【作者】 何鹏；

【导师】 颜军；

【作者基本信息】 中南大学 ， 无机化学， 2024， 博士

【摘要】 开发新型高效电磁波吸收材料对于民用电磁防护和军事装备升级具有重要的研究意义。传统的电磁波吸收材料存在吸波机制单一和构效关系不清等问题,难以满足现代电磁环境下的复杂需求。针对目前电磁波吸收材料的瓶颈问题,多金属氧酸盐（多酸）可以作为一类理想的分子设计平台或功能组分添加到吸波材料体系中。多酸精确且多样的结构,丰富的磁学性质,良好的有机无机复合能力,与周围组分间的极化效应都可以为吸波材料性能的提升提供有利的支撑。本论文围绕吸波材料的设计,开展了多酸类电磁波吸收材料的结构形貌设计与性能关联研究。采用限域构筑和原位转换等策略,控制合成了多种异质结构的多酸类复合材料。通过调控形貌,组分,界面和缺陷等,厘清不同因素对电磁参数和阻抗匹配的影响规律,并不断优化吸波材料的最小反射损耗（RL）和最大有效吸收带宽（EAB）,揭示了多酸类电磁波吸收材料的吸波机理和构效关系,为团簇基吸波材料的开发与探索提供了新的视野和数据支撑。本论文的具体工作如下:（1）首次利用Keplerate型钼蓝团簇系统地设计制备了一维钼蓝/聚苯胺/多壁碳纳米管({Mo₇₂X₃₀}/PANI/MWCNTs,X=Fe,V)三元电缆状纤维,并将其用于电磁波吸收。三元电缆结构层与层之间存在丰富的异质界面,改善了电磁波吸收过程中的偶极极化和界面极化效应,调节了传导损耗。此外,钼蓝团簇的引入增加了磁损耗,并平衡了阻抗匹配特性。最优的{Mo₇₂V₃₀}/PANI/MWCNTs在较薄的厚度（2.3 mm）下具有较高的最小RL可以达到-48.12 d B。在厚度为2.5 mm时,{Mo₇₂Fe₃₀}/PANI/MWCNTs表现出最大EAB为6.16 GHz。证明了多酸本体分子在电磁波吸收领域的应用前景。（2）结合实验（1）发现,Keplerate型钼蓝分子的结构多样性优势还远未被发掘。例如,钼蓝可以在分子结构中均匀定量地引入过渡金属组分。为分子重构后多组分复合材料的均匀分布提供了保证。此外,钼蓝表面的高负电荷可以使其在分子预组装初期与碳基材料很好地结合,有利于进一步的设计加工。因此将钼蓝作为分子预组装平台,制备了一系列可调谐的Fe_0.54Mo_0.73/Mo₂C@C（FMC）复合材料。钼蓝在限域空间内碳化保留了丰富的界面,促进了界面极化,而双金属Fe_0.54Mo_0.73粒子显著提高了Mo₂C@C的电磁波吸收性能。随着Fe_0.54Mo_0.73颗粒含量的增加,最小RL不断从高频区（Ku波段）向低频区（S波段）移动。优化后的FMC-5具有良好的电磁波吸收性能,在4.08GHz时最小RL为-48.91 d B。该工作为探索通过分子预组装策略制备多酸衍生吸波材料提供了思路。（3）除了组分和结构,形貌也是影响吸波材料性能的重要因素。师法自然,一系列仿生蜂巢结构的电磁波吸收材料（X-Mo S₂/Cu₉S₅MH,X=P,Si,Ge）通过限域生长和原位硫化的方法被成功制备。X-Mo S₂/Cu₉S₅ MH展现出低密度、高表面积和丰富的阴阳离子双空位(V_Cu和V_S)结构,是传统吸波材料无法比拟的。同时系统地研究了不同杂多酸对仿生蜂巢中空位的影响。实验结果和密度泛函理论计算表明,仿生蜂巢优异的吸波性能（-56.21 d B）是形貌设计、组分优化和空位调控等因素协同作用的结果。（4）以混合价态十钒酸盐为钒氧化物（VO_x）分子模型,成功制备了一种雷达,红外和热隐身气凝胶。超轻{V^ⅣV₉^V}/MXene气凝胶（0.0429 g/cm³）具有出色的雷达隐身性能,其最小RL为-57.74 d B,雷达截面减少值可达26.77 d B·m²。混合价态十钒酸盐的存在导致肖特基势垒的增加从而增强界面极化,而磁性能的增强促进了吸波过程中的磁损耗。中空结构和界面热阻效应保证了气凝胶的低红外发射率（0.479）和低导热系数(32.30 m W·m^-1K^-1),红外成像展示了该气凝胶的红外隐身和热隐身性能。因此,改变价电子的数目显著提高了兼容隐身能力。这些发现为进一步研究基于VO_x的兼容隐身材料的开发提供基础。图114幅,表15个,参考文献285篇更多还原

