Department of Chemistry and Biochemistry, Florida State University ; Tallahassee, Florida 32306-4390, United States.
Air Force Civil Engineer Center, Tyndall Air Force Base , Panama City, Florida 32403, United States.
ACS Nano. 2017 Oct 24;11(10):9957-9967. doi: 10.1021/acsnano.7b04040. Epub 2017 Oct 6.
The desire for designing efficient synthetic methods that lead to industrially important nanomaterials has led a desire to more fully understand the mechanism of growth and how modern synthetic techniques can be employed. Microwave (MW) synthesis is one such technique that has attracted attention as a green, sustainable method. The reports of enhancement of formation rates and improved quality for MW driven reactions are intriguing, but the lack of understanding of the reaction mechanism and how coupling to the MW field leads to these observations is concerning. In this manuscript, the growth of a metal nanoparticles (NPs) in a microwave cavity is spectroscopically analyzed and compared with the classical autocatalytic method of NP growth to elucidate the underpinnings for the observed enhanced growth behavior for metal NPs prepared in a MW field. The study illustrates that microwave synthesis of nickel and gold NPs below saturation conditions follows the Finke-Watzky mechanism of nucleation and growth. The enhancement of the reaction arises from the size-dependent increase in MW absorption cross section for the metal NPs. For Ni, the presence of oxides is considered via theoretical computations and compared to dielectric measurements of isolated nickel NPs. The study definitively shows that MW growth can be modeled by an autocatalytic mechanism that directly leads to the observed enhanced rates and improved quality widely reported in the nanomaterial community when MW irradiation is employed.
人们渴望设计出高效的合成方法，以制备具有工业重要性的纳米材料，这促使人们更全面地了解生长机制，以及如何利用现代合成技术。微波（MW）合成就是这样一种技术，它作为一种绿色、可持续的方法引起了人们的关注。MW 驱动反应中提高形成速率和改善质量的报道令人着迷，但缺乏对反应机制的理解以及 MW 场如何导致这些观察结果的理解令人担忧。在本文中，通过光谱分析研究了金属纳米颗粒（NPs）在微波腔中的生长，并将其与经典的 NPs 生长自催化方法进行了比较，以阐明在 MW 场中制备的金属 NPs 观察到的增强生长行为的基础。该研究表明，在低于饱和条件下，镍和金 NPs 的微波合成遵循成核和生长的 Finke-Watzky 机制。反应的增强源于金属 NPs 的 MW 吸收截面随尺寸的增加而增加。对于 Ni，通过理论计算考虑了氧化物的存在，并与孤立镍 NPs 的介电测量进行了比较。该研究明确表明，MW 生长可以通过自催化机制来建模，该机制直接导致在纳米材料领域广泛报道的观察到的增强速率和改善质量。
