PNNL

Abstract

The development of more efficient and greener 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 their pressure or temperature. In this work we study the dispersibility of gold nanocrystals of 3.8 nm core size stabilized with different ligand shells in near-critical (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 better understand the results obtained in this study three models, the total interaction theory, the sedimentation coefficient equation, and the Chrastil method, are briefly discussed. The dispersibility of the nanocrystals and its behavior with the variation of the fluid density is strongly dependent on the composition of the ligand shell and solvent employed. A correlation between the measured dispersibility values and the 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 larger nanocrystal dispersibilities, NcF ethane led to a greater tunability of nanoparticle dispersion in the pressure range of the study. Therefore, with a judicious selection of the fluid, NcFs seem to offer a remarkable advantage over conventional solvents for manipulation of nanomaterials, including transport, purification, and separation of nanocrystals.