Description
Surface charge is one of the most important properties controlling stability, phase behavior, and self-assembly of colloidal systems. Often, the ability of ‘patchy’ colloidal particles to assemble into functional materials depends on the heterogeneous distribution of local surface charges. Similarly, in applications such as catalysis, including photo- and electrocatalysis, local surface charge is essential for the performance of often faceted colloidal nanoparticles. Despite this crucial role, our ability to characterize surface charges of colloidal systems is typically limited to rather coarse techniques such as electrokinetic measurements that average over the entire surface areas of large ensembles of particles and thereby fail to provide a detailed picture of the system.Throughout recent years, we have developed an Atomic Force Microscopy-based approach that allows to quantify electrostatic, van der Waals and hydration forces on colloidal nanoparticles with sub-particle resolution [1]. By combining AFM probes of different sizes, we are able to extract local surface charge densities and charge regulation properties based on DLVO theory as well as the microscopic properties of the crystalline lattice and along with the adjacent solvation structure.
Here, we focus on photocatalytically active faceted semiconducting nanoparticles made of SrTiO3 [2]. We demonstrate that the (100) and (110) facets of these particles display different local surface charge densities over the entire range from pH 2 to pH 11, including in particular a region from pH 4 – 6 with opposite local charge densities, owing to a different in isoelectric point between the facet of approximately two pH units. This facet-dependent charge enables facet-selective electrostatically driven deposition of silica nanoparticles onto the SrTiO3 particles. Atomically resolved imaging and force spectroscopy further reveal a strong anisotropy of the hydration structure of the two facets, which can be attributed to a frustration of a H-bonding network on the (110) facets due to unfavorable spacing between adjacent hydrogen-bonding acceptor sites.
| Period | 28 Sept 2022 |
|---|---|
| Event title | German Colloid Society Meeting 2022 |
| Event type | Conference |
| Location | Berlin, GermanyShow on map |