Fernandez Carlos A, Bekhazi Jacky G, Hoppes Emily M, Fryxell Glen E, Wang Chongmin, Bays J Timothy, Warner Marvin G, Wiacek Robert J, Addleman R Shane
Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
Langmuir. 2009 May 5;25(9):4900-6. doi: 10.1021/la804058x.
The development of more efficient and environmentally benign methods for the synthesis and manipulation of nanomaterials has been a major focus of research among the scientific community. Supercritical (ScFs) and near-critical fluids (NcFs) offer numerous advantages over conventional solvents for these purposes. Among them, ScFs and NcFs offer dramatic reductions in the volume of organic waste typically generated during advanced material processes with the feasibility of changing a number of physicochemical properties by discrete variations in solvent pressure or temperature. In this work, we study the dispersibility of gold nanocrystals with a 3.7 nm core size stabilized by different ligand shells in NcF ethane and propane over a wide range of densities by fine-tuning the pressure of these fluids. Dispersibility vs density plots are obtained by following the variation in the surface plasmon resonance (SPR) absorption spectra of the nanoparticles. To understand the results obtained in this study, three models are briefly discussed: the total interaction theory, the sedimentation coefficient equation, and the Chrastil method. The dispersibility and behavior of the nanocrystals with variations in fluid density are strongly dependent on the surface chemistry of the nanocrystal and the solvent employed. A correlation between measured dispersibility values and calculated sedimentation coefficients was observed in both compressed solvents. In addition, we successfully applied the Chrastil equation to predict and describe the dispersibility of gold nanocrystals with different shells as a function of density, determining that the reason for the high stabilities of some of the nanocrystal dispersions is the strong solvent-nanocrystal interactions. While NcF propane showed higher nanocrystal dispersibilities, using NcF ethane led to improved tunability of nanoparticle dispersions formed in the pressure range studied. Therefore, with a judicious selection of the fluid, NcFs seem to offer a remarkable advantage over conventional solvents for manipulation of nanomaterials, which could be applied to transport, purification, and separation of nanocrystals.
开发更高效且环境友好的纳米材料合成与操控方法一直是科学界研究的主要焦点。超临界流体（ScFs）和近临界流体（NcFs）在这些方面相较于传统溶剂具有诸多优势。其中，ScFs和NcFs能显著减少先进材料加工过程中通常产生的有机废物量，并且通过改变溶剂压力或温度的离散变化来改变多种物理化学性质具有可行性。在本工作中，我们通过微调这些流体的压力，研究了在不同密度范围内，由不同配体壳层稳定的核心尺寸为3.7 nm的金纳米晶体在NcF乙烷和丙烷中的分散性。通过跟踪纳米颗粒的表面等离子体共振（SPR）吸收光谱的变化来获得分散性与密度的关系图。为理解本研究所得结果，简要讨论了三种模型：总相互作用理论、沉降系数方程和Chrastil方法。纳米晶体的分散性及其随流体密度变化的行为强烈依赖于纳米晶体的表面化学性质和所使用的溶剂。在两种压缩溶剂中均观察到测量的分散性值与计算的沉降系数之间存在相关性。此外，我们成功应用Chrastil方程来预测和描述不同壳层的金纳米晶体的分散性随密度的变化，确定某些纳米晶体分散体具有高稳定性的原因是溶剂与纳米晶体之间的强相互作用。虽然NcF丙烷表现出更高的纳米晶体分散性，但使用NcF乙烷可改善在所研究压力范围内形成的纳米颗粒分散体的可调性。因此，通过明智地选择流体，NcFs在纳米材料操控方面似乎比传统溶剂具有显著优势，这可应用于纳米晶体的运输、纯化和分离。
