【作者】 刘中飞；

【导师】 金绍维；

【作者基本信息】 安徽大学 ， 材料物理与化学， 2019， 博士

【摘要】 近年来,随着科学技术的迅猛发展,电子设备在生物系统、通信安全、医疗保健、电子器件等方面的广泛应用带来了许多电磁辐射污染问题。为了解决这些问题,研究并制备出高性能的电磁波吸波材料迫在眉睫。沸石咪唑酯骨架材料(ZIFs)是一类以Zn或Co为金属源、咪唑或咪唑衍生物为有机配体在溶剂中反应自组装成的具有沸石骨架结构的金属有机框架材料(MOFs),因其具有稳定性强、比表面积大、多孔结构、框架多样性等特点,则表现出更优异的电磁吸收性能;同时,ZIFs的组成和结构可调性为研究设计新型电磁波吸收材料提供了更多的可能性。石墨烯(RGO)作为一类导电材料,具有密度低、表面积大、缺陷多等特点,也是一类高效的电磁波吸收材料;一般情况下,将石墨烯与磁性材料进行复合制备出磁性材料/石墨烯复合材料来提高介电常数和磁导率的匹配程度,从而达到增强电磁波吸收的目的。本文以沸石咪唑酯骨架材料(ZIFs)和氧化石墨烯(GO)为前驱体,通过自组装和高温热解法制备出ZIFs衍生物与RGO的复合材料。通过调控ZIFs与GO不同摩尔比以及不同退火温度,对复合形成的ZIFs衍生物/RGO材料进行机理分析、形貌表征与结构表征,进而研究ZIFs衍生物/RGO复合材料的电磁波吸收性能。具体研究内容为:(1)本课题组采用Hummers法制备氧化石墨烯,通过在高温下煅烧得到石墨烯(RGO),对RGO进行XRD、SEM表征,并用网络矢量分析仪(VNA)测试其电磁参数,模拟计算石墨烯(RGO)的反射损耗(RL)值为-6.5 dB,进而来衡量其电磁波吸收性能的强弱。(2)先用Hummers法制备氧化石墨烯,然后将溶于甲醇溶液的2-甲基咪挫溶液缓慢地加入Zn(N03)2·6H20甲醇溶液中进行配位形成沸石咪唑酯骨架材料ZIF-8;再以GO和ZIF-8为前驱体,采用溶剂热法和碳化过程(800℃煅烧)制备出 ZIF-8 衍生物 ZnO@N-C/RGO 复合材料。利用 XRD、RAMAN、XPS、SEM、TEM、TG、BET和VNA等测试仪器进行测试,对其物相、形貌、结构和电磁波吸收性能进行表征和分析。通过调节GO和ZIF-8不同摩尔比的配比来调控ZIF-8衍生物ZnO@N-C/RGO复合材料的电磁参数,进而研究ZnO@N-C/RGO复合材料的电磁波吸收性能,其最大反射损耗(RL)值为-37.12 dB,此时厚度为 3.5 mm,RL≤-10 dB 的有效吸收带宽为 1.92 GHz(从 5.28 GHz 到 7.2 GHz)。(3)以沸石咪唑酯骨架材料ZIF-67和氧化石墨烯(GO)为前驱体,采用溶剂热法和碳化过程制备ZIF-67衍生物/RGO复合材料;通过对GO和ZIF-67不同摩尔比的调控,使用各种测试手段分析GO占比对复合材料电磁波吸收性能的影响,进而找到GO和ZIF-67的最佳摩尔比。当GO占比最佳摩尔比时,研究与分析在不同退火温度(500℃、600℃和700℃)下煅烧所形成复合材料的组成成分、形貌表征与结构表征,并探究其电磁波吸收性能。研究结果表明,ZIF-67衍生物/RGO复合材料随着煅烧温度的变化得到的复合物不同,造成其电磁波吸收性能不同;样品500-3的复合物是Co3O4@N-C/RGO,样品600-3的复合物是Co3O4/Co@N-C/RGO,样品 700-3 的复合物是 Co@N-C/RGO;且在 600℃煅烧下得到的ZIF-67衍生物Co304/Co@N-C/RGO复合材料电磁波吸收性能是最强的,其最大反射损耗(RL)值为-43.52dB,此时厚度为2.0mm,RL≤-10dB的有效吸收带宽可以达到4.81 GHz(从11.08 GHz到15.89 GHz)。(4)采用溶剂热法将ZIF-67与ZIF-8按照一定比例混合制备Coo.5Zn0.5ZIF,然后以GO和Coo.5Zn0.5ZIF为前驱体制得Co0.5Zn0.5ZIF/GO复合物,最后将其经过高温热解得到Co0.5Zn0.5ZIF衍生物与石墨烯复合材料,最终产物为Co/ZnO@N-C/RGO复合材料。通过调节GO和Co0.5Zn0.5ZIF的配比以及退火温度来探究复合材料的电磁波吸收性能,最终确定最佳或最合适的前驱体比例和退火温度,并对最终产物的物相、形貌、结构和性能进行表征与分析。研究结果表明,在600℃煅烧下得到的Coo.5Zno.5ZIF衍生物Co/ZnO@N-C/RGO复合材料电磁波吸收性能最强,其最大反射损耗(RL)值高达-52.2 dB,此时厚度为3.5 mm,RL≤-10 dB的有效吸收带宽可以达到5.6 GHz(从8.72 GHz到14.32 GHz)。更多还原

