Characterizing Size and Porosity of Hollow Nanoparticles: SAXS, SANS, TEM, DLS, and Adsorption Isotherms Compared

A combination of experimental methods, including transmission and grazing incidence small-angle X-ray scattering (SAXS and GISAXS), small-angle neutron scattering (SANS), transmission electron microscopy (TEM), dynamic light scattering (DLS), and N₂ adsorption–desorption isotherms, was used to characterize SiO₂/TiO₂ hollow nanoparticles (HNPs) of sizes between 25 and 100 nm. In the analysis of SAXS, SANS, and GISAXS data, the decoupling approximation and the Percus–Yevick structure factor approximation were used. Brunauer–Emmett–Teller, <i>t</i>-plot, and a spherical pore model based on Kelvin equation were applied in the treatment of N₂ isotherms. Extracted parameters from the scattering and TEM methods are the average outer and inner diameters and polydispersity. Good agreement was achieved between different methods for these extracted parameters. Merits, advantages, and disadvantages of the different methods are discussed. Furthermore, the combination of these methods provided us with information on the porosity of the shells of HNPs and the size of intrawall pores, which are critical to the applications of HNPs as drug delivery vehicles and catalyst supports