【作者】 许杰；

【导师】 尚利；

【作者基本信息】 西北工业大学 ， 材料学， 2022， 博士

【摘要】 金属气凝胶兼具金属（如导电性、催化活性和等离子体性质）和气凝胶（如三维自支撑性、高度多孔网络结构和超低密度）的优点,在过去十年中成为一种新兴的多孔材料,在电催化、表面增强拉曼散射和传感等方面展现出前所未有的潜力。有效的合成策略是金属气凝胶发展的关键因素,其中溶胶-凝胶法是制备金属气凝胶最常采用的方法。然而,由于金属体系中非常规的凝胶反应行为和复杂的凝胶反应环境,当前对金属气凝胶的凝胶形成机制尚不清晰。同时,有限的组分和结构调控能力也严重阻碍了金属气凝胶在实际应用中的进一步发展。此外,金属气凝胶的应用研究主要集中在电催化方面,迫切需要探索在其他领域的潜在应用。金纳米团簇（AuNCs）具有超小的尺寸、精确的结构、高的表面活性和良好的催化性能,因而极具潜力作为新颖的前驱体材料用以制备新型的多功能金属气凝胶。鉴于此,本论文研究工作围绕以超小的AuNCs作为功能基本单元,制备具有均匀线径大小、组分可调的金属气凝胶材料展开,深入研究AuNCs的凝胶反应过程,揭示基于超小AuNCs制备金属气凝胶的凝胶形成机制,并进一步探索所制备的金属气凝胶在类酶生物催化、抗菌等领域的应用性能。主要研究内容和结果如下:（1）通过系统研究不同配体密度（如谷胱甘肽,GSH）以及不同化学结构的硫醇配体对AuNCs理化性质的影响,揭示表面配体的密度和化学结构对AuNCs的性质及其反应活性的影响规律。基于荧光寿命光谱和X射线光电子能谱分析发现,AuNCs表面的富电子配体密度越高,越有利于增强其光学性质（如荧光）。此外,AuNCs表面配体覆盖度的差异会显著影响其与外加物质的相互作用,例如具有不同配体密度的GSH-AuNCs对Hg²⁺离子的荧光响应表现出显著性的差异。表面的配体密度和化学结构对AuNCs性质及其与外加物质反应活性的影响规律,为后续进一步研究AuNCs的凝胶化行为奠定了基础。（2）利用多巴胺为凝胶诱导剂,发展一种利用AuNCs作为功能单元制备金属气凝胶的新方法。以粒径为1.4 nm的D-青霉胺稳定的AuNCs为范例,通过优化各种实验条件,成功制备出具有均匀的超细线径（3.5 nm）和良好类过氧化物酶活性的Au气凝胶。该方法制备得到的Au气凝胶具有典型的三维自支撑多孔网络结构、较高的Au纯度（84.6%）和高的比表面积。通过实时的紫外-可见光谱分析和透射电子显微镜对凝胶形成的过程进行研究,结果表明超小的AuNCs首先生长成为大尺寸的纳米颗粒,然后逐步融合形成纳米线网络,最终得到三维的Au气凝胶结构。在此过程中溶液的p H和前驱体的浓度都起着较为重要的作用。基于其高度的多孔结构和丰富的金属节点,进一步研究Au气凝胶的类酶催化性质及其机理。结果表明这种自支撑的Au气凝胶具有良好的类过氧化物酶性质和较好的稳定性,有望进一步应用于生物医学领域,例如生物传感和疾病治疗等。（3）通过向AuNCs溶液中加入不同浓度的金属阳离子（Ag⁺）的方法,成功制备出组分可调、具有不同Ag含量的AuAg双金属气凝胶。该方法制备得到的AuAg气凝胶具有典型的三维多孔网络结构、丰富的孔道结构以及可调的金属组分。高角环形暗场扫描透射电子显微镜-能量色散光谱图像证实Au和Ag元素在AuAg双金属气凝胶中具有相对均匀的空间分布。通过涂布平板法考察AuAg气凝胶的抗菌活性,结果表明Ag含量最高的AuAg气凝胶对革兰氏阴性菌大肠杆菌（E.coli）和革兰氏阳性菌金黄色葡萄球菌（S.aureus）都表现出优异的抗菌效果,抑菌率达100%。通过对AuAg气凝胶的抗菌机理研究发现,Ag⁺的释放量是决定AuAg气凝胶抗菌能力的关键因素。在进一步的对比分析基础上,研究不同组分的AuAg气凝胶的抗菌活性与其Ag⁺释放能力之间的内在关联。其中,高银含量的AuAg气凝胶可以持续不断地释放Ag⁺,从而实现长期的抗菌活性。AuAg气凝胶这种优异且持久的抗菌性质有望进一步应用于生物医学、食品工业和制药等领域。更多还原

