used to modify the surface of Cu₂O/PPy CSNWs with Ag nanospheres and Ag nanopieces.Under 60?80°C and p H=9.2?9.7,Ag⁺ions with concentration?n=72.5 mM,145 mM?were reduced into Ag nanospheres on the surface of PVP modified Cu₂O/PPy CSNWs with a diameter of 270?980 nm.When PVP and D-glucose were used as surfactant and reductants,respectively,Ag⁺ions were reduced to Ag nanopieces on the surface of Cu₂O/PPy CSNWs at 80?95°C.Ag nanoparticles with different morphologies can promote the Cu₂O/PPy/Ag CSNWs to form a conductive network,which thus improves the conductivity of Cu₂O/PPy CSNWs.This study provides a new strategy for the surface and interface modification.