Porosity determination of nano- and sub-micron particles by single particle inductively coupled plasma mass spectrometry

Abstract

A new porosity determination method for nano- and sub-micron particles is proposed, which is based on single particle inductively coupled plasma mass spectrometry (spICP-MS) measurements. The performance of the new method was tested on core–shell Ag–Au, hollow Au and mesoporous SiO₂ nanoparticles of different sizes and porosities and it was found that its accuracy and precision (e.g. 1–2 rel.%) are comparable to those of reference methods, such as small angle X-ray scattering (SAXS), gas adsorption or transmission electron microscopy imaging (TEM). It can be applied to nano- and submicron particles in the complete mesoporous pore (2–50 nm) range. The application to macroporous particles is also possible, but it is limited in size to particles that can be fully decomposed by the plasma. The proposed new spICP-MS method provides an advantageous set of features that is unparalleled among the porosity determination methods, namely (i) it only requires a very small amount of particulate sample (micrograms or even less) in the form of a dilute dispersion (e.g. in a 10⁵ mL⁻¹ particle concentration), so there is not even a need for a dry sample; (ii) it works for open and closed pores equally well; (iii) the measurement and calculation are quick and simple, and only need the external diameter of the particle (from e.g. electron microscopy or dynamic light scattering (DLS) measurements) as input. The overall porosity determined can also be used to calculate the density of the particles, a feat which is not easy to achieve from such a small amount of sample.