笼状Ag/Au纳米材料的可控合成及近红外强吸收特性的研究

The silver/gold (Ag/Au) porous nano-cages with a controllable interior space and a distinctive porous shell have received increasing attention in recent years. The unique objects are characterized as fine nano-particles with lower densities, larger specific surface area, and higher permeability. They had the significant application in biomedicine for enhanced killing the cancer cells because of their excellent absorption in near-infrared and photo-thermal conversion properties. Since the properties of the Ag/Au nano-cages are strongly dependent on their porous surfaces and hollow interiors, a simple, versatile and rapid route to controllably synthesize Ag/Au nano-cages with designed shape and geometry is great significance for the specific applications. In this project, the Ag/Au nano-cages with a controllable hollow interior will be devised through Galvanic Replacement Reaction (GRR) due to photo-thermal heating by pulsed laser ablation of Ag target in aqueous HAuCl4 solutions. The parameters of laser ablation/irradiation and aqueous HAuCl4 concentration will play critical roles for controlling the replacement reaction degree and rate. The aim of this work is to obtain the Ag/Au nano-cages with an increased interior space and a distinctive thin shell, which exhibit unique absorption in near-infrared region. Based on isentropic flow relationships and hydrodynamic shock theoretical models, the evolution of the plasma generated on Ag target in liquid will be investigated to understand the fundamental principles/mechanism underlying pulse laser irradiation in aqueous HAuCl4 solutions. Then, UV-Vis-NIR optical absorption spectrum of Ag/Au nano-cages will be used to investigate the strong and super wide adsorption in NIR. The profile of the NIR absorption is characterized by the continuous red shift, broadened and intensive spectral lines. This project provides a new paradigm to obtain hollow like Ag/Au nano-cages directly from bulk materials and inspires deeper investigations for generation more complex structures by this strategy. The relevant physical mechanism obtained from theoretical models and experiments have significant implications for getting an insight into the properties of the Ag/Au porous nano-cages, offering the basis for further development of reliable applications with efficiency and defined purposes.

笼状Ag/Au双金属纳米材料的独特空心构型使其具有近红外强吸收特性，在肿瘤等疾病的光热治疗领域备受关注。探索一种兼具简便、环保、低成本等特点的合成技术能够有效调控合成这种特殊材料是目前迫切需要解决的重要课题。本项目申请利用脉冲激光在HAuCl4溶液中烧蚀Ag靶材，辐照诱导伽伐尼置换反应，实现可控合成笼状Ag/Au纳米材料。调节激光烧蚀和辐照参数，改变HAuCl4浓度进而有效控制置换反应速率及程度，保证笼状Ag/Au稳定构型的基础上最大限度提高内部空心比例并降低壳层厚度。结合激光烧蚀产生的等离子体演化特性和等熵绝热膨胀等理论系统探究其中的可控生长机理。通过研究吸收光谱的红移程度、谱线强度及展宽等演化特性，深入探索笼状Ag/Au纳米材料的近红外强吸收特性的主要影响机制及机理。本项目研究成果将为后续研究笼状Ag/Au纳米材料的众多优异特性奠定基础，推进该新型材料在众多特殊应用领域取得突破性进展。

笼状Ag/Au纳米材料所特有的空心构型使其具有近红外强吸收特性，在肿瘤等疾病的光热治疗领域备受关注。探索一种兼具简便、环保、低成本等特点的合成策略能够有效调控制备这种特殊材料是当今急需解决的关键问题。本项目基于脉冲激光液相诱导技术，紧紧围绕着可控合成具有近红外强吸收特性的笼状Ag/Au纳米材料的研究目标，完成了一系列的前沿探索工作。利用1064nm脉冲激光束在水溶液中烧蚀Ag靶，基于激光液相烧蚀/裂解机制实现了尺寸可调的单分散Ag纳米球体（60~2nm）的制备。研究表明，激光烧蚀产生的炙热Ag等离子体在溶液中急剧冷却结晶，形成了热力学非平衡态的晶体生长方式：激光瞬间的热烧蚀效应使得炙热的Ag在液相膨胀并成核过程中出现大量晶格缺陷，脉冲激光迅速淬灭又能使得Ag纳米颗粒的外壳更为稳定。这种具有外壳稳定、内部晶格多缺陷的独特Ag纳米构型为后续调控制备笼状Ag/Au纳米材料提供了理想的前驱体。据此，基于激光液相烧蚀并通过后续加入HAuCl4诱导伽伐尼置换反应机制，我们调节激光参数和HAuCl4浓度控制反应进程，有效提高了Ag/Au内部空心比例并调控了外壳的金属组份和厚度，最终实现了具有海胆形貌外壳的笼状Ag/Au纳米材料的可控制备。随着内部空心比例不断提高以及后续多支状外壳构型的生长，笼状Ag/Au纳米材料的吸收光谱峰位从~400nm明显红移到610nm以上，而且在复杂液相（NaCl溶液和H2O2溶液）的近红外强吸收特性具有良好的长效稳定性。理论与实验证实这种优异的近红外强吸收特性与稳定笼状骨架之间显著的AgAu协同效应密切相关。此外，我们还将这种新颖合成策略扩展到Au、Ag、Pt、Cu等其他众多复合构型的调控制备，深入探索了可控合成的内在机制。本项目的顺利完成为后续探究笼状金属纳米复合材料的众多优异特性奠定了基础，有利于扩展到光热治疗、新能源转化与存储以及环境污染处理等交叉研究。