Synchronizing the chemical composition of silver nanoparticle surfaces

非技术概述：银纳米颗粒（尺寸约1 - 100纳米，比人类头发的宽度小1000倍以上）被广泛应用，包括抗菌涂层、化妆品、电子、化学和生物传感器以及催化。然而，银是一种高度反应性的材料，特别是当缩小到纳米级尺寸时，并且容易产生不必要的副反应，例如当银饰或银器暴露在环境中时形成的众所周知的光泽。在关键应用中，这些不良副反应会影响银纳米材料的性能和可重复性。即使从同一瓶中取出的银纳米颗粒在第1天和第100天的表现也会有所不同，并且由于表面发生的反应的程度和化学性质，批次之间可能存在显著的不均匀性。这项提议的目的是确定是否有可能清洁银纳米颗粒表面，这些纳米颗粒经历了这些不必要的反应，并将它们恢复到更均匀、可再生的银表面。为了实现这一目标，银纳米粒子将暴露在各种化学和电化学条件下，并通过跟踪其光学性质的随时间变化来监测其表面的变化。通过跟踪大量单个纳米颗粒的行为，这些研究将确定产生从明显的表面非均质性到改善纳米颗粒群均匀性转变的特定条件。该提案还将支持研究生和本科生的培训，所有这些学生都将参与Willets实验室的社区外展活动（包括该小组开发的Silver高中化学实验室的冒险活动），并支持PI正在进行的专业发展工作，其重点是改善科学交流，并在化学领域创造一个更加公平和包容的环境。技术概述：金属纳米颗粒被广泛应用于许多领域，包括传感、纳米医学和催化，但其表面化学的动态变化会影响其再现性。与其试图在合成过程中控制纳米颗粒的表面，本提案寻求开发策略来同步纳米颗粒合成后的表面化学，从而在集成到设备和应用中创造更多可重复的行为。为了使银纳米粒子的表面化学反应同步，将引入牺牲壳，以化学或电化学的方式，以对抗纳米粒子表面不需要的污染物。然后，壳将通过电化学剥离去除，理想情况下是恢复原始的银表面。该提案将测试各种化学和电化学外壳，以评估它们在纳米粒子群中改善表面均匀性的能力。为了量化该方法的成功，暗场散射显微镜将用于跟踪整个外壳生长和剥离周期中单个纳米颗粒的散射强度、光谱分布和空间起源。单个纳米粒子的电溶解动力学将被用作确认所得银表面质量的指标，快速电溶解表明银接近原始，缓慢电溶解动力学表明表面杂质含量高。这些研究不仅将产生改善银纳米颗粒合成后/存储表面均匀性的策略，这将提高关键应用的可重复性，而且还将允许直接比较纳米颗粒在暴露于各种扰动时如何改变动力学和界面行为。向当地少数民族学校的高中生介绍银纳米粒子合成和光谱学的外展项目，以及由pi领导的研究生专业发展活动，补充了拟议的工作。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical Summary:Silver nanoparticles (~1 – 100 nm in size, more than 1000x smaller than the width of a human hair) are used in a wide range of applications, including antibacterial coatings, cosmetics, electronics, chemical and biological sensors, and catalysis. However, silver is a highly reactive material, particularly when shrunk down to nanoscale dimensions, and is susceptible to unwanted side reactions, such as the well-known tarnish that forms when silver jewelry or utensils are exposed to the ambient environment. These unwanted side reactions can impact the performance and reproducibility of silver nanomaterials in critical applications. Even silver nanoparticles taken from the same bottle will perform differently on day 1 vs. day 100, and there can be significant batch-to-batch heterogeneity, due to the extent and chemical nature of the reactions that have happened on the surface. The objective of this proposal is to determine whether it is possible to clean the surface of silver nanoparticles that have undergone these unwanted reactions and restore them to a more uniform, reproducible silver surface. To accomplish this, silver nanoparticles will be exposed to a variety of chemical and electrochemical conditions, and the change in their surface will be monitored by following time-dependent changes in their optical properties. By tracking the behavior of large numbers of single nanoparticles, these studies will determine specific conditions that produce a shift from significant surface heterogeneity to improved homogeneity across a nanoparticle population. The proposal will also support the training of graduate and undergraduate students, all of whom participate in community outreach with the Willets lab (including the Adventures in Silver high school chemistry lab developed by the group), as well as support the ongoing professional development efforts of the PI, which focus on improving scientific communication as well as creating a more equitable and inclusive environment within chemistry.Technical Summary:Metal nanoparticles are widely used across a number of applications, including sensing, nanomedicine, and catalysis, yet dynamic changes in their surface chemistry can affect their reproducibility. Rather than attempt to control the surface of nanoparticles during synthesis, this proposal seeks to develop strategies to synchronize the surface chemistry of nanoparticles post-synthesis, thereby creating more reproducible behaviors when integrated into devices and used in applications. To synchronize the surface chemistry across a population of silver nanoparticles, sacrificial shells will be introduced, either chemically or electrochemically, which outcompete unwanted contaminants on the surface of the nanoparticles. The shells will then be removed via electrochemical stripping, ideally recovering pristine silver surfaces. This proposal will test a variety of chemical and electrochemical shells, in order to assess their ability to improve the surface homogeneity within a nanoparticle population. To quantify the success of the approach, dark field scattering microscopy will be used to track the scattering intensity, spectral profile, and spatial origin of single nanoparticles throughout the shell growth and stripping cycle. The kinetics of single nanoparticle electrodissolution will be used as a metric to confirm the quality of the resulting silver surfaces, with fast electrodissolution indicating near-pristine silver and sluggish electrodissolution kinetics suggesting high levels of surface impurities. These studies will not only yield strategies for improving the post-synthesis/storage surface homogeneity in silver nanoparticles, which will improve reproducibility in critical applications, but will also allow for direct comparisons in how the kinetics and interfacial behaviors of nanoparticles change when exposed to various perturbations. Outreach projects introducing high school students from a local minority-serving school to silver nanoparticle synthesis and spectroscopy complement the proposed work, along with PI-led professional development activities for graduate students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.