Facet‐Dependent Surface Charge and Hydration of Semiconducting Nanoparticles at Variable pH

Abstract

Understanding structure and function of solid–liquid interfaces is essential for the development of nanomaterials for various applications including heterogeneous catalysis in liquid phase processes and water splitting for storage of renewable electricity. The characteristic anisotropy of crystalline nanoparticles is believed to be essential for their performance but remains poorly understood and difficult to characterize. Dual scale atomic force microscopy is used to measure electrostatic and hydration forces of faceted semiconducting SrTiO3 nanoparticles in aqueous electrolyte at variable pH. The following are demonstrated: the ability to quantify strongly facet‐dependent surface charges yielding isoelectric points of the dominant {100} and {110} facets that differ by as much as 2 pH units; facet‐dependent accumulation of oppositely charged (SiO2) particles; and that atomic scale defects can be resolved but are in fact rare for the samples investigated. Atomically resolved images and facet‐dependent oscillatory hydration forces suggest a microscopic charge generation mechanism that explains colloidal scale electrostatic forces.

Influence of particle size and shape on the rate of hydrogen produced by Al‐doped SrTiO3 photocatalysts

“…Previous studies of SrTiO 3 have shown that the {1 0 0} surfaces are photocathodic and {1 1 0} surfaces are photoanodic, 20–22 and this is supported by electronic band structure calculations showing that the conduction and valance band edges at the {1 1 0} surface are at a higher energy than at {1 0 0} 20,23 . Also, atomic force microscopy (AFM) measurements confirm that {1 1 0} surfaces have a more negative surface charge compared with {1 0 0} surfaces and are more favorable to photoanodic reactions 24 . Besides, SrTiO 3 nanocrystals with both {1 0 0} and {1 1 0} facets exposed are much more reactive than SrTiO 3 nanocubes (exposing only {1 0 0} facets) for photocatalytic water splitting 22,25 .…”

“…20,23 Also, atomic force microscopy (AFM) measurements confirm that {1 1 0} surfaces have a more negative surface charge compared with {1 0 0} surfaces and are more favorable to photoanodic reactions. 24 Besides, SrTiO 3 nanocrystals with both {1 0 0} and {1 1 0} facets exposed are much more reactive than SrTiO 3 nanocubes (exposing only {1 0 0} facets) for photocatalytic water splitting. 22,25 A more recent paper 26 reports that SrTiO 3 particles with {1 0 0} and {1 1 0} surfaces have reactivities that are inferior to those with only {1 0 0} surfaces, but the catalyst particles were significantly smaller than those in the previous work.…”

Interfacial layering of hydrocarbons on pristine graphite surfaces immersed in water

“…[26][27][28] This method is becoming the tool of choice for imaging with high-spatial resolution a large variety solid-liquid interfaces. [28][29][30][31][32][33][34][35]…”

Correlation between Electrostatic and Hydration Forces on Silica and Gibbsite Surfaces: An Atomic Force Microscopy Study

“…The forces between charged surfaces, colloidal particles, dissolved ions, and organic molecules in ambient aqueous electrolyte are essential in diverse scientific disciplines, like colloid science, biophysics, (electro/photo)­catalysis, and environmental geochemistry . They control colloidal stability, dynamics, self-assembly, − ion adsorption, friction, adhesion, and many other properties. For not too high salt concentrations, these forces are well described on the colloidal scale by the classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory of colloid science that combines electric double-layer (EDL) forces with a characteristic range set by the Debye screening length and van der Waals interaction. , Yet, it was already pointed out by Langmuir that this picture is incomplete and that the ultimate formation of contact between two solutes should be governed by short-range forces related to the molecular structure of the solvent, i.e., by hydration forces in the case of aqueous solutions. ,− …”