Department of Physics, Central Michigan University, Mt. Pleasant, Michigan 48858, USA.
Department of Chemistry, Duke University, Durham, NC 27708, USA.
Nanoscale. 2015 Nov 14;7(42):17902-22. doi: 10.1039/c5nr04678e.
The extent to which current theoretical modeling alone can reveal real-world metallic nanoparticles (NPs) at the atomic level was scrutinized and demonstrated to be insufficient and how it can be improved by using a pragmatic approach involving straightforward experiments is shown. In particular, 4 to 6 nm in size silica supported Au(100-x)Pd(x) (x = 30, 46 and 58) explored for catalytic applications is characterized structurally by total scattering experiments including high-energy synchrotron X-ray diffraction (XRD) coupled to atomic pair distribution function (PDF) analysis. Atomic-level models for the NPs are built by molecular dynamics simulations based on the archetypal for current theoretical modeling Sutton-Chen (SC) method. Models are matched against independent experimental data and are demonstrated to be inaccurate unless their theoretical foundation, i.e. the SC method, is supplemented with basic yet crucial information on the length and strength of metal-to-metal bonds and, when necessary, structural disorder in the actual NPs studied. An atomic PDF-based approach for accessing such information and implementing it in theoretical modeling is put forward. For completeness, the approach is concisely demonstrated on 15 nm in size water-dispersed Au particles explored for bio-medical applications and 16 nm in size hexane-dispersed Fe48Pd52 particles explored for magnetic applications as well. It is argued that when "tuned up" against experiments relevant to metals and alloys confined to nanoscale dimensions, such as total scattering coupled to atomic PDF analysis, rather than by mere intuition and/or against data for the respective solids, atomic-level theoretical modeling can provide a sound understanding of the synthesis-structure-property relationships in real-world metallic NPs. Ultimately this can help advance nanoscience and technology a step closer to producing metallic NPs by rational design.
当前理论模型在多大程度上可以揭示原子级别的实际金属纳米粒子（NPs）受到了仔细审查，并表明其作用是不充分的，以及如何通过使用涉及简单实验的务实方法来改进这一方法。特别是，对于催化应用，尺寸为 4 至 6nm 的二氧化硅负载的 Au(100-x)Pd(x)（x=30、46 和 58）通过总散射实验进行了结构表征，包括与原子配分函数（PDF）分析相结合的高能同步加速器 X 射线衍射（XRD）。基于当前理论建模的Sutton-Chen（SC）方法，通过分子动力学模拟为 NPs 构建了原子级模型。模型与独立的实验数据进行匹配，并证明其不准确，除非其理论基础，即 SC 方法，补充了关于金属-金属键的长度和强度的基本但关键的信息，并且在必要时，研究中实际 NPs 的结构无序。提出了一种基于原子 PDF 的方法来获取此信息并将其应用于理论建模。为了完整性，该方法还简要地演示了针对生物医学应用的 15nm 尺寸的水分散 Au 颗粒和针对磁性应用的 16nm 尺寸的正己烷分散 Fe48Pd52 颗粒。有人认为，当针对与金属和合金相关的实验进行“调整”时，这些实验受限于纳米尺寸，例如与原子 PDF 分析相结合的总散射，而不是仅仅依靠直觉和/或针对各自的固体数据，原子级理论建模可以为理解真实世界金属 NPs 的合成-结构-性能关系提供合理的理解。最终，这可以帮助纳米科学和技术更进一步，通过合理设计生产金属 NPs。
