Anand Madhu, McLeod M Chandler, Bell Philip W, Roberts Christopher B
Department of Chemical Engineering, Auburn University, Auburn, Alabama 36849, USA.
J Phys Chem B. 2005 Dec 8;109(48):22852-9. doi: 10.1021/jp0547008.
This paper presents an environmentally friendly, inexpensive, rapid, and efficient process for size-selective fractionation of polydisperse metal nanoparticle dispersions into multiple narrow size populations. The dispersibility of ligand-stabilized silver and gold nanoparticles is controlled by altering the ligand tails-solvent interaction (solvation) by the addition of carbon dioxide (CO2) gas as an antisolvent, thereby tailoring the bulk solvent strength. This is accomplished by adjusting the CO2 pressure over the liquid, resulting in a simple means to tune the nanoparticle precipitation by size. This study also details the influence of various factors on the size-separation process, such as the types of metal, ligand, and solvent, as well as the use of recursive fractionation and the time allowed for settling during each fractionation step. The pressure range required for the precipitation process is the same for both the silver and gold particles capped with dodecanethiol ligands. A change in ligand or solvent length has an effect on the interaction between the solvent and the ligand tails and therefore the pressure range required for precipitation. Stronger interactions between solvent and ligand tails require greater CO2 pressure to precipitate the particles. Temperature is another variable that impacts the dispersibility of the nanoparticles through changes in the density and the mole fraction of CO2 in the gas-expanded liquids. Recursive fractionation for a given system within a particular pressure range (solvent strength) further reduces the polydispersity of the fraction obtained within that pressure range. Specifically, this work utilizes the highly tunable solvent properties of organic/CO2 solvent mixtures to selectively size-separate dispersions of polydisperse nanoparticles (2 to 12 nm) into more monodisperse fractions (+/-2 nm). In addition to providing efficient separation of the particles, this process also allows all of the solvent and antisolvent to be recovered, thereby rendering it a green solvent process.
本文提出了一种环境友好、成本低廉、快速且高效的方法，用于将多分散金属纳米颗粒分散体按尺寸选择性分离成多个窄尺寸分布群体。通过添加二氧化碳（CO₂）气体作为反溶剂来改变配体尾端与溶剂的相互作用（溶剂化作用），从而控制配体稳定的银和金纳米颗粒的分散性，进而调整整体溶剂强度。这是通过调节液体上方的CO₂压力来实现的，从而提供了一种通过尺寸调节纳米颗粒沉淀的简单方法。本研究还详细阐述了各种因素对尺寸分离过程的影响，如金属、配体和溶剂的类型，以及递归分级的使用和每个分级步骤中沉降所需的时间。对于用十二烷硫醇配体包覆的银和金颗粒，沉淀过程所需的压力范围是相同的。配体或溶剂长度的变化会影响溶剂与配体尾端之间的相互作用，进而影响沉淀所需的压力范围。溶剂与配体尾端之间的相互作用越强，沉淀颗粒所需的CO₂压力就越大。温度是另一个变量，它通过改变气体膨胀液体中CO₂的密度和摩尔分数来影响纳米颗粒的分散性。在特定压力范围（溶剂强度）内对给定系统进行递归分级，可进一步降低该压力范围内所得级分的多分散性。具体而言，本工作利用有机/CO₂溶剂混合物高度可调的溶剂性质，将多分散纳米颗粒（2至12纳米）的分散体选择性地按尺寸分离成更单分散的级分（±2纳米）。除了能高效分离颗粒外，该过程还能回收所有的溶剂和反溶剂，因此使其成为一种绿色溶剂工艺。