【Abstract】 The development of new efficient electromagnetic wave absorption（EMWA）materials is of significant research significance for civilian electromagnetic protection and military equipment upgrades.Traditional EMWA materials face problems such as a single absorption mechanism and unclear structure-property relationships,making it difficult to meet the complex requirements of the modern electromagnetic environment.Addressing the bottleneck issues of current electromagnetic wave absorption materials,polyoxometalates（POMs）can serve as an ideal molecular design platform or functional component to be added to the absorption material system.The precise and diverse structures,rich magnetic properties,excellent organic-inorganic composite ability,and polarization effects between surrounding components of POMs can all provide favorable support for improving the performance of absorption materials.This thesis focuses on the design of absorption materials,conducting structural morphology design and performance correlation studies of POM-based EMWA materials.Various heterostructure POM-based composite materials were synthesized by controlling strategies such as confined construction and in situ transformation.By regulating morphology,composition,interfaces,and defects,the influence of different factors on electromagnetic parameters and impedance matching was clarified.Furthermore,the minimum reflection loss（RL）and maximum effective absorption bandwidth（EAB）of the absorption materials were continuously optimized,revealing the absorption mechanism and structure-property relationship of POM-based EMWA materials,providing new perspectives and data support for the development and exploration of cluster-based absorption materials.The specific work of this thesis includes:（1）For the first time,Keplerate-type molybdenum blue cluster systems have been utilized to design and prepare systematically one-dimensional molybdenum blue/polyaniline/multi-walled carbon nanotube({Mo₇₂X₃₀}/PANI/MWCNTs,X=Fe,V)ternary coaxial cable-like fibers,which were then applied in EMWA.The coaxial cable structure possesses rich heterogeneous interfaces between layers,which improves dipole polarization and interface polarization effects during EMWA,and adjusts conduction losses.Additionally,the introduction of molybdenum blue clusters increases magnetic losses and balances impedance matching characteristics.The optimized{Mo₇₂V₃₀}/PANI/MWCNTs exhibit a higher minimum RL of-48.12 d B at a thinner thickness of 2.3 mm.At a thickness of 2.5 mm,{Mo₇₂Fe₃₀}/PANI/MWCNTs demonstrate a maximum EAB of 6.16 GHz.This proves the application prospects of POM molecules in the field of EMWA.（2）Combining research（1）,it is found that the structural diversity advantages of Keplerate-type molybdenum blue molecules have yet to be fully explored.For instance,molybdenum blue can uniformly and quantitatively introduce transition metal components into molecular structures,ensuring the homogeneous distribution of multi-component composite materials after molecular reconstruction.Additionally,the high negative charge on the surface of molybdenum blue facilitates its excellent binding with carbon-based materials during the initial stage of molecular preassembly,which is advantageous for further design and processing.Therefore,we used molybdenum blue as a pre-assembly platform to prepare a series of tunable Fe_0.54Mo_0.73/Mo₂C@C composite materials.Molybdenum blue retains rich interfaces during the carbonization process in the confined space,promoting interface polarization,while bimetallic Fe_0.54Mo_0.73 particles significantly enhance the electromagnetic wave absorption performance of Mo₂C@C.With the increase in Fe_0.54Mo_0.73particle content,the minimum RL continuously shifts from the high-frequency region（Ku-band）to the low-frequency region（S-band）.The optimized FMC-5 exhibits excellent electromagnetic wave absorption performance,with a minimum RL of-48.91 d B at 4.08 GHz.This work provides insights into exploring the preparation of POM-derived absorbing materials through molecular preassembly strategies.（3）Apart from composition and structure,morphology is also an important factor influencing the performance of absorbing materials.Drawing inspiration from nature,a series of biomimetic microhoneycomb electromagnetic wave-absorbing materials（X-Mo S₂/Cu₉S₅ MH X=P,Si,Ge）are prepared using confined growth and in situ sulfurization methods.X-Mo S₂/Cu₉S₅ MH exhibits low density,high surface area,and rich anionic-cationic double vacancies(V_Cu and V_S)structure,which are unparalleled by traditional absorbing materials.Furthermore,we systematically investigated the influence of different heteropolyoxometalates on the vacancies in the biomimetic honeycomb.Experimental results and density functional theory calculations indicate that the excellent absorption performance（-56.21 d B）of the biomimetic honeycomb is the result of the synergistic effects of morphology design,composition optimization,and vacancy regulation.（4）Using mixed-valence vanadium oxides（VO_x）as the molecular model,a radar,infrared,and thermal stealth aerogel are successfully prepared.The ultra-light{V^ⅣV₉^V}/MXene aerogel（0.0429 g/cm³）exhibits excellent radar stealth performance,with a minimum RL of-57.74 d B and a radar cross-section reduction value of up to 26.77 d B·m².The presence of mixed-valence vanadium oxides leads to an increase in the Schottky barrier,thereby enhancing interface polarization,while the enhancement of magnetic properties promotes magnetic losses during the absorption process.The hollow structure and interface thermal resistance ensure the aerogel’s low infrared emissivity（0.479）and low thermal conductivity(32.30 m W·m^-1K^-1).Infrared imaging demonstrates the infrared stealth and thermal stealth performance of the aerogel.Therefore,altering the number of valence electrons significantly improves the compatibility stealth capability.These findings provide a basis for further research and development of VO_x-based compatible stealth materials.更多还原