Reverse micelle synthesis of silver nanoparticles in gas expanded liquids

• Published in: The Journal of supercritical fluids Vol. 79; pp. 236 - 243
• Main Authors: Hart, Ashley E., Akers, David B., Gorosh, Samuel, Kitchens, Christopher L.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2013
• Subjects: Carbon dioxide; Gas expanded liquid; Nanoparticles; Partial pressure; Particle size distribution; Reverse micelle; Reverse micelles; Silver; Silver nanoparticle; Solvents; Synthesis; Gas expanded liquid; Reverse micelle; Carbon dioxide; Silver nanoparticle
• ISSN: 0896-8446; 1872-8162
• DOI: 10.1016/j.supflu.2013.02.014

[Display omitted] ? The first demonstration of metallic nanoparticle synthesis within a gas expanded liquid (GXL) reverse micelle system. ? The tunable solvent properties of GXLs afforded size control for silver nanoparticle synthesized in AOT reverse micelles. ? Decreasing nanoparticle size and size distribution was observed with increasing CO2 pressure above a critical CO2 pressure. ? Solvent–surfactant interactions play a primary role in nanoparticle synthesis; yielding size control with CO2 pressure. The tunable solvent properties of gas expanded liquids (GXLs) have been previously used for the fractionation and separation of polydispersed ligand-stabilized metal nanoparticles into distinct monodispersed fractions. This work employs CO2 expanded hexane for silver nanoparticle synthesis within an AOT reverse micelle system where the tunable GXL solvent properties are used to control the nanoparticle size and polydispersity. The objective of this project is to answer two questions: (1) can nanoparticles with narrow and well-defined size distributions be synthesized in GXLs? and (2) how do the solvent properties impact the resulting nanoparticle size? In the reverse micelle synthesis, the AOT surfactant provides a nano-scale aqueous micelle core for nanoparticle nucleation, as well as, acts as a nanoparticle stabilizing ligand. Increasing the CO2 partial pressure in a GXL impacts the surfactant–solvent interaction and results in the synthesis of different sized nanoparticles. At ambient pressures, the mean particle diameter synthesized was 6.1±2.1nm with W=40 and 5.4±2.0nm with W=20, where W is the molar ratio of water to AOT. At CO2 partial pressures of 6.9 and 13.8bar, there was no significant change in particle size, but decreases in the size distributions were observed. At CO2 partial pressures ranging from 20.7 to 41.4bar, steady decreases in the mean particle diameter and size distribution were observed with values of 4.0±0.8 for W=40 and 4.1±1.0 for W=20 at 41.4bar. This demonstrates some degree of nanoparticle size tunability within the GXL solvent, where smaller particle diameters and size distributions are achieved at higher CO2 compositions.