Using Size-Exclusion Chromatography to Evaluate Changes in the Sizes of Au and Au/Pd Core/Shell Nanoparticles Under Thermal Treatment

In this study, we used size-exclusion chromatography (SEC) to evaluate the sizes of Au and Au/Pd core/shell nanoparticles (NPs) that had been subjected to thermal treatment, with the eluted NPs monitored through diode array detection (DAD) of the surface plasmon (SP) absorption of the NPs. In the absence of an adequate stabilizer, thermal treatment resulted in longer retention times for the Au NPs and shorter retention times for the Au/Pd core/shell NPs in the SEC chromatograms. Thus, thermal treatment influenced the sizes of these Au and Au/Pd core/shell NPs, through digestive ripening and Ostwald-type growth, respectively. In addition, the trends in the SP absorption phenomena of the NPs in the eluted samples, as measured using DAD, were consistent with the trends of their size variations, as measured from their elution profiles. In the presence of 3A-amino-3A-deoxy-(2AS,3AS)-β-cyclodextrin (H₂N-β-CD) as a stabilizer, the retention times and SP absorptions of the eluted Au and Au/Pd NP samples remained constant. Thus, H₂N-β-CD is a good stabilizer against size variation duration the thermal treatment of Au and Au/Pd core/shell NPs. A good correlation existed between the sizes obtained using SEC and those provided by transmission electron microscopy. Therefore, this SEC strategy is an effective means of further searching for suitable stabilizers for NPs, especially those exposed to harsh reaction conditions (e.g., in catalytic reactions).