Seed-mediated co-reduction: a versatile route to architecturally-controlled bimetallic nanostructures

印第安纳大学的Sara Skrabalak在化学系大分子、超分子和纳米化学计划的支持下，对具有高结构单分散性的双金属纳米颗粒的合理合成和表征进行了研究。像它们的单金属对应物一样，双金属材料在纳米尺度上经常表现出它们的物理化学性质的巨大变化。要实现双金属纳米结构的全部潜力，需要具有与最好的单金属实例相当的结构单分散性的样品；然而，在双金属纳米结构的合成过程中实现结构和成分控制仍然是一个巨大的挑战。这一挑战源于依赖共还原技术来成核和生长特定的双金属相，但Skrabalak实验室已经展示了种子介导的共还原作为一种策略，通过将其与为双金属沉积提供结构定义的晶体的种子方法的优点相结合，克服了共还原技术的局限性。本项目的目标是：1)确定在种子催化共还原过程中控制形态发展的合成参数，并量化它们对共还原和晶体生长动力学的影响；2)确定种子结构与最终形貌之间的对称关系，量化晶种和过度生长金属之间的晶格失配对形态发育的影响；以及3)确定能够实现种子催化共还原金属前体的合成条件，并通过原位同步加速器X射线衍射技术定量这一表面调控过程的动力学。总之，正在进行的实验是为了识别和量化在种子介导的共还原过程中有助于形貌发展的合成参数，并使新的结构控制的双金属纳米结构得以实现。此外，正在研究合成的独特纳米结构的光学和催化性能，以了解组成和结构化合物如何赋予新的功能。通过种子介导的共还原合成新的双金属纳米结构的通用设计标准正在被追求，以及共同还原技术的总体进步。双金属纳米结构是令人兴奋的多功能平台，有可能满足催化(例如，燃料电池)、能源可持续性、化学传感、医学等领域的关键需求。然而，由于目前合成策略的局限性，可预测地实现结构控制的双金属纳米结构只取得了一定的成功。该项目旨在获得新的双金属纳米结构的一般设计标准，并使纳米合成社区更接近具有特定组成和结构的纳米结构的预测性、按需合成。这项研究还产生了更广泛的影响：i)在包括纳米/无机/固体化学和胶体/表面/材料科学在内的科学学科之间建立联系；ii)通过多学科研究和通过教学加强学习的外展活动加强研究生/本科生的教育；iii)向非科学家介绍纳米尺度的概念，并通过他们的研究活动将本科生与他们的家庭社区联系起来；iv)使PI能够作为教育工作者、期刊和补助金审核者以及促进高等教育多样性的推动者为科学界服务；以及v)通过同行评议的出版物和演示文稿，根据建议的研究产生和传播新知识。

Sara Skrabalak from Indiana University is supported by the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry to conduct research into rational syntheses and characterization of bimetallic nanoparticles with high structural monodispersity. Like their monometallic counterparts, bimetallic materials often display dramatic changes in their physicochemical properties at the nanoscale. To realize the full potential of bimetallic nanostructures, samples with structural monodispersity on-par with the best monometallic examples are needed; however, it remains a grand challenge to achieve structural and compositional control during the synthesis of bimetallic nanostructures. This challenge arises from reliance on co-reduction techniques to nucleate and grow a defined bimetallic phase, but the Skrabalak laboratory has demonstrated seed-mediated co-reduction as a strategy to overcome the limitations of co-reduction techniques by coupling them with the advantages of seeded methods which provide structurally defined crystals for bimetallic deposition. The aims of this project are i) to identify the synthetic parameters which govern morphology development during seed-mediated co-reduction and quantify their effects on the kinetics of co-reduction and crystal growth, ii) to identify the symmetry relationships between seed structure and the final morphologies of branched bimetallic nanocrystals prepared by seed-mediated co-reduction and quantify the effect of lattice mismatch between seed and overgrowth metals to morphology development, and iii) to identify the synthetic conditions which enable seed-catalyzed co-reduction of metal precursors and quantify the kinetics of this surface-mediated process via in situ synchrotron X-ray diffraction techniques. Collectively, the experiments being carried out are to identify and quantify the synthetic parameters which contribute to morphology development during seed-mediated co-reduction and enable new architecturally-controlled bimetallic nanostructures to be achieved. Additionally, the optical and catalytic properties of the unique nanostructures synthesized are being studied to understand how composition and architecture compound to impart new functionality. General design criteria for the synthesis of new bimetallic nanoarchitectures by seed-mediated co-reduction are being pursued, as well as the advancement of co-reduction techniques in general.Bimetallic nanostructures represent exciting multifunctional platforms with the potential to address critical needs in catalysis (e.g., in fuel cells), energy sustainability, chemical sensing, medicine, and beyond. However, predictably achieving architecturally-controlled bimetallic nanostructures has met with only modest success on account of the limitations of current synthetic strategies. This project is to obtain general design criteria for new bimetallic nanostructures and to move the nanosynthesis community closer to the predictive, on-demand synthesis of nanostructures with defined composition and architectures. This research also has the broader impacts of i) forging links between scientific disciplines that include nano/inorganic/solid-state chemistry and colloidal/surface/material sciences, ii) enhancing graduate/undergraduate education through multidisciplinary research and outreach activities that reinforce learning via teaching, iii) introducing nanoscale concepts to non-scientists and connecting undergraduates to their home communities through their research activities; iv) enabling the PI to serve the scientific community as an educator, journal and grant reviewer, and promoter of diversity in higher education; and v) generating and distributing new knowledge based on the proposed research through peer-reviewed publications and presentations.