AFM-based measurements of local surface charge and hydration: from clays to faceted colloidal semiconductor nanoparticles

Description

Abstract: The stability of colloidal suspensions is governed by the interaction forces between particles. While such interaction forces are isotropic for simple spherical colloidal particles, crystalline nanoparticles are often facetted with very different densities of atoms, broken bonds, chemistries on different facets. In contrast to classical colloidal characterization tools which probe ensemble averages, AFM force spectroscopy in ambient electrolyte allows to measure interaction forces with nanometer resolution and thereby provides access to facet-dependent properties. After introducing the technique, I will illustrate these capabilities for gibbsite mineral nanoparticles and for semiconducting SrTiO3 nanoparticles. Measurements at variable pH demonstrate that this photocatalytically active material displays a variation for the isoelectric point by approximately 2 pH units between the (100) and the (110) facet. At the macroscopic (electrokinetically measured) isoelectric points, each particle thus in fact displays facets that are all locally charged but with opposite sign. Macroscopic consequences include selective adsorption of silica particles of well-defined negative charge to (100) surfaces at moderately acidic pH – and potentially facet-selective photocatalytic activity. The latter, however, is controlled by several more complex processes including hydration forces as well as electron transfer efficiencies.

Period	8 Apr 2021
Event title	Geneva Colloids 2021
Event type	Conference
Location	Geneva, SwitzerlandShow on map