(41a) Size-Selective Fractionation of Nanoparticles at Significant Scales Using CO2-Expanded Liquids

Size-based fractionation of nanoparticles remains a non-trivial task for the preparation of significant quantities of well-defined nanomaterials for certain applications and fundamental studies. Typical fractionation techniques prove to be inefficient for larger nanoparticle quantities due to the expense of equipment, low-throughput, and/or the amount of organic solvent waste produced. Through the use of the pressure-tunable physico-chemical properties of CO₂-expanded liquids, a rapid, precise, and environmentally sustainable size-selective fractionation of ligand-stabilized nanoparticles is possible through simple variations in applied CO₂ pressure. An apparatus capable of fractionating large quantities of nanoparticles into distinct fractions with targeted mean diameters with narrow distributions (± 1 nm) has been developed. This apparatus consists of three vertically mounted high pressure vessels connected in series with high pressure needle valves. This process at current design scales, operated at room temperature, and CO₂ pressures between 0 and 50 bar, results in a batch size-selective fractionation of a concentrated nanoparticle dispersion. This paper presents this technique and method of size-selectively fractionating large quantities of metallic nanoparticles from various solvents, as well as a computational model of this system.