【Abstract】 Armed with merits of both metals（e.g.,electrical conductivity,catalytic activity,and plasmonic properties）and aerogels（e.g.,three-dimensional（3D）self-supporting,highly porous network structure and ultralow density）,metal aerogels have stood out as an emerging class of porous materials in the last decade.Metal aerogels have shown unprecedented potential in electrocatalysis,surface enhanced Raman scattering（SERS）and sensing.Effective synthesis strategy is the key factor for the development of metal aerogels,and sol-gel method is the most commonly used method to prepare metal aerogels.However,due to the unconventional gelation behavior and complex gelation reaction environment in the metal system,researchers are suffering from the ambiguous understanding of the definite gelation mechanisms of metal aerogels at present.In the meantime,the limited regulation capacity of the component and structure also seriously hinders the further development of metal aerogels in practical applications.Moreover,the application research of metal aerogel mainly focuses on electrocatalysis,and it is urgent to exploit their potential applications in other fields.Gold nanoclusters（AuNCs）have the advantages of ultrasmall size,defined structure,high surface activity and good catalytic performance.Therefore,there are great potentials in the preparation of novel aerogels used AuNCs as a new type of precursors.Therefore,this thesis focuses on using ultrasmall AuNCs as the functional building blocks to fabricate metal aerogel materials with uniform ligament sizes and adjustable compositions.This work investigates the gelation reaction process of AuNCs,and elucidates the gelation mechanisms of metal aerogels based on ultrasmall AuNCs.Furthermore,this work also explores the application performance of metal aerogels in enzyme-like biocatalysis and antibacterial fields.The main research work and results are listed as follows:（1）Investigate the influence of ligand density（e.g.,glutathione,GSH）and ligand chemical structures on the physicochemical properties of AuNCs to elucidate the distinct role of surface ligands on the properties and reactivity of AuNCs.Fluorescence lifetime spectroscopy and X-ray photoelectron spectroscopy showed that AuNCs with a higher density of electron-rich ligands can enhance their optical properties（such as fluorescence）.Moreover,differences in the surface coverage of AuNCs can also significantly affect their interactions with foreign species.For example,GSH-AuNCs with different ligand densities show significant differences in their fluorescence response towards Hg²⁺.The effects of surface ligand density and chemical structure on the properties of AuNCs as well as their reaction behaviors with foreign substances lay a foundation for further study on the gelation behavior of AuNCs.（2）Develop a new approach to fabricate metal aerogels by using ultrasmall metal nanoclusters as functional building blocks and dopamine as the gelation inducer.By taking D-penicillamine-stabilized AuNCs with a diameter of 1.4 nm as an example,gold aerogels with uniform and ultrafine ligament sizes（3.5 nm）and good peroxidase-like activity were successfully prepared by optimizing various experimental conditions.Detailed characterization showed that the obtained gold aerogels possess typical 3D self-supported porous network structure with high gold purity（84.6%）and large surface area.Time-lapse UV-Vis absorption spectroscopic and transmission electron microscopic monitoring of the gelation process revealed that these ultrasmall AuNCs first grow into large nanoparticles before fusion into nanowire networks.Afterwards,a 3D gold aerogel structure is obtained.During this gelation process,both p H and the precursor concentration are identified to be the determining factors.Based on their highly porous structure and abundant metal nodes,the enzyme-like catalytic properties and mechanism of gold aerogel were further studied.The results showed that the self-supported gold aerogel has good peroxidase-like properties and good stability,which can be further applied in biomedical fields,such as biosensing and disease therapy.（3）AuAg bimetallic aerogels with adjustable compositions were successfully prepared by adding different concentrations of metal cation（Ag⁺ions）as the gelator of AuNCs.Detailed characterization showed that the obtained AuAg aerogels possess typical 3D self-supported porous network feature and abundant pore structures.The high-angle annular dark field scanning transmission electron microscopy-energy dispersive spectroscopy（HAADF-STEM-EDS）mapping images confirm a relatively homogeneous spatial element distribution of Au and Ag in the AuAg bimetallic aerogels.The antibacterial activities of AuAg aerogels were evaluated by the spread plate method.The antibacterial tests demonstrated that AuAg aerogels with the highest Ag content display the excellent antibacterial effects against both Gram-negative bacteria（E.coli）and Gram-positive bacteria（S.aureus）,with the bacterial inhibition rate up to 100%.Moreover,the Ag⁺ions release results showed that the release amount of Ag⁺from the AuAg aerogels is the key factor in determining their antibacterial ability,which suggests that the high antibacterial activity of AuAg aerogels is due to their strong Ag⁺ions release capability.AuAg aerogels with the best antibacterial effects can continuously release Ag⁺ions,which then results in long-term antibacterial activities.The excellent and long-lasting antibacterial performance of AuAg aerogels make them promising for further use in many antibacterial applications,such as the biomedicine,food industry and pharmaceutics.更多还原