Quantitative Evaluation of Fullerene Separation by Liquid Chromatography

Although a huge number of facile synthesis methods for nanoparticles (NPs) do exist, the products usually exhibit a distribution in particle size and shape. Thus, a separation step needs to be applied to adjust the particle properties according to the needs of the later application. Chromatography is a potentially scalable separation method which is well-established for separating molecules and promising for classifying NPs by size. Herein, we lay the foundations of particle chromatography by studying the separation of a C₆₀/C₇₀ fullerene mixture as well-defined particle probes using a pyrene-functionalized silica stationary phase. C₆₀ fullerenes are perfect model particles as they are spherical, roughly 1 nm in diameter, interacting via van der Waals interactions only. First, we extract the Henry coefficients for C₆₀ and C₇₀ fullerenes from the elution behavior of the fullerene mixture. Using a particle-wall as well as particle-particle model for the van der Waals interaction potential, we determine the Hamaker constant of the stationary phase material from the measured Henry coefficients. Moreover, we investigate the concentration-dependent diffusion and mass transport in the column by quantitative evaluation of the flow rate dependent elution behavior of the fullerenes. Our study shows the huge potential of chromatography for the separation of nanoparticles and demonstrates the strength of physical-chemical concepts for the quantitative analysis and the prediction of nanoparticle classification.