Synthesis And Characterization Of Conjugated Schiff Base And Its Composites With Graphene For Electromagnetic Wave Absorption

Conjugated Schiff base has the advantages of adjustable conductivity,simple synthesis,various structures and light weight.As a kind of dielectric loss absorbing agent,it has attracted extensive attention in the field of electromagnetic microwave absorption.However,the study of the absorbing agent of Schiff base and metal coordination has mostly focused on the coordination with alkaline earth metals.In this paper,we synthesized 18 conjugated Schiff bases and their rare earth metal salts,and their compositions were analyzed and the conductivity and electromagnetic parameters were tested.The results show that the conductivity of Schiff base and the rare earth metal are improved,but their absorbing properties need to be improved.Therefore,we selected a series of poly?p-phenylene terephthalene?Schiff base Ce³⁺salt and graphene oxide dispersion?GO?with best conductivity and absorbing performance to synthesize a kind of light,high-performance Schiff base rare earth metal salt/graphene composite absorbing material.The main contents of research are as follows:?1?Firstly,three kinds of short-chain conjugated Schiff bases and three kinds of long-chain conjugated Schiff bases were synthesized from ethylenediamine,p-phenylenediamine,benzaldehyde,cinnamaldehyde,terephthalaldehyde,p-benzoquinone and 1,4-naphthoquinone.Then as-prepared six conjugated Schiff bases were coordinated with the rare earth metal ions La³⁺and Ce³⁺to synthesize 12kinds of Schiff base rare earth metal salts.,and they were characterized and tested by FT-IR,UV-Vis,¹H-NMR,four probes conductivity meter and vector network analyzer.Finally,the relationships between their structure,conductivity and absorbing properties were analyzed.The results show that the conductivity of the conjugate Schiff base absorber can be improved by introducting rare earth metal and increasing conjugate degree;and the conductivity of Poly?p-benzoquinone p-phenylenediamine Schiff base?Ce³⁺salt is as high as 23.2S/cm.They do not have effective absorbing properties in the test range,but their electromagnetic parameters are not sensitive to frequency,and they exhibit multi-peak alternating incremental decreasing with frequency,which can improve absorbing performance and broaden absorption frequency width.?2?Poly?p-benzoquinone p-phenylenediamine Schiff base?Ce³⁺salt with best conductivity and absorbing properties was choosed to prepared composites according to above results.A series of Poly?p-benzoquinone p-phenylenediamine Schiff base?Ce³⁺salt/graphene composites were synthesized by Schiff base Ce³⁺salt and GO by chemical reduction self-assembly method..Composite materials were characterized and tested by FT-IR,Raman,XRD,SEM,four probes conductivity meter and vector network analyzer.The relationships between the structure,conductivity and absorbing properties of the composites were analyzed,and their absorbing mechanisms were studied.The results show that the composites have good absorbing properties,and the excellent performance is the result of multiple factors.Among them,SGA-51 has excellent performance.When its thickness is 3.3mm,the maximum reflection loss reaches-60.37dB at 11.24GHz;and the corresponding effective absorption bandwidth reaches 5.60GHz?8.96-14.56GHz?.At the same time,when the thickness of SGA-51 is 2.8mm,the corresponding effective absorption bandwidth is up to 7.04GHz?10.96-18.00GHz?,and the density of the material is only 0.0147g/cm^-3,which is a lightweight absorbing material with strong absorption and frequency bandwidth.