原位改性对石墨烯和石墨烯纳米带的电磁性能影响

发布时间：2018-09-07 10:28

【摘要】：吸波材料是一种重要的军事隐身功能材料,在军事和民用具有迫切的需求,石墨烯材料具有质量轻、比表面积大、高的介电常数等性质,是一种极具前景的吸波材料。但石墨烯能带间隙为零,性质不易调控,在吸波领域应用受到限制。石墨烯的能带带隙可以通过量子限域或化学掺杂产生,掺杂的杂原子可以有效调节其电子结构和其他内在特性。本论文从——氮掺杂石墨烯、不同程度氧化程度的石墨烯纳米带及其氮掺杂三个方面来调控石墨烯的电磁参数,实现材料的阻抗匹配和衰减吸收特性,制备出具有优异的吸波性能的石墨烯基材料。以氧化石墨烯前驱体,尿素作为氮源,采取水热还原法,制备氮掺杂石墨烯,调控氧化石墨烯与尿素质量比,制备出不同氮含量的氮掺杂石墨烯。采用化学氧化碳纳米管法制备氧化石墨烯纳米带,调节碳纳米管与高锰酸钾的比例,制备出不同氧化程度的氧化石墨烯纳米带,采用水热法对氧化石墨烯纳米带进行氮掺杂,得到氮掺杂石墨烯纳米带。掺氮石墨烯的微观形貌为多孔层状结构,有利于电磁波多重反射吸收,在氮掺杂过程中氧化石墨烯同时被还原,氮掺杂使得氮掺杂的晶面间距变小,片层部分发生堆叠,具有很大比表面积。10NG、30NG、50NG的氮含量分别为8.54 at%、7.52 at%、7.61at%,氮掺杂的氮含量越高,石墨烯的晶格缺陷越多。氮原子在石墨烯中掺杂的形式有三种吡啶型、吡咯型以及石墨型氮,本论文中制备出的氮掺杂石墨烯的氮掺杂类型主要是以吡啶型和吡咯型为主。采用化学氧化切割碳纳米管制备的氧化石墨烯的微观形貌呈现带状,宽度约为200nm。加入高锰酸钾的量越大,氧化石墨烯纳米带的氧化程度越大,带状打开越大,所含氧官能团比例越高。氧化石墨烯纳米带边缘具有丰富的官能团,这些官能团可以作为极化中心,有利于电磁波吸收。采用水热法制备的氮掺杂石墨烯纳米带,具有带状形貌,石墨烯层间间距变大。在氮掺杂过程,氧化石墨烯纳米带被还原,边缘的含氧官能团大大减少。3NGNR、5NGNR、7NGNR的氮含量为3.53at%、3.76 at%、4.77 at%,氮含量越高,石墨烯晶格上的缺陷越多。将制备出的氮掺杂石墨烯、氧化石墨烯纳米带、氮掺杂氧化石墨烯纳米带与石蜡进行混合,样品质量分数为30%,制作内径为3mm、外径为7mm、厚度在3mm左右的圆环进行电磁性能测试,测出其电磁参数,根据传输线理论计算出材料的损耗角正切和反射损耗。对于氮掺杂石墨烯,50NG在厚度3mm时,RL-10dB的频段为8.14-12.84GHz,有效带宽为4.7GHz,在9.84GHz处取得最大吸收为-16.03dB。对于氧化石墨烯纳米带,5GONR在厚度为3mm时,RL-10d B的频段为9.4GHz-18GHZ,频宽为8.6GHz,频率为12.5GHZ有最大反射耗为-23dB。对于氮掺杂石墨烯纳米带,7NGNR在3mm厚时,RL-10dB的频段为7GHz到11GHz,频宽为4GHz,频率为9GHZ最大反射损耗为-45dB。与石墨烯相比,量子限域或化学掺杂制备得到的氮掺杂石墨烯和石墨烯纳米带的吸波性能大大提高,有利于制备高性能的吸波复合材料。
[Abstract]:Absorbing material is an important military stealth functional material, which is urgently needed in military and civilian applications. Graphene is a promising absorbing material because of its light weight, large specific surface area and high dielectric constant. However, the gap between energy bands of graphene is zero, and its properties are difficult to control, so its application in absorbing field is limited. The band gap of graphene can be generated by quantum confinement or chemical doping, and the doped heteroatoms can effectively adjust its electronic structure and other intrinsic properties. In this paper, the electromagnetic parameters of graphene can be controlled from three aspects: nitrogen-doped graphene, graphene nanoribbons with different degrees of oxidation and nitrogen-doped graphene nanoribbons. Nitrogen-doped graphene was prepared by hydrothermal reduction method with graphene oxide precursor and urea as nitrogen source. Nitrogen-doped graphene with different nitrogen content was prepared by adjusting the ratio of graphene oxide to urea. Graphene oxide nanoribbons were prepared by hydrothermal method. graphene oxide nanoribbons with different oxidation degrees were prepared by adjusting the ratio of carbon nanotubes to potassium permanganate. nitrogen-doped graphene nanoribbons were prepared by hydrothermal method. nitrogen-doped graphene nanoribbons were obtained by hydrothermal method. Graphene oxide is reduced simultaneously in the process of nitrogen doping. Nitrogen doping reduces the interfacial spacing of nitrogen-doped graphene oxide and stacks the lamellae. The nitrogen contents of 10 NG, 30 NG and 50 NG are 8.54 at%, 7.52 at, 7.61 at, respectively. The higher the nitrogen content of nitrogen doping, the more defects of graphene lattice. There are three types of nitrogen doping in inks, pyrrole type and graphite type. The nitrogen doping types of nitrogen-doped graphene prepared in this paper are mainly pyrrole type and pyrrole type. The larger the amount of graphene oxide nanoribbons, the greater the degree of oxidation, the greater the opening of the ribbons, and the higher the proportion of oxygen-containing functional groups. The nitrogen content of 3NGNR, 5NGNR, 7NGNR is 3.53 at%, 3.76 at%, 4.77 at%. The higher the nitrogen content, the more defects on the graphene lattice. The nitrogen-doped graphene, graphene oxide nanobelts and nitrogen-doped oxygen are prepared. The graphene nanoribbon was mixed with paraffin wax, the mass fraction of the sample was 30%, the inner diameter was 3 mm, the outer diameter was 7 mm, and the thickness was about 3 mm. The electromagnetic parameters were measured. The loss tangent and reflection loss of the material were calculated according to the transmission line theory. For graphene oxide nanoribbons, the maximum absorption is - 16.03 dB at 9.84 GHz. For graphene oxide nanoribbons with a thickness of 3 mm, the RL-10dB band is 9.4 GHz-18 GHZ, the bandwidth is 8.6 GHz, and the maximum reflection loss is - 23 dB at a frequency of 12.5 GHz. For nitrogen-doped graphene nanoribbons, the RL-10dB band with a thickness of 3 mm has a 5GONR. Compared with graphene, N-doped graphene and graphene nanoribbons prepared by quantum confinement or chemical doping have better microwave absorbing properties, which is beneficial to the preparation of high-performance microwave absorbing composites.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB34;TQ127.11

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