【Abstract】 With the rapid development of science and technology in recent years,the widely applications of electronic equipment in biological systems,communication security,medical care and electronic devices has caused many electromagnetic radiation pollution problems.In order to solve these problems,it is extremely urgent to prepare and study the high-performance electromagnetic wave absorbing(EWA)materials.Zeolitic-imidazole-framework materials(ZIFs)are a class of metal organics with zeolite skeleton structure which are obtained through self-assembling reactions between the metal source(Zn or Co)and organic ligands(imidazole or imidazole derivatives)in a solvent.Metal-organic framework materials(MOFs)exhibit superior performance in electromagnetic absorption due to their high stability,large specific surface area,porous structure and diversified framework.At the same time,the chemical composition and structural adjustability of ZIFs have provide a great probability for design and research of new types of EWA materials.As a kind of efficient conductive material,reduced graphene oxide(RGO)has the characteristics of low density,large surface area and abundant defects.It is also a kind of high-efficiency electromagnetic wave absorbing material.In general,the composite materials based on RGO and magnetic materials can obviously improve the matching degree of dielectric constant and magnetic permeability to achieve in enhancement of electromagnetic wave absorption.In this paper,zeolitic-imidazole-framework materials(ZIFs)and graphene oxide(GO)were used as precursors to prepare composites of zeolitic imidazolate skeleton(ZIFs)material derivatives and reduced graphene oxide(RGO)through self-assembly process and high-temperature pyrolysis.The mechanism analysis,morphological characterization and structural characterization of the composites of ZIFs derivative/RGO materials were carried out by adjusting the different molar ratios of ZIFs and graphene and different annealing temperatures,and then the electromagnetic wave absorption properties of ZIFs derivatives/RGO composites were studied.The specific research content is as follows:(1)The research group used the Hummers method to prepare graphene oxide(GO).The reduced graphene oxide(RGO)obtained by calcination at high temperature was characterized by XRD and SEM,and vector network analyzer(VNA).In order to evaluate the electromagnetic wave absorption performance of the as-prepared samples,the electromagnetic parameters was tested,and the simulated calculation was carried out to obtain reflection loss(RL)value of RGO(-6.5 dB).(2)The graphene oxide(GO)was prepared by Hummers method and the ZIF-8 materials were synthesized through coordination reaction between the 2-methylimidazole solution and Zn(NO3)2·6H2O methanol solution by slowly adding the former into the latter.After that,ZnO@N-C/RGO composite was prepared by using GO and ZIF-8 as precursors through solvothermal method and carbonization process(800℃ calcination).The phase,morphology,structure and electromagnetic wave absorption properties of the ZnO@N-C/RGO composite were characterized and analyzed by XRD,Raman,XPS,SEM,TEM,TG,BET and VNA.The electromagnetic parameters of ZIF-8 derivative ZnO@N-C/RGO composites were regulated and controlled by the molar ratios of GO and ZIF-8,and the electromagnetic wave absorption properties of ZnO@N-C/RGO composites were studied.The maximum reflection loss(RL)of ZnO@N-C/RGO composites can reach up to-37.12 dB,the coating thickness is 3.5 mm,and the effective absorption bandwidth of RL≤-10 dB is 1.92 GHz(from 5.28 to 7.2 GHz).(3)ZIF-67 derivative Co3O4@N-C/RGO composite was prepared by solvothermal method and carbonization process(500℃ calcination)using ZIF-67 and GO as precursors.By controlling the molar ratios of GO and ZIF-67 and analyzing the effect of GO ratio on the electromagnetic wave absorption performance of the composite,the optimal molar ratio of GO and ZIF-67 in the composite materials was finally proposed.For the samples with the best molar ratio of GO,the composition,morphological characterization and structural characterization of the composites formed by calcination at different annealing temperatures(500℃,600℃and 700℃)were studied and investigated,and the electromagnetic wave absorption properties were explored.The results suggest that the variation of calcination temperature for preparing ZIF-67 derivative/RGO composites leads to different electromagnetic wave absorption properties.The composite of 500-3,600-3 and 700-3 samples obtained at the temperatures of 500℃,600℃ and 700℃ are Co304@N-C/RGO,Co3O4/Co@N-C/RGO and Co@N-C/RGO,respectively.The electromagnetic wave absorption property of the ZIF-67 derivative Co3O4/Co@N-C/RGO composite obtained by calcination at 600℃ is the best,of which the maximum reflection loss(RL)value is-43.52 dB and the coating thickness is only 2.0 mm.Remarkably,the effective absorption bandwidth of RL≤-10 dB can reach 4.81 GHz(from 11.08 to 15.89 GHz)for the Co3O4/CO@N-C/RGO composite.(4)By using solvothermal method,a certain ratio of ZIF-67 and ZIF-8 are mixed to prepare Coo.5Zno.5ZIF,which was used as precursor to synthesize the Co0.5Zn0.5ZIF/GO complex.After that,the Co0.5Zn0.5ZIF derivative and graphene composite material were obtained by pyrolysis at high temperature,and the final product was Co/ZnO@N-C/RGO composites.By adjusting the ratio of precursor(Coo.5Zno.5ZIF and GO)and annealing temperature,the electromagnetic wave absorption performance of the composite was explored,and the optimal or most suitable precursor ratio and annealing temperature are determined.Additionally,the phase,morphology and characteristics of the final product are characterized and analyzed.Our studies find that the Coo.5Zno.5ZIF derivative Co/ZnO@N-C/RGO composite obtained by calcination at 600℃ has the excellent electromagnetic wave absorption performance.The reflection loss value(RL)of this sample is as high as-52.2 dB with a thickness of 3.5 mm,and the effective absorption bandwidth of RL≤-10 dB can reach up to 5.6 GHz(from 8.72 to 14.32 GHz).更多还原